Question

- What event will cause the sender to initiate fast retransmit when using TCP?

- Describe briefly the relationship between the round trip time (RTT) observed between a sender and a receiver and the retransmit timer used in TCP.

- Describe briefly the basic difference in service provided by an email server using POP3 protocol compared to an email server using IMAP protocol.

Please don't copy and paste from the internet. Thank you

Answer 1

1. For sender to initiate fast retreansmission using TCP, the reciever should send an immediate duplicate acknowledgement packet i.e ACK packet and this is done when the reciever recieves a data segment above a gap in the sequence space.

2. Retransmission Timer is used so that if a packet is lost then it can be retransmitted after the retransmission timer.

Now the retransmission timer is caluclated based on the smoothed round-trip time and its deviation. So, the relation between the retransmission timer and the round trip time is,

RTO = RTTs + 4 x RTTd

3. POP3 or Post-Office-Protocol is used to download email form the derver to the client computer. After downloading the email it deletes the email form the server.

Whereas IMAP (Internet Message Access Protocol) stores the email in the server and then synchronises that email is synchronised which allows user to manipulate that email like it is stored on the computer.