Network Working Group Fatai Zhang
Internet Draft Huawei
Category: Informational O. Gonzalez de Dios
Telefonica Investigacion y Desarrollo
D. Ceccarelli
Ericsson
G. Bernstein
Grotto Networking
A. Farrel
Old Dog Consulting
Expires: September 14, 2011 March 14, 2011
Applicability of Generalized Multiprotocol Label Switching (GMPLS)
User-Network Interface (UNI)
draft-zhang-ccamp-gmpls-uni-app-01.txt
Status of this Memo
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This Internet-Draft will expire on September 14, 2011.
Abstract
Generalized Multiprotocol Label Switching (GMPLS) defines a series of
protocols for the creation of Label Switched Paths (LSPs) in various
switching technologies. The GMPLS User-Network Interface (UNI) was
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developed in RFC4208 in order to be applied to an overlay network
architectural model.
This document examines a number of GMPLS UNI application scenarios.
It shows how techniques developed after the GMPLS UNI can be applied
to automate or enable critical processes for these applications. This
document also suggested simple extensions to existing technologies to
further enable the UNI and points out some existing unresolved issues.
Conventions used in this document
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 [RFC2119].
Table of Contents
1. Introduction .................................................. 3
2. UNI Addressing ................................................ 5
3. UNI Auto Discovery ............................................ 6
4. UNI Path Computation .......................................... 7
4.1. UNI Link Selection ....................................... 7
5. UNI Path Provisioning ......................................... 9
5.1. Flat Model .............................................. 10
5.2. Stitching Model ......................................... 10
5.3. Session Shuffling Model ................................. 11
5.4. Hierarchy Model ......................................... 11
6. UNI Recovery ................................................. 12
6.1. End-to-end Recovery ..................................... 12
6.1.1. Serial Provisioning of Working & Protection Path ... 12
6.1.2. Concurrent Computation of Working & Protection Path. 13
6.2. Segment Recovery ........................................ 13
7. UNI Call ..................................................... 14
7.1. Exchange of UNI Link Information ........................ 15
7.2. Control of Call Route ................................... 15
8. UNI Multicast ................................................ 16
8.1. UNI Multicast Connection Model .......................... 16
8.2. UNI Multicast Connection Provisioning ................... 17
9. Security Considerations ...................................... 18
10. IANA Considerations ......................................... 18
11. Acknowledgments ............................................. 19
12. References .................................................. 19
12.1. Normative References ................................... 19
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12.2. Informative References ................................. 21
13. Authors' Addresses .......................................... 22
1. Introduction
Generalized Multiprotocol Label Switching (GMPLS) defines a series of
protocols, including Open Shortest Path Fist - Traffic Engineering
(OSPF-TE) [RFC4203] and Resource ReserVation Protocol - Traffic
Engineering (RSVP-TE) [RFC3473], which can be used to create Label
Switched Paths (LSPs) in a number of deployment scenarios with
various transport technologies.
The User-Network Interface (UNI) reference point is defined in the
Automatically Switched Optical Network (ASON) [G.8080]. According to
[G.8080], the UNI may be implemented as a peering between a client-
side entity (UNI-C) and a network-side entity (UNI-N). End-to-end
connectivity between UNI-C nodes is achieved across the core network
by three components: a UNI request from source UNI-C to source UNI-N;
a core network connection from source UNI-N to destination UNI-N; and
a UNI request from destination UNI-N to destination UNI-C.
The GMPLS overlay model, as per [RFC4208], can be applied at the UNI,
as shown in Figure 1.
Overlay Overlay
Network +----------------------------------+ Network
+---------+ | | +---------+
| +----+ | | +-----+ +-----+ +-----+ | | +----+ |
| | | | UNI | | | | | | | | UNI | | | |
| -+ EN1+-+-----+--+ CN1 +----+ CN2 +----+ CN3 +---+-----+-+ EN3+- |
| | | | +--+--+ | | | | | | | | | |
| +----+ | | | +--+--+ +--+--+ +--+--+ | | +----+ |
+---------+ | | | | | | +---------+
| | | | | |
+---------+ | | +--+--+ | +--+--+ | +---------+
| +----+ | | | | | +-------+ | | | +----+ |
| | +-+--+ | | CN4 +---------------+ CN5 | | | | | |
| -+ EN2+-+-----+--+ | | +---+-----+-+ EN4+- |
| | | | UNI | +-----+ +-----+ | UNI | | | |
| +----+ | | | | +----+ |
+---------+ +----------------------------------+ +---------+
Overlay Core Network Overlay
Network Network
Figure 1 - Applying GMPLS overlay model at UNI
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In Figure 1, assume that there is an end-to-end UNI connection
passing through EN1-CN1-CN2-CN3-EN3. For convenience, some terms used
in this document are defined below:
- "source EN" refers to the edge-node who initiates the connection
(e.g., EN1);
- "destination EN" refers to the edge-node where the connection is
terminated (e.g., EN3);
- "ingress CN" refers to the core-node to which the source EN is
attached (e.g., CN1);
- "egress CN" refers to the core-node to which the destination EN
is attached (e.g., CN3).
