Throughput Evaluation Of Link Layer Flow Control In Computer

Throughput Evaluation of Link Layer Flow Control in Computer Networks

Analyzing computer communication networks requires understanding how different protocols and configurations impact data transfer efficiency. This study investigates the throughput of a network segment comprising three nodes (A, B, and C) connected via full-duplex links, employing different flow control protocols. Through simulation in OMNeT++, it assesses how transmission probability (TxP) influences overall throughput under varying network data rates, providing insights into the performance characteristics of sliding window and stop-and-wait protocols in tandem.

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In contemporary computer networks, efficient data transfer relies heavily on the effective operation of link-layer protocols. The scenario under consideration involves three nodes—A, B, and C—connected sequentially, where nodes A and B communicate with a sliding window protocol while nodes B and C employ a stop-and-wait protocol. Investigating the throughput across this configuration provides valuable insight into how flow control mechanisms and data rates influence network performance.

The core objective is to evaluate the end-to-end throughput from node A to node C through node B, emphasizing the impact of the transmission probability (TxP) on overall data transfer efficiency. The simulation environment is built using OMNeT++, a widely-used discrete-event simulator for network research, allowing for detailed modeling of protocol behaviors and network conditions.

In this setup, node A continuously generates frames at a data rate of 100 kbps. Each frame's transmission attempt succeeds with probability TxP, which varies from 0.1 to 1.0 in steps of 0.1. Frames that are not transmitted successfully are discarded immediately, simulating a probabilistic link access environment. The propagation delay is 5 microseconds per kilometer for both links, modeling real-world latency factors. All data frames are 1000 bits, and ACK frames are considered to have negligible length, refocusing the simulation on effective data transfer rates.

The protocol configurations specify that between nodes A and B, a sliding window protocol with a window size of 7 manages data transfer, allowing multiple frames to be in transit simultaneously, thus optimizing throughput under ideal conditions. Conversely, between nodes B and C, a stop-and-wait protocol is employed, where each frame must be acknowledged before the next is sent, inherently limiting throughput.

All links are error-free in the simulation to isolate the effects of protocol mechanics and transmission probabilities. Infinite buffers at nodes A and B for the A-to-B link allow for unimpeded data queuing, while no buffer is specified for C to B, assuming immediate ACK transmission due to negligible ACK frame length.

The simulation experiment includes two primary scenarios distinguished by data rates at nodes B and C: first at 50 kbps, then at 150 kbps. For each data rate, the transmission probability (TxP) varies from 0.1 to 1.0, with simulations run sufficiently long to gather reliable statistical data. The primary output includes the end-to-end throughput, collected in a tabular format and visualized through plots of throughput versus transmission probability.

The results reveal how the transmission probability influences throughput under different link speeds, demonstrating the interaction between protocol efficiency, network latency, and congestion effects. It is expected that higher TxP generally produces increased throughput, but the mode of protocol operation and the data rate significantly modulate this trend.

Limitations and assumptions in this simulation include the idealized error-free environment and the constant propagation delay, simplifying real-world variable network conditions. Moreover, the simulation assumes perfect timing and acknowledgment handling, without considering retransmissions or error recovery mechanisms, focusing solely on throughput under ideal conditions.

In conclusion, this study provides an in-depth analysis of the throughput characteristics of combined sliding window and stop-and-wait protocols across different data rates and transmission probabilities. Such insights are valuable for designing efficient network protocols and understanding their performance boundaries, especially in scenarios involving heterogeneous protocol stacks and varying link qualities.

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