6. Reliable Communication

Question 1

How does TCP ensure a reliable transmission?

Answer 1

• 3 way handshake
• sequence numbers to ensure order and nothing is missing
• acknowledgement numbers to confirm reception of packets, contains next expected sequence number
• time-out triggers a retransmission
• checksums to ensure integrity
• flow control to prevent overrunning the receiver, reducing packet loss

Question 2

Which application protocols run over TCP?

Answer 2

• email
• ssh
• http(s)
• IRC
• SSL
• Transport Level Security

Question 3

What duplex is TCP?

Answer 3

Two way full-duplex, like a telephone call. Only unicast though.

Question 4

What is a problem with having sequence numbers in TCP?

Answer 4

The next one can be predicted by Trudy, interecpted or could send a new message with that sequence number.

Question 5

Disadvantages of TCP over UDP?

Answer 5

• bigger header size

- congestion control means data doens’t always get sent immediately