Subject: Re: [Mter] Need to decide on potential next steps for MTER

From: "Diego Caviglia" <[email-masked]>
Date: Tue, 16 May 2006 09:23:19 +0200

Some times ago I've published an ID about the requirements for interworking
between MS-SPRing and GMPLS, I think that this kind of interworking is
something that is MTER related and is also interesting from a carrier
prespective at least this is my feeling.

Regards

Diego

Michael Menth <[email-masked]> on 16/05/2006 09.12.08

Please respond to [email-masked]

To:    JP Vasseur <[email-masked]>
cc:    Rüdiger Martin <[email-masked]>,
       [email-masked], [email-masked]

Subject:    Re: [Mter] Need to decide on potential next steps for MTER

Dear JP, Jean-Louis, and Raymond,

we are working on the field of multi-layer resilience, in particular
regarding the required backup capacity of protection and restoration
mechanisms, e.g. MPLS-FRR and others:
http://www3.informatik.uni-wuerzburg.de/~menth/Publications/Menth04c.pdf
http://www3.informatik.uni-wuerzburg.de/~menth/Publications/Menth05f.pdf
http://www3.informatik.uni-wuerzburg.de/~menth/Publications/Menth06f.pdf

We, as a university, are interested in the mter discussion to share our
experience and to find new relevant issues for further research. I hope
that sufficiently many manufacturers and operators also express their
interest in this activity.

Kind regards,

    Michael

JP Vasseur wrote:
> Hi,
>
> Below the email we sent to the list some time ago, seeking for
> feed-backs but so far the list has been pretty quiet. During the past
> few months we received a very few off-line positive feed-backs
> indicating some interest in this work. It is now a good time to decide
> on whether there is enough interest to work on this topic by the IETF
> community in which case we will request a BOF approval or whether the
> interest is too weak to pursue this work.
>
> So we will follow up with a few discussion threads related to the
> scenarios described in the problem statement ID, for which we'd like
> to get your feed-back relatively quickly, should you think that it is
> worth being pursed.
>
> Thanks.
>
> JP, Jean-Louis and Raymond.
>
> Hi,
>
> It took a little while to come up with a clear problem statement but
> we now have an I-D (http://www.ietf.org/internet-drafts/draft-ahmad-
> mter-problem-statement-00.txt (thanks to the authors)) that will
> hopefully trigger some discussion with the objective to see whether
> there is enough interest to pursue this work at the IETF.
>
> The draft has been structured so as to first show three scenarios
> where various recovery mechanisms could be used in combination. This
> does not aim to cover all possible cases but some pretty common
> deployment scenario for the sake of illustration. Then various Multi-
> TEchnology Recovery (MTER) issues are discussed.
>
> What is the objective of this work ?
>
> Let's start with the set of non-objective first ...
> * There is no intention to come up with protocols extensions that are
> being worked out in existing WGs (ISIS, IDR, CCAMP, ....)
> * Discuss implementation-specific issues
>
> Now the objectives ...
>
> What has been shown through the three MTER deployment cases making use
> of multiple recovery mechanisms in combination is the following:
>
> -> There are cases where being able to identify the root failure cause
> would significantly improve various recovery metrics such as the
> convergence time, required backup capacity, ... and so on. Do we need
> to work on such mechanisms at the IETF is an open question ?
>
> -> MIBs and OAM tools have been defined for most of the recovery
> techniques (IGP, BGP, MPLS FRR, GMPLS, ... ) and there are clearly no
> such tool for the aspects related to their combined use. It looks like
> the availability of such tools would help Service Providers to manage,
> tune and troubleshooting their network. Again, feed-backs from this ML
> are critical to see how to move forward and if the community expressed
> some interest.
>
> Thanks for your feed-backs.
>
> JP, Jean-Louis and Raymond.
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> MTER mailing list
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/mter
>

--
Dr. Michael Menth, Assistant Professor
University of Wuerzburg, Institute of Computer Science
Am Hubland, D-97074 Wuerzburg, Germany, room B206
phone: (+49)-931/888-6644, fax: (+49)-931/888-6632
mailto:[email-masked]
http://www3.informatik.uni-wuerzburg.de/research/ngn

_______________________________________________
MTER mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/mter

_______________________________________________
MTER mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/mter

---

From: "Diego Caviglia" <[email-masked]>
Date: Tue, 16 May 2006 13:58:38 +0200

Hi JP,
       the ID expired in April this year so is no longer on the ID
database.