[RFC4208] provides mechanisms for UNI signaling, which are compatible
with GMPLS RSVP-TE signaling ([RFC3471] and [RFC3473]). A single end-
to-end RSVP session between source EN and destination EN is used for
the user connection, just as it would be for connection creation
between two core nodes. However, when considering the isolation of
topology information between core network and the overlay network,
additional processing of the RSVP-TE Explicit Route Object (ERO) and
Record Route Object (RRO) is required. For example, the ingress CN
should verify the ERO it received against its topology database
before forwarding the PATH message. And the ingress/egress CN may
edit or remove the RRO in order to hide the path segment used inside
the core network from the EN.
The UNI can be used in many application scenarios. For example, in a
multi-layer network [RFC6001], the interface between client layer
node and server layer node can be seen as a UNI. Or, when deploying
VPN services such as Layer One Virtual Private Networks (L1VPNs)
[RFC4847], [RFC5253], users can connect to a service provider network
via a UNI.
This document examines a number of current and future GMPLS
application scenarios. It shows how techniques developed after the
GMPLS UNI was developed can be used to automate or enable critical
aspects of these application scenarios. It points out some potential
technology extensions that could improve UNI operation, and
highlights some existing unresolved issues.
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2. UNI Addressing
In [RFC4208], the GMPLS overlay model is applied at the UNI reference
point, and it is required that the edge-node and its attached core-
node of the overlay network share the same address space that is used
by GMPLS to signal between the edge-nodes across the core network.
Under this condition, the user connection can be created using a
single end-to-end RSVP session, which is consistent with the RSVP
model. Therefore, RSVP-TE defined in [RFC3473] can be used for
support GMPLS UNI without any extensions.
However, in the practical deployment of GMPLS UNI, the requirement of
sharing the same address space between EN and its attached CN may not
be satisfied if the core network and the overlay network are designed
and deployed separately, especially if the two networks belong to
different carriers. For example, the core network may use IPv6
addresses, while the overlay network uses IPv4 addresses. Or, since
the core network is a closed system, the assignment of the IP
addresses of the CNs is independent of other IP addresses outside the
core network. This implies that the nodes in the core network may use
addresses which collide with the edge nodes in the overlay network.
Thus, the addressing deployment for the GMPLS UNI can be divided into
three scenarios:
1. Overlay network and core network share a common addressing policy.
As noted above, there are many situations where this may be
impractical, but it might be quite feasible in a multi-layer
network operated by a single carrier. In this scenario, end-to-end
UNI connectivity may use a single RSVP session, and the core
routing information (assuming it is shared and not stripped for
confidentiality reasons) will be meaningful to the ENs. Note,
however, that the overlay model examined by this document assumes
that there is some separation between the overlay and core
networks, and this might mean that the overlay network is not able
to see the topology or routing information of the core network
even when they share a common address space.
2. ENs have visibility into the core network, but overlay and core
networks have different address spaces. This is the more common
model envisaged by [RFC4208] and for basic mode L1VPN deployments
([RFC5251]), and the previous scenario can be seen to be a special
case of this scenario where the two address spaces are
complementary. In this deployment, the source EN is aware of the
addresses for itself, the ingress CN, the egress CN, and the
destination EN in the address space of the core network. It may
also have full visibility into the core network, but this is not a
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requirement. In this scenario, the ENs are responsible for
performing address mapping between the overlay network's addresses
for the ENs, and the core network's addresses for the same nodes.
Additionally, the source EN must use core network addresses to
identify the CNs. In this deployment, a single end-to-end RSVP-TE
session can still be utilized from source EN to destination EN.
3. ENs do not have any knowledge of the core address space and has no
visibility into the core network. The source EN must still know an
address for the ingress CN, but in this scenario, the EN uses an
overlay address to reach the CN and to identify the destination EN.
The ingress CN is responsible for mapping addresses to the core
address space and for filling in any additional routing
information. In this deployment the end-to-end connectivity must
be created either using "session stitching" (see Section 5.2) or
"session shuffling" (see Section 5.3).
