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Network Working Group                                        Fatai Zhang
Internet Draft                                                    Huawei
Category: Informational                              O. Gonzalez de Dios
                                   Telefonica Investigacion y Desarrollo
                                                               A. Farrel
                                                      Old Dog Consulting
                                                              Xian Zhang
                                                                  Huawei
                                                           D. Ceccarelli
                                                                Ericsson
Expires: August 21, 2013                               February 22, 2013



   Applicability of Generalized Multiprotocol Label Switching (GMPLS)
                      User-Network Interface (UNI)

                  draft-zhang-ccamp-gmpls-uni-app-03.txt


Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   time.  It is inappropriate to use Internet-Drafts as reference
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   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 21, 2013.



Abstract






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   Generalized Multiprotocol Label Switching (GMPLS) defines a set of
   protocols for the creation of Label Switched Paths (LSPs) in various
   switching technologies. The GMPLS User-Network Interface (UNI) was
   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 suggests simple extensions that could be made to
   existing technologies to further enable the UNI and points out some
   unresolved issues.



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...................................... 8
   5. UNI Path Provisioning........................................ 9
      5.1. Flat Model ............................................. 9
      5.2. Stitching Model........................................ 10
      5.3. Session Shuffling Model................................ 11
      5.4. Hierarchal Model....................................... 11
   6. UNI Recovery ............................................... 12
      6.1. End-to-end Recovery.................................... 12
         6.1.1. Serial Provisioning of Working and Protection Paths 13
         6.1.2. Concurrent Computation of Working and Protection Path14
      6.2. Segment Recovery....................................... 14
   7. UNI Call ................................................... 15
      7.1. Exchange of UNI Link Information ....................... 15
      7.2. Control of Call Route.................................. 16
   8. UNI Multicast .............................................. 16
      8.1. UNI Multicast Connection Model ......................... 17
      8.2. UNI Multicast Connection Provisioning .................. 18
   9. Security Considerations..................................... 19
   10. IANA Considerations........................................ 19
   11. Acknowledgments ........................................... 19
   12. References ................................................ 20
      12.1. Normative References.................................. 20
      12.2. Informative References................................ 22
   13. Contributors' Address...................................... 23
   14. Authors' Addresses ........................................ 23



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1. Introduction

   Generalized Multiprotocol Label Switching (GMPLS) [RFC3945] defines a
   set 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

                       Legend:   EN  -  Edge Node
                                 CN  -  Core Node

              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 which initiates the
      connection (i.e., EN1);

   "destination EN" refers to the edge-node where the connection is
   terminated (i.e., EN3);

   -   "ingress CN" refers to the core-node to which the source EN is
      attached (i.e., CN1);

   -  "egress CN" refers to the core-node to which the destination EN
      is attached (i.e., 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 the 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 receives against its topology database and
   may enhance it with additional path information 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 GMPLS 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 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
   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 some deployments of the GMPLS UNI, it is not practical
   for the EN and its attached CN to share the same address space. This
   can arise if the core and overlay networks were designed and deployed
   separately or 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 may be independent of other
   IP addresses outside the core network. This implies that the nodes in
   the core network may use addresses which could collide with the edge
   nodes in the overlay network.

   [RFC4208] does not state how to ensure that an edge-node and its
   attached core-node share the same address space. This document
   analyzes the addressing deployment scenarios as follows:

   1. Overlay network and core network share a common addressing policy.
      This 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]. 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 ENs each have two addresses: one in the
      overlay network and one in the core network. The source EN is


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      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 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 and/or its TE
      links. A typical deployment may assign addresses in the core
      network address space for the EN and/or its TE links at the EN
      side, so that EN can use these addresses to communicate with the
      core network for UNI connection provisioning.

      In this deployment, a single end-to-end RSVP-TE session can still
      be utilized from the source EN to the destination EN using
      addressing and naming from the core network's address space.

   3. ENs do not have any knowledge of the core address space, or do not
      support the address space the core network uses (e.g., ENs do not
      support IPv6 that is used by the core network). ENs will have no
      visibility into the core network.

      In this scenario, the ingress CN is responsible for mapping
      addresses to the core address space and filling in any additional
      routing information. A typical deployment is to assign addresses
      in the overlay address space for the ingress CN and/or its TE
      links at the CN side, so that the EN can use overlay addresses to
      reach the ingress CN and to identify the destination EN.

      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), address
   mapping needs to be performed by the source EN or the source CN.




