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Re: arbitrary contiguous concatenation question
Malcolm,
I agree with you, and that's why I wrote the email. I hadn't noticed this issue
of "STS-1 concatenation" until this morning unfortunately. As the
draft-ietf-ccamp-gmpls-sonet-sdh-01.txt document isn't approved yet, it isn't
too late to correct...
Some background for you. IETF is defining signalling support for concatenated
STS/VC signals, which are not defined in T1.105 or G.707. One of those is
"arbitrary contiguous concatenation" of STS-1 signals: STS-Xc, with X > 1 (e.g.
2,3,4,5,6,7,8,...). Refer to appendix 3 of
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-sonet-sdh-01.txt
Some background for other readers. In G.707 AU-3 concatenation has never been
defined, only AU-4 concatenation (G.707 1996 AU-4-2c, AU-4-3c, etc). In T1.105
1995 STS concatenation has been defined for STS-Nc with N restricted to
3,6,9,12,15,etc, but not for any other value of N. Essentially this is equal to
AU-4 concatenation.
Both G.707 and T1.105 have restricted this concatenation in their 2000 versions
to AU-4-4c/STS-12c, AU-4-16c/STS-48c, etc.
Arbitrary contiguous concatenation of STS-1 signals (STS-Xc, X>1) hasn't been
defined up to so far in any transport plane standard. And if we would define it
as true "contiguous" concatenation then an STS-Xc would use STS-1/AU-3 timeslots
TSi, TSi+1, .., TSi+X.
This would imply that the STS-1-3c and the STS-3c are not transported via the
same timeslots. Same for STS-1-6c and STS-3c-2c, etc.
The text in appendix 3 of draft-ietf-ccamp-gmpls-sonet-sdh-01.txt should in this
case not mix AU-4 with STS-1. AU-4-Xc and STS-3c-Xc are equivalent. STS-1-Xc and
AU-3-Xc are equivalent. STS-1-(3X)c and STS-3c-Xc are NOT equivalent.
Note that the STS SPEs associated with STS-1-(3X)c and STS-3c-Xc
are the same. Those are simply STS-(3X)c SPE signals.
As I wasn't involved from the start in this work, I do not know what the
supporters of arbitrary contiguous concatenation of STS-1 signals intended to
define. I am looking forward to more input from those.
Regards,
Maarten
> Malcolm Betts wrote:
>
> Maarten, the term "contiguous" may be confusing when applied in the context of
> the two stage multiplexing of AU-3's into an AUG (to occupy the same "space"
> as a AU-4) then into a STM-N (with N>1). The three STS-1 (AU-3) pointers for
> an STS-3c (VC-4) payload are adjacent (contiguous) within the OC-3N (STM-N)
> frame. For AU-4N (or STS-3N) and above concatenation, the pointers and
> payloads are contiguous (adjacent) within the STM-N frame.
>
> This is well know and has been in existence since about 1988 - the vintage of
> the first versions of the SONET standard T1.105 and the original SDH standards
> G.707, G.708 and G.709 - with numerous examples of interworking between SONET
> and SDH and between vendors.
>
> Malcolm Betts
>
> Advanced Network Technology
> Nortel Networks
> Phone: +1 613 763 7860 (ESN 393)
> FAX: +1 613 763 6608 (ESN 393)
> email: betts01@nortelnetworks.com
>
> -----Original Message-----
> From: Maarten Vissers [mailto:mvissers@lucent.com]
> Sent: Tuesday, July 10, 2001 5:14 AM
> To: ccamp
> Cc: t1x1.5; q11/15
> Subject: arbitrary contiguous concatenation question
>
> All,
>
> draft-ietf-ccamp-gmpls-sonet-sdh-01.txt defines signalling support for
> arbitrary
> contiguous concatenation in appendix 3. Looking a bit more into this arbitrary
>
> concatenation from the transport plane, I came across a question with respect
> to
> the definition of "contiguous STS-1/AU-3 timeslots". Let me introduce this
> question:
>
> Figure 7-25/G.707 (10/2000) lists the AU-3 numbering (within an STM-4) as
> follows
>
> Time 111
> Slot 123456789012123456789
>
> B 123412341234123412341...
> A 111122223333111122223...
>
> AU-3 timeslots have a TimeSlot number and a (B,A) number, with TS1 associated
> with (1,1) and TS12 associated with (4,3).
>
> Note - the figure in the pre-published version of G.707
> doesn't show the timeslot numbering in a correct manner.
>
> and the AU-4 numbering is as follows (figure 7-24/G.707)
>
> Time
> Slot 123412341234123412341
>
> B 123412341234123412341...
> A 000000000000000000000...
>
> An AU-4 [STS-3c] is as such essentially a "non-contiguous" concatenation of
> AU-3s [STS-1s]; i.e. every 4th AU-3/STS-1 is use; e.g. AU-4 (2,0) uses AU-3
> timeslots 2,6,10 [i.e. (2,1), (2,2), (2,3)].
>
> If we define STS-1 contiguous concatenation, which timeslots are then used for
>
> e.g. a STS-1-3c:
> i) timeslots (1,1),(2,1) and (3,1) [TS1,TS2,TS3], or
> ii) timeslots (1,1), (1,2) and (1,3) [TS1,TS5,TS9]
>
> Similarly, for the case of a STS-1-6c do we use:
> i) (1,1), (2,1), (3,1), (4,1), (1,2) and (2,2)
> [TS1,TS2,TS3,TS4,TS5,TS6] or
> ii) (1,1), (2,1), (1,2), (2,2), (1,3) and (2,3)
> [TS1,TS2,TS5,TS6,TS9,TS10]
>
> And which timeslots do we use for e.g. a STS-1-5c?
>
> If this detail is not specified, interworking is not possible unless we
> include
> the list of timeslots as we do with virtual concatenation (and as discussed
> for
> flexible arbitrary concatenation).
>
> Regards,
>
> Maarten
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