3. UNI Auto Discovery
When the end-to-end connection is set up across the core network it
must be targeted at the destination CN so that it can be extended to
the destination EN. This means that either the source EN must know
the identity of the destination CN to which the destination EN is
attached, or the source CN must know this information. This requires
some form of "discovery" (possibly including configuration), and
depending on the addressing scheme in use (see Section 2) will
require address mapping to be performed by the source EN or the
source CN.
The discovery problem may be exacerbated when the a variety of
services may be requested since the source EN will need to know the
capabilities and available resources on the link between the
destination CN and the destination EN. It could discover this by
attempting to set up a connection and by drawing conclusions from the
connection setup failures, but this is not efficient. Furthermore, in
the case of a dual-homed destination EN (such as EN2 in Figure 1), a
choice of destination CN must be made, and that choice may be
influenced by the capabilities and available resources on the CN-EN
links leading to the destination EN.
If the UNI is applied in L1VPN scenario, the auto discovery of UNI
using OSPFv2 is provided in [RFC5252]. A new L1VPN LSA is introduced
to advertise the L1VPN information via the L1VPN info TLV and the TE
information of the CE-PE link (in the language of UNI, it's the EN-CN
link) via the TE link TLV.
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4. UNI Path Computation
End-to-end UNI path computation includes three parts: the selection
of the source UNI link, the path computation inside the core network
and the selection of the destination UNI link.
The selection of UNI links may not necessary in some scenarios. One
example is in case of single-homing with only one UNI link between EN
and CN, and another example is manual selection of UNI link when the
service is requested. In such cases, the CN to which the source EN is
attached, or the path Computation Element (PCE) ([RFC4655]) which is
responsible for the core network, can perform the path computation
across the core network when the UNI signaling request is sent from
the source EN to the source CN.
4.1. UNI Link Selection
This document is specific to the overlay architectural model to the
source EN which does not have the topology and TE information of the
core network. Therefore, in the case of multi-homing (i.e., the
source EN is connected to more than one CN), the source EN does not
have enough information to make a correct choice among all the UNI
links between itself and the core network for an optimal end-to-end
connection.
In this case, a PCE whose computation domain covers both the core
network and the ENs attached to it can be used. Note that the GMPLS
UNI predates PCE and hence a PCE was not available to solve this
problem in early GMPLS UNI deployments. The PCE can use the UNI
discovery mechanism described in Section 3 to learn the EN-CN
relationship and the TE information of the UNI links, and therefore
has the ability to select the optimal UNI link for the connection.
Figure 2 shows an example of UNI path computation using a single PCE
with visibility into both networks. The PCE can help the source EN to
compute the end-to-end connection when the UNI path computation
request is received, so that the source EN can learn which UNI link
to be selected.
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1) PCReq: EN1-EN2 +-----+
+------------------------>| |
| | PCE |
| +----------------------| |
| | +-----+
| | 2) PCRep: EN1-CN4-CN5-CN6-EN2
| |
| | +----------------------------------+
| | | Core Network |
| | | +----+ +----+ +----+ |
| V +----+--+ CN1+------+ CN2+------+ CN3+--+----+
+----+ | | +--+-+ +--+-+ +--+-+ | | +----+
| +--+ | | | | | +--+ |
| EN1| UNI | | | | | UNI | EN2|
| +--+ | | | | | +--+ |
+----+ | | +--+-+ +--+-+ +--+-+ | | +----+
+----+--+ CN4+------+ CN5+------+ CN6+--+----+
---------> | +----+ +----+ +----+ |
3) Signaling +----------------------------------+
Figure 2 - PCE for UNI path computation (1)
Alternatively, the path can be computed by cooperating PCEs, as shown
in Figure 3. The source EN does not experience any difference in
behavior in that it sends its computation request to its local PCE,
and receives a response telling it what path to use. However, the
local PCE may not be aware of the topology of the core network and
may need to contact a second PCE to supply the missing information.
