IRTF MobOpts RG R. Shibui
Internet-Draft K. Gogo
Expires: May 5, 2006 K. Mitsuya
K. Mitani
F. Teraoka
KEIO University
November 2005
Unified L2 Abstractions for L3-Driven Fast Handover
draft-koki-mobopts-l2-abstractions-03.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This draft proposes unified L2 abstractions for L3-driven fast
handover. For efficient network communication, it is vital for a
protocol layer to know or utilize other layer's information such as
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L2 triggers. However, in current operating systems, each protocol
layer is designed independently and information exchange between
protocol layers is not allowed. To solve the problem, this draft
defines nine kinds of L2 abstractions in the form of "Primitive".
This concept can be applied to L3-driven fast handover mechanism
using "Primitives".
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Primitives for L2 Abstractions . . . . . . . . . . . . . . . . 7
4. Definitions of Primitives . . . . . . . . . . . . . . . . . . 9
4.1. L2-LinkStatus (Type 1) . . . . . . . . . . . . . . . . . . 9
4.2. L2-PeerList (Type 1) . . . . . . . . . . . . . . . . . . . 9
4.3. L2-PeerFound (Type 2) . . . . . . . . . . . . . . . . . . 9
4.4. L2-PeerLost (Type 2) . . . . . . . . . . . . . . . . . . . 9
4.5. L2-LinkUp (Type 2) . . . . . . . . . . . . . . . . . . . . 10
4.6. L2-LinkDown (Type 2) . . . . . . . . . . . . . . . . . . . 10
4.7. L2-LinkToBeDown (Type 2) . . . . . . . . . . . . . . . . . 10
4.8. L2-LinkConnect (Type 3) . . . . . . . . . . . . . . . . . 10
4.9. L2-LinkDisconnect (Type 3) . . . . . . . . . . . . . . . . 10
5. Definitions of Static Parameters . . . . . . . . . . . . . . . 11
5.1. Network Interface ID . . . . . . . . . . . . . . . . . . . 11
6. Definitions of Dynamic Parameters . . . . . . . . . . . . . . 12
6.1. Peer . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2. Condition . . . . . . . . . . . . . . . . . . . . . . . . 12
6.3. Peer List . . . . . . . . . . . . . . . . . . . . . . . . 12
6.4. Enable/Disable . . . . . . . . . . . . . . . . . . . . . . 12
6.5. Ack/Error . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Architectural Considerations . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Appendix A. Example Scenario . . . . . . . . . . . . . . . . . . 19
Appendix B. Example Operation for FMIPv6 . . . . . . . . . . . . 21
B.1. Example Operation-1 for FMIPv6 . . . . . . . . . . . . . . 21
B.2. Example Operation-2 for FMIPv6 . . . . . . . . . . . . . . 23
Appendix C. Example Mapping of Primitives and IEEE802.11 . . . . 26
C.1. L2-LinkStatus . . . . . . . . . . . . . . . . . . . . . . 26
C.2. L2-PeerList . . . . . . . . . . . . . . . . . . . . . . . 26
C.3. L2-PeerFound . . . . . . . . . . . . . . . . . . . . . . . 26
C.4. L2-PeerLost . . . . . . . . . . . . . . . . . . . . . . . 27
C.5. L2-LinkUp . . . . . . . . . . . . . . . . . . . . . . . . 27
C.6. L2-LinkDown . . . . . . . . . . . . . . . . . . . . . . . 27
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C.7. L2-LinkToBeDown . . . . . . . . . . . . . . . . . . . . . 27
C.8. L2-LinkConnect . . . . . . . . . . . . . . . . . . . . . . 27
C.9. L2-LinkDisconnect . . . . . . . . . . . . . . . . . . . . 28
Appendix D. Implementation and Evaluation of the Proposed
Model . . . . . . . . . . . . . . . . . . . . . . . . 29
Appendix E. Changes from 02 . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
Intellectual Property and Copyright Statements . . . . . . . . . . 34
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1. Introduction
In recent years, the environment around computers is not static and
changes dynamically. Especially, when a mobile node moves to a
different network, its environment considerably changes. For
example, in the case of wireless communication, parameters such as
radio strength changes widely depends on time or site.
For efficient network communication, it is vital for a protocol layer
to know or utilize other layer's information. There are several
proposals for seamless handovers in IPv6 network such as Fast
Handovers for Mobile IPv6 (FMIPv6) [1] and Hierarchical Mobile IPv6
(HMIPv6) [2]. In FMIPv6, the network layer must know the indication
of a handover from the link layer in advance to achieve seamless
handovers. However, each protocol layer is designed independently
and information exchange between protocol layers is not allowed.
