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Versions: 00 01 02 03 04 draft-ietf-pwe3-tdm-control-protocol-extensi

    Network Working Group               A. Vainshtein (Axerra Networks)
    Internet Draft                 Y(J) Stein (RAD Data Communications)

    Expiration Date:
    January 2006


                                                              July 2005

        Control Protocol Extensions for Setup of TDM Pseudowires

       draft-vainshtein-pwe3-tdm-control-protocol-extensi-04.txt


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Abstract

This document defines extension to the PWE3 control protocol [PWE3-
CONTROL] and PWE3 IANA allocations [PWE3-IANA] required for setup of
TDM pseudowires.













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 Control Protocol Extensions for Setup of TDM Pseudowires July 2005

TABLE OF CONTENTS

1. Introduction......................................................2
2. PW FEC for Setup of TDM PWs.......................................2
3. Interface Parameters for TDM PWs..................................3
  3.1. CEP/TDM Payload Bytes (0x04)..................................3
  3.2. CEP/TDM Bit-Rate (0x07).......................................4
  3.3. Number of TDMoIP AAL1 cells per packet (0x0D - subject to IANA
  approval)..........................................................4
  3.4. TDMoIP AAL1 mode (0x0E - subject to IANA approval)............5
  3.5. TDMoIP AAL2 Options (0x0F - subject to IANA approval).........5
  3.6. Fragmentation Indicator (0x09)................................6
  3.7. TDM Options (0x0B subject to IANA approval)...................6
4. Extending CESoPSN Basic NxDS0 Services with CE Application
Signaling............................................................8
5. LDP Status Codes..................................................9
6. IANA Considerations...............................................9
7. Security Considerations...........................................9
8. Acknowledgements.................................................10
9. Normative References.............................................10
10. Informative References..........................................10


1. Introduction

This document defines extension to the PWE3 control protocol [PWE3-
CONTROL] and PWE3 IANA allocations [PWE3-IANA] required for setup of
TDM pseudowires.

Structure-agnostic TDM pseudowires have been specified in [PWE3-SAToP]
and structure-aware ones in [PWE3-CESoPSN] and [PWE3-TDMoIP].

[PWE3-CONTROL] defines extensions to LDP [RFC3036] that are required to
exchange PW labels for PWs emulating various Layer 2 services
(Ethernet, FR, ATM, HDLC etc.). Setup of TDM PWs requires both
interpretation of the existing information elements of these extensions
and exchange of additional information.

Setup of TDM PWs using L2TPv3 will be defined in a separate document.

Status of attachment circuits of TDM PWs can be exchanged between the
terminating PEs using the mechanism defined in [PWE3-CONTROL] and
[SHAH-PWE3-CONTROL-EXT] without any changes. However, usage of these
mechanisms with TDM PWs is NOT RECOMMENDED since indication of status
of the TDM attachment circuits is carried in-band in the data plane.
2. PW FEC for Setup of TDM PWs

[PWE3-CONTROL] uses LDP Label Mapping message [RFC3036] for advertising
the FEC-to-PW Label binding, and defines two types of PW FEC that can
be used for this purpose:




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1. PWId FEC (FEC 128). This FEC contains:
    a) PW type
    b) Control bit (indicates presence of the control word)
    c) Group ID
    d) PW ID
    e) Interface parameters
2. Generalized PW FEC (FEC 129). This FEC contains only:
    a) PW type
    b) Control bit
    c) AGI, SAII and TAII that replace the PW ID

The Group ID and the Interface parameters are contained in separate
TLVs, called the PW Grouping TLV and the Interface Parameters TLV.

Both types of PW FEC MAY be used for setup of TDM PWs with appropriate
selection of PW types and interface parameters.


