- Server:
- Server = a
program that provides
a service
- A server will wait for requests
- Server = a
program that provides
a service
- Client:
- Client = a computer program that send requests to a server (program)
- Server programming:
- A server application
will be
contacted by a
client (program)
that requires the service
Therefore:
- Server application must have a fixed contact point (= port#) !!!
Analog:
- A pizza take out service must
has a fixed telephone number for
clients to
call to
order pizza !!!
(If the phone number can change, this pizza service will be impossible to find !!!)
- A server application
will be
contacted by a
client (program)
that requires the service
- Summary:
when writing a
server, use
a fixed (UDP) port#
- Client programming:
- The client will
always initiate
the communication
with the server
- Fact:
- Messages
sent by
client
will
contain:
- The IP address and the port# of the socket of the client program !!!
Analogy:
- We you calls to order pizza, the pizzaria will have your phone number (as in caller ID)
- Messages
sent by
client
will
contain:
- Consequently:
- The server can
find out the
network address of the
client !!!
- A client can use a arbitrary (available) port number !!!
- The server can
find out the
network address of the
client !!!
- The client will
always initiate
the communication
with the server
- Conclusion:
- When writing a client application, bind the socket to a system assigned port #
- Summary
