When I first scraped together some token ring cards for my linux network at home I searched around for information about token ring but I still had quite a few unanswered questions. Here are my (possibly incorrect) answers to those questions.

Two token ring cards with data connector tails plugged together don't work. This may be because the TX and RX pairs aren't crossed over when the data connecters are plugged together. It may not work even if the pairs are crossed over because the token ring cards are expecting to see an MAU.

The ring is supposed to be able to protect itself from a bad adaptor. This works by the first station after a dud adaptor sending a message around the ring to the dud adaptor which removes itself from the ring.
This doesn't seem to work when the 'dud' adaptor is actually merely a token ring adaptor set to 4Mbit/s in a 16Mbit/s ring (Doh!). Also if you plug the 9 pin D connecter end of a tail into a 9 pin serial connector instead of a token ring board, this stuffs the ring as well.. However if you just pull the connector out of an adaptor the ring does heal itself.

Cable

• Type 1: 2 individually shielded twisted pairs (solid 22 AWG) 150 Ohm
• Type 3: un shielded telephone type cable (solid 24 AWG) 105 Ohm
• Type 5: Optic Fibre
• Type 6: Common Shield Twisted pair (stranded 26 AWG) 150 Ohm

Data Connectors.

Data Connectors are the 'classic' token ring connectors. They are quite interesting in that they are hemaphreditic - that is there is only one sex of connector than can mate with itself. The connector also has internal switching so that when it is not plugged in it loops the TX pair back to the RX pair, hopefully keeping the ring intact.
All the Networks cards I have seen have a DB9 connector on them. A tail plugs into this that has a DATA connector on the far end.

RJ45

About all I can say is some Token Ring Cards have RJ45 connectors and use unshielded cable to an MAU that has similar connectors.

MAU

I have a genuine IBM 8228 MAU. It does not have any power source of its own, but it does have internal electronics. Associated with each port is a circuit with a couple of transistors and relays. I presume that they are part of the mechanism to keep the ring continuous when things are unplugged. There is supposed to be a 'relay tool' or similar to check the ports. I have been told that this is just a data connector with a led and a battery (and probably a few resistors). Some stuff I have seen refers to using this to 'reset' a port, but I don't have one, have never used one and my MAU works OK.

Speeds

Token Ring operates at 4Mbit/s or 16Mbit/s. If you use type 3 cable (telephone type cable) you should only run at 4Mbit/s

The clocking for token ring is generated from one station. I don't know how this station is selected

Unlike Ethernet, Token ring can probably actually cope with a data rate near to its 'wire rate' of transmission. On FDDI services (which use a token passing arrangement) I have seen a peak data rate of 97Mbit/s out of total bandwidth of 100Mbit/s.

Token Passing

Assuming we have a ring that looks like this ...

         A ----> B
        /         \
       /           \
      F             C
       \           /
        \         /
         E <---- D

If 'A' is sending to 'D', 'A' waits until it receives the token. It then appends its data to the token which now becomes a data frame with a destination of station 'D'. It is received by station 'B' who sees it isn't addressed to it and forwards it around the ring to C which sends it to 'D'. When 'D' receives a frame addressed to it, it reads the data and relays the frame to 'E' but with two bits in the frame set to indicate the address was recognized and the frame was read. 'E' sends this to 'F' which sends it to 'A'. 'A' realises that it originated the frame and doesn't relay it on, removing it from the ring. 'A' instead passes the Token to 'B' who can now send its own data.
One node is designated as network monitor and performs housekeeping functions to ensure the ring is operational.

Control field

Frame Types

GLOSSARY

• MAU Multistation Access Unit
• LOBE Basically the cable from an MAU to an adaptor and the adaptor itself. I guess you could say its the path the ring follows from the MAU and back again.
• TOKEN A packet that gets passed from station to station. While a Station has control of this packet it can transmit data. A station has to send on the Token after a pre determined time. The token is presumably initially generated by one of the token ring boards( I didn't have to do anything special to start things happening.)
• 802.X The 802.X series are IEEE standards for networking hardware/software. 802.3 is for Ethernet, 802.5 is for token ring.
• STATION A computer printer etc. which communicates via the ring
• MEDIA FILTER. A device to convert from DATA / DB9 connectors to RJ45 unshielded twisted pair.
• Early Token Release. Allows more efficient use of the ring by allowing the transmitting station to release the token immediately after transmitting the frame, rather than waiting to see the frame come back around the ring. This is only an issue if the ring length, in terms of bits on the wire, is less than the packet length