For further handover enhancements, this document defines nine kinds
of L2 triggers in the form of "Primitive". This concept can be
applied to L3-driven fast handover mechanism using "Primitives".
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2. Terminology
This document uses the following terms.
L3-Driven Fast Handover
The handover which is initiated by the network layer on a mobile
node. Since it allows L3 handover preparation during
communication, it can reduce packet loss during handover. L3-
driven fast handover mechanism requires L2 information as a
trigger of handover procedure.
Peer
The attachment point of a mobile node. (e.g., An access point in
IEEE 802.11 networks.)
Primitive
A unit of information which is sent from one layer to another.
There are four classes of primitives: Request, Confirm, Indication
and Response.
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3. Primitives for L2 Abstractions
Each layer offers its services by the form of primitives. There are
four classes of primitives as shown in Figure 1: Request, Confirm,
Indication, and Response. The request is issued by the layer that
wants to get services or information from another layer, and the
confirm is the acknowledgment of the request. The indication is a
notification of information to the layer that requested the service,
and the response is the acknowledgment of the indication. In this
architecture, each layer can communicate evenly.
------------------------------------------------------
Request Response
|| /\ /\ ||
Layer N || || || ||
------------||------||----------||------||------------
|| || || ||
\/ || || \/
Layer N-m Confirm Indication
------------------------------------------------------
Figure 1: Primitives
The primitive consists of five fields: the protocol layer id to which
this primitive should be sent, the protocol id to which protocol
entity this primitive should be sent, the primitive class (i.e.,
request, confirm, indication, or response), the primitive name, and
parameters.
There are three different usages of "Primitives":
Type 1. To provide L2 information to upper layers immediately
A "Request" primitive is an acquisition request for L2
informaiton. As a "Confirm" primitive, L2 information
returns immediately.
Type 2. To notify upper layers of L2 events asynchronously
"Request" and "Confirm" primitives are used just for
registration. When an event occurs, an "Indication"
primitive is asynchronously delivered to an upper layer.
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Type 3. To control L2 actions from upper layers
A "Request" primitive is a request for operation. Ack or
nack returns immediately as a "Confirm" primitive.
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4. Definitions of Primitives
In order to obtain and change L2 information, some sorts of
Primitives described below are necessary. The following Primitives
are defined.
4.1. L2-LinkStatus (Type 1)
The L2-LinkStatus.request is sent to the link layer when an upper
layer needs the current information of a link. The L2-
LinkStatus.request primitive contains "Network Interface ID"
parameter. In response, the L2-LinkStatus.confirm returns. The L2-
LinkStatus.confirm primitive contains three parameters: "Network
Interface ID", "Peer" and "Condition". "Peer" and "Condition"
indicate the current status about the link between a mobile node and
a peer.
4.2. L2-PeerList (Type 1)
The L2-PeerList.request is sent to the link layer when an upper layer
needs a list of candidate peers. The L2-PeerList.request primitive
contains "Network Interface ID" parameter. In response, the L2-
PeerList.confirm returns with "Network Interface ID" parameter and
"Peer List" parameter. "Peer List" parameter is the list of
candidate peers.
4.3. L2-PeerFound (Type 2)
The L2-PeerFound.indication is asynchronously provided to an upper
layer when new peers are detected. This primitive carries "Network
Interface ID" parameter and "Peer List" parameter. "Peer List"
parameter contains the information of new peers detected by a mobile
node. In order to use this notification, the registration process
using L2-PeerFound.request and L2-PeerFound.confirm is needed in
advance. The L2-PeerFound.request primitive has two parameters:
"Network Interface ID" and "Enable/Disable". "Enable/Disable"
parameter shows whether this notification function is turned on.
When this registration succeeds, the L2-PeerFound.confirm returns
with "Network Interface ID" parameter and "Ack" parameter in
response.
4.4. L2-PeerLost (Type 2)
The L2-PeerLost.indication is asynchronously provided to an upper
layer when a peer included in the list of candidate peers is got
lost. This primitive carries "Network Interface ID" parameter and
"Peer List" parameter. "Peer List" parameter contains the
information of the peers which disappeared from the candidates list.
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The registration process using the L2-PeerLost.request and the L2-
PeerLost.confirm is similar to the L2-PeerFound above.