Here is the ID, comments are very welcome.

Regards

Diego

   CCAMP
   Internet Draft                                   Diego Caviglia
(Marconi)
                                                      Dino Bramanti
(Marconi)
                                                     Huub van
Helvoort(Huawei
                                                            Technologies
Ltd)
   Document: draft-caviglia-ccamp-gmpls-msspring-
   req-00
   Expires: April 2006                                          October
2005

                     GMPLS Requirements for MS-SPRing support

      Status of this Memo

      By submitting this Internet-Draft, each author represents that any
      applicable patent or other IPR claims of which he or she is aware
      have been or will be disclosed, and any of which he or she becomes
      aware will be disclosed, in accordance with Section 6 of BCP 79.

      Internet-Drafts are working documents of the Internet Engineering
      Task Force (IETF), its areas, and its working groups.  Note that
      other groups may also distribute working documents as Internet-
      Drafts.

      Internet-Drafts are draft documents valid for a maximum of six months
      and may be updated, replaced, or obsoleted by other documents at any
      time. It is inappropriate to use Internet-Drafts as reference
      material or to cite them other than as ôwork in progressö.

      The list of current Internet-Drafts can be accessed at
      http://www.ietf.org/1id-abstracts.html

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

      Abstract

      GMPLS [1] provides ideally a robust and flexible control plane
      protocols set designed for application over generalized transport
      network. A typical application of GMPLS is, among others, the control
      of transport networks based on SDH/SONET [2] technology. In this
      scenario, the introduction of GMPLS based control plane should ensure
      support of and/or compatibility with the most important and widely
      exploited SDH/SONET features, making possible a seamless interworking
      with inherent data plane requirements. In this document we focus on
      one of the most attractive SDH/SONET protection mechanism,
      implemented through MS-SPRing (G.841 [3]), a widely deployed ITU
      standard for ring-shared protection.

   Caviglia                 Expires - April 2006                 [Page 1]
                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

      In general, when setting up and configuring a data plane circuit
      traversing a MS-SPRing ring (or segments of it) via traditional
      management plane control, special constraints, which are specific to
      this kind of technology, have to be considered in order to ensure its
      correct operation. The same constraints have to be carefully taken
      into account when the data plane circuit is no more set up in a
      traditional way, but through a GMPLS based control plane.
      The specific constraints imposed by MS-SPRing are related to:

      . Time Slot Interchange (TSI)
      . Ring Map filling in case of squelching

      In this document a brief overview of MS-SPRing operation is
      introduced and its specific requirements are explained, putting in
      evidence the way they may impact when GMPLS is used as control plane.

      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 [4].

                                Table of Contents

      1. MS-SPRing Bird Eye Overview...................................3
      1.1 Information needed by MS-SPRing..............................5
      1.2 MS-SPRing Example............................................6
      1.3 Time Slot Interchange (TSI).................................11
      1.4 Squelching..................................................11
      2. GMPLS requirements imposed by MS-SPRing......................13
      2.1 LSP Set-Up..................................................13
      2.2 Data Plane and Control Plane misalignment...................13
      2.3 Interworking between GMPLS restoration and MS-SPRing Protection14
      3. Security Considerations......................................14
      References......................................................14
      Acknowledgments.................................................15
      Author's Addresses..............................................15

   Caviglia                 Expires - April 2006                 [Page 2]
                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

   1. MS-SPRing Bird Eye Overview

      The main reference for this Section is ITU-T G.841.  G.841 defines
      two different kinds of MS-SPRing namely two fibers and four fibers.

      Two-fiber MS switched rings require only two fibers for each span of
      the ring. Each fiber carries both working channels and protection
      channels. On each fiber, up to half the channels are defined as
      working channels and up to half are defined as protection channels.

