Introduction to Data Communications
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45j. Ring Insertion

When any node or host wishes to attach to the ring, it initiates the Ring Insertion process. The Ring Insertion process has 5 phases:

Phase 0 Lobe Media Check

The Lobe Media Check is performed by the NIC and it verifies the Lobe cable by looping the station transmit signal to the station receiver at the MSAU. A Lobe Media test MAC frame is issued. The relay in the MSAU is not energized at this time. A special packet is sent from the NIC to the de-energized MSAU lobe relay. The packet loops back from the MSAU and returns to the NIC. The integrity of the wiring that makes up the lobe is be checked.

The NIC applies Phantom Power (DC voltage) on the Transmit pair to activate the relay at the MSAU port. The NIC is now physically connected to the Ring.

Phase 1: Monitor Check

The ring station waits for an Active Monitor Present frame, Standby Monitor Present frame or Ring Purge MAC frame. If the ring station does not receive one of these frames before the T(attach) timer runs out, the ring station initiates Token Claiming to re-elect an Active Monitor.

Phase 2: Address Verification

The station verifies that its MAC address is unique with the Ring. It sends a Duplicate Address Test MAC frame onto the ring. The Duplicate Address Test frame has the source and destination address set to its own MAC address. If the frame returns marked read, then the station knows that there is another node with an identical address.

Phase 3: Neighbour Notification

The station learns its Nearest Active Upstream Neighbour (NAUN) address and informs its downstream neighbour of its own address through the Neighbour Notification process.

Phase 4: Request Initialization

The workstation sends the Request Initialization MAC frame to the Ring Parameter Server (RPS), which responds with an Initialize Ring Station MAC frame containing the station's parameters, such as the local ring number, ring parameter timer values, etc.. If no RPS is available, the station will insert with its default parameters.

When Phase 4 is complete the station is physically and logically attached to the ring.

Introduction to Data Communications
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