User’s Manual
User Datagram Protocol (UDP) is a connectionless protocol that doesn’t require specific opening or
closing of the connection. UDP also uses checksum to ensure the entireness of the data, but it
doesn’t automatically take care of retransmission and it doesn’t ensure the receiving of the data.
UDP is less secure than TCP, but it is lighter and, therefore, more useful for general-purpose
applications. Since UDP doesn’t require a fixed connection, several Internet devices can use the
serial port simultaneously. ESERV-10 operates so that it transmits all the data coming to UDP port
(which is configurable) to that IP address from which a connection has lastly been established. Due
to that, ESERV-10’s UDP implementation is well suited for question-answer -type data
transmission, in case the retransmission feature is already built-in (which is the case in most serial
protocols).
As a conclusion one could say that the use of UDP protocol is simpler and even recommended if
possible. Some firewalls prevent UDP connections due to security reasons since Windows
networks use it to share files. When using such programs as Telnet, or if the data transmission
should be ensured, TCP may be a better alternative. It should be noted that in both cases the
firewalls might prevent outgoing traffic. In such occasions the firewall must be configured to support
the ports and the IP addresses used by ESERV-10 if one prefers to establish a connection
outwards (from the Internet).
Web Server
ESERV-10 includes a Web server in the TCP port 80. HTML pages, figures, documents and Java
applets smaller that 130 kB can be downloaded into that port. After downloading, these files are
accessible with a standard Web browser (Internet Explorer or Netscape Navigator) by writing the
ESERV-10’s IP address and the filename, for example http://172.16.1.1/mypage.html. If the file is
not available, the unit will return an error page.
An access to the ESERV-10 without the filename (http:// 172.16.1.1) results in that the unit tries to
find the default page (index.html) from its memory. If this page is available, ESERV-10 returns it,
otherwise an error page is displayed.
The contents of Web pages can be created by using standard development tools. However, before
they are downloaded into the unit’s memory, separate files must be copied into one single file that
ESERV-10 recognizes. This can be done with a Viola Configurator program.
All kind of files can be downloaded into ESERV-10’s memory. The text database “mimetypes.txt” in
the Viola Configurator’s set up directory (for example C:\Program Files\Viola Configurator\) lists all
the file types that ESERV-10 recognizes. The database consists of the file type extension (like .txt)
and the corresponding MIME type (like text/plain). It is possible to add more file types into the
database.
Web server can be used to save a HTML page, which includes a Java applet. That can be
downloaded into the user’s Web browser and it can be used as a virtual user interface in the
following manner:
1. User types ESERV-10’s address in the browser’s address field.
2. ESERV-10 returns the HTML page including the Java applet.
3. The applet runs in the user’s browser without reducing the processing capacity of
ESERV-10.
4. The applet makes a TCP or a UDP connection to ESERV-10’s configurable port, enabling
information transmission over the Internet between the applet and the serial port.
ESERV-10’s Web server supports 10 simultaneous connections. To ensure maximum capacity, the
number of objects (pictures, HTML pages, applets) should be limited to 10.
ESERV-10
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Viola Systems Ltd.
