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TDM Circuit Emulation over Packet (CEP-TDM)

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. Why do we need another TDM draft? .

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TDM Circuit Emulation over Packet (CEP-TDM)

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

  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. Timeslot 1 First 125us frame Timeslot 2 Timeslot 3 Timeslot 1 Second 125us frame Timeslot 2 Timeslot 3 Timeslot 1 Last 125us frame Timeslot 2 Timeslot 3 CAS1 CAS2 CAS substructure CAS1 pad 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

  7. Timeslot 1 First 125us frame Timeslot 2 Timeslot 3 Timeslot 1 Second 125us frame Timeslot 2 Timeslot 3 Timeslot 1 Timeslot 2 Last 125us frame Timeslot 3 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

  8. w w w . Z A R L I N K . c o m

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