Cisco Expressway->SIP PSTN Calling

[carlnewton]

Hi All,

I've just been doing some thinking about these technologies, and I wondered if this is possible?

My understanding is that when a call is sent from expressway (Via B2B) using user@domain.com notation, it does a lookup for the SIP SRV Record for that domain. Once it finds it, the SIP invite is then sent to that destination and the connection is established.

In the case of SIP PSTN circuits connected to a Cisco ISR CUBE gateway for regular PSTN Calling, I don't see any reason (technology capability wise) why a connection couldn't be established between that and an expressway cluster.  So long as the SIP SRV is in place for the domain, we shouldn't have an issue getting the invite to the terminating ISR CUBE router.

However I cannot find any information on it.  I'm sure it doesn't work, mainly because service providers wouldn't want to allow this sort of thing as it would detract from their call charge revenue - but I cant see any technological reason for it.

Any comments? Is this a thing or am I going crazy?

[Kevin Roarty · Accepted solution]

Hi Carl,

It's not clear to me what exactly you are trying to accomplish.  There's certainly technology overlap between CUBE and Expressway, but the two products are typically deployed for different use cases. 

Expressway is great for B2B or open video federation, allowing for direct voice/video communication between organizations without the requirement of a pre-existing peering relationship (ie. SIP trunk).  Whereas CUBE typically routes call over  pre-configured peering relationships between service providers and PBX. 

You can create SIP trunks (neighbor zones) on Expressway, but it's not a recommended deployment model to do your PSTN SIP trunking through Expressway.

Does that help?

[carlnewton]

Yes I agree regarding the technology overlap.

Lets say we have mycorp and beecorp.

MYcorp has E1 PSTN lines and a cisco expressway solution enabled for SIP B2B Calling.

Beecorp has a SIP CUBE for PSTN calls.

When someone from Mycorp calls someone from Beecorp via URI (or indeed telephone number), why can't we deliver that to the CUBE and connect the call?

[Janis Buikauskis]

I think the over lap is in capability alone as Kevin mentioned. The missing part is that the connections used for IP Telco will in most cases ride a controlled fiber link to the trunk providers CO, and then travers over SIP/TDM/ETC links through the PSTN.

Looks something like this:

PBX A-------- CUBE/SBC----------IP Telco A----------PSTN---------IP/TDM/POTS Telco B---SIP/TDM/POTS VG---- PBX B

Where as Expressway:

IP PBX A ------ExpressWay ----------(Internet)-----------ExpressWay------IP PBX B

The truth is, PSTN does not run on service records. There are Responsible Organizations that do careful control of the dial plan to ensure smooth operations.

Also, dialing via full URI from traditional phones would be a big hassle.

On the flip side, if you do deal heavily with an organization that also utilizes ExpressWay technology and you already have enough Traversal licenses, then you can take chunks of a dial plan and do the conversion from DN to URI and route via internet. Would work well as long as calls are allowed to have some jitter/loss and you don't expect to Fax anything to that company.