The PW Types for TDM PWs are allocated in [PWE3-IANA] as follows:

o  0x0011  Structure-agnostic E1 over Packet [PWE3-SAToP]
o  0x0012  Structure-agnostic T1 (DS1) over Packet [PWE3-SAToP]
o  0x0013  Structure-agnostic E3 over Packet [PWE3-SAToP]
o  0x0014  Structure-agnostic T3 (DS3) over Packet [PWE3-SAToP]
o  0x0015  CESoPSN basic mode [PWE3-CESoPSN]
o  0x0016  TDMoIP AAL1 mode [PWE3-TDMoIP]
o  0x0017  CESoPSN TDM with CAS [PWE3-CESoPSN]
o  0x0018  TDMoIP AAL2 mode [PWE3-TDMoIP]

The two endpoints MUST agree on the PW type, as both directions of the
PW are required to be of the same type.

The Control bit MUST always be set for TDM PWs since all TDM PW
encapsulations always use a control word.


3. Interface Parameters for TDM PWs
   3.1. CEP/TDM Payload Bytes (0x04)

This parameter is used for setup of all SAToP and CESoPSN PWs (i.e. PW
types 0x0011, 0x0012, 0x0013, 0x0014, 0x0015 and 0x0017) with the
following semantics:

1. The two endpoints of a TDM PW MUST agree on the same value of this
    parameter for the PW to be set up successfully.
2. Presence of this parameter in the PWId FEC or in the Interface
    Parameters Field TLV is OPTIONAL. If this parameter is omitted,
    default payload size defined for the corresponding service (see
    [PWE3-SAToP], [PWE3-CESoPSN]) MUST be assumed
3. For structure-agnostic emulation, any value consistent with the MTU
    of the underlying PSN MAY be specified



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4. For CESoPSN PWs:
    a) The specified value P MUST be an integer multiple of N, where N
       is the number of timeslots in the attachment circuit
    b) For trunk-specific NxDS0 with CAS:
       i)   (P/N) MUST be an integer factor of the number of frames per
          corresponding trunk multiframe (i.e. 16 for an E1 trunk and
          24 of a T1 trunk)
       ii)  The size of the signaling sub-structure is not accounted
          for in the specified value P.


   3.2. CEP/TDM Bit-Rate (0x07)

This interface parameter represents the bit-rate of the TDM service in
multiples of the "basic" 64 Kbit/s rate. Its usage for all types of TDM
PWs assumes the following semantics:

1. This interface parameter MAY be omitted if the attachment circuit
    bit-rate can be unambiguously derived from the PW Type (i.e. for
    structure-agnostic emulation of E1, E3 and T3 circuits). If this
    value is omitted for the structure-agnostic emulation of T1 PW
    Type, the basic emulation mode MUST be assumed.
2. If present, only the following values MUST be specified for
    structure-agnostic emulation (see [PWE3-SAToP]:
    a) Structure-agnostic E1 emulation  - 32
    b) Structure-agnostic T1 emulation:
       i)   MUST be set to 24 in the basic emulation mode
       ii)  MUST be set to 25 for the "Octet-aligned T1" emulation mode
    c) Structure-agnostic E3 emulation  - 535
    d) Structure-agnostic T3 emulation  - 699
3. For all kinds of structure-aware emulation, this parameter MUST be
    set to N where N is the number of DS0 channels in the corresponding
    attachment circuit.

Note: The value 24 does not represent the actual bit-rate of the T1
circuit (1,544 Mbit/s) in units of 64 kbit/s. The values mentioned
above are used for convenience.


   3.3. Number of TDMoIP AAL1 cells per packet (0x0D - subject to
     IANA approval)

This parameter MAY be present for TDMoIP AAL1 mode PWs (PW type 0x0016)
and specifies the number of 48-byte AAL1 PDUs per MPLS packet. Any
values consistent with the MTU of the underlying PSN MAY be specified.
If this parameter is not specified it should default to 1 PDU per
packet for low bit-rates (CEP/TDM Bit-Rate less than or equal to 32),
and to 5 for high bit-rates (CEP/TDM Bit-Rate of 535 or 699).