      It is possible that some channels are not protected at all, being
      defined as Non-pre-emptible Unprotected Traffic (NUT) channels.
      The traffic carried on working channels inside one fiber is protected
      by channels going in the opposite direction around the ring.  This
      allows for a bi-directional transport of normal traffic and makes
      possible a sharing of the protection resources when needed.

      The following picture illustrates the two fibers case, no NUT in this
      example.
      WPx links are 50% for worker traffic and 50% for protection traffic,
      e.g. and STM-16 links have 8 AU-4 timeslot for worker traffic and 8
      AU-4 timeslot for protection.

            TNE A                     TNE B                     TNE C
       +------------+            +------------+            +------------+
       |            |            |            |            |            |
       |            |            |            |            |            |
       |            |            |            |            |            |
       |            |----------->|            |----------->|            |
       |            |    WP1     |            |     WP2    |            |
       |            |<-----------|            |<-----------|            |
       |            |            |            |            |            |
       |            |            |            |            |            |
       |            |            |            |            |            |
       +------------+            +------------+            +------------+
         ^     |                                               ^     |
         |     |                                               |     |
         |     |                                               |     |
         | WP3 |             WP Links Resources are            | WP4 |
         |     |                50% Worker                     |     |
         |     |                50% Protection                 |     |
         |     v                                               |     v
       +------------+            +------------+            +------------+
       |            |            |            |            |            |
       |            |            |            |            |            |
       |            |            |            |            |            |
       |            |----------->|            |----------->|            |

   Caviglia                 Expires - April 2006                 [Page 3]
                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

       |            |    WP5     |            |    WP6     |            |
       |            |<-----------|            |<-----------|            |
       |            |            |            |            |            |
       |            |            |            |            |            |
       |            |            |            |            |            |
       +------------+            +------------+            +------------+
           TNE F                     TNE E                      TNE D

                Figure 1-1: MS-SPRing two fibers reference circuit

      Four-fiber MS shared protection rings require four fibers for each
      span of the ring. As illustrated in Figure 1-2, working and
      protection channels are carried over different fibers: two multiplex
      sections transmitting in opposite directions carry the working
      channels while two multiplex sections, also transmitting in opposite
      directions, carry the protection channels. This enables the bi-
      directional transport of normal traffic, sharing as well the
      protection capability.

      The following picture illustrates the reference circuit (four fiber
      MS-SPRing) used in this Section.

            TNE A                     TNE B                     TNE C
       +------------+            +------------+            +------------+
       |            |            |            |            |            |
       |            |----------->|            |----------->|            |
       |            |     W1     |            |     W2     |            |
       |            |<-----------|            |<-----------|            |
       |            |            |            |            |            |
       |            |===========>|            |===========>|            |
       |            |     P1     |            |     P2     |            |
       |            |<===========|            |<===========|            |
       |            |            |            |            |            |
       +------------+            +------------+            +------------+
         ^  |  ^  l                                          ^  l  ^  |
         |  |  l  l                                          l  l  |  |
         |  |  l  l                                          l  l  |  |
         |W3|  lP3l       ------------ Working Link          lP4l  |W4|
         |  |  l  l       llll and === Protection Link       l  l  |  |
         |  |  l  l                                          l  l  |  |
         |  v  l  v                                          l  v  |  v
       +------------+            +------------+            +------------+
       |            |            |            |            |            |
       |            |===========>|            |===========>|            |
       |            |     P5     |            |     P6     |            |
       |            |<===========|            |<===========|            |
       |            |            |            |            |            |
       |            |----------->|            |----------->|            |
       |            |     W5     |            |     W6     |            |

   Caviglia                 Expires - April 2006                 [Page 4]
                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

       |            |<-----------|            |<-----------|            |
       |            |            |            |            |            |
       +------------+            +------------+            +------------+
            TNE F                    TNE E                      TNE D

         Figure 1-2: Reference circuit for MS-SPRing, four fibers variant

   1.1 Information needed by MS-SPRing

      The MS-SPRing protection mechanism is implemented via a SDH
      signalling protocol known as Automatic Protection Switching (APS).
      This protocol makes use of SDH overhead bytes (K1 and K2, MS overhead
      bytes) as a means to transport its own information. APS is not
      detailed here as it is outside the scope of this document.

