[asterisk-ss7] ISUP over IP

Krzysztof Drewicz krzysztofdrewicz at gmail.com
Sat Jul 3 11:45:06 CDT 2010

2010/7/3 Jean Cérien <cerien.jean at gmail.com>

> Thanks
> Sigtran has signalling over IP and media over TDM - then,

Yes, 100% correct.

> you still need a TDM card for your voice - so you still need these
> expensive SS7 cards - or are there TDM cards that are not SS7, and cheaper ?

Digium's 4 port E1 / T1 card is not expensive and it's not SS7-only card.
Look for other vendors cards with SS7 and PRI support, you buy card +
license for SS7, extra license for PRI, for some MFC/R2/CAS signaling etc..
So in other words you buy TDM card that is just a TDM card with lots of
capabilities, today you use it for SS7, tomorrow you have PRI on it. Without
any license upgrade from your vendor.

> Initially, I thought that Sigtran was full ip, which is wrong, but that
> appealed me as a way to avoid the ss7 cards - just one redundant NIC, and as
> you say, unlimited traffic - but I see we still need them ! I am lost

Imagine that: you need to be redundant, so you install 4 servers with 4 E1
ports in each one. You got 16 E1, in 'normal' telco world, you will get at
most 2 signaling links, so TWO of your server would got TDM SS7 signaling,
and TWO other just voice. So 3 of your servers could go down, but not random
3, one of signaling server must be on-line! with sigtran you could imagine
that each server has it's own IP, and you use 'virtual' IP just for sigtran,
so when three servers go down, you don't cross your fingers to have one
'signaling' server up, each server could be 'the one' signaling.

Traffic on TDM is cheaper ! no DSP needed to have IP->TDM and TDM-> IP

And another thing: how you debug your SS7 link? with SS7 signaling on TDM
card to do it 'right way' you need a extra crosover cable to patch the SS7
analyzer (very, very expensive piece of hardware), you need to go where is
your server installed (so server room in closed building etc...) with
sigtran just fire up tcpdump, download your dump over internet and you got
it debugged with wireshark it's cheap and effective ! also, if you send a
.pcap file to any engineer over the world he will understand it !

Note: there are dedicated hardware gateways with SS7 and they got sigtran
internally ! So if you debug ss7 you got a pcap file, and that's good !
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