WorldDesk, Appendix B - Remote Communication Concepts

Appendix B
Remote Communication Concepts

Users often access local area networks (LANs) from a remote site. These users may need to perform a variety of tasks such as transferring program or data files, editing files stored on the LAN, operating programs stored on the LAN, and sending and receiving messages. However, the speed with which tasks may be performed remotely is limited by the connection between the remote site and the LAN. LANs generally use specially designed communications links that allow high-speed communications between the nodes of the LAN. An Ethernet LAN, for example, can currently transfer data at up to 100,000,000 bits per second.

Remote users do not have access to the higher speed communications links of the LAN and must generally rely upon analog telephone lines, or in some cases, digital communications lines such as ISDN lines. The fastest data rates currently available on most telephone lines and ISDN lines are 33,600 and 128,000 bits per second, respectively. Consequently, the speed of communications between the remote user and the LAN is substantially slower than the speed of communications within the LAN itself.

The slower communications rate can create a significant problem for some remote users. If the user wishes to transfer a large file or program between a LAN and the remote user’s computer, the time required to transfer the file may be prohibitively long. Other users may seldom need to transfer large files and are, therefore, not greatly affected by a slow communications rate. In order to meet the needs of various remote users, two different methods of remote communications have been developed: Remote Control and Remote Node. Each method has advantages and disadvantages and each method is best suited for different applications.

Remote Control

The remote control method enables a remote user to connect to a remote LAN and seize control of a computer on the LAN. The seized or host computer operates as any other computer on the LAN and is able to communicate with other devices on the LAN at normal LAN speeds. The host computer in a remote control environment may serve either a single user or multiple users concurrently. The latter configuration is commonly referred to as an "Access Server" or "Application Server." To perform operations, the remote user enters commands into the remote or client computer, which in turn transmits commands to the LAN-based host computer by way of a communications line. The commands are executed by the host computer, and screen data is transferred back to the remote computer to show the user the results of his or her commands.

The remote control method is best suited to situations where large files must be accessed. Because only screen data is transferred to the remote computer and not an entire file, the remote user can access large files and perform complex tasks while maintaining adequate display speeds for the program’s output. For example, consider the user that wishes to access a very large database file that is stored on a file server within a corporate LAN. By running the database management program that accesses the database in remote control, users can access the database at LAN speeds to perform faster lookups than would be possible over a remote node link.

Remote control has the inherent disadvantage of requiring more costly equipment than other remote access methods. It uses more processing power on the access server to perform remote control tasks, which increases cost and diminishes scaleability for large corporate installations. In addition, specialized software is required, and the user interface of the application software is usually different from the normal LAN-based operation of the software. The different user interface increases training costs and complexity of operation for the remote user. (Note: the terms remote control, remote application and run-at-server are used interchangeably.)

Remote Node

The remote node method allows a remote computer to operate like a computer on a remote LAN. A remote computer can access other devices on the LAN and can perform tasks just as if the computer were a node on the LAN. The remote computer gains access to the LAN through a remote communications server, which interfaces between the LAN and a communication line used by the remote computer.

The remote node method requires less equipment and software than the remote control method, and the remote user’s screen appears the same as if he or she were working directly on one of the LAN’s nodes. Consequently, the remote node method is less complicated and less expensive to implement than the remote control method.

The most significant disadvantage of the remote node method is the speed at which data may be transferred. Unlike the remote control method, accessing a file stored on the LAN requires transferring the file to the remote user. If the file is large, a large amount of time may be required to transfer the file. (Note: the terms remote node and run-at-client are used interchangeably.)