ssw@cica.cica.indiana.edu (Steve Wallace) (05/29/90)
When is an ethernet full? We have a campus backbone composed of a chipcom 10 Mbs ethernet over broadband and a UB 5 Mbs ethernet over broadband (buffered repeaters). The UB and chipcom networks are bridged to form one logical networks. According to our Network General sniffer, we constantly maintain about 10-15 percent utilization or (300 - 1000 packets per second). How much more traffic can this network support before performance falls off measurably? Any ideas? Thanks, Steven Wallace Indiana University wallaces@ucs.indiana.edu
craig@bbn.com (Craig Partridge) (05/29/90)
> When is an ethernet full? .... > According to our Network General sniffer, > we constantly maintain about 10-15 percent utilization or (300 - 1000 > packets per second). How much more traffic can this network support > before performance falls off measurably? Any ideas? The best place I know of to start answering this question is Boggs, Mogul and Kent's article in Proc. of SIGCOMM '88 pp. 222-233. The gist of that article is that you can drive the Ethernet all the way to its rated capacity assuming you are careful in the way you lay out your network, and all your systems have good Ethernet hardware. In practice of course, many of the systems won't have good Ethernet hardware (for example, Jacobson's talk at SIGCOMM '88 indicated he'd found an Ethernet chipset that could only go about 6 Mbits/sec). So you need to find some people out there with some good practical experience about when some of their systems start breaking down, to figure out when your network will die due to poor hardware/software. Craig
rsmith@vms.macc.wisc.edu (Rusty Smith, MACC) (05/30/90)
In article <1141@cica.cica.indiana.edu>, ssw@cica.cica.indiana.edu (Steve Wallace) writes... > >When is an ethernet full? We have a campus backbone composed of a >chipcom 10 Mbs ethernet over broadband and a UB 5 Mbs ethernet over >broadband (buffered repeaters). The UB and chipcom networks are bridged >to form one logical networks. According to our Network General sniffer, >we constantly maintain about 10-15 percent utilization or (300 - 1000 >packets per second). How much more traffic can this network support >before performance falls off measurably? Any ideas? > We have a similar setup here. There are about 50 Chipcom's connected to our broadband backbone. All but 3 are coupled to DEC Lanbridges to keep local traffic local. We have had similar 1 minute averages and peaks of 3-4 times as much. As far as we can tell everyone is satisfied with the performance with these numbers. We have had other performance problems not caused by traffic volume. Rusty Smith Internet: rsmith@vms.macc.wisc.edu MACC Data Communications Bitnet: rsmith@wiscmacc (608) 263-6307 Univ. of Wisconsin @ Madison
hedrick@athos.rutgers.edu (Charles Hedrick) (05/30/90)
>When is an ethernet full? We have a campus backbone composed of a >chipcom 10 Mbs ethernet over broadband and a UB 5 Mbs ethernet over >broadband (buffered repeaters). The UB and chipcom networks are bridged >to form one logical networks. According to our Network General sniffer, >we constantly maintain about 10-15 percent utilization or (300 - 1000 >packets per second). How much more traffic can this network support >before performance falls off measurably? Any ideas? I'd like to see you get data with a bit more time resolution. It's a bit unusual for networks to run at 10-15% all the time, day and night. More typically, there's a long-term variation over the course of a day, with more traffic during the day than night, and short-term variation as people boot machines, transfer big files, or do other things that cause a short-term demand for bandwidth. If you're running at 10% 24 hours a day, this suggests either a very odd mix of users and applications, or that most of your bandwidth is going to broadcast packets produced by rwhod or things of that nature. I have heard of networks with a constant broadcast load of that sort. In that case, replacing some or all of your bridges with routers might be more useful than trying to increase the bandwidth. In general I'd expect a peak to average ratio of about 10 to 1. That is, if you are averaging 10% usage, you are probably using 100% during brief periods. So you're about at capacity. If your 10% is made up mostly of a continuous background of broadcast packets, this might not be the case. But if you've really got that much broadcast traffic, you've got other problems. Like your hosts are all spending significant CPU dealing with it. If your 10% represents the maxima of your peaks, rather than a true average, then you're probably in good shape and still have some room to grow.
ssw@cica.cica.indiana.edu (Steve Wallace) (05/30/90)
A little more info.
We have about 45 IP subnets all behind cisco routers. We
route appletalk phase I, DECnet, and bridge IPX. Between the
hours of 9am to 5pm we see a pretty steady 10 - 15 percent load.
Sometimes this drops to 2 percent but only for very brief
periods.
