[Asterisk-Users] SS7 signaling/Softswitch

[Brad Waite]

Ray,

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 signalling
> protocol.
> 
> 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