Re: Re[2]: Can one use CUSM with TIA?
Fri, 3 Feb 1995 14:05:37 -0500

>At 12:01 PM 3/2/95 -0500, wrote:
>> I agree with The problem is not necessarily
>> TIA. I suspect it is the Windows/Reflector problem I worte about. If
>> there are people having trouble with TIA, I recommend that they try my
>> test bed at and contact me by e-mail and/or voice.
>Don't get me wrong here ... the problem is indeed TIA.
>I am simply saying that TIA does support UDP, but for some reason, not CUSM.
>Does CUSM use _any_ ICMP protocol, as well as UDP?

No, CU-SeeMe does not use any ICMP protocols. I think P. Stingley is
correct that it has to do with "funny" IP addresses. Each CU-SeeMe packet
contains the (apparent) IP address of the machine on which it originated
(CU-SeeMe trying to find its own IP address is the source of the dreaded
"GetHost" error that Windows folks experience). This is not intended to be
used for network addressing, but just as a unique ID, e.g., to identify
which window a video packet belongs to. Currently, the reflector software
compares this supposed IP address with the actual source IP address (from
the IP header) and rejects the packet if they don't match. I'm not sure
why it does that; I think it was a quick fix to some problem we observed.
In any case, anyone who is in a situation where the IP address that your
machine thinks it has is different from the actual IP source of the packet
that reaches the reflector will not be able to connect to a reflector.

Tim Dorcey
Sr. Programmer/Analyst (607) 255-5715
Advanced Technologies & Planning
CIT Network Resources
Cornell University
Ithaca, NY 14850