Does Anyone Still Use Token Ring?

blanchae asks: "Does anyone still use Token Ring, or is it dead? I remember hearing about 100 mbps TR a few years ago but nothing since. I remember that the strong point of TR over Ethernet was the QOS and the consistent response time. Does the banking community still use TR?"

Comments

Examing the publishing

[CRCulver]

There is clearly a lot of research going on, with results published, as in Raja's Optimal bandwidth utilization in wireless token ring networks released earlier this year. However, 1998 was the last big year for user's guides, which indicates that this technology has long since fallen from the mainstream and now survives only in academia.

Why its gone

[Spazmania]

The big deal with token ring was that the network would remain stable under 100% load. Classic 10mbps ethernet with hubs would start experiencing trouble around 60% load and collapse by the time load reached 90%. If you had a big, flat network it just plain wouldn't work.

Look at why: With token ring, only the card holding the token could transmit. Everybody else had to wait for the token. So each station would empty its transmit queue and then pass the token on to the next station. On ethernet, a station would send a packet whenever and if another station sent a packet at about the same time they'd collide. Every station observing the collision would assert a collision signal and after the collision signal cleared the two stations that transmitted would wait a random period of time and then retransmit. That's oversimplifying a bit but more or less correct.

So, token ring was much more stable in a large LAN with a high probability of multiple stations having outbound traffic ready at the same time.

Now, along comes 100baseTX on cat5, the end of coaxial ethernet and the proliferation of $50 switches. When you're plugged in to a switch there are only two devices in the collision domain: you and the switch. So, lots less collisions. When you're in full duplex mode (as you generally are), collisions are impossible since by definition both sides are allowed to transmit at the same time. Now your ethernet network remains stable at 100% utilization. And if the nic in the PC burns out, the rest of the network doesn't care.

Token ring is very sensitive to malfunctioning nics. A malfunctioning nic may drop the token, that is it may receive the token and then fail to transmit it to the next nic. That kills a token ring network dead until the admin wanders around with an analyzer and figures out which PC is at fault.

Suddenly the tables were turned. Token ring was an administrative headache and expensive to boot. Ethernet was simple, cheap and worked just as well.

Token ring died out except as an academic curiosity -- an interesting early answer to a problem that was eventually solved another way.