4.5. L2-LinkUp (Type 2)
The L2-LinkUp.indication is asynchronously provided to an upper layer
when a new link is connected. This primitive carries "Network
Interface ID" parameter and "Peer" parameter. The L2-LinkUp.request
contains "Network Interface ID" parameter and "Enable/Disable"
parameter for registration. When the registration succeeds, the L2-
LinkUp.confirm with "Network Interface ID" parameter and "Ack"
parameter returns.
4.6. L2-LinkDown (Type 2)
The L2-LinkDown.indication is asynchronously provided to an upper
layer when an existing link is disconnected. The registration
processing is same as the L2-LinkUp above.
4.7. L2-LinkToBeDown (Type 2)
The L2-LinkToBeDown.indication is asynchronously provided to an upper
layer when an existing link is to be disconnected. This notification
contains two parameters: "Network Interface ID" and "Peer". "Peer"
parameter is the attachment point at which the link quality is
degrading. In the registration processing, the L2-
LinkToBeDown.request carries "Network Interface ID" parameter and
"Enable/Disable" parameter.
4.8. L2-LinkConnect (Type 3)
The L2-LinkConnect.request is sent to the link layer when an upper
layer has to change or create a new link to the specific "Peer".
This primitive carries "Network Interface ID" parameter and "Peer"
parameter. This operation begins after sending L2-
LinkConnect.confirm with "Ack" by the link layer.
4.9. L2-LinkDisconnect (Type 3)
The L2-LinkDisconnect.request is sent to the link layer when an upper
layer has to destroy an existing link to the specific "Peer". This
primitive carries "Network Interface ID" parameter and "Peer"
parameter. This operation begins after sending L2-
LinkDisconnect.confirm with "Ack" by the link layer.
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5. Definitions of Static Parameters
This section lists static parameters. Once the values of static
parameters are configured, they do not change frequently during
communication. The following parameters are transferred as a part of
primitives.
5.1. Network Interface ID
"Network interface ID" parameter identifies uniquely the network
interface in a node. The identifier is an implementation-specific
consideration (e.g., name, index or unique address assigned to each
interface). This parameter also contains the network interface type
which indicates the kind of technology of the network interface
(e.g., IEEE802.11a/b/g, 3GPP, etc.). This parameter is required for
all the primitives.
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6. Definitions of Dynamic Parameters
This section lists dynamic parameters. The values of dynamic
parameters change frequently during communication. The following
parameters are transferred as a part of primitives.
6.1. Peer
"Peer" parameter uniquely identifies the peer.
6.2. Condition
"Condition" parameter consists of the following sub-parameters:
available bandwidth and link quality level. These sub-parameters are
the abstracted information for considering current quality-of
service. The abstraction algorithms of sub-parameters depend on
hardware device and software implementation. The useful range of
link quality is divided into five levels; EXCELLENT, GOOD, FAIR, BAD,
NONE in descending order.
6.3. Peer List
"Peer List" parameter consists of arbitrary couples of two sub-
parameters: "Peer" and "Condition". This parameter shows a list of
peers and its condition.
6.4. Enable/Disable
"Enable/Disable" flag is used for turning event notification on/off.
When an upper layer needs notifications, the "Request" primitive with
"Enable" is sent to the link layer as registration. When an upper
layer needs no more notifications, the "Request" primitive with
"Disable" is sent.
6.5. Ack/Error
When an upper layer requests some notifications, the link layer
receives and confirms this "Request". If the "Request" is valid, the
"Confirm" primitive with "Ack" is sent. And if it is invalid, the
"Confirm" with "Error" is sent to the upper layer.
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7. Architectural Considerations
The IAB document "Architectural Implications of Link Indications" [3]
discusses the role and the issues of link indications within the
Internet Architecture. This section discusses the architectural
considerations mentioned in Section 2 of the IAB document.
[1] Proposals should avoid use of simplified link models in
circumstances where they do not apply.
The information in each layer should be abstracted before it is
sent to another layer. For example, in IEEE 802.11, the
Received Signal Strength Indicator (RSSI), the number of
retransmissions and existence of association between the mobile
node and the access point are used so that the link layer
indications can adjust themselves to various environments or
situations. The thersholds needed for some link indications are
defined from empirical study.
