[c-nsp] MTU Question on T1

[Jon Lewis]

On Mon, 24 Jan 2005, Richard J. Sears wrote:

> On the dual T1 issue - correct me if I am wrong please but with ppp
> multilink interleaving turned on, won't it take that single 40000 byte
> packet and shove it down one T1 because it came in as a single packet..?

That might depend on whether you have multilink fragmentation
enabled...but since that packet is much larger than MTU anyway, it's going
to be fragmented and I suspect multilink fragmentation won't matter...its
still lots of 1500 byte packets.  You've got the gear setup.  What are you
seeing?

I started doing the math from the other direction before I saw Gert's
reply...and to move 40,000 bytes in 50ms, that'd be 800bytes/ms, or 6400
bits/ms, which is 6400000 bits/s (6.4Mbit/s).  Since you need to go back
and forth, you really need 40,000 bytes in 25ms (assuming no delay in
processing/responding), so that's 12.8Mbit/s.  Did the vendor say you'd be
able to do this with T1s?  It looks to me like you'd need a DS3 to meet
their specs.  Maybe doable with a whole bunch of (like >8) T1s.

BTW...given fast enough links, this is possible.  From my workstation, I
can ping -s 40000 an IP on our network that's separated from me by
1FE-router-1DS3-router-2DS3-router-1FE-router-1FE-host (several L2 switch
hops are omitted).  rtt avg was 33ms.

----------------------------------------------------------------------
 Jon Lewis                   |  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________