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Re: Inter-CO signaling?

  • From: James Carlson
  • Date: Thu Sep 10 17:29:19 1998
  • Newsgroups: lists.nanog ("Robert E. Seastrom") writes:
> RBS is often run on B8ZS/ESF too.
> The reason it is not commonly run on inter-office trunks is because of
> a remarkable new innovation called SS7.  Perhaps you have heard of it.
> Anyway, since the bits in robbed-bit signaling are "robbed" from the
> superframe not from your DS0, it is irrelevant to your throughput.

Uh, no.  If robbed bit signaling is used, every single DS0 gets
exactly one bit clobbered out of every six PCM samples (750us).  Out
of 24 frames (an "Extended Super Frame"), those four stolen bits form
the familiar ABCD signaling pattern.  (24 bit long pattern in the
framing bit signals the synchronization of the 24 frame sequence so
you can distinguish A from B, et cetera.)

(Perhaps you're thinking of FDL, which is carried purely over the
framing bit as a 4Kbps channel and doesn't affect any of the DS0s.)

Dan Hollis originally posted:
>    >    > Is there any way to determine if inter-telco links are using 
>    >    > robbed bit
>    >    > signaling? Eg from GTE to USwest in the Seattle area.
>    >    > 
>    >    > I suspect RBS may be causing lots of v.90 problems in 
>    > GTE country in
>    >    > Seattle. But id like to know how to confirm this. And just 
>    >    > maybe, get it
>    >    > fixed.

I doubt strongly that RBS would be the problem, since V.90 is designed
to work correctly with RBS channels.  Two things to check:

	- If they're using channel banks between you and the
	  customer's switch (like if they dropped you cheap T1s by
	  putting them line-side on your switch, rather than trunk-
	  side), then you lose.  24Kbps will be about the maximum.

	- Some misconfigurations will merely cause lots of errors and
	  poor performance rather than abject failure.  Check AMI
	  versus B8ZS (look for coding violations), and check for
	  clocking problems (extremely frequent slips noted by FDL).

James Carlson, Consulting S/W Engineer  <>
IronBridge Networks / 55 Hayden Avenue  71.246W    Vox:  +1 781 372 8132
Lexington MA  02421-7996 / USA          42.423N    Fax:  +1 781 372 8190
"PPP Design and Debugging" ---

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