Network Working Group                                              J.He
Internet Draft                                      Huawei Technologies
Intended status: Standard Track
                                                           China Mobile

                                                          E. Bellagamba

Expires: September 2011 March 14, 2012                                   September 13, 2011

                  Indication of Client Failure in MPLS-TP

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   document authors. All rights reserved.

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   Please review these documents carefully, as they describe your rights
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   This document describes a Multi-Protocol Label Switching Transport
   Profile (MPLS-TP) Operations, Administration and Maintenance (OAM)
   protocol to propagate a client failure indication across an MPLS-TP
   network in the case that propagation of failure status in the client
   layer is not supported as required in [RFC5860].

Table of Contents

   1. Introduction ................................................ 2
   2. Conventions used in this document............................ 3
      2.1. Terminology ............................................ 3
   3. Mechanisms of CSF ........................................... 4
      3.1. General ................................................ 4
      3.2. Transmission of CSF..................................... 5
      3.3. Reception of CSF........................................ 6
      3.4. Configuration of CSF.................................... 6
   4. Frame format of CSF ......................................... 7
   5. Consequent actions .......................................... 8
   6. Security Considerations...................................... 9
   7. IANA Considerations ......................................... 9
   8. Acknowledgments ............................................. 9
   9. References .................................................. 9
      9.1. Normative References.................................... 9
      9.2. Informative References................................. 10
   10. Authors' Addresses ........................................ 10

1. Introduction

   In transport networks, OAM functions are important and fundamental to
   ease operational complexity, enhance network availability and meet
   service performance objectives. This is achieved through automatic
   detection, handling, diagnosis, appropriate reporting of defects and
   performance monitoring.

   As defined in [RFC 5860] MPLS-TP OAM MUST provide a function to
   enable the propagation, from edge to edge of an MPLS-TP network, of
   information pertaining to a client (i.e., external to the MPLS-TP
   network) defect or fault condition detected at an End Point of a PW
   or LSP, if the client layer OAM functionality does not provide an
   alarm notification/propagation functionality (e.g. not needed in the
   original application of the client signal, or the signal was
   originally at the bottom of the layer stack and it was not expected
   to be transported over a server layer), while such an indication is
   needed by the downstream.

   This document defines a Client Signal Fail (CSF) indication protocol
   in order to propagate client failures and their clearance across a
   MPLS-TP domain.

   According to [RFC 5921], MPLS-TP supports two native service
   adaptation mechanisms via:

   1) a Pseudowire, to emulate certain services, for example, Ethernet,
      Frame Relay, or PPP / High-Level Data Link Control (HDLC).

   2) an LSP, to provide adaptation for any native service traffic type
      supported by [RFC3031] and [RFC3032]. Examples of such traffic
      types include IP packets and MPLS-labeled packets (i.e.: PW over
      LSP, or IP over LSP).

   As to the first adaptation mechanism via a PW, the mechanism of CSF
   function to support propagation of client failure indication follows
   [static-pw-status]. The PW status relevant to CSF function is AC
   fault as defined in [RFC 4447] and [RFC 4446].

   As to the second adaptation mechanism via LSP, the mechanism is
   detailed in this draft and is used in case the client of MPLS-TP can
   not provide itself with such failure notification/propagation.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC 2119].

2.1. Terminology

   The reader is assumed to be familiar with the terminology in MPLS-TP.
   The relationship between ITU-T and IETF terminologies on MPLS-TP can
   be found in [Rosetta stone].

       ACH: Associated Channel Header

       AIS: Alarm Indication Signal

       CSF: Client Signal Fail indication
       FDI: Forward Defect Indication

       G-ACh: Generic Associated Channel

       GAL: G-ACh Label

       LSR: Label Switching Router

       MEP: Maintenance Entity Group End Point

       MIP: Maintenance Entity Group Intermediate Point

       OAM: Operations, Administration, and Maintenance

       MPLS-TP: MPLS Transport Profile

       PW: Pseudowire

       RDI: Remote Defect Indication

3. Mechanisms of CSF

3.1. General

   Client Signal Fail(CSF) indication  provides a function to enable a
   MEP to propagate a client failure indication to its peer MEP across a
   MPLS-TP network in case the client service itself does not support
   propagation of its failure status. A MIP is not intended to generate
   or process CSF information.

   Packets with CSF information can be issued by a MEP, upon receiving
   failure information from its client service. Detection rules for
   client failure events are client-specific and are therefore outside
   the scope of this document.

