Terminals, Modems, Ports, and Services

Terminals and modems provide both local and remote access to system and network resources. Setting up terminals and modem access is an important responsibility of a system administrator. This section explains some of the concepts behind modem and terminal management in the Oracle Solaris operating system.

Terminal Description

Your system's bitmapped graphics display is not the same as an alphanumeric terminal. An alphanumeric terminal connects to a serial port and displays only text. You do not have to perform any special steps to administer the graphics display.

Modem Description

Modems can be set up in three basic configurations:

• Dial-out

• Dial-in

• Bidirectional

A modem that is connected to your home computer might be set up to provide dial-out service. With dial-out service, you can access other computers from your own home. However, nobody outside can gain access to your machine.

Dial-in service is just the opposite. Dial-in service enables you to access a system from remote sites. However, dial—in service does not permit calls to the outside world.

Bidirectional access, as the name implies, provides both dial-in and dial-out capabilities.

Ports Description

A port is a channel through which a device communicates with the operating system. From a hardware perspective, a port is a “receptacle” into which a terminal or modem cable might be physically connected.

However, a port is not strictly a physical receptacle, but an entity with hardware (pins and connectors) and software (a device driver) components. A single physical receptacle often provides multiple ports, allowing connection of two or more devices.

Common types of ports include serial, parallel, small computer systems interface (SCSI), and Ethernet.

A serial port, using a standard communications protocol, transmits a byte of information bit-by-bit over a single line.

Devices that have been designed according to RS-232-C or RS-423 standards, including most modems, alphanumeric terminals, plotters, and some printers, can be connected interchangeably by using standard cables into the serial ports of computers that are similarly designed.

When many serial port devices must be connected to a single computer, you might need to add an adapter board to the system. The adapter board, with its driver software, provides additional serial ports for connecting more devices than could otherwise be accommodated.

Services Description

Modems and terminals gain access to computing resources by using serial port software. Serial port software must be set up to provide a particular “service” for the device attached to the port. For example, you can set up a serial port to provide bidirectional service for a modem.

Port Monitors

The main mechanism for gaining access to a service is through a port monitor. A port monitor is a program that continuously monitors for requests to log in or access printers or files.

When a port monitor detects a request, it sets whatever parameters are required to establish communication between the operating system and the device requesting service. Then, the port monitor transfers control to other processes that provide the services needed.

The following table describes the two types of port monitors included in the Oracle Solaris release.

Table 1-1 Port Monitor Types

You might be familiar with an older port monitor, called a getty. The ttymon port monitor is more powerful. A single ttymon port monitor can replace multiple occurrences of getty. Otherwise, these two programs serve the same function. For more information, see the ttymon(1M) man page.