Connection Oriented Multiplexing And De multiplexing

TCP socket  identified by 4 tuple:

a.Source IP address

b.Source port number

c.Destination IP address

d.Destination port number

When a TCP segment  arrives  form the  network  to a host  the host  uses all  four values  to direct the segment  to the appropriate socket. In  particulars with different source IP  addresses or source port numbers will be  directed to two different socket.

The  server  host may support  may is simultaneous TCP sockets  with each  socket attached to a process  and with each  socket  identified by its  own  four tuple  when a TCP  segment  arrives  to the  host all  fours fields are used to direct the segment to the appropriate socket.

The  situations illustrated in figure in which host  c initiates two HTTP sessions to server B and  host A initiates one HTTP session B hosts A  and C and server B each have their own  unique IP address A , C and B, respectively  host  C assigns two different  source port  number its two  HTTP  connections. Because  host A is choosing  source  port number  independently of C. It  might  also assign a source  port of 61452 to its  HTTP connection. Nevertheless sever B will still  be able to correctly  de multiplex the two  connection  having  the same  source  port number since the two  connections  have different  source  IP addresses.

figure two clients using the same destination port  unmber (80) to communicate with  the same web server  application