Some troubleshooting books (like CIT) make a big deal about the reliability
and connection-oriented nature of ISDN which got me thinking...
Q.921 is definitely reliable and connection-oriented (looks just like LLC2,
in fact), but it only runs on the D channel, right? (It's also known as
LAPD.)
q.921 is D channel, but is like a layer two protocol in that it just cares
about addressing on the wire beteen the equip and the swich.
q.931 is only run on D channel. Q.931 is part of Q.SIG, the telecom
standard signalling. This is LAPD.
If an ISDN packet is lost in the end-user context, corr
Thanks, see comments in line.
At 04:31 PM 11/28/01, VoIP Guy wrote:
>q.921 is D channel, but is like a layer two protocol in that it just cares
>about addressing on the wire beteen the equip and the swich.
>
>q.931 is only run on D channel. Q.931 is part of Q.SIG, the telecom
>standard signallin
Priscilla Oppenheimer wrote:
>
> Q.921 is LAPD, isn't it?. Q.921 (LAPD) carries Q.931 info which is one
> layer up. Q.921 also does its own thing with TEI assignments, etc. It is
> reliable and connection-oriented and does include sequence numbers, etc.
>
>
>>If an ISDN packet is lost in th
I sent this to Priscilla on the topic and she suggested that the group
might benefit from my response, so here it is.
Priscilla,
I think that you may find it helpful to separate end - to - end data
transfer from signalling.
Very few L2 protocols offer error correction. The modern approach is to
I was wrong.
I looked it up last night and there is a seq. number in the control field of
LAPB, HDLC, and LABD. Both, the sending and receiving stations must keep
the same seq. numbers when transmitting, but I cannot find anything on
retransmission at that layer. But I asked an old IBM guy I us
VoIP Guy,
You weren't wrong! You said that Q.931 doesn't have sequence numbers, which
is true. Q.931 is not LAPD, however
LAPD (Q.921) does have sequence numbers. It looks just like LAPB, LLC2,
SDLC, etc. Each side has its own sequencing. They don't have to agree. Each
side also tells the oth
>"VoIP Guy" wrote, I was wrong.
>
>I looked it up last night and there is a seq. number in the control field of
>LAPB, HDLC, and LABD.
No problem with LAPB and LAPD, which are proper subsets of full HDLC.
Again, full HDLC is more of an architecture -- I've never known
ANYONE to implement ever
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