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Vendors use secret QoS sauces in home nets

Posted: 01 Mar 2007 ?? ?Print Version ?Bookmark and Share

Keywords:home networking? home network QoS? deal with home network QoS? home network clash? Rick Merritt?

The good news in home networking is that many companies and consortiums are gearing up products and initiatives to reliably shuttle voice, video and music around the house. The bad news is that many of the upcoming products and initiatives attack the core problem of QoS in slightly different ways.

Wireless vendors like TZero and Metalink are shipping components for sending multimedia over UWB and 802.11n links, respectively. Each company uses some proprietary secret sauce in its approach to QoS. Meanwhile, the ad hoc industry groups defining separate wired home networks for coaxial, power line and phone lines are not coordinating their approaches to QoS either.

Service providers have their own silos. Cable Labs considers QoS to be one of the most important aspects of its ongoing work in defining home networks for cable TV providers. The Home Gateway Initiative (HGI) takes a similar view with its separate work deploying IPTV networks for telephone companies.

Possible remedy
Two independent groups are trying to bridge the gap, working at opposite ends of the technology spectrum. But the work of the UPnP Forum (which promotes the Universal Plug and Play protocols) on an API and the IEEE 802.1 Audio/Video Bridging Task Group (AVB) on a revised media access controller will not be completed until after several months.

It's not clear how well the two technologies will work together, but both efforts are being closely watched by engineers as a possible remedy to the problem of fragmentation. "Everybody has a different notion of what QoS should be, but if you have more than one QoS, you don't have any," said Glen Stone, senior director of the Strategy, Standards and Architecture Division at Sony.

The problem is that many players!especially TV service providers!see the capability of delivering multimedia over a home network as a competitive advantage or core competency. "They fundamentally want to have control over QoS in the home net because if something goes wrong, people will call them for support," said Stone.

Problems only get worse with the move to HDTVs and DVDs. "We are focused on the HD experience, and that content really exacerbates the QoS issue," said Gary O'Neall, VP of global set-top development for Motorola.

"You don't see wireless video from Scientific-Atlanta yet because we believe people would get frustrated when they see effects like macro blocking," said Dave Clark, director of product strategy and management for the SA STB group, which is now part of Cisco Systems.

In October 2006, six top CE companies said they would solve the wireless HD problem by throwing yet another option into the ring: 60GHz radio technology. The WirelessHD group brings its own approach to QoS.

"Most engineers are not yet thinking about QoS as a network service linking different companies' products over different network types," said Stone. "Sadly, we may have to choose a lowest-common-denominator mechanism so everyone can map to it," he added.

Once a spec gets hammered out, there will still be implementation issues. "If you put one router in the path that doesn't know how to set up the path, you don't get the path," explained Clarke Stevens, a senior architect overseeing home network specifications at Cable Labs, the R&D consortium of cable TV providers. Cable Labs' initial goal is to define a spec for running media over a single isolated network where quality can be more easily controlled.

"In the long run, we hope there could be a confluence of efforts on QoS," said Duncan Bees, who leads QoS work at the HGI and is a tech advisor at PMC-Sierra, which makes chips for DSL gateways.

Two major efforts are in the works to provide a way to pull the increasingly fragmented parties together. The Universal Plug and Play consortium is developing a high-level QoS API that any vendor could use. Separately, an IEEE 802.1 working group is hammering out low-level hardware compatibility standards, initially for wired Ethernet and later for 802.11.

The two groups are expected to complete key planks of their work soon. So, just how well their efforts will mesh remains a question.

Although the two efforts work at opposite poles of the technology, they agree on the basic lay of the land. While engineers use many tricks to get good QoS out of their particular network or interconnect, there are only two fundamental techniques.

The most basic approach is to define a set of simple priorities and assign them to packets so a network knows what traffic goes first. Voice traffic usually takes top priority, followed by video, audio and lastly data.

"If you have enough bandwidth, that works great and it doesn't need much intelligence," said Clarke Stevens, senior architect overseeing home-net specifications at Cable Labs, the R&D consortium of cable TV providers.

A separate approach is to let a particular job discover and negotiate with devices on the home network for a guaranteed amount of bandwidth and latency for a given time. In this approach!called parameterization!some network jobs can be prevented from using the net if there is not enough bandwidth for them.

