RE: SDH Format

Both ETSI and ANSI were developed in parallel, ETSI is based on AU-4, and ANSI is using both AU-3 (for G.707's VC-3 payloads) and AU-4 (for G.707's C-4 payloads). ITU's agreement was to use ETSI's SDH name (vs. ANSI's SONET) and to include both AU-4 and AU-3 structures in Rec. G.707 as "SDH was designed to be universal". And resulting in G.707's rule for interconnection of the two different types is to use the AU-4 structure (demultiplexing to either VC-3 or TUG-2 for interconnection). Japan also uses both the AU-3 and AU-4. Later, ETSI radio applications did define an AU-3 structure, though I don't know if it is being used.

From: jerome.law@bt.com [mailto:jerome.law@bt.com]
Sent: Friday, February 11, 2005 7:47 AM
To: mvissers@lucent.com; Brungard, Deborah A, ALABS; dimitri.papadimitriou@alcatel.be
Cc: ccamp@ops.ietf.org
Subject: SDH Format

You guys are the experts behind this and from some thread on the internet regarding SDH; I just need your help to explain the differences between AU-4 and AU-3? American versus European or ETSI?