An active monitor is a computer on a token ring LAN that supervises and maintains the network by watching other computers, generating empty token frames, and setting a clock to keep all computers in sync. It is crucial for the network’s functioning and is elected through a process of election.
An active monitor, in computer networking terms, is the supervisory role that one of the computers on a token ring local area network (LAN) assumes to maintain the network. This monitor takes care of the network by watching all the other computers connected to the network and making sure that data can travel through them to others on the network. All other computers on a token ring network, therefore, are called stand monitors, and will only congregate for a new active monitor in case the current one goes offline.
The emergence of the active monitor on a token ring network can happen in a couple of different ways. In the case where a token ring starts when each computer joins the network individually, the first computer to start claims the role. In other cases, however, such as if the network is established after all computers are already running or the existing active monitor leaves the network for some reason, creating the active monitor is through a process of election. Each of the computers on the network will send what is called a claim token, declaring its intention to take over the network. As the request travels the network, it is quickly evaluated against all other requests, and the computer with the highest Media Access Control (MAC) address wins the election.
An active monitor is absolutely crucial in the functioning of a token ring LAN. The first empty token frame, the packet that handles data delivery to other computers on the network, is generated by the active monitor and sent around the ring. The monitor will send one of these tokens every seven seconds to ensure that all computers on the network have learned the address and have subsequently identified themselves to each other. If further tokens circulate in the network, the monitor is responsible for cleaning them.
Since a networked computer requires the use of the token for data transmission, it takes the token frame, converts it into a data frame, and provides it with an address. Then it fills it with the data it wants to send and puts it back in the ring. Since only one frame can be used at a time, the active monitor then checks that if one data frame is in play, the other tokens are held. Once the data has reached its destination, the frame is sent back to the originating computer, which is then required to drop the empty frame token onto the ring. If there is some sort of transmission error along the way, the monitor will drop a new token frame into the ring.
Among the token’s essential checks on the network, the active monitor also sets a clock which ensures that all other computers on the network stay in sync. They must acquire and release the token in time with each other to ensure that the network works efficiently. To be fair to all computers on the network, active monitor also adds a delay so that the token can go around the ring.
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