802.11g repeater repeating a repeater

Discussion in 'Windows Networking' started by eug k, Jun 13, 2004.

  1. eug k

    eug k Guest

    hi!

    Can a Linksys 802.11G AP in repeater mode repeat a
    repeated signal?

    i.e.

    [AP] <---> [repeater] <---> [repeater] <---> [client]

    i'd assume the speed would be halved once again if
    it's possible...


    thanks!


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    eug k, Jun 13, 2004
    #1
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  2. Yes, it works. It the principle behind all the community wireless networks
    that are springing up.
    Speed is about the same but latency will be longer.


    gtoomey
    www.ausinvestor.com Australian Investor Forum
     
    Gregory Toomey, Jun 13, 2004
    #2
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  3. eug k

    Uncle Bully Guest

    If it halved then it wouldn't be a repeater would it. The whole purpose of
    a repeater is to pick up a weak signal and repeat it at full power.
     
    Uncle Bully, Jun 13, 2004
    #3
  4. eug k

    eug k Guest

    that is how a normal FDM-based [normally] passive repeater works. Receive the
    RF signal, amplify it, and retransmit it at full power... no processing done.

    wifi repeaters are active and TDM-based, which means that half the time
    it's receiving and half the time it's transmitting on the same freq ranges
    because there's only one transceiver. it stores the data after receiving,
    and forwards it in the next frame. So the net result is, your speed is
    halved.

    (fdm = frequency division multiplexing, tdm = time division multiplexing)


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    eug k, Jun 13, 2004
    #4
  5. eug k

    eug k Guest

    excellent, thanks!

    hm, are you sure? how would it get around the inherent speed-halving
    of the store-and-forward method?



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    eug k, Jun 13, 2004
    #5
  6. eug k wrote:

    TCP/IP is a sliding window protocol. You keep on sending packets af full
    speed, and the receiver sends ACK (acknowledgemets) back. There can be
    quite a delay betweend sending a packet and sending the acknowledgment, and
    many packets in the "pipeline".

    See
    http://www.efd.lth.se/~d92pa/SUB/Linkhandler/node57.html


    gtoomey
    www.ausinvestor.com Australian Investor Forum
     
    Gregory Toomey, Jun 13, 2004
    #6
  7. eug k

    eug k Guest

    yes, but APs only have one radio, so they can only transmit on
    one channel at once. So in repeater mode, it receives it, stores
    it, and retransmits it

    Just found a site that explains it well:

    http://www.cisco.com/univercd/cc/td/doc/product/wireless/airo_350/350brdgs/brscg/br350ch1.htm

    (or)

    http://tinyurl.com/35e9s

    check figure 1-4, Repeater Bridge.


    What I wanted was confirmation that it works with the linksys
    in particular. Looks like it probably will! :)

    Hooking up two APs back to back will solve the bandwidth
    issue, but that'll double the costs.


    thanks


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    eug k, Jun 13, 2004
    #7
  8. eug k

    Yousuf Khan Guest

    But the halving of receive and transmit would occur whether or not you had a
    repeater or not. That is to say if you had just a single base station, it
    would spend half of its time receiving data and the other half transmitting
    it. The halving of the bandwidth has already occurred at the first hop. Just
    adding additional access points is simply going to add latency to the
    signal, but it won't reduce bandwidth.

    Yousuf Khan
     
    Yousuf Khan, Jun 16, 2004
    #8
  9. eug k

    eug k Guest

    That would be true if all the additional access points did were to receive
    the RF signal, amplify it, and retransmit it. But that is not what happens.

    As you've said, wifi is half-duplex. The second access point receives a frame
    from the first, stores it, switches to transmit, reads it, then transmits it.
    The halving occurs on every hop. The net result is half the bandwidth
    and increased latency at each hop.

    This is well-documented and widely known, e.g. in the cisco link i posted earlier
    in this thread.

    one way to get around it is to use two APs back-to-back. But that would double
    the costs. :)




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    eug k, Jun 17, 2004
    #9
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