45m. Token Ring Monitors and Servers (cont'd)

Ring Parameter Server (RPS)

The Ring Parameter Server provides 3 main services to the ring:
1. Assigns operational parameters to the station at the time of insertion onto the ring. These are parameters such as: Ring Number, Physical Location and Soft Error Report Timer Value. If there is no RPS present, the ring station uses its default values.
2. Ensures that all stations on the ring have the same operational values.
3. Forwards registration information to the LAN Managers from stations attaching to the ring

Configuration Report Server (CRS)

A Configuration Report Server accepts commands from the network management software to get station information, set station parameters and remove stations from the ring. It also collects and forwards configuration reports generated by stations on its ring to the LAN manager.

The network management software is a program that monitors the Network and is used by the System Administrator. It can monitor many Rings and may include Ethernet segments and connections to WANs.

45m. Token Ring Monitors and Servers (cont'd)

Monitoring Token and Frame Transmission

The AM monitors the ring to make sure that Tokens and Frames only circle the ring once. There is a Monitor bit in the MAC frame and whenever a MAC frame is repeated by the AM, the AM sets the Monitor bit to "1". All frames that are received with the Monitor bit set to 1 are not repeated - this means that the frame has already circulated the ring once

Detecting Lost Tokens and Frames

The AM has a timer to check that there are Tokens and Token Frames circulating the ring. The timer is set for the absolute longest time that it would take for a Token or Frame to circulate the ring. If the timer times out before a new Token or frame is received. The ring is purged and a new Token is released.

Purging the Ring

The AM broadcasts the Ring Purge MAC frame to all ring stations on its ring before originating a new Token. Receipt of the returned frame indicates to the AM that a frame can circulate the ring without incident. The Ring Purge Frame resets the ring stations to Normal Repeat mode.

45m. Token Ring Monitors and Servers (cont'd)

Monitoring Neighbour Notification

At any time during the neighbour notification cycle, certain events could happen that could affect the Neighbour Notification process. The Active Monitor checks for these conditions and takes appropriate action:

. The Active Monitor's Neighbour Notification Timer runs out. The ring is taking too long to complete the Neighbour Notification process. The Active Monitor restarts the Neighbour Notification process and reports a Neighbour Notification Incomplete MAC frame to the Ring Error Monitor (REM - just another node on the ring that has the job of monitoring ring errors).
2. The Active Monitor Present Frame takes too long to circle the Ring. The AM initiates token claiming so it can retransmit an Active Monitor Present frame.
3. If a Standby Monitor Present Frame is received after Neighbour Notification is complete, the Neighbour Notification is ignored and restarted. Another station has just connected to the ring and by inserting into the ring, has changed the NAUN order.
4. If another Active Monitor Present Frame is received with a source address different from its own. This means that there is another Active Monitor on the Ring. The receiving Active Monitor shuts down and becomes a Standby Monitor.
5. A hard error (cable fault, student playing with RI and RO ports) causes the ring to go down. After the hard error is fixed, the Neighbour Notification process is restarted.

45k. CAUs & LAMs

CAUs & LAMs

A CAU can control up to 4 LAMs (pronounced lambs). LAM stands for Lobe Access Module and LAMs have the Lobe connections. The CAU is connected to the LAMs by a Power Connection and a Data Connection. A LAM has 20 lobe connections. A LAM is an active concentrator.
Active Concentrators
An active concentrator is a concentrator that retimes and regenerates the data signal. It does the job of a repeater. Since it retimes and regenerates the data signal it is not used in Ring Length calculations.

45g. MSAUs (cont'd)

Physical Star/ Logical Ring

With an understanding of how an MSAU works, it is easier to see how we get a Logical Ring for Token Ring. The Physical Star results from the Lobe cabling fanning out to the Nodes.

IEEE 802.5 and the OSI Model

45g. MSAUs (cont'd)

Wrapping

If the Main Ring fails due to cable faults or MSAU problems, the Main Ring can be wrapped to the Backup Ring. Wrapping is a term that is used to indicate that the Backup Ring is being used in addition to the Main Ring.
The Backup Ring is connected to the Main Ring. The Main Ring or a portion of the Main Ring is still being used. Wrapping is only associated with the Ring In and Ring Out connectors on the MSAUs.

This can be done either of 3 ways:
Passive Hermaphroditic Style MSAUs - remove the suspected RI or RO Hermaphroditic connector. The connector will automatically short and wrap the Main Ring to the Backup Ring
Passive RJ11 & RJ45 Style MSAUs - Manually switch the suspected RI or RO connector with the available switches
Active MSAUs - They will automatically wrap if there is a problem.

45g. MSAUs (cont'd)

MSAU Relay

When a Token Ring NIC is first turned on, it goes through a process called Ring Insertion. It checks the Lobe to see if the wiring is okay and then applies a DC voltage on the Transmit pair of wires. The DC voltage is often called phantom power.

This voltage energizes a relay in the MSAU and attaches the Lobe to the ring. If you disconnect a cable at the MSAU, the relay will de-energize and automatically disconnect the lobe from the ring. You can actually hear the relays clicking in and out.

Ring In/ Ring Out

On a MSAU are 2 connectors called Ring In (RI) and Ring Out (RO). These are used for connecting MSAUs together. Two pairs of wires are run between MSAUs to connect them together, one pair is used for the Main Ring and one is used for the Backup Ring.

The following figure indicates the Main Ring and the Backup Ring. Notice that the Backup Ring runs in parallel with the Main Ring and is not normally used. Also notice that the direction of data flow on the Backup Ring is opposite to the Main Ring.