The cable industry is studying how ENUM (tElephone Number Mapping) can help keep VoIP calls on cable’s private IP networks and off the PSTN. ENUM is the IP version of the telco-based SS7 (Signaling System 7) a telecommunications protocol used to offload PSTN data traffic congestion onto a wireless or wireline digital broadband network so that one telephone company knows that a number is valid and a call can go through. With ENUM, an IP call initiated by one cable subscriber to another cable subscriber – conceivably even another MSO – would be identified and moved the cable networks without touching the public phone network. Right now when a call is made on a cable system, the information goes to the PSTN where a look-up determines the call’s status and “every time the look-up is done, we pay money to the LECs,” said Steve Craddock, Comcast’s senior vice president for new business development. “There’s extraordinary value to us in doing that for peering and getting the information back without having to pay the LECs,” Craddock says. Secrets and third parties There are also hassles. Phone numbers – and the IP addresses to which they’re attached – are well guarded secrets. The organization that stores and authorizes the numbers would have to be trusted. If cable doesn’t figure a way to do the number storage itself, “it might be a third party, a NeuStar or a VeriSign … somebody that would have a good enough relationship with the LECs that it’s not to interface with them,” Craddock said. NeuStar admits to having conversations with the cable industry and being in good standing in the existing telecom space. “We have very strict policies and procedures about how we operate that. It’s a very necessary evil these days when you have to share information among multiple companies for them to interoperate and that is what NeuStar is in the business of doing,” said Tom McGarry, vice president of technical issues for NeuStar. Sense of urgency ENUM would be an element in what is increasingly becoming a virtual private network among MSOs. “The cable companies are incented to share traffic among themselves and keep it off the public switched network so they don’t give money to their main competitors … the telephone companies,” McGarry said. It is, said Craddock, important to start resolving the issue now. “It’s an extraordinarily high priority for our industry to figure out and figure out soon,” he said. “You really want to do this on your own.” – Jim Barthold

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