RuggedCom RS400 manual Use of Port Redirectors, Message Packetization

Serial Protocols

2.2.1.5 Use of Port Redirectors

Port redirectors are PC packages that emulate the existence of communications ports. The redirector software creates and makes available these “virtual” COM ports, providing access to the network via a TCP connection.

When a software package uses one of the virtual COM ports, a TCP connection request is sent to a remote IP address and IP port that has been programmed into the redirector. Some redirectors also offer the ability to accept connection requests.

2.2.1.6 Message Packetization

The server buffers received characters into packets in order to improve network efficiency and demarcate messages.

The server uses three methods to decide when to packetize and forward the buffered characters to the network:

•Packetize on a Specific Character

•Packetize on timeout

•Packetize on full packet.

If configured to packetize on a specific character, the server will examine each received character and will packetize and forward upon receiving the specific character. The character is usually a <CR> or an <LF> character but may be any 8 bits (0 to 255) character.

If configured to packetize on a timeout, the server will wait for a configurable time after receiving a character before packetizing and forwarding. If another character arrives during the waiting interval, the timer is restarted. This method allows characters transmitted as a part of an entire message to be forwarded to the network in a single packet, when the timer expires after receiving the very last character of the message.

Note: Some polling software packages which perform well over DOS have been known to experience problems when used over Windows based software or port redirection software. If the OS does not expedite the transmission of characters in a timely fashion, pauses in transmission can be interpreted as the end of the message. Messages can be split into separate TCP packets. A locally attached RuggedServer™ or a port redirector could packetize and forward the message incorrectly. Solutions include tuning the OS to prevent the problem or increasing the packetizing timer.

Finally, the server will always packetize and forward on a full packet, i.e. when the number of characters fills its communications buffer (1K bytes).

ROS™ v3.5 58 RS400