Quoting Jaap Winius <[email protected]>: Being both impatient and charitable, I'll try answering this myself:
> "ISDN uses LAPD for the D-channel and LAPB for data connections over > the B-channels. However, LAPB is irrelevant for Asterisk, because when > the B-channels are used for voice they carry no signaling. This is why > it is necessary to specify a line code protocol, such as AMI, for the > B-channels, and a frame type, typically CCS, for the D-channel." > > Would that statement be correct? Basically, although the last line is a little muddled. > Also, would someone care to elaborate on how the CCS protocol fits into > this picture, in particular how it relates to LAPD? LAPD, described in ITU-T recommendations Q.920 and Q.921, is an OSI network layer 2 protocol, while CCS (Common Channel Signaling), which is described by Q.930 (I.450) and Q.931 (I.451), is layer 3. Two things that I found confusing here are: 1.) The documentation that explains the Zaptel span configuration statement (in /etc/zaptel.conf) describes the D-channel signaling type as "framing," which I find misleading. IMO "signaling" would have been more accurate. 2.) CCS is a connection control signaling type. The problem is that there is more than one CCS type, although my impression is that the one used most often for the ISDN D-channel is Q.930/Q.931. The others I've heard of are QSIG CCS (Q.931/Q.933) and SS7 (Q.700-series with many variants). Cheers, Jaap -- _____________________________________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- New to Asterisk? Join us for a live introductory webinar every Thurs: http://www.asterisk.org/hello asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
