RFC 1619 (rfc1619) - Page 2 of 4

PPP over SONET/SDH

RFC 1619                   PPP over SONET/SDH                   May 1994


      The octet stream is mapped into the SONET/SDH Synchronous Payload
      Envelope (SPE), with the octet boundaries aligned with the SPE
      octet boundaries.

      No scrambling is needed during insertion into the SPE.

      The Path Signal Label (C2) is intended to indicate the contents of
      the SPE.  The experimental value of 207 (cf hex) is used to
      indicate PPP.

      The Multiframe Indicator (H4) is currently unused, and MUST be
      zero.

   Transmission Rate

      The basic rate for PPP over SONET/SDH is that of STS-3c/STM-1 at
      155.520 Mbps.  The available information bandwidth is 149.760
      Mbps, which is the STS-3c/STM-1 SPE with section, line and path
      overhead removed.  This is the same super-rate mapping that is
      used for ATM and FDDI [4].

      Lower signal rates MUST use the Virtual Tributary (VT) mechanism
      of SONET/SDH.  This maps existing signals up to T3/E3 rates
      asynchronously into the SPE, or uses available clocks for bit-
      synchronous and byte-synchronous mapping.

      Higher signal rates SHOULD conform to the SDH STM series, rather
      than the SONET STS series, as equipment becomes available.  The
      STM series progresses in powers of 4 (instead of 3), and employs
      fewer steps, which is likely to simplify multiplexing and
      integration.

   Control Signals

      PPP does not require the use of control signals.  When available,
      using such signals can allow greater functionality and
      performance.  Implications are discussed in [2].



3.  Framing

   The framing for octet-synchronous links is described in "PPP in HDLC
   Framing" [2].

   The PPP frames are located by row within the SPE payload.  Because
   frames are variable in length, the frames are allowed to cross SPE
   boundaries.



Simpson