Shared Internet Connection thru Speedtouch 530 modem/Router

Discussion in 'Wireless Networking' started by Dennis Jelavic, Jan 13, 2005.

  1. This is a conclusion to two previous posts on the 29 Dec and 5 Jan for those
    who might be interested.

    I've installed a Netgear DG834G wireless router and all the problems
    reported above have magically disappeared. The cause of the problems is
    contained within the following response I got from a network consultant when
    I asked him whether a wireless router was necessary.

    "a) I am glad you are getting rid of the Speedtouch device - they are

    b) I am glad you are getting rid of USB for broadband internet connect - it
    is flaky!

    c) I am glad you are getting rid of ICS for sharing the internet with other
    computers - it doesnt work in a mixed environment!

    Ok, now some explanations, basically the speedtouch has known problems with
    the MSS size when used with the Telstra network. MSS is the Maximum Segment
    Size - the size of a packet that can be transmitted between two end points
    (eg. a web server somewhere in the internet and your PC). Are you using this
    device as a modem or as a router? You can tell the difference because as a
    modem your ICS machine would be actually logging into the internet, as a
    router it would be the Speedtouch that logs in.

    MSS should be negotiated between end points each time a PC connects to a
    server. However different versions of windows handles the MSS negotiation
    differently. XP usually works fine, older versions dont do MSS negotiation
    well or at all. ICS also usually breaks MSS negotiation, therefore anything
    sitting behind the ICS can load some pages, but not others.

    MSS has a maximum of 1500 bytes, usually the same as the MTU (a network
    setting for Maximum Transmit Unit), but it can be anywhere between 512 and
    1500. MSS should always negotiate lower than the MTU, but if it does not
    occur, than the MSS is assumed to be 1500. If a transfer is required that is
    larger than the MSS, it breaks the transfer up into smaller segments. The
    problem is if the MTU is less than 1500 (usually 1480 on the telstra
    network) and MSS is not negotiated (therefore the default of 1500) then
    larger transfers will not occur, and the "hanging" you experience is the
    typical symptom.

    Basically its like this, you have a 1500mm wiget trying to fit into a 1480mm
    hole. Its not going to go, and windows because of its poor implementation of
    the TCP/IP stack just sits there and "hangs".

    Why to some pages load and others not, the size of the files being
    transferred are less than 1480 bytes, or the pages are already locally
    cached. Why does it work via dialup modem, the MTU will be set to 1500 bytes
    on the dialup modem, So if MSS negotiation fails because of old OS, or ICS
    it defaults to 1500 bytes anyway. 1480 bytes is used on the Telstra ADSL
    network because of the issues with PPPoE over ATM. PPPoE and Ethernet to ATM
    takes an overhead of about 20 bytes.

    So want to do - well it cannot be fixed with what you have, therefore what
    you suggested in the first sentence is correct.

    Replace the ICS, ICF and Speedtouch with a broadband router that has a
    wireless connection such as the Linksys WAG54G

    a.. An ADSL modem, which enables a permanent and quick Internet connection
    without monopolising a telephone line - Approved for use on the Telstra ADSL
    a.. A 4-port Ethernet 10/100 switch, to connect Ethernet devices for network
    gaming and to share files, printers and broadband Internet connection
    throughout the home
    a.. A Wireless G access point (802 .11G), to connect up to 32 devices on
    your network at a speed data rate of up to 54Mbit/s, without installing the
    slightest cable in your house. This access point is of course compatible
    with all 802.11b devices functioning at 11Mbit/s.
    a.. A powerful firewall, to help prevent intrusions, protect your data and
    your private life, by the encryption of wireless transmissions or by
    blocking access by key words, without limitation of access time.

    These integrated devices can be very expensive. You can also get two
    seperate devices to do the same job."
    Dennis Jelavic, Jan 13, 2005
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