Understanding the network.pdf - Back to Home

they first join the ring or in the event that they lose phase lock with the ring. The
active monitor is also responsible for setting the minimum latency for the ring,
which is based on the size of the active token. The minimum latency is 24 bits.The
IBM and IEEE electromechanical interface specifications for the PHY differ somewhat.
IBM defines the use of three different cable and connector specifications with an
active hub or MAU. The IEEE specification provides a description for a two-wire
shielded 150-ohm cable, known as a Medium Interface Cable (MIC). This provides
the interconnection between the end-station network adapter and the Trunk
Coupling Unit (TCU). This model is in essence the IBM Type 1 cabling specification.
According to IBM, a Token Ring network consists of three elements:
• Token Ring Network Adapter Card (TR-NAC)—The TR-NAC provides the logic
and signaling functions to implement the MAC and PHY layers of the network.
It provides the physical interface between the connected end-station and the
other adjacent end-stations attached to the physical network media.
• Token Ring Network Multistation Access Unit (MAU)—The IBM MAU (IEEE
TCU) using Type 1 cabling is a ten-port active hub that can connect up to
eight end-stations. The remaining two ports are used for interconnecting
with additional MAUs, which enables multiple MAUs to be connected together
to form a logical ring. One port is the "ring in," the other is the "ring out" (see
Figure 4.21). Connections between MAUs are made with patch cables, and
connections between MAU and end-stations are made with lobe cables (IEEE
MIC). Today, Token Ring MAUs are almost identical to Ethernet repeaters,
with port densities ranging between 12 and 24 ports, using RJ-45 connectors
instead of the type 1 MIC connector (see Figure 4.22).