In the conventional protocol layering model, the Protocol Entity
(PE) is defined as the entity that processes a specific
protocol. Our proposal introduced the Abstract Entity (AE) to
achieve link independency of the link indications. An AE and a
PE make a pair. An AE abstracts the PE-dependent information to
the PE-independent information.
Figure 2 shows AEs and PEs using primitives.
[2] Link indications should be clearly defined, so that it is
understood when they are generated on different link layers.
To make the link information/indications clear, our proposal
defines the 4 types of primitives; request/confirm and
indication/response as described in Section 3. The request is
used to obtain the information of another layer. The confirm is
the reply to the request and it includes the requested
information. The indication is generated when a particular
event occured. The resopnse is the reply to the indication.
In our proposal about IEEE 802.11b, L2-LinkUp is defined as the
status in which an association to the AP is established, and L2-
LinkDown is defined as the status in which an associatio to the
AP is not established. L2-LinkToBedown is generated when the
link quality becomes below the predefined threshold. Since the
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Received Signal Strength Indicator (RSSI) and the number of
retransmissions are used to abstract and evaluate the link
quality, L2-LinkToBeDown represents the link quality in both
directions. It should use an average of RSSI or the number of
retransmissions damped for one second or more to cope with
transient link conditions.
[3] Proposals must demonstrate robustness against misleading
indications.
As described above, our proposal uses the RSSI, the number of
retransmissions, and the existence of an association to
calculate the link status. Further work is necessary to define
appropriate parameters and calculation.
[4] Upper layers should utilize a timely recovery step so as to
limit the potential damage from link indications determined to
be invalid after they have been acted on.
The proposed L3-driven handover decribed in Appendix D uses the
L2-LinkToBeDown indication as the trigger for starting handover.
L2-LinkToBeDown is indicated when the link quality goes down
below the specific threshold. This indication is not canceled
even if the link quality goes up soon. In the circumstance
where the link quality is changing frequently and widely, the
invalid indication may cause redundant handover and degrade the
link quality further. Further work is necessary to examine this
problem.
[5] Proposals must demonstrate that effective congestion control is
maintained.
In the circumstance where the link quality is changing
frequently and widely or a mobile node is moving rapidly, the
proposed mechanism may continuously generate many and various
indications. Some traffic may be generated with these
indications, or frequent handovers may negatively affect to the
upper layers. Both of them can cause congestion. Further work
is necessary to solve this problem.
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[6] Proposals must demonstrate the effectiveness of proposed
optimizations.
In IPv6 mobility, a L3-driven handover mechanism using link
indications can dramatically reduce gap time due to handover.
The L3-driven handover mechanism needs the L2-LinkTobeDown
indication to predict disconnection. But L2-LinkToBeDown is
sometimes untrusted because it is difficult to abstract the link
quality. Invalid L2-LinkToBeDown may cause redundant handover.
A handover mechanism using only L2-LinkUp/L2-LinkDown can also
reduce gap time modestly. An example of an implementation and
an evaluation of a L3-driven handover mechanism is described in
Appendix D.
[7] Link indications should not be required by upper layers, in
order to maintain link independence.
Interoperability between the ordinary host and the host which
implements the proposed indications is kept. The ordinary host
can also start a handover by receiving the Router Advertisement
message although there may be long gap time due to a handover.
The gap time due to a handover can be reduced by using L2-LinkUp
or L2-LinkDown. In addition, L2-LinkToBeDown can dramatically
reduce the gap time.
[8] Proposals should avoid race conditions, which can occur where
link indications are utilized directly by multiple layers of the
stack.
Since our proposal defines the link indications to only the IP
layer, race conditios between multiple layers never happen.
Further work is necessary when this proposal defines link
indications to the transport and upper layers.
[9] Proposals should avoid inconsistencies between link and routing
layer metrics.
Our proposal does not deal with routing metrics.
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[10] Overhead reduction schemes must avoid compromising
interoperability and introducing link layer dependencies into
the Internet and Transport layers.
As described above, the link indications in our proposal are
abstracted to the information independent of link types to
reduce the gap time due to a handover, and the orndinary host
can execute handover without using the link indications defined
in our proposal.
[11] Proposals advocating the transport of link indications beyond
the local host need to carefully consider the layering, security
and transport implications. In general, implicit signals are
preferred to explicit transport of link indications since they
add no new packets in times of network distress, operate more
reliably in the presence of middle boxes such as NA(P)Ts, are
more likely to be backward compatible, and are less likely to
result in security vulnerabilities.
Our proposal does not define exchange of link indications
between nodes.
