IETF Next Steps in Signaling S. Lee, Ed.
Internet-Draft Samsung AIT
Expires: September 7, 2006 S. Jeong
HUFS
H. Tschofenig
Siemens AG
X. Fu
Univ. of Goettingen
J. Manner
Univ. of Helsinki
March 6, 2006
Applicability Statement of NSIS Protocols in Mobile Environments
draft-ietf-nsis-applicability-mobility-signaling-04.txt
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Copyright (C) The Internet Society (2006).
Abstract
The mobility of an IP-based node affects routing paths, and as a
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result, can have a significant effect on the protocol operation and
state management. This draft discusses the effects mobility can
cause to the NSIS protocols, and how the protocols operate in
different scenarios, and together with mobility management protocols.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Requirements Notation and Terminology . . . . . . . . . . . . 4
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 7
3.1. General problems . . . . . . . . . . . . . . . . . . . . . 7
3.2. Mobility-Related Issues with NSIS Protocols . . . . . . . 9
3.2.1. NTLP-Specific challenges . . . . . . . . . . . . . . . 10
3.2.2. QoS-NSLP-Specific challenges . . . . . . . . . . . . . 10
3.2.3. NAT/FW NSLP-Specific challenges . . . . . . . . . . . 11
3.2.4. Common challenges related to both NTLP and NSLP . . . 12
4. Basic Operations for Mobility Support . . . . . . . . . . . . 13
4.1. Route changes caused by mobility . . . . . . . . . . . . . 13
4.2. CRN discovery . . . . . . . . . . . . . . . . . . . . . . 15
4.2.1. Possible approaches for CRN discovery . . . . . . . . 15
4.2.2. The identifiers for CRN discovery . . . . . . . . . . 17
4.2.3. The procedures of CRN discovery . . . . . . . . . . . 19
4.3. State Update . . . . . . . . . . . . . . . . . . . . . . . 20
4.3.1. State setup and update . . . . . . . . . . . . . . . . 20
4.3.2. State teardown . . . . . . . . . . . . . . . . . . . . 22
5. Applicability Statement . . . . . . . . . . . . . . . . . . . 23
5.1. Support for macro mobility-based scenarios . . . . . . . . 23
5.1.1. Interfaces between Mobile IP and NSIS . . . . . . . . 24
5.1.2. Mobile IPv4-specific issues . . . . . . . . . . . . . 25
5.1.3. Mobile IPv6-specific issues . . . . . . . . . . . . . 28
5.1.4. Interaction with Mobile IP tunneling . . . . . . . . . 30
5.1.4.1. Scenarios for interaction with Mobile IPv4
tunneling . . . . . . . . . . . . . . . . . . . . 31
5.1.4.2. Scenarios for interaction with Mobile IPv6
tunneling . . . . . . . . . . . . . . . . . . . . 37
5.2. NSIS operations in multihomed mobile environments . . . . 42
5.2.1. Multihomed mobile environments . . . . . . . . . . . . 43
5.2.2. Receiver-initiated reservation in the multihomed
environment . . . . . . . . . . . . . . . . . . . . . 44
5.2.3. Sender-initiated reservation in the multihomed
environment . . . . . . . . . . . . . . . . . . . . . 46
5.2.4. Link/node failure recovery . . . . . . . . . . . . . . 46
5.2.5. Load balancing . . . . . . . . . . . . . . . . . . . . 47
5.3. QoS performance considerations in mobility scenarios . . . 49
5.4. Support for Ping-Pong type handover . . . . . . . . . . . 51
5.5. Peer failure scenarios . . . . . . . . . . . . . . . . . . 52
6. Security Considerations . . . . . . . . . . . . . . . . . . . 53
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6.1. MN as data sender . . . . . . . . . . . . . . . . . . . . 54
6.1.1. MN is authorizing entity . . . . . . . . . . . . . . . 54
6.1.2. CN is authorizing entity . . . . . . . . . . . . . . . 56
6.1.2.1. CN asks MN to trigger action (on behalf of the
CN) . . . . . . . . . . . . . . . . . . . . . . . 57
6.1.2.2. CN uses installed state to route message
backwards . . . . . . . . . . . . . . . . . . . . 58
6.1.2.3. MN and CN are authorized . . . . . . . . . . . . . 59
6.1.3. CN as data sender . . . . . . . . . . . . . . . . . . 59
6.1.3.1. CN is authorizing entity . . . . . . . . . . . . . 59
6.1.3.2. MN is authorizing entity . . . . . . . . . . . . . 61
6.1.4. Multi-homing Scenarios . . . . . . . . . . . . . . . . 61
6.1.4.1. MN as data sender . . . . . . . . . . . . . . . . 61
6.1.4.2. CN as data sender . . . . . . . . . . . . . . . . 62
6.1.5. Proxy Scenario . . . . . . . . . . . . . . . . . . . . 63
6.1.6. Conclusion . . . . . . . . . . . . . . . . . . . . . . 63
7. Change History . . . . . . . . . . . . . . . . . . . . . . . . 64
7.1. Changes from -00 version . . . . . . . . . . . . . . . . . 64
7.2. Changes from -01 version . . . . . . . . . . . . . . . . . 65
7.3. Changes from -02 version . . . . . . . . . . . . . . . . . 66
7.4. Changes from -03 version . . . . . . . . . . . . . . . . . 66
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 67
8.1. Normative References . . . . . . . . . . . . . . . . . . . 67
8.2. Informative References . . . . . . . . . . . . . . . . . . 67
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 69
A.1. Acknowledgement . . . . . . . . . . . . . . . . . . . . . 69
Appendix B. Generic Route Changes . . . . . . . . . . . . . . . . 69
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 71
Intellectual Property and Copyright Statements . . . . . . . . . . 73
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1. Introduction
The mobility of IP-based nodes incurs route changes, usually at the
edge of the network. Route changes may also be caused by reasons
other than mobility, such as routing protocol adaptation in response
to varying network conditions (load sharing, load balancing, etc), or
host multi-homing. Macro mobility also involves the change of the
mobile node's IP addresses. Since IP addresses are usually part of
flow identifiers, the change of IP addresses implies the change of
flow identifiers. Local mobility usually does not cause the change
of the global IP addresses, but affects the routing paths within the
local access network [3].
In multi-homed mobile networks, mobile nodes (MNs) can have an access
to multiple interfaces and obtains multiple addresses (e.g, CoAs and
HoAs). It enables the MN to choose the most appropriate interface or
address according to application (or flow) types or network
conditions in homogeneous/heterogeneous environments. The
Multihoming helps alleviate various problems caused by the wireless
bottleneck and mobility events, e.g., limited bandwidth and frequent
handovers for examples.
The NSIS protocol suit consists of two layers: NSIS Transport Layer
Protocol (NTLP) and the NSIS Signaling Layer Protocol (NSLP). The
General Internet Signaling Transport [2] is the NTLP protocol. GIST
is an application independent protocol and transports service-
related information between nodes in a network. Each specific
service has its own NSLP protocol; currently there two standardized
NSLP protocols, the QoS NSLP [5], and the NAT/Firewall NSLP [3].
The goals of this draft are to present the effects of mobility on the
NTLP/NSLPs and to provide guides on how such NSIS protocols should
work in various mobility scenarios including multihoming. Most of
all, this draft mainly discusses the operations of the NSIS protocols
in fundamental mobility scenarios (e.g., macro mobility management
protocols such as Mobile IPv4 and Mobile IPv6), including support for
multi-homing. More complex scenarios and issues on interworking with
various mobility-related protocols, such as the Context Transfer
Protocol, and Candidate Access Router Discovery, and local mobility
management protocols, are left for future work.
2. Requirements Notation and Terminology
The key words "MUST," "MUST NOT," "REQUIRED," "SHALL," "SHALL NOT,"
"SHOULD," "SHOULD NOT," "RECOMMENDED," "MAY," and "OPTIONAL" in this
document are to be interpreted as described in [1].
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The terminology in this draft is based on [2] and [4]. In addition,
the following terms are used. Note that in this draft, a generic
route change caused by regular IP routing is referred to as a 'route
change', and especially, the route change caused by mobility is
referred to as 'mobility' like [4].
(1) Downstream
The direction from a data sender towards the data receiver.
(2) Upstream
The direction from a data receiver towards the data sender.
(3) Crossover Node (CRN)
A Crossover Node is a node that for a given function is a merging
point of two or more paths along which states are installed. The
CRN may not necessarily be a physical route splitting point.
There exist different types of logical (but not necessarily
physical) CRNs depending on the signaling states, flow directions,
mobility management types, and the routing infrastructure:
From the perspective of NSIS states (i.e., NSLP and NTLP
state), the types of CRN can be classified as follows.
NSLP CRN: a signaling application-aware node in the network
where the corresponding signaling flows begin to merge or
split after a route change or mobility. Even if multiple
signalling application sessions refer to the same data flow,
the NSLP CRN after a route change may be different for each
NSLP involved.
NTLP CRN: an NTLP-aware network node where multiple NTLP
state begin to merge or split after a route change or
mobility.
NSIS CRN: A node is called an NSIS CRN if it is an NSLP or
an NTLP CRN.
The types of CRN can be further classified according to their
location in the network, with respect to the path from data
sender to data receiver, as follows.
In the mobility scenarios, there are two different types of
merging points in the network according to the direction of
signaling flows followed by data flows as shown in Figure 1
of Section 4.1, where we assume that the MN is the data
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sender.
Upstream CRN (UCRN): the node closest to the data sender
from which the state information in the direction from
data receiver to data sender begins to diverge after a
handover.
Downstream CRN (DCRN): the node closest to the data
sender from which the state information in the direction
from the data sender to the data receiver begins to
converge after a handover.
In general, the DCRN and the UCRN may be different due to
the asymmetric characteristics of routing although the
data receiver is the same.
In case of the route changes, the path change of signaling
flows results in forming a chain of two CRNs regardless of
the direction of signaling flows followed by data flows as
shown in Figure 14 of Appendix A. The CRN chain is referred
to as a divergence-convergence pair:
Divergent-convergent UCRN pair: a chain of the nodes at
which the state information towards the 'data sender'
begins to diverge and to converge after a route changes.
Divergent-convergent DCRN pair: a chain of the nodes at
which the state information towards the 'data receiver'
begins to diverge and to converge after a route changes.
Routing CRN is the node where the old and new paths (rather
physically) merge using regular IP routing. For example, the
merging points caused by mobility management protocols are a
kind of Routing CRN. Depending on the location of nodes, the
routing CRN may not be equal to the NSLP CRN or NTLP CRN.
(4) State Update
State Update is the procedure for the re-establishment of NSIS
state on the new path, the teardown of NSIS state on the old path,
and the update of NSIS state on the common path due to the
mobility. The State Update procedure is used to address mobility
for the affected flows.
Upstream State Update: State Update for the upstream signaling
flow which is initiated by an upstream signaling initiator. If
the MN is a data sender, the State Update is initiated by an NI
on the common path (e.g., a CN, an HA, or an MAP).
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Downstream State Update: State Update for the downstream
signaling flow which is triggered by a downstream signaling
initiator. If the MN is a data sender, the State Update is
triggered by an NI on the new path (e.g., an MN, a mobility
agent, or an AR).
In case of route changes except for mobility, the update of NSIS
state on the common path is not required because the flow
identifiers do not change, which limits the scope of the required
NSIS signaling . Especially, in mobility scenarios, if the NSIS
signaling interacts with local mobility management (LMM) protocols
(e.g., HMIPv6), the State Update can be localized within the
access network. In this case, setup delay of NSIS signaling can
be minimized.
(5) Dead Peer Discovery (DPD)
The procedure for finding a dead NSIS peer due to a link/node
failure or due to an MN moving away.
3. Problem Statement
IP mobility in its simplest form only includes route changes. This
section identifies problems caused by mobility and multihoming, which
may have significant impacts on the operations of NSIS protocols.
3.1. General problems
The general problems caused by mobility are as follows.
(1) Change of route and possibly change of the MN IP address
Topology changes might lead to path changes for data packets sent
to or from the MN and may lead to an IP address change of the MN.
(2) Frequency of route changes
The change of route and IP addresses in mobile environments is
typically much faster and more frequent than traditional route
changes caused by node or link failure.
(3) Explicit routes
Path-coupled signaling protocols usually expect the data traffic
to follow the same path as the signaling , but the data traffic
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sometimes traverses a path different from the path of signaling
traffic due to the adaptation of routing tables to varying network
conditions and to techniques such as load balancing, load sharing
and mobility. For example, Mobile IP may use the routing headers
to define explicit routes, which diverts the traffic from an
expected path.
(4) IP-in-IP encapsulation
Mobility protocols may use IP-in-IP encapsulation on the segment
of the end-to-end path for routing traffic from the CN to the MN,
and vice versa. Encapsulation harms any attempt to identify and
filter data traffic belonging to, for example, a QoS reservation.
Moreover, encapsulation of data traffic may lead to changes in the
routing paths since the source and the destination IP addresses of
the inner header differ from those of the outer header. If the
signaling packets are encapsulated it might be necessary to
perform a separate signaling exchange for the tunneled region.
(5) Ping-pong type handover
Signaling protocols need to remove states quickly along the old
path under the environments with scarce resources. However, in a
ping-pong type handover, the MN returns to the previous AR after
staying with the new AR only for a short while, so the prompt
removal of state along the old path would cause the state to be
re-established soon, and thus it adds overhead.
(6) Upstream State Update vs. Downstream State Update
Since the upstream and downstream paths are likely not to be the
same, the upstream and downstream CRNs may not coincide, either.
Therefore, the State Update needs to be handled independently for
the upstream and the downstream, including the discovery of
upstream and downstream CRNs.
(7) State identification problem
A mobility event typically causes the addresses of corresponding
flow endpoints to change, and thus it is desirable that the
signaling application state is independent of the underlying flows
to avoid the state being re-installed completely. Therefore, the
identifiers for the session and the flow must not be dependent on
each other. This makes it possible to associate the session
identifier with the signaling application and with different data
flows.
(8) Double reservation problem
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Since the state on the old path (and the common path) still
remains as it is after re-establishing the state along the new
path due to mobility (or route changes), the double reservation
problem occurs. Although the state on the old path will be
deleted automatically based on the soft state timeout, the refresh
timer value may be quite long (e.g., 30s as a default value in
RSVP). This problem might result in the waste of resources and
lead to failure of other reservations (due to lack of resources).
Note, however, that the degree of impact depends on the frequency
of path changes and also on the chosen refresh interval.
(9) End-to-end signaling problem
Mobility may change the flow identifier (e.g., macro-mobility),
and the change of flow identifier requires state update along the
entire path to reflect the physical location of the MN, resulting
in the end-to- end signaling. This also incurs a long state setup
delay and increased signaling overhead, which affects overall
performance of signaling protocols. The long state setup delay
may ultimately give rise to service blackout or degradation of
multimedia services in mobile environments.
(10) Identification of the crossover node
When a handover at the edge of network has happened, in the
typical case, only some parts of the end-to-end path used by the
data packets changes. In this situation, the CRN plays a central
role in managing the establishment of the new signaling
application state, and removing any useless state.
(11) Key exchange
When a handover happens, nodes on the new path must be able to
verify the signaling messages of the MN, and vice versa. For
example, if signaling messages are encrypted on a hop-by-hop
basis, the new access router should be able to continue the
message encryption and decryption with the incoming MN.
(12) Authorization Issues
The procedure of State Update may be initiated by the MN, the CN,
or even nodes within the network (e.g., MAP in HMIP). This State
Update on behalf of the MN raises authorization issues about the
entity that is allowed to make these state modifications.
3.2. Mobility-Related Issues with NSIS Protocols
Considering the issues identified in Section 3.1, this section
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discusses challenges when deploying NSIS protocols..
3.2.1. NTLP-Specific challenges
(1) Interfaces between Mobile IP and NSIS protocols
To continue to support the existing NSIS state for a session, the
NTLP protocol should be immediately involved in the CRN discovery
and State Update after a mobility event (e.g., handover) happens.