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   The discovery problem may be exacerbated when a variety of services
   are 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 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 an L1VPN scenario, two mechanisms for auto
   discovery have been defined. Auto discovery of UNI using OSPFv2 is
   provided in [RFC5252] using an L1VPN LSA 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. Auto discovery of UNI using BGP is provided in [RFC5195] by
   having each edge CN advertise to other edge CN the following
   information, at a minimum: its own IP address and the list of
   <private address, provider address> tuples local to that PE.  Once
   that information is received, the remote PEs will identify the list
   of VPN members they have in common with the advertising PE, and use
   the information carried within the discovery mechanism to perform
   address resolution during the signaling phase of Layer-1 VPN
   connections.



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 be necessary in all scenarios. One
   example is in the case of single-homing with only one UNI link
   between EN and CN. Another example is manual selection of the UNI
   link when the service is requested (i.e., as a function of the
   service request such as the port mapping used in a L1VPN). 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.





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4.1. UNI Link Selection

   This document is specific to the overlay architectural model, and
   that means that the source EN 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 in early GMPLS UNI
   deployments. A PCE that has the topology and TE information of the
   core network 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 the procedures for UNI path computation using a single
   PCE with visibility into the core network and information about all
   of the CN-EN links. When the UNI path computation request is received,
   the PCE can help the source EN to compute the end-to-end route of the
   UNI connection based on routing information it has accesses to, so
   that the source EN can create the UNI connection using the optimal
   UNI link. As shown in Figure 2, the following steps are carried out:

   Step 1: EN1 requests a path from EN1 to EN2 by sending a PCReg
   message to the PCE;

   Step 2: The PCE computes a path based on its view of the core network
   and knowledge of all the EN-CN links. In this case, it returns the
   path En1-CN4-CN5-Cn6-EN2 to the EN1 node;

   Step 3: EN1 starts the signaling process to set up the LSP by using s
   standard RSVP signaling process, using the path information as
   computed.

   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, EN1 only
   learns the selected UNI link from the PCE. When CN4 receives the UNI
   signaling message from EN1 carrying the PKS, CN4 asks the PCE to
   decode the PKS and then continues to signal the LSP.



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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 - Procedure using a PCE for UNI path computation


   Note that in both cases described in this section, the PCE needs to
   be visible to the ENs, and there also needs to be a control channel
   between the PCE and the ENs for the exchange of PCE Protocol (PCEP)
   messages. An alternative implementation could be that a 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. This
   section briefly describes four ways in which the end-to-end LSP can
   be created and operated across the core network.

5.1. Flat Model

   In this model, the edge-nodes have the same switching capability 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 3.


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                +----------------------------------+
                |          Core Network            |
   +----+  UNI  |  +----+      +----+      +----+  |  UNI  +----+
   | EN +-------+--+ CN +------+ CN +------+ CN +--+-------+ EN |
   +----+       |  +----+      +----+      +----+  |       +----+
      |         |                                  |         |
      |         +----------------------------------+         |
      |                                                      |
      |<------------- End-to-end RSVP Session -------------->|
      |                                                      |
                         Figure 3 - The Flat Model

   If the edge-nodes and their attached core-nodes share the same
   address space, or the ENs can perform address mapping into the core
   network address space, the GMPLS signaling described in [RFC3471],
   [RFC3473] and other related specifications, with special ERO and RRO
   processing as described in [RFC4208], can be used to create a
   connection.

5.2. Stitching Model

   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 4.

                +----------------------------------+
                |          Core Network            |
   +----+  UNI  |  +----+      +----+      +----+  |  UNI  +----+
   | EN +-------+--+ CN +------+ CN +------+ CN +--+-------+ EN |
   +----+       |  +----+      +----+      +----+  |       +----+
      |         |    |                        |    |         |
      |         +----+------------------------+----+         |
      |              |                        |              |
      |              |<-LSP Segment (S-LSP)-->|              |
      |                                                      |
      |<------------- End-to-end RSVP Session -------------->|

                      Figure 4 - The Stitching Model

   This model allows the core network a degree of independence so that
   the S-LSP can be set up and modified without the knowledge of the
   overlay network. Remember that stitching is a data plane function, so
   that the EN-CN LSP segments are cross-connected to the S-LSP at the
   edge CNs. This means that, just as in Section 5.1, the overlay and
   core networks must have the same switching capabilities. However, the
   control plane for the stitching model operates just as the


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   hierarchical model described in Section 5.4, so the S-LSP appears as
   a single hop in the overlay network.

5.3. Session Shuffling Model

   The session shuffling approach ([RFC5251]) is a modification of the
   flat model described in Section 5.1. 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 replace the addresses with
   values from the correct address space. The ERO and RRO are stripped
   from the messages as previously discussed, so there is no need for
   the CNs to examine those objects to map addresses. However, all other
   addresses must be mapped including the important session identifiers
   (the source and destination addresses). Viewed from the outside
   (perhaps through an NMS) this gives the impression of session
   stitching because the session has different identifiers as it crosses
   the core network. An NMS might, therefore, present the shuffling
   model as the stitching model, or it might operate the same address
   shuffling/mapping as is used by CNs.

