The New 802.11n Standard

After years of waiting out the standards battle, wireless networks are getting ready for the speedy 802.11n. With its peak data throughput reaching the golden 100-Mbps threshold, this marks the first time a wireless technology will rival the network-edge-access incumbent, wired Fast Ethernet. Although Ethernet jacks won't disappear for some time, 802.11n brings with it the prospect of computing in which the preferred method of jumping on the network is wireless rather than wired.

The standard won't be finalized until 2008, but many consumer "pre-N" products are appearing on store shelves. Based on a draft of the final standard, these products offer increases in range and throughput as long as both the access point (AP) and client device use identical chipsets from the same vendor. This stipulation may be fine in a small office or home office, but an enterprise is likely to see little benefit to using "pre-N" gear because most client devices support only the slower 802.11a/b/g standards, and upgrading all client devices to "pre-N" gear is impractical.

Particularly noteworthy is the lack of interoperability among "pre-N" consumer products. Netgear sells two RangeMax Next AP products, the WN511B (based on Broadcom's Intensi-fi chipset) and the WN511T (based on Marvell's TopDog chipset), for example, and claims both are compliant with the draft version of 802.11n 1.0, but when a client based on one "pre-N" chipset is connected to an AP based on different "pre-N" chipset, their peak speeds barely rival 802.11g performance.

On the enterprise front, very few existing products can be considered "pre-N." Because the current 802.11n standard is only a 1.0 working draft of the final version, products based on this draft might not be compatible with the approved standard. As the draft version matures, many of the interoperability hurdles will be overcome and vendors should be able to guarantee upgradability to the final revision with software updates for products released in late 2007. Until then, organizations looking to harness the throughput and range advantages of MIMO (multiple input, multiple output) technology--one of 802.11n's core features--can deploy the Airgo TrueMIMO-based BlueSecure Access Point 1700 from Bluesocket. Although this device doesn't use "pre-N" technology, it uses 802.11n-like technology, which claims increased range across any client type (including existing 802.11a/b/g equipment). Apart from Bluesocket, no other enterprise WLAN infrastructure vendor has yet released or hinted at its 802.11n road map.

But if 802.11n's shift from draft to final standard plays out like 802.11g did, expect these vendors to offer interim solutions such as a field-upgradable AP that will support the final 802.11n revision through a hardware radio replacement.

802.11n
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Mighty MIMOMIMO is the technological cornerstone of the 802.11n standard. Just as OFDM (orthogonal frequency-division multiplexing) technology was paramount to 802.11a/g speed increases, MIMO enables this speed increase by taking advantage of a radio frequency phenomenon know as multipath. Multipath occurs because a signal between an AP and a client can transverse multiple unique paths (see "Multiple Streams With MIMO" below). By sending different data streams in each signal path (known as spatial multiplexing), the effective throughput can be increased with each additional unique data stream. Of course, there's a catch: Each unique data stream requires a separate antenna on both ends.

Although 802.11a/b/g networks use both the 2.4- and 5-GHz bands, 802.11n will make better use of the underused 5-GHz band, allowing for denser AP deployments. Administrators will need to upgrade their WLAN analysis chops by capturing packets in real time at the AP or controller. And with regard to backward compatibility, admins should be aware that legacy clients will likely bring down the total aggregate throughput when operating in an 802.11n cell.

Core Considerations

Increased throughput at the wireless network edge will mean a big boost in data bandwidth requirements at the network core. Each 802.11n AP will be capable of 100-Mbps effective peak throughput, a quadruple speed increase from the 25 Mbps available on today's 802.11a/g networks. This increase ultimately aggregates at the WLAN infrastructure controller; for example, an 802.11n 100-AP controller will be forced to deal with a theoretical peak of 10 Gbps of traffic, though peak utilization will likely be 10 percent to 25 percent of that.

The solution is multipart but not yet completely implemented by infrastructure vendors. First, the wired link between AP and controller will become gigabit. The network core also will become faster, interconnected over the 10-Gbps links of today or the 40-Gbps links of tomorrow. Equally important, the encryption and firewall engines of today's controllers must be improved. For example, Aruba's 2400 Mobility Controller supports 48 APs but only 2 Gbps of firewall throughput--not necessarily a bottleneck today, but an issue if those APs are upgraded to 802.11n.Despite these challenges, the future of 802.11n looks bright. Although the draft of the standard's 1.0 version was released in May, full ratification won't likely happen till 2008, giving manufacturers time to address 802.11n upgrade issues. For now, WLAN administrators should begin researching their 802.11n migration path but be wary of deploying "pre-N" devices since they come with little guarantee of supporting the official 802.11n standard. Especially in enterprises, it's best to wait until the standard is set and interoperability guaranteed.

Jameson Blandford is the Lab Director At The Center For Emerging Network Technologies at Syracuse University. Write to him at [email protected].

MIMO Amplifies 802.11n |

2x2, 2x3 and 4x4: No, these aren't the latest all-wheel drive systems. They signify how many antennas and unique data streams are used in a MIMO device. A 2x3 system can send two separate data streams and includes three receive antennas, for example. It's beneficial to add additional receive antennas because the device will combine (resulting in a perceived stronger signal) and decode the transmission automatically from all the receive antennas, increasing the likelihood of a complete and uncorrupted transmission. But this advantage comes with a power-consumption cost. For APs, this is of little concern, but for laptops and other mobile devices it's important.

MIMO also can be used to increase the range of wireless networks by "beam forming" a transmission in the direction of the client. Instead of sending a transmission on one antenna, the same transmission can be sent intelligently (through processes such as phase shifting) through multiple antennas, increasing signal quality on the receiving end. Although not officially part of the draft standard, it's likely that this functionality will be added to support single 802.11n radio and antenna configurations, useful in low-power devices, such as VoIP handsets.