Therefore, it might be necessary to develop a Mobile IP-specific
API or reuse/extend existing APIs from Mobile IP [21] (if
applicable) in NSIS, to learn quickly about mobility events at the
NTLP or at the NSLP layer. Although this is close to the
implementation-specific issue, a common triggering mechanism
between routing and NSIS processes need to be considered to
monitor the operations of other mobility protocols and trigger a
relevant event accordingly.
(2) Localized State Update
The State Update needs to be localized to improve the performance
metrics, such as signaling setup delay and resource utilization.
A few issues on the interaction between the micro mobility
management protocols and the NSIS protocol suite arise. For
example, when interacting with HMIP [22], how is the Path Update
performed with scoped signaling messages within the access network
under the control of MAP needs to be considered.
3.2.2. QoS-NSLP-Specific challenges
(1) Invalid NR problem
If MN is receiver, it might be determined as the last QNE (QNR) on
the signaling path [5]. If MN, however, moves into a new network
attachment point, the old AR can not forward QoS-NSLP messages any
further to the MN (QNR). In this case, the old AR's QoS-NSLP may
trigger an error message to indicate that the last node fails or
is truncated. This error message forwarded to QNI may mistakenly
cause the removal of the state on the existing paths. It is
called the 'invalid NR problem' [12]. The erroneous state removal
may happen, if the QoS NSLP CRN has not received a message from
the new reservation path, where the MN moved to. Therefore, a QNE
should be conservative when it receives an indication for a state
removal caused by a change in routing.
(2) Optimal refresh timer value for mobile environments
IIn the situation where handover occurs frequently, the
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maintenance of signaling state on the old path for a long time is
not necessary. The QoS-NSLP needs to choose appropriate refresh
intervals depending on the network environments (e.g., access
network, or core network) or access technologies (e.g., 3G, IEEE
802.16, WLAN, etc.).
(3) Authorization-related issues with teardown
When tearing down the obsolete state after CRN discovery, the
teardown message can be sent toward the opposite direction to the
state initiating node. This leads to an authorization problem
because a node which does not initiate signaling for establishing
the NSLP state may delete the state. The QoS NSLP solves this
problem by a notification message. When a QNE notices a change in
downstream routing paths for a given session, it should send a
NOTIFY message upstream and indicate the change in routing [5].
(4) Dead peer discovery
A dead peer can occur either because a link or a network node
failed, or because the MN moved away without informing QoS-NSLP
(it is recommended to link mobility and NSIS signaling such that
this does not happen). Rerouting can be detected on three levels,
routing modules, GIST, and the QoS NSLP. More details can be
found in Section 3.2.10 of the QoS NSLP specification [2]. Yet,
the dead peer detection can be enhanced, e.g., by making use of
link layer hints.
3.2.3. NAT/FW NSLP-Specific challenges
The NAT/FW-NSLP establishes and maintains firewall pinholes and NAT
bindings at NAT/FW-NSLP nodes along the data path [10]. With regard
to mobility, a few issues need to be considered:
(1) Update of firewall rules and NAT bindings
When an IP address changes by mobility, firewall rules and/or NAT
bindings become invalid because the established flow identifier
refers to a non-existent flow, which effectively blocks the end
host's traffic. For example, without updating the firewall
pinhole by an NSIS-aware data sender (located behind a firewall),
data packets with a new source IP address are most likely dropped
at the firewall. if a data receiver (located behind a NAT) changes
its IP address, incoming packets are rewritten at the NAT and
forwarded to the wrong IP address.
The impact of a out-dated flow identifier is more servere in the
NAT/FW case than in QoS case. In the latter case, the impact is
only that the flow experiences best-effort treatment for a limited
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period of time (until the flow identifier is updated again).
(2) Re-use of NAT/FW-NSLP's old state
Although NSIS state can be released by applying the soft state
principle after a mobility event, states (such as firewall
pinholes) can be left in place for some time. Since the NAT/ FW-
NSLP aims to install pinholes (and NAT bindings), it is still
possible to re-use this installed state although a mobile node
roams to a new location. This means that another host can send
data through a firewall without any prior NSIS NAT/FW signaling
because of the previous state which is not yet expired. This
might be a problem since an unauthorized end host might be able to
inject packets through the firewall for a limited period of time.
Deleting state along the old path might help to limit this
problem. However, this problem exists anyway due to the
capability of IP spoofing as identified in [7], and the main
problem is the missing data origin authentication (i.e., missing
cryptographic protection of data traffic).
3.2.4. Common challenges related to both NTLP and NSLP
(1) CRN discovery-related issues
Which layer should be responsible for the CRN discovery, NTLP
(GIST) or NSLP (QoS-NSLP or NAT/FW-NSLP) needs to be discussed.
Although the QoS-NSLP, for example, can detect the change of
signaling path and discover the CRN by keeping track of SII, the
CRN discovery at the NTLP layer may also be preferred to at the
QoS-NSLP. Concerning CRN discovery, the pros and cons of two
mechanisms on CRN discovery dependent on NSIS layers (i.e., either
NTLP or NSLP) need to be identified (see Section 4.2.1)
(2) CRN discovery and State Update on the IP-tunneling path
Mobile IP uses tunneling mechanisms to forward data packets among
end hosts. Traversing over the tunnel, NSIS signaling messages
are transparent on the tunneling path due to the change of flow's
addresses. In case of interworking with Mobile IP-tunneling, CRNs
can be discovered on the tunneling path. It enables NSIS
protocols to perform State Update procedure over the IP-tunnel.
In this case, GIST needs to cope with the change of Message
Routing Information (MRI) for the CRN discovery on the tunnel.
Also, NSLP signaling needs to determine when to remove the
tunneling segment on the signaling path and/or how to tear down
the old state via interworking with the IP-tunneling operation.
The problem of tunneling is solved in NSIS by having a separate
signaling session for the tunneled path. Thus, NSIS signaling
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messages are transported through the tunneled segment within a
separate signaling session.
(3) Issues on API between NTLP and NSLP
In mobile environments, mobility-related information for State
Update can be exchanged through the API specified in [2]. Based
on the information, the involved NSLP can initiate State Update by
sending necessary signaling messages through the API. However,
what information should be sent from GIST to an NSLP to inform of
the route changes needs to be discussed further. The details on
the API can be an implementation issue.
(4) Multihoming-related issues
An NSIS-aware node (e.g., Mobile Node (MN)) may be multihomed.
Such multihomed environments help NSIS signaling have some
advantages in mobility scenarios (see in Section 5.2). However,
which NxLP functionality is needed in various multihoming
scenarios (e.g., bandwidth increase, load balancing, bi-casting,
resilience, etc.) is an open question. An overall coordination
for interworking between the NSIS protocol suite and multihoming
capability needs to be discussed further.
4. Basic Operations for Mobility Support
In this section, the basic operations on the NSIS protocol suite
needed after mobility related route changes is discussed. The
operations include how to discover an appropriate CRN and how to
perform the State Update according to the direction of data flows.
The procedures for CRN discovery (explained in Section 4.2.3) can be
applied in the same way for both the generic route changes and
mobility. However, the State Update for mobility is different from
that for the generic route changes because of the change of flow
identifier as explained in Section 2 (4).
4.1. Route changes caused by mobility
The route change caused by mobility occurs due to the change of the
network attachment point of an MN. It causes divergence (or
convergence) between the old path where the NSIS state has already
been installed and the new path where data forwarding will actually
happen.
Mobility may be considered similar to generic route changes.
However, the main difference is that the Message Routing Information
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(MRI: e.g., flow identifier) may not change after generic route
changes while mobility may cause the change of MRI by having a new
network attachment point. Since the session should remain the same
after any mobility event, the MRI should not be used to determine the
session of any signaling application [10].
The route change brings on the change of signaling topology different
from the mobility. That is, the route change results in forming a
loop of signaling path that the old path and the new path meet both
starting point and end point of the route change (i.e., divergence-
convergence pair) (see Appendix). However, as shown in Figure 1, the
mobility generally causes signaling path to either converge or
diverge depending on the direction of each signaling flow.
Old path
+--+ +-----+
original |MN|<------ |OAR | ---------^
address | | |NSLP1| ^
+--+ +-----+ ^ common path
| C +-----+ +-----+ +--+
| | |<---|NSLP1|---|CN|
| |NSLP2| |NSLP2| | |
v New path +-----+ +-----+ +--+
+--+ +-----+ V B A
New CoA |MN|<------ |NAR |----------V >>>>>>>>>>>>
| | |NSLP1| ^
+--+ +-----+ ^
D ^
>>>>>>>(Binding process)>>>>>>>>>>>>^
<=====(upstream signaling followed by data flows) =====
(a) The topology for upstream NSIS signaling flow due to
mobility
Old path
+--+ +-----+
original |MN|------> |OAR | ----------V
| | |NSLP1|
address +--+ +-----+ V common path
| K +-----+ +-----+ +--+
| | |---|NSLP1|--->|CN|
| |NSLP2| |NSLP2| | |
v New path +-----+ +-----+ +--+
+--+ +-----+ ^ M N
New CoA |MN|------> |NAR |-----------^ >>>>>>>>>>>>
| | |NSLP1| ^
+--+ +-----+ ^
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L ^
>>>>>>>(Binding process)>>>>>>>>>>>>^
====(downstream signaling followed by data flows) ======>
(b) The topology for downstream NSIS signaling flow due to
mobility
Figure 1: The topology for NSIS signaling caused by mobility.
These topological changes caused by mobility make the NSIS state
established on the old path useless and thus it needs to be removed
(in the end). In addition, NSIS state needs to be established newly
along the new path and be updated along the common path.
Re-establishment of NSIS signaling needs to be localized when route
changes (including mobility) occur to minimize the impact on the
service and scalability. This localized signaling procedure is
referred to as State Update (refer to the terminology section). In
mobile environments, for example, the NSLP/NTLP needs to limit the
scope of signaling information only to the affected section of the
signaling path because the path in the wireless access network
usually changes only partially.
One of the most appropriate nodes to perform the State Update is the
CRN where the old and new session paths meet. The CRN should be
logical merging point, not physical merging point. In the end, CRN
discovery can be a crucial element to alleviate the double
reservation and end-to-end signaling problems identified in Section
3.1.
The NTLP (of a node experiencing a topological change) needs to
detect the route change through the various mechanisms (described in
[4]) at the transport level and notify the relevant NSLP(s). The
NSLP needs to initiate NSIS state re-establishment (i.e., QoS re-
establishment) along the new path and the update or removal of the
existing state at the signaling application level.
4.2. CRN discovery
4.2.1. Possible approaches for CRN discovery
The approaches for CRN discovery can be divided into two classes
depending on which layer is responsible for the CRN discovery
(addressed in Section 3.2.2), and whether or not the discovery is
coupled with the transport of signaling application messages.
From the NSIS protocol stack point of view, the CRN can be discovered
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at either NTLP or NSLP layer. For the CRN discovery at the NSLP
layer, the information contained in NSLP signaling messages sent from
the NSIS initiator (NI) can be used. For example, the QoS-NSLP of an
NSIS node can determine whether or not the node is a CRN by comparing
the Source Identification Information (SII) contained in the incoming
signaling message to the one stored previously in the node. That is,
when a RESERVE message with an existing SESSION ID and different SII
is received, the QNE knows its upstream peer has changed and realizes
it is implicitly the CRN [5].
It is also possible to discover the CRN at the NTLP layer since NTLP
is responsible for detecting the path change of data (or signaling)
flow (and the route changes may easily be detected at the NTLP level
rather than at the NSLP). The CRN discovery at the NTLP level can be
considered as a partial process of the peer discovery (e.g. using
GIST query-response message [2]). In general, the GIST messages have
message routing state information such as flow/session/signaling
application identifiers, so the signaling application can be
identified at the NTLP level. In the connection mode of GIST, two
NTLP peers exchange message routing state information through GIST
query and response messages when GIST establishes a messaging
association between two adjacent peers. In procedure of the
messaging association, CRN is implicitly discovered by comparing MRI
contained in the coming signaling to the one stored previously in the
node. Therefore, although the CRN is discovered at the NTLP level,
the discovered CRN is actually an NSLP-aware node which has an
involved signaling application.
The CRN discovery at the NTLP layer is only one part of peer
discovery procedure, and it does not require any explicit process for
CRN discovery itself except for GIST notification on the information
('CRN-is-discovered to NSLP') to NSLP over API. The NTLP level
approach results in decreasing complexity of overall NSIS protocol
processing. If a route change is directly detected by NSLP, the CRN
discovery at the NSLP layer is considered as a way to report the
rerouting. However, this NSLP-level approach requires additional
messages at corresponding NSLPs and thus results in adding complexity
of overall NSIS protocol processing.
There can also be two different approaches for the CRN discovery
messaging depending on whether or not the discovery is coupled with a
signaling message: coupled approach and uncoupled approach. In the
coupled approach, the signaling to install the NSIS state along the
new path or update the state along the common path is performed
simultaneously with the CRN discovery. In the uncoupled approach,
the signaling for the State Update is performed after the CRN
discovery is completed. These two approaches may differ in terms of
security. Generally, the coupled approach would be preferred to the
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uncoupled approach to reduce the delay for state update. Note that
messaging for the CRN discovery and State Update described in this
draft are based on the coupled approach.
4.2.2. The identifiers for CRN discovery
There are some basic identifiers which can be used for the CRN
discovery at the NTLP level: session identifier (SID), flow
identifier (MRI), and signaling application identifier (NSLP_ID)
related to message routing state [2], and NSLP branch identifier
(NSLP_Br_ID) which identifies an NSIS signaling branch.
The SID in GIST messages is used to identify the involved session
because it remains the same while the MRI may change. The MRI is
used to specify the relationship between the address information and
the state (e.g., QoS-NSLP state) re-establishment. In other words,
the change of MRI indicates a topological change to the CRN and
therefore it represents that the state along the common path should
be updated and the refresh reduction mechanism needs to be used on
the common path if any.
The NSLP_ID is used to refer to the corresponding NSLP at the NTLP
level, and it helps to discover an appropriate NSLP CRN using the
GIST peer discovery message.
As a virtual branch identifier, the NSLP_Br_ID is a pointer which
identifies peer nodes in GIST messaging association, and it can be
used to establish or delete messaging associations between NSIS
peers. It can also be used as an identifier to determine the CRN at
the NTLP layer. The NSLP_Br_ID includes the location information of
NSIS peer nodes with the corresponding NSLP ID obtained by the
procedure of GIST message association. For instance, as shown in
Figures 1 (a) and 2 (a), for the upstream flow case, node A has
messaging association with node C for NSLP 1 on the old path. In
this case, the NSLP_Br_ID for node C at the node A is set to 1-D-#1:
1, D, and #1 indicate an NSLP_ID, a direction of node (Downstream or
Upstream), and a value of the branch counter, respectively. After a
handover, NSLP 1 of node A requires a messaging association for
sending its messages towards node D. In this case, NSIS entity A
creates another NSLP_Br_ID for NSLP 1 toward node D and increases the
counter of NSLP_Br_ID to locally distinguish each virtual interface
identifier between adjacent NSLP peers: the NSLP_Br_ID for the node D
at the node A is 1-D-#2. Note that the NSLP_Br_ID can be included in
the NSIS message, but it can also be considered as an implementation
issue. This identifier would be more useful when the physical
merging point of the old path and the new path is not an NSLP CRN as
shown in Figure 1. Note that GIST message routing state table [2]
including the NSLP_Br_ID can also be created as Figure 2.