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+-----+ +-----+
| |---------------->| |
| PCE1| 2) BRPC | PCE2|
| |<----------------| |
+-----+ +-----+
^ |
1) | |3) PCRep: EN1-CN4-CN5-CN6-EN2
PCReq:| | +------------------------------+
EN1-EN2| | | Core Network |
| | | +----+ +----+ +----+ |
| V +----+--+ CN1+----+ CN2+----+ CN3+--+----+
+----+ | | +--+-+ +--+-+ +--+-+ | | +----+
| +--+ | | | | | +--+ |
| EN1| UNI | | | | | UNI | EN2|
| +--+ | | | | | +--+ |
+----+ | | +--+-+ +--+-+ +--+-+ | | +----+
+----+--+ CN4+----+ CN5+----+ CN6+--+----+
---------> | +----+ +----+ +----+ |
4) Signaling +------------------------------+
(BRPC: Backward-Recursive PCE-Based Computation, see [RFC5441])
Figure 3 - PCE for UNI path computation (2)
If confidentiality of the topology within the core network needs to
be preserved, the Path Key Subobject (PKS) can be used for either
approach outlined here (see [RFC5520] and [RFC5553]). In the PCRep
message returned to EN1, the Confidential Path Segment (CPS) (i.e.,
CN4-CN5-CN6) is encoded as a PKS by the PCE. Therefore, the EN1 only
learns the selected UNI link from PCE. When receiving the UNI
signaling carrying the PKS from EN1, CN4 can request the PCE to
decode the PKS and then continue to create the connection.
Note that in both cases the PCE should be visible to the ENs and
there should be control channel between PCE and EN for the
transmission of PCEP messages. An alternative implementation could be
that the PCE is located inside each CN to which the source EN is
attached, so that the source EN can use the UNI control channel to
send and receive the PCEP messages.
5. UNI Path Provisioning
The basic GMPLS UNI application is to provide end-to-end connections
between edge-nodes through a core network via the overlay model.
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5.1. Flat Model
The edge-nodes may have the same switching capability and switching
capacity as the nodes in the core network. In this case, one single
end-to-end RSVP session through the edge-nodes and a series of core-
nodes can be used to create the connection, which forms a flat LSP
model, as shown in Figure 4.
+----------------------------------+
| Core Network |
+----+ UNI | +----+ +----+ +----+ | UNI +----+
| EN +-------+--+ CN +------+ CN +------+ CN +--+-------+ EN |
+----+ | +----+ +----+ +----+ | +----+
| | | |
| +----------------------------------+ |
| |
|<------------- End-to-end RSVP Session -------------->|
| |
Figure 4 - Flat model
If the edge-nodes and their attached core-nodes share the same
address space, the GMPLS signaling described in [RFC3471], [RFC3473]
and other related standards, with special ERO and RRO processing as
described in [RFC4208], can be used to create a connection.
5.2. Stitching Model
Alternatively, the stitching mechanism described in [RFC5150] can be
used to create an LSP segment (S-LSP) between the ingress and the
egress CN, and to stitch the end-to-end UNI connection to the created
S-LSP, as shown in Figure 5.
+----------------------------------+
| Core Network |
+----+ UNI | +----+ +----+ +----+ | UNI +----+
| EN +-------+--+ CN +------+ CN +------+ CN +--+-------+ EN |
+----+ | +----+ +----+ +----+ | +----+
| | | | | |
| +----+------------------------+----+ |
| | | |
| |<-LSP Segment (S-LSP)-->| |
| |
|<------------- End-to-end RSVP Session -------------->|
| |
Figure 5 - Stitching model
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5.3. Session Shuffling Model
The session shuffling approach ([RFC5251]) is a hybrid of the flat
model and the stitching model described in the previous two sections.
In this approach a single end-to-end session is established, but as
the signaling messages pass through the ingress and egress CNs,
address mapping is performed on all addresses carried by the messages
to place the addresses into the correct address spaces. The ERO and
RRO would normally be stripped (as previously discussed) but the
important session identifiers (the source and destination addresses)
are changed giving the impression that the session identifiers have
been changed.
5.4. Hierarchy Model
In case that the ENs and the CNs have the same switching capability,
a tunnel between the ingress and egress core-nodes can be provisioned.
The tunnel may have a larger capacity than the end-to-end UNI
connection, which may depend on the policies configured at the
ingress of the core network. The end-to-end connection can be nested
into the tunnel, which forms the LSP hierarchy.
Another case is that the edge-nodes have different switching
capabilities with the core network. In such a case, the LSP hierarchy
model should also be used.
+----------------------------------+
| Core Network |
+----+ UNI | +----+ +----+ +----+ | UNI +----+
| EN +-------+--+ CN +======+ CN +======+ CN +--+-------+ EN |
+----+ | +----+ +----+ +----+ | +----+
| | | | | |
| +----+------------------------+----+ |
| | | |
| |<-Core Network Tunnel-->| |
| |
|<------------- End-to-end RSVP Session -------------->|
| |
Figure 6 - Hierarchy model
In the hierarchy model, the end-to-end connection can be divided into
three hops: one for each UNI link and one hop across the core network.
The core network tunnel can be pre-provisioned via network planning,
or triggered by the UNI signal. For the latter case, the [RFC5212],
[RFC6001] and other multi-layer network related standards are
possible to be used to create the hierarchical LSP.