              +---+     +---+                 +---+      +---+
              |   |     |   |-->CSF           |   |      |   |
              | A |--X--| B |-----------------| C |------| D |
              +---+     +---+                 +---+      +---+
                          |<--MPLS-TP domain-->|

                         Figure 1 Use case of CSF

   Figure 1 depicts a typical connection scenario between two client
   network elements (Node A and Node D) interconnected through MPLS-TP
   transport network. Client Node A connects to MPLS-TP Node B and
   Client Node D connects to MPLS-TP Node C. Node B and C support MPLS-
   TP MEP function.

   If a failure is detected between Node A and Node B and is taken as a
   native client failure condition, the MEP function in Node B will
   initiate CSF signal and it will be sent to Node C through MPLS-TP
   network. CSF signal will be extracted at Node C as an indication of
   client signal failure. Further, this may be mapped back into native
   client failure indication and regenerated towards client Node D.

   Node B learns the failure between A and B either by direct detection
   of signal fail (e.g. loss of signal) or by some fault indications
   between A and B (e.g. RDI, AIS/FDI).

   If the connection between Node A and B recovers, Node B may stop
   sending CSF signals to Node C (implicit failure clearance mechanism)
   or explicitly send failure clearance indication (e.g. by flags in CSF
   PDU format) to Node C to help expedite clearance of native client
   failure conditions.

   Accordingly, Node C will clear client failure condition when a valid
   client data frame is received and no CSF is received (implicit
   failure clearance mechanism) or upon receiving explicit failure
   clearance indication.

3.2. Transmission of CSF

   When CSF function is enabled, upon learning signal failure condition
   of its client-layer, the MEP can immediately start transmitting
   periodic packets with CSF information to its peer MEP. A MEP
   continues to transmit periodic packets with CSF information until the
   client-layer signal failure condition is cleared.

   The clearance of CSF condition can be communicated to the peer MEP

   - Stopping of the transmission of CSF signal but forwarding client
     data frames, or
   - Forwarding CSF PDUs with a clearance indication.

   Transmission of packets with CSF information can be enabled or
   disabled on a MEP (e.g. through management plane).

   Detection and clearance rules for CSF events are client and
   application specific and outside the scope of this draft.

   The period of CSF transmission is client and application specific.
   Examples are as follows:

   - 3.33ms: for protection switching application.
   - 1s: for fault management application.

   However, the value 0 is invalid.

3.3. Reception of CSF

   Upon receiving a packet with CSF information a MEP either declares or
   clears a client-layer signal fail condition according to the received
   CSF information and propagates this as a signal fail indication to
   its client-layer.

   CSF condition is cleared when the receiving MEP

   - does not receive CSF signal within an interval of N times the CSF
     transmission period (Suggested value of N is 3.5), or
   - receives a valid client data frame, or
   - receives CSF PDU with CSF-Clear information

3.4. Configuration of CSF

   Specific configuration information required by a MEP to support CSF
   transmission is the following:

   CSF transmission period - this is application dependent. Examples are
   3.3 ms and 1s.

   PHB - identifies the per-hop behavior of packet with CSF information.

   A MIP is transparent to packets with CSF information and therefore
   does not require any information to support CSF functionality.

4. Frame format of CSF

   Figure 2 depicts the frame format of CSF. CSF PDUs are encapsulated
   using the ACH, according to [RFC 5586]. GAL is used as an alert based
   exception mechanism to differentiate CSF packets (with ACH as G-ACh
   packets) from user-plane packets as defined in [RFC 5586].

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       |0 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0|      MPLS-TP CSF(0xXX)        |
       |    Version    |  Reserved 1   |     Flags     |   Reserved 2  |
       | Total TLV Len |                                               ~
       +-+-+-+-+-+-+-+-+           TLVs                                ~
       ~                                                               |

                       Figure 2  Frame format of CSF

   The first four bytes represent the Generic ACH ([RFC 5586]):

       - first nibble: set to 0001b to indicate a control channel
       associated with a PW, a LSP or a Section;

       - ACH Version(bits 4 to 7): set to 0, as specified in [RFC 5586]

       - ACH Reserved (bits 8 to 15): set to 0 and ignored on reception,
       as specified in [RFC 5586];

       - ACH Channel Type (Bits 16 to 31): value 0xXX identifies the
       payload as CSF PDU. To be assigned by IANA.

