802.11n Primer - Understanding Spatial Streams
Clients That Support Three Spatial Streams
Clients with 3SS support are starting to become commonplace. As the new 802.11ac specification starts to get traction, many newer client adapters will have the newer chipsets and support 3SS as a subset to 802.11ac. Additionally, unlike many of our competitors the Cisco AP 1600/2600 and 3600 fully supports all the DFS channels for more usable channels in the 5 GHz range. More clients, especially 802.11ac clients, will start to emerge supporting these newer channels in 802.11n modes as well.
Currently the most popular 3SS client is the Apple 2011 MacBook Pro, as it is based upon the Broadcom BCM4331 chipset and a small USB adapter by Trendnet, “TEW 684UB”, based on the Ralink chipset.
Additionally, the Intel 5300 and 6300 has supported 3SS for a long time. Perhaps because of the different hardware platforms this card is installed in, testers have observed good throughput on many notebooks (+320 Mbps) and reduced throughput on other notebooks such as 240 Mbps. If you experience low throughput using the Intel card, one suggestion might be to try a MacBook Pro or Trendnet adapter, and if they perform well try another notebook with the Intel card or perhaps open a case with Intel or the laptop manufacturer for a possible remedy. During the AP 3600 beta trials we observed differences in performance with different notebooks using the Intel 6300 card.
Note Sometimes it can be difficult to reliably maintain a 3SS link as it is easy for the client to
The AP 3600 with its extra radio per band can use the extra redundant radio to beamform (thanks to ClientLink 2.0) and uses this to maintain the advantage of 3SS links. Cisco ClientLink 2.0 can also improve the overall performance of 802.11n clients using 1, 2 and 3 spatial streams and legacy .11a/g clients.
Understanding Beamforming – ClientLink 1.0 and 2.0
ClientLink 1.0 was first introduced with the AP 1250 and AP 1140 series Access Points; it is a method of creating a stronger signal on the downlink side for 802.11a/g clients by hearing the clients on the uplink and then adjusting the transmitter timing so the signal appears much stronger at the client end.
This feature used to be user configurable; however, starting with 7.2 code stream it is now on by default and is not user configurable as there is no benefit to disabling it.
The AP 3600 fully supports ClientLink 1.0 for 802.11a/g clients but has a greater advantage as it also supports all 802.11n clients including 1, 2 and 3 spatial stream clients. This capability is called ClientLink 2.0. There is a distinct advantage with ClientLink 2.0 over the 802.11n enhanced beamforming specification, as ClientLink 2.0 works with ALL clients today and does not require any client sounding or support (Figure 54).
Cisco Aironet Series 1600/2600/3600 Access Point Deployment Guide, Release 7.5
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