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.

IEEE 802.4 Token Bus

An industrial version of Token Ring is standardized under IEEE 802.4 Token Bus. It is used in manufacturing process equipment for plant operation. It is used in automobile plants for computerized assembly. It uses a Logical Ring and a Physical Bus topology.

IEEE 802.5 Token Ring

IEEE 802.5 Token Ring standard is based on the IBM Token Ring network. Token Ring has been used mainly in large corporations and was considered in the past to be the only way to handle data communications in large networks (1000+) nodes.
Token Ring equipment is more expensive than Ethernet and is one of the reasons that Ethernet is more popular. The other reason is that Token Ring is much more complex bus arbitration method than CSMA/CD and few network personnel understand the full capabilities of Token Ring.

IEEE 802.5 Bus Arbitration

Token Ring is a token passing bus arbitration. A token is circulated on the ring. If a node on the ring needs to access the ring (transfer information), it claims the token.

Token Ring

STOP - You are now leaving Ethernet IEEE 802.3 Please fasten your seatbelts and place your trays in the fully upright position
Token Ring is a token passing bus arbitration topology for the Physical and Data Link Layers. It is a logical ring and a physical star topology.

Token Ring uses a token passing scheme for bus arbitration. A special packet is passed around the ring called a token. When a node requires access to the ring, the node claims the token and then passes its information packet around the ring. All nodes read the destination address and if it is not addressed for them, the information packet is then passed on to the next node. When the destination node reads the packet, it marks it as read and passes it on to the next node. When the information packet completely circulates the ring and arrives back at the source node, the source node releases the token back on to the ring.
Token Rings are not usually drawn as the above drawing indicates: a separate line between each node. They are usually represented as understood that separate paths exist between nodes and are drawn as in the figure to the right.

IBM Token Ring

Token Ring was originally developed by IBM for their PC LAN networks. It started out in 1969 as the Newhall Network, named after the originator of the token ring concept. IBM's Token Ring is the basis for the IEEE 802.5 standard Token Ring. They are very similar and have minor differences which we will cover.

Brouters (Bridge/Routers)

Brouters are protocol dependant devices. When a brouter receives a frame to be forwarded to the remote segment, it checks to see if it recognizes the Network layer protocol. If the Brouter does, it acts like a router and finds the shortest path. If it doesn't recognize the Network layer protocol, it acts like a bridge and forwards the frame to the next segment.

The key advantage to Brouters is the ability to act as both a bridge and a router. It can replace separate bridges and routers, saving money. This is, of course, provided that the Brouter can accomplish both functions satisfactorily.

EGRP - Exterior Gateway Routing Protocol

EGRP was created to solve many of the problems with RIP and has become the default routing protocol across the Internet. EGRP is an enhanced distance vectoring protocol, it uses up to 5 metrics (conditions) to determine the best route:
Bandwidth
Hop Count (Delay) - maximum of 255
Maximum Packet size
Reliability
Traffic (Load)
These routing metrics are much more realistic indicators of the best routes compared to simple hop counts

OSPF - Open Shortest Path First

OSPF is a link state premise, this means that it has several states of routers linked together in a hierarchical routing model:

The top of the root is the Autonomous Router, it connects to other autonomous systems (the Internet). The next is the Backbone Routers, which is the highest area in the OSPF system. Border routers are attached to multiple areas and run multiple copies of the routing algorithm. Last is internal routers which run a single routing database for one area.
Basically, by dividing the network into a routing hierarchy, substantial reduction of routing update traffic and faster route convergence results on a local basis. Each level has a smaller routing table and less to update.

Router Addressing

Routers combine the Network Number and the Node Address to make Source and Destination addresses in routing Network Layer PDUs across an network. Routers have to know the name of the segment that they are on and the segment name or number where the PDU is going to. They also have to know the Node Address: MAC Address for Novell and the IP address for TCP/IP.
For Novell's SPX/IPX (Sequential Packet eXchange/Internetwork Packet eXchange), the Network Layer PDUs address is composed of the Network Address (32 bit number) and the Host address (48 bit - MAC address).

Routing Protocols

Routing Protocols are a "sub-protocol" of the Network Layer Protocol that deal specifically with routing of packets from the source to the destination across an internetwork. Examples of Routing Protocols are: RIP, IGRP and OSPF

RIP - Routing Information Protocol

RIP was one of the first routing protocols to gain widespread acceptance. It is described in RFC1058 which is an Internet standard. RFC stands for request for comment and the RFC1058 is the 1,058 RFC standard published. Commercial NOS such as Novell, Apple, Banyan Vines and 3Com, use RIP as the base routing algorithm for their respective protocol suites.
RIP is a distance vector algorithm. Routers maintain a detailed view of locally attached network segments and a partial view of the remainder of the routing table. The routers contain information on the number of hop counts to each segment. A hop is considered to be one transverse through a router. Pass through a router and the Hop count increases by 1.

The routers are updated every 30 seconds, each router sending out a RIP broadcast. This advertisement process is what enables RIP routing to be dynamic. Dynamic routers can change routing tables on the fly as the network configuration changes. By using the Hop Count information from their routing tables, routers can select the shortest path - the least number of hops to the destination.
Apple uses RTMP (routing table maintenance protocol) which adds a route status indicator: good, bad or suspect depending on the age of the route information.
Novell adds ticks to the RIP algorithm, Ticks are dynamically assigned values that represent the delay associated with a given route. Each tick is considered 1/18 of a second.