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6. UNI Recovery
One of the significant uses of GMPLS is to provide recovery
mechanisms for connections, which is also needed in many UNI
scenarios.
6.1. End-to-end Recovery
In the case of multi-homing, UNI end-to-end recovery is possible. As
shown in Figure 7, the working path (W) and the protection path (P)
are disjoint from each other not only inside the core network, but
also at both the source and destination sides of the UNI. Mechanisms
need to be provided to ensure the selection of disjoint working and
backup paths.
+----------------------------------+
| Core Network |
W | +----+ +----+ +----+ |
+----+--+ CN +------+ CN +------+ CN +--+----+
+----+ | | +----+ +----+ +----+ | | +----+
| +--+ | | +--+ |
| EN | UNI | | UNI | EN |
| +--+ | | +--+ |
+----+ | | +----+ +----+ +----+ | | +----+
+----+--+ CN +------+ CN +------+ CN +--+----+
P | +----+ +----+ +----+ |
+----------------------------------+
Figure 7 - UNI end-to-end recovery
6.1.1. Serial Provisioning of Working & Protection Path
In the case that the working path is computed and created before the
protection path, path computation needs to compute a disjoint (or
maximally disjoint) protection path given this existing working path.
If the information concerning the working path segment traversing the
core network is known by the EN without considering the
confidentiality, then the EN can easily use the RRO to collect the
working path information, and use the XRO to exclude the working path
when creating the protection path, as described in [RFC4874].
But in most cases, in order to preserve the confidentiality of
topology within the core network, the information of path segment
traversing the core network should be hidden from the EN. In such
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case, the RRO & XRO mechanism in [RFC4874] cannot be used. An
alternative would be to only collect the Shared Risk Group (SRG)
information but not the full path information. This is because the
SRG information is normally less confidential than the information of
node ID and link ID.
In an application scenario where a PCE is involved inside the core
network, then the Path Key mechanism can be used. The confidential
path segment, i.e., the working path segment traversing the core
network, is encoded as a PKS by the PCE when computing the working
path. This PKS can be brought to the source EN, so when it request
that the PCE compute a protection path, the PKS can be used to
exclude the working path segment inside the core network.
[RFC5520] provides a mechanism to hide the CPS using PKS in the PCEP
message, while [RFC5553] makes extensions to RSVP-TE to carry the PKS
in ERO and RRO objects. It is required that the PKS should also be
allowed to be carried in the XRO in both PCEP message and RSVP-TE
signaling.
6.1.2. Concurrent Computation of Working & Protection Path
Alternatively, the working and protection path can be computed at the
same time (e.g., by PCE or by one of the CNs to which the source EN
is attached).
[PCE-GMPLS] allows requesting the PCE for path computation with
specified protection type defined in [RFC4872]. Therefore, it's
possible that the source EN requests the edge CN or PCE to compute
both the working and the protection path at the same time. At this
time, the disjunction problem can be resolved inside the path
computation server.
Same as described in the previous section, the path segment
traversing the core network can be encoded as a PKS if
confidentiality is requested.
6.2. Segment Recovery
The UNI connection may only request protection inside the core
network, especially in case of single-homing. One UNI segment
protection example is shown in Figure 8.
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+--------------------------------------+
| Core Network |
| W +----+ +----+ |
| +--+ CN +--+ CN +--+ |
+----+ | +----+ | +----+ +----+ | +----+ | +----+
| | | | +--+ +--+ | | | |
| EN +-----+-+ CN | | CN +-+-----+ EN |
| | UNI | | +--+ +--+ | | UNI | |
+----+ | +----+ | +----+ +----+ | +----+ | +----+
| +--+ CN +--+ CN +--+ |
| P +----+ +----+ |
+--------------------------------------+
Figure 8 - UNI segment recovery
[RFC4873] provides the mechanism of segment recovery, in which the
PROTECTION Object is extended to indicate the segment recovery, and
the SERO object is introduced for the explicit control of the
protection LSP between the branch node and the merge node.
However, due to the overlay model, the source EN may not have the
information concerning the CN to which the destination EN is attached.
In other words, the source EN does not know which node is the merge
node of the UNI segment protection, so the SERO object cannot be used
to request the edge CN for the UNI segment recovery. Therefore,
segment recovery may not be controlled explicitly by the source EN.
