RE: [PWE3] comments on draft-ietf-pwe3-requirements-03.txt

[neil.2.harrison@bt.com]

Please see below.  regards, Neil

> -----Original Message-----
> From: Ron Cohen [mailto:ronc@ntear.com]
> Sent: 08 October 2002 10:36
> To: 'Yaakov Stein'; neil.2.harrison; stbryant
> Cc: pwe3
> Subject: RE: [PWE3] comments on draft-ietf-pwe3-requirements-03.txt
> 
> 
> Yaakov,
> 
> There is a different between the classification of TDM circuits into
> plesiochronous digital hierarchy (PDH) and synchronous 
> digital hierarchy
> and the actual synchronization architecture deployed in the 
> network, or
> their internal multiplexing characteristics.
> 
> E1 and T1 are referred in the ITU specs as belonging to the
> plesiochronous digital hierarchy (PDH). It does not matter 
> that in most
> deployments they are not operated in a plesiochronous timing
> architecture, or that they carry DS0 synchronously.
NH=> It jolly well does Ron!  E1/T1 *must* be synchronous to the nx64k
clients they carry as there is no justification scheme that relates these 2
layer networks.  And in a PDH stack uncontrolled bit slips get removed at
the E1/T1 framing level. 
> 
> To understand the difference, you might note that plesiochronous
> synchronization is used in certain SDH deployments. This mode of
> operation is typical for connections across administration boundaries.
> SDH networks do not carry their PDH tributaries synchronously, but
> rather asynchronous mapping are the dominant ones.
> 
> See an additional remarks below
> 
> Ron
> 
> 
> > -----Original Message-----
> > From: pwe3-admin@ietf.org [mailto:pwe3-admin@ietf.org] On 
> > Behalf Of Yaakov Stein
> > Sent: Tuesday, October 08, 2002 10:17 AM
> > To: neil.2.harrison@bt.com; stbryant@cisco.com
> > Cc: pwe3@ietf.org
> > Subject: RE: [PWE3] comments on draft-ietf-pwe3-requirements-03.txt
> > 
> > 
> > 
> > > E1 and T1 belong to PDH and only PDH.
> > 
> > Sorry Neil, but PLESIOchronous refers ONLY
> > to multiplexing of sources with NEARLY (BUT NOT EXACTLY)
> > the same clock (PLESIO is Greek for near or close).
> > (See G.701)
> 
> Below is G.701 definition. Please see Note 1.
> 
> 6019	plesiochronous
> 	F:  plésiochrone
> 	S:  plesiócrono
> The essential characteristic of time-scales or signals such that their
> corresponding significant instants occur at nominally the 
> same rate, any
> variation in rate being constrained within specified limits.
> NOTES
> 1	Two signals having the same nominal digit rate, but not stemming
> from the same clock or homochronous clocks, are usually 
> plesiochronous.
> 2	There is no limit to the time relationship between corresponding
> significant instants.
> 
> 
> > PDH thus refers to the hierarchy of multiplexing schemes 
> > that use with stuffing bits, e.g. E2,T2,E3,T3.
> > 
> > E1 and T1 mandate a single clock for all the DS0s they multiplex. 
> > They are thus not PLESIOchronous by any stretch of the imagination. 
> > They are simply synchronous (SYN means SAME).
> > 
> > Please do not fall into the same pit as someone did in
> > a previous thread on this list, and claim that various ITU 
> > standards refer to E1 and T1 as PDH.  They don't. They use 
> > the term BASED ON the 1544 kbps or 2048 kbps hierarchy. The 
> > PDH hierarchy is BASED ON the E1 or T1 clocks, but the E1/T1 
> > signals themselves are NOT PDH.
> > 
> > Y(J)S
> > _______________________________________________
> > pwe3 mailing list
> > pwe3@ietf.org
> > https://www1.ietf.org/mailman/listinfo/pwe3
> > 
> 
> 
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