Voice Communication via Network/Internet

This article was contributed by
Zhaohui Xing.

Environment: Windows NT4/2000 and Visual C++ 5.0 (and greater)

This is the simplest prototype to demonstrate how to realize a basic Voice
Communication via Internet/Network on PC platforms. The technique in this demo can be
applied to develop the PC internet voice communication software, such as Internet Phone.

To save development time, I borrowed the idea of Client/Server design in Microsoft MSDN
sample "GlabolChat". 

This sample has been tested in a intranet consisted of NT4.0 Server/Workstation and a
LAN consisted of Win2000 Professional. The CPUs in the testing PC are at least  Intel
P2 266 or faster, and SoundCard, Mic, Speaker are must.

In the tests, it can work smoothly in bi-directions voice talk with the a acceptable
sound quality.

The basic system design

This sample contain two modules, Talkserver and Talkclient.

The basic system diagram is like:

System diagram


Server Module

Server module has two type sockets, server sockets and client sockets. One server
socket supports a certain network protocol and listens the incoming connection with such
protocol. When a client connection request comes, the server socket create a client socket
to build the link with the client. The client socket works to receive the messages from
its client, transit the message to peer client socket, then the peer client socket send
the messages to the target client. The client socket also get the messages from the peer
  socket and send these message to its client.  


Client Module

The user can use the client modules to communicate in voice with each other. The socket
in the client is implemented as sending/receiving messages to/from the server.

The method to capture and transit sound data in client module is  building and
runing a wave input device, when this wave input device records enough to size of the data
buffer in its wave header structure, it notifies client instance. When the client receives
the wave input device message, client retrieves the sound data in the wave input device
buffer, then encodes the sound data into the voice communication message and sends to the
peer (or target) client.

To play a voice message is similar. The client has a wave out device. After the client
receive voice message from other client, it decodes the sound data from the message, put
the sound data to the wave output device and drives it to play the sound. 


Change sound quality

By changing the wave device buffer and wave format type defined in vtDef.h, you can
change the sound quality in some kind of levels. 


Download the project – 253 Kb

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