7. UNI Call
The Call is a fundamental component of the ASON model [G.8080]. It is
used to maintain the association between one or more user
applications and the network to control the set-up, release,
modification and maintenance of sets of connections. In simple cases,
the Call and Connection can be established at the same time and in a
strict one-to-one ratio. In this case, Call signaling is simple and
requires only minor extensions to connection signaling. However, if
Calls are to be handled separately from Connections, or if more than
one Connection can be associated with a single Call, additional Call
signaling is required.
The GMPLS Call, defined in [RFC4974], provides a mechanism to
negotiate agreement between endpoints possibly in cooperation with
the nodes that provide access to the network. Typically the GMPLS
Call can be applied in the UNI scenario for access link capability
exchange, policy, authorization, security, and so on.
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7.1. Exchange of UNI Link Information
It is possible that the TE attributes of the access link (i.e., the
UNI link) are not shared across the core network. So the source EN
may not have the TE information of the destination access link as
well as the capability of the destination EN. For example, in case of
TDM network, the Virtual Concatenation (VCAT) and Link Capacity
Adjustment Scheme (LCAS) capability of the destination EN may not be
known.
In this case, the source EN can raise a Call carrying the
LINK_CAPABILITY object to have a capability exchange with the
destination EN, as described in [RFC4974].
7.2. Control of Call Route
When applying the Call, it's possible that there are multiple core
network domains between the source EN (Call initiator) and the
destination EN (Call terminator), or there is more than one Call
manager in the core network (e.g., in the multi-homing scenario where
the CNs to which the ENs are attached act as the Call managers).
In the both cases, when establishing the Call, there may be multiple
alternative routes for the Call message to reach the destination EN.
One can simply use the hop-by-hop manner (i.e., each Call manager
determines the next Call manager to which the Call message will be
sent by itself) to control the path of the Call.
However, in the practical deployment of UNI Call, commercial and
policy motivations normally play an important role in selecting the
Call route, especially in the multi-domain scenario. In this case,
the hop-by-hop manner is not practical because the route of the Call
needs to be pre-determined in consideration of commercial and policy
factors before establishing the Call.
Therefore, it is desirable to allow full control of the Call by the
source EN. That is, the source EN can identify the full Call route
and signal it explicitly, so that the Call message can be forwarded
along the desired route. Moreover, the management plane needs to be
able to identify the Call route explicitly as an instruction to the
source EN.
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8. UNI Multicast
Data plane multicasting is supported in the existing Traffic-
Engineering networks. GMPLS provides extensions to the RSVP-TE to
support provisioning of point-to-multipoint (P2MP) TE LSPs via
control plane, as described in [RFC4461] and [RFC4875].
In the scenarios where the overlay architectural model is used, it's
a requirement to transport signals from one source EN to multiple
destination ENs which are located in other overlay networks. One
could create multiple point-to-point connections between the source
EN and each destination EN, but it will be a waste of bandwidth
resource of both UNI links and the core network.
Therefore, there are some scenarios required to support point-to-
multipoint (P2MP) TE LSPs from one source EN to multiple leaf ENs.
8.1. UNI Multicast Connection Model
There are two cases for the UNI multicast. For the first case, only
the ingress and egress CNs in the core network support the multicast.
The core network has to provide multiple P2P connections between
ingress CN and each egress CN for the end-to-end UNI multicast, as
shown in Figure 9.
+----------------------------------------+
| Core Network |
| +-----+ +-----+ +-----+ |UNI +---+
+---+ UNI| | +--------+-----+-------+ +--+----+EN2|
|EN1+----+--+ CN1 +--------+-\CN2| | CN3 | | +---+
+---+ | | +--------+\ \ | | | | Leaf A
Source | +-----+ +-+-+-+ +-----+ |
| | | |
| +-+-+-+ +-----+ |UNI +---+
| | | \+-------+ +--+----+EN3|
| | |CN4| | CN5 | | +---+
| +-+---+ +-----+ | Leaf B
| | |
| +-+---+ +-----+ |UNI +---+
| | \---+-------+ +--+----+EN4|
| | CN6 | | CN7 | | +---+
| +-----+ +-----+ | Leaf C
+----------------------------------------+
Figure 9 - Only ingress/egress CNs support multicast
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For example, in the PSC over TDM multi-layer scenario, the
ingress/egress CNs may have the packet multicast capability and
therefore can adapt the packets from EN into multiple TDM connections
inside the core network, while other CNs inside the core network may
only support point-to-point (P2P) TDM connections.
In another case, all the CNs in the core network can support
multicast, so that the core network can create a P2MP LSP to provide
the end-to-end UNI multicast, as shown in Figure 10.
