Token-Ring (Network Architectures)

Token ring uses a token - passing architecture. The topology is physically a star, but it uses a logical ring to pass the token from station to station. Each node in token ring is attached to a concentrator called a multistation access unit (MSAU or MAU). Because of MSAU, a single computer failure does not stop the whole network. 

Token ring cabling 

Traditionally, token ring uses twisted pair cables. The standard IBM cable types are: 

Type 1: Uses two twisted pairs of solid copper wire with a braided shield for terminal and panel connections. Max distance: 101 meters (331 feet). Utilizes two STPs. 

Type 2: Uses six twisted pairs (two STPs, four UTPs) for voice and data. Max distance: 100 meters. 

Type 3: Uses UTP copper with two twists per inch. Lower cost but slower signal speed. Max distance: 45 meters. 

Passing data on token rings 

A token circulates around the token ring, and the computer holding it controls the transmission medium. The process is as follows: 

1. A computer captures the token.
2. If it has data to send, it transmits a data frame while holding the token.
3. Each computer checks if it is the intended recipient.
4. The destination computer copies the frame, updates the status, and returns the frame to the ring.
5. The sender receives the frame, acknowledges successful transmission, removes it from the ring, and releases the token back onto the ring.

Token ring frame 

Start delimiter: Indicates the start of the frame. 

Access control: Specifies frame priority and identifies if it's a token or data frame. 

Frame control: Contains media access control info. 

Destination address: Receiving computer's address. 

Source address: Sending computer's address. 

Data: The transmitted data. 

Frame check sequence: Error-checking data (CRC). 

End delimiter: Marks the frame's end. 

Frame status: Confirms if the destination was found and the frame recognized.