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TCP/IP 57
Figure 3.15: Client Server model over TCP/IP
3.6.2 Endpoint and Internetsocket
Figure 3.15 shows a Client Server communication over the TCP/IP stack. Several Clients and
Servers can be active at the same time on computer systems. It is important here that every
application is identified unambiguously although the computer, on which several applications
run, only has one physical connection with the Internet.
For this reason, transport protocols give each communication service a unique name. TCP
uses protocol port numbers. A specific protocol port number is assigned to each Server. The
Server waits passively for communication via this port number. When sending a request, the
Client mentions the port number of the required service. The TCP software on the Server’s
computer uses the destination port number in an incoming message to determine which
Server has to handle the request.
Figure 3.16: Endpoint and socket concepts
endpoint
The endpoint concept and socket concept can sometimes be confusing. The original definition
of a socket according to ARPANET is the combination of the IP address and the port