1. TDM Circuit Emulation over Packet (CEP-TDM) Tom Johnson tom_johnson@litchfieldcomm.com (presented by Tim Frost, tim.frost@zarlink.com) IETF 56, 19 March 2003 http://www.ietf.org/internet-drafts/ draft-johnson-pwe3-tdm-00.txt

2. Why do we need another TDM draft? Deadlock between the two major contributions in the PDH space for almost two years (draft-anavi-tdmoip and draft-vainshtein-cesopsn) Several attempts at a compromise failed Previous compromise presented at IETF 55 (Atlanta) didn’t survive for various reasons New design team formed following Atlanta to attempt to break the deadlock Design team consisted of: Tom Johnson, Sasha Vainshtein, Yaakov Stein, Prayson Pate, Max Riegel, Shahram Davari and Tim Frost

3. Advantages of previous solutions draft-anavi-tdmoip –based on tried and tested AAL1 and AAL2 techniques –ease of data-plane inter-working with ATM CES –CAS signaling carried within the data packet for guaranteed synchronization –large number of deployments in the field draft-vainshtein-cesopsn –simple payload structure based on native TDM framing –same payload structure regardless of attachment type –constant delay, regardless of service bit-rate –no pointers buried within the payload

4. What is draft-johnson? RTP Header (may be suppressed) PSN and Multiplexing layer headers CEP-TDM Header TDM Fragment 0Sequence numberFlagsStructure pointer 0 1 5 18 31 CEP-TDM Header control word format:

5. Unstructured Emulation Mode treated as a pure bitstream, with no knowledge of contents regular segmentation default payload length 376 bytes, to give ease of inter- working with ATM CES (one packet = 8 ATM cells) option to use other payload lengths to improve efficiency or reduce latency broad agreement on this mode –although some debate on size of default payload, e.g. should it be reduced to say 188 bytes (4 cells)?

6. Structured Emulation: NxDS0 with CAS based on TDM multiframe format, with an AAL1-like CAS sub-structure, with a whole multiframe as the default payload: option to use an arbitrary payload size, with structure pointer indicating first timeslot of multiframe structure easy to inter-work with ATM (based on same structure) guarantees relationship of CAS to data CAS1 First 125us frame Second 125us frame Last 125us frame CAS substructure Timeslot 1 Timeslot 2 Timeslot 3 CAS2 pad Timeslot 1 Timeslot 2 Timeslot 3 Timeslot 1 Timeslot 2 Timeslot 3

7. Structured Emulation: NxDS0 without CAS Still based on TDM multiframe format, with a whole multiframe as the default payload size: option to use an arbitrary payload size, with structure pointer indicating first timeslot of multiframe structure First 125us frame Second 125us frame Last 125us frame Timeslot 1 Timeslot 2 Timeslot 3 Timeslot 1 Timeslot 2 Timeslot 3 Timeslot 1 Timeslot 2 Timeslot 3

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