The DS has two ports- Ethernet port and serial port . Typically, the serial port of the DS is connected to a certain serial device ("attached serial device"). Ethernet port links the DS to the Ethernet (TCP/IP) network (see figure below). Potentially, any network host (including another DS) on the network can communicate with the DS and the serial device "behind" it.

The job of the DS (i.e. the firmware described in this Manual ) is to ensure transparent communications between the network host and the attached serial device by routing the data between the Ethernet and serial ports of the DS. Routing means that the data received into the Ethernet port is sent out via the serial port and vice versa. Routing is effected through two routing buffers- one for each routing direction*. In addition to routing the serial data itself, the DS allows the network host and the attached serial device to exchange the state of RTS, CTS, DTR, and DSR lines.

DS operation is governed by settings , parameters , and instructions :

Settings are permanent functioning parameters that are stored in the non-volatile memory (EEPROM) of the DS. Once programmed, they remain intact even when the DS is powered off. Many (but not all) settings require the DS to be rebooted for the new setting value to take effect. For example, the Baudrate (BR) setting defines the baudrate of the serial port. When the DS boots up it sets the baudrate of its serial port according to the value of this setting.

Parameters are temporary overrides for settings. Parameters are not saved into the EEPROM and have immediate effect (no rebooting required). For example, there is a Baudrate (BR) parameter that can be used to immediately change communications speed of the serial port (and override the permanent value defined by the Baudrate (BR) setting ).

Instructions are used to make the DS perform a certain action. For example, Establish Connection (CE) instruction makes the DS establish a data connection with a specified network host.

Because parameters can override settings this Manual will sometimes make references to current values. For example, current Baudrate (BR) will mean, quite literally, the baudrate at the moment, regardless of what caused it to be such- a permanent value obtained from the setting or a temporary overriding parameter value.

Settings and parameters are manipulated and instructions are issued by sending commands to (and getting replies from) the Ethernet or serial port of the DS- the process that will be referred to as programming .

* The size of routing buffers is hardware-dependent and is different for different models and modifications of Tibbo Device Servers. Routing buffer size can be verified using the Status (U) command.