TCP connection establishment

Posted by AJ × 10:50

TCP sender, receiver establish “connection” before exchanging data segments

• initialize TCP variables:

– seq. nubers

– buffers, flow control info (e.g. RcvWindow)

• client: connection initiator

Socket clientSocket = new Socket("hostname","port number");

• server: contacted by client

Socket connectionSocket = welcomeSocket.accept();

Three way handshake

Step 1: client end system sends TCP SYN control segment to server

– specifies initial seq number

Step 2: server end system receives SYN, replies with SYNACK control segment

– ACKs received SYN

– allocates buffers

– specifies server-> receiver initial seq. number

Step 3: client sends the request and the ack for the server seq number

The three way handshake is over

Connection Release

client closes socket: clientSocket.close();

Step 1: client end system sends TCP FIN control segment to server

Step 2: server receives FIN, replies with ACK. Closes connection, sends FIN

Step 3: client receives FIN, replies with ACK.

– Enters “timed wait” - will respond with ACK to received FINs

Step 4: server, receives ACK. Connection closed.

Note: with small modification, can handle simultaneous FINs.

The connection management client side can be shown in a flow diagram

The connection management server side can be shown in a flow diagram

Connection management

The two figures

(a) TCP connection establishment in the normal case.

(b) Call collision.

• TCP connection management finite state machine.

• The heavy solid line is the normal path for a client.

• The heavy dashed line is the normal path for a server.

• The light lines are unusual events.

• Each transition is labeled by the event causing it and the action resulting from it, separated by a slash.

All Syllabus