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Optionally, the Mobility identifier as an object form can also be
used to inform of the handover of an MN or a route change [12] and
therefore to expedite the CRN discovery. The Mobility object is
defined in the NTLP (e.g., in GIST payload) [8] or NSLP messages to
notify of any mobility event explicitly, and it contains various
mobility-related fields such as mobility_event _counter (MEC) and
handover_init (HI) fields. For example, the mobility_event_counter
(MEC) field in the mobility object can be used to detect the latest
handover event to avoid any confusion about where to send the
confirmation message in case of Ping-pong type handover. Therefore,
the Mobility identifier is useful to discover the most appropriate
CRN. The handover_init (HI) field can be used to inform the old
access router of the movement event. HI field helps resolve the
invalid NR problem (see Section 5.5)
+------------------+-------+-------+--------+------------+-------+
| Message Routing |Session| NSLP |Upstream| Downstream | NSLP |
| Information | ID | ID | Peer | Peer |Br. ID |
+------------------+-------+-------+--------+------------+-------+
| Method = Path | 0xABCD| NSLP1 | | Pointer to | 1-D-#1|
|Coupled; Flow ID =| | | | A-C | |
| {IP-#X, IP-#V, | | | | Pointer to | 1-D-#2|
| protocol, ports} | | | | A-D | |
| | | | Z | | 1-U-#1|
| Method = Path | | | | | |
|Coupled; Flow ID =| 0x1234| NSLP2 | | B | 2-D-#1|
| {IP-#X, IP-#V, | | | | | |
| protocol, ports} | | | Z | | 2-U-#1|
+------------------+-------+-------+--------+------------+-------+
(a) Routing state table at node A (NSLP CRN)
+------------------+-------+-------+----------+----------+-------+
| Message Routing |Session| NSLP |Upstream |Downstream| NSLP |
| Information | ID | ID | Peer | Peer |Br. ID |
+------------------+-------+-------+----------+----------+-------+
| Method = Path | 0xABCD| NSLP1 |Pointer to| | 1-U-#1|
|Coupled; Flow ID =| | | K-N | | |
| {IP-#X, IP-#V, | | |Pointer to| | 1-U-#2|
| protocol, ports} | | | L-N | | |
| | | | | O | 1-D-#1|
| Method = Path | | | | | |
|Coupled; Flow ID =| 0x1234| NSLP2 | | Pointer | 2-D-#1|
| {IP-#X, IP-#V, | | | | to N-R | |
| protocol, ports} | | | M | | 2-U-#1|
+------------------+-------+-------+----------+----------+-------+
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(b) Routing state table at node N (NSLP CRN)
Figure.2 Routing state table and NSLP branch ID
4.2.3. The procedures of CRN discovery
When a mobility event occurs, the CRN can be recognized by comparing
the previously stored identifiers with the identifiers included in
the incoming NSIS peer discovery message initiated by an NI (e.g., an
MN or a CN). For example, if an GIST message is routed to an NSIS
peer node, the following information (shown in Figure 2 (a) and (b))
is checked to determine if the current node is CRN:
- Whether or not the same NSLP_ID exists
- Whether or not the corresponding CRN has already been discovered:
for example, whether CRN_DISCOVERY (CD) flag is set.
- Whether or not the same SID and MRI exist
- Whether or not the NSLP_Br_ID has been changed: for example, as
shown in Figure 2 (a), for NSLP 1 it has been changed to 1-D-#2
from 1-D-#1 at the node A.
- Optionally, the Mobility identifier can be examined, if any. For
example, the MEC field of the Mobility object can be used to find
out which message has been sent due to the latest handover.
The CRN discovery is further divided into the UCRN discovery and DCRN
discovery depending on which node is a signaling initiator (by
upstream or downstream), or whether the MN is the data sender or
receiver:
- If the MN is a data sender and undergoes a handover, the MN begins
to transmit signaling messages toward a CN in the downstream
direction. If an NSLP-aware node recognizes that the session
paths logically converge at that node, then the node determines
that it is the DCRN; for instance, the procedure for CRN discovery
corresponds to the creation of the routing table of node N as
shown in Figure 2 (b).
- - When an MN (as a sender) undergoes handover, the UCRN can be
discovered for the upstream flow. The UCRN should be the node
(closest to the MN) where the signaling flow begins to logically
diverge: it corresponds to the creation of the routing table of
node A as shown in Figure 2 (a).
4.3. State Update
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The CRN discovery procedures are different depending on the direction
of signaling flows in mobility scenarios, and also the procedures for
State Update are different according to the direction of the
signaling flow. The State Update can be divided into upstream State
Update and downstream State Update. For both types of State Update,
the NSIS protocol suite needs to interact with various mobility
management protocols, if any (during or after handover) to obtain
performance gains (e.g., through fast establishment of the NSIS state
on the new path). For this purpose, NSIS may also need to monitor
the movement of the MN through several methods [4]. In this section,
we assume that an MN is the data sender.
4.3.1. State setup and update
Before initiating the State Update, the MN or the CN needs to have
its session ownership by the procedures of authentication and
authorization. The MN or the CN may also check the availability of
resources on the new path. In case of QoS-NSLP, the Query message
can be used to find the availability of resources in the networks
(e.g., access networks or core networks). If the resources along the
new path are not sufficient, it may be needed to keep the state
established previously using multihomed interfaces while blocking
incoming new requests (see Section 5.2).
In the downstream State Update, if resources are available, the MN
initiates the NSIS signaling for state setup toward a CN and also the
implicit DCRN discovery is performed by the procedure of signaling as
described in Section 4.2.3. When the DCRN is discovered,
'CRN_DISCOVERY (CD)' flag bit is set. The CD flag bit helps prevent
downstream NEs from perform unnecessarily CRN discovery process. And
then, DCRN may send a response message towards the MN to notify of
the NSLP state installed (e.g., QoS-NSLP state) or installs the NSLP
state as a response to the initiated NSLP signaling (e.g., as in
RSVP). Afterward, the DCRN sends a refresh message towards the
signaling destination to update the MRI on the common path and also
sends a teardown message towards the old AR to delete the NSIS state
(if possible). Note that in case of QoS-NSLP, the sender-initiated
approach leads to faster setup than the receiver-initiated approach
as in RSVP as shown in Figure 3.
In the scenario of upstream State Update, the CN (or a HA/ a GFA/MAP)
sends a refresh message toward the MN to perform State Update. UCRN
is discovered implicitly by the CN-initiated signaling along the
common path as described in Section 4.2.3 . In this case, the CN
should be informed of the mobility event using an NSIS signaling
message sent by the MN or monitoring the mobility signaling procedure
(e.g., detecting a change in its binding entry (see Section 5.1)).
After the UCRN is discovered, it may send a refresh message to the MN
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along the new path while establishing the messaging association
between the newly found peers. Afterwards, the UCRN may send a
teardown message towards the old AR to delete the NSIS state (if
possible).
NI (MN) NF NF NR (CN)
| RESERVE | | |
+--------->| RESERVE | |
| +--------->| RESERVE |
| | +--------->|
| | | |
| | | RESPONSE |
| | RESPONSE |<---------+
| RESPONSE |<---------+ |
|<---------+ | |
| | | |
(a) Sender Initiated Reservation
NI (MN) NF NF NR (CN)
| QUERY | | |
+--------->| QUERY | |
| +--------->| QUERY |
| | +--------->|
| | | |
| | | RESERVE |
| | RESERVE |<---------+
| RESERVE |<---------+ |
|<---------+ | |
| | | |
| RESPONSE | | |
+--------->| RESPONSE | |
| +--------->| RESPONSE |
| | +--------->|
(b) Receiver Initiated Reservation
Figure.3 Sender- vs. Receiver-initiated reservation
The State Update on the common path to reflect the changed MRI brings
issues on the end-to-end signaling addressed in Section 3.1.
Although the State Update over the common path does not give rise to
re-processing of AAA and admission control, it may lead to the
increased signaling overhead and latency.
One of the goals of the State Update is to avoid the double
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reservation (in QoS signaling) on the common path as described in
Section 3.1. The double reservation problem on the common path can
be solved by establishing a signaling association using a unique SID
and by updating packet classifier/flow identifier. In this case, the
NSLP state should be shared for flows with different flow
identifiers.
4.3.2. State teardown
After establishment of the NSIS state along the new path, the state
on the obsolete path may need to be quickly removed by the State
Update mechanism. It helps prevent the waste of resources due to
double reservation and resource re-allocation problem by call
blocking, and reduce the cost of using resources in the access
network as identified in Section 3.1. Although the release of the
existing state on the old path can be accomplished by the timeout of
soft state, the refresh timer value may be quite long for reducing
the overhead of signaling messages. Especially, in mobility
scenarios, the maintenance of the NSIS state on the old path for a
long time is not necessary. Therefore, the transmission of teardown
messages is useful to quickly delete the old state.
The CRN is an appropriate point to initiate the teardown toward the
old AR after establishment of the state along the new path. The
release of the state on the obsolete path can be accomplished by
comparing the NSLP_Br_IDs and through reverse routing using SII.
This can prevent the teardown message from being forwarded toward
along the common path. Note that, however, it is not necessary for
GIST state to be explicitly removed because of the inexpensiveness of
the state maintenance at the GIST layer [2].
It may not be desirable to allow the teardown message to be sent
toward the opposite direction to the state initiating node. This is
because it leads to an authorization problem because a node which
does not initiate signaling for establishing the NSIS state can
delete the already established state. One simple way to avoid the
authorization problem is to disallow the transmission of the teardown
message in the reverse direction [7].
The immediate removal of state along the old path may not be always
appropriate for some mobility situations addressed in Section 3. For
instance, in the ping-pong type of fast handover, it increases
signaling overhead, and thus when to delete the state along the
obsolete path needs to be discussed further (see Section 5.4).
Another example is the 'invalid NR' problem. If the old AR is the
last node on the signaling path due to handover, its NSLP may trigger
an error message to indicate that NSLP messages cannot be forwarded
any further. This error message can immediately remove the state on
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the old path, which should not be deleted before re-establishing the
state along the new path (make-before-break handover). More details
are given in Section 5.5.
5. Applicability Statement
5.1. Support for macro mobility-based scenarios
This section describes how NSIS protocols should interact with the
basic macro mobility protocols such as Mobile IPv4 [12] and Mobile
IPv6 [11]. Basically, the following scenarios need to be considered.
(1) A flow associated with an MN, either sent or received by the MN,
desires to continually get signaling services even after a Mobile
IP handover. In this case, NSIS needs to be able to signal for
such flows upon the MN's movement to provide seamless service
(e.g., seamless QoS). The signaling procedures will create a new
NSIS state branch in the changed direction of flow by using the
CRN discovery and State Update.
(2) Either the sender or the receiver (e.g., MN or CN) of a flow may
initialize NSIS signaling, and a node within the network (e.g.,
FA, HA, or CRN) may also initiate NSIS signaling for the given
session to handle route changes caused by Mobile IP-based routing,
to interact with Mobile IP tunneling, or to support seamless
handover if necessary. In this case, NSIS signaling needs to be
triggered immediately and initiated via a mobility routing
interface (e.g., mobility API) between the NSIS protocol and the
Mobile IP or by the query routing tables.
(3) Signaling flows, in either direction between an MN and a CN, can
be routed directly using a routing header, or indirectly by
IP-in-IP encapsulation (or a combination of both approaches) on
different segments of the data path depending on the type of the
mobility protocols (e.g., Mobile IPv4, Mobile IPv6, LMM, reverse
tunneling, etc.). In this case, the IP-tunneling mechanism makes
it difficult for nodes on the tunneling path to intercept or deal
with NSIS signaling messages (which require special treatments at
NSIS-aware nodes) because of change of message routing
information. Therefore, to perform end-to-end signaling, NSIS
needs to interact with such IP-tunneling mechanisms.
(4) An MN undergoes either intra-domain (within an access network
domain) handover or inter-domain (from an access network domain to
another) handover. In case of the inter-domain handover, topology
information exchange, authorization and accounting issues may be
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more complicated. In such various handover scenarios, the
interaction between NSIS signaling and some local mobility
management protocols (e.g., HMIP, FMIP, etc.) can give rise to
significant performance gains (see Section 5.3).
(5) With Mobile IPv6, an MN can support multiple CoAs simultaneously,
if it is connected to multiple access networks simultaneously
(even if it is connected to one access network). Although only
one primary CoA will be used for routing traffic from the CN to
the MN, this multi-homing feature potentially can be used to
enhance the NSIS signaling performance (see Section 5.2).
5.1.1. Interfaces between Mobile IP and NSIS
As the NSIS WG concentrates on path-coupled signaling, one imposed
requirement here is that the NSIS protocols are to be associated with
route changes to support route optimization between the CN & the MN,
and the IP-in-IP encapsulation from the HA to the MN. This
interaction needs to be notified to all NSLPs (through the API
between GIST and NSLP) for the CRN discovery and the State Update.
Therefore, either NTLP or NSLP needs to have an interface with the
Mobile IP to immediately react to the mobility event. In other
words, an NSIS implementation needs to be developed to react on
mobility events based on the endpoint notification depending on which
behaviour of a mobility protocol has taken place (e.g., the timer of
Mobile IP expires).
An ideal interface between the NSIS signaling and the Mobile IP
should make it possible for NSIS signaling to immediately react to
the mobility event whenever Mobile IP changes its related
characteristics in any place for the flows. In general, it is
appropriate that NTLP (rather than NSLP) is involved in the
interaction with Mobile IP because NTLP is responsible for routing
NSIS messages. Therefore, it is reasonable to assume NTLP should be
able to notify NSLP for the necessity of State Update through API
between NTLP and NSLP when the mobility event is detected.
The following issues also arise concerning the API between the NSIS
protocol and the Mobile IP.
- Which information should be used to detect the movement? After an
MN moves to a new network attachment point, the new reachability
information is transferred from the MN to its HA as the last
procedure of handover. This procedure indicates that the NTLP may
need to interact with a binding process (e.g., a registration
request in Mobile IPv4 and Binding Update in Mobile IPv6) to
detect the IP address change and refer to the tunneling-related
information. Provided that the NTLP detects the mobility using
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the information on binding process, faster state establishment and
removal can be performed. However, in the fast or ping-pong type
handover, it may result in significant signaling overhead and some
possible errors (see Section 5.4).
- How and what information can the NSLP expect from NTLP, or
directly from the routing interface after a mobility event
happens?
- How is the mobility binding update interval coordinated with the
NSIS signaling interval? Since the binding update or the
registration request occurs periodically even for the MN with the
same point of attachment, the movement detection based on the
binding process may cause the NTLP/NSLP to initiate the CRN
discovery and the State Update inappropriately. To avoid the
problem, the change of CoA should be checked carefully. Although
this issue is closely related to implementation, it should be
considered to obtain any performance gains in signaling.
An overall coordination/synchronization for the interworking between
the NSIS and the Mobile IP needs to be discussed further.
5.1.2. Mobile IPv4-specific issues
With Mobile IPv4, the data flows are forwarded based on the
triangular routing, and an MN retains a new CoA from the FA (or an
external method such as DHCP) in the visited access network [5].
When the MN acts as a sender, the downstream data flows sent from the
MN are directly transferred to the CN not necessarily through the HA
or indirectly through the HA using the reverse routing. On the other
hand, upstream data flows sent from the CN are routed through the IP
tunneling between the HA and the FA (or the HA and the MN in case of
the Co-located CoA). With this approach, routing is dependent on the
HA, and therefore the NSIS protocols need to interact with the IP
tunneling procedure of Mobile IP for signaling.
Note that in QoS-NSLP scenarios, if MN is a sender and its Mobile
IPv4 protocol stack uses triangular routing mechanism, the receiver-
initiated approach is not suited to establish QoS states over the
Mobile IPv4. For this reason, the path of QUERY messages directly
sent from an MN to a CN (as shown in Figure 4 (a)) is not identical
with that of RESPONSE messages, as response of QUERY, forwarded via
HA from the CN to the MN (as shown in Figure 4 (d) or (e)).
Therefore, in this case, the Mobile IP should use the reverse
tunneling mechanism and the QUERY messages need to be forwarded over
reverse tunneling from FA to HA (as shown in Figure 4 (b) or (c)).
On the other hand, since in the sender-initiated approach, RESERVE
messages travel in the same direction as data flow without any QUERY
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message to establish the desired QoS states, this approach can be
used for both triangular routing and reverse tunneling mechanisms.
The Figures 4 (a) to (e) show the NSIS signaling flows depending on
the direction of data flows and the routing methods.
