Token Ring

Token Ring is a form of LAN (Local Area Network) protocol, which is embedded in a Data Link Layer or DLL. This is different from Ethernet since it utilizes a Ring topology wherein the data is transferred from one machine to another. This in turn will revert to the initial location, thus circling around the Ring.

Today, a Token passing control is also being implemented in order to limit access to a network to those that have control of the Token. This ensures that no collision will take place since only one machine is allowed to use the network within a given time.

The Basics

The process of Ring insertion goes through five phases until it is allowed into the Ring network. Therefore, when any one of the five phases fails, it refuses the insertion of the Token Ring station into the Ring. In fact, it may even register an error in the driver.

  1. Lobe Check – The station performs the standard lobe media check. A station sends test frames to its transmit pair, which will then follow a loop that will lead it back to its receive pair. This enables the station to validate whether it will be able to receive frames free of error.
  2. Physical Insertion – The station sends signal to the Multi Station Access Unit (MSAU) to initiate a relay.
  3. Address Verification – The station sends Media Access Control (MAC) frames using its MAC address to a specified destination address of a token ring frame. As soon as the frame returns and the address is copied, the station will then take part in a Ring poll process which will run every 7 seconds. This is also the part wherein the station identifies which ones are parts of the network within the MAC management functions.
  4. Participation in Ring Poll – Once the station has determined its NAUN address and has shared its address to the nearest downstream neighbor, a Ring map is then created. Then, the station will wait until the SMP or AMP frame is received. After the station has successfully participated in the Ring Poll process, it is now time to proceed to the request initialization, which is the last part of this 5-part process.
  5. Request Initialization – This is the phase wherein a station sends its parameter server a special request so that the configuration information can be obtained. Then the frame is forwarded to a special function address, usually a Token ring bridge. The said frame will consist of a Ring number information and timer that is sent to the new station.