Suppose the round-trip propagation delay for Ethernet is 46.4 μs. This yields a minimum packet s

step 1 Okay, so if the delay time is held constant at 46 .4 microsecond and the signaling rate rises to

Suppose the round-trip propagation delay for Ethernet is...

Suppose the round-trip propagation delay for Ethernet is $46.4 \mu \mathrm{s}$. This yields a minimum packet size of 512 bits ( 464 bits corresponding to propagation delay $+$ 48 bits of jam signal). (a) What happens to the minimum packet size if the delay time is held constant, and the signalling rate rises to $100 \mathrm{Mbps}$ ? (b) What are the drawbacks to so large a minimum packet size? (c) If compatibility were not an issue, how might the specifications be written so as to permit a smaller minimum packet size?

Suppose the round-trip propagation delay for Ethernet is $46.4 \mu \mathrm{s}$. This yields a minimum packet size of 512 bits ( 464 bits corresponding to propagation delay $+$ 48 bits of jam signal).
(a) What happens to the minimum packet size if the delay time is held constant, and the signalling rate rises to $100 \mathrm{Mbps}$ ?
(b) What are the drawbacks to so large a minimum packet size?
(c) If compatibility were not an issue, how might the specifications be written so as to permit a smaller minimum packet size?

Key Concepts

Minimum Packet Size

The minimum packet size is a protocol requirement designed to ensure that a transmitting node is still sending data during the round trip propagation delay, so that if a collision were to occur, it would be detected. This size is calculated based on the delay and the signaling rate, as well as additional bits necessary for collision resolution procedures like jam signals.

Ethernet Collision Detection and Jam Signal

Ethernet collision detection ensures that when two devices transmit at the same time, the collision can be detected by both parties. To guarantee that a collision can be detected, the frame must be long enough in time. If a collision occurs, a jam signal is sent to notify all nodes on the network. The additional jam signal bits are included in the calculation of the minimum packet size.

Propagation Delay

Propagation delay refers to the time it takes for a signal to travel from the sender to the receiver and back. In network design, this delay is a critical factor because it dictates how long a device should be transmitting to ensure that all collisions are detectable within the network.

Signaling Rate

The signaling rate defines the number of bits transmitted per second. When the signaling rate increases, each bit occupies less time, which means that the number of bits needed to occupy a given time interval (such as the round-trip propagation delay) increases. This has direct implications on the number of bits required for a minimum packet size for reliable collision detection.

Network Efficiency and Compatibility Constraints

While a larger minimum packet size ensures robust collision detection, it can lead to inefficiencies such as increased overhead proportionally for small data transmissions, reduced network throughput, and higher latency. Compatibility constraints also come into play, as network standards might require maintaining a fixed minimum size, limiting the ability to optimize performance by allowing smaller frame sizes based on actual propagation delays.

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