+----------------------------------------+
| Core Network |
| +-----+ +-----+ +-----+ |UNI +---+
+---+ UNI| | +--------+-+-->+-------+ +--+----+EN2|
|EN1+----+--+ CN1 | | |CN2| | CN3 | | +---+
+---+ | +-----+ +-V---+ +-----+ | Leaf A
Source | | |
| +-+---+ +-----+ |UNI +---+
| | +-->+-------+ +--+----+EN3|
| | |CN4| | CN5 | | +---+
| +-V---+ +-----+ | Leaf B
| | |
| +-+---+ +-----+ |UNI +---+
| | \-->+-------+ +--+----+EN4|
| | CN6 | | CN7 | | +---+
| +-----+ +-----+ | Leaf C
+----------------------------------------+
Figure 10 - All CNs support multicast
For example, in the Ethernet over OTN scenario, if the core network
can support ODU0 multicast, then an ODU0 P2MP LSP can be created
inside the core network to carry the client Gigabit Ethernet (GE)
signal for the ENs.
Note that the branching of the multicast may also happen at the
source EN in the multi-homing scenario. In this case, each branch of
the source EN uses a separate UNI link connecting the source EN to
the core network. For each UNI branch, the connection model inside
the core network is the same as described in this section.
8.2. UNI Multicast Connection Provisioning
The four UNI connection provisioning models, as described in Section
5, should also be applied in the UNI multicast scenario.
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For the flat model, one end-to-end P2MP session as described in
[RFC4875] can be used directly to create the P2MP LSP from source EN
to leaf ENs.
For the stitching model, multiple P2P LSP segments or one P2MP LSP
segment between the ingress CN and each egress CNs needs to be
created and then stitched to the UNI P2MP LSP. GMPLS UNI signaling
should have the capability to convey the multicast information by
using stitching model.
For the session shuffling model, one end-to-end P2MP session can be
used to create the P2MP LSP, with an address mapping performed at
both ingress and egress CNs.
For the hierarchy model, multiple P2P LSP tunnels or one P2MP LSP
tunnel between the ingress CN and each egress CNs needs be triggered
by the UNI signaling for creating P2MP LSP. GMPLS UNI signaling
should have the capability to convey the multicast information by
using hierarchy model.
9. Security Considerations
[RFC5920] provides an overview of security vulnerabilities and
protection mechanisms for the GMPLS control plane, which is
applicable to this document.
The details of the specific security measures of the overlay network
architectural model are provided in [RFC4208], which permits the core
network to filter out specific RSVP objects to hide its topology from
the EN.
Furthermore, if PCE is used, the security issues described in
[RFC4655] and other related standards should also be considered.
Additionally, when the PKS mechanism is applied, the security issues
can be dealt with using [RFC5520] and [RFC5553].
10. IANA Considerations
This informational document does not make any requests for IANA
action.
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11. Acknowledgments
TBD.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] D. Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC3209, December 2001.
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC3473] L. Berger, Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4203] Kompella, K., and Rekhter, Y., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC4206] K. Kompella et al, "Label Switched Paths (LSP) Hierarchy
with Generalized Multi-Protocol Label Switching (GMPLS)
Traffic Engineering (TE)", RFC4206, October 2005.
[RFC4208] G. Swallow et al, "Generalized Multiprotocol Label
Switching (GMPLS) User-Network Interface (UNI): Resource
ReserVation Protocol-Traffic Engineering (RSVP-TE)
Support for the Overlay Model", RFC4208, October 2005.
[RFC4655] A. Farrel et al, "A Path Computation Element (PCE)-Based
Architecture", RFC4655, August 2006.
[RFC4847] T. Takeda, Ed., "Framework and Requirements for Layer 1
Virtual Private Networks", RFC4847, April 2007.
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[RFC4872] J.P. Lang et al, "RSVP-TE Extensions in Support of End-
to-End Generalized Multi-Protocol Label Switching (GMPLS)
Recovery", RFC4872, May 2007.
[RFC4873] L. Berger et al, "GMPLS Segment Recovery", RFC4873, May
2007.
[RFC4874] CY. Lee et al, "Exclude Routes - Extension to Resource
ReserVation Protocol-Traffic Engineering (RSVP-TE)",
RFC4874, April 2007.
[RFC4875] R. Aggarwal et al, "Extensions to Resource Reservation
Protocol - Traffic Engineering (RSVP-TE) for Point-to-
Multipoint TE Label Switched Paths (LSPs)", RFC4875, May
2007.
[RFC4974] D. Papadimitriou and A. Farrel, Ed., "Generalized MPLS
(GMPLS) RSVP-TE Signaling Extensions in Support of Calls",
RFC4974, August 2007.
