is what one
am starting a new job tomorrow putting in structured (cat 5e & 6)
and fibre cable which I have never done before. After watching these videos
and reading the material it has given me a great head start in the job.
Thanks for the information, money well spent."
Although 16Mbps is the standard ring speed these days (and Fast Token Ring is being developed) we will consider a 4Mbps Token Ring in this tutorial to explain the basic concepts.
Hit 'Refresh' on your browser to start the animation from the beginning
At the start, a free Token is circulating on the ring, this is a data frame which to all intents and purposes is an empty vessel for transporting data. To use the network, a machine first has to capture the free Token and replace the data with its own message.
In the example above, machine 1 wants to send some data to machine 4, so it first has to capture the free Token. It then writes its data and the recipient's address onto the Token (represented by the yellow flashing screen).
The packet of data is then sent to machine 2 who reads the address, realizes it is not its own, so passes it on to machine 3. Machine 3 does the same and passes the Token on to machine 4.
This time it is the correct address and so number 4 reads the message (represented by the yellow flashing screen). It cannot, however, release a free Token on to the ring, it must first send the message back to number 1 with an acknowledgement to say that it has received the data (represented by the purple flashing screen).
The receipt is then sent to machine 5 who checks the address, realizes that it is not its own and so forwards it on to the next machine in the ring, number 6.
Machine 6 does the same and forwards the data to number 1, who sent the original message.
Machine 1 recognizes the address, reads the acknowledgement from number 4 (represented by the purple flashing screen) and then releases the free Token back on to the ring ready for the next machine to use.
That's the basics of Token
Ring and it shows how data is sent, received and acknowledged, but Token
Ring also has a built in management and recovery system which makes it
very fault tolerant. Below is a brief outline of Token Ring's self maintenance
Ring Self Maintenance
The job of the Active Monitor is to make sure that none of the machines are causing problems on the network, and to re-establish the ring after a break or an error has occurred. The Active Monitor performs Ring Polling every seven seconds and ring purges when there appears to be a problem. The ring polling allows all machines on the network to find out who is participating in the ring and to learn the address of their Nearest Active Upstream Neighbour (NAUN). Ring purges reset the ring after an interruption or loss of data is reported.
Each machine knows the address of its Nearest Active Upstream Neighbour. This is an important function in a Token Ring as it updates the information required to re-establish itself when machines enter or leave the ring.
When a machine enters the ring it performs a lobe test to verify that its own connection is working properly, if it passes, it sends a voltage to the hub which operates a relay to insert it into the ring.
If a problem occurs anywhere
on the ring, the machine that is immediately after the fault will cease
to receive signals. If this situation continues for a short period of
time it initiates a recovery procedure which assumes that its NAUN is
at fault, the outcome of this procedure either removes its neighbour from
the ring or it removes itself.
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