Date: Mon, 3 May 2004 16:01:06 -0400
From: Tyler van Houwelingen
Subject: Re: [ptp-general] Client mode for WAPs
We have some 300 radios all tied together wirelessly across an urban environment using a combination of tradional PtMP wireless bridging, WDS repeating and AP-client bridging. Although ours is a commercial endeavor, the experiences should be relevant so here are some random points of interest that we picked up along the way. ty
- You cannot do reliable wireless backhaul at 2.4Ghz. There is simply too much interference and not enough channels to simultaneously provide for access. You must use 11a or WiMAX.
- WDS is good and cheap for wireless hops, but when connecting multiple APs to a central AP each additional AP detracts from the signal of the existing links. The most we have is about 5 APs running from a single central AP. After this, you need to add a second AP at the center and use sector antennas. Setting the RTS value on both ends will help alleviate this.
- WDS allows for lower latency hops vs traditional bridging solutions which will have to go through multiple radios. The most wireless hops you can use for backhaul and still have good VoIP is 5. Up to this point, VoIP (VoWiFi) works incredibly well. This was done, however, using proxim equipment which does priortize traffic flows.
- We have tried a couple different mesh solutions (stryx, firetide) and while this will be good at some point, it is premature becuase of the 2.4Ghz limitations and increased overhead. Dual radios using 802.11a for the mesh and 11b for the access will be strong. We are now building this box using soekris and pebble.
- AP-client bridging (e.g. wet11, dlink 810+, etc) is very troublesome when dealing with many urban located APs on the same SSID. The client bridge will flip back and forth to different APs depending on the layout. To get around this, you need to specify a BSSID (lock it to a single AP), but this feature is only available on the dlink 810+, which is a troublesome box. The WET11 will die if you pass VoIP traffic through it.
- 11a will not work unless you have very near 100% LOS. 1 moving tree branch will cause the signal to fade in and out. Currently there is only 1 11a access point on the market with an external antenna, the Proxim AP4000. Also, you will not find 11a omnis over 8dB. There are no 802.11a client bridges on the market. Will somebody PLEASE build one of these already.
- Overall, wireless backhaul can be reliable, high performance and inexpensive, but there is a steep learning curve.
Tyler van Houwelingen
CEO Ottawa Wireless, Inc.