Even better, don't worry about upgrading your edge ports. I challenge an organization to document a pre-standard 802.11n AP filling up a 100-Mbps Ethernet switched port over a 5-minute period. While link rates may climb to 600 Mbps, data throughput will likely peak out at 300 to 400 Mbps when using two radios in an AP. Yes, a 100-Mbps Ethernet port will cap bursty traffic, but those application requirements don't reflect a typical usage scenario. Mix in several clients operating at a variety of distances from the AP, and aggregate throughput will likely fall into the 100-Mbps range. Meru demonstrated in a private suite its new pre-standard 802.11n AP using eight laptop clients, each playing different unicast HD video streams running at 7 Mbps. Trapeze also demonstrated its pre-standard 802.11n AP using a single client downloading a file with FTP. Link rates hovered at 130 Mbps and throughput was shown to be in the 65-Mbps range. Although it was exciting to see greater than 50-Mbps throughputs on pre-IEEE standard products, they were still not at the top end for speed.
By the time 802.11n traffic flows consistently require 100 Mbps, you will be swapping out any remaining 10/100 switches with their gigabit equivalents. And don't forget that because Wi-Fi is a half-duplex medium, even 120 Mbps of usage that is split 90/30 between downstream and upstream will still operate effectively against a 100-Mbps full-duplex connection.
Several distributed switching WLAN vendors have suggested that their competitors' centralized architectures will force organizations with 802.11n to upgrade their distribution layer to 10 Gbps, but the reality is that if you don't need that kind of link capacity today for your wired users, who likely have 1-Gbps interfaces on their desktops, it's very unlikely that your wireless users are going to force that transition.
Migration Strategy: One element of consensus among all the vendors we spoke with is that mixing legacy 802.11a/b/g clients with 802.11n clients will effectively eliminate the significant performance benefits that the 802.11n standard brings. This is not unlike 802.11b and 802.11g coexistence, where a pure 802.11g environment will support an aggregate throughput over 20 Mbps but in a mixed environment top out in the low teens. The vendors almost unanimous solution? Dedicate a radio to 802.11n clients in the 5-GHz range. In a greenfield situation, an organization could use a dual-radio AP where the 2.4-GHz radio serves legacy 802.11b/g clients and the 5-GHz radio serves any new 802.11n clients.
In existing deployments it becomes a bit more complicated, though it can be boiled down to two scenarios. If the organization offers only 2.4-GHz service today (either 802.11b or 802.11b/g), then the existing APs can be swapped out for dual-radio APs supporting 802.11b/g in the 2.4-GHz range and 802.11n in the 5-GHz range. The extended level of viable coverage achievable in 802.11n via MIMO (and beamforming in future chipsets) will make up for the traditional shorter signal propagation of 5 GHz. The vendors we spoke with said it was too earlier to make any firm predictions, but we heard conservative numbers of 10 percent beyond 802.11a and I'm willing to bet that we'll see double or triple that number once chipsets have been revised and the vendors have had more experience. Interestingly enough, Atheros was not able to share any coverage data for the 5-GHz range.