Steven Wallace
wallaces@ucs.indiana.edujim@syteke.be (Jim Sanchez) (05/30/90)
One thing you want to be SURE and remember is that the ethernet on broadband stuff has a significant distance limitation. If your campus cable system is a as large as I suspect, then the 10broad36 channel is probably working more as csma than csma/cd and the effective channel capacity is ~2 Mb not 10 Mb. That is why we use 802.4 for backbone applications it also uses much less bandwidth. The UB stuff is also just CSMA (if my memory serves me). In both cases, the effective channel capacity is approximately 35% of the data rate. If you calculate the maximum number of packets on an 802.3 channel it is about 13,000 and scale accordingly I don't think you are overloaded based on your numbers. However, this is a tricky thing to find out. -- Jim Sanchez | jim@syteke.be (PREFERRED) | OR {sun,hplabs}!sytek!syteke!jim Hughes LAN Systems | OR uunet!mcsun!ub4b!syteke!jim Brussels -- Jim Sanchez | jim@syteke.be (PREFERRED) | OR {sun,hplabs}!sytek!syteke!jim Hughes LAN Systems | OR uunet!mcsun!ub4b!syteke!jim Brussels
wyatt@cfa250.harvard.edu (Bill Wyatt) (05/31/90)
>When is an ethernet full? [...] >we constantly maintain about 10-15 percent utilization or (300 - 1000 [...] I highly recommend you get a copy of the DEC Western Research Lab WRL Research Report 88/4, titled: `Measured Capacity of an Ethernet: Myths and Reality' by Boggs, Mogul, and Kent. It's also in the SIGCOMM '88 proceedings. They conducted real-world measurements on a test Ethernet, and found that the wire is capable of sustaining >90% utilization under most circumstances. The report is available via email from wrl-techreports@decwrl.de.com in PostScript form. (Or {...}!decwrl!wrl-techreports for UUCP.) All you do is send mail to an archive server with the Subject line containing `send postscript 88/4', and no message in the body. The file is 602 Kbytes, so the server may take a while to send the to you, but you will get an acknowledgement of your request. You can also say `send help' to get a more informative message, see how to get an index to all the reports, etc. Bill Wyatt, Smithsonian Astrophysical Observatory (Cambridge, MA, USA) UUCP : {husc6,cmcl2,mit-eddie}!harvard!cfa!wyatt Internet: wyatt@cfa.harvard.edu SPAN: cfa::wyatt BITNET: wyatt@cfa -- Bill Wyatt, Smithsonian Astrophysical Observatory (Cambridge, MA, USA) UUCP : {husc6,cmcl2,mit-eddie}!harvard!cfa!wyatt Internet: wyatt@cfa.harvard.edu SPAN: cfa::wyatt BITNET: wyatt@cfa
nigelc@lnfgi1.UUCP (Nigel T. Cook) (06/06/90)
In article <1920@cfa200.cfa250.harvard.edu> wyatt@cfa250.harvard.edu (Bill Wyatt) writes: >I highly recommend you get a copy of the DEC Western Research Lab >WRL Research Report 88/4, titled: [Stuff deleted] >All you do is send mail to an archive server with the Subject line >containing `send postscript 88/4', and no message in the body. >The file is 602 Kbytes, so the server may take a while to send the >to you, but you will get an acknowledgement of your request. I tried doing this some time back. I got my ack from the server, then some time later a message saying that the mailer limit was something like .5MB. I cant understand why dec has these things on-line but unobtainable, or why it isnt sotred on the server as Part1 and Part2 so it can be fetched. -- Nigel Cook, Mail Drop 257 Fax: +1 215 6993702 Leeds and Northrup Co Voice: +1 215 6992000 Ext 3045 Sumneytown Pike, UUCP: ..!uunet!lnfgi1!nigelc North Wales. PA 19454
ihsan@ficc.ferranti.com (jaleel ihsan) (06/08/90)
In article <265@lnfgi1.UUCP>, nigelc@lnfgi1.UUCP (Nigel T. Cook) writes: > In article <1920@cfa200.cfa250.harvard.edu> wyatt@cfa250.harvard.edu (Bill Wyatt) writes: > >I highly recommend you get a copy of the DEC Western Research Lab > >WRL Research Report 88/4, titled: > [Stuff deleted] > >All you do is send mail to an archive server with the Subject line > >containing `send postscript 88/4', and no message in the body. > >The file is 602 Kbytes, so the server may take a while to send the > >to you, but you will get an acknowledgement of your request. > > I tried doing this some time back. I got my ack from the server, then some > time later a message saying that the mailer limit was something like .5MB. > I cant understand why dec has these things on-line but unobtainable, or > why it isnt sotred on the server as Part1 and Part2 so it can be fetched. > -- It happened to me too. You people at DEC's wrl should clean up your act :-( Jaleel
davew@viper.gvg.tek.com (Dave White) (06/08/90)
> >I cant understand why dec has these things on-line but unobtainable, or > > why it isnt sotred on the server as Part1 and Part2 so it can be fetched. > > It happened to me too. You people at DEC's wrl should clean up your act :-( Hmm... I sent mail to the server and got the document back within a couple of hours. Are you sure that the problem isn't with some intermediate site? I received the paper as one part with no problem. I notice that your mail forwarder is uunet.uu.net. Perhaps the limitation is there and not with decwrl.
ihsan@ficc.ferranti.com (jaleel ihsan) (06/10/90)
In article <1062@gold.GVG.TEK.COM>, davew@viper.gvg.tek.com (Dave White) writes: > > > >I cant understand why dec has these things on-line but unobtainable, or > > > why it isnt sotred on the server as Part1 and Part2 so it can be fetched. > > > > It happened to me too. You people at DEC's wrl should clean up your act :-( > > Hmm... I sent mail to the server and got the document back within a > couple of hours. Are you sure that the problem isn't with some > intermediate site? I received the paper as one part with no problem. > I notice that your mail forwarder is uunet.uu.net. Perhaps the limitation > is there and not with decwrl. I get big files from nic and bitftp all the time through uunet :-) Jaleel