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   3.4. TDMoIP AAL1 mode (0x0E - subject to IANA approval)

This parameter MAY be present for TDMoIP AAL1 mode PWs (PW type 0x0016)
and specifies the AAL1 mode. If this parameter is not present, the AAL1
mode defaults to "structured". When specified, the values have the
following significance:
   0 unstructured AAL1
   2 structured AAL1
   3 structured AAL1 with CAS.
The two endpoints MUST agree on the TDMoIP AAL1 mode.


   3.5. TDMoIP AAL2 Options (0x0F - subject to IANA approval)

This parameter MUST be present for TDMoIP AAL2 mode PWs (PW type
0x0018) and has the following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    0x0F       |    Length     | V|      ENCODING              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Maximum Duration                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      CID mapping bases                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields in this parameter as defined as follows:

V defines the VAD capabilities. Its values have the following
significance:
     0 means that the CID is only switched by signaling
     1 means that voice activity detection is employed
     3 means this channel is always active. In particular, this channel
     may be used for timing recovery.

Encoding specifies native signal processing performed on the payload.
When no native signal processing is performed (i.e. G.711 encoding)
this field MUST be zero.

Maximum Duration specifies the maximum time allowed for filling an AAL2
PDU, in units of 125 microseconds. For unencoded 64 kbps channels this
numerically equals the maximum number of bytes per PDU, and MUST be
less than 64. For other encoding parameters, larger values may be
attained.

CID mapping bases is an OPTIONAL parameter, its existence and length
determined by the length field. If the mapping of AAL2 CID values to
physical interface and time slot is statically configured, or if AAL2
switching [Q.2630.1] is employed, this parameter MUST NOT appear. When
it is present, and the channels belong to N physical interfaces (i.e. N
E1s or T1s), it MUST be N bytes in length. Each byte represents a
number to be subtracted from the CID to get the timeslot number for
each physical interface. For example, if the CID mapping bases

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parameter consists of the bytes 20 and 60, this signifies that timeslot
1 of trunk 1 corresponds to CID 21 and timeslot 1 of trunk 2 is called
61.


   3.6. Fragmentation Indicator (0x09)

This interface parameter is specified in [PWE3-IANA] and its usage is
explained in [PWE3-FRAG]. It MUST be omitted in the FEC of all TDM PWs
excluding trunk-specific NxDS0 services with CAS using the CESoPSN
encapsulation. In case of these services, it MUST be present in the PW
FEC if the payload size specified value P differs from Nx(number of
frames per trunk multiframe).


   3.7. TDM Options (0x0B subject to IANA approval)

This is a new interface parameter. Its Interface Parameter ID has to be
assigned by IANA, and its format is shown in Fig. 1 below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Parameter ID |    Length     |R|D|F|X|SP |CAS|   RSVD-1      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|     PT      |   RSVD-2      |               FREQ            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         SSRC                                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 1. Format of the TDM Options Interface Parameter


The fields shown in this diagram are used as follows:




















