D-Link DWL-G810 802.11g Wireless Bridge – 支援論壇

Daisy chain... [D-Link DWL-G810 802.11g Wireless Bridge - 110214]

  • Grimbo
  • 投稿: 6
  • 註冊日期: 25 十月 2004
Is it possible to create a daisy chain of extenders throughout a site, all stemming from one router?
  • Grimbo
  • 投稿: 6
  • 註冊日期: 25 十月 2004
please?
  • Grimbo
  • 投稿: 6
  • 註冊日期: 25 十月 2004
I assume nobody is going to answer this then :-(
  • rperkin
  • 投稿: 2535
  • 註冊日期: 12 八月 2003
  • 地點: UK
You have posted to the DWL-G810 forum. As I understand it, the DWL-G810 is not a range extender (ie repeater) but a wireless client bridge. So no, you can't do it with this specific device. The DWL-G810 acts a a wireless client to an access point. The device behind it gains wireless connectivity to other devices on the network. It is also possible (although I haven't tried it with this specific device) to connect it to an Ethernet switch and so provide wireless connectivity to multiple devices behind the switch. I suspect you are thinking of the DWL-G800AP. This has both an Access Point mode and a Repeater mode. Usually it is stated that such devices cannot be used to 'repeat a repeater'. My experience with other similar devices (specifically the DWL-900AP+) is that they *do* work, but without testing with the specific model I can't confirm this. The major problem is the drop in throughput. Consumer class devices such as this have a single radio. So to repeat a signal requires the device to first listen, then re-transmit. This leads to an approximate 50% drop in throughput when communicating via a wireless repeater. So daisy chaining two repeaters will drop the throughput to 1/4, three repeaters to 1/8 etc. This rapidly leads to unacceptably low performance, particularly over large distances where the network speed is already lower than the maximum. Whether it will work you will need to test. Repeater mode is an implementation of Wireless Distribution Service, which although it is described in IEEE 802.11 is not defined in sufficient specific, unambiguous detail to make its implementation fully standard. One way to improve performance when extending the range of a wireless network is to use two devices back-to-back, a wireless client connected to an access point. Clearly this is more expensive, but because there are now two radios the drop in throughput will not be so severe. The cheapest way to obtain increased range is to fit higher gain antennae to the wireless devices. The stock antennae usually fitted as standard have a gain of 2dBi. Replacing these (preferaby both on the 'root' access point and client devices) with a higher gain antenna will increase the range quite significantly. Even using a modest gain 5dBi or 6dBi antenna can provide significant improvement. Hope this helps
  • Grimbo
  • 投稿: 6
  • 註冊日期: 25 十月 2004
Thank you for your reply... I have a quite specific problem! I need to get wireless access through a very large building but (for empire building reasons) the IT dept. won't allow us to use their network! So I need to provide my client with wireless connectivity without the ability to use multiple access points. Is there an access point device that can cover a very large building (think about the size of a large school or small hospital) Many thanks.
  • rperkin
  • 投稿: 2535
  • 註冊日期: 12 八月 2003
  • 地點: UK
To the best of my knowledge, no. It's not to do with power (although depending on your local country regulation, and certainly in Europe, this may well be a factor) but to do with signal propagation loss as it passes through walls and the building environment, and by local 'blind spots' or 'coverage holes'.. Just as with a wired network, the design of a wireless network to cover a large building is not one which can be just be done (or certainly shouldn't be done!) on the back of an envelope. In outline, and depending on the size of the building and the number of floors to be covered, I would recommend a mix of wired and wireless. In a roughly central point or wherever convenient, I would place an Ethernet switch and from there run CAT5 cable in the roofspace or ceiling void. At appropriate points depending on the wireless coverage required, I would connect a number of wireless access points. You may also need to use cascading switches, given that the limit for 100Base-T network segments is 100m. Each wireless access point should provide a signal overlapping slightly with the adjacent access points, but using as wide a channel separation as possible to avoid interference. In the US, this would be channels 1, 6, 11. Here is a diagram which shows an outline of this. In a building with multiple floors, you will need to consider the coverage in 3D - and you may be forced to use a greater number of slightly overlapping channels, for example 1, 4, 7, 11. In Europe there are two further channels available, so you might consider using 1, 5, 9, 13. The use of four channels should allow positioning of access points covering multiple floors without much problem with interference given that although there is some frequency overlap, signal strength falls away sharply at the limits of each channel. If using the ceiling void you will also need to consider power supply issues (power over Ethernet?) and fire regulations. Of course, much of this could be avoided by cooperation with the IT Department and I would recommend that route if at all possible. Then you can also delegate the management and support of the wireless network to them (presumably at a cost - which might be a bargaining point if they want a new project with additional income). Do not underestimate the effort involved in this side of things - performance issues and problem resolution can consume a lot of time, and there are always staff succession issues when the local 'super user' moves on. The IT Department may also have investment in WLAN planning tools - or even buy them for this project! If you do want to 'go it alone' then a gradual rather than a 'big bang' approach may be best, with a site survey after each access point or repeater installation to determine coverage, and testing to empirically determine bandwidth requirements for the user population. However, an ad hoc approach is no substitute for a sound network design. If you are in a country whose radio regulations allow high power devices, then do a Google search for "200mW access point" and you should come up with some helpful products. And if not, then who will know unless you cause interference? - not that I recommend this, of course. What I have described is pretty conventional stuff. Another option may be to use an access point model able to 'mesh' with multiple others on a single channel. I believe this is claimed for the Linksys WRT54G running third party software from Sveasoft, but I don't know much about this other than that it is part of their implementation of Wireless Distribution Service.
  • ekplus
  • 投稿: 8
  • 註冊日期: 16 三月 2004
  • 地點: Las Palmas (Canary Islands, Spain)
Looking for wifi repeaters, I found your explanation. I learn a lot today.Thanks. ekplus Las Palmas (Spain)
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