A Made IT project
This type of network was developed by IBM and first published as IEEE 802.5 in December 1984. Token Ring is a star wired ring architecture. With a couple of predefined elements:
|Level 1||2-pair, red+green, orange+black, solid wire, 22 AWG, pairs individually, foil shielded, overall braided shield, smooth PVC jacket|
|Level 2||same as Level 1 + 4 UTP 22 AWG pairs for RS232, voice, etc.|
|Level 3||2-pair, solid wire, 24 AWG, unshielded cable, PVC jacket|
|Level 4||not an IBM cable type|
|Level 5||Fiber Optic cable|
|Level 6||2-pair, white/red+white/green, white/orange+white/black, stranded wire, overall foil shield, overall braided shield, thinly ridged PVC jacket, patch cable|
|Level 7||not an IBM cable type|
|Level 8||not an IBM cable type|
|Level 9||same as Level 1, but with plenum jacket|
With this in mind IBM created two Token Ring types which both have the possibility to run 4 and 16 Mbps. Those types are called type 1 and 3 and are defined as follows:
Token Ring Type 1
Level 1 cabling with IBM Data Connectors (IDC). MAUs have regularly 8 ports, one Ring In and one Ring Out port. Stations are attached to the MAU through IDC to Sub-D9 male lobe cables. Devices have a Sub-D9 female. Two MAUs are connected through patch-cables with two IDCs. The Ring Out from one MAU is connected to the Ring In of the other MAU.
A cabling system with IDC connectors and type 1 cabling is called ICS (IBM Cabling System).
Token Ring Type 3
Unshielded twisted pair cabling with RJ45 connectors (or RJ11 for the older types). The 4 Mbps version uses level 3 or higher and 16 Mbps needs level 4 or higher. The MAUs have the same modular connectors. Stations with a Sub-D9 female connector are connected with a Media Filter, which is actualy a balun that adapts to level 1 cable.
All lobe cables should be constructed of level 1, 2, 6 or 9 cable. At the station side they have normaly a Sub-D9 male to be connected to a Sub-D9 female of the station.
Patch cables should be of Level 6 cable and shall not exceed the 45 meter or 150 feet.
|IBM Data Connector|
|MAU RO||MAU RI||MAU Lobe||Sub-D9F||RJ11||RJ45|
|Tx+||Red||Orange||Red||Orange (9)||Orange (2)||Orange (3)|
|Tx-||Green||Black||Green||Black (5)||Black (5)||Black (6)|
|Rx-||Black||Green||Black||Green (6)||Green (3)||Green (4)|
|Rx+||Orange||Red||Orange||Red (1)||Red (4)||Red (5)|
So far the cabling and connectors. Most of the times the most important thing with networking is what can I do with it, that is, how many stations can I attach and what are the maximum lengths I can use?
To give you a rough idea there is the following table, but read this entire section before you start designing a complex network.
|Level 1||Level 3|
|Lobe length||100m / 330 ft||45m / 150 ft|
|Max. Ring length 16 Mbps||160m||60m|
|Max. Ring length 4 Mbps||360m||150m|
|Max. 8 port MAUs||32||9|
More precise cabling length calculation
Token Ring, as the name implies, is a ring structure with stations attached to that ring through special units called MAUs (Media Access Unit). To give you a general idea about what a Token Ring network looks like:
Here you see three import different items. First the MAUs, second the cables that connect the MAUs (patch cables) and which form the ring, and third the cables which connect the MAU to the PC and those are called lobe cables.
Token Ring has the benefit of redundancy. The ring is actual a dual ring, when a one cable connecting two MAUs becomes corrupt the MAUs will shorten their associated ports and use the back-up ring to make sure the packets will arrive at their destination. The disadvantage is that a packet might traffel the ring almost twice. This is something you have to keep in mind when designing a Token Ring network.
The maximum ring length depends on the number of MAUs, the number of wiring closets (MAUs connected with eachother with cables shorter than 3 meters are expected to be in the same wiring closet) and the speed of the network. To calculate the maximum ring length there is parameter called ARL (Adjusted Ring Length), which is the worst case distance between two MAUs.
ARL = total cable length used between all the MAUs minus the shortest MAU-MAU cable
Adjust ARL by the following points:
The ARL times 2 should not exceed 366 meter or 1200 feet
The Maximum Drive Distance for a station is the ARL plus the longest lobe length
Or you could use one of the following tables for the maximum ring length:
In the previous text we have spoken about MAUs as the attachment units for workstation to the ring, but there are several types. The MAU is the oldest one, which is actually just a switch unit. The inside of the box contains some relays which are normaly closed and as soon as a station is attached to the port the relay is opened and the station is added to the ring. Relays do have the problem that they sometimes switch during transport, that's why you need to a relay-tool to reset the relays before installing a unit.
There are active and passive MAUs. Passive MAUs only have the switching technique, while active MAUs also act as repeaters, so they regenerate the signal.
Next to the MAU there are TAUs, CAUs and LAUs.
A CAU is a Controlled Access Unit. This type is managed remotely, e.g. through SNMP.
A LAU is a Lobe Access Unit. This unit makes it possible to connect several (mostly 2) to one Lobe port on a MAU or CAU.
A TAU is a ..., I wish I knew. If someone can tell me I would be very happy!!!
According to the OSI layers an token ring network looks like this:
|2||Data Link||LLC or LLC + SNAP|
|1||Physical||Interface + PHY|
For SNAP and IEEE802.2 (LLC) see the corresponding documents.
MAC: IEEE802.5 Token Passing
Token Ring is a star wired ring architecture. Work stations gain access to the network in a predetermined way through the use of a token that runs around on the ring. In the idle state (no traffic is generated) the token is send from station to station. As soon as it reaches a station that has something to send that station captures the token, changes it to a frame and sets the busy bit. It adds frame header, information and trailer fields and releases the packet on the network. Each station reads the packet, looks at the destination address and if necessary copies it and sends it out again. This means that every station acts as a repeater(!). When the originating station receives the packet again it removes it from the network. After that it releases a new token and someone else may take it's turn.
In every ring there is one station that acts as the 'Active Monitor'. The Active Monitor takes care of generating the token, the ring clock, etc. The first station in the ring that powers up becomes the active monitor. If there are two or more Active Monitors at the same time, the one with the highest MAC address will stay alive. When the Active Monitor leaves the network another will be generated.
The token consists or 3 bytes: SD AC ED
A frame looks like this:
|Start delimiter||1 bit|
|Access control||1 bit|
|Frame control||1 bit|
|Destination address||2 or 6 bits|
|Source address||2 or 6 bits|
|Ending delimiter||1 bit|
|Frame status||1 bit|
The MAC layer offers 19 different MAC frames for network management.
|00000000||Duplicate Address Test||Test if two stations have the same address|
|00000010||Beacon||Locate breaks in the ring|
|00000011||Claim Token||Attempt to become Active Monitor|
|00000100||Purge||Reinitialize the Ring|
|00000101||Active Monitor Present||Periodically send message by the Active Monitor to show its presence|
|00000110||Standby Monitor Present||Announce presence of potential Monitors|
OSI layer 1