[Mr.Dearthian]

Recently I received my first Mac, a brand spanking new ibook (absolutely dig the heck out of it). I mainly use it at work and on the road. At the house I mainly use a Wintel PC (I am a pretty well seasoned PC user). At work, all the other machines are Wintel machines (it is a workgroup setup).

At work, I can connect to a shared folder on any of the PC's and get great transfer rates when transfering files between machines. At the house, with a PC that smokes anything here at work, my transfer rates are horrible!! We're talking rates around .5Mbit (this is about as fast as my 768 DSL connection at the house).

Here are the setups at different locations:

Home:
iBook connected via ethernet port to Linksys 4 port switch
PC running Windows XP w/SP2 and all updates connected via ethernet to above switch
Switch connected to Linksys Router via ethernet uplink port with CAT5

Work
iBook connected via Airport Extreme to Linksys Wirless B Router (obviously 11mBit)
PC running Windows XP w/SP1, connected to Router via Ethernet cable
PC laptop running Windows 2000 w/SP4 connected via wireless to Wireless Router

I want to make sure I'm not missing something on the Mac side since I'm new to Macs and not on the PC side. If it's not something on the Mac side, it's probably something to do with XP SP2.

Thanks,
Mr.Dearthian

[Mr.Dearthian]

Anyone? Buehler? Buehler?

Mr.Dearthian

[ghporter]

I think it's a matter of something called MTU, or Maximum Transmission Unit. In general, DSL users need to set both their computers and their routers to use an MTU setting of 1492.

Most DSL providers, including all the SBC providers, use the Point to Point Protocol over Ethernet (PPPoE) to authenticate users and establish connections. There's an overhead of 8 bytes in every packet for the PPPoE connection, so you lose a small fraction of the potential payload. But your computer (and probably router) are set up to use the whole packet, all 1500 bytes of it. You're trying to put 1500 bytes into a (now) 1492 byte package; this means a lot of packet fragmentation. Aside from being nasty sounding, this fragmentation loses you a lot of effective speed, since it results in a lot of retransmitted packets.

(This assumes you have a recent firmware version in your Linksys router-let me know if you need more instructions.) In your Linksys router's setup pages, in the Basic Setup section, there's an area for your connection type, and below that is a box and a couple of radio buttons for MTU. You need to select "Enable" and enter 1492 in the box. Then click the Save Settings button to make the change permanent.

This may or may not totally fix the problem, but it will almost certainly help. I can't find any really good sources to back me up on this, but I think that OS X will automatically determine the appropriate MTU size and adjust accordingly. I never had to do anything to our iBook when we put it on the DSL-connected network here at home.