TCP/IP settings

The most commonly used network protocols today are TCP (Transport Control Protocol) and UDP (User Datagram Protocol). TCP is a proven and reliable protocol, and probably the most widely implemented protocol in use on IP networks today. However, TCP has a lot of overhead and payload issues, and can sometimes be ‘too-reliable’ or robust for many applications. In fact, when used as transport, for many serial based applications TCP can actually hinder reliable communications. In contrast, UDP is a much simpler protocol, and is being used more frequently today - particularly in areas where bandwidth or throughput is constrained. An example is the predominant use of UDP for transport of wireless data applications.

UDP is first a connectionless protocol. Like TCP, UDP runs on top of IP networks. But unlike TCP, UDP does little to help with transport delivery or error recovery. Instead it offers a direct way to send and receive packets, letting the software application manage things like error recovery and data retransmission. Once primarily used for broadcasting small messages, UDP is now used for everything from browsers to Instant Messaging, Video, and Voice over IP applications.

While a powerful tool, the downside to using UDP is that there is not ‘connection’ report to know that you have end-to-end connectivity. This often makes detecting whether or not a packet is ‘making it’ from one place to another quite a hassle.

Serial Printer Logger can be configured to log data from as many ports that you like simultaneously on a single PC. The program uses a multi configurations. Each configuration may contain different settings for each TCP/IP port. Each configuration has a set of TCP/IP parameters that are described below.

Each port configuration (i.e. TCP/IP connection) in Serial Printer Logger can act as:

Client. You will need to specify the remote host IP address and the port number for the TCP/IP server that you want to connect to. The IP address that you specify in Serial Printer Logger when configuring it as a client may also be either a URL or the name of a computer located on your network. For example, if you want to connect to a computer named "Plant1", you can simply enter "Plant1" for the IP address instead of the actual IP address. If you are configuring Serial Printer Logger as a client and your network is set up to assign IP addresses dynamically to each individual workstation, then you may need to use the name of the PC that you want to connect to instead of an actual IP address in order to guarantee a connection;

Server. In this mode you should specify the IP address of the local PC will be used and you only need to specify the port number that you would like to use. If your PC has more than one network interface card (NIC) then Serial Printer Logger will display a list of all the IP addresses for each NIC installed in your system so that you can select the IP Address that you want to use. In order for Serial Printer Logger to act as a server, the PC that it is running on must have at least one network interface card with an IP address assigned to it. In Microsoft Windows, the TCP/IP protocol can be configured to automatically obtain an IP address from a host computer. This means that your PC may not have an IP address until it is connected to a network server or a host computer. You may need to contact your network administrator to assign an IP address to your PC if you wish to configure a TCP/IP server connection. This is done in the network settings for the TCP/IP protocol in your control panel.

After you enter the parameters that you would like to use, you must click the "OK" button to establish a connection between Serial Printer Logger and the TCP/IP port. If the current port configuration is set up as a client, it will immediately try to establish a connection to the specified remote server. If the server is not available, Serial Printer Logger will continually try to establish the connection until it is successful. If the port configuration is set up as a server, it will listen the specified port until a client establishes a connection to it.

If one or more port are configured already, then Serial Printer Logger is opening these ports and starting logging. If the port is opened successful, then the status bar in the main window displays a status of this port (pic.1). But, before you should configure port parameters that are described below.

You can create the new configuration by clicking the "Plus" button in the main window (pic.1) or through the "Options" menu. After you clicked the "Plus" button, the dialog window will be opened (pic.5). The dialog window contains few sections with parameters. The "IP settings" section is described in this chapter.

To log data from more than one TCP/IP connection you would create and configure multiple port configurations. You can manage the configuration created with a drop down menu near the "Plus" button (pic.4).

The "IP settings" tab contains indispensable settings of any TCP/IP port: IP address and port.

In addition to IP address, you should specify how to connect to a remote machine. Our software can be thought of as a trunk line with thousands of individual lines (the ports) which are used to connect machines. Some ports are considered well-known ports. For example, the port typically used for network mail systems (SMTP) is port 25, the telnet port is port 23, the network news server port (NNTP) is typically port 119, and so on. To see a list of well-known ports, inspect the SERVICES file in the Windows directory (for Windows NT it is in the WINNT\SYSTEM32\DRIVERS\ETC directory). The SERVICES file is a text file used by Serial Printer Logger to perform port lookups (which return the service name for the specified port) and port name lookups (which return the port number for the specified service name). You can open this file in any text editor to see a list of port numbers and their corresponding service names. While these well-known ports are not set in stone, they are traditional and their use should be reserved for the service which they represent. When writing network applications, you should select a port number that is not likely to be duplicated by other applications on your network. In most cases you can choose a port number other than any of the well-known port numbers.

The IP address and port number are used in combination to create a socket. A socket is first created and then is used to establish connection between two computers. How the socket is used depends on whether the application is a client or a server. If an application is a server, it creates the socket, opens it, and then listens on that socket for computers trying to establish a connection. At this point the server is in a polling loop listening and waiting for a possible connection. A client application, on the other hand, creates a socket using the IP address of a particular server and the port number that the server is known to be listening on. The client then uses the socket to attempt to connect to the server. When the server hears the connection attempt, it wakes up and decides whether or not to accept the connection. Usually this is done by examining the IP address of the client and comparing it to a list of known IP addresses (some servers don’t discriminate and accept all connections). If the connection is accepted, the client and server begin communicating and data is transmitted.

If the remote server (in the client mode) or local network interface (in the server mode) is not available and the "Try to connect after unsuccessful attempt" options is True, then Serial Printer Logger will continually try to establish the connection until it is successful. The program will try to establish the connection each N seconds that you can specify in the "Next try after XXX seconds" field.

This option is active in the server mode and allows you to enter one or more IP addresses that have access to the server. IP addresses that are not listed in this fields will be refused by the server. This options is very useful if you transfer your data over Internet connection or your server PC is connected to a big corporate network. You can specify multiple addresses - one per row. If you'll not specify any address here, then Serial Printer Logger will accept connections from all IP addresses.

After you install Microsoft Windows XP Service Pack 2 (SP2), our Serial Printer Logger may not seem to work. Windows Firewall, enabled by default, blocks unsolicited access to your computer via the network and may be blocking the normal operation of the program. To provide increased security to Windows XP users, Windows Firewall blocks unsolicited connections to your computer. When Windows Firewall detects incoming network traffic that it does not recognize, a Security Alert dialog box appears. The security alert dialog box looks like this:

In order for our program to function properly, you must unblock the program by clicking the Unblock button. Unblocking allows Windows XP SP2 to allow the program to continue to work by adding it as an exception to your Windows Firewall configuration. Exceptions are specific programs and processes that you allow to bypass the firewall. After you add a program as an exception, you no longer receive the security alert. If you choose to continue blocking the program certain functions will be disabled.

Note: If you are using another firewall software, then please, refer to a firewall manual for corresponding settings.

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