1.1. Clients and Servers
FlashCom is a server-side
application that is installed on a host machine much like a web
server; however, FlashCom works very differently than a web server.
Instead of accepting many brief connections from browsers requesting
a web page or other resource, FlashCom accepts persistent connections
from Flash movies running in a Flash Player. Each Flash movie can
share data with other Flash movies via the server using
Macromedia's proprietary Real-Time
Messaging Protocol (RTMP). Unlike the HTTP request/response model
used by browsers to communicate with web servers, the Flash
Player's RTMP connection to the FlashCom Server is
persistent, so no special steps are needed to maintain session
information. Once the server accepts a client connection, the
connection can be used to exchange audio, video, and ActionScript
data until either the client or server disconnects.
The Flash Player may be running within the Standalone Player or
within a web browser. The Flash Player (and any movie playing within
it) is considered the client. FlashCom cannot initiate a connection
to a movie; the connection must be initiated from the Flash Player
running on the client. Let's review the architecture
briefly so you can understand all the pieces to the puzzle. The
client/server architecture for FlashCom applications is shown in
Figure 1-1.
Web browsers load Flash movie
files (.swf files), load the Flash Player, and
pass the .swf file to the Player to execute. The
Flash movie provides the user interface and can attempt to connect
via the Player to any FlashCom Server. Once connected, the Flash
movie can communicate with the server. Furthermore, it can
communicatevia the serverwith movies playing on other
Flash clients. A Flash movie can stream audio and video to the
FlashCom Server so that other Flash clients with access to the same
server can play recorded streams stored on the server and live
streams from other clients.
A live stream is usually one that is
published to the server by one client so that other clients can
receive it. As the client's data arrives at the
server, the server duplicates it and forwards it to each client,
where it is seen and heard. In contrast, recorded streams are stored
on the server and can be played from any point within the stream,
paused, and restarted. It is also possible to stop a recorded stream,
seek to any point within it, and begin playing again.
If multiple FlashCom Servers are
connected to one another, clients connected to one server may be able
to communicate with clients connected to another server. The ability
to communicate between servers and the clients connected to them
makes possible large-scale applications, such as live event streaming
to many thousands of viewers.
FlashCom can host many different
applications.
More than one instance of an application can be
run at the same time. Each instance is given its own unique name.
When a client connects to the server, it always connects to an
instance of an application by name. For example, many separate
instances of an application named chatRoom may
be available. Each instance has its own unique name and may provide
unique resources for the client. Figure 1-2
illustrates three clients connected to the same instance of the
chatRoom application.
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