Specifications

TOKEN RING OVERVIEW
2-14
Station Insertion
The act of powering up a station does not immediately enable it to become
part of the ring. Certain tests are performed while the adapter is being
initialized by the software drivers. The basic tests are known as insertion
tests. These tests are made whenever an attempt is made to open the
Token Ring adapter.
Lobe Test
The Lobe Test involves the station sending a string of Lobe Media MAC
frames on that station’s lobe. This test ensures there are no faults on the
lobe.
Physical Insertion
If the Lobe Test is successful, the station activates its phantom drive and
inserts into the ring. The time allowed to insert into the ring is 5 ms, which
is the maximum time a ring may be broken. The phantom current is two
separate DC circuits that enable the station to detect open or short circuits
in either the receive or transmit pairs.
During the Physical Insertion test, the station also learns the ring’s
operating speed and it determines whether an AM exists on the ring. It
does this by first starting a timing process, called the Timer Standby
Monitor (TSM), which specifies the time allotted the station to detect
Active Monitor Present (AMP), Standby Monitor Present (SMP), or Purge
Ring (PRG) MAC frames on the ring. The presence of any of these frames
indicates a another station is or has been designated as the AM. If not
detected within seven (7) seconds, the station transmits Claim Token
frames to contend for designation as the AM.
Address Verification
After determining the presence of an AM on the ring, the station checks
for a duplicate address on the ring using the Duplicate Address Test (DAT)
frame. The station sends the frame addressed to itself out onto the ring.
If the frame returns with its address recognized bits set by another station
on the ring with the same address, the transmitting station will then
remove itself from the ring.