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, 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. ""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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=27577&t=27568 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
