Subject: draft-anavi & draft-davari summaries

From: Shahram Davari <[email-masked]>
Date: Thu, 29 Aug 2002 10:35:45 -0700

Hi Danny and All,

Please find below the required statements for the following two drafts.

NAME OF I-Ds:

http://www.ietf.org/internet-drafts/draft-davari-pwe3-aal12-over-psn-00.txt
http://www.ietf.org/internet-drafts/draft-anavi-tdmoip-04.txt

SUMMARY:

These drafts describe an efficient method for transporting AAL1/2 and TDM
over IP/MPLS networks, using effectively the ATM AAL5 PDU transport
mode with only minor (non-format) changes.

RELATED DOCUMENTS:

http://www.ietf.org/internet-drafts/draft-martini-atm-encap-mpls-01.txt
http://www.ietf.org/internet-drafts/draft-bocci-pwe3-app-frame-over-psn-00.txt
http://www.ietf.org/internet-drafts/draft-koleyni-pwe3-app-cell-over-psn-01.txt

WHERE DOES IT FIT IN THE PICTURE OF THE PWE WORK:

The PWE charter calls for encapsulation and emulation/maintenance document(s) 
for ATM and TDM (e.g. DS1, DS3, SONET).
 
Our drafts describe both a method of transporting native DS1 TDM, 
as well as AAL1 and AAL2 modes of ATM.

WHY IS IT TARGETED AT THIS WG:

As we have mentioned, the WG charter calls for ATM and TDM emulation over PSN. 
[draft-martini], [draft-koleyni] and [draft-bocci] already cover the ATM
cell transport and the AAL5 frame transport. draft-davari complements
them by covering the AAL1/2 frame transport. draft-anavi leverages
effectively draft-davari to do TDM emulation over PSN.

JUSTIFICATION:

These drafts address two PWE3 Charter deliverable items:

1) Efficient transport of AAL1/2, by reusing the AAL5 PDU mode with only
minor changes, (non-format changes which is also applicable to AAL5 and 
to which most of the ATM draft authors have agreed). Currently [draft-martini]
and [draft-koleyni] only address the AAL1/2 cell encapsulation, which is much
less efficient in the present case.

2) Efficient transport of TDM by emulating TDM over AAL1/2 and then transporting AAL1/2. 
The advantages are as follows:
  i)  AAL1/2 emulation is a proven technology and the HW/SW are commercially available.
 ii)  Unlike an alternative method being suggested [CESoPSN] for TDM emulation, 
      it does not require the definition of any new, untested, protocols.
 iii) Service interworking with ATM and AAL1/2 networks is simplified.
 iv)  AAL1 and AAL2 are mature technologies, known to operate well in practice.
 v)   The specific mechanism being proposed has already been widely deployed and 
      proven to function well.
 vi)  AAL1 allows flexible latency/efficiency tradeoff.
 vii) AAL1 has mechanisms for robustness under presence of packet loss.
      The other TDM methods being proposed have not been demonstrated to function
      at even moderate packet loss rates.
 viii)AAL2 allows for bandwidth conservation when not all TDM timeslots are in use.
      As such it is the most bandwidth efficient of the protocols being proposed for TDM
      transport.

The PWE3 WG should consider these drafts, due to the following reasons:

i) It maximizes reuse one of PWE3 transport methods to support other functionalities 
   that are required by the charter (AAL1/2 and TDM transport).
 
ii) Even were the WG to decide to endorse the [CESoPSN] draft,
    the possibility of transporting TDM in the manner suggested by
    these drafts would still exist, because it reuses 2 available protocols
   (i.e, AAL1 CES and AAL5 PDU transport). This would lead, de-facto, to there being two
   TDM over PW transport methods. Since the AAL1/2 method would leverage
   readily available HW/SW, there would be a tendency for implementers to 
   adopt it, even without an explicit draft.
 
iii)[draft-ietf-pwe3-sonet-vt] describes a method of leveraging [draft-ietf-pwe3-sonet]
    for the transport of TDM. While in principle similar in approach, the SONET-VT approach
    is much more complex, and would only be used in practice when at least one 
    of the CEs is SONET-based. It is not reasonable to require building of SONET frames
    for the transport of native DS1 streams. In addition, requiring the use of SONET technology 
    would produce too high a barrier for implementers. Finally, the SONET-VT approach
    is the least bandwidth efficient of those being proposed.

Thanks,

Shahram Davari
Senior Product Research Engineer
PMC-Sierra, Inc.
Phone: (613) 271-4018

Yaakov (Jonathan) Stein 
Chief Scientist 
RAD Data Communications 
Phone: +972 3 6455389 +972 2 5889159