      Each node on the ring shall be assigned an ID that is a number from 0
      to 15, allowing a maximum of 16 nodes on the ring. Such ID value is
      not related to the position of corresponding node in the ring, i.e.
      the order of the nodes is not tied to nodes ID assignment.

      Each node has a ring topology map that associates a nodeÆs ID with
      its address.

      With respect to the Figures 1-1/2 the ring topology map is:

                              TNE-ID   TNE-Address
                                 1           B
                                 2           F
                                 3           A
                                 4           E
                                 5           C
                                 6           D

                           Table 1-1 Ring Topology map

      The following tables represent the traffic matrix of the ring and the
      squelching (for definition of squelching please refer to Section 1.4)
      tables of the TNEs.

      +------------------------------------------------------------------+
      |   AU   | <---- West               Nodes                East ---->|
      | Number |  A         B          C        D        E        F     A|
      +--------+---------------------------------------------------------+
      |  1     |  <--------> <------------------>                        |
      |  2     |  <----------------------------->                        |
      |  3     |  <--------------------><------------------------->      |
      +------------------------------------------------------------------+

   Caviglia                 Expires - April 2006                 [Page 5]
                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

                             Table 1-2 Traffic Matrix

      +---------------------------------+---------------------------------
                        TNE-A           |                TNE-B
         AU       West           East   | AU       West              East
               Src   Dst      Src   Dst |       Src   Dst         Src   Dst
         1                     A     B  | 1      B     A           B     D
         2                     A     D  | 2      D     A           A     D
         3                     A     C  | 3      C     A           C     F
      ----------------------------------+----------------------------------

      ----------------------------------+---------------------------------
                        TNE-C           |                TNE-D
         AU       West           East   | AU       West              East
               Src   Dst      Src   Dst |       Src   Dst         Src   Dst
         1      D     B        B     D  | 1      D     B           B     D
         2      D     A        A     D  | 2      D     A           A     D
         3      C     A        C     F  | 3      F     C           C     F
      ----------------------------------+---------------------------------

      ----------------------------------+---------------------------------
                        TNE-E           |                TNE-F
         AU       West           East   | AU       West              East
               Src   Dst      Src   Dst |       Src   Dst         Src   Dst
         1                              | 1
         2                              | 2
         3      F     C        C     F  | 3      F     C           C      F
      ----------------------------------+---------------------------------

                            Table 1-3 Squelching Table

      When a node determines that a protection switch is required, it
      sources the appropriate bridge request using the APS protocol to the
      node at the far end of the affected MS (for more details on how APS
      carries that information please refer to G.841 [4]).

      WeÆll call Ring Map the sum of the information contained in all the
      above Tables.

   1.2 MS-SPRing Example

      The worker circuit follows this path (4_fibers/2_fibers):

      TNE-A <-Link W1/WP1-> TNE-B <-Link W2/WP2-> TNE-C <-Link W4/WP4->
      TNE-D : AU Timeslot 1

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                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

      In four fibers scenario failure of Links W2 and P2 triggers the MS-
      SPRing protection.

      Traffic is protected using this path:

      TNE-A <-Link W1-> TNE-B [Internal Bridge] <-Link P1-> TNE-A <-Link
      P3-> TNE F <-Link P5-> TNE-E <-Link P6-> TNE-D <-Link P4-> TNE-C
      [Internal Bridge] <- Link W4 -> TNE-D: AU Timeslot 1.

      The following picture illustrates the state of the network after the
      recovery, by means of MS-SPRing, of the failure.