MN FA (or FL) CN
| | |
| IPv4-based Standard IP routing |
|------------ |--------------------------------->|
| | |
(a) MIPv4: MN-->CN, no reverse tunnel
MN FA HA CN
| IPv4 (normal) | | |
|--------------->| IPv4(tunnel) | |
| |--------------->| IPv4 (normal)|
| | |------------->|
(b) MIPv4: MN-->CN, the reverse tunnel with FA CoA
MN (FL) HA CN
| | | |
| IPv4(tunnel) | |
|------------------------------->|IPv4 (normal) |
| | |-------------->|
(c) MIPv4: MN-->CN, the reverse tunnel with Co-located CoA
CN HA FA MN
|IPv4 (normal) | | |
|-------------->| | |
| | MIPv4 (tunnel) | |
| |---------------->| IPv4 (normal)|
| | |------------->|
(d) MIPv4: CN-->MN, Foreign agent Care-of-address
CN HA (FL) MN
|IPv4(normal ) | | |
|-------------->| | |
| | MIPv4 (tunnel) | |
| |------------------------------->|
| | | |
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(e) MIPv4: CN-->MN with Co-located Care-of-address
Figure 4. NSIS signaling flows under different Mobile IPv4
scenarios
Concerning CRN discovery and State Update, the following signaling
procedures occur depending on the direction of signaling flows, i.e.,
either downstream or upstream signaling flow.
When an MN (as a sender) arrives at a new FA and the corresponding
binding process for the FA CoA is completed,
- for the downstream signaling flow, the MN needs to perform the CRN
discovery (DCRN) and the (downstream) State Update toward the CN
(as described in Section 4) to establish the NSIS state along the
new path between the MN and the CN as shown in Figure 4 (a). If
the reverse tunnel is used and the state along the tunneling path
does not exist, the NSIS state should be established along the
tunneling path from the FA to the HA as shown in Figure 4 (b). In
this case, a DCRN may be discovered on the tunneling path and the
new flow identifier for the State Update on the tunnel may need to
be created. That is, signaling flows over the tunnel are
considered as separated flows and thus the tunnel endpoints can
initiate a new signaling session for the flow over the tunnel (see
Section 5.1.3).
- for the upstream signaling flow, the CN may initiate the NSIS
signaling to update the existing state between the CN and the HA,
and afterwards HA forwards the NSIS signaling to FA. In this
case, NSIS signaling should interact with the IP tunneling
operation to update the state along the tunneling segment from the
HA to the FA as shown in Figure 4 (d). During this operation, a
UCRN may be discovered on the tunneling path, and the new flow
identifier for the state update on the tunnel may need to be
created.
When the MN (as a sender) arrives at a new foreign link (FL) and the
corresponding binding process for the co-located CoA is completed,
- for the downstream signaling flow, the NSIS signaling for the DCRN
discovery and the State Update is the same as the case of using FA
CoA above except for the use of the reverse tunneling path from
the MN to the HA as shown in Figure 4 (C). That is, in this case,
one of tunnel end points is the MN, not the FA.
- for the upstream signaling flow, the NSIS signaling for the UCRN
discovery and the State Update is also the same as the case of
using FA CoA above except for the end point of tunneling path from
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the HA to the MN as shown in Figure 4 (e).
Note that the DCRN and UCRN may be the same node on the tunneling
path of Mobile IP. For example, NSIS CRN may be usually the HA if
the HA and the FA are NSIS-aware but the NSIS signlaing over the
tunneling path is not coped with. Therefore, the CRN discovery will
be affected depending on the type of interaction between NSIS
signaling and IP tunneling. The FA and the HA need to be NSIS-aware
to do the State Update along the appropriate path. The impact that
the IP tunneling has on the CRN discovery and the State Update is
discussed in Section 5.1.4.
5.1.3. Mobile IPv6-specific issues
Unlike Mobile IPv4, with Mobile IPv6, the FA is not required on the
data path and the route optimization process between the MN and CN
can be used to avoid the triangular routing in the Mobile IPv4
scenarios as shown in Figure 5 [9]. If the use of route optimization
is not mandatory, data flow routing and NSIS signaling procedures
(including the CRN discovery and the State Update) will be similar to
the case of using the Mobile IPv4 with co-located CoA described in
Section 5.1.2.
In Mobile IPv6-based scenarios, the non-existence of FA implies that
the endpoint of IP-tunneling is extended to the MN. If the MN is a
sender and route optimization is optional, it should initiate both
tunnel signaling session and end-to-end signaling session by using
reverse tunneling. In this case, HA as another tunnel endpoint needs
to respond to the tunnel signaling messages and to forward the
end-to- end NSIS signaling messages to the CN. However, if the route
optimization in Mobile IPv6 is used as mandatory, it is not necessary
for NSIS signaling to interact with IP-tunneling any more. This also
means that NSIS signaling should not be initiated simultaneously with
the Binding Update message.
For CRN discovery and State Update, the following signaling
procedures occur depending on the direction of signaling flows, i.e.,
either downstream or upstream signaling flow.
When an MN (as a sender) arrives at a new AR and the binding process
is successfully completed,
- for the downstream signaling flow, the MN initiates NSIS signaling
for the DCRN discovery and the (downstream) State Update to
establish the state along the new optimized path between the MN
and the CN as shown in Figure 5 (a). On the other hand, the MN
initiates NSIS tunnel signaling for DCRN discovery and the State
Update over the tunneling path from the MN to the HA if the
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reverse tunnel is used, as shown in Figures 5 (b). In this case,
CRN discovery over tunnel can be performed using the same approach
described in Section 4.2.3 and more detailed considerations are
described in Section 5.1.4.
- for the upstream signaling flow, the CN may also update the state
along the common path toward the HA through the State Update, and
afterward the NSIS state along the tunneling segment from the HA
to the MN may be updated via the interaction with IP tunneling
operation as shown in Figure 5 (d). In this case, the HA (as the
tunnel endpoint for UCRN discovery and the State Update) needs to
create a new NSIS tunnel signaling toward the MN. The obsolete
path of the existing tunneling segments needs to be removed after
re-establishment of NSIS state along the new tunneling path. When
to remove the tunneling segment and/or how to tear it down through
interworking with the IP-tunneling operation is still an open
issue. However, if the route optimization is used between the CN
and the MN, for the upstream flow, CN needs to newly initiate end-
to-end NSIS signaling to discover an appropriate UCRN and do the
State Update along a new path between the CN and the MN as shown
in Figure 5 (c): the bidirectional state establishment may be
required between the CN and the MN.
MN CN
| |
|IPv6+HomeAdressOpt |
|--------------------------------------------->|
| |
(a) MIPv6: MN-->CN, no reverse tunnel
MN HA CN
|IPv6(tunnel) | |
|------------->| IPv6(normal) |
| |------------------------------>|
| |
(b) MIPv6: MN-->CN, with reverse tunnel
CN MN
| |
| MIPv6(RH Type 2) |
|--------------------------------------------->|
| |
(c) MIPv6: CN-->MN, route optimization
CN HA MN
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|IPv6(normal) | |
|------------->| |
| | MIPv6(tunnel) |
| |------------------------------>|
(d) MIPv6: CN-->MN, no route optimization
Figure 5 NSIS signaling flows under different Mobile IPv6
scenarios
5.1.4. Interaction with Mobile IP tunneling
In this section, we assume that MN acts as a sender and CN acts as a
receiver in interworking between Mobile IP and NSIS signaling
As described in Section 5.1.2, scenarios for interaction with Mobile
IP tunneling vary depending on
(i) whether the IP mobility management protocol is Mobile IPv4 or
Mobile IPv6,
(ii) whether the mode of QoS-NSLP signaling is sender-initiated or
receiver-initiated,
(iii) whether the signaling mode over tunnel is sequential or
parallel.
(iv) whether tunnel signaling supports per-flow or per-aggregate
approach.
In Mobile IPv4 scenarios, Mobile IP stack of an MN can use direct
routing or reverse tunneling to send data flows from the MN itself to
its CN. If the sender-initiated approach for the mode of QoS-NSLP
signaling is used and MN is a sender, both the direct routing and
reverse tunneling can be used to perform QoS-NSLP signaling.
However, if the receiver-initiated approach is used, the delivery of
QoS-NSLP signaling messages is available only using reverse
tunneling.
On the other hand, in Mobile IPv6 scenarios, route optimization or
bi- directional tunneling can be utilized to transport data flows
between MN and CN. In case of interaction with Mobile IPv6
tunneling, bi-directional tunneling needs to be taken into
consideration. That is, both sender-intiated and receiver-initiated
modes use only reverse tunneling to forward signaling flows from the
MN to the CN to interwork with tunneling and solve the ingress
filtering- related problem.
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5.1.4.1. Scenarios for interaction with Mobile IPv4 tunneling
The procedure of NSIS tunnel signaling in Mobile IPv4-based scenarios
is as follows.
In case that QoS-NSLP operates under the sender-initiated approach,
when an MN moves into a new network attachment point, QoS- NSLP in
the MN initiates RESERVE (end-to-end) message to start the State
Update procedure. The GIST below the QoS-NSLP adds GIST header and
then sends the encapsulated RESERVE message to peer GIST node with
corresponding QoS-NSLP for DCRN discovery. In this case, the peer
GIST node is a FA if the FA is an NSIS-aware node. The FA is one of
the endpoints of Mobile IP tunneling: Tentry. In case of interaction
with tunnel signaling originated from the FA, there can be two
scenarios depending on whether NSIS signaling interacts with the
Mobile IP tunneling. The first scenario is that the NSIS signaling
is discerned on the tunneling path between the FA and corresponding
HA, and then the tunneling path becomes an NSIS-aware cloud. The
second one is otherwise, and here the tunneling path is transparent
as a logical link to NSIS signaling [19].
In the NSIS-aware tunneling scenarios, as shown in Figures 6 and 7,
upon receiving the RESERVE message from the MN, the QoS-NSLP of FA
explicitly creates a new RESERVE-t (tunnel) message, which keeps the
existing (end-to-end) Session ID and includes a new (tunneling) Flow
ID different from the (end-to-end) flow ID, to distinguish the NSIS
signaling messages over the Mobile IPv4 tunneling path. The
RESERVE-t message is forwarded toward HA, another end point of Mobile
IPv4 tunneling. Also, after receiving the RESERVE-t message from the
FA, the HA should decide whether it needs to initiate a RESPONSE-t
(tunnel) message toward FA for responding to the RESERVE-t message,
or make the RESPONSE-t message wait until a RSESPONSE message, which
is created to react the RESERVE message, arrives from the CN.
In this procedure of NSIS-tunnel signaling, again, two categories of
tunnel signaling mode are taken into consideration, i.e., either
sequential or parallel mode.
As shown in Figure 6, provided that the tunnel signaling mode is
sequential,
- the RESERVE signaling toward the HA resumes after confirming
completeness of NSIS tunnel signaling through the RESERVE-t and
the RESPONSE-t messages as. Arriving at HA, the RESERVE message
is forwarded to CN to update or refresh the existing NSIS states
(QoS-NSLP and GIST) on the common path. The CN initiates a
RESPONSE message, responding to the RESERVE message, toward the HA
as its destination. The HA forwards the RESPONSE message to FA
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after encapsulating the message. Finally, the RESPONSE message is
sent to MN after being decapsulated at the FA . Note that both
end-to-end signaling messages, the RESPONSE and the RESERVE
messages, are not discernible on the tunneling path, like a
logical link, and those messages just play a role of NSIS
signaling for establishing end-to-end state.
- In this case, CRN discovery on the tunneling path is reconciled
with that over the end-to-end path. That is, the CRN formed by
mobility is discovered just one time between the FA and the HA.
This is possible by using the 'CRN_DISCOVERY (CD) flag bit'
mentioned in Section 4.2.3. Since the tunnel signaling at first
is performed, the FA can set the 'CD flag bit' in the RESERVE
message, to address that CRN is already discovered in the forward
direction. Therefore, CRN discovery by end-to-end NSIS signaling
is not performed any further. Note that the 'CD flag bit'
prevents downstream NEs to unnecessarily perform the process of
CRN discovery.
- After the CRN is discovered on the tunneling path, the CRN can now
perform the State Update procedure. If the CRN on the tunneling
path teardowns the state on the old path, the CRN may initiate
RESERVE-t message toward the old FA.
MN (Sender) FA (Tentry) Tnode HA (Texit) CN (Receiver)
| | | | |
| RESERVE | | | |
+--------->| | | |
| |RESERVE-t | | |
| +=========>| | |
| | |RESERVE-t | |
| | +=========>| |
| | |RESPONSE-t| |
| | |<=========+ |
| |RESPONSE-t| | |
| |<=========+ | |
| | RESERVE | |
| +-------------------->| |
| | | | RESERVE |
| | | +--------->|
| | | | RESPONSE |
| | | |<---------+
| | RESPONSE | |
| |<--------------------+ |
| RESPONSE | | | |
|<---------+ | | |
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| | | | |
Figure 6: Sender-Initiated QoS-NSLP over Tunnel -
Sequential Mode
Provided that tunnel signaling mode is parallel as shown in Figure 7,
- upon receiving the RESERVE message from the MN, the FA forwards it
to the HA at the drop of a hat. Also, arriving at the HA from the
CN, the RESPONSE message is again forwarded from the HA to the FA
regardless of the delivery of RESPONSE-t message. Since in this
parallel mode the end-to-end signaling messages do not reconcile
with both NSIS-tunnel signaling messages, the RESERVE-t and
RESPONSE-t messages, the tunneling path operates like a logical
link and thus NON-QoS-HOP flag is set within the RESERVE message
although NSIS-tunnel signaling messages are available on the
tunnel path.
- CRN discovery on the tunneling path is not reconciled with that
over end-to-end path. That is, two CRNs formed by mobility are
discovered through tunnel signaling and end-to-end signaling
messages, respectively. For CRN discovery through the tunnel
signaling messages, the CRN is discovered over the tunneling path
from the FA to the HA, which the discovered CRN between the FA and
the HA sets the 'CD flag bit'. However, for the CRN discovery
through the end- to-end signaling messages, the CRN is ferreted at
HA provided that the HA is an NSIS-aware node, which the HA sets
the 'CD flag bit' in RESERVE message. Note that the first
crossover node on the end-to- end signaling path is the HA because
the tunneling path is considered as a logical link for the end-to-
end signaling messages.
- The State Update at the CRN on the tunneling path is the same as
in the case of sequential mode. However, the CRN (e.g., HA)
discovered by the end-to-end signaling messages may also perform
the State Update procedure to remove the old state from itself to
the old FA.
MN (Sender) FA (Tentry) Tnode HA (Texit) CN (Receiver)
| | | | |
| RESERVE | | | |
+--------->| | | |
| |RESERVE-t | | |
| +=========>| | |
| | |RESERVE-t | |
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| | +=========>| |
| | RESERVE | |
| +-------------------->| |
| | | | RESERVE |
| | | +--------->|
| | | | RESPONSE |
| | | |<---------+
| | |RESPONSE-t| |
| | |<=========+ |
| |RESPONSE-t| | |
| |<=========+ | |
| | RESPONSE | |
| |<--------------------+ |
| RESPONSE | | | |
|<---------+ | | |
| | | | |
Figure 7: Sender-Initiated QoS NSLP over Tunnel - Parallel Mode
In case of QoS-NSLP signaling mode, provided that QoS-NSLP operates
under the receiver-initiated approach, QoS-NSLP in the MN initiates a
QUERY message to start the State Update procedure after a mobility
event. The GIST below the QoS-NSLP adds GIST header to it and sends
the encapsulated QUERY message to peer GIST node with corresponding
QoS-NSLP. In this case, the peer GIST node is a FA as the Tentry.
As the sender-initiated approach, Two scenarios can be considered
depending on whether NSIS signaling interacts with the Mobile IPv4
tunneling: One is that the tunneling path becomes an NSIS-aware
cloud, and another is the tunneling path is shown as a logical link
to NSIS signaling.
In the NSIS-aware tunneling scenarios, upon receiving the QUERY
message from the MN, the FA just transfers it toward the HA unlike
the receipt of the RESERVE message, and then the HA sends the QUERY
message to its CN. To respond to the QUERY message, CN initiates the
RESERVE message toward the HA to update or refresh the existing NSIS
states (QoS-NSLP and GIST) on the common path. The HA forwards it
toward the FA. After the receipt of the RESERVE message, the FA as
Tentry begins to perform the NSIS tunnel signaling as shown in
Figures 8 and 9. Moreover, receiving the RESERVE message from the
HA, the FA should decide whether it needs to forward the RESERVE
message toward MN irregardless of procedure of NSIS tunnel signaling.
