Thanks for the clarification, this makes it clearer. Eric
----- Original Message ----- From: "Vikram JeetSingh" To: "ericbrouwers" ; Sent: Friday, April 04, 2003 1:28 PM Subject: RE: CAS and CCS - out-of-band and in-band [7:66607] > Yah Eric you mentioned almost all of them rightly, but I would like to > specify the T1 and E1 part a bit > > > First thing T1 uses some bits of each timeslot (6th,12th,18th and 24th bit > of every timeslot and these bits are also known as A,B,C and D bits) and > since these bits are part of the timeslot only, a CAS T1 would be a true > In-band signaling circuit. > > On to E1s, they can be used in both the flavors, but confusion mostly arises > for CAS E1. A CAS E1 though uses A,B,C and D bits but all these bits are > sent in the 16th timeslot, so as per my understanding a CAS E1 should be > termed as out-band signaling circuit. > > Please correct me if I am wrong on this. > > Regards, > Vikram > > -----Original Message----- > From: ericbrouwers [mailto:[EMAIL PROTECTED] > Sent: Friday, April 04, 2003 3:35 PM > To: [EMAIL PROTECTED] > Subject: Re: CAS and CCS - out-of-band and in-band [7:66607] > > > Interesting discussion, > > In-band, out-of-band are very confusing terms when used in digital > telecoms/datacoms. People and books will tell you contradicting things. For > the right definitions you can best refer to ITU or ANSI specs. > > I haven't been involved in classical telecoms for years, but this is my > interpretation: > > With in-band signalling the signalling is conveyed on the same channel > (timeslot, connection, ...) as the voice or data is carried. So for example > pressing digits during a phone call can be considered as in-band signalling > (DTMF signals). Fax and modem calls may also be considered in-band. Early > phone systems also used signalling systems like R2 to control the call > (specific frequencies were used to control the call). > > Out-of-band systems either used specific wires or specific frequencies that > were out of the normal frequency band. I can't remember exactly, I have some > coursebooks somewhere, but I can't find them right now. Anyway, as far as I > know in-band and out-of-band originate from the old analog telecoms world, > and may be ambiguous when applied to the digital world. > > Nowadays, if you really want to classify digital signalling is in-band or > out-of-band, I would say the following: out-of band signalling is signalling > that is transported over a different channel (timeslot, connection, ...) > than the data or voice. So for example: > - ISDN BRI and PRI both have a dedicated signalling channel (the D-channel), > so it's out-of-band. > - In the European PSTN and GSM networks there are dedicated signalling links > for voice trunks. The call setup is controlled by common signalling > channels, hence the name common channel signalling. Signalling system number > 7 (SS7), also called common channel signalling system number 7 (CCS7) is an > out-of-band signalling system, since the signalling is not conveyed in the > same channel as the voice (or data). Note that the signalling channels can > be implemented in different ways: the signalling channel can be part of the > same E1 trunk (for instance timeslot 16 or any other timeslot except 0 !!!) > that carries the voice, this is called associated signalling; the signalling > channel can also be in a timeslot of an E1 different to the E1 that carries > the voice. The latter is called quasi-associated signalling: there are > dedicated redundant signalling links that do not follow the same path as the > voice trunks, only the begin- and end-points of the voice and signalling > paths are the same...confusing, isn't it? > > ISDN BRI and PRI use the same concept as SS7: multiple voice or data calls > are controlled by one signalling channel, which makes them common channel > signalling and out-of-band. > > Channel-associated signaling is very confusing to me. $%^*!