Terminal Emulator Task Force Report
Manfred Chan,Gary Fung, Angela Tang
The existing terminal emulators used at City University, PCTERM and PC240, were developed by the Computer Centre in 1987. The emulators are DOS-based and contain many excellent features, some of which are unique to meet special needs at City University.
However, the Windows environment has begun to dominate the market because of its user-friendly interface. Subsequently, the Computer Centre wished to identify a suitable Windows-based emulator that provides the same features as PC240. In July 1994, a task force was formed to source, evaluate emulators currently available, and make recommendations. The task force drew various areas of expertise together from within the Computer Centre, such as emulator development, network management and host application development. The task force aimed to identify a Windows-based emulator which supported multi-windows, multi-tasking, window re-sizing, pull-down menus and mouse operation, with minimal modifications required for existing host application systems.
Selection of Candidate Emulators
Numerous software distributors such as Borland, SIS, Tech Pacific, Kenfil, Digital Equipment Corporation (DEC), Jardine Network System (JNS), Attachmate, and Automaton Ltd., were contacted. However, we found that there are very few emulators alone for sale, as most communication software includes terminal emulation as one of many functions.
After consideration, two products were selected for more detailed evaluation, Pathworks VT320/VT382 for Windows and KEAterm VT340. VT320/VT382 are identical text-based Windows emulators, except VT382 supports Chinese. KEAterm VT340 is a graphics terminal emulator for a DEC VT340 terminal.
Apart from basic emulator functions such as terminal emulation, key mapping, communication protocol, etc., each candidate was tested against the special features of PC240 listed below. The results are summarised in the next section.
PC 240 Special Features
- Automatic login with username/password encrypted
- Automatic file transfer (i.e. initiated by application)
- Chinese support under DOS environment
- Graphics support
- Automatic unload/close the emulator after logout
- Disable change of parameter settings
- Selective session log
PC240 emulates DEC VT52, VT100, VT240 terminals, the Tektronix 4010 graphics terminal, the DG Dasher D210 terminal and the Esprit terminal in Haxeltine H1500 mode. KEAterm VT340 not only emulates the REGIS, Sixel and Tektronix graphics features of the VT340 terminal, but also the text features of the VT52, VT100, VT220, VT320, VT340 and VT420. VT320/VT382 emulates non-graphics VT52, VT100, VT200 and VT320 terminals.
- Key Mapping
When using PC240, different sets of pre-defined key mapping are applied according to the terminal type chosen. For KEAterm VT340 and VT320/VT382, each function key can be individually defined and is not bounded by the emulation type used. KEAterm VT340 provides a VT keyboard layout for users to click on, making it more convenient than the VT320/VT382 key mapping.
- Communication Protocol
The major communication protocols used in CTNET, such as LAT/CTERM, TCP/IP and serial communication are supported both by PC240 and the two selected candidates.
- File Transfer Protocol
KEAterm VT340 supports more file transfer protocols than the other testing emulators. While PC240 and VT320/VT382 support only Kermit, KEAterm VT340 also supports Xmodem, Ymodem and Zmodem. Compared with Kermit, Zmodem provides much faster file transfer. Additionally, both PC240 and KEAterm VT340 can upload an ASCII file to a host computer without using any file transfer protocol.
- Automatic Login to a Host Computer Account
PC240 can be invoked with an encrypted parameter file to auto-login a specified account for running a requested application. KEAterm VT340 provides the Marco language, and VT320/VT382 provides the Script language. Both languages support the writing of auto-login procedures. Nevertheless, both Macro and Script languages are text files. The host computer account username/password of an application system is not encrypted and this may cause security problems.
- File Transfer initiated by Application
With PC240, file transfer is set up and initiated by pressing keys. The same key stroke sequence can be transmitted from within an application procedure/program. As a result, automatic file transfer can be done by embedding the required key sequences into an existing program. Similar algorithms can be implemented using KEAterm VT340 by sending an appropriate escape sequence using KEAterm Macro. Although VT320/VT382 supports script writing, a script cannot be invoked within the application program. Thus, it is impossible to have automatic file transfer using VT320/VT382.
- Chinese Input and Display
Under a DOS environment, Eten can first be loaded before invoking PC240, such that PC240 can work together with Eten for handling Chinese input and display. The same mechanism does not work under a Windows environment. Yet, KEAterm VT340 and VT320 do not support Chinese at all. VT382 is the only candidate which supports Chinese input, display and printing. The Chinese codeset can be DEC Hanyu, Big-5 and CNS. Run-time conversion between the codesets is possible.
- Graphics Support
PC240 and KEAterm VT340 are graphics emulators which provide similar graphic features such as ReGIS, Tektronix 4010 graphics instruction set, different font types and colour mapping. KEAterm VT340 supports 4014 and 4105 line styles/colours, sixel and VGA screen mode. On the contrary, VT320/VT382, being a text-based emulator, does not support any graphics features.
- Exit from Emulator after Logout
PC240 can be unloaded upon exit from an application program, thereby dropping all connections. VT320/VT382 window can be closed automatically upon logout from a host computer. Using KEAterm, a user has to exit manually to close the KEAterm VT340 window.
- Disable change of parameter settings
KEAterm VT340 menu options or commands can be easily disabled to create suitable menus for different applications. Using PC240, this can only be done by creating a new tailor-made version of the emulator. VT320/VT382 allows a user to modify any default settings.
- Selective Session Log
This is a tailored feature of PC240 as required by some administrative systems. The emulator would start logging for a pre-defined length of record as soon as it detects a special code. It was found that the same function can only be partially implemented using KEAterm VT340 and is not supported by VT320/VT382 at all.
Before making recommendations, the task force made two assumptions. First, the transition period from the old PC240 to the new Windows-based emulator would be short. Second, only one Windows environment, either English or Chinese Windows, would be chosen as the default. Departments not upgraded from a DOS to a Windows environment may still need to use the DOS-based PC240 as their default emulator.
At this time, no single Windows emulator on the market can support both Chinese and Graphics capabilities. If only one emulator is chosen, one of the two features has to be sacrificed. Since graphics are now used mostly for colour menu displays, most graphic functions would go unused. Consequently the high cost of graphics may not be justified now.
Graphics emulators in general are more expensive, and usually cost double the price of non-graphics emulators. Most host packages that require graphics capabilities have PC versions, and users who want to use this software could be persuaded to use the PC version instead. Another factor in using graphics is the use of colour display for information services host applications such as CityLink, CityData, and PolyLink. If the Client/Server model is adopted in the near future, this factor can be eliminated, or else we will still have to consider this in future.
Another crucial factor is the need to support some Chinese features, such as displaying a portion of Chinese data. For example, the library uses this with Chinese names for authors and titles, and not all the information needs to be displayed in Chinese. The description should remain in English, and this simplifies the Chinese supporting functions.
The third factor is that we should provide consistent user interface whether in an English or Chinese Windows environment. This is a must because it can ease user training and promote the transition from a DOS to Windows-based environment.
A special requirement must be noted here in the selection process. The selection of Chinese internal code is critical since it is very likely that Windows emulators may not explicitly support other Chinese internal codes such as CNS internal code. Even though they may support Chinese in the future, Windows emulators might pass all the input and output controls to Chinese Windows, i.e. Big5 internal code, and may not support other Chinese internal codes such as CNS or CJK codes.
In conclusion, we found that no single Windows emulator on the market can fit all our requirements. Therefore, we will continue to use the existing DOS-based PC240 for the Windows environment until a suitable windows-based emulator is found in the future.