Telecom Technical Different clock sources for STM-1 and E1 ??

Hi!

Maybe someone here can help me with a problem we have with our PSTN
gateway.
We receive 63 E1's channelized into a STM-1. The E1's are provided by
DTAG (German PSTN) and are multiplexed into the STM-1 provided by
Verizon. STM-1 directly terminates in a Audiocodes Mediant 3000 which
demultiplexes STM-1 and routes E1's respectively.

We see a huge number of Controlled Slips (one in 20 seconds) and it
seems this condition causes fax calls to crash.

We got in contact with Verizon and they told us, that they are
receiving DTAG's E1's in sync with a PDH clock and transparently
multiplex that into the STM-1 which is clocked by a different master
clock. (As it is not their policy to generate clock from external
sources and PDH can not be used for SDH clock source - that's what
they said)
[For what I read on the interwebs SDH was specially designed to
support relaying of PDH - so I don't really get the point...]

So we receive E1's and STM-1 on different source clocks. Unfortunately
Audiocodes tells us the gateway only supports one single clock source,
which has to be the STM-1 or any external clock directly connected to
the device.

I appreciate any hints or tips on this issue (or any lesson on PSTN
clocking) as I am used to deal with IP networks on the very higher
layers...

Cheers Ren=E9

When=20setting=20up=20a=20system=20that=20transports=20E1s=20over=
=20an=20STM-1=20interface,=20you=20can=20use=20one=20clock=20for=
=20the=20STM-1=20interface=20and=20a=20different=20clock=20for=20t=
he=20E1=20interface.=20These=20two=20clocks=20should=20be=20locked=
=20to=20each=20other=20and=20be=20derived=20from=20the=20same=20so=
urce,=20but=20do=20not=20have=20to=20be=20which=20your=20case=20is=
=20=e2=80=93=20The=20E1=20clock=20from=20DTAG=20and=20the=20SDH=20=
from=20Verizon=20are=20not=20locked=20to=20each=20other.
=20
The=20source=20of=20your=20slips=20is=20coming=20from=20the=20mis-=
match=20of=20these=20two=20clock=20rates.=20=20What=20is=20happeni=
ng=20is=20that=20on=20your=20Audiocodes=20receive=20side,=20it=20i=
s=20receiving=20the=20STM-1=20and=20de-multiplexing=20it=20into=20=
E1s.=20=20The=20differences=20in=20frequencies=20of=20the=20STM-1=
=20and=20the=20E1=20are=20dealt=20with=20pointer=20justifications=
=20happening=20at=20the=20TU-12=20path=20level=20(A=20TU-12=20is=
=20what=20is=20used=20to=20transport=20an=20E1=20over=20a=20SDH=20=
network=20=e2=80=93=20you=20have=2063=20TU-12=20paths=20=e2=80=93=
=20one=20for=20each=20E1).=20=20Since=20these=20frequencies=20are=
=20different,=20if=20your=20Audiocodes=20box=20does=20performance=
=20monitoring,=20you=20should=20be=20able=20to=20look=20for=20poin=
ter=20changes=20at=20the=20TU-12=20level=20to=20see=20that=20these=
=20two=20clocks=20are=20different.
=20
Pointer=20changes=20are=20not=20the=20same=20as=20slips.=20=20A=20=
slip=20occurs=20when=20the=20receive=20clock=20on=20the=20E1=20is=
=20different=20from=20the=20system=20clock=20in=20your=20Audiocode=
s=20box.=20=20Inside=20the=20E1=20framer=20of=20the=20Audiocodes=
=20box,=20there=20is=20a=20block=20of=20memory=20that=20the=20time=
slots=20of=20the=20E1=20are=20stored=20as=20they=20arrive=20on=20t=
he=20E1=20using=20the=20receive=20E1=20clock=20rate.=20=20The=20ti=
meslots=20are=20then=20readout=20of=20this=20block=20of=20memory=
=20at=20the=20system=20clock=20rate.=20=20NOTE:=20This=20block=20o=
f=20memory=20is=20called=20the=20elastic=20store=20or=20slip=20buf=
fer.=20=20=20So,=20what=20happens=20when=20the=20rate=20of=20times=
lots=20arriving=20on=20the=20E1=20is=20faster=20than=20the=20syste=
m=20takes=20them=20out.=20=20Since=20there=20is=20not=20infinite=
=20memory,=20the=20E1=20framer=20will=20do=20a=20controlled=20slip=
=20which=20would,=20in=20this=20case,=20would=20delete=20an=20enti=
re=20frames=20worth=20of=20timeslots.=20=20Conversely,=20if=20the=
=20rate=20of=20timeslots=20arriving=20on=20the=20E1=20is=20slower=
=20than=20the=20speed=20the=20system=20takes=20them=20out,=20the=
=20E1=20framer=20device=20will=20create=20timeslots=20by=20duplica=
ting=20the=20last=20frames=20worth=20of=20timeslots.=20=20The=20de=
leting/creating=20timeslots=20during=20slips=20will=20be=20hardly=
=20noticeable=20to=20the=20human=20ear,=20but=20for=20data=20servi=
ces=20like=20fax,=20it=20will=20cause=20the=20kind=20of=20problems=
=20you=20are=20seeing.
=20
So,=20the=20solution=20to=20you=20problem=20is=20to=20get=20the=20=
system=20timing=20of=20the=20Audio=20codes=20box=20to=20be=20locke=
d=20to=20the=20E1=20clock=20rate.=20=20That=20may=20be=20difficult=
,=20if=20not=20impossible,=20given=20the=20features=20you=20descri=
be=20that=20are=20available=20in=20the=20Audiocode=20box.=20=20You=
=20indicate=20that=20you=20only=20have=20two=20choices=20for=20sys=
tem=20timing=20on=20the=20Audio=20codes=20box:=20=20Receive=20STM-=
1=20or=20external=20input.
=20
Since=20the=20STM-1=20clock=20is=20derived=20from=20Verizon=e2=80=
=99s=20network=20and=20the=20E1=20clock=20is=20from=20the=20DTAG=
=20network,=20you=20cannot=20use=20the=20STM-1=20clock=20because=
=20they=20are=20not=20locked=20to=20each=20other.=20
=20
Thus,=20you=20need=20to=20provide=20a=20clock=20on=20the=20externa=
l=20input=20that=20is=20locked=20to=20the=20DTAG=20timing=20someho=
w.=20=20You=20don=e2=80=99t=20have=20enough=20description=20to=20d=
etermine=20if=20that=20is=20a=20difficult=20thing=20to=20do=20or=
=20not.
=20
Finally,=20you=20can=20find=20a=20different=20receive=20device=20t=
hat=20allows=20the=20system=20timing=20to=20be=20locked=20to=20the=
=20receive=20E1=20clock.
=20
Good=20luck.
=20
Bill=20Matern
wtm=20at=20ncomm.com

On=20Mon=20Jan=209=2007:21:42=202012=20Ren=c3=a9=20H=c3=bcftlein=
=20=20wrote: