Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 alpha 4/15/85; site ucbvax.ARPA
Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!tcp-ip
From: tcp-ip@ucbvax.ARPA
Newsgroups: fa.tcp-ip
Subject: TCP Timer
Message-ID: <8067@ucbvax.ARPA>
Date: Wed, 12-Jun-85 10:37:08 EDT
Article-I.D.: ucbvax.8067
Posted: Wed Jun 12 10:37:08 1985
Date-Received: Thu, 13-Jun-85 02:16:37 EDT
Sender: daemon@ucbvax.ARPA
Organization: University of California at Berkeley
Lines: 29

From: zhang%erlang.DEC@decwrl.ARPA  (Lixia Zhang)

I have a few questions concerning setting timers for outstanding TCP
segments.

The following paragraph from the TCP spec (rfc-793, page 10) sounds like
that a timer should be set for each outstanding segment:

"When the TCP transmits a segment containing data, it puts a copy on a
retransmission queue and starts a timer;  when the acknowledgment for that 
data is received, the segment is deleted from the queue.  If the
acknowledgment is not received before the timer runs out, the segment is
retransmitted."

My questions are:

- Should we understand it as one timer need be set for each outstanding
  segment?

- What are the situations in real implementations?  From what I've heard, most
  implementations use a single timer per connection - am I right?
  I sort of remember this was mentioned in a recent msg
  that some implementations set a timer for each segment, some others use a
  single timer.  What is the population percentage for each side?

- Does anyone have any idea, or observations, about the performance
  difference, big or small, between the two different implementations?

Lixia