                  1
           TNE A  v                  TNE B                      TNE C
       +----------|-+            +------------+            +------------+
       |          | |            |            |            |            |
       |          +------------->----->----+  |XXXXXXXXXXXX| +--------+ |
       |            |     W1     |         |  |     W2     | |        | |
       |            |<-----------|         |  |XXXXXXXXXXXX| |        | |
       |            |            |         v  |            | ^        v |
       |            |===========>|         |  |XXXXXXXXXXXX| |        | |
       |            |     P1     |         |  |     P2     | |        | |
       |          +--<===========-----<----+  |XXXXXXXXXXXX| |        | |
       |          | |            |            |            | |        | |
       +----------|-+            +------------+            +-|--------|-+
         ^  |  ^  l                                          ^  l  ^  |
         |  |  l  l                                          l  l  |  |
         |  |  l  l                                          l  l  |  |
         |W3|  lP3l       ------------ Working Link          lP4l  |W4|
         |  |  l  l       llll and === Protection Link       l  l  |  |
         |  |  l  l                                          l  l  |  |
         |  v  l  v                                          l  v  |  v
       +----------|-+            +------------+            +-|--------|-+
       |          | |            |            |            | |        | |
       |          +--===========>------->------===========>--+        | |
       |            |     P5     |            |     P6     |          | |
       |            |<===========|            |<===========|          | |
       |            |            |            |            |          v |
       |            |----------->|            |----------->|          | |
       |            |     W5     |            |     W6     |          | |
       |            |<-----------|            |<-----------|          | |
       |            |            |            |            |          | |
       +------------+            +------------+            +----------|-+
        TNE F                     TNE E                     TNE D     v
                                                                      1
                 Figure 1-3: MS-SPRing four fibers ring-switching

   Caviglia                 Expires - April 2006                 [Page 7]
                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

      The extra traffic in spans P1, P3, P4, P5 and P6 is affected.

      Note that in this case working traffic passes the same section two
      times, i.e. link W1 and link P1, link P4 and link W4.
      If these sections are very long, e.g. in trans-oceanic applications,
      the propagation delay is affected considerably and will result in a
      degradation of performance.
      For trans-oceanic applications intermediate nodes, not adjacent to an
      affected section, will switch bridges as well.

      Traffic is now protected using this path:

      TNE-A [Internal Bridge] TNE-A <-Link P3-> TNE F <-Link P5-> TNE-E <-
      Link P6-> TNE-D [Internal Bridge] TNE-D: AU Timeslot 1.

      The following picture illustrates the state of the network after the
      recovery, by means of trans-oceanic MS-SPRing, of the failure.

                  1
           TNE A  v                  TNE B                      TNE C
       +----------|-+            +------------+            +------------+
       |          | |            |            |            |            |
       |          | |----------->|            |XXXXXXXXXXXX|            |
       |          | |     W1     |            |     W2     |            |
       |          | |<-----------|            |XXXXXXXXXXXX|            |
       |          v |            |            |            |            |
       |          | |===========>|            |XXXXXXXXXXXX|            |
       |          | |     P1     |            |     P2     |            |
       |          | |<===========|            |XXXXXXXXXXXX|            |
       |          | |            |            |            |            |
       +----------|-+            +------------+            +------------+
         ^  |  ^  l                                          ^  l  ^  |
         |  |  l  l                                          l  l  |  |
         |  |  l  l                                          l  l  |  |
         |W3|  lP3l       ------------ Working Link          lP4l  |W4|
         |  |  l  l       llll and === Protection Link       l  l  |  |
         |  |  l  l                                          l  l  |  |
         |  v  l  v                                          l  v  |  v
       +----------|-+            +------------+            +------------+
       |          | |            |            |            |            |
       |          +--===========>------->------===========>------>----+ |
       |            |     P5     |            |     P6     |          | |
       |            |<===========|            |<===========|          | |
       |            |            |            |            |          v |
       |            |----------->|            |----------->|          | |
       |            |     W5     |            |     W6     |          | |
       |            |<-----------|            |<-----------|          | |
       |            |            |            |            |          | |
       +------------+            +------------+            +----------|-+

   Caviglia                 Expires - April 2006                 [Page 8]
                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

        TNE F                     TNE E                     TNE D     v
                                                                      1
          Figure 1-4: MS-SPRing four fibers trans-oceanic ring-switching

      Only the extra traffic in spans P3, P5 and P6 is affected.

