Return to BSD News archive
Newsgroups: comp.unix.bsd.freebsd.misc Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.bhp.com.au!mel.dit.csiro.au!munnari.OZ.AU!news.ecn.uoknor.edu!qns3.qns.com!imci4!newsfeed.internetmci.com!info.ucla.edu!news.bc.net!news!news From: rmcouat@dowco.com (Ron McOuat) Subject: Re: FreeBSD Losing to Linux - Please Help Sender: news@dowco.com Message-ID: <DpL2y7.6zx@dowco.com> Date: Tue, 9 Apr 1996 06:17:15 GMT References: <4ju4rb$67q@post.gsfc.nasa.gov> <SCOTTE.96Apr4083440@odie.center.uscs.com> <316524bc.175490932@news.teir.com> Nntp-Posting-Host: ppp49.dowco.com Organization: Dowco Computer System Ltd. X-Newsreader: Forte Free Agent 1.0.82 Lines: 47 cwilliam@teir.com (Curtis Williams) wrote: >On 04 Apr 1996 16:34:39 GMT, scotte@center.uscs.com (L. Scott Emmons) >wrote: >>In article <4ju4rb$67q@post.gsfc.nasa.gov> kjeffers@nastg.gsfc.nasa.gov (Karen Jefferson x2857) writes: >> >>> Although our preference had been to use FreeBSD, the UDP performance >>> was terrible (200 Kbps over Ethernet), and we kept getting ENOBUF >>> errors which makes FreeBSD an unacceptable choice. >> >Another item to check is your tcp retransmit rate. Since udp is a >datagram service it doesn't guarantee delivery. tcp will guarantee >delivery and will retransmit any lost packets. tcp should lose packets >at the link layer at the same rate udp does; consequently if you are >losing a lot of udp packets you should also see a correspondingly high >tcp retransmit rate. Unless something else is going on that is. There >are many factors contributing to udp packet loss including >transmission rate, line quality, router congestion etc. With the >exception of transmission rate (tcp has a max packets outstanding >sliding window) all of these factors effect both udp and tcp packets >at the link level. At the link layer the only difference between tcp >and udp is the packet type field (can't remember any more but tcp has >a value of 7 and udp is 15 or something link that). The difference is >that tcp retansmits so the user never sees "lost" tcp packets. udp, by >design, doesn't retransmit so you do see the lost packets. The sliding window algorithm should throttle back the sender to the point where there are none to very few lost packets in the TCP case. The problem with UDP is you can just keep hammering out new datagrams unless you implement some sort of application level handshake. Most applications I can think of do a send-get_response type of handshake when using UDP (e.g. SNMP, NFS, TFTP). Ron McOuat [snip] >Hope this helps. >Curt Williams >VP, Technology >Thomson Electronic Information Resources (TEIR) >cwilliam@teir.com