LAN segments are typically assigned a value of 1 tick, a T1 link may have a value of 5 to 6 ticks and a 56 Kbps line may have a value of 20 ticks. Larger number of ticks indicate a slower routing path.
Three commonest problems that can occur with RIP are:
Routing loops: the router indicates that the shortest path is back the way the packet came from.
Slow Route Convergence: routers have delay timers that start counting after the RIP advertising packet is broadcasted. This gives the routers time to receive and formulate a proper routing table from the other routers. If the delay timer is too short, the routing table can be implemented with incomplete data causing routing loops
Hop Count Exceeded: the maximum number of hop counts is 15 for RIP. A hop count of 15 is classified as unreachable which makes RIP unsuitable for large networks where hop counts of 15 and above are normal.

Router Segment to Segment Characteristics

Routers that only know Novell IPX (Internetwork Packet Exchange) will not forward Unix's IP (Internetwork Packet) PDUs and vice versa. Routers only see the Network Layer protocol that they have been configured for. This means that a network can have multiple protocols running on it: SPX/IPX, TCP/IP, Appletalk, XNS, etc..

In the following network, Router #3 is a Novell SPX/IPX router, it only sees the Network Layer protocol IPX. This means that any TCP/IP PDUs will not pass through, the router does not recognize the PDUs and doesn't know what to do with them.

Purpose of Routers

The purpose of a router is to connect nodes across an internetwork regardless of the Physical Layer and Data Link Layer protocol used. Routers are hardware and topology independent. Routers are not aware of the type of medium or frame used (Ethernet, Token Ring, FDDI, X.25, etc...). Routers are aware of the Network Layer protocol used: Novell's IPX, Unix's IP, XNS, Apples DDP, etc.

Router OSI Operating Layer

Routers operate on the OSI Model's Network Layer. The internetwork must use the same Network Layer protocol. Routers allow the transportation of the Network Layer PDU through the internetwork even though the Physical and Data Link Frame size and addressing scheme may change

Figure D: The Windows Network Diagnostic Tool is designed to help you troubleshoot connectivity issues

Conclusion

As you can see, the Network Center offers some promising tools for managing network connections within Vista. Right now some of these tools are a little buggy, but hopefully Microsoft will work out some of the kinks before the next beta.

Figure C: The Status screen provides summary information related to the connection

If you look at the bottom of Figure C, you will notice the Configure and Diagnose buttons. Clicking the Configure button simply takes you to the connection’s configuration screen. This screen is very similar to the one that you are used to seeing in Windows XP. What’s more interesting though is the Diagnose button.
Clicking the Diagnose button takes you to a diagnostic tool that you can use to figure out why the connection is not working. This tool is a neat concept, but it’s one of those areas where Microsoft needs to do a little more work.
As I mentioned earlier, IPv6 is kind of a big deal in Windows Vista. IPv6 is Vista’s preferred protocol, but Vista runs IPv4 along side IPv6 for backward compatibility with existing networks. The reason why I say that Microsoft needs to do a little more work on the diagnostic tool is because as you saw in Figure C, my network connection is working fine. The only catch is that I am using IPv4 instead of IPv6. However, when I click the Diagnose button, Windows returns a bunch of errors related to IPv6, which I am not actively using, as shown in Figure D.

Figure B: This is the main Network Center screen

The Network Map
If you look at the network map shown in Figure B, you will see that it shows the current computer passing through the local network to access the Internet. Just above the Internet icon, there is an option to view a full map. As it stands right now, if you click on the View Full Map link, you will pretty much see the same diagram except that the Network icon has been replaced by a Gateway icon.
Obviously, the current network map isn’t of much help to anyone. I have been told that as Vista gets closer to being released, that the network map will become a more comprehensive tool that displays the network in much greater detail than it does now.

Network Details

Although the network map doesn’t really do much yet, the network details option is useful right now. If you look at Figure B, you will see that there are two options in the Network Details section; Personalize and View Status.
I have to tell you that I absolutely love the Personalize option. What the Personalize option does is that it allows you to change the name and icon associated with a network connection. So why is this a big deal? Well, Microsoft created this feature for the benefit of people who connect to wireless networks. This feature gives you the ability to assign a meaningful name to various wireless networks that you connect to rather than having to be stuck with whatever name the access point might be using as its SSID. For example, I sometimes connect to a friend’s access point. The SSID for my friend’s wireless network is simply Linksys (this bothers me to no end). If I were running Vista on my laptop, I could assign a friendly name to the network instead though so that I would see a name like Phil’s House rather than Linksys.
I’m not actually running Vista on a computer that has a wireless network connection. So why do I love the Personalize feature so much? It’s because you can personalize wired connections too. Most of the computers that I buy, including the ones that I am running Vista on, have integrated network adapters. The problem is that these integrated network adapters usually have a maximum throughput of 100 Mbps. The network in my home is running at gigabit speeds, so the last thing that I want to do is to use a slow NIC just because it came with the computer. I therefore end up buying at least one NIC for each computer. Windows then displays a separate connection for every NIC that’s installed. The reason why I like the personalization feature in Vista so much is because I can assign each connection a meaningful name that helps me to keep track of which network connection I am actually using.
I mentioned earlier that the Network Details section includes a View Status option. If you click on the View Status link, you will see a screen similar to the one shown in Figure C. As you can see in the figure, this status screen provides you with information such as the connection speed, the connection’s duration, and whether the connection is using IPv4 or IPv6 (IPv6 is kind of a big deal in Vista). If you click the Details button, Windows will provide you with detailed information regarding the machine’s TCP/IP configuration.