You are correct in regards to what SS7 is and does, although you can lose the "meta meta" in your description.
What I was inquiring about was Gus' comment about a PRI treated as "route" on a 5E.
I'm also trying to find out what types of SS7/AIN features may be available over a PRI D channel. For instance, message waiting indication (MWI) signals are sent interoffice over SS7. Could one formulate a packet that's sent over a PRI D channel that would end up in a remote switch via SS7?
Brad
Ray Burkholder wrote:
From what I've heard and learned, SS7 appears to be a meta meta signallingprotocol.
First we had analog lines. Then ATT started grouping 24 analog lines to form a T1. Inband signalling was used in each channel. Time studies indicate that these channels can be more effectively used if the signalling (ringing, busy, etc) is removed out of each channel and put into a common data channel, or D Channel as they call it in ISDN parlance. So for a North American PRI line, a T1 with 24 channels is sectioned off into a 1 D channel, which is used for signalling, and 23 B channels (bearer channels) which are used strictly for voice traffic. So ISDN/PRI lines use meta signalling to control the voice channels.
SS7 is strictly a signalling and control protocol. It carries no voice traffic, but controls how voice is routed between locations. For instance, some one picks up the telephone and dials a number across the country. The local telco switch signals the telco switch at the other end to ring the destination phone. This signalling is handled by SS7. If the destination party picks up, it is at that moment when the the source telco and the destination telco open up a voice circuit and connect the two parties. If the destination party does not pick up, and the source party hangs up, no voice channels have been opened up, and the telco enjoys a cost saving by not having to dedicate a resource to the conversation, such as like back in the good old days of RBS (Robbed Bit Signalling) T1's.
SS7 also handles the CLASS series of value-add signalling services. SS7 is therefore useful for handling the signalling on large channel volumes (loosing a B channel to a D channel in a PRI for every 24 channels is expensive overhead), and is good for geographically distributed dialling plans.
So, to wrap up, SS7 is a meta meta signalling protocol. It controls the signals going down a PRI which signals the PBX on what it needs to do with the call.
If any others on this list can contribute their thoughts and experiences, it would be greatly appreciated.
Regards, Ray Burkholder http://www.oneunified.net 704.576.5101
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