Extending Point-to-Point Protocol (PPP) over Synchronous Optical NETwork/Synchronous Digital Hierarchy (SONET/SDH) with virtual concatenation, high order and low order payloads
Extracted elements (11)
The extension is grounded in a completed global standard for SONET/SDH high order and low order payload virtual concatenation, developed by ITU-T (SG13/SG15), ANSI T1X1, and ETSI TM1/WP3, ensuring international standards alignment before documenting PPP use.
Virtual concatenation dramatically improves bandwidth efficiency; for example, carrying 10 Mbit/s over STS-1 without virtual concatenation yields only 20% efficiency, whereas VT-1.5-7v achieves 89% efficiency for the same payload.
Virtual concatenation is introduced to allow selection of the right-size SONET/SDH bandwidth for PPP links, addressing the limitation of the relatively small number of contiguously concatenated signals available in RFC 2615.
RFC 2615 supports only STS-3c-SPE, STS-12c-SPE, STS-48c-SPE, and STS-192c-SPE on the SONET side (VC-4, VC-4-4c, VC-4-16c, VC-4-64c on SDH side), with VC-4-4c and above not widely supported in SDH networks at the time of publication.
The C2 byte usage in virtual concatenation differs from contiguous concatenation: contiguous concatenation uses a single C2 byte, while virtual concatenation requires the same C2 value in each constituent channel's overhead.
For SONET/SDH STS-1/VC-3 and above SPE/VCs using virtual concatenation, the path signal label (C2 byte) value is required to be the same for all constituent channels, in accordance with RFC 2615 values.
For SONET VT-1.5/2/6 and SDH VC-11/12/2 virtual concatenation, the path signal label (V5 byte bits 5-7) is required to be the same for all constituent channels per ITU-T G.707 and ANSI T1.105.02.
For virtual concatenation based on SONET VT-1.5/2/6 and SDH VC-11/12/2 channels, bit 2 of the path overhead K4 byte must be set to the value indicated per ITU-T G.707 and ANSI T1.105.02.
When virtual (as opposed to contiguous) concatenation is used for SONET/SDH STS-1/VC-3 and above SPE/VCs, the H4 multi-frame indicator byte must be populated as per ITU-T G.707 or T1.105.02; it is unused for contiguously concatenated links.
With virtual concatenation, PPP over SONET/SDH gains access to VT-1.5-nv (n=1-64, 1.6–102 Mbit/s), STS-1-nv (n=1-64, 49–3100 Mbit/s), and STS-3c-nv (n=1-64, 150–10000 Mbit/s) on SONET, and corresponding VC-12-nv, VC-3-nv, VC-4-nv on SDH.
The security discussion in RFC 2615 applies to this document. No new security features have been explicitly introduced or removed compared to RFC 2615.