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.

16 Mbps Transfer Rate

The transfer rate for Token Ring is 4 Mbps for older systems or 16 Mbps for newer systems (1990 and newer). There are several products in development and available that will increase Token Ring's transfer rate using Switching Hubs and even faster transfer rates over existing cabling.
NOTE: 16 Mbps NIC cards will operate at both 16 and 4 Mbps speeds.
4 Mbps NIC cards will only operate at 4 Mbps.
To identify the speed of an unknown card, exam the integrated circuits on the card. There is only 1 chipset that implements IEEE 802.5's 4 Mbps standard for Token Ring. It was developed jointly by Texas Instruments and IBM. It is a 5 chip set and consists of:
TMS38051 Ring Interface Transceiver
TMS38052 Ring Interface Controller
TMS38010 Communications Protocol Processor
TMS38021 Protocol Handler for 802.5 Functions
TMS38030 DMA Controller between NIC and PC Bus 4 Mbps Token Ring NICs are usually full length expansion cards.
16 Mbps NICs have typically 1 large IC with 132 pins and several small ones. They are typically 1/2 length cards. The IC number is TMS380C16 for the Texas Instrument version or TROPIC for the IBM version or DP8025 for the National version.

IEEE 802.5 Topology

Token Ring is a Logical Ring / Physical Star topology. So far we've been only discussing the logical portion. Nodes on the network are physically connected via their NICs to a central concentrator or hub. The concentrator is called a MAU or MSAU both stand for MultiStation Access Unit. To avoid confusion with Ethernet MAUs, we will refer to a Token Ring hub as a MSAU (pronounced "M sow") or as a concentrator.

MSAUs

A Token Ring MSAU has connections to connect to the nodes and it also has special connections called Ring In and Ring Out to connect to other MSAUs

The Ring In connector is abbreviated RI and the Ring Out connector is abbreviated RO. The nodes (PCs) would be attached to connectors 1 to 8 for this 8 node MSAU.

45d. IEEE 802.5 Bus Arbitration (cont'd)

When the packet arrives at node G, node G reads the destination address and reads the information. Node G marks the information packet as read and passes it on.

Note: the Source and Destination addresses remain unchanged after passing through Node G. Node B is still the Source address and Node G is still the Destination address.
The packet continues around the ring, until it reaches the source address Node B. Node B checks to make sure that the packet has been read - this indicates that Node G is actually present. The information packet is erased. Node B then releases the token onto the ring.

Information marked READ is passed through the ring back to the Source - Node B
The information packet is called the Token Frame. The token is called the Token (sometimes referred to as the free token). This can be confusing. Remember, when we talk about a frame, we are talking about data/information. When talking about a token, we are talking about bus arbitration and permission to use the bus.

45d. IEEE 802.5 Bus Arbitration (cont'd)

The token is a special packet, that is circulated around the ring. It is read from one node than passed to the next node until it arrives at a node that needs to access the ring (transfer information/data). When a node receives the token, the node is allowed to send out its information packet.

Example: The token is circulating the ring, Node B needs to send some data to Node G. Node B waits for the token to come by. There is only one token allowed on the ring. When it receives the token, it can then send out its information packet. Node G is the destination address.

Node C receives the packet, reads the destination address and passes it on to the next node. Node D, E & F do likewise.