In this procedure of NSIS tunnel signaling, again, two categories of
tunnel signaling mode are taken into consideration, i.e., either
sequential or parallel mode.
Provided that the tunnel signaling mode is sequential as shown in
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Figure 8,
- after confirming completeness of NSIS tunnel signaling through the
Query-t, the RESERVE-t, and the RESPONSE-t signaling messages, the
RESERVE signaling toward the MN is transferred. Concerning the
procedure of tunnel signaling, upon receiving the RESERVE message
from the HA, the QoS-NSLP of FA creates a new QUERY-t message,
which keeps the existing (end-to-end) Session ID and includes a
new (tunneling) Flow ID different from the (end-to-end) flow ID,
to interact with Mobile IPv4 tunneling. The QUERY-t message is
forwarded toward HA as Texit. Also, upon receiving the QUERY-t
message, the HA initiates RESERVE-t message, responding to the
QUERY-t message, toward FA to discover the UCRN and perform the
State Update. If the FA sends the RESPONSE-t toward HA as a
response to the RESERVE-t message, NSIS tunnel signaling is
finalized. In this case, all the NSIS tunnel signaling messages
are just valuable on the tunneling path between the FA and the HA.
Note that FA can forward the RESERVE message to MN as soon as
initiating the RESEPONSE-t message, as a response to the RESERVE-t
message, toward the HA.
- CRN discovery on the tunneling path is not reconciled with that
over end-to-end path unlike the sender-initiated mode of QoS-NSLP.
That is, firstly, the CRN formed by mobility is discovered at the
HA through the end-to-end signaling (e.g., RESERVE message), which
the HA sets the 'CD flag bit' in the RESERVE message. Next, the
tunnel CRN is discovered at a certain tunnel node between the HA
and FA, which the CRN discovered at any node over the tunneling
path sets the 'CD flag bit' in the RESERVE-t message.
- In this case, the procedure for the removal of the state on the
old path is identical to the case of the parallel tunnel signaling
mode in sender-initiated QoS NSLP signaling.
MN (Sender) FA (Tentry) Tnode HA (Texit) CN (Receiver)
| | | | |
|QUERY | | | |
+--------->| QUERY | |
| +-------------------->| QUERY |
| | | +--------->|
| | | | RESERVE |
| | RESERVE |<---------+
| |<--------------------+ |
| | QUERY-t | | |
| +=========>| QUERY-t | |
| | +=========>| |
| | |RESERVE-t | |
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| |RESERVE-t |<=========+ |
| |<=========+ | |
| |RESPONSE-t| | |
| RESERVE +=========>|RESPONSE-t| |
|<---------| +=========>| |
| RESPONSE | | | |
+--------->| RESPONSE | |
| +-------------------->| RESPONSE |
| | | +--------->|
| | | | |
Figure 8: Receiver-Initiated QoS NSLP over Tunnel - Sequential Mode
On the other hand, provided that tunnel signaling mode is parallel as
shown in Figure 9,
- upon receiving the RESERVE message from the HA, the FA forwards it
to the MN at the drop of a hat. After receiving the RESERVE
message from the FA, the MN forwards the RESPONSE message to the
HA via FA regardless of the delivery of RESPONSE-t message. Since
in this parallel mode the end-to-end signaling messages do not
reconcile with both NSIS tunnel signaling messages, the RESERVE-t
and RESPONSE-t messages, the tunneling path operates as like a
logical link and thus NON-QoS-HOP flag is set within the RESERVE
message although NSIS tunnel signaling messages are available on
the tunnel path.
- CRN discovery on the tunneling path is not also reconciled with
that over end-to-end path. That is, all the procedure of CRN
discovery is identical with the sequential mode of tunnel
signaling. In this case, the procedure for the removal of the
state on the old path is also identical with the case of the
sequential tunnel signaling mode in receiver-initiated QoS NSLP
signaling.
MN (Sender) FA (Tentry) Tnode HA (Texit) CN (Receiver)
| | | | |
|QUERY | | | |
+--------->| QUERY | |
| +-------------------->| QUERY |
| | | +--------->|
| | | | RESERVE |
| | RESERVE |<---------+
| RESERVE |<--------------------+ |
|<---------+ | | |
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| | QUERY-t | | |
| +=========>| QUERY-t | |
| | +=========>| |
| | |RESERVE-t | |
| |RESERVE-t |<=========+ |
| |<=========+ | |
| |RESPONSE-t| | |
| +=========>|RESPONSE-t| |
| | +=========>| |
| RESPONSE | | | |
+--------->| RESPONSE | |
| +-------------------->| RESPONSE |
| | | +--------->|
| | | | |
Figure 9: Receiver-Initiated QoS-NSLP Operation over Tunnel -
Parallel Mode
5.1.4.2. Scenarios for interaction with Mobile IPv6 tunneling
In Mobile IPv6-based scenarios, tunneling path is further extended to
MN from HA unlike the Mobile IPv4-based scenario. That is, the MN
itself is one of the end points of tunneling path, and is in charge
of most tunnel-related functionalities of FA. All the procedures of
State Update in interaction with Mobile IPv6 is similar to those in
interaction with Mobile IPv4 except there is no FA. The procedure of
NSIS tunnel signaling in Mobile IPv6-based scenarios is as follows.
Provided that QoS-NSLP operates under the sender-initiated approach,
after MN moves into a new network attachment point, QoS-NSLP over MN
initiates RESERVE message to start the State Update procedure. The
GIST below the QoS-NSLP adds GIST header and sends the encapsulated
RESERVE message to peer GIST node with corresponding QoS-NSLP for
DCRN discovery. In this case, the peer GIST node would be a HA if
the HA is NSIS-aware, and the MN is one of the endpoints of Mobile
IPv6 tunneling (Tentry). Two scenarios can be considered depending
on whether NSIS signaling interacts with the Mobile IPv6 tunneling.
One is that the NSIS signaling is discerned on the tunneling path
between the MN and corresponding HA, and then the tunneling path
becomes an NSIS-aware cloud. The other is otherwise, and here the
tunneling path is shown as a logical link to NSIS signaling.
In this procedure of NSIS tunnel signaling, again, two categories of
tunnel signaling mode are taken into consideration, either sequential
or parallel mode.
On the one hand, provided that the tunnel signaling mode is
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sequential as shown in Figure 10,
- before initiating the RESERVE message, the QoS-NSLP of MN creates
a new RESERVE-t message, which keeps the existing (end-to-end)
Session ID and includes a new (tunneling) Flow ID different from
the (end-to-end) flow ID, to interact with Mobile IPv6 tunneling.
The RESERVE-t message is forwarded toward HA as another end point
of Mobile IPv6 tunneling to discover the DCRN and perform the
State Update. Also, upon receiving the RESERVE-t message from the
MN, the HA should initiates a RESPONSE-t message toward MN
reacting to the RESERVE-t message. The RESERVE signaling toward
the HA is performed after confirming completeness of NSIS tunnel
signaling through the RESERVE-t and the RESPONSE-t signaling
messages. Arriving at HA from the MN, the RESERVE message is
forwarded to CN to update or refresh the existing NSIS states
(QoS-NSLP and GIST) on common path. The CN initiates RESPONSE
message, responding to the RESERVE message, toward the HA as its
destination, and then the HA forwards the RESPONSE message to MN
via corresponding AR.
- CRN discovery on the tunneling path is reconciled with that over
end-to-end path. That is, the process of CRN discovery caused by
mobility is performed just one time between the MN and the HA.
This can be possible by using the 'CRN_DISCOVERY (CD) flag bit'.
Since tunnel signaling in the first place is performed for CRN
discovery, the MN sets the 'CD flag bit' in the RESERVE message by
checking the tunnel signaling messages, to address that already
CRN is discovered for forward direction, if the CRN over the
tunnel path is already discovered through NSIS-tunnel signaling
messages. Therefore, CRN discovery by end-to-end NSIS signaling
is not performed any further.
- After the tunnel-CRN is discovered, the CRN can perform the State
Update procedure. If the tunnel-CRN teardowns the state on the
old tunnel path, the CRN may initiate RESERVE-t message toward the
old AR.
MN (Sender: Tentry) Tnode HA (Texit) CN (Receiver)
| | | |
| RESERVE-t | | |
+====================>| | |
| |RESERVE-t | |
| +=========>| |
| |RESPONSE-t| |
| RESPONSE-t |<=========+ |
|<====================+ | |
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| | | |
| RESERVE | |
+------------------------------->| |
| | | RESERVE |
| | +--------->|
| | | RESPONSE |
| | |<---------+
| RESPONSE | |
|<-------------------------------+ |
| | | |
Figure 10: Sender-Initiated QoS-NSLP Operation over Tunnel -
Sequential Mode
On the other hand, provided that tunnel signaling mode is parallel as
shown in Figure 11,
- MN initiates both the RESERVE and the RESERVE-t messages toward
the HA at the same time. Also, arriving at the HA from the CN,
the RESPONSE message is again forwarded from the HA to the MN
regardless of the delivery of RESPONSE-t message. Since in this
parallel mode the end-to-end signaling messages do not reconcile
with both NSIS-tunnel signaling messages, the RESERVE-t and
RESPONSE-t messages, the tunneling path operates as like a logical
link and thus NON-QoS-HOP flag is set within the RESERVE message
although NSIS-tunnel signaling messages are available on the
tunnel path.
- CRN discovery on the tunneling path is not reconciled with that
over end-to-end path. That is, in this case the CRN discovery
procedure is identical to the parallel mode of Mobile IPv4 tunnel
signaling except for extension of the tunnel path from the FA to
the MN.
- provided that the CRN is discovered on the tunneling path, the CRN
can perform the State Update procedure. In order to teardown the
state on the old tunnel path, the CRN discovered on the tunneling
path may be able to initiate RESERVE-t message toward the old AR.
Also, the CRN discovered by the end-to-end signaling messages
(e.g., HA) can perform the State Update procedure to remove the
old state from itself to the old AR. In this case, the RESERVE
message for removal of obsolete state is transparent over the
nodes within the tunnel path.
MN (Sender: Tentry) Tnode HA (Texit) CN (Receiver)
| | | |
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| RESERVE | |
+------------------------------->| |
| | | RESERVE |
| | +--------->|
| RESERVE-t | | |
+====================>| | |
| |RESERVE-t | |
| +=========>| |
| |RESPONSE-t| |
| RESPONSE-t |<=========+ |
|<====================+ | |
| | | RESPONSE |
| | |<---------+
| RESPONSE | |
|<-------------------------------+ |
| | | |
Figure 11: Sender-Initiated QoS-NSLP Operation over Tunnel
- Parallel Mode
In case of QoS-NSLP signaling mode, provided that QoS-NSLP operates
under the receiver-initiated approach, after MN moves into a new
network attachment point, QoS-NSLP over MN initiates QUERY message to
start the State Update procedure as shown in Figure 12 and 13. The
GIST below the QoS-NSLP adds GIST header and sends the encapsulated
QUERY message to peer GIST node with corresponding QoS-NSLP. In this
case, the peer GIST node can be a HA if the HA is an NSIS-aware node.
Also, as the sender-initiated approach, the MN is a Tentry. Two
scenarios can be considered dependent on whether NSIS signaling
interacts with the Mobile IPv6 tunneling: One is that the tunneling
path between the MN and the HA becomes an NSIS-aware cloud. Another
is otherwise, and here the tunneling path is shown as a logical link
to NSIS signaling.
In this procedure of NSIS-tunnel signaling, again, two categories of
tunnel signaling mode are taken into consideration, i.e., either
sequential or parallel mode. On the one hand, provided that the
tunnel signaling mode is sequential as shown in Figure 12,
- MN initiates a QUERY message toward the HA, and then the HA send
the QUERY message to its CN. In this case, as reacting to QUERY
message, CN initiates the RESERVE message toward the HA to update
the existing NSIS states (QoS-NSLP and GIST) on common path.
Afterwards the HA forwards it to the MN as destination. After the
receipt of the RESERVE message, the MN as Tentry begins to perform
the NSIS-tunnel signaling.
- Concerning the procedure of NSIS-tunnel signaling, upon receiving
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the RESERVE message, the QoS-NSLP of MN creates a new QUERY-t
message, which keeps the existing (end-to-end) Session ID and
includes a new (tunneling) Flow ID different from the (end-to-end)
flow ID, to interact with node within the tunneling path. The
QUERY-t message is forwarded toward HA as Texit. Also, upon
receiving the QUERY-t message from the MN, the HA again initiates
the RESERVE- tunnel message toward MN. If the MN sends the
RESPONSE-t toward HA as react of the RESERVE-t message, NSIS-
tunnel signaling is finalized. Note that MN can initiate the
RESPONSE (e2e) message to HA as soon as the RESERVE- tunnel
message from the HA is received.
- CRN discovery on the tunneling path is not reconciled with that
over end-to-end path unlike sender-initiated mode of QoS-NSLP.
That is, firstly, the CRN caused by mobility is discovered at the
HA through the end-to-end signaling (e.g., RESERVE message), which
the HA sets the 'CD flag bit' in the RESERVE message. Next, the
tunnel CRN is discovered at a certain tunnel node between the HA
and MN, which the CRN discovered at any node over the tunnel path
sets the 'CD flag bit' in the RESERVE-t message. In this case,
the procedure for the removal of the state on the old path is
identical to the case of the parallel tunnel signaling mode in
sender-initiated QoS NSLP signaling.
MN (Sender: Tentry) Tnode HA (Texit) CN (Receiver)
| | | |
| QUERY | |
+------------------------------->| QUERY |
| | +--------->|
| | | RESERVE |
| RESERVE |<---------+
|<-------------------------------+ |
| QUERY-t | | |
+====================>| QUERY-t | |
| +=========>| |
| |RESERVE-t | |
| RESERVE-t |<=========+ |
|<====================+ | |
| RESPONSE-t | | |
+====================>|RESPONSE-t| |
| +=========>| |
| RESPONSE | | |
+------------------------------->| RESPONSE |
| | +--------->|
| | | |
Figure 12: Receiver-Initiated QoS NSLP over Tunnel - Sequential Mode
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On the other hand, provided that tunnel signaling mode is parallel as
shown in Figure 13,
- MN initiates both the QUERY and the QUERY-t messages to the HA at
the same time. Also, arriving at the HA, the Query message is
again forwarded from the HA to the CN regardless of the delivery
of QUERY-t message. Since in this parallel mode the end-to-end
signaling messages do not reconcile with both NSIS- tunnel
signaling messages, the QUERY-t, the RESERVE-t and RESPONSE-t
messages, the tunneling path operates like a logical link. Thus,
NON-QoS-HOP flag is set within the RESERVE message although NSIS-
tunnel signaling messages are available on the tunnel path.
- CRN discovery on the tunneling path is not also reconciled with
that over end-to-end path as like the sequential mode of tunnel
signaling. That is, the CRN discovery procedure is identical with
the parallel mode of sender-initiated QoS-NSLP signaling. In this
case, the procedure for the removal of the state on the old path
is also identical with the case of the sequential tunnel signaling
mode in receiver-initiated QoS NSLP signaling.
MN (Sender: Tentry) Tnode HA (Texit) CN (Receiver)
| | | |
| QUERY | |
+------------------------------->| QUERY |
| | +--------->|
| QUERY-t | | |
+====================>| QUERY-t | |
| +=========>| |
| |RESERVE-t | |
| RESERVE-t |<=========+ |
|<====================+ | |
| | | RESERVE |
| RESERVE |<---------+
|<-------------------------------+ |
| RESPONSE-t | | |
+====================>|RESPONSE-t| |
| +=========>| |
| RESPONSE | | |
+------------------------------->| RESPONSE |
| | +--------->|
| | | |
Figure 13: Receiver-Initiated QoS NSLP over Tunnel-Parallel Mode
5.2. NSIS operations in multihomed mobile environments
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In multihomed mobile environments, multiple interfaces and addresses
(i.e., CoAs and HoAs) are available and thus how to select or acquire
the most appropriate interface and/or address is of great concern
[18]. One of the NSIS's goals is to achieve end-to-end signaling for
various signaling applications. However, some reasons such as scarce
wireless resources, usage of tunneling, and frequent change of end
host's address make it difficult for NSIS signaling to achieve end-
to-end signaling. In this case, the interaction between the
multihoming schemes and NSIS signaling protocols could alleviate
problems caused by wireless bottleneck and mobility events. In this
section, we discuss some NSIS signaling issues on interworking with
multihomed networks and also present on how NSIS signaling (in
particular QoS signaling) should perform multihomed signaling in
mobility scenarios.
