[Asterisk-ss7] My Take on the SS7

Matthew Crocker matthew at crocker.com
Fri Aug 26 11:51:42 CDT 2005

SS7 is what a telco uses to interconnect their switches.  SS7 is  
*not* for customer access.   Telcos take SS7 links and generate PRIs  
to customers from their switch.  With SS7 you can establish Inter  
Machine Trunks (IMTs) to carry your voice traffic between your  
switch.  If you are a CLEC trying to connect to the PSTN you would  
use SS7 to link with the ILEC and IMTs to link with the ILEC End  
Office and Access Tandems.   ISDN PRI uses a subset of the SS7 ISUP  
signalling.   SS7 also handles database access for Local Number  
Portability (LNP) and CNAM, LIDB and E-911 ALI information.

A single SS7 link set (2 64K channels) can handle an entire switch  
worth of traffic,  thousands of calls per second.


On Aug 26, 2005, at 12:45 PM, Richard Gintz wrote:

> Can someone give me an example of the cost/feature differences  
> between SS& and
> PRI ISDN?  I just got a PRI line in from XO Communications  
> (Texas).  And how
> much differently would Asterisk configurations be using SS7 vs. PRI?
> Thanks
>>> To me the reason I'd really like SS7 over PRI ISDN is that I would
>>> really like to get the CPC data on incoming calls which PRI
>>> ISDN cannot
>>> do and thats it in total.
>> I am not sure what _I_ would do with the CPC information in my  
>> case.  It may
>> be good to know where the call came from so that I can setup more  
>> cost
>> effective route in the future but Caller ID (number) seems good  
>> enough to
>> start. So simply converting the SS7 message to a PRI should be  
>> good enough.
>> If I can pass the caller ID information down to the Voip  
>> Subscribers that
>> would be the only reason I need it.
>> What do _you_ use the CPC information for?
>>> I think not many people need SS7 - maybe its not big/available in  
>>> the
>>> US?  Also normal businesses will get by fine with PRI ISDN
>>> (they don't  want/need the CPC switch data).
>> It is the primary way to interconnect to the ILEC (at least Qwest  
>> in the
>> Northwest).  The cost of lines controlled by SS7 is only a  
>> fraction of PRIs
>> from Qwest or other providers.
>>> Markku Korpi's driver is not cheap for sure
>> Yes but it is certainly less money than most hardware solutions I  
>> have seen
>> out there. (Markku hasn't gotten back to me yet from my first  
>> email to him
>> so I am not even sure whether I will be able to get it if I want it)
>>> Best of luck!  When you are finished I you might want lots of
>>> money for
>>> your non-opensource SS7 software too! :)
>> I am not a greedy person but of course I wouldn't mind lots of  
>> money (That
>> is why I am in business).  Asterisk has helped us a ton and at  
>> very little
>> cost.  We might be able to give back depending on what it will end up
>> costing.  There is always a consulting / support income  
>> possibility even if
>> it is open sourced.  (I don't want to talk like it is done before  
>> I even
>> start though)
>> _______________________________________________
>> Asterisk-SS7 mailing list
>> Asterisk-SS7 at lists.digium.com
>> http://lists.digium.com/mailman/listinfo/asterisk-ss7
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Matthew S. Crocker
Vice President
Crocker Communications, Inc.
Internet Division
PO BOX 710
Greenfield, MA 01302-0710

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