[2177] in North American Network Operators' Group
Re: MCI [ATM overhead]
daemon@ATHENA.MIT.EDU (Vadim Antonov)
Wed Mar 20 18:40:24 1996
Date: Wed, 20 Mar 1996 12:10:13 +0800
From: avg@postman.ncube.com (Vadim Antonov)
To: cook@cookreport.com, forster@cisco.com
Cc: jogden@merit.edu, nanog@merit.edu
Jim Forster <forster@cisco.com> wrote:
>He's talking about the overhead due to carrying variable length IP packets
>in fixed length ATM cells.
...
>There's beginning to be some expectation that there will be a transmission
>capacity crunch in the carrier's Sonet nets, and this ~25% ATM cell tax may
>be looked at carefully as packet over Sonet solutions emerge.
Given the bimodailty of IP traffic size distribution (about 40% of packets are
small, like TCP ACKs or telnet/rlogin keystrokes) the ATM "cell tax" is
closer to 32%.
I.e. a dual clearline DS-3 actually carries as much user data as OC-3c ATM.
Which, incidentally, was why SprintLink backbone design is easily expandable
to dual links (that includes carefully considering implications for routing).
Sean presented that design on NANOG a year ago, BTW. Funny thing, the design
is expandable beyond that, too, so OC-3 ATM is already obsolete.
--vadim
