IETF-55 PWE3 Workgroup 21-Nov-02 Unstructured TDM over PSN draft-vainshtein-pwe3-ucesopsn-00.txt

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IETF-55PWE3 Workgroup 21-Nov-02 Unstructured
TDM over PSN draft-vainshtein-pwe3-ucesopsn-00.t
xt

• Sasha Vainshtein, Yaakov Stein, Israel Sasson,
  Akiva Sadovski, Eduard Metz, Tim Frost, Prayson
  Pate

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UCESoPSN Motivation

• Many transport applications carry the entire TDM
  stream transparently
• It is up to the CEs to detect any structure
• Suits "Leased Line" applications
• All the "signaling" is carried transparently
• E.g., FDL/FEAC
• An evolution/merge of "unstructured" approaches
  earlier presented in
• draft-vainshtein-cesopsn-03.txt
• The -04-revision is limited to nDS0 only
• draft-anavi-tdmoip-04.txt (in unadapted (raw)
  mode)
• Simple enough to overcome most of the
  differences
• No payload mangling in both approaches
• Minor encapsulation layer differences easy to
  eliminate
• Supported by the editors of the all the separate
  TDM drafts

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UCESoPSN Scope and Alignment

• In scope
• DS1 (a.k.a T1) - explicitly in the charter
• E1 - not explicitly in the Charter, but as
  popular out of North America as DS1 is there
• DS3 - explicitly in the charter
• E3 - used in Europe and elsewhere.
• Currently out of scope "Unstructured" SONET/SDH
• Fully aligned with
• The PWE3 Charter
• The PWE3 Requirements draft
• The PWE3 Architecture draft
• The PWE3 TDM requirements document

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UCESoPSN - Encapsulation

• Basic packet format has been aligned with the
  SONET/SDH draft(s)
• RTP header is part of the header
• By default is present, MAY be suppressed if both
  PEs agree
• One of the PT values from the dynamic range MUST
  be used - a default value not specified yet
  (127?)
• The control word is MANDATORY
• Flags approximately aligned with SONET/SDH
• The sequence number provides the sequencing
  function if the RTP header is suppressed
• Two modes of timestamp generation
• Use the clock recovered from AC - default, MUST
  be supported
• Use a common reference clock (if available) -
  OPTIONAL
• The clock frequency MUST be a multiple of 8 kHz
• The default value has not been specified yet (8
  kHz?)

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UCESoPSN - Procedures

• Handling of lost packets
• Always replace a lost packet with the equivalent
  amount of "replacement data"
• The actual choice of "replacement data" is a
  local issue
• "All ones" MAY be used (is it the default
  action?)
• Other techniques MAY be used to increase CE
  resistance to an occasional loss of packets
• E.g., replay the contents of the last received
  packet
• No need to have the same procedure at both ends
  of the PW
• Some flags in the control word may require
  framer-based monitoring
• Other procedures similar to what you find in
  SONET/SDH drafts

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UCESoPSN - Payload

• Payload carried as captured
• As required by the principle of Minimum
  Intervention
• Two packet payload size modes defined
• A multiple of a 125 microseconds' sample per
  packet - RECOMMENDED
• Facilitates usage of local procedures for
  improving CE resilience to effects of occasional
  packet loss - an issue that has been actively
  discussed on the list
• Limits packetization latency for DS1 to multiples
  of 1 millisecond (or payload size to multiples of
  193 bytes)
• DS1 payload may be padded to 25 bytes per 125
  microseconds sample as defined in ITU-T G.802 to
  allow other multiples
• A multiple of 47 bytes per packet - OPTIONAL
• Facilitates interworking with AAL1-based ACs

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UCESoPSN - Issues

• The default "must-be-implemented" payload size
  value(s)
• Not specified yet
• Looks like the only unresolved issue at the
  moment
• The Design Team has been working on that

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UCESoPSN - Discussion in the TDM Design Team

• The TDM Design Team is considering a compromise
  based upon
• Solutions for structured and unstructured TDM
  emulation being documented in two separate drafts
• Having a single must-be-implemented mode in each
  of then
• Having one or more optional modes for special
  cases
• The details are being worked out
• The unstructured draft seems ready for adoption
  as the WG document once the default payload size
  issue is resolved

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Questions?