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---------------------------------------------------------
----------=========== ----------===========
| |[ ] | |[ ]
| PE |[ AE ] | PE |[ AE ]
| |[ ] | |[ ]
----------=========== ----------===========
Layer N || /\ || /\
------------||---||-------------------||---||------------
Request|| || Response|| ||
|| || || ||
|| || || ||
|| ||Confirm || ||Indication
------------||---||-------------------||---||------------
\/ || \/ ||
----------=========== ----------===========
| |[ ] | |[ ]
| PE |[ AE ] | PE |[ AE ]
| |[ ] | |[ ]
----------=========== ----------===========
Layer N-m
----------------------------------------------------------
Figure 2: AE and PE with Primitives
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8. Security Considerations
The IAB document "Architectural Implications of Link Indications" [3]
discusses the role and the issues of link indications within the
Internet Architecture. This section discusses the security
considerations mentioned in Section 4 of the IAB document.
[12] Spoofing
In the proposed link indication architecture, the link layer
information is obtained from frames sent by the AP. This
proposal relies on these frames. Therefore, it is necessary to
make the link layer protocol secure to avoid spoofing.
[13] Indication validation
Transportation of the link indications between nodes is not
assumed, hence this consideration is out of scope in our
proposal.
[14] Denial of service
In the proposed link indication architecture, the link layer
information is obtained from frames sent by the AP. This
proposal relies on these frames. Therefore, it is necessary to
make the link layer protocol secure to avoid spoofing.
9. References
[1] Koodli, R., Dommety, G., Malki, K., Khalil, M., Perkins, C.,
Soliman, H., Tsirtsis, G., and A. Yegin, "Fast Handovers for
Mobile IPv6", draft-ietf-mipshop-fast-mipv6-03 (work in
progress), October 2004.
[2] Soliman, H., Castelluccia, C., Malki, K., and L. Bellier,
"Hierarchical Mobile IPv6 mobility management (HMIPv6)",
draft-ietf-mipshop-hmipv6-02 (work in progress), June 2004.
[3] Aboda, B., Andersson, L., Daigle, L., Falstrom, P., Hinden, B.,
Lindqvist, K., Meyer, D., Nikander, P., Rescorla, E., Resnick,
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P., Rosenberg, J., and L. Zhang, "Architectural Implications of
Link Indications", draft-iab-link-indications-03 (work in
progress), August 2005.
[4] Teraoka, F., Ishiyama, M., and M. Kunishi, "LIN6: A Solution to
Multihoming and Mobility in IPv6", draft-iab-link-indications-03
(work in progress), January 2004.
[5] Ishiyama, M., Kunishi, M., and H. Esaki, "LINA: A New Approach
to Mobility Support in Wide Area Networks", IEICE Transactions
on Communication vol. E84-B, no. 8, pp. 2076-2086, August 2001.
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Appendix A. Example Scenario
For example, the picture below shows L3-driven fast handover
mechanism using the L2 triggers on MN.
L2 L3
| |
|<----------LinkUP.req-----------|
|-----------LinkUP.cnf---------->|
|<-------LinkToBeDown.req--------|
|--------LinkToBeDown.cnf------->|
= =
| |
Low |
Signal-----LinkToBeDown.ind------->|
| |
|<---------PeerList.req----------|
|----------PeerList.cnf------>Handover
| Preparation
|<-------LinkConnect.req---------|
L2 Handover--LinkConnect.cnf-------->:
: :
: :
finish---------LinkUp.ind----->L3 Handover
| finish
| |
L2: Link Layer on MN
L3: Network Layer on MN
req: Request
cnf: Confirm
ind: Indication
Figure 3: L3-Driven Fast Handover Mechanism
First, the L3 issues LinkUp.request to receive LinkUp.indication when
the link becomes available. The L3 also issues LinkToBeDown.request
to receive LinkToBeDown.indication when the link quality goes down
below the threshold.
In the beginning of the L3-driven handover procedure, the L2 detects
the radio signal strength is going down. Then the L2 sends L2-
LinkToBeDown.indication to the L3. The L3 prepares for handover
(e.g., CoA generation, DAD, ND cache creation, and routing table
setting) and sends L2-PeerList.request to the L2 if the list of
access points is needed.
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If the L3 decides to perform handover according to some rules, the L3
sends L2-LinkConnect.request with some parameters about candidate
access points to request L2 handover. L2 handover begins after the
L3 sends L2-LinkConnect.confirm to the L2. When the L2 handover
finished, the L2 sends L2-LinkUp.indication to notify the L3.