[RFC5150] A. Ayyangar et al, "Label Switched Path Stitching with
Generalized Multiprotocol Label Switching Traffic
Engineering (GMPLS TE)", RFC5150, February 2008.
[RFC5251] D. Fedyk and Y. Rekhter, Ed., "Layer 1 VPN Basic Mode",
RFC5251, July 2008.
[RFC5252] I. Bryskin and L. Berger Ed., "OSPF-Based Layer 1 VPN
Auto-Discovery", RFC5252, July 2008.
[RFC5520] R. Bradford, Ed., "Preserving Topology Confidentiality in
Inter-Domain Path Computation Using a Path-Key-Based
Mechanism", RFC5520, April 2009.
[RFC5553] A. Farrel, Ed., "Resource Reservation Protocol (RSVP)
Extensions for Path Key Support", RFC5553, May 2009.
[RFC6001] Dimitri Papadimitriou et al, "Generalized Multi-Protocol
Label Switching (GMPLS) Protocol Extensions for Multi-
Layer and Multi-Region Networks (MLN/MRN)", RFC6001,
October, 2010.
[RFC6107] K. Shiomoto, A. Farrel, "Procedures for Dynamically
Signaled Hierarchical Label Switched Paths", RFC6107,
February 2011.
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[G.8080] ITU-T Rec. G.8080/Y.1304, "Architecture for the
Automatically Switched Optical Network (ASON)," June 2006
(and Amend.2, September 2010).
12.2. Informative References
[RFC4461] S. Yasukawa, Ed., "Signaling Requirements for Point-to-
Multipoint Traffic-Engineered MPLS Label Switched Paths
(LSPs)", RFC4461, April 2006.
[RFC5212] K. Shiomoto et al, "Requirements for GMPLS-Based Multi-
Region and Multi-Layer Networks (MRN/MLN)", RFC5212, July
2008.
[RFC5253] T. Takeda, Ed., "Applicability Statement for Layer 1
Virtual Private Network (L1VPN) Basic Mode", RFC 5253,
July 2008.
[RFC5339] JL. Le Roux et al, "Evaluation of Existing GMPLS
Protocols against Multi-Layer and Multi-Region Networks
(MLN/MRN)", RFC5339, September 2008.
[RFC5441] JP. Vasseur et al, "A Backward-Recursive PCE-Based
Computation (BRPC) Procedure to Compute Shortest
Constrained Inter-Domain Traffic Engineering Label
Switched Paths", RFC5441, April 2009.
[RFC5623] Oki, E., Takeda, T., Le Roux, J.L., and Farrel, A.,
"Framework for PCE-Based Inter-Layer MPLS and GMPLS
Traffic Engineering", RFC 5623, September 2009.
[RFC5920] L. Fang, Ed., "Security Framework for MPLS and GMPLS
Networks", RFC5920, July 2010.
[Call-ext] Fatai Zhang et al, "RSVP-TE extensions to GMPLS Calls",
draft-zhang-ccamp-gmpls-call-extensions-01.txt, July 08,
2009.
[PCE-GMPLS] C. Margaria et al, "PCEP extensions for GMPLS", draft-
ietf-pce-gmpls-pcep-extensions-01.txt, October 24, 2010
[SRLG-FA] Fatai Zhang et al, "RSVP-TE Extensions for Configuration
SRLG of an FA", draft-zhang-ccamp-srlg-fa-configuration-
01.txt, October 20, 2010.
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[VCAT] G. Bernstein et al, "Operating Virtual Concatenation
(VCAT) and the Link Capacity Adjustment Scheme (LCAS)
with Generalized Multi-Protocol Label Switching (GMPLS)",
draft-ietf-ccamp-gmpls-vcat-lcas-11.txt, March 9, 2011.
13. Authors' Addresses
Fatai Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972912
Email: zhangfatai@huawei.com
Oscar Gonzalez de Dios
Telefonica Investigacion y Desarrollo
Emilio Vargas 6
Madrid, 28045
Spain
Phone: +34 913374013
Email: ogondio@tid.es
Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: daniele.ceccarelli@ericsson.com
Greg M. Bernstein
Grotto Networking
Fremont California, USA
Phone: (510) 573-2237
Email: gregb@grotto-networking.com
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Adrian Farrel
Old Dog Consulting
EMail: adrian@olddog.co.uk
Yi Lin
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972914
Email: yi.lin@huawei.com
Young Lee
Huawei Technologies
1700 Alma Drive, Suite 100
Plano, TX 75075
USA
Phone: (972) 509-5599 (x2240)
Email: leeyoung@huawei.com
Dan Li
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28973237
Email: huawei.danli@huawei.com
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