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 signalling. This is LAPD.
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 the end-user context, corrupted, or whatever, I >would think a higher level protocol would request retans if it was reliable >(TCP) and not ISDN. Theres not even a seq number in q.931, so I would't >think it would know it was missing a frame. Good. That's what I thought. Also, since Q.921 and Q.931 are on the D channel and user traffic is on the B channel, they wouldn't help anyway. Sound right? Just trying to correct a misconception that I have heard about ISDN being reliable. Thanks. Priscilla >""Priscilla Oppenheimer"" wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > 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.) > > > > How about Q.931? Does it only run on the D channel? It seems to deal with > > signalling issues, such as call setup. (Does it have a LAP designation, by > > the way?) > > > > For end-user data, my theory is that ISDN doesn't provide any reliability. > > Is that right? Data on the B channel would typically be encapsulated in >PPP > > which does not offer reliability (ACKs and retransmissions). > > > > I'm trying to synthesize an answer to the silly question about who > > retransmits when a bit is changed or dropped on a WAN network. Here's my > > summarization. Does it look OK? > > > > Technology Provides Reliability? (ACKs and retransmissions) > > ATM No > > BISYNC Yes > > Cisco's HDLC No > > ISDN No, except on the D Channel which uses LAPD > > Frame Relay No > > LAPB Yes > > LAPD, Q.921 Yes > > PPP No > > SDLC Yes > > X.25 Uses LAPB, so Yes > > > > Thanks! > > > > Priscilla > > > > ________________________ > > > > Priscilla Oppenheimer > > http://www.priscilla.com ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=27605&t=27568 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