5.4. Hierarchal Model

   If the ENs and CNs have the same switching capability, a tunnel
   between the ingress and egress core-nodes can be provisioned to carry
   the end-to-end connection. The tunnel may have a larger capacity than
   the end-to-end UNI connection, depending on the policies configured
   at the ingress CN of the core network. The end-to-end connection can
   be nested into a tunnel, which forms the LSP hierarchy [RFC4206] as
   shown in Figure 5. If the tunnel has a larger capacity, other LSPs
   can also be nested within the same tunnel.

   Alternatively, if the ENs and CNs have different switching
   capabilities the LSP hierarchical model can also be used exactly as
   described in [RFC4206].

   In the hierarchal 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 signalling. For the latter case,
   [RFC5212], [RFC6001] and other multi-layer network related
   specifications can be used to create the hierarchical LSP.







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                +----------------------------------+
                |          Core Network            |
   +----+  UNI  |  +----+      +----+      +----+  |  UNI  +----+
   | EN +-------+--+ CN +======+ CN +======+ CN +--+-------+ EN |
   +----+       |  +----+      +----+      +----+  |       +----+
      |         |    |                        |    |         |
      |         +----+------------------------+----+         |
      |              |                        |              |
      |              |<-Core Network Tunnel-->|              |
      |                                                      |
      |<------------- End-to-end RSVP Session -------------->|
      |                                                      |

                      Figure 5 - The Hierarchal Model



6. UNI Recovery

   One of the significant uses of GMPLS is to provide recovery
   mechanisms for connections. Recovery and protection mechanisms are
   also needed in many UNI scenarios, and the relationship between the
   overlay and core network provide obvious places at which to operate
   the recovery techniques.

6.1. End-to-end Recovery

   In the case of multi-homing, UNI end-to-end recovery is possible. As
   shown in Figure 6, 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 as discussed in the following subsections.

   It should be noted that end-to-end recovery can be operated even when
   the ENs are single-homed. However, obviously, in this case there is
   no protection against the failure of an EN-CN link, or of the edge CN
   itself.



                +----------------------------------+
                |          Core Network            |
             W  |  +----+      +----+      +----+  |
           +----+--+ CN +------+ CN +------+ CN +--+----+
   +----+  |    |  +----+      +----+      +----+  |    |  +----+
   |    +--+    |                                  |    +--+    |


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   | EN | UNI   |                                  |   UNI | EN |
   |    +--+    |                                  |    +--+    |
   +----+  |    |  +----+      +----+      +----+  |    |  +----+
           +----+--+ CN +------+ CN +------+ CN +--+----+
             P  |  +----+      +----+      +----+  |
                +----------------------------------+

                    Figure 6 - UNI End-to-End Recovery

6.1.1. Serial Provisioning of Working and Protection Paths

   In serial provisioning, one path is computed before another and the
   associated LSP may even be set up before the second path is computed.
   In the case where the working path is computed and created before the
   protection path, path computation for the protection path needs to
   select a (maximally) disjoint path given this existing working path.

   If the EN is allowed to see details of the core network, the EN can
   use the RRO to collect the route of the working path. It can then use
   the Exclude Route Object (XRO) to exclude the working path when
   signaling the protection path, as described in [RFC4874].

   But in most cases, in order to preserve the confidentiality of
   topology within the core network, the route of the working path as it
   traverses the core network will be hidden from the EN. In such cases,
   the RRO and XRO mechanism 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.  Another possible solution is encrypted the SRG information and
   provide it to the EN nodes, so that the EN nodes can using this
   information to convey the diversity constraint, as the method
   specified in [UNIExt].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 route of the working
   path as it traverses the core network, is encoded as a PKS by the PCE
   when computing the working path [RFC5520]. This PKS can be used by
   the EN when it requests the PCE to compute a protection path, to
   exclude the nodes and links used by the working path. As previously
   described, the PKS is also used in signaling [RFC5553] so that the EN
   can indicate to the CN what path to use across the core network.

   In order to specify the diversity requirement, it is required that
   the PKS should be carried in the XRO in both PCEP message and RSVP-TE
   signaling.




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6.1.2. Concurrent Computation of Working and Protection Path

   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] adds support for an end node to request a protected
   service using the protection types 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 requirement 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 request protection only inside the core
   network, especially in case of single-homing. A UNI segment
   protection example is shown in Figure 7. In this case, the core
   network provides a "recovery domain".

