BEAME@MCMASTER.BITNET (02/28/88)
I've been asked by my boss, to comment on a document that deals with
Ethernet Vs IBM Token Ring. It is EXTREMLY biased in favour of IBM Token
Ring.
I recall just recently a message about Token Ring Bridges source routing
and what the IEEE said about it. If someone has that message saved and
could sent it to me, I would be very appreciative.
If anyone has figures on maximum through-put of 10 Mbps Ethernet, I could
make good use of them.
Also if anyone has information on "token" loss and its impact on a Token
Ring, I could include it in my comments. (The above document never mentions
the posibility).
- Carl Beame
Beame@MCMASTER.BITNEThedrick@athos.rutgers.edu (Charles Hedrick) (03/07/88)
The early Ethernet design studies claimed you could get at least 9Mbits out of Ethernet. However you normally don't want to configure networks so that they are working that way. THis is true for any network, whether Ethernet or token. In order to give people good response on demand, you want peak capacity to be about a factor of 10 above what you expect typical useage to be. In fact people are now getting transfers in excess of 1Mbit over Ethernet. (I've heard claims of several Mbits with highly tuned software on fast machines, but 1Mbit is fairly common these days.) In order to allow several things to go on at once, this says you really do want a medium that's at least 10Mbit. This is why the whole business about token delivering predictable response is so wierd. Even if it is true that a heavily loaded token system splits bandwidth evenly, nobody in his right mind would configue a network so that it runs at full capacity for anything more than a few milliseconds at a time. (And anecdotal evidence is that token rings aren't really any more predictable anyway.) The main argument for IBM token ring is when you have lots of IBM equipment and want to do things like have your IBM 3270 cluster controllers talk over the LAN. This is quite a reasonable thing to do. On one of our campuses we expect to set up a token ring for administrative use. However we expect to limit it to that. It will handle 3270's and IBM PC's on administrative desks. For security reasons, we don't want any student traffic on the same LAN. So we'll use Ethernet and related technology for most of the general traffic. Unless you have this sort of specific need for IBM-related networking, Ethernet has the advantages of ubiquity and robustness. That is, you can get Ethernet support for everything. Token ring hasn't been a great success in the market. According to all the guys in Datamation it's been about to wipe out Ethernet for the last 5 years now, but somehow it has never taken off. Ethernet was also designed to be very robust. You can install new taps without disrupting traffic. People have violated the specs in all sorts of ways and still gotten it to work. It is very conservative technology, and very well understood. One of the chief designers for a well-known token ring company gave a talk here a few years ago. He showed a bunch of performance statistics and sort of surprised people by saying that as far as he was concerned at 10Mbits and lower, token ring has only a minor performance advantage. Certainly IBM's attempt to convince people that 4 > 10 is simply absurd. It would be impossible to do Ethernet at 100Mbits (cables would be restricted to 50 meters in length), so all new protocols being designed are token ring. But that has led some people to think that somehow token ring is a newer and better technology. Not so. It's that we are beginning to move to faster technology, and token rings make sense there. For 10Mb and slower, the tradeoffs are different, and there are situations where each is faster. In general Ethernet is better for a random mix, e.g. terminal traffic and random FTP's, whereas token ring would be better for certain kinds of graphics applications or real-time control work. For most LAN's I'd say you're going to be better off to stick with Ethernet unless you have good reason to do otherwise. The magic initials IBM do carry some weight. When they first released the token ring, I can see why people thought it was bound to succeed. But IBM does sometimes fail to dominate an industry. Look at their attempt to foist PL/I on us all. Token ring looks like one of these cases.
kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England)) (03/08/88)
Hedrick, as always, makes a clear and concise exposition of Ethernet versus Token Ring. I think most users don't have a choice with network technology, you take what your vendor gives you. 802.5 for Big Blue, 802.3 for DEC and Un*x. I see great usefulness for Token Ring bandwidth allocation schemes, such as proposed in the IEEE MAN work, for allocating bandwidth and minimizing packet delays for voice traffic versus data. I'm not really looking to integrate voice/data on the campus, but it will be indispensible in the MAN standard. Coupled with the need for high bandwidth and the preference for fiber (what ever happened to the promises of the CATV evangelists?), Token Ring (not 802.5) is a clear technology winner. This means that TR will trickle down to eventually supplant Ethernet, although there is no technical reason to do so until 50Mbps link speeds are required for workstations. (Can't wait!) Kent England Boston University