5.2.1. Multihomed mobile environments
In order to achieve the multihomed QoS signaling, the MN would need
to register several CoAs with the unique HoA. However, since the
present specification of MIPv6 only allows the MN to register a
single CoA per HoA, a solution like [20] needs to be used for
multiple CoAs registration. On the other hand, when the MN has more
than one HoA given either by one HA or multiple HAs, multiple CoAs
registration may not happen because each CoA could be bound with
single HoA. Throughout the scenario in this draft, we assume that an
appropriate multiple CoAs registration mechanism is provided.
When a route optimization is used, a direct connection is established
between an MN and a CN, in which case another reservation needs to be
made while releasing the existing reservation engaged in the HA. In
order to avoid this situation, the NSIS signaling for resource
reservation needs to be performed only after finishing the route
optimization, which is the way assumed in the following scenarios.
On the other hand, without route optimization the resource
reservation could be performed immediately after establishing the
reverse tunnel.
In this section we are detailing the two scenarios for multihomed QoS
signaling: receiver-initiated reservation and sender-initiated
reservation. Figure 14 depicts the multihomed mobile environment
where an MN with multiple interfaces moves to new area in which
several ARs could possibly serve the MN. After handover, the MN
checks the strength of the beacon signal and the available link
bandwidth that neighboring ARs provide, and chooses the most stable
ARs. An MN acquires multiple CoAs from the chosen ARs each of which
is advertising single prefix, and then each CoA is assigned to one of
the interfaces of the MN.
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...........................
. +---+ . +---+ +---+
+--.----------+ R1|----------.----+ CR+------------+ R3|
| . +-----+-+-+-----+ . +---+ +------+-+-+
+---+ . | | | . | |
| . | | | . +-+-+ +-+-+
+-+-+ . +-+-+ +-+-+ +-+-+ . | HA| | CN|
|OAR| . |AR1| |AR2| |AR3| . +---+ +---+
+---+ . +---+ +---+ +---+ .
. .
+---+ . +---+ .
| MN| =====> | MN| .
+---+ . +---+ .
...........................
Figure 14. Illustration of the Multihomed environment
We assumed homogeneous wireless interfaces in this draft although
multihoming with multiple interfaces would be more efficient on
heterogeneous interfaces due to the increased path diversity. The
issues on heterogeneous interfaces are for further study.
Seamoby protocols such as CARD [RFC4066] and CTP [RFC4067] are not
considered in this draft because an anticipated handover mechanism is
not used. As a first step, this draft discusses interaction with
basic macromobility management protocols (e.g., Mobile IPv4/6). The
interaction with mircomobility management protocols are for further
study for performance optimization.
5.2.2. Receiver-initiated reservation in the multihomed environment
o BU and QUERY message transmission
|--Handover-->|
MN OAR AR1 AR2 AR3 CRN CRN CRN CN
(OAR/AR1)(OAR/AR2)(OAR/AR3)
| | | | | | | | |
|---QUERY(1)->|-------------------->|---------------------->|
| | | | | | | | |
|---QUERY(2)-------->|--------------------->|-------------->|
| | | | | | | | |
|---QUERY(3)--------------->|---------------------->|------>|
| | | | | | | | |
| | | | | | | | Primary CoA
| | | | | | | | Selection(4)
| | | | | | | | |
| | | | | | |<--RESERVE(5)--|
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| | | |<------RESERVE(6)-----| (Flow ID |
| | | | (Actual reservation) | Update) |
|<----RESERVE(7)-----| | | | | |
| | | | | | | | |
| |<-----------teardown(8)-------------| | |
| | | | | | | | |
| | | | Multimedia Traffic | | |
|<=================->|<===================->|<=============>|
| | | | | | | | |
Figure 15. Receiver-initiated reservation in the multihomed
environment
After handover, an MN acquires multiple CoAs through aforementioned
procedures and immediately sends a Binding Update to the CN for each
of newly acquired CoAs. The CN acknowledges the binding update (BU)
by sending a binding acknowledgment (BA) to the MN.
On receiving each BA, the MN immediately sends a QUERY message toward
the CN through the interface associated with the CoA, to probe the
network for information about the data path (the procedure (1)-(3) in
Figure 15). The available resource on the path is recorded in the
`QoS Available' object of the QSPEC contained in the QUERY message.
o Intermediate node operation
The intermediate node inspects the 'QoS Available' object of the
received QUERY message, and if its available resource is less than
what 'QoS Available' says currently, the node adapts it accordingly.
Therefore, when the QUERY message reaches the CN, the `QoS available'
reflects the bottleneck of the resources on the path.
o Primary CoA selection
On receiving the QUERY messages the CN performs the Primary CoA
determination procedure for the MN (4). The QUERY messages received
no later than a certain time period after the reception of the first
QUERY message are taken into account for the procedure. The time
period is used to prevent the QUERY messages that arrive too late or
have been dropped on the way from delaying the decision procedure.
Though the small waiting time might exclude several messages from the
procedure it would be desirable to maintain the time period to be
small because the QUERY messages along the path with good condition
would have been arrived earlier than others. On the other hand, the
procedure could be immediately started even before the time period
elapses when all Query messages are received, which is possible
because the CN is aware of the total number of QUERY messages to
receive beforehand through the number of BU messages.
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The CN determines the Primary CoA based first on the available
bandwidth and second on the arrival time of Query messages. When the
available resource pertained in a QUERY message is conforming to the
MN's BW requirement, the CoA delivered in the QUERY message is
selected as the Primary CoA. In the case of more than one conforming
QUERY messages, the message arrived first is selected.
o Reservation re-establishment and teardown
The CN sends a RESERVE message toward the MN to reserve resources
along the path the Primary CoA takes. In this case, the RESERVE
message activates two different actions: flow ID update and resource
reservation. A flow ID consisting of source and destination
addresses is used to identify the data communication route. On
receiving RESERVE message, the nodes between the CN and the CRN
updates the existing flow ID by replacing the old CoA with the new
one, and uses the existing reservations for new path (5). On the
other hand, resource reservations are performed between the CRN and
new AR to establish new path (6). If the reservation is not
successful the CN transmits another RESERVE message using the CoA
with the next highest priority.
The CRN may initiate a teardown (RESERVE with the TEAR flag set)
message toward old access router (OAR) to release the reserved
resources on the old path (8).
5.2.3. Sender-initiated reservation in the multihomed environment
Sender-initiated reservation shares the procedure of receiver-
initiated approach except that in the sender-initiated reservation,
the QUERY and RESERVE messages are initiated by an MN, where the MN
selects the Primary CoA based on the information delivered by the
QUERY message. As in the receiver-initiated reservation, the
teardown message (RESERVE with the TEAR flag set) is initiated by the
CRN to release the reservation in the obsolete path.
5.2.4. Link/node failure recovery
In case of link or node failures in the networks, NSIS state on the
affected path will be removed. In this case, NSIS state immediately
needs to be recovered on an alternative path to provide the seamless
service for applications. If an on-going session is temporarily
disrupted due to a wireless link failure in the multihomed
environment, an MN needs to find an alternative path via an available
interface to re-establish the session state. Suppose that an MN has
three interfaces each of which is associated with a wireless link.
If the current wireless link which is used for communication fails,
the MN selects an alternative link via an alternative interface which
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is able to support the MN's QoS requirement and re-establishes NSIS
state along the new path. The path selection and NSIS signaling
procedure are similar to the case above except for the absence of the
teardown message (RESERVE with the TEAR flag set).
5.2.5. Load balancing
There may be a situation where an MN may need to distribute its
traffic load to multiple paths via multiple interfaces. In this
case, the MN can send multiple QUERY messages to multiple interfaces
to establish NSIS state on multiple paths.
Suppose that an MN wants to set up NSIS state on a path which is able
to support the specific bandwidth requirement for a certain
application in the multihomed environment. It may not be possible to
find a feasible path for such a requirement. In this case, multiple
paths can be used at the same time so that the bandwidth requirement
can be met. Note that the flow identifier on each path may be
different although the session identifier is unchanged.
When the same Session ID (SID) is used for multiple paths, special
functionalities can be required for handling various paths,
especially for proper CRN discovery and operation. This is because,
there can be two types of CRNs, one is the CRN between two on-going
paths, and the other is the CRN between the old and new paths caused
by MN's handover. Here we call the former CRN "Load Balancing CRN
(LB-CRN)" and the latter one "Handover CRN (HO-CRN)". The CRNs need
to know which type of CRN they are, either HO-CRN or LB-CRN, so as to
correctly carry out the State Update.
An example scenario is depicted in Figure 16. If an MN uses path 1
and path 2 for the same session, where path 1 and path 2 have the
same SID but different Flow IDs (FIDs), respectively, as mentioned
previously, the CRN between path 1 and path 2, LB-CRN has information
about two FIDs for the same SID (see Figure 16 (a)). Now when one of
the interfaces of MN (e.g., an interface over Path 1) performs a
handover and obtains a new Care of Address (CoA), the MN will try to
establish a new path (say Path 3) with the new CoA which shall have a
new FID (see Figure 16 (b)). In this case, impact of this handover
in multihoming scenario on the NSIS signaling will be that the CRN
can unnecessarily or incorrectly perform an State Update. For
example, if the new path (Path3) crosses over with path 2, the CRN
between path 2 and path 3 cannot distinguish if it is LB-CRN or HO-
CRN since for both the cases, SID is the same but FIDs are different.
Hence the CRN will not know if State Update is required.
+--+ Path 1 +---+ +--+
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| |<---------------------|LB |common path | |
|MN| |CRN|------------|CN|
| | Path 2 | | | |
| |<---------------------| | | |
| | +---+ +--+
| |
+--+
(a) NSIS Path classification in multihomed environments
+--+ Path 1 +---+ +--+
| |<---------------------|LB |common path | |
|MN| |CRN|------------|CN|
| | Path 2 -| | | |
| |<------- +------+ | | | | |
| | \_|??-CRN|--v +---+ +--+
| | / +------+
+--+<-------
Path 3
(b) NSIS Path classification after handover
Figure 16: The topology for NSIS signaling in multihomed mobile
environments
In order to solve this problem, all on-going paths need to be
differentiated by using some ways. One possible solution is to have
an identifier with a few bits, such as "Path type ID." The Path type
ID provides a different identifier for all on-going paths, e.g., path
type "x" for path1 and path type "y" for path2 as shown in Figure 17.
When a path changes, the route after a handover needs to be assigned
to the same path type ID. If path2, for example, is changed to path
3, "y" is also used as path type id for path 3. When these two paths
meet, the CRN checks the path type IDs of the two paths. If Path
type IDs are the same (case 1), the CRN is HO-CRN. Otherwise (case
2), the CRN becomes LB-CRN. Another solution would be for the new
path to carry the FID of the old path. It also enables the CRN to
determine if it is a HO-CRN or LB-CRN, and to perform the required
State Update operations. However, since FID is very long, it will
cause high overhead if used for this purpose.
+--+ Path 1 (x) +---+ +--+
| |<---------------------|HO |common path | |
|MN| |CRN|------------|CN|
| | Path 2 (y) -| | | |
| |<------- +------+ | | | | |
| | \_|LB-CRN|--v +---+ +--+
| | / +------+ (x,y)
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+--+<-------
Path 3 (x)
Figure 17: The topology for NSIS signalling with Path Type ID
in multihomed mobile environments (case 2)
Having extra information, such as path type ID or previous FID, to
differentiate LB-CRN and HO-CRN will have some effects on signaling
messages and NEs' behaviors at NTLP and/or NSLP layers. That is, the
identiifers can be implemented on either of the two signaling
messages (GIST or NSLP). For instance, if the identifier is included
at the GIST message format, the information can be stored in the MRI,
and be propogated as part of the peer discovery process. if it is
included at the QoS-NSLP signaling messages, at least the RESERVE
message needs to be modified to add the extra information. In this
case, the identifier-related information needs to be stored at NEs by
GIST or NSLP messages, and thus the NEs can differenciate HO-CRN from
LB-CRN.
5.3. QoS performance considerations in mobility scenarios
The routing characteristics of Mobile IP described in Section 5.1
cause the session path to frequently be changed and thus the NSIS
signaling in such dynamic environments needs to cope with the various
challenges mentioned in Section 3.1. In QoS-NSLP, critical issues
which make QoS performance being degraded should be resolved to
guarantee services for that data flow. In this section,
particularly, QoS performance in terms of resource utilization and
signaling latency is discussed to give some guidelines on how NSIS
protocols should interact with mobility management protocols.
The double reservation problem can be alleviated by using a unique
session identifier and the State Update procedure including CRN
discovery. However, management of the resource utilization in
overall NSIS signaling processing point of view should be taken into
account; in this regard, the adjustment of refresh interval is one of
the crucial elements which decide performance metrics of resource
utilization as mentioned in Section 3.2. This issue needs to be
discussed further in the case of the soft state approach to release
the obsolete state in mobility scenarios which is preferred to any
explicit tear-down approach.
The NSIS protocol suite normally uses a soft-state approach based on
the peer-to-peer refresh to manage state in NEs. The peer-to-peer
based refresh allows the NSIS to appropriately select the refresh
interval by considering the current network environment. For
example, the refresh timer value in networks with scarce resources
(e.g., mobile/wireless (access) networks ) may set for a long time to
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decrease the overhead of signaling messages. If any explicit
teardown messages for state removal are not used, in the situation
where handover happens very frequently, the dynamic adjustment of the
refresh interval can reduce the waste of resources. In this case,
the refresh timer value needs to be set to a smaller value in the
mobile/wireless networks than that in the core (wired) network as in
[5]. To create dynamic refresh intervals, a general mechanism to be
able to choose an optimal refresh timer value according to various
mobile environments needs to be considered. However, this approach
requires refresh interval traits dependent on specific network
environments. When an MN, for example, roams from WLAN to UMTS or
WIMAX (or WiBro) networks, the refresh interval in the UMTS or
WIMAX(or WiBro) networks need to be set up differently from the WLAN
networks. This advanced approach to automatically decide refresh
intervals is further study.
Note that unlike the QoS-NSLP, the refresh timer of NTLP state does
not need to be adjusted in the network since signaling application as
resource reservation is not involved directly. Furthermore, the NTLP
state along the obsolete path does not need to be explicitly removed
before the expiration of refresh timer.
In mobile wireless networks, QoS-NSLP (rather than the NTLP) should
be able to set the refresh timer value depending on the handover type
(e.g., make-before-break or break-before-make) or the reservation
style (e.g., pre-establishment or re-establishment) to optimize the
resources utilization. For example, in the make-before-break
handover, an appropriate refresh time interval can be notified using
the reserved field of REFRESH object. If the refresh timer value is
set to a little higher value than the estimated handover latency, the
MN can be provided with seamless QoS service using the pre-reserved
resources without the waste of resources [6].
After the state setup on the new path, QNEs on the signaling path may
send a refresh message to the neighboring peer node before the
refresh timer expires to update only the state previously installed
along the path, or update the changed MRI along the common path . In
this case, the overhead required to perform refresh can be reduced,
in a way similar to the refresh reduction in RSVP [16]. Once a
RESPONSE message which indicates the successful installation of a
reservation has been received, subsequent RESERVE messages for
refresh can simply refer to the existing reservation, rather than
including the complete reservation specification. For example, in
case of QoS-NSLP, only the SID and the SII with no QSPEC are sent to
just refresh the state (e.g., reservation) previously installed. The
changed flow ID together with those IDs is only sent to update it
along the common path. Especially, transmission of the reduced
number of refresh messages over wireless channels, access networks,
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or core networks results in the efficient utilization of resources.