      Instead of bridging all working traffic to the protections channels
      in the nodes adjacent to the failure in trans-oceanic ring-switching
      the individual AU tributaries are switched in their ingress and
      egress nodes using ring maps and APS information. Due to the transfer
      and evaluation of the information more time is required for the
      protection switch to complete, the objective is 300 ms or less.
      Because tributaries are switched in their ingress and egress nodes no
      squelching is required and protection channels not required for
      protection may carry pre-empted extra traffic.
      A mechanism is required to auto-provision the ring maps and maintain
      their consistency.

      In two fibers scenario failure of Links W2 and P2 triggers the MS-
      SPRing protection.

      Traffic is protected using this path:

      TNE-A <-Link WP1-> TNE-B [Internal Bridge] <-Link WP1-> TNE-A <-Link
      WP3-> TNE F <-Link WP5-> TNE-E <-Link WP6-> TNE-D <-Link WP4-> TNE-C
      [Internal Bridge] <- Link WP4 -> TNE-D: AU Timeslot 1 is used on all
      the links.

      The following picture illustrates the state of the network after the
      recovery from the failure done by means of MS-SPRing mechanism.

                  |
         TNE A    v                    TNE B                     TNE C
       +------------+            +------------+            +------------+
       |          | |            |            |            |            |
       |          | |            |            |            |            |
       |          | |            |            |            |            |
       |          +-|----------->|------+     |xxxxxxxxxxx>|   +-----+  |
       |            |    WP1     |      |     |     WP2    |   |     |  |
       |       +----|<-----------|------+     |<-----------|   ^     v  |
       |       |    |            |            |            |   |     |  |
       |       |    |            |            |            |   |     |  |
       |       |    |            |            |            |   |     |  |
       +------------+            +------------+            +------------+
         ^     |                                               ^     |
         |     |                                               |     |
         |     |                                               |     |
         | WP3 |             WP Links Resources are            | WP4 |

   Caviglia                 Expires - April 2006                 [Page 9]
                 draft-caviglia-ccamp-GMPLS-MSSPRing-Req-00  October 2005

         |     |                50% Worker                     |     |
         |     |                50% Protection                 |     |
         |     v                                               |     v
       +------------+            +------------+            +------------+
       |       |    |            |            |            |   |     |  |
       |       |    |            |            |            |   |     |  |
       |       |    |            |            |            |   |     |  |
       |       +----|----------->|------------|----------->|---+     |  |
       |            |    WP5     |            |    WP6     |         |  |
       |            |<-----------|            |<-----------|         |  |
       |            |            |            |            |         |  |
       |            |            |            |            |         |  |
       |            |            |            |            |         |  |
       +------------+            +------------+            +------------+
           TNE F                     TNE E                    TNE D  v

                 Figure 1-5: MS-SPRing two fibers ring-switching

      Figure 1-3 and 1-5 illustrates the so-called ôring-switchingö
      protection.

      In four-fiber MS-SPRing there exists also ôspan-switchingö and in
      this case only the working fibers are cut while the protection fibers
      remain intact. See figure 1-6. The protection switch affects the
      extra traffic in span P2.

                  1
           TNE A  v                   TNE B                     TNE C
       +----------|-+            +------------+            +------------+
       |          | |            |            |            |            |
       |          +------------->----->----+  |XXXXXXXXXXXX| +--------+ |
       |            |     W1     |         |  |     W2     | |        | |
       |            |<-----------|         v  |XXXXXXXXXXXX| ^        | |
       |            |            |         |  |            | |        | |
       |            |===========>|         +---===========>--+        v |
       |            |     P1     |            |     P2     |          | |
       |            |<===========|            |<===========|          | |
       |            |            |            |            |          | |
       +------------+            +------------+            +----------|-+
         ^  |  ^  l                                          ^  l  ^  |
         |  |  l  l                                          l  l  |  |
         |  |  l  l                                          l  l  |  |
         |W3|  lP3l       ------------ Working Link          lP4l  |W4|
         |  |  l  l       llll and === Protection Link       l  l  |  |
         |  |  l  l                                          l  l  |  |
         |  v  l  v                                          l  v  |  v
       +------------+            +------------+            +----------|-+
       |            |            |            |            |          | |
       |            |===========>|            |===========>|          | |

