A Framework for Explicit Control of Region Boundary in PCE-Based Inter-Layer Architecture
draft-fuxh-pce-boundary-explicit-control-framework-01

Abstract

This document defines the framework for explicit control of region boundary in PCE-based inter-layer architecture.

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 RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

Status of this Memo

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Table of Contents

1.  Introduction
2.  Explicit Control of Region Boundary
    2.1.  Procedure for Region Boundary Explicit Contorl
3.  Explicit Control Model of Region Boundary
    3.1.  Explicit Region Control in Single PCE Inter-Layer
    3.2.  Explicit Region Control in Multiple PCE Inter-Layer with inter-PCE communication.
    3.3.  Explicit Region Control in Multiple PCE Inter-Layer without inter-PCE communication.
4.  Protocol Extension Requirements for Explicit Control of Region Boundary
5.  Security Considerations
6.  IANA Considerations
7.  References
    7.1.  Normative References
    7.2.  Informative References
§  Authors' Addresses

1.  Introduction

PCE can determine regions' boundaries. Without cooperating with VNTM or policy configuration, a intermediate LSR has to determine regions' boundaries by using the IGP database and ERO as described in [RFC4206] in order to trigger the lower layer signaling. A centralized routing and distributed signaling application is foreseen in the PCE architecture. Without any or enough TED within the intermediate LSR, it could not determine regions' boundaries during the signaling.

This document defines the framework for explicit control of region boundary in PCE-based inter-layer architecture. The solution isn't limited to specific Inter-Layer Path Computation and Inter-Layer Path Control Models. The solution in this document can also be applied in the situation where TED can be maintained by the intermediate LSR in order for less signaling time.

2.  Explicit Control of Region Boundary

PCE can determine regions' boundaries. After PCE compute an end-to-end paths across multi-layer, multi-layer EROs must be carried in PCRep and Path message in terms of RFC5623. In order to explicit control of regions' boundaries, this document introduces a new object (ERBO- Explicit Region Boundary Object). It is carried in PCRep and RSVP-TE Signaling message. Regions' boundaries must be carried in ERBO.

2.1.  Procedure for Region Boundary Explicit Contorl

PCC request the PCE computate a multi-layer path with an indication of whether inter-layer path computation is allowed. The PCE computes and returns a multi-layer path to the PCC converted to an Explicit Route Object (ERO) for use in RSVP-TE signaling. The PCRep also must includs the region boundaries information which contains zero or multiple pairs of nodes. This document introduces a new object (ERBO- Explicit Region Boundary Object). It is carried in PCRep and RSVP-TE Signaling message. Regions' boundaries must be carried in ERBO. One pairs or multiple pairs of nodes within the ERBO can belong to the same layer or different layers. The RSVP-TE signaling message among the PCC and intermediate nodes must carry the region boundaries information provided by PCE.

If the intermediate nodes receive the signaling message with region boundaries information, it must check whether it is one of the region boundaries. If it isn't one of region boundaries, the signaling should be continued. If the intermediate nodes receive the signaling message without region boundaries information, the signaling should be continued.

If it is one of region boundaries, it must get another end of region boundary from the next hop in ERBO. It must get the detailed routing information between the pair of region boundaries from the ERO in order to initiate the signaling of lower layer path. Because there may be more further region boundaries information within the lower layer in ERBO, it must get the region boundaries information for lower layers from ERBO.

Once the pair of region boundaries, the region boundaries information of lower layers and the routing information of lower layers are determined, the ingress node of region boundaries initiates the lower layer signaling. The signaling of lower layers must also include the region boundaries information.

3.  Explicit Control Model of Region Boundary

3.1.  Explicit Region Control in Single PCE Inter-Layer

Because inter-layer path computation is performed by a single PCE that has topology visibility into all layers in this model, PCE can determines the region boundaries within all the layers. It must return the detailed routing information in ERO and region boundaries information in ERBO.

PCC initiates the signaling based on the ERO and ERBO returned by the PCE. The intermediate nodes will initiate the signaling procedure of lower layers based on the routing information in ERO and the region boundaries information in ERBO.

The process of creating a LSP from H1 to H6 based on the following figure is as follows:

1. H1 sends a route request between H1 and H6 to PCE,and PCE responses to H1 with ERO = {H1,H2,L3,L4,H5,H6} and ERBO = {H2,H5}.
2. H1 Sends Path to H2 with ERO = {H2,L3,L4,H5,H6} and ERBO = {H2, H5}.
3. After H2 receivs the Path message, H2 confirm that it is the initiator of lower layer LSP and H5 is another end of region boundaries in terms of the ERBO and ERO. H2 extracts the complete route of the lower layer LSP from ERO in terms of the other end of the region boundaries. The routing information of lower layer is {H2,L3,L4,H5}. There is no any further region boundaries information within lower layer based on the ERBO.
4. Then H2 starts the creation of lower layer LSP, the route is H2,L3,L4,H5.
5. After the creation of the lower layer LSP, the Higher-Layer LSP's creation is to be continued. H2 sends the Path message to H5. And the ERO and ERBO in the Path message is cut out. So there isn't any information in ERBO.

