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WRT54G + multiple WRE54G as repeaters = messy results?

Discussion in 'Networking Issues' started by Bearmatic, Dec 11, 2004.

  1. Bearmatic

    Bearmatic Network Guru Member

    Hi

    I'm planning to implement a wireless network in a hotel where wiring is a "rather not". I thought of using a WRT54G on ground floor and then install a WRE54G in every floor after that. The idea is to let the first floor WRE54G talk to WRT54G, the second floor WRE54G talk to the first floor WRE54G and so on. Same channel and SSID.

    Shaky business? Think so.

    I have tested 1 WRT54G and 2 WRE54G that:
    WRE54G(1) is extending the net from WRE54G(2) which again is extending net from the WRT54G. This actually works OK it seems.

    Trouble begins when I move my wireless laptop between the WRE54G's or even between a WRE54G and the WRT54G. The laptop seems very confused and can't decide which point to connect to and starts dropping ping packets to both conflicting AP's and eventually loses all contact with the WRT54G and WRE54G ("request timed out").

    I also tried placing all 3 devices (2xWRE54G and 1xWRT54G) around my laptop in a 2m radius to see what happened. They all have different IP addresses, so I pinged all at the same time. Again, the ping wen't well to the WRT54G and WRE54G(1), but none to WRE54G(2). After a while it lost packets to the WRE54G(1), and got some response from the WRE54G(2) but eventually ended up losing connection to all devices after 10 minutes. I'm sure this has to do with confusing as all devices has same SSID and same channel. Maybe the WRE54G is best used as an extender at the fringe of a wireless lan.

    That aside, I thinking about using multiple WAP54G's in Wireless Repeater Mode instead of WRE54G's. But from what I've read, some say that the WRE54G IS a WPA54G in Wireless Repeater Mode. If that's true, is it impossible for the WAP54G to overlap other WAP54G in repeater mode and get a laptop to properly "lock on" to an AP with best signal?

    My third option is to lay a wire to WAP54G's in the ceiling between floors, but this building being a concrete maze, it's rather avoidable. But will such a solution with wired WAP54G's to WRT54G provide seemless roaming for hotel guests, or at least have the laptops "lock on" to the strongest signal without fluttering about?

    If you made it this far and still follow me, you deserve a purple heart :)
     
  2. ssam

    ssam Network Guru Member

    i'd rather suggest you Linksys WAP54G or WRT54G in repeater mode;) Will work without problems;)
     
  3. Bearmatic

    Bearmatic Network Guru Member

    Thanks ssam, for the suggestion. I'm trying right now to set a WAP54G in repeater mode towards a WRT54G. I've followed the guide at www.linksys.com as to how to set WAP54G in repeater mode for a WRT54G.

    Problem is, when I unplug the cable that goes from WRT54G from the WAP54G (after configuring for repeater mode) I can't ping the WAP54G anymore (192.168.1.245). SSID and channel are the same.

    Because of that, I thought maybe the WAP54G got "transparent" in repeater mode. Hooked up a PC in the LAN port of the WAP54G as to try to get an IP adress from the WRT54G. No result. Also tried to set fixed IP on the PC and tried to ping from wireless laptop -> WRT54G -> WAP54G -> cabled PC. No result.

    Any idea what I'm doing wrong?
     
  4. Bearmatic

    Bearmatic Network Guru Member

    Ooooppps. My Bad! Disregard the last post. After closer inspection, I had entered the LAN mac address in the configuration for reaper mode in the WAP54G instead of the wireless MAC address.
    The setup works fine now.

    The next step would be to add another WAP54G(2) to the LAN port of the existing WAP54G(1). This because I guess the WAP54G(1) in repeater mode does not accept clients whatsoever. What I hope is that WAP54G(2) will function as the connection node for clients.

    Step after that would be to install a WAP54G(3) to set this in repeater mode against WAP54G(1) to extend the range even further if it's at all possible...
     
  5. Bearmatic

    Bearmatic Network Guru Member

    Hmmmmm... I tried to connect the wireless laptop directly to WAPG54(1) (the one in repeater mode with a different SSID than WRT54G) and it accepted the request.

    I could ping and access the web-interface on the WRT54G from the wireless laptop with no cable between the laptop,WAP54G and the WRT54G.

    Does this mean that the WAP54G in repeater mode accepts clients even in repeater mode? Interesting...
     
  6. 4Access

    4Access Network Guru Member

    Yup, repeater mode repeats the signal it receives from wireless clients, which is why it's called repeater mode. Bridge mode on the other hand does not accept wireless client connections, but instead is intended to bridge the ethernet traffic from the LAN port of one WAP to the LAN port of another WAP wirelessly. (At least it was Linksys's intention that bridge mode would only work with other WAPs. Notice the note in the bottom of the last screenshot here.)

    I believe it might also be possible to configure a WAP54G in bridge mode to connect to a WRT54G running Sveasoft's firmware with WDS enabled, but won't swear to that since I've never tried.

    If I were in your situation I would probably use all WRT54Gs since when combined with custom firmware they can do everything the WAP54G or WRE54G can and you'll have much more flexibility.

