[cisco-voip] SP VoIP edge options: SIP trunks vs PRIs

[Justin Shore]

I'd like to get everyone's thoughts on whether to hand voice customers 
SIP trunks or PRIs.  We're beginning to offer voice service in a new 
area that's heavily populated with businesses.  Besides selling Internet 
and ELAN-type services, we're also going to be selling a new voice 
service.  We're selling a basic turnkey VoIP system to the smaller shops 
that registers back to our MetaSwitches.  Our initial plan for bigger 
customers or those with existing PBXs or key systems was to use IADs to 
hand off either FXS lines or PRIs as needed.  Now the question has been 
raised as to why we're not handing off SIP trunks directly to the 
customers.  Below is my reasoning for not wanting to do SIP trunks, 
right or wrong.  I'm open to ideas though; I can certainly be looking at 
this from the wrong viewpoint.

While I know the industry is moving towards SIP trunks to the CE, I 
don't think it's really ready for the prime-time at this point.  Every 
vendor has interpreted the assortment of SIP standards differently (and 
some not at all), requiring major interop testing before reliable 
solutions can be signed off on.  Interop testing between CCM and 
MetaSwitch is several revisions behind and the minor revs (with all the 
bug fixes) seldom if ever get tested.  We aren't going to perform a 
MetaSwitch upgrade just because a user upgraded their CCM to an untested 
rev to fix an unrelated issue.

Providing SIP trunks also creates the opportunity for a finger pointing 
game between the customer's network admins and us.  Without a window 
into their network they're on their own for QoS and capacity planning. 
We'll take the blame though if they don't do something right or have 
something broken in their network (core network hub, anyone?).  This is 
a major concern for me.  We manage the small customer's networks in our 
other deployment scenario which lets us ensure proper QoS settings and 
capacity planning just like we do for the SP backbone.  We're at the 
customer's mercy if we entrust them to do it.

And if/when we do run into problems there aren't exactly a lot of 
options for testing a SIP trunk on the customer's side to prove that 
we're not the problem.  We could assume the IP of their gateway with 
some sort of test gateway of our own but that completely takes down 
their phone system.  Whereas with PRIs or FXS lines I can hook up a test 
set and definitively prove line quality right then and there, thus 
ending the blame game.  FXS lines and PRIs bring far fewer interop 
issues to the table as well.  While getting a SIP trunk to work on 
Vendor X's gateway may prove entertaining, getting a FXS line or PRI to 
work usually goes off without a hitch.


Overall FXS lines and PRIs seem to be far superior in terms of ongoing 
support, interoping with other vendors, and minimizing the blame game 
and finger pointing.  The down side is that it adds cost both for us and 
the customer.  So should we be planning on doing SIP trunks to customers 
today?  How would you as a service provider provide voice at the edge if 
you had your choice?  What would you as a customer want the provider to do?

Thanks for your insight
  Justin