As mentioned in Section 3.1, unlike the generic route changes, in
mobility scenarios, the end-to-end signaling problem by the Path
Update gives rise to the degradation of network performance such as
increased signaling overhead, service blackout, and so on. To reduce
signaling latency in the Mobile IP-based scenarios, the NSIS protocol
suite needs to interwork with localized mobility management (LMM).
If the GIST/NSLP( QoS-NSLP or NAT/FW-NSLP) protocols interact with
Hierarchical Mobile IPv6 and the CRN is discovered between an MN and
MAP, the State Update can be localized by address mapping. However,
how the State Update is performed with scoped signaling messages
within the access network under the MAP is for further study.
In the inter-domain handover, a possible way to mitigate the latency
penalty is to use the multi-homed MN. It is also possible to allow
the NSIS protocols to interact with mobility protocols such as
Seamoby protocols (e.g., CARD [RFC4066] and CXTP [RFC4067]) and FMIP.
Another scenario is to use peering agreement which allows aggregation
authorization to be performed for aggregate reservation on an inter-
domain link without authorizing each individual session. How these
approaches can be used in NSIS signaling is for further study.
5.4. Support for Ping-Pong type handover
NSIS signaling needs to consider the interaction with ping-pong type
handover as addressed in Section 3.1 because it has a significant
effect on when to initiate signaling for state setup or for state
release. With the sender-initiated approach, if an MN (as a sender)
undergoes a handover into a new AR, the NTLP interacts with the
binding process of Mobile IP to initiate state setup. However, if
the MN moves to other ARs or the previous AR again in a short while,
signaling using the interaction with the binding process may result
in considerable signaling overhead and some possible errors.
Immediate teardown of state on the old path may also bring on the
similar result. Some identifiers defined in [5] [6] may be useful
for this situation.
An NE (e.g. QNE) can determine if it is a merging point (i.e. an
NSLP CRN) of the old and new paths, and then it can perform an
involved state setup on the new path and state teardown on the old
path . However, if the QNE receives an NSIS message (e.g., RESERVE)
with a special flag (e.g. NO_REPLACE flag) set but with the
different SII, state teardown on the old path should not happen.
This may apply to a ping-pong type handover where the MN wishes to
keep state to its old attachment point in case it moves back there.
For interaction with the ping-pong type handover, NSIS should
determine when to set the NO_REPLACE flag depending on when and where
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the MN handovers. It requires NSIS to monitor or react on the
mobility events over possible API. It is stil an open issue and
needs to be discussed further.
The Reservation Sequence Number (RSN) may be useful in detecting
duplicate messages in the mobile environment. For example, it is
possible for the MN to move to the second NAR soon after being
attached to the 1st NAR. The CRN may receive the RESERVE messages
(with different RSN) twice when the RESERVE message from the 1st NAR
arrives later than the RESERVE message from the 2nd NAR. In this
case, the CRN should determine which RESERVE message is the latest
one via the RSN.
The Mobility object described in Section 4.2.2 can be defined in the
NTLP (e.g., in GIST payload) or NSLP messages to notify of any
mobility event explicitly, and it may contain various mobility-
related fields, e.g., mobility_event_counter (MEC). The MEC field
can inform the CRN of which incoming massage is the latest and so it
is useful to detect the latest handover event for avoiding any
confusion about where to send a confirmation message and to handle
the ping-pong type of movement.
5.5. Peer failure scenarios
A dead peer can occur either because a link or a network node failed,
or because the MN moved away without informing NSLP/NTLP (it is
recommended to link mobility- and NSIS signaling such that this does
not happen).
Dead peers of interest in mobility scenarios include CRN, MN, AR (or
FA), and HA. In general, it is possible that only NSIS functions
(i.e., NTLP/NSLP) of the node may fail, or the that the node itself
fails completely. In this regard, the following issues arise.
- An MN may either fail or move (or just operate normally). When it
fails, it becomes a dead peer. If it moves and changes its IP
address without notifying NSLP/NTLP, it also becomes a dead peer.
The failure or movement of an MN may cause the 'invalid NR'
problem [8] where the NR is the MN mentioned in Section 3.2. If
the MN moves, care should be taken to prevent the teardown of NSIS
state on the old path before the NSIS state is re-established on
the new path . In this case, an error message (or refresh
timeout) should not be generated (or happen) to avoid any teardown
on the old path and common path. The problem can be solved by
using hanover_init (HI) field of the Mobility object described in
Section 5.4. The HI field can explicitly inform AR (or CRN) that
a handover is now initiated, and thus the AR does not initiate any
error messages (or refresh timeout) when it does not receive
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responses to refresh messages from the MN [6]. In this case, AR's
possible approach may be a proxy for the MN (the last node) and it
may be able to send RESPONSE messages in response to REFRESH (or
RESERVE) messages from a upstream node. AR may also forward the
error message including the HI field toward CN to prevent the NI
from removing the NSIS state. However, it is sill an open issue
whether the hint information such as the HI field through NSIS
signaling messages needs to be forwarded.
- The failure of a (potential) NSIS CRN may result in incomplete
state re-establishment on the new path and incomplete teardown on
the old path after handover. In this case, a new CRN should be
re-discovered immediately by the CRN discovery procedure described
in Section 4.2.3.
- The failure of an AR may make the interactions with Seamoby
protocols (such as CARD and CXTP) impossible. In this case, the
neighboring peer closest to the dead AR may need to interact with
such protocols. A more detailed analysis of interactions with
Seamoby protocols is left for future work.
- In Mobile IP-based scenarios, the failures of NSIS functions at a
FA and a HA may result in incomplete interaction with IP-
tunneling. In this case, recovery for NSIS functions needs to
immediately be performed. Also, a more detailed analysis of
interactions with IP-tunneling is left for future work.
In any case, dead peers should be discovered fast to minimize service
interruption. The procedures for dead peer discovery (DPD) should be
the same no matter why a peer is dead, because an NE discovering a
dead peer cannot judge the specific reason. The procedures for DPD
should be handled by the NTLP. In fact, the DPD can be considered as
an extension to the GIST peer discovery. A peer discovery message
can be periodically transmitted to the neighboring peer (e.g.,
responding node in [2]), and the responding node can send a response
message. To determine if the peer is alive, the use of a timer may
be helpful. For example, the response message may need to be
received by the sender (e.g., querying node in [2]) before the timer
expires. Otherwise, the responding node can be considered dead.
6. Security Considerations
This section describes authorization issues for mobility scenarios in
NSIS. It tries to raise additional questions beyond those discussed
in [7].
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For the discussion of various authorization problems we assume that
initial authorization is strongly coupled to authorization handling
in subsequent message interactions. Making this assumption has some
implication to the signaling message behavior. It is certainly
possible that the entities who request the initial reservation or a
firewall pinhole and those who subsequently cause modifications are
not the same entities.
NSIS NSLPs define a flexible authorization scheme. As argued in [8]
it is necessary to consider cases where the sender, the receiver or
both are authorizing a reservation. For NAT and Firewall signaling
it is necessary that, the sender and the receiver, authorize the
creation of a NAT binding and the creation of a firewall pinhole and
the reason is described in [8].
Subsequently, we will consider the case where the mobile node acts as
a data sender followed by a discussion of the CN as a data sender.
6.1. MN as data sender
This section refers to Figure 1 where the MN acts as a data sender
which moves from one point of attachment to another.
This description starts with an initial signaling exchange triggered
by the MN. The user (or another entity associated the initial setup)
provides the credentials for setup as part of the NSLP authorization
procedure (e.g., QoS reservation).
6.1.1. MN is authorizing entity
This scenario considers the initial flow setup executed by the MN
whereby the MN provides authorization for the initial flow setup.
The initial setup might be used to create state for subsequent
authorization actions by the MN. It is obvious that the
authorization for the NSLP application (e.g., QoS NSLP) has to be
provided. Depending on the underlying authorization model it might
be either peer-to-peer or end-to-middle. This authorization decision
can possibly be treated independently of the authorization issues
discussed in this section.
The following questions seem to be interesting:
- Should the MN indicate that it is the authorizing entity for
subsequent actions to all entities along the path?
- What information should be used for this purpose?
- Who should add this information? Should the visited network of
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the MN add something to the signaling message during the initial
flow setup?
- How do other entities along the path learn this information?
MN CN
------>----->------>------>------>------>------> +
ACTION (MN is authz) |
|
<-----<-----<------<------<------<------<------- | Flow
ACK | Setup
|
|
===============================================> +
Traffic
Figure 18: MN authorized initial reservation
Next, the case for a mobile node authorizing the DCRN is considered.
This communication is illustrated in Figure 19.
The movement of the mobile node after the initial flow setup requires
authorization. Various session ownership authorization issues are
illustrated in [7].
MN DCRN CN
+ E.g.
------>----->------>------>------>------>------> | Movement
ACTION | with state
| creation at
<-----<-----<------<------<------<------<------- + new path
ACK
Figure 19: MN authorizes DCRN
The following questions are of interest:
- Why should the DCRN execute something on behalf of the MN? (i.e.,
why should it trust the MN and what information can the DCRN use
for verification? [the trust is not the other way round: the MN
trusts the DCRN?]) As an example, the DCRN might delete state
along the old segment.
- Should the DCRN alone be able to start signaling (the DCRN might
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be a dedicated node in some mobility protocols (e.g., MAP)) since
it is the node which has more information than other nodes based
on the mobility signaling protocols?
- How should other nodes between the MN and the DCRN and the nodes
between the DCRN and the CN know that the DCRN is now acting on
behalf of the MN?
The case of a corresponding node triggering an action is discussed in
the paragraph below. Figure 20 shows the exchange graphically.
In this scenario the CN wants to, for example, tear-down a
reservation.
MN DCRN CN
<~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +
TRIGGER | E.g.
| Tear
| Down
------>----->------>------>------>------>------> |
ACTION |
|
<-----<-----<------<------<------<------<------- +
ACK
Figure 20: CN triggers action
The following questions arise:
- Why should the MN trust the trigger? Why should the intermediate
nodes trust it?
- Is it possible to specify the security properties of the trigger
message in more detail? Is this an NSIS signaling message?
- The discussions about an indicator which entity to charge for the
reservation might be relevant (see [8]).
- Should the CN restrict the actions of the MN (e.g., delete,
update, create action of established state information)? On the
shared segment it might, for example, be possible to restrict the
allowed action to a flow identifier update.
6.1.2. CN is authorizing entity
This scenario is similar to the CN triggering in Section 6.1.1. Two
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slightly different protocol variations will be considered.
Authorizing some actions in the reverse data flow direction is more
difficult as it can easily be seen in Figure 21.
6.1.2.1. CN asks MN to trigger action (on behalf of the CN)
In Figure 21 the CN authorizes the MN to start signaling after, for
example, a movement. After receiving the trigger message (and some
authorization information) the mobile node starts signaling along the
new segment and automatically discovers the DCRN. The message
travels along the shared segment to the CN and updates the flow
identifier (if necessary). The MN might additionally allow the DCRN
to delete the reservation along the old segment.
MN DCRN CN
<~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +
TRIGGER |
|
------>----->------>------>------>------>------> |
ACTION (CN is authz; MN on behalf of CN) |
+-----------------+ +-----------------+ |
| Action: | | Action: | |
| 'create' along)| | 'update' along)| |
| new segment) | | shared segment)| | Action
+-----------------+ +-----------------+ |
<------<------<------- |
+-----------------+ |
| Action: | |
| 'delete' along)| |
| old segment) | |
+-----------------+ |
<-----<-----<------<------<------<------<------- |
ACK |
|
|
===============================================> |
Traffic +
Figure 21: CN asks MN to trigger an action (on behalf of the CN)
The following questions need to be considered:
- How should the "delegation" mechanism work such that intermediate
nodes believe the MN that it is acting on behalf of the CN?
- Is it possible to carry this information with the trigger message
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from the CN and the MN?
6.1.2.2. CN uses installed state to route message backwards
The CN uses NSIS installed state to route a signaling message
backwards along the path. In some rare cases the DCRN node might be
known already. In this case it is possible to stop the update
process along the shared segment and to possibly mark installed state
along the old segment for deletion. When the MN receives the message
it again has to install state along the new segment towards the DCRN.
The mobile node might also trigger the deletion of resources along
the old segment together with this state creation (pessimistic
delete). An optimistic delete operation is certainly more error
prone.
MN DCNR CN
[ ~~~~~~~~~~~~ TRIGGER (e.g., MIP) ~~~~~~~~~~~~~~> ] +
------<-----<------<------<------<------<------< |
ACTION (CN is authz) |
+--------------------+ +-----------------+ |
| Action:optimistic | | Action: | |
| 'delete' along | | 'update' along)| |
| old segment) | | shared segment)| |
+--------------------+ +-----------------+ |
>------>------>----------->------>------>------- |
+-----------------+ ACK |
| Action: | | Action
| 'create' along)| |
| new segment) | |
+-----------------+ |
<------<------<------- |
+-------------------+ |
| Action:pessimistic| |
| 'delete' along) | |
| old segment) | |
+-------------------+ |
=================Traffic==========================> +
Figure 22: CN uses installed state to route message backwards
Figure 22 raises a few questions:
The security properties of the trigger message need to be
evaluated.
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It is not always possible to route signaling message backwards
from the CN to the MN:
- state at the new path might not be established (hence the
signaling message cannot travel backwards)
- the signaling message might not reach the MN via the old
segment.
In the multi-homing case where the mobile node can be reached via
more than one path it is possible to execute this exchange. The
same might be true for some local repair cases.
The messages triggered by the MN (namely create state along the
new segment and the pessimistic 'delete along the old segment)
still need to be executed on behalf of the CN. Compared to the
first variant there might be some room for optimization since the
first message was transmitted by the CN.
6.1.2.3. MN and CN are authorized
If we argue that the authorization at the NSLP layer is somehow tight
to the authorization for certain protocol actions then we also have
to consider the case where the MN and the CN have to contribute to
the authorization decision. This situation appears, for example, in
the NAT/Firewall signaling case but also in the area of QoS
reservation where both parties might need to share the cost of a
reservation.
If both end hosts are authorized then some signaling message
exchanges are less difficult since the trigger message does not need
to delegate the authorization decision. Some problems, however, do
not disappear such as the session ownership problem and additional
problems might be caused by certain solution approaches. Since this
section does not discuss solutions the reader is referred to the [7]
draft which lists a few proposals for addressing the session
ownership problem.
6.1.3. CN as data sender
In this section we consider the scenarios where the CN acts as a data
sender. Figure 1 shows the topology and the participating entities.
6.1.3.1. CN is authorizing entity
This scenario is similar to the one described in Section 6.1.1. No
additional problems arise with a scenario where the CN is both data
sender and also the authorizing entity. In Figure 8 the CN
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authorizes the UCNR to delete the old segment and to establish a new
reservation along the new segment. Furthermore, at the shared
segment only an update of the flow identifier might be necessary.
MN UCRN CN
+ E.g.
<-----<-----<------<------<------<------<------- | Create
ACTION | new
+-----------------+ | +-----------------+ | State
| Action: | | | Action: | |
| 'create' along)| | | 'update' along)| |
| new segment) | | | shared segment)| |
+-----------------+ | +-----------------+ |
<------<------<--------+ |
+-----------------+ |
| Action: | |
| 'delete' along)| |
| old segment) | |
+-----------------+ |
|
>----->----->------>------>------>------>------> |
ACK (along new path) |
|
<=================== Traffic==================== +
Figure 23: CN as data sender is authorized
Since the mobile node first detects the route changes. A trigger to
the CN allows the CN to quickly react on the route changes. There
are three variants:
- The MN sends a trigger to the CN and the CN starts signaling as
shown in Figure 23.
- The MN routes the message back along the reverse path using the
previously established state along the old route. This mechanism
only works if the MN is able to send messages along the old path.
As a generic mechanism this is not suggested.
