mitzy miroy wrote: > > Can anyone tell me whether the D channel in ISDN uses in-band > or out-of-band signaling? I'm having a heck of a time finding > this. > > Thanks
It's a strangely worded question. You could say that ISDN uses out-of-band signaling and that the signaling is carried on the D channel. The entire D channel is used for signaling in most applications. ISDN Layer 2 signaling is provided by LAPD (Q.921). ISDN Layer 3 signaling is provided by Q.931. Q.921 establishes a connection with the local switch. Q.931 is end-to-end. Both of these run on the D channel. In most applications, the only job of the D channel is to carry signalling. The D channel provides signaling for the 2 B channels when ISDN BRI is used and for the 23 B channels for PRI in the U.S. and 30 B channels for PRI in Europe. The B channels carry user data. So, from the point of view of the B channels, I guess the D channel signaling could be considered out-of-band signaling. It could be compared to the robbed-bit signaling used on T1. In the T1 Superframe format, signaling is placed in the least significant bit position of every DS0 channel in the 6th and 12th frame of every Superframe. With Extended Superframe (ESF), the least significant bits of every channel in the 18th and 24th frame are also borrowed. So, robbed bit signaling could be considered in-band signaling, and in comparison, signaling on a separate D channel could be conisdered out-of-band signaling. But, the D channel doesn't use a different path or require a separate interface, as is the case in somes uses of the term "out-of-band." Priscilla Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=50359&t=50352 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