   -----
  | PCE |
   -----
   ^    |
   |  2:PCRep
   |    | (ERO)  (ERBO)
   |    |  ----   ----
   |    | | H1 | | H2 |
   |    |  ----   ----
   |    | | H2 | | H5 |
   |    |  ----   ----
   |    | | L3 |
   |    |  ----
   |    | | L4 |
   |    |  ----
   |    | | H5 |
   |    |  ----
   |    | | H6 |
   |    |  ----
   |    |
1:PCReq |
   |    v
   -----    -----                  -----    -----
  | LSR |--| LSR |................| LSR |--| LSR |
  | H1  |  | H2  |                | H5  |  | H6  |
   -----    -----\                /-----    -----
                  \-----    -----/
                  | LSR |--| LSR |
                  | L3  |  | L4  |
                   -----    -----
 --------------->                --------------->
   3:Path                             4:Path
   (ERO) (ERBO)                       (ERO)
   ----   ----                         ----
  | H2 | | H2 |                       | H2 |
   ----   ----                         ----
  | L3 | | H5 |
   ----   ----
  | L4 |
   ----
  | H5 |
   ----
  | H6 |
   ----

3.2.  Explicit Region Control in Multiple PCE Inter-Layer with inter-PCE communication.

In the following figure, there are two PCEs with inter-PCE communication. PCE Hi has the topology visibility restricted to the upper layer. PCE Lo has the topology visibility of two layers. The end-to-end path is computated by the cooperation between PCE Hi and PCE Lo.

The region boundaries within all the layers can be determined by the cooperation between the PCE Hi and PCE Lo. The PCE Hi must return the detailed routing information in ERO and region boundaries information in ERBO.

PCC initiates the signaling based on the ERO and ERBO returned by the PCE. The intermediate nodes will initiate the signaling procedure of lower layers based on the routing information in ERO and the region boundaries information in ERBO.

The process of creating a LSP from H1 to H10 is as follows:

1. H1 sends a route request bwtween H1 and H10 to PCE Ho. Without the topology visibility of lower layers, PCE Ho has to compute a multi-layer path with inter-communication with PCE Lo. PCE Lo computes two multi-layer paths. One is between H2 and H5. Another is between H6 and H9. PCE Lo responses to PCE Hi with the derailed routing information and region boundaries information. In the end, PCE Hi responses to H1 with ERO = {H1,H2,L3,M1,M2,L4,H5,H6,L7,L8,H9,H10} and ERBO ={H2,H5,L3,L4,H6,H9}.
2. H1 Sends Path to H2 with ERO = {H2,L3,M1,M2,L4,H5,H6,L7,L8,H9,H10}, ERBO = {H2,H5,L3,L4,H6,H9}
3. After H2 receives the Path, H2 determines it is the one end of region boundaries and H5 is another end based on the ERO and ERBO. So it abstracts the derailed routing information and region boundaries information of lower layer. The region boundaries information is {L3,L4}. It is to create lower layer LSP with ERO = {H2,L3,M1,M2,L4,H5} and ERBO = {L3,L4}.
4. H2 Sends Path to L3 with ERO = {L3,M1,M2,L4,H5} and ERBO = {L3,L4}.
5. After L3 receives the Path, L3 determines it is the one end of region boundaries and L4 is another end based on the ERO and ERBO. So it abstracts the derailed routing information and region boundaries information of lower layer. The routing information of lower layer is {L3,M1,M2,L4}. The region boundaries information is empty. L3 is to create lower layer LSP with ERO = {L3,M1,M2,L4}.
6. L3 Sends Path to M1 with ERO = {M1,M2,L4} and ERBO = empty.
7. After the creation of the lower layer LSP between L3 and L4, L3 continues to send Path to L4 with ERO = {L4,H5} and ERBO = empty.
8. After the creation of the lower layer LSP between H2 and H5, H2 continues to send Path to H5 with ERO = {H5,H6,L7,L8,H9,H10} and ERBO = {H6,H9}.
9. H5 send the Path message to H6 with the with ERO = {H6,L7,L8,H9,H10} and ERBO = {H6,H9}.
10. After H6 receives the Path, H6 determines it is the one end of region boundaries and H9 is another end based on the ERO and ERBO. So it abstracts the derailed routing information and region boundaries information of lower layer. The routing information of lower layer is {H6,L7,L8,H9}. The region boundaries information is empty. H6 create the lower layer LSP with ERO = {H6,L7,L8,H9} and ERBO = empty.
11. After the creation of the lower layer LSP between H6 and H9, the higher layer LSP's creation is to be continued.

