ArgMeMatey
join:2001-08-09
Milwaukee, WI
 ·AT&T Midwest
| Don't include transport overhead in the quoted speeds
AT&T includes the transport overhead of their internal network (Layer 2) in the speed claim.
I believe they use ATM so packet segmentation uses up a lot of additional bytes for headers. 53 byte packet, 48 payload and 5 byte header if my lousy memory is somewhere in the ballpark.
So for example "up to 3000 kbps" will NEVER exceed about 2500 kbps of data at layer 3 and above.
This is deceptive because transport overhead is easily calculated unlike burstiness effects and other statistical guesses. Although they declare their true meanings in the fine print, they should be required to say, "3000 is the cap, and we use 500 of that just to get you to the internet. So you really have 2500 to play with when things are otherwise at their best."
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