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Free CISSP Certification Practice Questions:

Which of the following LAN transmission protocols is ideal for a factory automation environment where transmission delays must be predictable and deterministic?



C) Ethernet network

D) Token Ring network

E) IEEE 802.3

  • [Ans: D]

  • Token passing networks are deterministic and predictable. In a token ring network, it is possible to calculate the maximum transmission delay experienced by any end station. Token passing networks use a token, or series of bits, to grant a device permission to transmit over the network. The token acts like a ticket, enabling its owner to send a message across the network. When transmission is complete, the device passes the token along to the next device in the topology. Since there is only one token for each network, there is no possibility that a collision will occur, i.e. two computers attempting to transmit messages at the same time. In addition, rules in the protocol specifications mandate how long a device may keep the token, how long it can transmit for and how to generate a new token if there isn't one circulating. Hence, token passing networks, such as Token Ring networks, are ideal for environments where transmission delays must be predictable.

    On the other hand, CSMA/CD (specified in the IEEE 802.3 standard) networks, such as Ethernet networks, are non-deterministic. In these types of networks, nodes constantly monitor the line to make sure that no other hosts are transmitting. A node must wait until the line is clear before starting to transmit and must continue to monitor the line while transmitting. If two nodes transmit at the same time, the transmission will be corrupted and the frames will be discarded. In this situation, each device then waits a random amount of time and retries until transmission is successful. As a result of its non-deterministic nature, CSMA/CD (IEEE 802.3) networks, such as Ethernet, are NOT ideal for network environment where transmission delays must be predictable and deterministic.

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