Wireshark Lab TCP V60 Supplement To Computer Networking

Wireshark Lab Tcp V60 Supplement To Computer Networking A Top Do

Wireshark Lab: TCP v6.0 Supplement to Computer Networking: A Top-Down Approach, 6th ed., J.F. Kurose and K.W. Ross. In this lab, we will analyze the TCP protocol behavior through capturing and interpreting network traffic during a file transfer using Wireshark. The focus will include understanding TCP’s reliable data transfer mechanisms, congestion control algorithms (slow start and congestion avoidance), flow control via receiver advertises, and connection setup and performance metrics such as throughput and round-trip time. We will explore a packet trace collected from transferring a 150KB file (the text of Lewis Carroll’s Alice’s Adventures in Wonderland) from a computer to a remote server, analyze key TCP segments, and assess TCP's behavior in realistic network conditions.

Paper For Above instruction

Understanding the behavior of the Transmission Control Protocol (TCP) is fundamental to comprehending reliable data communication over the Internet. This paper presents a detailed analysis based on a packet trace captured during a file transfer from a client computer to a remote server, examining core TCP mechanisms including connection establishment, flow control, congestion control, retransmission strategies, and performance metrics.

During the capture, the initial TCP handshake was observed, where a three-way handshake involving SYN, SYN-ACK, and ACK segments established the connection. The TCP segment with the SYN flag set, containing a specific sequence number, initiated the connection. The subsequent SYN-ACK segment from the server responded with its acknowledgment number and its own sequence number, confirming the connection setup. The sequence numbers and acknowledgment fields enable TCP to synchronize data streams and maintain reliable delivery. Analyzing these fields, as well as the TCP flags, offers insights into how TCP distinguishes different types of segments within a connection.

Following connection setup, the transfer of a large file involved multiple TCP segments carrying parts of the data payload, identified by their sequence numbers. The segment containing the HTTP POST command marked the start of data transfer. Notably, TCP uses sequence numbers to identify the position of each segment within the data stream, and acknowledgment numbers to confirm receipt of data, facilitating reliable transfer. The captured trace shows the sequence of segments sent from the client to the server, with varying sequence numbers and timestamps indicating the flow of data.

RTT (Round Trip Time) calculations are critical for performance evaluation and congestion control. In the trace, RTT can be measured by tracking the time difference between the transmission of a data segment and the receipt of its acknowledgment. Wireshark's RTT plotting features assist in visualizing this behavior, revealing the dynamics of network delay. The analysis indicates fluctuating RTT values, affected by network congestion or variability, and allows estimation of the EstimatedRTT using standard formulas, such as exponential weighted moving averages, to adapt TCP’s retransmission timers.

Flow control is managed through the receiver's advertised window size, which indicates available buffer space. In the trace, the minimum advertised window size helps determine whether the sender's transmission rate was throttled, preventing buffer overflow at the receiver. The presence of zero or small window advertisements would imply temporary or persistent flow control constraints.

Retransmissions in the trace were identified by repeated segments with identical sequence and acknowledgment numbers, often triggered by packet loss or delayed acknowledgments. The trace also demonstrates TCP’s strategies for detecting missing segments—via timeouts or duplicate ACKs—prompting fast retransmission mechanisms. Identifying such retransmissions helps evaluate TCP's robustness and efficiency in congested networks.

The size of acknowledged data varies, often with the receiver acknowledging large blocks—sometimes in multiples of the segment size—indicating efficient batching. Conversely, acknowledgment of every other segment suggests delayed acknowledgments or conservative flow control.

Throughput calculation involved computing the total amount of data transferred divided by the duration of the transfer, from the initial data segment to the last ACK. This measure provides insights into network performance and the efficiency of TCP's congestion management under given conditions.

The trace further reveals TCP's congestion control behavior: initial slow start phase, where window size increases exponentially, followed by congestion avoidance with linear growth, and recovery phases involving fast retransmit and fast recovery algorithms. The plot of TCP window size over time confirms these phases, with the window expanding until it reaches a threshold, after which it grows more cautiously. Packet loss indicated by triple duplicate ACKs or timeouts triggers reduction of the congestion window and adjustment of the threshold, aligning with TCP Reno’s congestion control strategies.

Specifically, the TCP segment length was consistent with Ethernet constraints, often less than 1460 bytes, reflecting standard MTU restrictions. Analyzing segment lengths and timing helped verify link-layer interactions and possible packet segmentation issues.

Finally, detailed assessment of TCP's congestion window over multiple transmission rounds demonstrated how TCP adapts to network conditions. For instance, after a loss event, the congestion window decreases rapidly, and slow start resumes, illustrating TCP’s responsiveness to congestion signals. The analysis underscores TCP's fundamental role in maintaining reliable, flow-controlled, and congestion-aware data transmission across diverse network scenarios.

References

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