The former approach is the familiar territory of "best efforts" computer networks using Ethernet's TCP/IP protocol, either over wired or wireless links. The latter approach has been pushed hard by consumer electronics companies that want to deliver glitch-free digital TVs and stereos, often using the 1394!a.k.a FireWire!interconnect.

"There is not much out there in parameterized QoS," said Stevens. "But that's what cable providers feel they need to differentiate their services. We don't want video to be downgraded because someone submitted a print job," he added.

Mixed systems
Home network routers in the retail shops today are a mix of systems that support prioritization, but sometimes have no QoS. Some Wi-Fi products claim they support parameterization, but wireless nets are inherently subject to interference from microwaves, cordless phones and walls.

Like Cable Labs, HGI is moving its focus from priority to parameterized methods. Initially, the group aimed to make sure that home network traffic didn't collide with the video and voice from its IPTV service providers, focusing on Ethernet and Wi-Fi links on their DSL gateways.

"Service providers need to define a set of parameters to roll out their triple-play offerings," said Bees, the deputy chair of HGI's QoS group.

HGI's Phase I spec, which was launched last year, relied heavily on management policies for QoS prioritization defined by the DSL Forum. "But there are a lot of bells and whistles and tricks beyond setting priorities" in it, said Bees.

In September, the group started work on Phase 2. It will consider parameterized QoS and network admission control. The group also hopes to find a way to map LAN and WAN QoS techniques, and let users define custom QoS policies.

As part of their work, both Bees and Stevens of Cable Labs are paying close attention to the efforts of the UPnP and the 802.1 AVB group.

Bridging the divide
"We want to make home net QoS homogenous with a single API," said Alan Messer, a Samsung home-networking R&D manager who chairs the UPnP.

In 2005, the group defined an API for supporting up to eight priority levels. Recently, it completed work on an update that cleared up ambiguities about how to handle conflicting policies and provided a tool to measure network availability.

Now UPnP has embarked on ver 3.0, an effort to set an API for parameterized QoS. It will study and build on existing work on interconnects such as FireWire and power line. Parameterization will be defined not so much as a new feature but as an extension of the existing priority API, said Messer.

Groups such as HGI, Cable Labs and the Digital Living Network Alliance (DLNA) expect to refer to the UPnP API on parameterization when they write their own specs. DLNA also hopes to become a forum for a broader discussion about how to unify separate QoS efforts.

"We want to define an interoperability model where different QoSes can coexist and leverage each other's strengths," said Scott Smyers, DLNA chairman.

"The problems of the hybrid home network will be the burden of the upper layers of the software stack for people like Mediabolic to sort out," said Andres Melder, a senior VP of business development at power-line chipmaker Intellon. Mediabolic is one of a growing handful of home network software specialists/

Another middleware company, NetStreams, aims to address the same issues with its StreamNet software for handling multimedia over any distributed home net supporting TCP/IP. Its software, runningon a TI DSP, is available on an integrated chip or a board.

Hard answers
Not everyone is convinced an API is the answer. "We don't believe this problem could be solved at the higher layers," said Michael Teener, a technical director in Broadcom's networking division, who is heading up the IEEE 802.1 AVB work.

The UPnP may be forced to create unique QoS mappings for every PHY-layer network in the home. Due to the complexity of that work, they often may be forced to just make intelligent guesses on how to translate the priorities and parameters from one link into something that makes sense on another, said Teener.

"The work can be done better at the lower levels, but all devices on the network path must participate. If even one doesn't cooperate, you can't really guarantee anything," said Teener.

The AVB group's effort aims to bring deterministic parameterized QoS to Ethernet by the end of this year.

Generic sublayer
The group will define a sublayer in the Ethernet media access controller (MAC) that could be applied to any 802-based network. The work includes more tightly defining existing priority levels and applying the Stream Reservation protocol for parameterization.

It also aims to build a mechanism into switches so they can reliably determine the bandwidth and latency capabilities of a given link.

The approach will force hardware changes in MACs such as setting up multiple transmission queues for shaping traffic!something already supported in some high-end networking products.

When the work is completed, Teener said, for a MAC designer, those changes will require a "near trivial" number of new gates.

- Rick Merritt
EE Times

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