Finally, the L3 performs handover (e.g., sending BU).
One of the important features of L3-driven fast handover using
Primitives is that the L3 handover preparation can be done during
communication. So, it can reduce disruption time during handover.
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Appendix B. Example Operation for FMIPv6
Here shows 2 scenarios of L3 driven fast handover for FMIPv6.
Scenario 2 is differ from scenario 1 for the timing of sending some
messages.
B.1. Example Operation-1 for FMIPv6
Figure 4 shows the predictive mode of FMIPv6 operation with L3-driven
link switching mechanism.
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MN-L2 MN-L3 PAR-L3
| | |
AP<---------PeerList.req----------| |
Scan---------PeerList.cnf--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
|---------PeerFound.ind--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
| | |
~ ~ ~
| | |
Low | |
Signal-----LinkToBeDown.ind------->| | NAR-L3
| |-----FBU---->| |
| | |----HI---->|
| | |<--HAck----|
| |<----FBack---| |
|<-------LinkConnect.req---L3 Handover | |
L2 Handover--LinkConnect.cnf-------->: |
: : |
: : |
finish---------LinkUp.ind---------->: |
| :-----------FNA---------->|
| finish<======packets=========|
| | |
MN-L2 : Link Layer on Mobile Node
MN-L3 : Network Layer on Mobile Node
PAR-L3 : Network Layer on Previous Access Router
NAR-L3 : Network Layer on New Access Router
req : Request
cnf : Confirm
ind : Indication
RtSolPr : Router Solicitation for Proxy
PrRtAdv : Proxy Router Advertisement
FBU : Fast Binding Update
FBack : Fast Binding Acknowledgment
FNA : Fast Neighbor Advertisement
HI : Handover Initiate
HAck : Handover Acknowledge
Figure 4: L3-Driven Fast Handover Mechanism with FMIPv6 scenario1
When the MN establishes link connectivity with the PAR, it performs
router discovery. Then, the MN can send RtSolPr message to the PAR
in order to resolve access point identifiers to subnet router
information. To send RtSolPr, a MN discovers one or more access
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points by sending L2-PeerList.request to the link layer. As a
response to L2-PeerList.request, L2-PeerList.confirm returns with
"Peer List" parameter which contains identifiers and conditions of
nearby access points. After initial AP discovery, L2-
PeerFound.indication with "Peer List" is also sent from the link
layer when one or more access points are discovered.
When the link layer of the MN detects radio signal strength is going
down, it sends L2-LinkToBeDown.indication to the network layer.
Then, the MN sends FBU to PAR as the beginning of L3 handover
procedure. The NCoA required for FBU message is determined according
to the MN's policy database and received PrRtAdv message. As a
response to FBU, the MN receives FBack and then switches its link by
L2-LinkConnect.request with specific "Peer" parameter immediately.
The handover policy of the MN is outside the scope of this document.
After L2 handover, the link layer of the MN sends L2-
LinkUp.indication to the network layer. The MN sends FNA message to
NAR immediately. The NAR will send tunneled and buffered packets to
the MN.
B.2. Example Operation-2 for FMIPv6
Figure 5 shows the predictive mode of FMIPv6 operation with L3-driven
link switching mechanism.
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MN-L2 MN-L3 PAR-L3
| | |
AP<---------PeerList.req----------| |
Scan---------PeerList.cnf--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
|---------PeerFound.ind--------->| |
| |---RtSolPr-->|
| |<--PrRtAdv---|
| | |
~ ~ ~
| | |
Low | |
Signal-----LinkToBeDown.ind------->| | NAR-L3
| |-----FBU---->| |
|<-------LinkConnect.req---L3 Handover | |
L2 Handover--LinkConnect.cnf-------->: | |
| | |----HI---->|
| | |<--HAck----|
| | |---FBack-->|
| |<----FBack---------------|
: : |
finish---------LinkUp.ind---------->: |
| :-----------FNA---------->|
| finish<======packets=========|
| | |
MN-L2 : Link Layer on Mobile Node
MN-L3 : Network Layer on Mobile Node
PAR-L3 : Network Layer on Previous Access Router
NAR-L3 : Network Layer on New Access Router
req : Request
cnf : Confirm
ind : Indication
RtSolPr : Router Solicitation for Proxy
PrRtAdv : Proxy Router Advertisement
FBU : Fast Binding Update
FBack : Fast Binding Acknowledgment
FNA : Fast Neighbor Advertisement
HI : Handover Initiate
HAck : Handover Acknowledge
Figure 5: L3-Driven Fast Handover Mechanism with FMIPv6 scenario2
Differ from the scenario 1, MN in scenario 2 sends LinkConnect.req
from network layer to link layer after MN sends FBU. Actually, as MN
sends FBack to both AR(not only PAR but also NAR), MN can get the
FBack that sent out by PAR and passed through NAR, after it moves to
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under the NAR.
