Virtual Modem Architecture

The Essence of Virtual Modem PRO

The main advantage Virtual Modem PRO delivers is the speed and reliability.

In case you are using the application that sends/receives data to/from remote host via conventional telephone line (PSTN – public switched telephone network), but however would like to use faster Ethernet network (VPN, WAN, LAN/VLAN/Wireless LAN, etc.) instead, then Virtual Modem PRO is right for you!

Indeed, re-writing the current application may take months or even years of development, debugging, testing and may not be the option in today’s hectic and dynamic world. Virtual Modem PRO is a low-cost solution that acts as a middleware between telephone line and Ethernet. That means that virtual modem (once installed) is identified by operating system (and, therefore, by any other application) as the standard physical modem, but it uses TCP/IP protocol to send and receive data to the other end (acts as IP-modem).

TCP/IP protocol is a reliable and connection-oriented transport mechanism, which guarantees that data will arrive complete, undamaged, and in correct sequence order between two endpoints on the Internet.

Among other benefits of such approach is a client/server architecture which ensures bi-directional connection and guarantees that data is sent to correct host. Please, note that virtual modem can work as a client or server at any time, but server modem can accept just one connection.

Differences Between Two Architectures

Old, conventional way to establish connection link between two endpoints via phone line is using remote end’s phone number. The caller initiates the connection (calls) and calling party accepts it. Once the connection is established, the application itself usually handles all data flows.

Virtual modem usage differs a bit. From application’s point of view nothing has changed: the caller still initiates the link and on successful connection it sends the data. However, the user must perform intermediate steps of setting up Virtual Modem PRO application on both hosts. First of all, he/she must decide who is going to call. The host which is going to initiate the call must be configured as a client, and, on the other hand, the accepting party must be configured as a server.

Basically, in order to set up the server you must provide TCP/IP port number which the server will listen at for incoming connections. Make sure that it doesn’t interfere with other services such as DNS, Mail, HTTP and other services running on in your computer. We advise you to use unreserved TCP/IP ports that start from 1024 (up to 65535).

If your company uses firewall, make sure that chosen port is not blocked, otherwise the connection will fail. To set up the client you must provide it with server’s IP number (the unique number to identify computer in the net) and TCP/IP port (which should be already chosen).

Please, note that setting up your computer as a client (caller) doesn’t necessarily means that it will only send data, while the server (accepting party) will just receive it. Virtual Modem PRO allows sending it both ways, however your application that will use Virtual Modem PRO may only send or receive.

Basically, the difference between client and server is that client is always initiating the connection and server is always responsible to accept it or decline.