The technology, 'Ethernet' at the early age was quite simple. As it was developed much before the advent of 'Microprocessor', the whole technology was much more less demanding to intelligence of the network structure and the workstations. Though this forms a low cost network, but there reliability in data communication was very poor. But 'Token Ring' came into play at the time when we are already enjoying the microprocessor technology.

With the growth of the microprocessor, the network adapters start to have their own small CPU. The Token Ring supports much more complicated protocols, having support from more intelligent network adapters. This is much more costly technology, but is able to provide us a reliable data transfer and precise way of controlling the congestion over the network.

In the Ethernet structure, every workstation is connected to a single data bus. The bits sent by any of the workstation, were received by all other workstation. But in Token Ring, all the stations are connected in ring shaped structure, where all workstation is connected to its next neighbor with a pair of cable. Data flows along the ring until it reaches at the origin. The physical structure is a bit different. Actually all the workstations are connected to a centralized location through two pairs of wires. The connecting wire from the center to the workstation is known as "Lobe". One pair is for receiving data and the other pair is to transmit.

The lobe is connected to the central closet through a relay, that is operated independently by the network adapter of the connected workstation. One position of relay allows all the traffic and at the other position it isolates the lobe from all the data flow and the receiver is connected to the transmission of the same workstation. This is a sparkling feature the Token Ring. This enables the whole structure to flow data within the closet and any single workstation. This is a lookback mechanism. When any problem is detected is the communication, the network adapter activates the loopback and verifies the integrity. In occurrence of any fault, the workstation generates a one byte token and circulates along the ring. In this faulty condition of the whole structure, any workstation can transmit its data after receiving the flowing token.

Among all the workstations, a single workstation is elected as Active Monitor. Its primary task
is to minutely monitor every data and token passing through the ring. If somehow any token is lost, the active monitor waits for the timeout duration and then generates a fresh new token. If a particular data segment could not be received by any of the workstations and keep circulating through the ring, the active monitor removes the data segment at its second pass.

After sending a data segment, a station must generate a token and circulate it around the ring. So that every workstation gets a chance to send its data segment by capturing the token, before any workstation sends its next data segment. In this way token ring controls the congestion which is much better than that of Ethernet technology.

Every workstation in the ring has its unique identity. That can be either the hardware address of the adapter card or numbers assigned by the network administrator. With the data flow between workstations, they learn the address of nearest upstream neighbor. If any workstation does not receive any data or token for a certain period of time, it stats transmitting an alert message called "Beacon". The beacon contains the identity of both the transmitting station and its nearest upstream neighbor. Thus all other stations comes to know that a station is handling a fault and forwards the beacon. Thus any problematic section in the whole network identified very rapidly. Now the upstream neighbor triggers its relay for loopback, removing itself from the ring.

The Ethernet technology was based on the working with the dumb network adapters and single wire connection with closet. Though the actual Token Ring was also assumed to be based on the same dumb cards, but it improved the network technology with more advanced adapters. Modern Ethernet technology also applies much more intelligent devices than that of those earlier days. So as Token Ring improved in parallel. Never we can judge the cost effectiveness or efficiency or reliability on some features of any technology in the vast field of Computer Networking.

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Автор : btamedia press