Cisco Announces PoE Supportable 802.11n Access Point
Cisco announced a new wireless LAN access point today dubbed the Aironet 1140. Importantly, the new 802.11n capable unit can operate on standard Power over Ethernet (PoE). Cisco has also incorporated a beamforming technology called ClientLink, which they claim can significantly improve the performance of legacy 802.11a, b, g devices in mixed-mode networks. With Cisco’s share of the enterprise WLAN market at roughly 65% and the overall migration to 802.11n, you can be sure that the new access point will sell in large numbers.
The basic specs for the1140 are adequate. It comes in single radio (2.4 GHz ) and dual radio (2.4 GHz/5GHz) configurations. The dual radio model can support two separate networks simultaneously out of the same unit. Both feature sleek packaging with no external antennas and use the same mounting brackets as the Aironet 1200 series to simplify change-outs. Like most other n-capable devices, it can support either standard 20 MHz or 40 MHz double-wide channels for higher transmission rates.
On the downside, the unit supports only two transmit chains; it does include three receive antennas (i.e. a 2x3 configuration). The major performance gain with 802.11n comes from the ability to transmit multiple independent signals or transmit chains in the same frequency band. The more transmit chains you have, the higher the transmission rate you can provide. While the 802.11n standard defines up to 4 transmit chains, products today have a maximum of 2 or 3. The maximum bit rate on a 20 MHz channel with 2 chains is 144 Mbps or 217 Mbps with 3 chains.
One very important feature is the device’s ability to operate using standard 802.3af Power over Ethernet (PoE). Power consumption has been a major issue with 802.11n, with the result that most n-capable access points could not be supported without some special powering option, dual LAN connections, or limiting some of the capabilities of the unit (e.g. reducing the number of transmit chains). Siemens delivered the first access point that could be supported on standard PoE almost a year ago, and that is a 3x3 configuration.
The other feature of the 1140 is the incorporation of a beamforming technique called ClientLink that is designed to optimize performance when n-devices share channels with legacy 802.11a/b/g devices. The basic technology for beamforming was developed in the 1940s and is used in phased array antennas. The technique involves sending radio signals from two or more antennas (two in Cisco’s case) and by shifting their relative phases the radiation pattern can be reinforced in a particular direction. With beamforming, the access point can aim a stronger transmission signal in the direction of the client device thereby improving link performance. The access point notes the antenna on which the incoming transmission appears stronger to decide how to shape the outbound transmission. On the inbound side, the access point uses Maximum Ratio Combining, a standard feature in 802.11n to improve the receive signal strength.
Cisco’s announcement cites tests from Miercom that showed an increase in throughput up to 65% for legacy devices using ClientLink along with a reduction in the incidence of retransmissions.
The migration to 802.11n is clearly underway, and Cisco is looking to capitalize on their already dominant position. They claim to have shipped over 175,000 n-capable Aironet 1250 series access points. However, power consumption is still a challenge for 802.11n, so PoE support is an important step; PoE on a unit with 3 transmit chains would have been a bigger step. The addition of the ClientLink technology should help us make the best use of legacy devices and it will be interesting to see how well lit performs in the real world. Over the past year I’ve done a number of posts on 802.11n technology, standards, and planning. Suffice it to say that anyone who is planning a WLAN deployment or upgrade today, should be considering the impact of 802.11n.