CST311 - Week 34

This week we learned about the transport layer, which was covered in chapter three of the textbook. The transport layer provides logical communication between processes on different hosts and uses one of two protocols: UDP or TCP. The transport layer utilizes multiplexing and demultiplexing to deliver segments. Multiplexing occurs on the source host, gathering data from different sockets encapsulating the data into segments, and then sending these segments to the network layer. Demultiplexing occurs on the receiving host, which examines the header fields in each segment and directs the segments to the correct destination socket. UDP is a connectionless protocol and its advantages include: UDP encapsulates data and sends segments to the network layer immediately (without delays due to congestion control), there is no connection established to further increase delay, and has UDP has small packet header overhead. TCP is a connection-oriented protocol and provides reliable data transfer and congestion control. TCP incorporates sequence numbers, cumulative acknowledgments, timers, retransmission, and error detection to provide reliable data transfer. Additionally, TCP provides a flow-control service to prevent the overflow of a receiver's buffer which thereby causes packet loss. Lastly, TCP has a congestion-control mechanism that has three states: slow start, congestion avoidance, and fast recovery, to throttle senders to prevent too many sources from sending data at the same time at rates that are too high.

We also completed two labs. The first lab was a DNS Wireshark lab where we used the nslookup command and traced DNS queries and response messages. The second lab featured Mininet Iperf traffic measurements.