Understanding the network.pdf - Back to Home

includes ring station insertions and removals, token claiming process initiations,
NAUN changes, and throughput and utilization statistics.
In a multi-ring Token Ring environment, bridges are use to interconnect rings.
Token Ring supports two bridging methodologies. IEEE 802.5 transparent bridging
(the same method defined for use with Ethernet) is the defined bridging
methodology. In IBM Token Ring environments, an additional bridging method
known as source route bridging can also be used. With transparent bridging, only
one bridge link is permitted between two ring segments. With source route bridging,
multiple bridge interconnections are permitted between ring segments. Source
route bridging has two advantages over transparent bridging in large multi-ring
Token Ring LANs. First, because source route bridging enables multiple paths to
exist between different segments, this provides for a higher level of fault tolerance,
then transparent bridging. In case of a bridge failure, the two rings can still
communicate over a different bridge link. Second, because multiple paths exist
between rings, it is possible to set a "preferred" delivery path for the tokens, which
ensures that the token will travel the shortest path to its final destination. The LAN
Bridge Server (LBS) monitors the traffic passing through both successful and
dropped tokens on the bridge ports in the LAN, and keeps track of the available
route path options. The LBS sends its bridge status data to the LAN management
console.
Now that we have looked at the various ring station management roles that have
been defined by the IEEE 802.5 and IBM Token Ring specifications, let's look at how
the ring's operation is established and maintained by examining the different
phases of the ring insertion process. Before a station can become an active member
of the ring, each station must go through the ring insertion process. The ring
insertion process is a series of test and management functions that ensure the
station's NIC is configured for the proper ring speed (each station on the ring must
operate at the same speed) and is functioning properly. The ring insertion process
also, if need be, initiates any additional ring management functions that might be
needed to stabilize the ring in response to the addition of a new ring member.
Additionally, certain phases of the ring insertion process are used in the ring
recovery process in response to certain types of Token Ring errors. The following
details each phase of the ring insertion process:
• Phase 0: Lobe test—The interconnect cable between the station and the
Token Ring MAU is known as the lobe cable. When a station join's the ring, it
generates a lobe test signal that verifies the integrity of the connection and
verifies the ring's operating speed. Each MAU is a collection of looped
electrical gates that form a logical ring. When nothing is attached to an MAU
port, the port's gate is looped so the port is effectively bypassed from the
active ring. When a station is initially attached to the MAU, it transmits a lobe
test signal, which is looped back to the station because the MAU port is
looped. The station uses this signal to verify the port's operating rate and to