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Parameter ID       Identifies the TDM PW Options interface parameter,
                    value TBA by IANA
Length             4, 8 or 12 (see below)
R                  The RTP Header Usage bit: if set, indicates that
                    the PW endpoint distributing this FEC expects to
                    receive RTP header in the encapsulation. RTP header
                    will be used only if both endpoints expect to
                    receive it. If this bit is cleared, Length MUST be
                    set to 4, otherwise it MUST be either 8 or 12 (see
                    below). If the peer PW end point cannot meet this
                    requirement, the Label Mapping message containing
                    the FEC in question MUST be rejected with the
                    appropriate status code (see Section 4 below).
D                  The Dynamic Timestamping Mode bit: if set,
                    indicates that the PW endpoint distributing this
                    FEC expects the peer to use Differential
                    timestamping mode in the packets sent to it. If the
                    peer PW end point cannot meet this requirement, the
                    Label Mapping message containing the FEC in
                    question MUST be rejected with the appropriate
                    status code (see Section 4 below).
F, X               Reserved for future extensions. MUST be cleared by
                    when distributed and MUST be ignored upon reception
SP                 Encodes support for the CESoPSN signaling packets
                    (see [CESoPSN]):
                    o  '00' for PWs that do not use signaling packets
                    o  '01' for CESoPSN PWs carrying TDM data packets
                       and expecting CE application signaling packets
                       in a separate PW
                    o  '10' for a PW carrying CE application signaling
                       packets with the data packets in a separate PW
                    o  '11' - for CESoPSN PWs carrying TDM data and CE
                       application signaling on the same PW
CAS                MUST be cleared for all types of TDM PWs excluding
                    trunk-specific NxDS0 services with CAS. For these
                    services it encodes the trunk framing like
                    following:
                    o  '01' - an E1 trunk
                    o  '10' - a T1/ESF trunk
                    o  '11' - a T1 SF trunk
RSVD-1 and RSVD-2  Reserved bits, MUST be set to 0 by the PW endpoint
                    distributing this FEC and MUST be ignored by the
                    receiver
PT                 Indicates the value of Payload Type in the RTP
                    header expected by the PW endpoint distributing
                    this FEC. Value 0 means that PT value check will
                    not be used for detecting malformed packets
FREQ               Frequency of timestamping clock in units of 8 kHz
SSRC               Indicates the value of SSRC ID in the RTP header
                    expected by the PW endpoint distributing this FEC.
                    Value 0 means that SSRC ID value check will not be
                    used for detecting misconnections. Alternatively,
                    Length can be set to 8 in this case.

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Notes:

1. This interface parameter MAY be omitted in the following cases:
    a) SAToP PWs that do not use RTP header [PWE3-SAToP]
    b) Basic CESoPSN NxDS0 services without CE application signaling
       [PWE3-CESoPSN]
    c) TDMoIP AAL1 mode 0 or 2 PWs that do not use RTP.
    d) TDMoIP AAL2 PWs that do not relay CAS signaling and do not use
       RTP.
2. This interface parameter MUST be present in the following cases:
    a) All TDM PWs that use RTP header
    b) CESoPSN PWs that carry basic NxDS0 services and use CESoPSN
       signaling packets to carry CE application signaling. This case
       is discussed in detail in Section 4 below
    c) CESoPSN PWs that carry trunk-specific NxDS0 services with CAS
    d) TDMoIP AAL1 mode 1 PWs
    e) TDMoIP AAL2 PWs that relay CAS signaling.
3. If RTP header and Differential timestamping mode are used, the
    value of the Length field MUST be set to 8 or 12 in order to
    include at least the Timestamping Clock Frequency field in the
    value
4. A TDM PW encapsulation MUST either use or not use RTP in both
    directions. However, it is possible to use Differential
    timestamping mode in just one direction of the PW.


4. Extending CESoPSN Basic NxDS0 Services with CE Application
   Signaling

[CESoPSN] defines that basic NxDS0 services can be extended to carry
also CE application signaling (e.g., CAS) in separate signaling packets
carried in a separate PW.

The following rules define setup of matching pairs of CESoPSN PWs using
the PW Id FEC and the extensions defined above:

1. The value of PW ID for the CESoPSN PW carrying TDM data packets
    MUST be even
2. The value of PW ID for the CESoPSN PW carrying CE application
    signaling MUST be the next odd value for the (even) value of PW ID
    for the CESoPSN PW carrying TDM data packets
3. The two PWs MUST:
    a) Have the same PW Type
    b) Have the same values of all the Interface Parameters with the
       exception of the code point in the SP field of the TDM Options
       parameter.
       i)   The PWId FEC of the PW carrying TDM data packets must be
          marked with SP bits set to '01' in this field
       ii)  The PWId FEC of the PW carrying CE signaling packets must
          be marked with SP bits set to '10' in this field.


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If only one of the two PWs required to carry a CESoPSN basic NxDS0
service and associated CE signaling packets has been established and
the other one failed, the established PW MUST be torn down.

Setup of CESoPSN PWs with CE application signaling using the
Generalized PW FEC is left for further study.


