Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!decvax!ucbvax!LOKI.BBN.COM!craig From: craig@LOKI.BBN.COM.UUCP Newsgroups: mod.protocols.tcp-ip Subject: 4.2/4.3 TCP and long RTTs Message-ID: <8612070135.AA05419@ucbvax.Berkeley.EDU> Date: Sat, 6-Dec-86 20:38:02 EST Article-I.D.: ucbvax.8612070135.AA05419 Posted: Sat Dec 6 20:38:02 1986 Date-Received: Sun, 7-Dec-86 02:25:27 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 34 Approved: tcp-ip@sri-nic.arpa I'm in the midst of doing comparisons between an RDP implementation and the 4.2/4.3 TCP implementations and have run into a problem which I'm hoping someone else can shed light on. I'm running tests on two machines, a VAX 750 running 4.3 and a SUN workstation running 4.2. The two machines are on the same Ethernet and use the same gateway. If I set up an experiment to test behaviour over paths with long network delays (for example, bouncing packets off Goonhilly), the TCP connections are established and then typically fail part way through the transfer. I don't understand this because the RDP connections work just fine, and typically complete in 1/4 the time it takes for a TCP connection to send about 20% of the data and faint. The experiment generally involves passing 50-100 segments of anywhere from 64 to 1024 bytes to the protocols to send. This is on weekends so the delays aren't that long. The question I'm trying to answer is whether the problem is in the RDP implementation (what anti-social things could it be doing to maintain that connection?), or the TCP implementation (what might it be doing wrong to die where another implementation succeeds?). If I can, I'd like to discourage invective. I'm simply trying to figure out why this is happening so I can identify and fix the problem and do a comparison between the two implementations/protocols. (And soon -- hair pulling over this problem is beginning to threaten the health of my scalp and beard). General information on the RDP implementation: it will retransmit up to 10 times and calculates the round-trip time based on the first packet sent with the caveat that it ignores round-trip times of segments with sequence numbers lower than those of segments whose round-trip time has already been computed (this feature is an experiment which may not stay). The maximum RTT is 2 minutes, the minimum is 2 seconds. Craig