Boston Linux & Unix (BLU) Home | Calendar | Mail Lists | List Archives | Desktop SIG | Hardware Hacking SIG
Wiki | Flickr | PicasaWeb | Video | Maps & Directions | Installfests | Keysignings
Linux Cafe | Meeting Notes | Blog | Linux Links | Bling | About BLU

BLU Discuss list archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Verizon DSL question

[John Jannotti: Tue, Apr 30, 2002 at 11:47:06PM -0400]

> frames have to get through instead of one in order to get a packet through.
> So, roughly speaking a 1% (Ethernet frame) loss rate becomes a 2% (IP

the truth is somewhere in between.

packet size is *not* independent of the packet loss rate. Smaller
packets are lost less often, though not strictly proportionately less often.

Also interesting, consider the resend granularity. If you lose 1 of
two packets you resend that lost packet. If you lose 1 of 2 fragments
you have to resend them both.

> Matching your IP packet size to the true MTU size of the path gets you down
> to the true loss rate, and TCP works better.

yep.. PMTUd exists exactly because fragmentation hurts so bad
(fragmentation doesn't even exist in ipv6 - PMTUd is a
requirement). but PMTUd has significant costs too, much better to
short circuit the whole process by setting your host's mtu
appropriately when you know there is a smaller mtu in the path (this
also serves as a hint to the other end to use your mtu, the PMTU cost
is much more expensive to him because the fragmentation point is so
much farther away from his perspective.).


BLU is a member of BostonUserGroups
BLU is a member of BostonUserGroups
We also thank MIT for the use of their facilities.

Valid HTML 4.01! Valid CSS!

Boston Linux & Unix /