DOCSIS & WiMAX
A match made in IP heaven?
Although DOCSIS is a wired broadband technology and WiMAX enables high-speed via wireless, the two technologies are like kissing cousins in more ways than one.
That technical connection could bode well for cable operators as they mull their options to deliver mobile broadband services or deploy lucrative revenue drivers such as cellular backhaul.
The DOCSIS-WiMAX connection can be traced all the way to the early phases of WiMAX’s creation. As technical development of WiMAX was getting underway more than half a decade ago, many people involved arrived with plenty of ties to cable and broadband, according to Mohammed Shakouri, a WiMAX Forum board member, and vice president of marketing for Alvarion.
“The focus of development and the initial focus of WiMAX was how to build a wireless cable option,” or a high-speed wireless alternative, he says. “The initial MAC used [for WiMAX] was the best of what was available.” In this case, the best available was the MAC used for DOCSIS.
“The DOCSIS MAC is ingrained in the WiMAX standard,” Shakouri notes. “It was done from the ground up to support broadband and video and voice and data.”
If one views the IEEE 802.16 spec, which includes the WiMAX core physical layer and Layer 2, “it looks almost identical to DOCSIS at Layer 2,” says Geoff Devine, chief architect for Cedar Point Communications.
“There’s a lot of good commonality between DOCSIS and WiMAX,” adds Dave Park, vice president of product marketing for BelAir Networks, a maker of WiFi and WiMAX gear, including nodes that can mix and match both technologies. “WiMAX is almost an evolution of the DOCSIS specifications.”
Digging deeper, WiMAX also leverages the DOCSIS 1.1 scheduler, notes Randy Fuller, senior director for alliances and solutions for policy server vendor Camiant Inc.
That means WiMAX also taps into the QoS granularity found in DOCSIS 1.1, and can control who gets to transmit packets and when. Although DOCSIS is a shared network, its QoS elements make it act as if it’s not.
Further out, the 1.5 release of WiMAX, Fuller says, will look and smell a lot like PacketCable Multimedia (PCMM), which can apply QoS to all forms of IP-based apps and services–everything from VoIP, to video telephony, video streaming, online gaming and “turbo buttons.” That version is slated for completion toward the end of 2007 and into 2008. According to Fuller, expectations are that WiMAX radio gear will begin to support the 1.5 release by the second quarter of 2008.
Although cable operators will support some mobile services with cellular 2.5 and 3G platforms, WiMAX is a different animal because it’s fundamentally based on IP technology, a trait shared by DOCSIS.
“I think that’s a key thing...as you look at more interesting applications,” Park says, pointing to services like Skype or the place-shifting capabilities of the Slingbo
“Cable networks today are highly evolved IP networks. WiMAX is basically an IP-based platform.”
“Architecturally, WiMAX mimics what they’re doing with DOCSIS. The applications you build on top...don’t care if they’re talking to a CMTS or a gateway in the WiMAX infrastructure,” says Devine.
Of course, the biggest obstacle in cable’s way is that the industry presently doesn’t own any WiMAX spectrum.
“That’s a key question from our point-of-view,” Shakouri says.
However, one key cable partner–Sprint Nextel–certainly does.
Sprint plans to spend as much as $800 million on WiMAX in 2007, with launches expected first in the Chicago and Washington, D.C. areas, followed by a broader rollout in 2008.
“It’s clear to everyone that MSOs have no choice but to have a high-quality wireless offering,” Devine says. “The only question is how Sprint is going to fit into this.”
Sprint has gobs of 2.5 GHz spectrum, the location of the WiMAX profile and the range at which supported devices will become available. WiMAX is also specified in profiles for 2.3 GHz, 3.5 GHz and 5.8 GHz.
The AWS (Advanced Wireless Services) spectrum purchased by SpectrumCo (a joint venture of Comcast, Time Warner Cable, Cox Communications, Advance/Newhouse and Sprint) falls outside the traditional WiMAX profile.
SpectrumCo bought two 10 MHz bands that provided close to nationwide coverage. At 10 MHz, the spectrum is good enough for voice services, but a tad light for mobile broadband services, Devine estimates. He adds that it would be smart to keep an eye on an upcoming auction that will sell off 5 GHz spectrum, where WiMAX can run in an unlicensed form.
Another key difference: WiMAX uses TDD (Time Division Duplexing), while SpectrumCo uses FDD (Frequency Division Duplex). WiMAX is capable of using both, but the majority of uses in the 2.5 GHz spectrum tap TDD mode.
“It’s not as simple as saying Sprint has WiMAX to suggest that cable should also use WiMAX,” because of these complexities and differences with the licenses purchased by SpectrumCo, Park said.
Assuming cable operators also had access to a WiMAX network, it follows that they could support the same types of apps–and apply the same level of QoS–whether it was running on the HFC plant or via the wireless connection.
Despite the cable industry’s present lack of WiMAX spectrum, WiMAX should be considered a “lead candidate” for mobile cable services, Park says. “It’s fair to say the right choice will be an IP-based wireless technology. That [WiMAX] matches their infrastructure best.”