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 session initiation protocol (SIP)-based services. That’s fine, according to experts in the field, but be forewarned that SIP alone probably won’t be able to provide the quality of service (QoS) 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 also 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 says Net2Phone’s SIP offerings provide advanced features such as online 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. Net2Phone’s virtual phone number feature was one of the advanced features that sold Northland Cable Television on the company’s solution, according to Northland SVP Jack Dyste. Based in Seattle, WA, Northland has launched VoIP service in Clemson, SC; Highland, NC, and Corsicana, TX. The company is rolling out VoiceLine, a SIP-based system by Net2Phone. Opting for a turnkey solution allowed the company to launch quickly with low startup costs, according to Dyste. "We were able to launch in our smaller markets with no headend costs," he says. "Capital costs under this platform are strictly limited to multimedia terminal adapters (MTAs)," Dyste says. "We went into trials with Net2Phone last August and finished on Feb. 1." Tradeoffs and flexibility
Arris is another vendor that offers both technologies, although it reports many customers opting for PacketCable because of its QoS guarantees and record-keeping capabilities. "We think there are some benefits associated with PacketCable," says Gordon Thompson, director of software development at Arris. "It’s a little more mature than most SIP implementations." 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. (See related story on page 14.) "PacketCable 1.0 and 1.5 describe a complete end-to-end architecture for offering primary line voice services-LEC (local exchange carrier)-equivalent services," says 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 PacketCable depends largely on existing network capabilities and the expected future demands of customers.
-Art Cole Integrates Specs, Improves Maintenance & Adds ITU Standard CableLabs, which has gradually added functionality to PacketCable since its introduction in 1999, has moved to consolidate the various iterations of into one document. PacketCable 1.5’s "reversioning," according to Ed Miller, CableLabs vice president for advanced network systems, integrates PacketCable 1.0, which sets forth the baseline architecture; PacketCable 1.1, which focused on primary line telephony capacity; and PacketCable 1.2, which focuses on enabling MSOs to exchange traffic between zones and networks across IP links. It also includes a minor release, PacketCable 1.3, which added call management server (CMS) subscriber provisioning capabilities. It does not include PacketCable Multimedia (PCMM), however. "It really makes the specification maintenance process a little easier," Miller says. "It aligns the PacketCable spec versioning approach with that of other projects at CableLabs, such as DOCSIS (Data Over Cable Service Interface Specification)." The big payoff will be in the future. "If in the future we decide to add significantly new capabilities or come out with a new release, that new release (by being added to PacketCable 1.5) would include all the prior specs," Miller says. Fixing faxes
PacketCable 1.5 also contains some new specs, Miller says. Earlier versions of PacketCable struggled with faxes because, unlike voice, fax tones can’t be compressed. They also are more sensitive to packet loss. (For more on the fax problem, see Communications Technology, November 2004, p. 12.) PacketCable handles the problem of packet loss by incorporating T.38, an International Telecommunication Union standard, into the protocol. T.38 simply changes the fax tones into Internet protocol (IP) packets at the transmission site and transcodes them back into fax tones at the receiver. "Currently, faxes are encoded and transmitted as ‘voice’ inband," said an emailed statement from Texas Instruments. "If there is increased packet loss on the network or some kind of network issue causing packet loss, digits may not get through or the fax transmission may drop mid-call. With T.38 fax relay, packets are encoded with forward error correction (FEC) or redundant packets to ensure the fax reaches the receiver without error." The benefit of the new approach is that the switch to and from IP happens very close to subscribers, says Sonit Mahey, Cedar Point‘s manager of systems applications engineering. Once the switch detects a fax tone, he says, "the MTA (multimedia terminal adapter) is instructed by the switch to transfer the data stream to T.38. So the pure IP packet stream is largest segment-from the transmitting MTA to the receiving MTA." -Carl Weinschenk