The following text is copyright 1998 by Network World, permission is hearby given for reproduction, as long as attribution is given and this notice is included.
Colliding with reality
By Scott Bradner
Network World, 3/30/98
Did someone skip a decade somewhere?
I thought the Ethernet vs. token-ring wars ended long ago, and that
Ethernet won hands down. But if that was the case, why are we
seeing so much hype about High-Speed Token Ring? And why is the
hype presented in such a way that it reminds us of contests fought
There has been a spate of articles in this and other publications that
explains how token ring is superior to Ethernet. The most commonly
mentioned differences are the relatively small maximum frame sizes
for Ethernet and token ring's support for link-level traffic
prioritization. In addition, many articles point out the ability of
token-ring networks to have multiple simultaneous paths between
switches, whereas Ethernet environments can only have one such
path between switches. Less frequently mentioned these days, but
showing up from time to time, are the claims that Ethernet collapses
under a high load and is less predictable than token ring.
There are problems with most of these arguments. Strings of large
packets are quite rare, and simple delayed-interrupt tricks in the
interface cards can deal with most performance issues. Most corporate
network designs do not have multiple paths between switches and
even fewer will as Layer 3 switches continue to get deployed. The
disputable claims that Ethernet collapses or is less predictable than
token ring do not apply in the increasingly common full-duplex
switched Ethernet networks. The link-level prioritization issue is
interesting, but the Ethernet people are also working on that.
My problem is not that the claims are false or irrelevant, but that they
are context free. They are presented in a way that implies network
designers should seriously consider moving their Ethernet networks
to token ring.
It is silly to imagine much of that happening. The disparity in cost
between Ethernet and token ring is just too great. For example,
4M/16M bit/sec token-ring PC interfaces cost more than six times as
much as 100M bit/sec full-duplex Ethernet interfaces. Token-ring
switches cost four times more per port than 100M bit/sec full-duplex
Ethernet is vastly outselling token ring. I do not have the actual
numbers, but in a data communications catalog I got yesterday, there
were 53 pages of Ethernet products and one third of a page featuring
some token-ring products. If you think that the token-ring-is-better
argument is relevant, check out the local video store to see how many
Betamax tapes they have.
Don't get me wrong. The development of fast and gigabit token ring
is a fine thing. Those sites that use token ring - and there are quite a
few - will benefit greatly from devices that provide an upgrade path. I
just think that High-Speed Token Ring proponents should be a bit
more realistic in describing just who should be paying attention to this
technology. To do otherwise, as a co-worker once said, is to do
data-free analysis, and the result is a collision with reality.
Disclaimer: Harvard people collide with reality often and occasionally
emerge winners, but the above expresses my own frustration.