Cabletron Systems bridges, Networking Manual

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Review of Networking
2-6 Token Ring
The transmission and reception of the token determines the amount of time that
any station will have to transmit data during its turn, offering a measure of
predictability not available in Ethernet or Fast Ethernet. This predictability also
allows Token Ring networks to incorporate special error-detection and correction
functions which can locate and correct network problems without human
intervention.
The predictability of the Token Ring technology also leads to a number of
limitations on the number of stations that can be connected to a network and the
maximum cable lengths that a signal may be passed across. Since the stations are
configured to expect reception of the token at certain increments of time,
exceeding the maximum number of stations or the maximum length of cabling
between stations can delay the token’s progress, causing the Token Ring network
to suffer errors and poor performance.
In order to stretch the capabilities of a Token Ring network, various technologies
are available which extend the distance a signal can travel before suffering
degradation or loss of signal timing due to cable lengths or high station count.
One method of increasing the resilience of a Token Ring network is the
incorporation of what is called “active circuitry.” Token Ring station ports with
this active circuitry regenerate, strengthen, and re-time any Token Ring signal
received by or transmitted from that interface.
Token Ring devices can also extend the distance that a ring can cover through the
use of Ring-In/Ring-Out, or RI/RO cables. RI/RO cables are designed only to
make connections between Token Ring concentrator devices, and extend the area
that a ring can support by allowing long-distance links to other Token Ring
devices.
NOTE
All Cabletron Systems stackable and standalone Token Ring
products incorporate active circuitry on all ports.
NOTE
RI/RO connections are not bridge or switch interfaces. They do
not create a new Token Ring network.