story@can503.UUCP (Robert Story) (08/24/89)
We are thinking of implementing TCP/IP and one my co-workers says that he
has heard that TCP/IP is not reliable for file transfers. Comments?
Thanks!
--
[ Robert Story ..{!utzoo!censor,!uunet!zardoz!avcoint}!avcocan!story ]
[ SnailMail : AFS 201 Queens Avenue London Ontario Canada N6A 1J1 ]
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[ Voice : +1 519 672-4220 xtn 233 ]karl@asylum.SF.CA.US (Karl Auerbach) (08/27/89)
In article <294@can503.UUCP> story@avcocan (Robert Story) writes: > >We are thinking of implementing TCP/IP and one my co-workers says that he >has heard that TCP/IP is not reliable for file transfers. Comments? TCP *is* reliable. The chances of bad data are extremely small. (No prototol can guarantee perfect reliability -- not SNA, not OSI.) This brings to mind another bit of mis-information: Seems that down in Los Angeles some IBM-oriented MIS group was saying, in a knowing authoritative voice, that Ethernet should not be used to carry financial information because it has collisions and drops digits. And since token rings don't have collisions, they don't lose digits and are thus much better for moving critical data! --karl--
karn@ka9q.bellcore.com (Phil Karn) (08/27/89)
In article <3582@asylum.SF.CA.US> karl@asylum.UUCP (Karl Auerbach) writes: >This brings to mind another bit of mis-information: Seems that down >in Los Angeles some IBM-oriented MIS group was saying, in a knowing >authoritative voice, that Ethernet should not be used to carry >financial information because it has collisions and drops digits. And >since token rings don't have collisions, they don't lose digits and >are thus much better for moving critical data! Yes, token rings don't have collisions. But some DO occasionally duplicate packets (examples on request). I'd sure like to see the faces of the MIS financial types when they learn this little tidbit. Better yet, let me see if I can get my employer to use a token ring when they transfer my pay into my checking account. :-) Phil
roy@phri.UUCP (Roy Smith) (08/28/89)
In article <3582@asylum.SF.CA.US> karl@asylum.UUCP (Karl Auerbach) writes: > Seems that down in Los Angeles some IBM-oriented MIS group was saying, > in a knowing authoritative voice, that Ethernet should not be used to carry > financial information because it has collisions and drops digits. I remember reading (handwave: about 2 years ago, in RISKS-DIGEST) about a hospital which was putting in a network. They had pretty much decided on ethernet, when some suit found out about collisions: "You mean sometimes data is transmitted and network errors cause it to be lost!? We can't have any data get lost in a hospital!" And so they decided that they couldn't use ethernet. -- Roy Smith, Public Health Research Institute 455 First Avenue, New York, NY 10016 {att,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy@alanine.phri.nyu.edu "The connector is the network"
kasten@interlan.interlan.COM (Frank Kastenholz) (08/28/89)
TCP/IP as a suite IS reliable (or at least as reliable as the rest of the network world:-). Where the confusion may have arisen is that IP, in and of itself is NOT reliable. In a middle to large sized network, IP datagrams can and ARE dropped, lost, duplicated, corrupted, misordered, etc, etc. The TCP layer corrects for this. To quote from the TCP Spec (RFC 793): "This document focuses its attention primarily on .... computer communication requirements, especially robustness in the presence of communication unreliability and availability in the presence of congestion" and "Very few assumptions are made as to the reliability of the communication protocols below the TCP layer. TCP assumes it can obtain a simple, potentially unreliable datagram service from the lower level protocols." and finally, "The TCP must recover from data that is damaged, lost, duplicated, or delivered out of order by the internet communication system." TCP/IP is reliable. Cheers Frank Kastenholz Racal InterLan
patterso@hardees.rutgers.edu (Ross Patterson) (08/31/89)
Frank Kastenholz <kasten@interlan.interlan.COM> writes: >TCP/IP as a suite IS reliable (or at least as reliable as the rest of the >network world:-). Where the confusion may have arisen is that IP, in and >of itself is NOT reliable. Reliable has several definitions. Webster offers "suitable or fit to be relied on" and "giving the same result on successive trials". TCP as defined in the RFCs meets both, but as implemented in many cases, fails the latter. In particular, the "keepalive abomination" causes connections that might otherwise survive brief outages or reconfigurations. MIS departments (the original message cited one) generally understand a third definition, embodied in the IBMism "RAS" (Reliability, Availability and Servicability): "safe, tested, designed to avoid problems". Any system that aborts a 100MByte FTP that's already 85% complete because an intervening gateway was rebooted flunks this. Proper use of exponential backoff and avoidance of keepalives put the R back in RAS. Just ask Phil ("I Hate KeepAlives") Karns, who has reported FTP sessions that succeeded after being interrupted for *days* in the ham radio world, where such things are done right. Ross Patterson Rutgers University
bin@primate.wisc.edu (Brain in Neutral) (09/01/89)
From article <3582@asylum.SF.CA.US>, by karl@asylum.SF.CA.US (Karl Auerbach): > This brings to mind another bit of mis-information: Seems that down > in Los Angeles some IBM-oriented MIS group was saying, in a knowing > authoritative voice, that Ethernet should not be used to carry > financial information because it has collisions and drops digits. And > since token rings don't have collisions, they don't lose digits and > are thus much better for moving critical data! Gosh! You mean... that *isn't true*?!?