- An intermediate node act on its own. This might be possible that
the UCRN is an entity which participates in the mobility signaling
(e.g., Mobility Anchor Point (MAP)) exchange. Depending on the
message exchange it needs to be studied whether the signaling
message provides sufficient authorization to trigger the NSIS
exchange.
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6.1.3.2. MN is authorizing entity
In this scenario we consider the case where the CN is the data sender
but the MN authorizes actions. The considerations are similar to
those elaborated in Section 6.1.3 where the MN is the data sender but
the CN is the authorizing entity.
6.1.4. Multi-homing Scenarios
Multi-homing scenarios have the property that more than one path
belongs to a signaling session. In Figure 12 the MN uses two
interfaces to route NSIS message towards the CN. The two individual
flows are tight together by using the same session identifier and
then associate it with the two flow identifiers. The MN needs to
indicate that both reservations need to be kept alive (and the DCRN
should not delete a reservation). At the shared segment only a
single reservation might be stored (if desired).
From an authorization point of view the session ownership issues is
applicable since the DCRN needs to merge the two reservations into a
single one along the shared segment.
6.1.4.1. MN as data sender
This section shows the multi-homing scenario with the MN as a data
sender.
If the MN is the authorizing entity then the session ownership
problem needs to be solved. Without solving this type of
authorization problem it is possible for an adversary to "join" the
reservation at the shared segment. Furthermore, it is an open issue
whether reservation merging is allowed only for cases where one flow
identifier is used at different interfaces or even with different
flow identifiers.
If the CN is the authorizing entity then, again, some message needs
to be sent from the CN to the MN to trigger the exchange or to route
the request backwards along the established path. The MN is
reachable via the two paths.
segment 2
+---+
^>>>>>>>>>>>>>>>| AR|>>>>>>>>>>>>>V
^ +---+ V
+----+ +----+ +--+
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| MN | |DCRN|>>>>>>>>>>|CN|
|UCRN| | |>>>>>>>>>>| |
+----+ +----+ +--+
v +---+ ^ shared
v>>>>>>>>>>>>>>>| AR|>>>>>>>>>>>>>^ segment
+---+
segment 1
=======================Traffic===============================>
Figure 24: Multi-homed MN as data sender
6.1.4.2. CN as data sender
This section shows the multi-homing scenario with the CN as a data
sender. The scenario is simpler (for the CN authorizing case) than
the one described in Section 6.1 since the signaling message along
the shared segment travels the previously established path. It shows
some similarities with a route change scenario. At the mobile node
itself the two paths merge which again leads to a session ownership
problem. How should the MN know whether a signaling message with the
same session identifier hitting a different interface belongs to the
indicated session authorized by the CN?
segment 2
+---+
v<<<<<<<<<<<<<<<| AR|<<<<<<<<<<<<<^
v +---+ ^
+----+ +----+ +--+
| MN | |UCRN|<<<<<<<<<<|CN|
|DCRN| | |<<<<<<<<<<| |
+----+ +----+ +--+
^ +---+ v shared
^<<<<<<<<<<<<<<<| AR|<<<<<<<<<<<<<v segment
+---+
segment 1
<======================Traffic===============================
Figure 25: Multi-homed CN as data sender
If the MN is the authorizing entity then again communication between
the end hosts is required as a trigger. Routing the signaling
messages in the reverse path might, in some cases, also be possible.
6.1.5. Proxy Scenario
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The proxy scenarios refer to those cases where one of the end hosts
or even both end hosts are not NSIS aware. Two security implications
need to be studied:
- First, there is an authorization issue with regard to the NSLP
application. For QoS signaling the end host (and the user) has to
authorize the QoS reservation since the reservation might require
the user is charged for it. Since the end host is not NSIS aware
some other mechanism or protocol needs to be available which
provides this functionality. For NAT/Firewall signaling delayed
authorization assures that both end hosts authorize the packet
filter creation at their local networks (particularly in case of
missing trust relationship between intermediate networks).
- Second, the authorization issues which relate to the session
ownership problem also need to be studied. Since the session
ownership issues are related to the signaling participating nodes
and not to the users or the true end points we think that it does
not lead to complications. This is, however, only true if we
assume that authorization at the NSLP and authorization decisions
for the signaling message handling is decoupled.
6.1.6. Conclusion
This section tries to point to some authorization aspects for NSIS
signaling in a mobility environment. Performance is important in
mobility environments but a proper security handling accounts for a
high percentage of the total performance. It is important to
consider this aspect in the analysis of mobility proposals.
From the scenarios we can observe the following issues:
- Signaling in the direction of the data path is simpler than in the
opposite direction.
- There are many similarities between the scenarios where the MN
acts as a data sender and the scenarios the CN acts as a data
sender, particularly if multi-homing scenarios are included.
- Many authorization problems arise after the initial setup of
resources along the path. This problem can be stated as: "Is an
entity allowed to perform the indicated action?" Only a few
problems are related to the initial signaling message exchange.
- If the data sender triggers the signaling message exchange and
also provides authorization then the complexity can be kept fairly
low.
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- NSLP authorization decisions should be treated separately from
authorization decisions which affect the signaling message
exchange.
During the work a few open issues have been selected:
- This section does not consider the different message types.
- The implication of price determination caused by mobility is
excluded from this description.
- It was tried to keep the description in this section very generic.
Implications of certain mobility protocols are therefore not
considered.
7. Change History
7.1. Changes from -00 version
The major change made to the initial (-00) version of the draft is to
re-arrange the issues addressed in the draft in order to clearly
identify general issues caused by mobility itself and NSIS protocols-
specific issues. The generic route changes-related text in Section 4
was moved into Appendix to make this draft more mobility-specific.
Specifically, the following changes have been made:
1. Removed the terminologies, 'uplink' and 'downlink' in Section 2.
2. Removed the terminology, 'local repair' in Sections 2 and 4.
3. Re-arranged all problems in Section 3 by merging the 'mobility-
related issues with NSIS protocols' section and the 'problem
statement and general considerations' section.
4. Removed the general considerations section in Section 3.
5. Modified the problem statement section and moved it into the
general problem section in Section 3.1.
6. Added more problems including 'Identification of the crossover
node', 'Key exchanges', and 'AA-related Issues' to Section 3.1
7. Added the 'Multihoming-related issues' to Section 3.2.4
8. Removed the issues on 'how to immediately delete the state on the
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old path' in Section 3.2.
9. Moved the generic route changes-related text in Section 4.1 into
Appendix.
10. Removed the figure describing "NSIS signaling topology for
downstream signaling flow after the route changes in the middle of
the network" in Figure 2.
11. Added 'NSLP_IDs' to each node in Figure 1.
12. Removed the 'use cases of identifiers' section, and instead,
added the 'support for ping-pong type handover' section to Section
5.
13. Added this change history.
7.2. Changes from -01 version
Version -02 includes mainly a number of clarifications on the issues
raised in this draft and more details in some specific areas.
Specifically, the following changes have been made:
1. Defined the terminologies, 'route change' and 'mobility' in
Section 2.
2. Clarified the terminology, 'Crossover node (CRN)' in Section 2.
3. Removed the terminology, 'mobility CRN' in Section 2.
4. The issue, 'Priority of signaling messages' in Section 3.2.2 was
closed, and thus removed it.
5. Clarified the issue, 'CRN discovery and State Update on the IP-
tunneling path in Section 3.2.4.
6. Added the pros and cons of two mechanisms on CRN discovery
dependent on NSIS layers to Section 4.2.1.
7. Clarified the identifier, NSLP_Br_ID for CRN discovery in Section
4.2.2.
8. Added the scenario on interaction between NSIS and Mobile IP to
Section 5.1.
9. Clarified interaction issues with IP-tunneling according to
reservation initiation type (receiver-initiated or sender-
initiated) in Mobile IPv4-based scenarios and added those to
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Section 5.1.1.1.
10. Clarified interaction issues between NSIS protocols and IP-
tunneling in Mobile IPv6 and added those to Section 5.1.1.2.
11. Clarified the multihoming-related issues in Section 5.2.
12. Added the issues on usage of 'hint' information to trigger NSIS
signaling in mobility to Section 5.5.
13. Identified the dead peer-related issues in Mobile IP-based
scenario in Section 5.5.
7.3. Changes from -02 version
In version -03, tunneling-related and multihoming-related scenarios
were newly added in Sections 5.1.3 and 5.2, respectively. Also, the
terminology, 'Path Update' is changed into 'State Update' in Section
3.2.4.
7.4. Changes from -03 version
Version -04 includes mainly a number of clarifications on the issues
raised in this draft and more details in some specific areas.
Specifically, the following changes have been made:
1. The issue, 'Peering agreement issue' in Section 3.2.2 was closed,
and thus removed it.
2. Clarified the issue, 'Interfaces between Mobile IP and NSIS
protocols' in Section 3.2.1.
3. Clarified the issue, 'Authorization-related issues with teardown'
in Section 3.2.2.
4. Clarified the issue, 'Dead peer discovery' in Section 3.2.2.
5. Clarified the issue, 'Invalid NR problem' in Section 3.2.2.
6. Clarified the issue, 'CRN discovery and State Update on the IP-
tunneling path' in Section 3.2.4.
7. Clarified the issue, 'Multihoming-related issues' in Section
3.2.4.
8. Changed Figure 1 (a) into (b) in Section 4.1.
9. Changed Figure 1 (b) into (a) in Section 4.1.
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10. Clarified the identifier, NSLP_Br_ID for CRN discovery in Section
4.2.2.
11. Clarified the identifier, Mobility identifier for CRN discovery
in Section 4.2.2.
12. Added the text on 'CRN_DISCOVERY flag bit' in Section 4.2.3, and
clarified the role of 'CD flag bit' in Section 4.3.1.
13. Clarified the issues on 'interaction with Mobile IP tunneling'
and added those to Section 5.1.4.
14. Clarified the issues on 'load balancing in multihomed mobile
environments' and added those to Section 5.2.5.
15. Changed "Problems" of the heading name in Section 3.2 into
"Challenges."
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Schulzrinne, H. and R. Hancock, "GIST: General Internet
Signaling Transport", draft-ietf-nsis-ntlp-09 (work in
progress), February 2006.
[3] Stiemerling, M., "NAT/Firewall NSIS Signaling Layer Protocol
(NSLP)", draft-ietf-nsis-nslp-natfw-09 (work in progress),
February 2006.
8.2. Informative References
[4] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[5] Manner, J., "NSLP for Quality-of-Service signalling",
draft-ietf-nsis-qos-nslp-09 (work in progress), February 2006.
[6] Lee, S., "Mobility Functions in the QoS-NSLP",
draft-lee-nsis-mobility-nslp-01 (work in progress),
November 2003.
[7] Tschofenig, H., "Security Implications of the Session
Identifier", draft-tschofenig-nsis-sid-00 (work in progress),
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June 2003.
[8] Tschofenig, H., "NSIS Authentication, Authorization and
Accounting Issues", draft-tschofenig-nsis-aaa-issues-01 (work
in progress), March 2003.
[9] Braden, B., Zhang, L., Berson, S., Herzog, S., and S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, September 1997.
[10] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
Bosch, "Next Steps in Signaling (NSIS): Framework", RFC 4080,
June 2005.
[11] Dommety, G., "Fast Handovers for Mobile IPv6",
draft-ietf-mobileip-fast-mipv6-05 (work in progress),
October 2002.
[12] Perkins, C., "IP Mobility Support for IPv4, revised",
draft-ietf-mip4-rfc3344bis-02 (work in progress), October 2005.
[13] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[14] Tschofenig, H., "Path-coupled NAT/Firewall Signaling Security
Problems", draft-tschofenig-nsis-natfw-security-problems-00
(work in progress), July 2004.
[15] Fessi, A., "Security Threats for the NAT/Firewall NSLP",
draft-fessi-nsis-natfw-threats-02 (work in progress),
October 2004.
[16] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F., and S.
Molendini, "RSVP Refresh Overhead Reduction Extensions",
RFC 2961, April 2001.
[17] Ernst, T., "Goals and Benefits of Multihoming",
draft-ernst-generic-goals-and-benefits-02 (work in progress),
October 2005.
[18] Montavont, N., "Analysis of Multihoming in Mobile IPv6",
draft-montavont-mobileip-multihoming-pb-statement-05 (work in
progress), October 2005.
[19] Shen, C., "NSIS Operation Over IP Tunnels",
draft-shen-nsis-tunnel-01 (work in progress), October 2005.
[20] Soliman, H., Castelluccia, C., El Malki, K., and L. Bellier,
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"Hierarchical Mobile IPv6 Mobility Management (HMIPv6)",
RFC 4140, August 2005.
Appendix A. Contributors
Many individuals have contributed to this draft. Since it was not
possible to list them all in the authors section, this section was
created to have a sincere respect for other authors, Paulo Mendes,
Robert Hancock and Roland Bless. Separating authors into two groups
was done without treating any one of them better (or worse) than
others. Shivanajay Marwaha and Takako Sanda have contributed the text
on load balancing-related issues in multihoming.
A.1. Acknowledgement
The authors would like to thank Byoung-Joon Lee, Charles Q. Shen,
Cornelia Kappler, Henning Schulzrinne, and Jongho Bang for
significant contributions in four earlier drafts and the previous
draft. The authors would also like to thank Robert Hancock, Andrew
Mcdonald, John Loughney, Dakako Sanda, Rudiger Geib, Cheng Hong Elena
Scialpi, and Pratic Bose for their useful comments and suggestions. .
Appendix B. Generic Route Changes
The mobility occurs due to the change of the network attachment
point, but the generic route changes is associated with load sharing,
load balancing, or a link (or node) failure. These cause divergence
(or convergence) between the old path along which state has already
been installed and the new path along which data forwarding will
actually happen.
The route changes brings on the change of signaling topology and it
results in difference according to the types of route changes (e.g.,
the route changes or mobility). The route changes generally forms
two common paths, an old path, and a new path, where the old path and
the new path begin to diverge from one common path and afterward to
converge to another common path for each direction of signaling flows
(e.g., downstream or upstream flows) as shown in Figure 14.
Old path
+---+ +---+
^ --->|NE | ... |NE | ------V
common path ^ +---+ +---+ V common path
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+--+ +----+ +----+ +--+
|S |-----> |DCRN| |DCRN| -------> |R |
| | | | | | | |
+--+ +----+ New path +----+ +--+
V +---+ +---+ ^
V --->|NE | ... |NAR| ------^
+---+ +---+
=======(downstream signaling followed by data flows) ======>
(a) The topology for downstream NSIS signaling flow after
route changes
Old path
+---+ +---+
v <---|NE | ... |NE | ----- ^
common path v +---+ +---+ ^ common path
+--+ +----+ +----+ +--+
|S |<----- |UCRN| |UCRN| <------- |R |
| | | | | | | |
+--+ +----+ New path +----+ +--+
^ +---+ +---+ v
^ <---|NE | ... |NAR| ----- v
+---+ +---+
<=====(upstream signaling followed by data flows) ======
(b) The topology for upstream NSIS signaling flow after
route changes
Figure.14 The topology for NSIS signaling in case of the route
changes
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Authors' Addresses
Sung-Hyuck Lee
SAMSUNG Advanced Institute of Technology
San 14-1, Nongseo-ri, Giheung-eup
Yongin-si, Gyeonggi-do 449-712
KOREA
Phone: +82 31 280 9585
Email: starsu.lee@samsung.com
Seong-Ho Jeong
Hankuk University of FS
89 Wangsan Mohyun
Yongin-si, Gyeonggi-do 449-791
KOREA
Phone: +82 31 330 4642
Email: shjeong@hufs.ac.kr
Hannes Tschofenig
Siemens AG
Otto-Hahn-Ring 6
Munich, 81739
Germany
Phone:
Email: Hannes.Tschofenig@siemens.com
Xiaoming Fu
University of Goettingen
Telematics Group
Lotzestr. 16-18
Goettingen 37083
Germany
Email: fu@cs.uni-goettingen.de
Jukka Manner
Department of Computer Science University of Helsinki
P.O. Box 26 (Teollisuuskatu 23)
HELSINKI, FIN-00014
Finland
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Phone: +358-9-191-44210
Email: jmanner@cs.helsinki.fi
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