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Appendix C. Example Mapping of Primitives and IEEE802.11
This section shows examples of the mapping between "Primitives" and
IEEE802.11 parameters.
C.1. L2-LinkStatus
Most of parameters for L2-LinkStatus are related to the configuration
of network interface hardware. So, the operating system and the
device driver module can easily collect such information. However,
to create the "Condition" parameter, the MN should maintain
statistics and parameters related to current wireless environment.
There are two sub-parameters of the "Condition" parameter: available
bandwidth, link quality level. An available bandwidth of the current
peer can be obtained by maintaining transmission rate indication and
statistics of frame transmission at every time the frame transmission
occurs. A link quality level can be updated by maintaining the
following parameters and statistics at every time the frame reception
occurs: receive signal strength indication (RSSI), transmission/
reception rate indication, transmit/receive latency, bit error rate,
frame error rate and noise level. Link quality level is divided into
five levels: EXCELLENT, GOOD, FAIR, BAD, and NONE in descending
order. Some parameters can be managed by setting threshold from
software. When the parameters cross the threshold, an interrupt is
generated for the software.
C.2. L2-PeerList
In IEEE 802.11 networks, L2-PeerList returns detected APs which
quality is exceeding the provided threshold as peer candidates (by
"Peer List" parameter). Therefore, the MN should always maintain the
database of available access points according to reception of beacon
frame, probe response frame and all frames. This AP database is
managed in consideration of time, number of frames and signal
strength. There are some network interface hardwares that can notify
events to operating system only when the desired event occurs, by
setting threshold from software. Moreover, the MN can transmit probe
request frame for access point discovery, if needed.
C.3. L2-PeerFound
In IEEE 802.11 networks, L2-PeerFound is notified when new peers that
link quality level exceeds the provided threshold are detected by
listening beacons or scanning APs. If the received frame (mainly
beacon or probe response) is not in the AP database described in
Appendix C.2, then the link layer can create L2-PeerFound.indication.
For example, if L2-PeerFound's provided threshold of link quality is
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GOOD , the L2-PeerFound.ind is made and sent to upper layer when
peer's link quality becomes stronger than to the level of GOOD.
C.4. L2-PeerLost
In IEEE 802.11 networks, L2-PeerLost is notified when an AP included
in the list of candidate APs is got lost by listening beacons or
scanning APs. If the entry in the AP database described in
Appendix C.2 expires, or link quality level is under threshold, then
the link layer can create L2-PeerLost.indication. To calcurate the
link quality level, signal strength of the received frame(mainly
beacon or probe response) can be used. For example, if L2-PeerLost's
provided threshold of link quality is BAD, the L2-PeerLost.ind is
made and sent to upper layer when peer's link quality becomes weaker
than the level of BAD.
C.5. L2-LinkUp
In IEEE 802.11 networks, L2-LinkUp is notified when association or
reassociation event occurs. When such event occurs, the MN receives
association response frame or reassociation response frame.
Immediately after receiving it, the link layer can create L2-
LinkUp.indication.
C.6. L2-LinkDown
In IEEE 802.11 networks, L2-LinkDown is notified when disassociation
event occurs or when getting no beacon during the certain time. When
such event occurs, the MN sends disassociation frame to AP, or the
entry of the specific AP is deleted from the AP database described in
Appendix C.2. By detecting such events, the link layer can create
L2-LinkDown.indication.
C.7. L2-LinkToBeDown
In IEEE 802.11 networks, L2-LinkToBeDown is notified when radio
signal strength of the connected AP is going down and becomes under
of the provided threshold. By maintaining parameters for a link
quality level like the description in Appendix C.1, the link layer
can create L2-LinkToBeDown.indication.
