[cisco-nas] SS7 signalling vs ISDN

[Pierre Nepveu]

Lewis,

The difference between PRI and CAS is in where the signaling occurs : PRI (and
BRI, for that matter) use OOB (out-of-band) signaling. That is what the D
channel is for. When a call come in, the originating equipment will tell the
other side "I have a call for you on channel x". And, since this kind of info
circulates on a dedicated channel, it can also occur during the call. CAS's
signaling is in-band, like for the phone in your home.

The difference between PRI and SS7 is the kind of signaling that occurs. SS7 is
the signaling network for telcos. Like ISDN, inter-telco signaling is OOB.
However, SS7 links carry only signaling. And signaling is not solely related to
call passing. LNP (Line Number Portability) transactions occur on this kind of
link. You may think of ISDN as an IGP and SS7 as an EGP. ISDN is for processing
calls between the telco and the customer. SS7 is for processing signaling,
generally between telcos. 

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Le 2004-12-15 à 21:12, Lewis Watson a écrit:

LW> > The monthly cost of SS7 Trunks are usually cheaper then ISDN trunks 
LW> > and SS7 trunks can carry more information about the calls.
LW> > (Such as Payphone identifier or Number of Satellite hops for the call)
LW> > Darryl Sladden
LW> 
LW> 
LW> Hi Darryl,
LW> This brings a question to mind. What's the difference between a PRI, CAS,  and SS7. I am familiar with the fact the PRI uses the 24th channel for a "D Channel" used for timing on the other 23 B channels and that the CAS gives all 24 lines for usage and uses 8 bits per line for timing. hence  referred to as "RBS". So where does the SS7 fit in with those?
LW> 
LW> Thank you,
LW> Lewis
LW> 
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