Xref: utzoo comp.dcom.lans:7464 comp.protocols.tcp-ip:15256 Path: utzoo!news-server.csri.toronto.edu!rutgers!usc!samsung!uunet!shl!phil From: phil@shl.com (Phil Trubey) Newsgroups: comp.dcom.lans,comp.protocols.tcp-ip Subject: Re: TELNET slow through bridge. Message-ID: <1991Mar12.223827.12815@shl.com> Date: 12 Mar 91 22:38:27 GMT References: <1991Mar11.161437.13053@shl.com> Organization: SHL Systemhouse Inc. Lines: 46 In an earlier posting to comp.dcom.lans, I mentioned a problem we were having telneting to an HP 3000 through a bridge using PC/TCP. Well, it turns out that the problem is not related to the bridge, and is actually composed of three separate problems. The original problem was that telneting from PC/TCP on a PC to the HP 3000 would occationally slow way down when the HP was outputing lots of text to the PC's screen. In the middle of transmission, it would start to display one line at a time every four seconds. With a protocol analyzer we were able to determine what was going on. The problem occurs when the PC drops a packet. The HP doesn't realize that this has occured, of course, and merrily blasts the TCP window size number of bytes to the PC. The PC meanwhile keeps sending an ACK that acks everything up to the dropped packet. So far so good. The HP realizes that the PC has dropped a packet when its timeout timer kicks in (4 seconds later). It then proceeds to retransmit the dropped packet and just the dropped packet. The PC, not having kept the packets after the dropped packet, calmly acks the retransmitted packet from the HP and waits for the HP to send the rest of the packets. The HP waits for another retransmission interval and then retransmits the next packet that it had sent. This continues until the HP has sent all outstanding packets - at a rate of one every four seconds. Questions: 1. Is it normal for PC TCP implementations to drop packets fairly frequently? Ie about one packet every 100 or so? 2. The original TCP spec seems to be silent here, but surely this can't be the 'standard' way retransmission works? I would have though that the retransmitter would send all outstanding packets all at once after an ack timeout, rather than one packet every timeout interval, the way the HP 3000 does. 3. Is it normal for TCP implementations to discard all out of sequence packets? Thanks for any info! -- Phil Trubey | Internet: phil@shl.com SHL Systemhouse Inc. | UUCP: ...!uunet!shl!phil 50 O'Connor St., Suite 501 | Phone: 613-236-6604 x667 Ottawa, Ontario, Canada | Fax: 613-236-2043