* where are those > course books??? Hmm, let's use this definition from Cisco: > > "...Channel associated signaling: The transmission of signaling information > within the voice channel...." > > So that seems to imply that all in-band signalling is also CAS signalling, > which makes sense to me. > > So what about X.25? Initial call setup and data follow the same path: so > CAS. Would you classify it is in-band??? > > So what about E1s and T1?? You can't just classify a standalone E1 as one or > the other. In my opinion it depends on the application, the signalling > system and the scope of reference. When you make a call to certain > international locations, you may still hear some old signalling along the > path, caused by inband CAS systems. A channelized E1 that carries voice or > data calls is normally controlled by a common channel signalling system. > However, maybe I shouldn't mention this, since it is too confusing: an E1 > can also be classified as CAS, when you allocate a 2kbps signalling channel > to each 64kbps channel....32*2 = 64 kbps, isn't it? And what about timeslot > 0, it's always present and it is used to convey information...we should > classify this as CAS, shouldn't we? You see very confusing. It really > depends on your definitions and scope. > > I'm not familiar with T1s, I always ignored them, because we don't use them > here in Europe. T1s seem to have 24 timeslots: 24 * 64 = 1536 kbps. T1s > don't seem to have a dedicated timeslot 0, instead framing/sync/O&M is > handled by the remaining 8kbps (1544-1536 kbps) of bandwidth. This is CAS, > just like TS0 in an E1 is CAS. You may classify this CAS as in-band, > although some may debate that, since you're using dedicated bits in the > multiframe structure for CAS, just like an E1 is using certain bits in the > multiframe structure as TS0 and most people will classify this TS0 as > out-of-band... So both in T1s and E1s bits are robbed from the T1/E1 > bandwidth. If a voice timeslot in a T1 is really 64kbps (and not 56 kbps as > some say ....) , if I had to classify it, I would classify it as out-of-band > a well, since you're not stealing bits from the individual voice channel, > but from the T1 trunk.....Aarghh...We should ask a PCM E1/T1 guru!!! > > However, your ISDN PRI is 23 B + D, and this D-channel again is CCS (and > out-of-band) ! I also assume that the voice trunks in your PSTN/GSM/PCS > networks use dedicated SS7 signalling links, again CCS, out-of-band. > > Hope this helps? > > Eric Brouwers > > > ----- Original Message ----- > From: "Priscilla Oppenheimer" > To: > Sent: Tuesday, April 01, 2003 7:43 PM > Subject: RE: CAS and CCS - out-of-band and in-band [7:66607] > > > > alaerte Vidali wrote: > > > > > > The URL following states: > > > > Alas, the URL didn't get posted. If it's CVOICE materials, be wary. They > > munged this topic. > > > > > > > > "Channel-associated signaling, which uses E1 time slot 16 (the > > > D channel) for signaling, fits into the out-of-band signaling > > > category." > > > > Cisco and other documents consider the use of E1 time slot 16 to be > > out-of-band signaling because it's an entire channel used for signaling > > instead of using bits that are in-band with the data bits. > > > > It could be CAS or it could be CCS. Channel-Associated Signaling (CAS) > means > > that the channel is structured in such a way that each data channel can > use > > some bits for its signaling. > > > > Common Channel Signaling means that the signaling channel is unstructured > > and could be used by any data channel that currently needs it. That may be > a > > gross over-simplification. Someone can correct me if I'm confused. > > > > It's weird that they threw ISDN into the statement (by saying the D > channel > > in parentheses.) ISDN PRI uses CCS, doesn't it? I guess I'm not sure about > > that. I've seen that it does, but that might have been the CVOICE class, > > which really did munge this topic. > > > > > > > > "Robbed-bit signaling, which uses bits from specified frames in > > > the user data channel for signaling, fits into the in-band > > > signaling category." > > > > > > Robbed-bit is used in T1-CAS. > > > > That sounds right. The robbed-bit signaling used on T1s is considered both > > in-band and CAS, according to most documents... > > > > > > > > So I can say E1-CAS is classified in out-of-band signaling and > > > T1-CAS is classified in in-band signaling. > > > > > > Is that right? > > > > Sounds right to me. > > > > Priscilla > > > > > I have seen questions stating that CAS is just > > > one thing, in-band signaling. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=66911&t=66607 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
