1. An HTTP clients opens a TCP connection using an ISN 0f 14,535 and port number
ID: 662621 • Letter: 1
Question
1.
An HTTP clients opens a TCP connection using an ISN 0f 14,535 and port number of 59,100. The server opens the connection with an ISN of 21,732. assume the client sends a request of 100bytes, and the server responds with a segment of 1200bytes. Show the contents (src port #, dest. port #, Seq #, Ack #, Flags, Data) of the final segment from the server.
2.
Explain why UDP provides better performance( data rate) for data transmission than TCP in general. If we test sending 300 bytes 50 times, which protocol shows better performance?
Explanation / Answer
UDP uses a simple connectionless transmission model with a minimum of protocol mechanism. It has no handshaking dialogues, and thus exposes any unreliability of the underlying network protocol to the user's program. There is no guarantee of delivery, ordering, or duplicate protection. UDP provides checksums for data integrity, and port numbers for addressing different functions at the source and destination of the datagram.
With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol(IP) network without prior communications to set up special transmission channels or data paths. UDP is suitable for purposes where error checking and correction is either not necessary or is performed in the application, avoiding the overhead of such processing at the network interface level. Time-sensitive applications often use UDP because dropping packets is preferable to waiting for delayed packets, which may not be an option in a real-time system.[1] If error correction facilities are needed at the network interface level, an application may use the Transmission Control Protocol (TCP) or Stream Control Transmission Protocol (SCTP) which are designed for this purpose.
In situations where your really want to get a simple answer to another server quickly, UDP works best. In general, you want the answer to be in one response packet, and you are prepared to implement your own protocol for reliability or resends. DNS is the perfect description of this use case. The costs of connection setups are way to high (yet, DNS does support a TCP mode as well).
Another case is when you are delivering data that can be lost because newer data coming in will replace that previous data/state. Weather data, video streaming, a stock quotation service (not used for actual trading), or gaming data come to mind.
Another case is when you are managing a tremendous amount of state and you want to avoid using TCP because the OS cannot handle that many sessions. This is a rare case today. In fact, there are now user-land TCP stacks that can be used so that the application writer may have finer grained control over the resources needed for that TCP state. Prior to 2003, UDP was really the only game in town.
One other case is for multicast traffic. UDP can be multicasted to multiple hosts whereas TCP cannot do this at all.
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