Will SIP Federation Services Get Bypassed with Cisco's IME?

By Doug Mohney, Contributing Editor

For a variety of reasons, service providers have dragged their feet on providing full-up SIP connectivity among themselves to provide seamless HD voice and video and other rich media services -- not that anyone is clamoring for ubiquious rich media services, mind you, but that's a story for another day.

Enterprises have gotten tired of waiting for service providers to start wholesale mapping of phone numbers into IP-based ENUM directories and establishing peering/federation relationships, so Cisco (News - Alert) has jumped into the void with the development of the Intercompany Media Engine (IME) to start independently linking together SIP islands together in a peer-to-peer fashion without having to pay a provider for the 'service' of setting up and managing the relationship.

Cisco Distinguished Engineer Cullen Jennings (News - Alert) describes the IME as 'provisioning a virtual SIP trunk' to enable two companies to directly exchange SIP traffic without an intermediary -- so that can be vanilla VoIP to directly bypass the PSTN, billable minutes and long distance charges or (my favorite, of course) HD voice traffic or video traffic.

But I'm getting ahead of myself. The best way to describe what the IME does is to walk through how a configuration/installation would occur for an enterprise (With apologies to Cisco if I get a step wrong!).

Step one would be to size and buy an IME box or boxes. The IME serves as a manager/number publisher of SIP-enabled devices -- VoIP phones, desktop video devices, potential telepresence suites -- within the enterprise, with the entry-level device able to hold up to 10,000 phone numbers for devices and the larger one to hold up to 40,000 phone numbers. If you have more than 10,000 or 40,000 phones per installation, it is likely you have more than one IP PBX (News - Alert) servicing the location, so you end up buying multiple boxes and scaling accordingly.

Generation one of the IME uses IETF-proposed standards, but only works 'just with [Cisco] Call Manager and Session Manager' at this point in time, said Cullen.  Other vendors are looking at implementing the various IETF draft protocols in their own solutions to enable communication from their IP PBXes to the IME, but when/if that happens is an open question.

Once the IME box(es) arrive, the system manager needs to configure them by loading in phone numbers and the capabilities of the devices each phone number is associated with, as well as various access lists as to what sort of SIP traffic to allow. For security and management reasons, a business many want to only enable a select number of devices full-blown SIP connectivity with other businesses; for example,  so everyone might be able to get VoIP and HD voice on the desktop, but only managers and conference rooms might have desktop video enabled.

Configured, the IME is turned on and 'publishes' its list of phone number to a virtual distributed hash table (DHT) run on a peer-to-peer basis  among all the IMEs around the world. Cisco says that the DHT should be able to handle up to 10 billion phone numbers.

The fun begins when IME-using company A and company B make a phone call between the two of them. The first phone call is routed through the PSTN and after the call is completed, a call agent looks at the number at some point and does a lookup to see if the called number can be routed over IP, referencing the number against the DHT. If it can, then the calling IME looks up the ID of the called IME and the two then go through a 'shared secret' validation process using the details of the call (call length, start time, stop time, and caller ID).

If validation works out, then the two boxes share information, including a cryptographic 'ticket,' to set up a virtual SIP trunk to route future calls directly over the internet, rather than defaulting to the PSTN; the crypto ticket is supplied to prevent spam and denial-of-service (DoS) attacks.

Yes, there's a lot of juggling (i.e. processing) going on to make this happen in a relatively secure without the need of a service provider putting their fingers into the process. But there are numerous advantages to the IME -- and some arguable disadvantages as well. More on those in another column.

(source: http://next-generation-communications.tmcnet.com/topics/nextgen-voice/articles/81385-will-sip-federation-services-get-bypassed-with-ciscos.htm)