UDP

Question 1

Describe the steps of a UDP client

Answer 1

1) Make a DatagramSocket
2) Make a DatagramPacket with payload and destination (server) host & port
3) .send the DatagramPacket a UDP packet
4) Make an empty DatagramPacket
5) .receive the next UDP packet into that DatagramPacket

Question 2

Describe the steps of a UDP server

Answer 2

1) Make a DatagramSocket with known port
2) (repeat)
3) Make an empty DatagramPacket
4) .receive the next UDP packet into that DatagramPacket
5) …
6) Make a DatagramPacket with payload
7) .send the DatagramPacket as a UDP packet

Question 3

Name 4 UDP considerations

Answer 3

Message size, blocking, receive from any, failure model

Question 4

Describe message size

Answer 4

Hard limit of 65508 bytes but often 8k or less
Larger messages are broken up into smaller fragments on most physical networks and is reassembled by the receiver - less reliable

Question 5

Describe blocking

Answer 5

Receive normally blocks until a message is received

Question 6

Describe receive from any

Answer 6

Normally a socket will accept messages from any sender

Question 7

Describe failure model

Answer 7

Best effort like IP
Checksums detect most corruption of messages and discard them
Messages may be dropped due to corruption, no space in buffer at end system or in network (congestion)
Messages may arrive out of order and may be occasionally duplicated

Question 8

Describe the uses of TCP