Am 31.08.2005 um 00:27 schrieb Niccolo Zapponi:
Hey Lance,
thank you for that stuff but I'm just a newbie so I didn't
understand anything!
Can you explane me how to set up a really easy server and client
or just re-explane me how that work?
[Disclaimer: This might not be exact in each detail. I just
tried to explain the main concepts. Feel free to add details.]
Well, I'll jump in and try to explain certain details:
- Multicasting
Multicasting a special way of network communication. While
Network communication is often performed between two single
computer [ a client computer and a server computer ], multicasting
allows to send a message from once computer to a group
of computers sharing certain network properties.
In your local area network, this will work find, because all
system
are directly connected through an Ethernet hub or switch.
As soon as certain TCP/IP network need to exchange data, routers
come up. A router works as an intermediate to transfer data
from TCP/IP network A to network B.
In fact, the whole internet is a system of meshed TCP/IP networks
interconnected by routers.
Theoretically, Multicasting works fine through the internet. In
practice, most internet routers do not forward multicasting
data packets, because such packets could flood the whole
internet.
To enable Chat applications to find each other and exchange data, the
apps need to know the TCP/IP address of each other or a central
system, which know the address of all chat application's system.
Thus, the central system is called the server, which sits and waits
for
clients to contact him. As soon as a clients asks to join the chat
'network', the server would record the chat client's user ID and its
internet TCP/IP address.
Such a server - which registers clients and probably intermediates
messages from client A to client B - could be a CGI application
on a Webserver or a special application.
A CGI could be used, but not too simple. Why? Because HTTP is
a stateless system. A browser talks to the server, the server
recived the data, calls a CGI and finally returns data. Then the
CGI quits (most likely). Thus, if you would like to use a CGI,
the CGI would most likely need to save certain details of its
communication partner.
Opposed to this, one could set up a special server application -
just like a mailserver application - which permanently runs,
accepts client application's request and keep communication
session to the client. If the server keeps several client
communication session, it can exchange data received from client
A to all other clients - now the chat system is alive.
[Sorry, it's too late and I worked the whole day and just
arrived in the office. Thus, no time to write more.]
Kinds
Stefan
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