[asterisk-ss7] ISUP over IP

Paul Timmins paul at timmins.net
Sat Jul 3 15:01:39 CDT 2010

Krzysztof Drewicz wrote:
> 2010/7/3 Paul Timmins <paul at timmins.net <mailto:paul at timmins.net>>
>     There's a reason that it hasn't taken the world by storm. Let's
>     make our
>     voice network needlessly dependent on our data network so we can save
>     ourselves a few 56k links to the telco in exchange for IP links to the
>     telco, right?
> Yeap. But still you could use a 56k ( U r from USA?) or 64k for PPP 
> connection and have a IP over a 56k/64k channel :)
> So you could have some more things on this PPP connection than just a 
> ss7 signaling (like critical DNS traffic or accouting over a network 
> of PBXes, or sms exchange or VM connectivity like the IIRC 'VPIM' 
> protocol to send some VM messages by IP very old but could still be in 
> use).
No you couldn't. The 56k link uses FISUs when there's nothing to say, so 
when you throw in IP and PPP overhead you won't even be able to align 
your link.

But no, I don't want my data network to engage in fate sharing with my 
voice network. There's no such thing as critical DNS traffic when you 
compare it to how critical a IAM is, especially if it's for something 
like an E911 call.

> If you see voice network as a whole: there is a SMS service. How 
> should SMS go from one smscenter to another? on some SS7 signaling (so 
> license for your SS7 exchange should be bought in 99% vendors cases) 
> or just put it on extra IP that is avalible on this 56/64 kbps ?
That adds even more overhead.

On Asterisk , SS7 is free. On my "real" switch, it was such a small part 
of the cost they don't itemize it.

So why try to add complexity to a network critical part of your network? 
Without those two 56k links, my network, connecting to several tandems 
on the DS3 level (obviously not with asterisk) is dead in the water.

My SS7 is built into my DC powered switch. The links go straight from my 
switch to the ILEC's STPs. Adding IP in that would let me put it over my 
AC powered data network, and then pass it off onto random other carriers 
in order to get to likely the same place on the ILEC's network. And as 
long as my upstream providers aren't idiots, or there's some BGP 
convergence issue, or there's not a DDoS on my data network, it will 
likely work fine. But never as well as the two T1s going to two 
geographically different locations on the ILEC's network.

So what's the argument for SS7 over IP again?


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