Virtual Modem PRO - 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.

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