FYI - unproven technology

Ken Latta klatta at
Wed Oct 19 20:51:20 UTC 1994

Curtis I'm not sure I understand your use of the term "unproven."

In Lan circles we've been discussing this exact same phenomena for the
last 9 months (I raised it with Jessica as a potential explanation
of some of the problems we were seeing in our early testing).

Bob Metcalfe (coinventor of ethernet) discovered the some ethernet chip
sets were also violating the inter-packet gap spec. A particular problem
was that many of the devices used for sniffing themselves had the same
chip sets and simply couldn't see what was happening to the packet
stream (silent discards withour errors signalled at the receiving end).

He needed very expensive signal analysis hardware before
the cause could be isolated.

Ken Latta, Merit Network, Inc.
NSFNET Project, Internet Engineering Group
1071 Beal, Ann Arbor, MI 48109-2103
313.936.2115 voice,  313.747.3745 fax
klatta at, USERLFQF at umichum.bitnet

> From:    Curtis Villamizar <curtis at>
> To:      nanog at

> FYI-
> For those that don't appreciate the consequences of using unproven
> technology.  The good news on Mae-East is packet loss is down to 15%
> from 40%?  :-(
> Congratulations to Sprint for picking a technology that is known to
> work for the Sprint NAP.  FDDI works.  We'll see how the others NAPs
> do, though I'm not encouraged by test results so far.
> Curtis
> BTW - this is Mae-East (the MFS bridged ethernet), not Mae-East+ (the
> bridged FDDI).
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> From: Sean Doran <smd at>
> Reply-To: smd at
> To: mae-east at
> Subject: Moderately urgent: getting rid of annoying packet losses
> Date: Wed, 19 Oct 1994 02:07:06 -0400
> Sender: smd at
> The Magnum boxes are *very* unhappy with inter-packet gaps of less
> than about 23 microseconds, and drop back-to-back packets like
> superheated rocks.
> We have a kludge which will help until the MFS hardware gets fixed.
> Those of you running one Cisco with EIP 10-0 microcode or better should
> set the transmitter-delay of your MAE-EAST interface to 96 (0x60).
> This will dramatically reduce the packet loss across MAE-EAST.
> IMPORTANT: Those of you who have more than one box on your ethernet
> drop to MFS will need to a/ acquire EIP 171-1 from Cisco and load
> it in then b/ set the transmitter-delay of each of your MAE-EAST
> interfaces to 0x360 (864).
> The new microcode has apparently been well tested, and is doing the
> right thing for and (drops
> to most of you have fallen from 40% to much less than 15%).  It
> works by assigning new meanings to the upper 8 bits of the transmitter-
> delay value; this particular setting will delay the transfer of
> the packet to the datalink controller when there is traffic
> on the wire, then require an additional quiet time of 30usec, 
> after which there will be the standard 9.6 usec IEEE 802.3 delay.
> (The original intent apparently was to avoid drops when bursting
> ethernet traffic encounters collisions by backing off on handing
> the packet to the datalink layer; the application here is not quite
> exactly what was intended, but definitely helps us).
> Each of your routers attached to MAE-EAST must run the new EIP 171-6
> microcode and have the 0x360 transmitter-delay setting.
> Thanks to Robert M. Broberg of Cisco for the code.
> Those of you without Ciscos will have to come up with a similar hack 
> somehow.
> 	Sean.
> P.S.: We are *very* keen on PSI, NETCOM, and MCI to implement the
>       change, especially PSI.  We aren't having problems with anyone
>       else we exchange traffic with at MAE-EAST (other than Dante
>       AS1133, but that's not a Cisco) but everyone would probably 
>       benefit from the upgrade anyway.  Try pinging each of your peers
>       in 192.41.177 a hundred or so times.
> - - --
> Sean Doran <smd at>  SprintLink/ICM engineering   +1 703 904 2089
> ------- End of Forwarded Message

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