What is Token Ring?

IBM originally developed the Token Ring protocol in 1970, but IEEE later adopted it as the 802.5 network specification. The IEEE 802.5 network specification is compatible and almost identical to the Token Ring protocol develops by IBM. Token Ring is the name used in regards to both.However there exist some other newer,faster and more improved token ring specifications whith more features such those are FDDI(Fiber Distributed Data Interface) and CDDI(Coper Distributed Data Interface).

The main advantage of Token Ring over Ethernet is that Token Ring solves the problem of packet collisions. The solution is implemented by allowing stations to transmit data by taking turns in their use of the transmission link. The Host that has the ability to transmit data is determined by the use of a metaphorical Token that is sent around the link connecting all the Host computers. When a Host wants to transmit data, the Token is taken off the link and then that Host can transmit its data. When the Host that sent the data finishes it takes the data off the link and places the Token back on the link so that another Host can gain access to the Token in order to send data. The release of the Token is done in two ways depending on the ring rate. With slower rings the token is released only after the response bit has been received but with higher speed rings it is released after the transmission of the last frame and is called early token release. The topology of the network is a ring, which consists of a set of Host stations connected to each other by a transmission medium. Data flows in a particular direction around the ring and each station receives data from its upstream neighbor and forwards it to the neighbor downstream. Although the abstraction of this topology is almost always a ring it can physically be implemented as ring, bus or star.

In order to detect network faults the Token Ring protocol employs one station in the Token Ring network as an active monitor. An active monitor can be any Host connected to the network. The main purpose of the active monitor is to act as a centralized source of timing information, for other Host stations connected to the ring and performs a variety of ring -maintenance functions. Ring-maintenance functions include the removal of continuously circulating frames from the ring. When a sending Host fails, its data may continue to circle the ring. This can prevent other stations from transmitting their own data and essentially can lock up the network. The active monitor can detect such circulating data, remove them from the ring, and generate a new token.