neal@mnopltd.UUCP (03/20/90)
Dear Abby,
Is it possible to run 10Mbps Ethernet over a star topology of offices up to 80
miles apart connected via 9.6 dedicated voice grade lines?
We are trying to help a company put in a big Unix system to support many
offices. We are handling the unix/Pc Lan end of things, someone else the
wiring/ethernet stuff.
The wiring experts say "no problem... we'll just run ethernet over the whole
region." As a result, I am pushed into a single big server configuration.
Which is fine except if the wiring won't work, the whole schmutz is wrong.
And something about this smells fishy... what about propagation times?...
Signed,
Puzzled in Paradise.
------------------------------------------------------------------------------
Neal Rhodes MNOP Ltd (404)- 972-5430
President Lilburn (atlanta) GA 30247 Fax: 978-4741
uunet!emory!jdyx!mnopltd!neal Or uunet!gatech!stiatl!mnopltd!neal
------------------------------------------------------------------------------rnicovic@polyslo.CalPoly.EDU (Ralph Nicovich) (03/21/90)
In article <173@mnopltd.UUCP> gatech!stiatl!mnopltd!neal writes: >Dear Abby, > >Is it possible to run 10Mbps Ethernet over a star topology of offices up to 80 >miles apart connected via 9.6 dedicated voice grade lines? You are correct in being concerned. There are two types of connections you might make. One is a Data Link Bridge. This is protocol independent, and might seem the best, but... Just a small amount of Broadcast traffic would Swamp the 9.6 lines. Also the delays caused bu retransmitting the packets with such a slow line might cause most packages that "think" you are on a local ENET to retransmit because of that delay. I would not do this unless you are extreemly careful of your aplication. The other aproach is some type of router. This is of course protocol dependent. Mail, FTP and TELNET would work well in a IP enviornment, but you did not say what your aplication was. A third aproach might be to pick a machine on each network to work as a communication processor of some sort, but this is not connecting the "networks" per say.. 9.6 is suprisingly fast, we connect many things over one line...But keep up to a 10Mbs Ethernet....Thats some compression alogrithim!!! Ralph Nicovich Network Engineering Cal Poly State University
dave@fps.com (Dave Smith) (03/21/90)
In article <173@mnopltd.UUCP> gatech!stiatl!mnopltd!neal writes: >Dear Abby, > >Is it possible to run 10Mbps Ethernet over a star topology of offices up to 80 >miles apart connected via 9.6 dedicated voice grade lines? Nope. You will have 9.6 Kb/sec Ethernet running between your offices. > >The wiring experts say "no problem... we'll just run ethernet over the whole >region." As a result, I am pushed into a single big server configuration. > >Which is fine except if the wiring won't work, the whole schmutz is wrong. >And something about this smells fishy... what about propagation times?... Propogation would only come into play if you were running it as one big (electrically) Ethernet. This is not possible and if they think it is you should 1) fire them and 2) have them committed. If they think they are going to run large amounts of data through bridge boxes connected at 9.6 Kb/sec you should 1) fire them and 2) have them committed. If the kind of traffic you are talking about is 1 to 4 users at the remote sites running rlogin sessions to the main site with additional traffic running locally only this could be acceptable. If it's just going to be 1 to 4 users with terminal hooked to a 386 running rlogin with no other network traffic it will probably be cheaper to get a stat mux to hook the terminals directly to and run them across the line. 56Kbp/sec lines are probably more feasible. You really need to figure out how much data needs to go across the line in time X and make decisions on what kind of speed you need. Be sure to leave room for growth. -- David L. Smith FPS Computing, San Diego ucsd!celerity!dave or dave@fps.com "We are a bigger musical genius than any Bob Dylan" - Milli Vanilli
jbvb@ftp.COM (James Van Bokkelen) (03/22/90)
In article <173@mnopltd.UUCP>, neal@mnopltd.UUCP writes: > Is it possible to run 10Mbps Ethernet over a star topology of offices up to 80 > miles apart connected via 9.6 dedicated voice grade lines? 1. Under un-loaded conditions, you will get a large variance in transit time depending on packet length. This may result in unnecessary retransmissions. 2. Under loaded conditions, when the number of packets that need to traverse the link exceed the capacity for significant periods of time, you may get a syndrome of repeated retransmits, and possibly what is called "congestive collapse". In this condition, the load is so high that packets are delayed or dropped, which generates more retransmitted packets, etc. 3. Depending on how many packet the bridges will queue for transmit, some protocols (e.g. ARP) may fail under some conditions, because implementations frequently assume that the round-trip time *can't* exceed X on an Ether. I'd advise that you investigate other people using similar software across slow links; If you can't find any, you might not want to be the first. If you can, go cautiously when trying anything that you haven't seen working in a similar environment. Above all, *don't* let the demand across any of the serial links exceed capacity for long. -- James B. VanBokkelen 26 Princess St., Wakefield, MA 01880 FTP Software Inc. voice: (617) 246-0900 fax: (617) 246-0901