802.11g standard slowed to 10 - 20 Mbps

Discussion in 'Macintosh Computers' started by BubbaTAC, May 23, 2003.

  1. BubbaTAC macrumors member

    Joined:
    Jan 12, 2002
    #1
    Check out this link:

    http://www.computerworld.com/mobiletopics/mobile/story/0,10801,81450,00.html?nas=PM-81450

    It looks like the "54Mbps" standard (which really runs at the speed of B if both are using the same base station) will now officially be slowed to 10-20Mbps.
    This isn't a huge deal to me because I always knew it was only this fast, but what do you think about it. Will it hurt Apple to have to say that the standard was changed and the money you spent on g is now going to slower technology?

    bizarre
     
  2. flahiker macrumors member

    Joined:
    Jan 3, 2003
    #2
    No, the IEEE standard refers mostly to the interoperability between .11g and .11b networks.

    If you bring a .11g device to a .11b network (say a public access point) you will get .11b speeds.

    If you bring a .11b device to a .11g network, it will still get .11b speeds but the .11g devices will suffer a performance hit. But rather than throtteling all the way down to .11b rates they can maintain 10Mbsp throughput.

    In a sole .11g environment, the added overhead will reduce the ACTUAL throughput from ~22Mbps to ~20Mbps. The broadcast rate is still 54Mbps.

    Remember that the .11b Actual through put is somewhere around 5Mbps.
     
  3. maradong macrumors 65816

    maradong

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    Mar 7, 2003
    Location:
    Luxembourg
    #3
    huh !
    nicely said :D
     
  4. mmcneil macrumors regular

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    Sep 4, 2001
    Location:
    San Diego, CA
    #4
    Throughput

    This is really no different than almost any communications medium - Theoretical speeds are never matched in practice.

    I believe a common rule of thumb for ethernet is that actual throughput is about 40% of theoretical throughput.
     
  5. peterjhill macrumors 65816

    peterjhill

    Joined:
    Apr 25, 2002
    Location:
    Seattle, WA
    #5
    Re: Throughput

    On a shared network (using hubs) the theoretical maximum is indeed about 40%. Wireless networks are shared networks. Clients must use collision detection and avoidance. They must listen to here if anyone is sending, send a RTS (request to send) packet. Wait for the Access Point (AP) to send a CTS (Clear to Send) packet to the client. They then can only send as much data as can fit into a predefined time slice. We (the Network Group of Carnegie Mellon University) have done extensive testing with 11g and 11a and 20 mbps is about the top end one can achieve, in the same manner 5 mbps on 11b is a great transfer rate.

    One a switched network, where a host is connected to a port on a switch that learns which hardware addresses (MAC Addresses) are connected to which port, it is possible to send traffic at very close to the stated speed. 95-97 mbps on a Fast Ethernet. On Gigabit Ethernet, you are limited in most cases by the amount of data the CPU can send to the network port. Intel has a new architecture that basically puts the Ethernet interface in direct contact with the memory bus and allows asynchronous transfers direct from memory to the Ethernet with hardware assist building packets. This architecture is very exciting, as it will potentially allow hosts (like servers) to perform at very high rates.

    So, on a hub 40% is the limit, on a switch, the limit is within 5% of the stated rate.
     
  6. bennetsaysargh macrumors 68020

    bennetsaysargh

    Joined:
    Jan 20, 2003
    Location:
    New York
    #6
    54Mbps is cool and all, but why would you need something that fast? i also don't get why they don't use the actual speeds instead of the raw speeds.
     
  7. mmcneil macrumors regular

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    Sep 4, 2001
    Location:
    San Diego, CA
    #7
    Why speed?

    Because they can :) but it does make the transfer of video and large files much speedier.:D
     
  8. Freg3000 macrumors 68000

    Freg3000

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    Sep 22, 2002
    Location:
    New York
    #8
    Yeah, faster is always better. I am just wondering, I know 802.11 a also has the same theoretical throughput, but does it have the same actual throughput?
     
  9. ZildjianKX macrumors 68000

    ZildjianKX

    Joined:
    May 18, 2003
    #9
    Haha, I'll tell your wife/GF you said that... :rolleyes:
     
  10. MisterMe macrumors G4

    MisterMe

    Joined:
    Jul 17, 2002
    Location:
    USA
    #10
    Yes, 802.11a has about the same actual throughput of 802.11g. Due to its higher carrier frequency, however, its useable range is much shorter.
     

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