IP BEHAVIOUR

Hi all,

Today I come up with some most basic and important concepts in IP networks. This will briefly explain you that how the datagram packet is crafted and what are all the parameters will help us to achieve the reliable delivery of the packet over the TCP/IP enabled network.


TCP AND UDP(TRANSPORT LAYER):

1. Transport layer has the responsibility to deliver the packet end-host to end-host across the network.
2. TCP makes the guaranteed delivery of the packet. (There is a lot of overhead involved in ensuring the packet delivery. It makes TCP slower).
3. But UDP won’t care about the packet delivery. (So it is faster than TCP).


TCP:

1. It only supports UNICAST only.
2. TCP packets are transported in IP packets since each packet takes a different route. So re-arranging the packet also takes care by TCP.
3. TCP protocol number is 6.

SEQUENCE NUMBER:

For achieving reliable packet delivery TCP uses SEQ.NO, it is 32-bit number. It will be chosen randomly.


ACKNOWLEDGEMENT NUMBER:

Acknowledgement number is last sequence number.

TCP DELIVERY FAILURES:

1. If TCP packet is lost from the middle of the stream, the receiver should be able to detect this. He keeps track of the next expected SEQ.NO.
2. If it receives the TCP packet with the SEQ.NO after one it expects, it will not acknowledge the OUT-OF-ORDER SEQ.NO ERROR. Instead it will send ACK of the next expected SEQ.NO.
3. There are three maximum duplicate acknowledgement packets to convenience the sender that there is some packet drop.

RETRANSMISSION TIMER:

What happens when a sending host fails to get an ACK of sent data?.

If there is response from the receiver side, then sender again will try to send the same packet again. If SRC.PORT and DEST.PORT are same for the sequence of the packets then we know that it is a retry packet.

How do we know that these are retries of the same connection not completely new connection?

First sending host waits 3 sec between the initial attempt and first try. Then it double the waiting time before sending the 2nd packet. It doubles the back off time before sending 3rd packet 12 sec later.

So here rule is IT DOUBLES THE TIME BEFORE SENDING THE SAME CONNECTION TO THE SAME HOST.

So up to now we have learned some basic concepts of TCP/IP network. From next i will come with some more in-depth concepts about the same.