All of these audio/video applications are placing more importance on latency rather than throughput, which is another factor driving the draft 802.11n standards efforts that combine improvements on both fronts.
While greater bandwidth is critical, advanced wireless applications will not work acceptably on today's networks without reducing latency times. The difference is important: latency is the total round-trip time that information takes—going from client request to server response and back to the client.
Even the fastest networks suffer from long latencies, which can wreak havoc with audio synchronization, or give users the feeling that "nothing is happening" when they hit the Enter key on their PC browsers. With 802.11n, there is an opportunity to make huge improvements in both latency and bandwidth.
There are several improvements that will help reduce latency. Latency matters most in synchronizing audio applications, particularly with streaming video and with VoIP situations. Delays of a just a few milliseconds can add up over various network router links and result in a mismatched picture to the sound, or turn a phone call with crisp quality into a jumbled mess.
One of the more important is frame aggregation, which groups data packets into larger frames to minimize packet overheard. While throughput is still important, without low latency times, many of these newer applications would not work acceptably on today's networks.
Speaking of the higher data rates supported by 802.11g, here is another lesson. The high end of 802.11g networks sounds very promising, supposedly delivering 54 Mbps data rates. However, what is really going on at these speeds is that there is an almost a 50% overhead that is created to sustain the highest throughput.
Lesson 5: Minimize packet overhead.
Going from 24 to 54 Mbps doesn't buy twice the performance that the raw data rate numbers imply. Any new protocol must do a better job at managing packet overhead than 802.11g, which uses nearly half of its available bandwidth for overhead at the highest data rates.
During 802.11n development, engineers worked hard to reduce overhead and eliminate turnarounds wherever possible. One of the most prolific improvements is frame aggregation.
Instead of sending a single data frame with its overhead, the transmitting client combines and sends a series of frames with a single overhead frame without waiting for each packet to be individually acknowledged.
As a result, an 802.11n client will send more data in a given time period " which makes the transmission more efficient.
Figure 1: How frame aggregation improves packet efficiencies
Lesson 6: Bring consensus whenever possible.
As the wireless technology impacts a greater number of manufacturers and vendors, relevant working groups get bigger and it becomes more difficult to gain consensus on technical aspects of a standard. By offering an alternate venue for drafting the 802.11n specification, the Enhanced Wireless Consortium (EWC) enabled vendors to put aside their differences and move more quickly towards an agreed-upon standard.
As previously mentioned, the 802.11n specification is much more technically complex than earlier 802.11 standards. One of the byproducts of this complexity is a longer input and approval cycle for new wireless standards. As the membership of various 802.11n working groups had grown, it became harder to achieve consensus.
Late last year, Broadcom and several competitors united stakeholders from competing standards camps to iron-out technical issues and achieve consensus more quickly. This new body, called the Enhanced Wireless Consortium, brought together talented engineers from the major Wi-Fi chip vendors, device manufacturers and PC OEMs to put differences aside and develop a draft specification.
By jump-starting consensus, the EWC laid the groundwork for moving the 802.11n standard towards finalization. The EWC draft was universally accepted by the IEEE 802.11n working group earlier this year, and is on track to be approved early in 2007.
Lesson 7: It isn't only about PCs anymore.
It is clear that PCs aren't the only wireless devices that matter. Any new wireless standard needs to take into account scores of other consumer electronics that will find their way onto home and corporate networks. The 802.11n standard must specifically embrace these devices and support their operation on formerly all-PC networks.
One of the major obstacles for the digital home is putting in new wires to connect everything. Some estimates indicate that Wi-Fi is used to connect devices in half of all homes with broadband connections. This number will continue to climb as the wireless products become more capable. The increasing popularity of wireless networks will spur an increase in the number of applications that will run over these networks.
Indeed, as wireless networks become more pervasive, all of us will see more Wi-Fi enabled printers, music and video devices, cell phones, digital cameras, etc. This new generation of products will enable the wireless transfer of images music and video content that are stored on media servers and media players like Apple's iPod, and Voice over IP telephones.
All of these devices want to share content, applications, and IP addresses wirelessly on the same network. The shear volume of wireless-enabled devices will also place more demand on wireless throughput, requiring higher performance networking protocols.