    Also you didn't mention how many floors you have, but if I understand you correctly and you intend to daisey-chain your APs together wirelessly (eg. 5th floor > 4th floor > 3rd floor > 2nd floor > 1st floor > internet) you've just cut the 5th floor's bandwidth in half 5 times! Not to mention that the lower floors are going to have to be able to handle all the traffic of the floors above them in addition to their own and could potentially be overwhelmed.
     
  7. Bearmatic

    Bearmatic Network Guru Member

    Thank you 4access for your enlightening information. Yes, I do believe WRT54Gs with Satorini firmware mod would be as good as WAP54G.

    I was planning on daisychaining the APs, and I temporarily forgot the fact that it will half the transmission speed for every repeater due to the internal radios capabilities. But I believe I only need a repeater at every second floor and there are 4 floors + a small conference room at 5th floor.

    So the setup would be: Base station at ground floor -> repeater(1) in ceiling between floors 1 and 2 -> repeater(2) in ceiling between floors 3 and 4. I also believe this last repeater would reach the conference room at floor 5.

    Actual bandwith would approximately between the first repeater(1) and base router be around 20Mbps (or so my tests showed in Windows XPs' bandwith measurer). So let's say that the first repeater(1) cuts the actual bandwith in half, you still got maybe 8-10Mbps between repeater(2) and repeater(1).

    Will it then also cut this bandwith in half for the clients connecting to repeater(2)? So that the clients connecting to repeater(2) would have maybe 3-5Mbps between themselves and repeater(2)?

    Or am I thinking wrong about the speeds? I know it says 54Mbps on the box, but...
     
  8. 4Access

    4Access Network Guru Member

    Short answer: Yes, clients associated with AP2 are going to be getting 3-5Mbps throughput at best.

    Long answer: An 802.11g radio is able to transmit data at 54Mbps which is actually only good for throughput in the low-mid 20Mbps range, under optimal conditions. This is asuming there is only one radio that must transmit for the data to reach its destination. For example:

    [Wireless Client] ~~~ [AP] --- [Wired Device]

    This is because the AP can receive the wireless data and forward it to the wired device simultaneously.

    Unfortunately since most consumer APs only have a single radio, they can't receive and transmit wirelessly at the same time. They must do one or the other, which means throughput will be halved if the data an AP is receiving needs to be forwarded to another wireless device.

    Therefore the theoretical max throughput available to a wireless client trying to communicate with a wired segment is cut in half for every radio that must repeat the signal.

    In your case a wireless client associated with AP2 will have its throughput halved twice (once for each repeater) before the data reaches the wired segment. Assuming the client could commuinicate at 20Mbps were it talking directly with the "root" base station, after the signal has been repeated twice, you're only going to get about 3-5Mbps, just like you guessed.

    Also you must also consider the impact of multiple wireless clients trying to use the network simultaneously. While every additional client shouldn't cut the bandwidth in half since presumably they will mostly just be surfing the web, even a few busy clients are definitely going to make a noticible impact.

    The situation will be worse if the wireless clients don't have a strong signal with the AP and are forced to associate at slower than optimal speeds. Also you must consider that legacy 802.11b clients (and all current PDAs) will be taking an initial throughput hit.

    Lastly I find it a little hard to believe you're going to get away with just one AP per 2 floors! How big is this hotel? Have you done any testing to see just what coverage you can get from a single AP?

    And assuming that you do need more APs I'm afraid you would have more to worry about than just the basic half-duplex nature of the radios if you try and daisy chain them all together into one big multihop wireless configuration...

    A quick google search for multihop wireless throughput turns up a lot of very technical documents about problems with the reliability and performance of TCP over these types of links...

    I can think of a few different options you may have and others may have some imput as well but I think it would be a safe bet to start by testing to see just how many APs you are going to need to cover a single floor. If you discover that a single WRT54G isn't going to cover as much area as you thought then the possibility of high gain and or directional antenna's etc may change the number of repeaters you use...

    Regardless, here's a tool that you may find useful for throughput testing: Qcheck
    Remember though that in a network like you're looking to setup a large number of users will make a huge difference in actual performance when compared to a single client test environment.

    This is going to be a busy week for me so I may not be posting here much but I wish you luck with your project!
     
  9. Bearmatic

    Bearmatic Network Guru Member

    Again, 4Access, I bow in the dust for your time, effort and throughout clear information you've provided. What should us wireless-virgins do without your help? :)

    I've totally diregarded the idea of daisy-chainging APs. I lent some WRT54Gs form work and flashed them with Satori 4. Although I got it working in a test-environment with one single client, after reading your post and taking a second look at the wobbly/shaky setup laying scattered on the table, I decided to abandon the idea. Instead I will urge the hotel to wire every floor and install one wired AP to every floor and possibly set one AP in repeater mode to every wired one. That would probably sufficient. If the cable-guy doesn't charge too much, I'll ask him to wire every AP.

    By the way, by your standards, this is a small hotel. 4 floors of about 15 rooms in each floor. I've tested a WRT54G in the very end of the hallway with my laptop in the farthest most room in the same hallway and still got a signal. Weak. But it was there. So I think 2 in each floor would be enough.

    Again, I thank you for your time.
     

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