Improving Audio/Video Quality of Service Over WLANs
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Two IEEE Standards Collaborate
Last week, the IEEE 1394 Trade Association's (TA) Wireless Working Group (WWG) announced that the IEEE 802.11e QoS task group adopted QoS enhancement proposals made by the 1394TA WWG. IEEE 1394 is a wired multimedia standard defining a single, high speed interconnection bus that has been broadly adopted in connecting digital media (A/V) devices and high-speed storage devices to a PC. IEEE 1394 currently has two flavors, 1394a and 1394b, the former supporting data transfer rates of up to 400 Mbps and the latter up to 1.6 Gbps. Only the 1394a flavor is in current use at this time. The collaboration could mean significant improvements in the quality and functionality of WLANs for both the home and enterprise markets.
Peter Johansson is the IEEE P1394.1 chairman and author of the proposal attempting to improve IEEE 802.11 QoS for A/V streams by applying fundamental principals and mechanisms based on the IEEE 1394 architecture. "Both the 1394 TA Wireless working group and 802.11 Task Group E concur on the fundamental QoS concepts necessary for high-quality audio and video streams, such as scheduling and channel access," Johansson said in explaining the motivation behind the collaboration. "Wireless 1394 to some extent is an oxymoron," he added, further explaining that it's more of the paradigms and behaviors of data transfer that are applicable to wireless LANs than the actual 1394 technology as it is implemented by PC manufacturers for wired devices.
What is QoS Anyway?
As the use of wireless local area networks spreads far beyond simple data transfer to intense multimedia applications, the need to address Quality of Service (QoS) issues becomes extremely important. QoS is a networking term that is a bit more complex than it might sound. QoS refers to the concept of being able to control and measure data transmission rates, or throughput, and error rates. Specifically, QoS refers to implementing guarantees of meeting specified data transmission rates and error percentages. "Back in March, a number of us went to the 802.11 meeting," Johansson explained, and "we discovered that they [802.11] were interested in A/V (audio/video) QoS."
Who Cares About QoS for WLANs? Delivering text and other relatively simple types of data around a network doesn't necessarily require complex QoS mechanisms. For much of what networks historically moved around in business applications strict measures for QoS didn't matter because the data wasn't multimedia and the end-user wouldn't notice or be materially affected by latencies. But, as WLANs sprang up and evolved both technologically in terms of data transfer speeds, and in terms of their market orientation incorporating home users, QoS requirements ramped-up. Both the enterprise and consumer markets are beginning to demand data-intensive, time-sensitive movement of things like audio and video around a WLAN. Johansson and the 1394 group "discovered that they [802.11] didn't have sufficient QoS [for A/V]."
IEEE 1394 Collaborates with IEEE 802.11
The IEEE 802.11e QoS group "looks at things from an Ethernet perspective," stated Johansson, and has "focused mainly on Voice over IP (VoIP) over 802.11 networks." But, Johansson explained, "voice characteristics are very different from A/V... and the data arrives differently." Voice doesn't require the same type of QoS guarantees as A/V because data loss is less of an issue. The same cannot be said for multimedia though. For a high-quality, smoothly displayed multimedia, all of the data must arrive, and arrive at the same time. The goal of applying the IEEE 1394 QoS behaviors to IEEE 802.11 is to address the problems encountered with intensive multimedia delivery over what is essentially an Ethernet standard evolved for the wireless world - hence the name of one of the trade groups associated with 802.11 - WECA, or the Wireless Ethernet Compatibility Alliance.
The 1394TA's WWG proposal to enhance QoS for IEEE 802.11 is designed to establish QoS based on scheduled management of channel access guarantees. The behaviors of 1394 that the group seeks to emulate for 802.11 involve things like: accurate clock distribution, connection management protocols, and command sets. The 1394TA WWG's goal is to "complete a spec showing how you re-produce 1394 behaviors," said Johansson. Ultimately, the 1394 WWG will develop a 1394 protocol adaptation layer (PAL) for devices using the 802.11e QoS provisions. Audio and video experts agree that 802.11 must address MAC (medium access control) services encompassing scheduled access to the radio channel. James Snider, the 1394TA Executive Director, said that the experience gained with wired 1394 devices can be applied, and the firmware adapted, for use in the wired or wireless environment.
The Net Effect
Pardon the pun, but the net effect of the application of a 1394 PAL to devices using the 802.11e QoS will be data transfer methods that are in fact suitable for multimedia over WLANs. While it's wonderful for companies to show off HDTV delivered over 802.11a in an isolated environment, its quite another leap to do so when integrated into an enterprise or business network with other traffic on the pipes. Therefore, the collaboration between these seemingly unlikely partners should prove quite beneficial for WLAN users everywhere.
Matthew Peretz is Managing Editor of 802.11-Planet.com