Clearwire and Sprint both have voice-ovr-IP plans for WiMAX -- but they aren't the only ones

Clearwire and Sprint's upcoming WiMAX launches are promising wireless broadband connectivity, but there's another service available in the mix that the two companies aren't so vocal about: voice. WiMAX has the capacity and low latency necessary to support voice-over-IP services, and although there have been no announcements of a voice service, both companies are setting the stage for VoIP rollouts.

“VoIP is going to be a very key feature in WiMAX,” said Lars Johnsson, vice president of business development for Beceem Communications, which designs the subscriber chipsets going into many WiMAX devices. “We see a strong customer interest in VoIP from both [original equipment manufacturers] and [original design manufacturers] as well as operators. They don't think broadband as a stand-alone service is enough.”

The wireless home gateways made by vendor partners Motorola and ZyXEL both sport analog-to-digital phone ports, making them VoIP-ready. The question is whether those VoIP services will come from the operators or from third-party providers. Clearwire already offers VoIP over its proprietary broadband access network, and as it rolls out mobile WiMAX, it's likely to extend the service. Clearwire and Nortel Networks last week announced a VoIP services deal, which Nortel said would lay the groundwork for transitioning VoIP to a mobile network. The end result could be a residential voice service that customers can take anywhere.

Sprint is a different story. While its initial launch likely will focus on residential broadband service, it ultimately plans for its Xohm network to be a wide-area mobile network, focusing on portable data-centric devices. So along with the digital cameras, music players and laptops that Sprint will welcome onto the network, it also can expect VoIP services from Skype and Vonage — and possibly even specific devices such as the VoIP phone Skype launched in Europe. However, Sprint does intend to offer a commercial VoIP service by the end of the year for residential customers.

“We're looking at VoIP as another application on the network,” said Ali Tabassi, vice president of technology development for Sprint. Just as Sprint won't be regulating what sites a subscriber can visit or what content he or she can download, Tabassi said, Sprint won't prevent customers from bringing an outside VoIP service to Xohm.

But Tabassi added that Sprint's service will set itself apart from the rest simply by accessing WiMAX's quality-of-service capabilities. “If someone wants to offer their own WiMAX device over our network, that's fine,” he said, “but because of quality of service, we can prioritize our own VoIP traffic.”

Sprint VoIP packets would contain different header classifications that the network's media access control layer would identify to push the packets ahead of third-party VoIP traffic, thus ensuring better voice quality and network availability for Sprint's service. The advantages of this could be considerable because WiMAX offers shared access with capacity being allotted to multiple users in a single sector.

However, the benefits of that prioritization may be more theoretical than actual, Johnsson said. Most problems associated with VoIP in the wireline world are not access problems but backhaul problems. “It doesn't matter if you have 4 Mb/s from your home to your DSLAM if you only have a lousy T-1 backhauling to the network,” Johnsson said.

There always will be network bottlenecks, whether in the access or backhaul sections, and the huge channels of WiMAX alleviate many of these on the access side. Sure, there is a chance Sprint's channels could be overloaded, Johnsson said, but that would require an awful lot of subscribers on the network. “That,” he said, “is a good problem to have.”