Subject: UDP Lite

From: Mikael Degermark <[email-masked]>
Date: Thu, 19 Aug 1999 10:19:56 +0200

Vernon,

I believe I understand and I definitely support the end-to-end argument.
There is absolutely no question in my mind that the TCP checksum is needed.
There is also definitely a need for an end-to-end checksum over the header(s)
of packets even if damage to the payload is tolerated.

Fact is, part of the reason I'd like to see UDP Lite happen is that
I've seen some of the horrors people (whose names shall mercifully not
be exposed) have produced to make UDP work for the class of applications
that prefer delivery of damaged packets over discard. 

Example: One proposed scheme I saw was to recompute the UDP checksum after the
error-prone link to make it appear that the packet was in fact intact even if
the cellular link had damaged it. The rationale for doing that was
to fool the receiving UDP into delivering the packet to the application
instead of discarding it (!).

I hope we all agree that that scheme is an abomination.

These applications will be in the Internet. We should make the Internet
suitable for them to avoid the abovementioned horrors. The way to do 
that is simple: slightly redefine the semantics of the UDP Length and 
UDP Checksum fields to produce UDP Lite. In addition, the lower layers 
in question need to accomodate the partial checksumming policy, that 
is a battle to be fought elsewhere. 

At 11:52 PM 8/18/99 -0600, Vernon Schryver wrote:

>It seems to me that every 3-5 years someone demands to know why we waste
>all of those CPU cycles on TCP checksums when there is a perfectly good
>Ethernet CRC, and then describes the newly invented solution.
>
>
>Vernon Schryver    [email-masked]
>
>

http://www.cdt.luth.se/~micke