[afnog] VoIP

[Sunday A Folayan]

At 08:37 AM 7/27/2005, Bill Woodcock wrote:
>     > Please look at the Visio or JPEG and advise accordingly!
>     > How can I achieve ability to call PSTN, GSM and also international 
> from the
>     > IP network, i.e. A to be able to call B, C or D!
>
>To summarize in ASCII (and please tell me if I've misunderstood):
>
>You have a Cisco Skinny network (7900 phones running against a legacy Call
>Manager back-end instead of a SIP back-end), with a Skinny-to-FXO gateway
>interconnecting the Skinny network to an Ericsson PBX.  You have tried
>both analog and ISDN FXO ports.
>
>The Ericsson PBX has both analog and digital proprietary Ericsson
>station sets on it, as well as some sort of dial-out to your GSM network,
>and some sort of gateway to an international voice minutes wholesaler.
>
>The entire Ericsson PBX-to-GSM and PBX-to-international part works fine,
>and the Ericsson extensions can call each other, and the Skinny devices
>can call each other.
>
>What's not working is the FXO gateway between the Skinny network and
>everything else.
>
>We presume that if the Skinny phones were able to reach anything on the
>Ericsson PBX, they'd be able to reach everything on the PBX, and the
>problem would be solved.
>
>So this may be stating the obvious, but that would lead me to look really
>closely at the interface between the Ericsson PBX and the Skinny Call
>Manager.  Am I interpreting your diagram correctly, that you've tried both
>analog and ISDN BRI FXO interfaces on the 1760?  (Both Cisco part VIC-2FXO
>or VIC2-2FXO and Cisco part VIC-2BRI-NT/TE or VIC2-2BRI-NT/TE.)
>
>Have you tried an E&M (Ear & Mouth or Earth & Metal, the ill-defined
>inter-PBX trunking "standard") interface between the 1760 and the
>Ericsson?  The Ericsson line card will be a more expensive one than an
>extension line card, or will have fewer ports, but it will be designed
>expressly for this purpose.  Which isn't to say that it can be made to
>work easily, E&M interfaces are notoriously difficult to configure
>(different ways of passing caller-ID, different ways of sharing ground
>between the devices, different pinouts, et cetera), but at least it's an
>interface that Ericsson _knows_ is supposed to talk to another
>non-Ericsson PBX device, and will give you support for that purpose,
>however mediocre it may be.
>
>Ideally, the handoff between the Ericsson and the Skinny gateway would be
>digital (i.e. ISDN), so that there won't be any loss in voice quality, and
>so that signalling like dialed-digits and caller-ID will be passed
>cleanly, out-of-band of the voice portion of the call.  Is the interface
>that you're plugging into on the Ericsson side actually specifically ISDN,
>and if so, is it the correct "flavor" of ISDN, intended to talk to a
>station device, and is the 1760 set to match the Ericsson's "switch type?"
>(See
>http://www.cisco.com/en/US/products/sw/iosswrel/ps5013/products_feature_guide09186a0080080de8.html#62113
>for a list of the switch types and their corresponding configuration
>keywords.)
>
>Have you checked to make sure that the version of IOS you're running on
>the 1760 fully supports the VIC?  Take a look at the table at
>http://www.cisco.com/en/US/tech/tk652/tk653/technologies_tech_note09186a0080111b16.shtml#ps
>to be sure.
>
>Have you turned on debugging on the Cisco when you've tried to pass calls
>through it, and checked for any error messages?
>
>A useful debugging tool in situations like this is to also have an FXS
>card on the gateway, so you can plug in a simple desk-set for debugging
>purposes.  That would allow you to verify call-completion in both
>directions from the gateway, so you could be absolutely sure which side
>the problem is on, and at least simplify it considerably.  It would be
>unfortunate to put a lot of work into debugging the Ericsson connection,
>only to find out that you had a simple configuration error between the
>gateway and the Skinny Call Manager, for instance.
>
>All of this is in answer to your short-term question, which is, I presume,
>what you're looking for.  In the long term, you probably want to download
>a SIP standards-based software load into the 7900 phones, get rid of the
>Call Manager and the gateway, and have everything talk to everything via
>SIP, as God and the IETF intended.  That would get rid of the long chain
>of devices which you're currently stymied by trying to pass calls through,
>and make everything much simpler and more reliable.  Which is what you
>want, as a service provider.
>
>Good luck.  I hope something above proves helpful.
>
>                                 -Bill

Bill,

I am not sure of what he means by "analog or isdn extensions". To me, seems 
the task is to trim the fat :-) He can make it simpler by just replacing 
the entire chain from the cisco 1760 Voice gateway with a PC running 
asterisk, with 2FXO cards.  Asterisk supports the cisco skinny protocol. 
Apart from the cost of the PC, the FXO cards cost $15 a piece.

Cheers.

SF.