C.8. L2-LinkConnect
In IEEE802.11 networks, each AP is identified by BSSID, the service
set of several APs is identified by SSID. When L2-LinkConnect is
used to connect specific AP or service set, the link layer should set
BSSID or SSID. Also, the channel should be set appropriately at the
same time by searching database described in Appendix C.2. To
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connect to the AP, MN should be authenticated by the AP, by sending
authentication message from MN's link layer, and then MN sends
association message to associate with the AP.
C.9. L2-LinkDisconnect
In IEEE802.11 networks, the MN sends disassociation message to the AP
for disconnection. When L2-LinkDisconnect is used for disconnection
from the current AP, the link layer should send disassociation
message to the appropriate AP, and stop data transmission.
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Appendix D. Implementation and Evaluation of the Proposed Model
This section describes an implementation of the proposed link
indication architecture and its evaluation.
An IEEE802.11a wireless LAN device driver was modified to provide
abstract link layer information in the form of primitives defined in
Sec.4. The modified driver has two AP lists. One contains the
device dependent information such as the RSSI, the retransmission
count, various AP parameters and various statistics. The device
dependent information except for the AP parameters is updated
whenever the device receives a frame. If the received frame is the
management frame, the AP parameters are also updated based on the
parameters in the frame.
Another AP list contains the abstract information. The abstract
information is updated periodically by using the device dependent
information. In the abstraction processing, for example, the RSSI or
the retransmission count is converted to the common indicator "link
quality".
L2-PeerList and L2-LinkStatus were implemented by using only the
abstract information. Thus, the upper layers can use information of
current AP and adjacent APs without depending on the devices. L2-
PeerFound and L2-PeerLost is notified if the link quality went up or
down beyond the thresholds when the abstract information is updated.
If the link quality of the current AP went down below the specific
threshold, L2-LinkToBeDown is notified. L2-LinkUp and L2-LinkDown
are notified when an association with an AP is established or
destroyed. To realize L2-LinkConnect and L2-LinkDisconnect,
functions to connect or disconnect to the specified AP were
implemented. In these functions, since only abstract information is
needed to specify the AP, other layers need not to know the device
dependent information.
There are eight ARs, each of which is located 80-100m interval. The
AP is collocated at the AR. IEEE802.11a was used as the link layer.
The same wireless channel was used at all the APs. Thus there are
eight wireless IPv6 subnets in the testbed. The mobile node moved at
a speed of 30-40 km/h. When link quality of current AP goes down,
the mobile node executes L3-driven handover described in Appendix A.
In this measurement, assume that the mobile node can know the static
information of adjacent AR/AP. An application called DVTS was
running on the mobile node and sends digital video data at about a
15Mbps data rate through the wireless IPv6 subnet to the
correspondent node, which replays received digital video data. In
this environment, the L2 handover needs less than 1 msec and mobility
protocol LIN6 needs a few msec for location registration. And the
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total gap time due to the handover was 3-4 msec. In most case, there
was no influence to the replayed pictures over handover.
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Appendix E. Changes from 02
- "Section 7 Architectural Considerations" was added.
- "Section 8 Security Considerations" was modified.
- In Appendix A, the hanover procedure was modified.
- "Appendix D. Implementation and Evaluation of the Proposed
Model" was added.
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Authors' Addresses
Rie Shibui
Graduate School of Science and Technology, KEIO University
3-14-1 Hiyoshi, Kohoku-ku
Yokohama, Kanagawa 223-8522
Japan
Phone: 45-566-1425
Email: shibrie@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Kazutaka Gogo
Faculty of Science and Technology, KEIO University
3-14-1 Hiyoshi, Kohoku-ku
Yokohama, Kanagawa 223-8522
Japan
Phone: 45-566-1425
Email: gogo@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
Koshiro Mitsuya
Jun Murai Lab, Shonan Fujisawa Campus, KEIO University
5322 Endo
Fujisawa, Kanagawa 252-8520
Japan
Phone: +81-466-49-1100
Email: mitsuya_at_sfc.wide.ad.jp
URI:
Koki Mitani
Graduate School of Science and Technology, KEIO University
3-14-1 Hiyoshi, Kohoku-ku
Yokohama, Kanagawa 223-8522
Japan
Phone: 45-566-1425
Email: koki@tera.ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
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Fumio Teraoka
Graduate School of Science and Technology, KEIO University
3-14-1 Hiyoshi, Kohoku-ku
Yokohama, Kanagawa 223-8522
Japan
Phone: 45-566-1425
Email: tera@ics.keio.ac.jp
URI: http://www.tera.ics.keio.ac.jp/
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