ESF vs ISDN PRI
gbou...@presticom.ca
I have seen a few messages in this newgroup's archive mentioning that an
ISDN PRI line may have ESF on it. I do not see why that would be
necessary since the D-Channel takes care of the signalling. Are there
case where ESF is used on ISDN PRI lines?
Gaetan Boucher
ACT/Presticom
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Aaron Leonard
In article <881937582...@dejanews.com>, gbou...@presticom.ca writes:
|I have seen a few messages in this newgroup's archive mentioning that an
|ISDN PRI line may have ESF on it. I do not see why that would be
|necessary since the D-Channel takes care of the signalling. Are there
|case where ESF is used on ISDN PRI lines?
|
|Gaetan Boucher
|ACT/Presticom
A US PRI *always* uses ESF framing (and B8ZS encoding.)
ESF is *not* a "signalling" method, it's a framing method.
The D-channel is a whole nother layer in the protocol stacks.
From the T1 perspective, the D-channel is just another timeslot
(which happens to be slot 24 in the US.) Within that 64Kbps
slot, the D channel has its own protocol stack.
Aaron
Stefan Doll
gbou...@presticom.ca wrote:
>I have seen a few messages in this newgroup's archive mentioning that an
>ISDN PRI line may have ESF on it. I do not see why that would be
>necessary since the D-Channel takes care of the signalling. Are there
>case where ESF is used on ISDN PRI lines?
Hi Gaetan ,
It's roughly the other way round. To implement 23B+D ISDN you can use
ESF framers. 23 channels will carry user information (B-channels) and
1 channel is used for signalling. With ESF you can employ bit-robbing
to exchange signalling information, but for ISDN use you have to
disable that option.
-Stefan
Gaetan Boucher
ste...@eda2.racal.com (Stefan Doll) wrote:
>> gbou...@presticom.ca wrote:
>>
>> >I have seen a few messages in this newgroup's archive mentioning that an
>> >ISDN PRI line may have ESF on it. I do not see why that would be
>> >necessary since the D-Channel takes care of the signaling. Are there
>> >case where ESF is used on ISDN PRI lines?
>>
>> Hi Gaetan ,
>>
>> It's roughly the other way round. To implement 23B+D ISDN you can use
>> ESF framers. 23 channels will carry user information (B-channels) and
>> 1 channel is used for signalling. With ESF you can employ bit-robbing
>> to exchange signalling information, but for ISDN use you have to
>> disable that option.
>>
>> -Stefan
So if I understand correctly, in North America, when we have an ISDN PRI
line, it uses the ESF framing and (i guess) CRC but does not use the ABCD
signaling bits? It would make sense since otherwise I do not see how we
could get 64K clear channel.
Is is also possible to have a PRI with D4 type framing (no signaling)?
Thanks
Gregory Boop
Gaetan Boucher wrote:
> ste...@eda2.racal.com (Stefan Doll) wrote:
> >> gbou...@presticom.ca wrote:
> >>
> >> >I have seen a few messages in this newgroup's archive mentioning that an
> >> >ISDN PRI line may have ESF on it. I do not see why that would be
> >> >necessary since the D-Channel takes care of the signaling. Are there
> >> >case where ESF is used on ISDN PRI lines?
> >>
> >> Hi Gaetan ,
> >>
> >> It's roughly the other way round. To implement 23B+D ISDN you can use
> >> ESF framers. 23 channels will carry user information (B-channels) and
> >> 1 channel is used for signalling. With ESF you can employ bit-robbing
> >> to exchange signalling information, but for ISDN use you have to
> >> disable that option.
> >>
> >> -Stefan
>
> So if I understand correctly, in North America, when we have an ISDN PRI
> line, it uses the ESF framing and (i guess) CRC but does not use the ABCD
> signaling bits? It would make sense since otherwise I do not see how we
> could get 64K clear channel.
>
> Is is also possible to have a PRI with D4 type framing (no signaling)?
Yes, it is. But practically this is never done. Usually when utilizing D4
SuperFrame
framing the link is set up for AMI (D7) zero substitution rather than B8ZS. The
AMI
substitution does not work very well for data because it forces bits to one
rather
than using a replacement algorithm (like B8ZS). This, of course, would mess up
the PRI signalling channel located (normally) in timeslot 24.
You can configure some equipment to use D4 framing and B8ZS zero substitution.
(Is it found in the field this way...No).
- Greg
>
>
> Thanks
> Gaetan Boucher
> ACT/Presticom
>
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John Agosta
Gaetan Boucher wrote:
>
>
> So if I understand correctly, in North America, when we have an ISDN PRI
> line, it uses the ESF framing and (i guess) CRC but does not use the ABCD
> signaling bits? It would make sense since otherwise I do not see how we
> could get 64K clear channel.
>
> Is is also possible to have a PRI with D4 type framing (no signaling)?
Really, PRI services can be accessed by any type of DS1 facility, ESF or
SF/D4 framed.
All signaling on PRI is 'message oriented' and carried by a D channel in
the 24th timeslot.
ESF is the reccomended way to frame the physical transport facility, but
when an
ESF facility is not available, other types - such as an SF/D4 can be
used.
The physical framing type is not related to the D channel; they are
seperate considerations.
Hope this helps.
-ja