Subject: [PWE3] Generic vs Preferred CW

From: Stewart Bryant <[email-masked]>
Date: Mon, 25 Apr 2005 11:56:05 +0100

I am working on -04 of the CW draft that takes into a/c
the feedback that I have received from the list and
AD on -03.

Before I complete this I need to ask the list to
consider the following proposed text:

---------------------------------------------------------------

3.   Generic PW MPLS Control Word

    The Generic PW MPLS Control Word is shown in Figure 1.

     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|          Specified by PW Encapsulation                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 1: Generic PW MPLS Control Word

    The PW set-up protocol or configuration mechanism determines whether
    a PW uses a PW MPLS Control Word (PWMCW). Bits 0..3 differ from the
    first four bits of an IP packet [BCP] and hence provide the
    necessary MPLS payload discrimination.

    When a PWMCW is used, it MUST adhere to the Generic MPLS Control
    Word format as illustrated in Figure 1 above. It SHOULD also follow
    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| Flags |FRG|  Length   | Sequence Number               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 2: PW Preferred MPLS Control Word

    The meaning of the fields of the PW Preferred MPLS Control Word
    (Figure 2) is as follows:

--------------------------------------------------------------------

With the proposed changes to the CEP draft, the only encaps that do not
use the preferred CW is ATM 1 to 1 Cell Mode AAL5 PDU Frame Mode.

We therefore have two choices:

a) Leave the text above and thereby leave the ambiguity as to how
important it is to use preferred vs generic CW.

b) Change the text to say that the encap MUST use the Preferred
CW, and add exception text to the ATM draft.

I think that option (b) is better, because it requires
future encapsulations that do not adhere to the Preferred CW
to draw attention to the technical reasons why.

Views?

- Stewart

_______________________________________________
pwe3 mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/pwe3

---

From: Alia Atlas <[email-masked]>
Date: Mon, 25 Apr 2005 08:17:03 -0400

I agree that option (b) sounds better, because it requires an explicit 
reason to diverge.

Alia

---

From: "Andrew G. Malis" <[email-masked]>
Date: Mon, 25 Apr 2005 10:02:12 -0400

Stewart,

I prefer option a.  There is now another draft, 
http://www.ietf.org/internet-drafts/draft-ash-avt-hc-over-mpls-protocol-00.txt 
, that follows the generic control word (the first four bits are 0000) but 
diverges from the preferred CW.  This draft defines a new pseudowire type, 
header-compressed VoIP over MPLS (voice/RTP/UDP/IP/MPLS labels).  The CW is 
only one octet in length, because for this application every octet counts 
and packet reordering is allowed.

Thanks,
Andy

---------

---

From: "Mustapha Aissaoui" <[email-masked]>
Date: Mon, 25 Apr 2005 10:14:18 -0400

I agree with Andy. Option (a) is all what is required for the BCP. We cannot
anticipate the preffered control word will be suitable to future application
of PWs.

Regards,
Mustapha.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Andrew G. Malis
Sent: Monday, April 25, 2005 10:02 AM
To: Stewart Bryant
Cc: Ash, Gerald R (Jerry), ALABS; pwe3
Subject: Re: [PWE3] Generic vs Preferred CW

Stewart,

http://www.ietf.org/internet-drafts/draft-ash-avt-hc-over-mpls-protocol-00.t
xt

Thanks,
Andy

---------

At 4/25/2005 11:56 +0100, Stewart Bryant wrote:
>I am working on -04 of the CW draft that takes into a/c the feedback
>that I have received from the list and AD on -03.
>
>Before I complete this I need to ask the list to consider the following
>proposed text:
>
>b) Change the text to say that the encap MUST use the Preferred CW, and
>add exception text to the ATM draft.
>
>I think that option (b) is better, because it requires future
>encapsulations that do not adhere to the Preferred CW to draw attention
>to the technical reasons why.
>
>Views?
>
>- Stewart
>