Subject: TDM draft comparison

From: [email-masked]
Date: Wed, 3 Apr 2002 08:57:52 +0000

My name is Geoff Floyd. I attended the IETF PWE3 working group at the
Minneapolis and have followed relevant discussions on the board for several
months. My intention with this Email is to clarify the differences between
the three TDM draft proposals and promote discussion, resulting in unified
draft proposal. To this end I have generated a comparison of the three TDM
drafts.

Comments and corrections are welcome especially regarding ATM and Sonet
where my knowledge is more limited.

Here is my summary of the three drafts:
TDMoIP - Anavi
CESoP - Pate
CESoPSN - Vainshtein

1) Transport and demultiplexing protocols:
All drafts support a wide range of protocols. IP, MPLS, L2TP, UDP etc

2) Supported Formats                             Anavi  Pate  Vainshtein
Support unstructured T1/E1                         Yes   Yes    Yes
Supports fractional T1/E1                          Yes    No    Yes
Packetization based on ATM cells                   Yes    No     No
Packetization based on TU/VT Sonet tributaries      No   Yes     No
Raw data packetization with frame alignment         No    No    Yes

3) Header overhead
Ignoring transport and demultiplexing headers which are common to all
drafts.
Anavi - RTP (12 optional), PW (4) = Total 16
Pate - PW (4), CEP (4) = Total 8
Vainshtein - RTP (12 optional), PW (4) = Total 16

4) Payload encapsulation
Anavi - ATM AAL1 and AAL2 format
Pate - SONET/SDH format: T1 into VT1.5, E1 into VT2
Vainshtein - Complete TDM frames placed in the packet.

5) Payload encapsulation delay (how long to create a packet)
Anavi - 1 to 30 AAL1 cells in a packet. Therefore delay depends on the
number of channels encapsulated.
Pate - Insufficient knowledge of Sonet/SDH to comment
Vainshtein - Min 1 TDM frame period - 125us.

6) Payload encapsulation overhead
Anavi - Structured AAL1 - 2.1%, Unstructured AAL1 - 2.4%, AAL2 - 6.3%
Pate - 12.5% for VT2 (E1), 12% for VT1.5 (T1)
Vainshtein - None, except for T1 where the payload is padded out to 25
bytes per frame - 3.6%.

7) Payload encapsulation "robustness"
Anavi - Sequence numbers allow detection and recovery from missing or out
of order packets. Single packet loss will lose more than the data in one
packet as the following packets must be searched for a pointer to a frame
boundary.
Pate - Insufficient knowledge of Sonet/SDH to comment.
Vainshtein - Sequence numbers allow detection and recovery from missing or
out of order packets. Single packet loss will lose only the data in the
packet.

8) TDM Clocking support                          Anavi  Pate  Vainshtein
Central Clocking                                   Yes   Yes    Yes
Clock recovery using synchronous source            Yes    No    Yes
Adaptive clock recovery                            Yes    No    Yes
Note: Anavi draft needs more information on use of RTP and NTP for adaptive
and synchronous source clock recovery to ensure implementations are
interoperable.

9) Jitter and wander
Anavi & Vainshtein - Will depend on the implementation.
Pate - No Jitter or wander as only central clocking mode supported.

10) CAS support
Anavi - AAL2 encapsulation
Pate - Insufficient knowledge of Sonet/SDH to comment.
Vainshtein - Sent using RTP packets using different payload type. Uses
timestamp for synchronisation with payload.

Regards
    Geoff Floyd
System Architect
Zarlink Semiconductor
Plymouth England.
[email-masked]
Tel: 44 1752 693322