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 PacketCable and SIP: Costs and Speed Influence Choice The PacketCable specification has garnered the lion’s share of attention during the latest rush to present advanced services to customers. But when it comes to getting a foot in the door in the voice market, many operators are finding it quicker and easier to launch SIP-based services. That’s fine, according to experts in the field, but be forewarned that SIP (Session Initiation Protocol) alone probably won’t be able to provide the quality of service and data management capabilities that customers and regulators demand, particularly for a primary line. Because SIP is a signaling protocol, while PacketCable is an entire system architecture covering not only signaling but provisioning, management, codecs and a host of other functions, backers of the two approaches are not competing to dominate the market one way or the other. Vendors do both
“It’s less of a rivalry and more like a religion,” said Mike Pastor, president of Net2Phone Cable Telephony. “There are people who love Unix and people who love Windows. There are good reasons for both.” Most vendors say they are agnostic when it comes to deploying either SIP or PacketCable. Net2Phone, for example, offers both solutions, as well as wireless offerings, but reports that many smaller operators are opting for SIP because it is less expensive and can be put into operation quicker than PacketCable. Pastor claims that its SIP offerings provide advanced features like on-line account management and virtual phone numbers, which allow customers to register their phones under any area code in the country regardless of the physical location of the phone. Callers in Miami, for example, could make a “local” call to a phone in New York that was listed under a Miami exchange. Arris is another vendor that offers both technologies, although it reports many customers opting for PacketCable because of its Quality of Service (QoS) guarantees and record-keeping capabilities. “We think there are some benefits associated with PacketCable,” said Gordon Thompson, director of software development at Arris. “It’s a little more mature than most SIP implementations.” Tradeoffs and flexibility
Because PacketCable is a complete system architecture, it is certainly more costly and time-consuming to implement. However, CableLabs continues to add versatility and functionality to the system, as evidenced by the PacketCable 1.5 spec recently posted on the organization’s web site ( [For a concise update on PacketCable 1.5, see Carl Weinschenk’s feature in the February 22 issue of Pipeline; or visit] “PacketCable 1.0 and 1.5 describe a complete end-to-end architecture for offering primary line voice services – LEC-equivalent services,” said Ed Miller, vice president of advanced network systems. “The SIP protocols address all of the legacy telephony-type capabilities, but it is certainly progressing as well.” As usual with advanced technology, there are no quick and easy answers when it comes to deploying voice services. The choice between SIP and PC depends largely on existing network capabilities and the expected future demands of customers. – Art Cole

The Daily


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