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       |            |     P5     |            |     P6     |          | |
       |            |<===========|            |<===========|          | |
       |            |            |            |            |          v |
       |            |----------->|            |----------->|          | |
       |            |     W5     |            |     W6     |          | |
       |            |<-----------|            |<-----------|          | |
       |            |            |            |            |          | |
       +------------+            +------------+            +----------|-+
          TNE F                     TNE E                     TNE D   v
                                                                      1

                        Figure 1-6: MS-SPRing span-switch

   1.3 Time Slot Interchange (TSI)

      TSI is the connection function capability of changing the time slot
      position of through-connected traffic (i.e. traffic that is not added
      or dropped from the node). At present there is no TSI capability
      specified in nodes belonging to a MS-SPRing sub network. Channels at
      MS-SPRing nodeÆs egress are nailed to the same timeslot used by the
      same channels at nodeÆs ingress. This is a currently required
      condition to ensure MS-SPRing correct operation.

   1.4 Squelching

      Squelching is defined as the process of inserting AU-AIS in order to
      prevent misconnections. The squelching process application over
      traffic results in an ôall 1Æsö signal.

   1.4.1 Squelching to avoid misconnected traffic

      To perform a ring switch, the protection channels are essentially
      shared among each span of the ring. Also, extra traffic may reside in
      the protection channels when the protection channels are not
      currently being used to restore normal traffic transported on the
      working channels. Thus, each protection channel time slot is subject
      to use by multiple services (services from the same time slot but on
      different spans, and service from extra traffic). With no extra
      traffic on the ring, under certain multiple point failures, such as
      those that cause node(s) isolation, services (from the same time slot
      but on different spans) may contend for access to the same protection
      channel time slot. This yields a potential for misconnected traffic.
      With extra traffic on the ring, even under single point failures,
      normal traffic on the working channels may contend for access to the
      same protection channel time slot that carries the extra traffic.
      This also yields a potential for misconnected traffic.

      Without a mechanism to prevent misconnection, the following failure
      scenario would yield misconnections.

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      Referring to Figure 1-1, two circuits traverse the MS-SPRing namely
      circuit Q and R the path that they traverse is:

      Circuit R:  TNE-A <-Link WP3 AU 1-> TNE-F
      Circuit Q:  TNE-A <-Link WP1 AU 1-> TNE-B <-Link WP2 AU 1-> TNE-C

      Suppose a cut in both the spans between nodes A and F and between
      nodes A and B (isolating node A, that is the same as a TNE A failure)
      causes circuits Q and R to attempt to access time slot #1P on the
      protection channels.  The mechanism for the MS-SPRing protection is
      as depicted in previous sub-section.

      A potential misconnection is determined by identifying the nodes that
      will act as the switching nodes for a bridge request, and by
      examining the traffic that will be affected by the switch. The
      switching nodes can be determined from the node addresses in the K1
      and K2 bytes. The switching nodes determine the traffic affected by
      the protection switch from the information contained in their ring
      maps and from the identifications of the switching nodes. Potential
      misconnections shall be squelched by inserting the appropriate AU-AIS
      in those time slots where misconnected traffic could occur.
      Specifically, the traffic that is sourced or dropped at the node(s)
      isolated from the ring by the failure shall be squelched. For rings
      operating at an AU-4 level, this squelching occurs at the switching
      nodes. AU level squelching occurs for the normal or extra traffic
      into or out of the protection channels (i.e. normal traffic into or
      out of working channels is never squelched).

      For example, consider a segment of a ring consisting of three nodes,
      A, B, and C where B has failed. In a typical scenario, both A and C
      will send bridge requests destined for B. When A sees the bridge
      request from C, and sees that B is between A and C (from the node
      map) it can deduce that B is isolated from the ring. A and C will use
      their respective maps to find out which channels are added or dropped
      by B. A and C will squelch these channels before the ring switch is
      performed by inserting AU-AIS. Thus, any node on the ring that was
      connected to B will now receive AIS on those channels.

