Switch means "data switch" and is a network device used for electrical (optical) signal forwarding. It can provide an exclusive electrical signal path for any two network nodes of the access data switch. The most common switches are Ethernet switches. Other common ones are telephone voice switches, fiber switches and so on.
1. Introduction of data switch
A communication device used to complete the transfer of data information. Through the data switch, any two data terminals in the data communication network can be connected to communicate, so as to effectively utilize the communication equipment and telephone resources in the network. Data switches are mainly divided into circuit switching, message switching and packet switching data switches. The functions and principles of circuit-switched and message-switched data exchanges are similar to program-controlled telephone exchanges. The packet switch is an improved version of the above two switches. This is a special electronic computer with strong functions, which has the advantages of simplifying the processing content and shortening the processing time. It is widely used in modern data communication and computer communication.
Historically, switches were used to replace hubs and relieve traffic congestion in LAN workgroups. Switches can also be used to replace routers on the network backbone. Including switches on the backbone has at least two advantages. First, because the switch isolates the data traffic between the various devices from each other, it improves security. Second, the switch potentially provides a separate channel for each device. As a result, applications that transmit large amounts of data and are sensitive to time delays, such as videoconferencing applications, can fully utilize the network's capacity.
The data switch looks like a box and acts like a PC's telephone system. Through the data switch, the PCs can be interconnected, or the PCs can be interconnected with peripherals such as Modem and printers through standard serial circuits. Usually PCs utilize simple software, typically occupying only a few Kbytes of RAM, and do not affect the performance of the application.
Although data switches are less technologically advanced than full media sharing LANs, more and more companies are successfully bringing this product to market as an easy and efficient way to connect PCs and printers.
Data switches are simple, inexpensive, and attractive, costing just over $100 per workstation, around $275 per station for the lowest-end media-sharing LAN, and around $275 per station for a full-featured media-sharing LAN. It's about twice as expensive. Data switches are most suitable for small networks (mostly managing 8-24 users). With appropriate software, multiple networks can be interconnected to form large networks with hundreds or even thousands of nodes. Because they use standard serial or parallel connections, they can integrate various types of computers (from PCs, laptops, Macintosh to minicomputers, mainframes) on the same network.
There is a tradeoff between speed and functionality, for example, most data switches are rate limited to 19200 bps, well below the 10 Mbps supported by media sharing & hemet, and require it to use dedicated cables to connect sites. In addition, they do not have the ability to support multiple users accessing the same data file at the same time, so PCs connected to the data switch cannot use complex multi-user databases.
2. Function of data switch
It is difficult to fully evaluate the capabilities of a data switch in terms of basic aspects such as sharing printers and exchanging files. The main difference between printer sharing through a data switch and printer sharing through a zero-slot or media sharing LAN is that the former does not require a PC to be used as a print server. The switch maintains and arranges printing services and sends them to multiple printers. The flexibility and ability to connect different types of computers shared by modems makes switches a more attractive computer interconnection device.
In fact, if you have a minicomputer, you can overcome the data switch that does not allow multiple users to access the same file at the same time, by running billing, inventory management, and other multi-user programs on the minicomputer, making the PC as a minicomputer through the data switch. the terminal of the machine to access it. Compared with multi-user LAN, this kind of system has the same cost, but has simple structure, better performance, and has the characteristics of minicomputer operating system in terms of confidentiality and data management.
3. The working principle of the data switch
From the outside, the data switch is a box that can vary in size from a hardcover novel to the size of a PC-AT compatible machine. There are many ports inside, usually 8 to 24. For the Commix 32 product of Infotron System, there are 32 ports, while Western Telematic's INC-64 Intelligent Network Controller (Intelligent Network Controller) can manage 64 ports, and the internal microprocessor realizes port control and switching functions to Make the data switch have enough capacity to handle traffic through all ports. Use dedicated serial cables to connect the switch to workstations and other devices. Since today's PCs are equipped with at least one serial port, it is generally unnecessary to install a special interface card on the workstation.
The working process of the data switch is simple and clear. It continuously monitors the commands from the workstation during operation. When a station requests to connect the signaling of another station, the switch completes the connection between the corresponding two stations and keeps it until the line is disconnected. This way, workstations use modems and printers as if they were local devices.
If the link has been established between the workstations, the exchange of files between the two stations can be realized by using appropriate communication software at this time. If the workstation is connected to a minicomputer, terminal emulation software can be installed on the workstation to form a remote system. In all cases, after the data switch completes the connection, it transmits the message.
4. Characteristics of data switches
To cache printing services, most data switches are equipped with a certain amount of RAM, usually 8Mb. Some are equipped with parallel ports to connect parallel printers and realize automatic serial-to-parallel conversion. There are also switches that can use parallel printers attached to remote workstations. If the switch does not provide a parallel port, an external serial-to-parallel converter can be used to connect a parallel printer. Many switches allow serial rates higher than 19200bps but the maximum rate should be within the range of the RS-232C standard, which makes the cable more sensitive to electrical interference. Some data switches also provide RS. 422 serial connection, its transmission distance is farther than RS-232C, and the rate can reach 38400bps. In any case, most switches can transmit information between serial devices at different rates. There is also no need for downshifting when the line printer communicates with the Modem.
If the data switch supports parallel port work, you can often use the parallel port of the PC to connect to the switch, so that the working speed is high, but the average length of the parallel printer cable is limited to less than 15 feet.
