North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: IPv6 news

  • From: Andre Oppermann
  • Date: Tue Oct 18 11:53:52 2005

Paul Jakma wrote:
On Tue, 18 Oct 2005, Andre Oppermann wrote:
SS7 over IP is quite popular these days. However call routing != SS7 message routing.
By call-routing you mean the actual circuit switching of each call? I don't mean that, I mean the number routing, which SS7 /does/ do - you referred to it as being more analogous to DNS iirc in operation.
Nope, it's not.  Can you name a phone prefix routing protocol?
Ehm, SS7 ;).

You might call it DNS-like because it's request based, but it still provides routing information.
SS7 is not a routing protocol.  SS7 is a transport stack like what
we refer commonly to as TCP/IP.  There are a number of protocols that
run atop the basic SS7 transport network.  Some protocols are datagram
oriented and some are session oriented.  For call handling ISUP or
derivates are used.  The main difference to the IP world is the limited
scope in the PSTN.  A PSTN switch consults its (static) number routing
table for the trunk to forward the call on.  Then it contacts the switch
at the other end of the tunk and hands over further forwarding to it.
If that doesn't work out the circuit gets shut down backward switch to
switch.  For special numbers like 800 and 900 there is another protocol
called IN (Intelligent Network) which is nothing else than DNS.  Each
special number has a 'real' number in its shadow.  The originating
switch requests the real number through IN and then the normal call
forward happens.  IN may deliver different numbers based on the location
of the orginating switch or daytime or any other criteria you may think
of.  A little bit like Akamai if you wish.

However there is nothing akin BGP or OSPF in the SS7 suite of protocols.
All the forwarding/trunk tables are computed offline for each switch and
then stored on the switches by some bulk data transfer.  Variantions are
emerging with extended IN platforms where you have one more central
databases of forwarding information but that is just a large geographically
distributed switch then.