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

["Ron Cohen" <ronc@ntear.com>]

Neil,

> 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. 

Yes. 
My point is that the fact that DS0s are carried synchronously within T1
and E1 does not change the fact that T1 and E1s belong to the
plesiochronous digital hierarchy (PDH)

Ron

> -----Original Message-----
> From: neil.2.harrison@bt.com [mailto:neil.2.harrison@bt.com] 
> Sent: Tuesday, October 08, 2002 12:03 PM
> To: ronc@ntear.com; yaakov_s@rad.co.il; stbryant@cisco.com
> Cc: pwe3@ietf.org
> Subject: RE: [PWE3] comments on draft-ietf-pwe3-requirements-03.txt
> 
> 
> 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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