RFC 1619 (rfc1619) - Page 2 of 4
PPP over SONET/SDH
Alternative Format: Original Text Document
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