              +--------------------------------------+
              |            Core Network              |
              |         W  +----+  +----+            |
              |         +--+ CN +--+ CN +--+         |
   +----+     | +----+  |  +----+  +----+  |  +----+ |     +----+
   |    |     | |    +--+                  +--+    | |     |    |
   | EN +-----+-+ CN |                        | CN +-+-----+ EN |
   |    | UNI | |    +--+                  +--+    | | UNI |    |
   +----+     | +----+  |  +----+  +----+  |  +----+ |     +----+
              |         +--+ CN +--+ CN +--+         |
              |         P  +----+  +----+            |
              +--------------------------------------+

                      Figure 7 - UNI Segment Recovery

   [RFC4873] provides a mechanism for segment recovery, in which the
   PROTECTION Object is extended to indicate segment recovery, and the
   Secondary ERO (SERO) is introduced for the explicit control of the
   protection LSP between the branch node and the merge node.




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   However, in the overlay model, the mechanisms of segment recovery
   described in [RFC4873] may not be appropriate. In particular, the
   source EN might not know the CN to which the destination EN is
   attached. That means that the source EN knows the branch for the
   protection segment, but does not know the merge node.

   But the model shown in Figure 7 is particularly important because it
   places the responsibility for service delivery with the edge CNs.
   This will be a common operational model in overlay networks.
   Fortunately the stitching model (Section 5.2) and the hierarchical
   model (Section 5.4) are good at providing the necessary protection
   within the core network without the ENs having to be aware of the
   paths in the core network.



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, and to control the set-up, release,
   modification, and maintenance of sets of Connections (LSPs). 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
   requires only minor extensions to connection signaling. However, if
   Calls are 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.

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


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   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.



8. UNI Multicast

   Data plane multicasting is supported in existing Traffic-Engineering
   networks. GMPLS provides extensions to RSVP-TE to support
   provisioning of point-to-multipoint (P2MP) TE LSPs via the control
   plane, as described in [RFC4461] and [RFC4875].

   In the scenarios where P2MP is supported using the overlay
   architectural model, it is a requirement to transport signals from
   one source EN to multiple destination ENs. One could create a point-
   to-point (P2P) connection between the source EN and each destination
   EN, but it will likely be a waste of bandwidth resource both of the
   UNI link and in the core network.




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   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 P2MP. 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 8. This relieves the pressure on the source UNI link, but does
   not help the over use of the core links such as CN1-CN2.


            +----------------------------------------+
            |              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 8 - Only ingress/egress CNs support multicast



   For example, in multi-layer scenario of a packet overlay network with
   a TDM core, the ingress/egress CNs may have packet multicast
   capabilities and therefore can adapt the packets from EN into
   multiple TDM connections to transit the core network, but the CNs
   inside the core network 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 9.



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            +----------------------------------------+
            |              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 9 - 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 P2MP connection could also happen at
   the source EN if the EN is multi-homed. In this case, each branch
   from 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.

   For the flat model, one end-to-end P2MP session as described in
   [RFC4875] can be used 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.




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   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 hierarchical 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 the P2MP LSP. GMPLS UNI signaling
   should have the capability to convey the multicast information by
   using the hierarchical 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] 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.



11. Acknowledgments

   TBD.








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12. References

12.1. Normative References

    [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.

   [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.





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   [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.

   [RFC5195]   Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP-Based
               Auto-Discovery for Layer-1 VPNs", RFC 5195, June 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.

   [G.8080]    ITU-T Rec. G.8080/Y.1304, "Architecture for the
               Automatically Switched Optical Network (ASON)," June 2006
               (and Amend.2, September 2010).




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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-07.txt, October 21, 2012.

   [SRLG-FA]   Fatai Zhang et al, "RSVP-TE Extensions for Configuration
               SRLG of an FA", draft-ietf-ccamp-rsvp-te-srlg-collect-
               01.txt, October 22, 2012.

   [RFC6344]   G. Bernstein et al, "Operating Virtual Concatenation
               (VCAT) and the Link Capacity Adjustment Scheme (LCAS)
               with Generalized Multi-Protocol Label Switching (GMPLS)",
               RFC6344, August 2011.




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   [UNIExt]    D. Fedyk, D. Beller, Lieven Levrau, D. Ceccarelli, F. Zhang,
               et al, "UNI Extensions for Diversity and Latency Support",
               draft-fedyk-ccamp-uni-extensions-00.txt, Feb. 2013;



13. Contributors' Address

   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


14. 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


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   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


   Adrian Farrel
   Old Dog Consulting

   EMail: adrian@olddog.co.uk


   Xian Zhang
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28972913
   Email: zhang.xian@huawei.com


   Daniele Ceccarelli
   Ericsson
   Via A. Negrone 1/A
   Genova - Sestri Ponente
   Italy

   Email: daniele.ceccarelli@ericsson.com



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