   -----
  | PCE |
  | Hi  | <----------------------
   -----                        |
   ^    |                       |
   |    |                       |
   |    |                       |
   |    |                       |
   |    |                       |
   |    v                       |
    -----    -----              |                -----    -----                -----    -----
   | LSR |--| LSR |.............|...............| LSR |--| LSR | .............| LSR |--| LSR |
   | H1  |  | H2  |             v               | H5  |  | H6  |              | H9  |  | H10 |
    -----    -----\           -----             /-----    -----\              /-----    -----
                  |          | PCE |            |              |              |
                  |          | Lo  |            |              |              |
                  |           -----             |              |              |
                  \-----                  -----/               \-----    -----/
                  | LSR |................| LSR |               | LSR |..| LSR |
                  | L3  |                | L4  |               | L7  |  | L8  |
                   -----\                /-----                 -----    -----
                        |               |
                        |               |
                        |               |
                        \-----    -----/
                        | LSR |..| LSR |
                        | M1  |  | M2  |
                         -----    -----

3.3.  Explicit Region Control in Multiple PCE Inter-Layer without inter-PCE communication.

In the following figure, the PCE Hi has the topology visibility of higher two layers. The PCE Lo has the topology visibility of lower two layers.

The process of creating a LSP from H1 to H10 is as follows:

1. H1 sends a route request between H1 and H10 to PCE Ho. PCE Ho could not computate a multi-layer path within four layers. PCE Ho computes a multi-layer path for higher two layers without inter-communication with PCE Lo, and responses to H1 with ERO = {H1,H2,M3,M8,H9,H10} and ERBO ={H2,H9}.
2. H1 Sends Path to H2 with ERO = {H2,M3,M8,H9,H10} and ERBO = {H2,H9}.
3. After H2 receives the Path, H2 determines it is the one end of region boundaries and H9 is another end based on the ERO and ERBO. So it abstracts the derailed routing information and region boundaries information of lower layer. The routing information of lower layer is {H2,M3,M8,H9}. The region boundaries information is empty. H2 is to create lower layer LSP with ERO = {H2,M3,M8,H9}.
4. H2 Sends Path to M3,with ERO = {M3,M8,H9} and ERBO = empty.
5. There is no any connectivity between M3 and M8. M3 can communicates with PCE Lo. PCE Lo has the capability of Inter-Layer path computation. So M3 consults the PCE Lo with responsibility for the lower-layers network. PCE Lo computes the route to expand the loose hop route (i.e., M3 and M8) in the higher-layer LSP and responses to M3 with ERO = {M3,L4,L5,L6,L7,M8}, ERBO ={L4,L7}.
6. M3 Sends Path to L4, with ERO = {L4,L5,L6,L7,M8}, ERBO = {L4,L7}.
7. After L4 receives the Path, L4 determines it is the one end of region boundaries and H7 is another end based on the ERO and ERBO. So it abstracts the derailed routing information and region boundaries information of lower layer. The routing information of lower layer is {L4,L5,L6,L7}. The region boundaries information is empty. L4 is to create lower layer LSP with ERO = {L4,L5,L6,L7} and ERBO = empty.
8. L4 Sends Path to L5, with ERO = {L5,L6,L7} and ERBO = empty.
9. After the creation of the lower layer LSP between L4 and L7, L4 continues to send Path to L7 with ERO = {L7,M8} and ERBO = empty.
10. After the creation of the lower layer LSP between M3 and M8, M3 continues to send Path to M8 with ERO = {M8,H9} and ERBO = empty.
11. After the creation of the lower layer LSP between H2 and H9, H2 continues to send Path to H9 with ERO = {H9,H10} and ERBO = empty

         -----
        | PCE |
        | Hi  |
         -----
        ^    |
        |    |
        |    |
        |    |
        |    |
        |    v
         -----    -----                                            -----    -----
        | LSR |--| LSR |..........................................| LSR |--| LSR |
        | H1  |  | H2  |                                          | H9  |  | H10 |
         -----    -----\                                          /-----    -----
                       |                                          |
                       |                                          |
                       |                                          |
                       \-----                               -----/
                       | LSR |............................ | LSR |
                       | M3  |<-------------               | M8  |
                        -----\             |               /-----
                             |             v               |
                             |            -----            |
                             |           | PCE |           |
                             |           | Lo  |           |
                             |            -----            |
                              \-----                 -----/
                              | LSR |...............| LSR |
                              | L4  |               | L7  |
                               -----\               /-----
                                    |               |
                                    |               |
                                    |               |
                                    \-----    -----/
                                    | LSR |..| LSR |
                                    | L4  |  | L7  |
                                     -----    -----

4.  Protocol Extension Requirements for Explicit Control of Region Boundary

A requirements for PCRep (RFC5440) extensions to support explicit control of region boundary is foreseen. A requirements for Path (RFC3473) extensions to support explicit control of region boundary is also foreseen. A new object (ERBO) could be introduced in PCRep and Path message. The format of new object is the same as an ERO. [draft-fuxh-ccamp-region-boundary-explicit-control-rsvp-ext-00] defines the RSVP-TE signaling extension for explicit control of region boundary during the signaling procedure. [draft-fuxh-pce-region-boundary-explicit-control-pcep-ext-00] defines the PCEP protocol extension for explicit control of region boundary in PCE-based inter-layer architecture.

5.  Security Considerations

TBD

6.  IANA Considerations

TBD

7.  References

7.1. Normative References

7.2. Informative References

Authors' Addresses