Re: TCP vs UDP

[Philip Brown <philb@soda.berkeley.edu>]

>>>>[From Carl Edman]

    > So when calculating required bandwidth to sustain a fast game with
    > TCP, you've also got to allow packet acknowledgement for TCP. This is
    > what makes for bad net lag (as opposed to just "mild" net lag with
    > udp ;-)
    
    That I think is misleading.  The really slow connections (which is  
    those we need to worry about -- any reasonable protocol will do well on  
    even medium speed connections) are all full duplex (like modem links or  
    57.6 kbps leased lines).  Sending acknowledgments on the back channel  
    doesn't subtract any bandwidth on the forward channel.

Eh... it does and it doesn't.
Sort of like the amusing line,

"In theory, there is no difference between theory and practice.
 In practice, there is."
 
Speaking specifically of 14.4 modem lines, since that is what I am
directly familiar with, sending data the other way shouldn't slow things
down. But it does.

This is on a sparc 1, with a USR sportster 14.4k sportster Fax/modem.


Then there's the whole "latency" issue.

IFF there is a holdup, and a packet gets lost with tcp... the server tcpd
will retransmit until it gets through. That is stupid, since by the time
it is retransmitted, you won't WANT the data anyway! It only serves to
screw up your responsiveness.
This is especially bad if a whole chunk of packets gets lost or delayed
(as often happens playing xtrek in tcp mode)
(although i wouldn't dare play xtrek over my 14.4 line. but it was bad
 enough over ethernet)