       - CSF Version (Bits 32 to 39): Set to 0;

       - CSF Reserved 1 (Bits 40 to 47): This field MUST be set to zero
       on transmission and ignored on receipt;

       - CSF Reserved 2 (Bits 56 to 63): This field MUST be set to zero
       on transmission and ignored on receipt;

       - Total TLV Length: Total of all included TLVs. No TLVs are
       defined currently. The value is 0.

       - TLVs: No TLVs are defined currently.

                       0   1   2   3   4   5   6   7
                     |  Res  |    Type   |   Period  |

                    Figure 3 Format of Flags in CSF PDU

   Figure 3 depicts the format of Flags in CSF PDU.

       - Flag Reserved (Bits 48 to 49): Set to 0;

       - Type (Bits 50 to 52): Set to the following values to indicate
       CSF types

         Value   Type

         111     Client Signal Fail - Loss of Signal (CSF-LOS)

         001     Client Signal Fail - Forward Defect Indication (CSF-FDI)

         010     Client Signal Fail - Reverse Defect Indication (CSF-RDI)

         000     Clearance of Client Signal Fail - (CSF-Clear)

       - Period (Bits 53 to 55): CSF transmission period and can be

5. Consequent actions

   The primary intention of CSF is to transport a client signal fail
   condition at the input of the MPLS-TP network to the output port of
   the MPLS-TP network for clients that do not have alarm
   notification/propagation mechanism defined.

   Further, CSF allows creating a condition at the output port of the
   MPLS-TP network such that the customer input port is able to detect
   and alarm that there is no data arriving i.e. the connection is
   interrupted. In this case, customers may choose another transport
   network or another port to continue communication.

6. Security Considerations

    Malicious insertion of spurious CSF signals (e.g. DoS) is not quite
    likely in a transport network since transport networks are usually
    self-managed by operators and providers.

7. IANA Considerations

    MPLS-TP CSF function requires a new Associated Channel Type to be
    assigned by IANA from the Pseudowire Associated Channel Types

   Value       Description
   -----       -----------------------
   0xXX        MPLS-TP Client Signal Fail indication (CSF)

8. Acknowledgments

   The authors would like to thank Haiyan Zhang, Adrian Farrel, Loa
   Andersson, Matthew Bocci, Andy Malis and Thomas D. Nadeau for their
   guidance and input to this work.

9. References

9.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
             Label Switching Architecture", RFC 3031, January 2001.

   [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci,
             D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC
             3032, January 2001.

   [RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
             Emulation (PWE3)", RFC4446, April 2006

   [RFC4447] Martini, L., et al., "Pseudowire Setup and Maintenance
             Using the Label Distribution Protocol (LDP)", RFC4447,
             April 2006.

   [RFC5586] Vigoureux, M., Bocci, M., Swallow, G., Ward, D., and R.
             Aggarwal, "MPLS Generic Associated Channel", RFC5586, June

   [ITU-T Recommendation G.7041] "Generic framing procedure (GFP)", ITU-
             T G.7041, October 2008

   [RFC 5654] Niven-Jenkins, B., Brungard, D., and M. Betts,
             "Requirements of an MPLS Transport Profile", RFC 5654,
             September 2009

   [RFC 5860] Vigoureux, M., Ward, D., and M. Betts, "Requirements for
             OAM in MPLS Transport Networks", RFC5860, May 2010

   [RFC 5921] Bocci, M., Bryant, S., and D. Frost, "A Framework for MPLS
             in Transport Networks", RFC 5921, July 2010

   [static-pw-status] Martini, L., Swallow, G., Heron, G., and M. Bocci,
             "Pseudowire Status for Static Pseudowires", draft-ietf-
             pwe3-static-pw-status-06 (work in progress), March July 2011

9.2. Informative References

   [MPLS-TP OAM Frmk] Busi,I., and D. Allan, "MPLS-TP OAM Framework and
             Overview", draft-ietf-mpls-tp-oam-framework-11(work in
             progress),  February 2011

   [Rosetta stone] Van Helvoort, H., Andersson, L., Sprecher, N., "A
             Thesaurus for the Terminology used in Multiprotocol Label
             Switching Transport Profile (MPLS-TP) drafts/RFCs and ITU-
             T's Transport Network Recommendations", draft-ietf-mpls-tp-
             rosetta-stone-04 (work in progress), November 2010 June 2011

10. Authors' Addresses

   Jia He
   Huawei Technologies Co., Ltd.

   Han Li
   China Mobile Communications Corporation


   Elisa Bellagamba


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