Understanding the network.pdf - Back to Home

check the lobe cable. If the lobe test signal is returned without error, the
station transmits a ring attach signal, which opens the MAU port's gate. With
the MAU's gate open, the connected station is now part of the active ring.
• Phase 1: Active monitor check—The insertion of a new station interrupts the
ring's transmission signal. This causes an error in the transaction occurring
during the new ring station's insertion. This error forces the active monitor to
purge the ring, notify the connected stations of the AM's existence, and start
the neighbor notification process. The newly attached station waits to see
the management messages, which indicate that the ring is functioning
correctly. If the new station fails to see these messages within an
appropriate amount of time, the new station initiates the token claiming
process. This action is needed because the failure to receive these messages
indicates that either the active monitor for the ring has failed or it is the first
station on the ring and no active monitor exists.
• Phase 2: Duplicate address check—After the active monitor is detected (or
elected), the new station generates a duplicate address message. This
message contains the same source and destination address of the new ring
station. If the new station receives the message back without the frame
status bit being set as received, it assumes that no other station has the
same destination address as itself, and removes the message from the ring.
If the message is returned with the frame status bit set as received, the
station removes itself from the ring. This test is done mainly to
accommodate for Token Ring implementations that use locally assigned
addresses instead of universal addressing.
• Phase 3: Neighbor notification—This process is normally initiated by the AM.
So, each station periodically announces itself to its downstream neighbor.
When a new station joins the ring, it announces itself to its downstream
neighbor and waits for a notification announcement from its upstream
neighbor.
• Phase 4: Ring initialization request—Each station has its own default
operational configuration. The station's defaults might not be adequate by
themselves, depending on the special operational needs of the ring. The last
step of the new station's insertion process is to send a ring initialization
request message to the ring parameter server, containing the new stations
MAC address, its microcode version and its NAUN. The ring parameter server
replies with basic information about the ring and any additional configuration
information needed in order for the requesting station to function properly. If
no RPS exists or no additional configuration information exists, the
requesting station uses its default settings.
Token Ring MAC Frame Format and MAC Frame Types
There are three Token Ring frame formats: the token, which is 16 bits in size, the
IEEE 802.5 data frame, and the IBM Token Ring data frame. The 4Mbps data frame