      Each of the ring maps, then, shall contain at minimum:
      1. a ring map that contains information regarding the order in which
         the nodes appear on the ring;
      2. a cross-connect map that contains the AU-4 time-slot assignments
         for traffic that is both terminated at that node and passed-
         through that node;
      3. a squelch table that contains, for each of these AU-4 time slots,
         the node addresses at which the traffic enters and exits the ring;
         and

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      4. an optional indication of whether the AU is being accessed at the
         lower order VC level somewhere on the ring (not covered by this
         Document)
      An example of such ring maps and squelching table is given in Section
      1.1.

   2. GMPLS requirements imposed by MS-SPRing

      When setting up (either via traditional management plane actions or
      via GMPLS control plane protocols) a data plane circuit going across
      parts of the network that include MS-SPRing based protection
      mechanism, it MUST be done according to MS-SPRing specific needs as
      explained in previous sections.

   2.1 LSP Set-Up

      When GMPLS is used for circuit setup, the presence of MS-SPRing rings
      in the network results in a set of requirements that have to be
      handled at control plane level.
      Basically when setting up an LSP over a data plane that includes TNEs
      connected in MS-SPRing scheme, the control plane taking care of
      routing and signaling of such LSP has to behave in a way that

      1. the label(corresponding to a SDH/SONET timeslot) must not be
         changed within the MS-SPRing ring traversed;
      2. involved TNE MUST have all the information necessary to fill the
         Ring Map.

      From the NMS point of view it is important to be able to univocally
      identify a ring in the network, this leads to the Ring Identifier
      (RingId) concept.  Even if the RingId is not needed for the MS-SPRing
      operation it is needed for management issues.
      Given the above there is the requirement to add the RingId
      information to the information stored when an LSP traverses a node
      that is part of a MS-SPRing.

      The above requirements can be satisfied either via signaling only or
      signaling plus routing.

   2.2 Data Plane and Control Plane misalignment

      When a failure affects an LSP that traverse an MS-SPRing protected
      ring the data plane scenario is the same as in Figure 1-3.

      Data Traffic is flowing through:
      Node-A<-->Node-B<-->Node-A<-->Node-F<-->Node-E<-->Node-D<-->Node-C<--
      >Node-D while from a control plane perspective traffic is still
      flowing through Node-A<-->Node-B<-->Node-C<-->Node-D.
      It may be noted that the loop Node-A<-->Node-B<-->Node-A can be

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      bridged and releases the protection channels for use by extra traffic
      thus increasing the availability of extra traffic, however this
      requires an update to the Ring map.

      The misalignment between control and data plane arises because the
      control plane is un-aware of the failure.

      In this case there is the need for a control plane data plane re-
      alignment.

      When, without the intervention of the control plane, inherent
      protection scheme changes some characteristic of an LSP there should
      be a communication mechanism that re-aligns control plane and data
      plane information.

   2.3 Interworking between GMPLS restoration and MS-SPRing Protection

      A hold-off timer e.g. 50 ms should be provided in order to allow MS-
      SPRing protection to react firstly to a failure.

      In case of failures unrecoverable by MS-SPRing the hold-off elapse
      triggering the control plane recovery mechanism, of course in order
      to recover the traffic control plane and data plane must be aligned,
      see above Section about control plane and data plane misalignment.

   3. Security Considerations

      This document does not introduce any additional Security issues.

   References

      [1] Mannie, E. öGeneralized Multi-Protocol Label Switching (GMPLS)
          Architectureö Standard Track, RFC 3945, October 2004

      [2] ITU-T G.707 ôNetwork node interface for the synchronous digital
          hierarchy (SDH)ö, December 2003

      [3] ITU-T G.841 "Types and characteristics of SDH network protection
          architectures", October 1998.

      [4] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
          9, RFC 2026, October 1996

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Acknowledgments

   Greg Bernstein
   Grotto Networking
   Email: [email-masked]

Author's Addresses

   Diego Caviglia
   Marconi
   V. A. Negrone 16/A
   16153 Cornigliano (GE)
   Italy
   Phone: +390106003736
   Email: [email-masked]

   Huub van Helvoort
   Huawei Technologies Ltd.
   Kolkgriend 38
   NL-1356 BC  Almere
   the Netherlands
   Phone: +31365315076
   Email: [email-masked]

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