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 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. Yes, that sounds exactly right to me. There is no connection between the data transmitted on the B and D channels. The D channel data is only used for call control (set up, tear down, etc.). D channel functionality does not include making the B channel reliable. While the call is up, the ISDN network shouldn't care a fig about what is going over the B channel -- its simply a 64 kb/s (or 56, 112, or 128) connection between two endpoints. It certainly doesn't know or care if you are running ppp, hdlc, or grandpa's layer 2 protocol on the b channel. ISDN provides no reliability for the user (properly, the bearer) data. However, the call control (D-channel) combination of q.921 and q.931 is reliable. While its not exactly correct (because there is addressing - the TEIs), if we think of the B channels as layer 1, with no possibility of reliability, I think we won't be too far off. -- Jason Author of Boson's BCMSN1, BSCN2, and BSCI2 and Quizware's CCIE Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=27622&t=27568 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