5. LDP Status Codes

In addition to the status codes defined in section 5.3 of [PWE3-
CONTROL], the following status codes defined in [PWE3-IANA] MUST be
used to indicate the reason of failure to establish a TDM PW:

1. Incompatible bit rate:
    a) In the case of mismatch of T1 encapsulation modes (basic vs.
       octet-aligned)
    b) In case of mismatch in the number of timeslots for NxDS0 basic
       services or trunk-specific NxDS0 services with CAS
2. CEP/TDM mis-configuration:
    a) In the case of mismatch in the desired usage of RTP header
    b) In the case of mismatch of the desired timestamping clock
       frequency
    c) In the case of mismatch of expected signaling packets behavior
       for basic CESoPSN NxDS0 services extended to carry CE
       application signaling in separate signaling packets
    d) In the case of trunk-specific NxDS0 services with CAS if the
       framing types of the trunks are different
    e) In the case of TDMoIP AAL1 PWs with different AAL1 modes
       specified by the end points

In cases 2a, 2b, 2c and 2e above, the user MAY reconfigure the end
points and attempt to setup the PW once again.

In the case 2d the failure is fatal.

Note that setting of the Control bit (see section 2 above) to zero MUST
result in an LDP status of "Illegal C-Bit".

6. IANA Considerations

Many of the IANA assignments required by this draft are also listed in
[PWE3-IANA]. PW type 0x0018 is redefined here as compared to section
2.1 of [PWE3-IANA], and needs to be redefined there in the next
version. Assignments in sections 3.3 through 3.5 are required for three
additional interface parameters.

7. Security Considerations

This draft does not have any additional impact on security of PWs above
that of basic LDP setup of PWs.



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8. Acknowledgements

AV thanks Sharon Galtzur for reviewing this text.



9. Normative References

[RFC2119] S. Bradner, Key Words in RFCs to Indicate Requirement Levels,
RFC 2119, IETF, 1997

[RFC3036] L. Andersson et al, LDP Specification, RFC 3036, IETF, 2001

[PWE3-CONTROL] L. Martini et al, Pseudowire Setup and Maintenance using
LDP, Work in progress, March 2005, draft-ietf-pwe3-control-protocol-
16.txt

[PWE3-IANA] L. Martini, M. Townsley, IANA Allocations for pseudo Wire
Edge to Edge Emulation (PWE3), Work in progress, April 2005, draft-
ietf-pwe3-iana-allocation-09.txt

[PWE3-FRAG] A. Malis, M. Townsley, PWE3 Fragmentation and Reassembly,
Work in progress, February 2005, draft-ietf-pwe3-fragmentation-08.txt

[PWE3-SAToP] A. Vainshtein, Y. Stein, Structure-Agnostic TDM over
Packet (SAToP), Work in Progress, December 2003, draft-ietf-pwe3-SAToP-
01.txt


10. Informative References


[PWE3-CESoPSN] A. Vainshtein et al, Structure-aware TDM Circuit
Emulation Service over Packet Switched Network (CESoPSN), Work in
progress, January 2005, draft-ietf-pwe3-cesopsn-02.txt

[PWE3-TDMoIP] Y(J) Stein et al, TDM over IP, Work in progress, draft-
ietf-pwe3-tdmoip-03.txt, Feb. 2005.

[Q.2630.1] ITU-T Recommendation Q.2630.1, December 1999, AAL type 2
signalling protocol - Capability set 1










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 Control Protocol Extensions for Setup of TDM Pseudowires July 2005

Authors' Addresses

Alexander ("Sasha") Vainshtein
Axerra Networks
24 Raoul Wallenberg St.,
Tel Aviv 69719, Israel
email: sasha@axerra.com

Yaakov (Jonathan) Stein
RAD Data Communications
24 Raoul Wallenberg St., Bldg C
Tel Aviv  69719
ISRAEL

Phone: +972 3 645-5389
Email: yaakov_s@rad.com




Copyright (C) The Internet Society (2005).

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Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.















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