TCP Three-Way handshake

initialize TCP variables:

sequence numbers

buffers,flow control info

Client: connection initiator

Socket clientSocket = new Socket("hostname","portnumber");

Server: contacted by client

Socket connectionSocket  = welcomeScoket.accept();

Three-Way handshake:

step1: Client sends TCP SYN segment to server 

specifies initial seqnum = x

no data

step2: server receives SYN replies with SYN/ACK segment

server allocates buffers

specifies server initial seq =y

acknowledgement = x+1

step3: client receives SYN/ACK replies with ACK segment .which my contain data

acknowledgement = y+1

TCP Three-Way handshake

原文：http://blog.csdn.net/susser43/article/details/46728419