TCP

Question 1

Describe the steps of a TCP client

Answer 1

1) Make a socket and connect it to a port
2) Prepare input stream (from server)
3) Prepare output stream (to server)
4) Write request bytes to output stream
5) Read response bytes from input stream
6) …
7) Close socket and terminate connection

Question 2

Describe the steps of a TCP server

Answer 2

1) Make a ServerSocket with known port
2) (repeat)
3) .accept a new client connection represented by a new Socket
4) Make a thread to handle the client

Question 3

Name 4 TCP considerations

Answer 3

Message size, message destination, blocking, failure model

Question 4

Describe message size

Answer 4

Application reads/writes any number of bytes at a time until the connection is closed - the application does not see any message boundaries so needs to communicate boundaries explicitly in the bytes sent

Question 5

Describe message destination

Answer 5

A server can accept connection requests from any client - once the connection is established then bytes are communicated only between that pair of processes

Question 6

Describe blocking

Answer 6

A limited amount of data is buffered at sender and receiver sockets and sends will block once the sender buffer is full (known as flow control)

Question 7

Describe failure model

Answer 7

Communication is reliable short of complete connection failure
Lost messages are automatically retransmitted, duplicate packets are discarded and out-of-order packets are reordered using sequence numbered
If a loss is not resolved within a time limit then the whole connection fails

Question 8

Describe the uses of TCP

Answer 8

Can transfer almost all data reliably and/or in large amounts
e.g. HTTP, SSH, FTP, SMTP