[asterisk-ss7] KNK SS7-27 - first experiences - part 1

Pavel Troller patrol at sinus.cz
Tue Jun 25 12:51:11 CDT 2013

Hi Nick!

> Hello Gentlemen,
> I find this post very interesting. I have set up many traditional T1s
> with my father here in Canada (I am 17), and looking to experiment
> with SS7 signaling. I have been reading up on it quite a bit and have
> some questions. I see you guys are using T1 cards for the
> interconnect. Is this after the link has been muxed? Or is the
> signaling coming in on T1/E1s? Sorry if this is a stupid question.

There are no stupid questions :-), there are just stupid people, which
judge the other's questions :-).
  I think that there is no simple answer to your question. It may depend
on many circumstances, like the network topology, internal traditions and
rules in different countries etc.
  In such a simple setup as this one discussed, the signaling links are
obviously occupying one of the timeslots in one of the bearers (we use
E1s in Europe). So, for example, the case discussed here uses 8 E1s between
Asterisk and the other switch (EWSD), i.e. 8x31 timeslots, and the first
timeslot on the first E1 (which would have CIC 1) is used for signaling
link. In the case of more signalink links in the linkset, the second one
would occupy the first timeslot in the second E1 etc. However, there are
countries which prefer TS 16 instead of TS1. And some carriers have strict
SS7 routing rules and direct links between switches are forbidden - in
such a case the links must be connected to the STP(s), which require to
drop/insert them out of the E1 stream using some muxing equipment.

> More specifically is the SS7 interconnect with the CO done using
> grouped PRI trunks mapped in a T&E1/3 transport layer. Or A-Links,
> STM-1.....

Again, you can find almost all theoretically working solutions being
used all around the world.

> I really want to experiment with an interconnect using the SS7
> signaling to help bring to light what I have been studying. What is
> the minimum I would need to ask a service provider for in terms of
> service (i.e., T1 with SS7 signaling?), and hardware.

I would recommend you to start in your own lab - run two Asterisk boxes,
buy two cheapest T1 cards on Ebay, interconnect the boxes (don't
forget to properly synchronize one from the other) and setup your 
first signalling link. Then, ask somewhere to get interconnect rules
used in Canada. You will probably have to apply for a national SPC to be
able to interconnect with another carrier, but it's possible that there
are carriers which will give you their internal SPC for this purpose.
In Czech Republic, we are using Network Indicator (NI) of 10 for
internal, uncoordinated operator networks, while NI 11 is reserved for
so called "Interconnect network", where you have to apply for the SPC.
And in Poland, they have the same principle, but the NIs are reversed -
11 is for the uncoordinated internal networks and 10 is for the
coordinated national network.

> Last question I promise!!! It seems that this setup
> Asterisk+lib_ss7+digium cards act as a media gateway? This is really
> cool once stable!

You can use it in many scenarios, for example as a Class 5 switch with
Class 4 interconnect to some carrier and operate this setup as a CLEC,
but yes, my particular application is working as a media gateway for
500 simultaneous calls between SIP/H.323 and SS7.

> Kind Regards,
> Nick.

If you have more questions, feel free to mail me privately, to avoid spamming
the mailing list.

With regards,

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