[PWE3] Proposed Changes to CEP

[ronc at lyciumnetworks.com]

Dear PWE3ers

Below is a proposal by CEP authors that aligns the CEP draft with draft-ietf-pwe3-cw-03.txt and with the other TDM emulation drafts. Please send your comments as soon as possible. If no substential comments are received in the coming week a new draft CEP-11 will be issued detailing these changes. New CEP header description is attached.

Proposed changes to CEP-10:

Changes summary:
1. CEP header: align with recommended control word. Use L and R
  bits similar for remote/forward defect indications. Use 16 bit
  sequence number, length and fragmentations bits. Shorten structure
  pointer from 13 to 12 bits supporting payload sizes up to 4096 bytes. 
2. Align LDP interface parameters with above changes. Align MIB
  with above changes
3. Remove L2TPv3 encapsulation (to be described in a separate
  draft at a later time)
4. Remove RTP encapsulation

Happy tax day
Ron

Ron Cohen
CTO
Resolute Networks
Redux and Lycium Unite 




CEP header


   The CEP control word 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |0|0|0|0|L|R|N|P|FRG|Length[0:5]|    Sequence Number[0:15]      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Reserved                |Structure Pointer[0:11]|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2 - CEP Control Word Format


   The above fields are defined as follows:

   L bit: CEP-AIS. This bit MUST be set to one to signal to the
   downstream PE that a failure condition has been detected on the
   attachment circuit.
   Failure conditions leading to generation of CEP-AIS and the
   mapping of CEP-AIS siganl on the downstream attachment
   circuit are described in section 6.

   R bit: CEP-RDI. This bit MUST be set to one to signal to the
   upstream PE that a loss of packet synchronization has occurred.
   This bit MUST be set to zero once packet synchronization is
   acquired.

   N and P bits: These bits are used to explicitly relay negative
   and positive pointer adjustments events across the PSN. The use
   of N and P bits is OPTIONAL. See section 8 for details.

   Table 2 describes the interpretation of N and P bits settings.

         +---+---+--------------------------------------+
         | N | P |         Interpretation               |
         +---+---+--------------------------------------+
         | 0 | 0 | No Pointer Changes                   |
         | 0 | 1 | Positive Pointer Adjustment          |
         | 1 | 0 | Negative Pointer Adjustment          |
         | 1 | 1 | Error Condition                      |
         +---+---+---+----------------------------------+

             Table 2 - Interpretation of N and P bits

   N and P bits MUST be set to 1 when L bit is set to 1.

   FRG bits: FRG bits MUST be set to zero by sender and ignored
   by receiver.
   SONET data is continuously fragmented into packets.
   The structure pointer field designates the offset between the 
   SONET SPE or VT structure and the packet boundary.

   Length [0:5]: The Length field, if non zero, indicates the
   length of the control word plus the length of the payload field.
   The Length field MUST be set if it is less or equal to 64 bytes
   and MUST be set to zero otherwise. In particular, if DBA mode
   is used, and the packet does not carry any payload, the Length
   field MUST be set to the control word length.

   Sequence Number [0:15]:  The packet sequence number
   MUST continuously cycle from 0 to 0xFFFF.  It is generated and
   processed in accordance with the rules established in [RFC1889].

   Structure Pointer [0:11]: The Structure Pointer MUST contain the
   offset of the first byte of the SONET structure within the packet
   payload. For SPE emulation, the structure pointer locates the J1
   byte within the CEP packet.  For VT emulation the structure
   pointer locates the V5 byte within the packet.  The structure
   pointer value is from 0 to 0xFFE, where 0 means the first byte
   after the CEP header. The Structure Pointer MUST be set to 0xFFF
   if a packet does not carry the J1 (or V5) byte.
   An arbitrary pointer change (NDF event) in the attachment circuit
   changes the offset of the SONET structure within the CEP packet
   and therefore changes the Structure Pointer value.

   Reserved Field: The reserved field MUST be set to zero by sender
   and ignored by receiver.

Ron Cohen
CTO
Resolute Networks
Redux and Lycium Unite

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