Dialing In Remote terminal access to the VS
From "Migration",  Access to Wang, September 1995
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When Wang introduced serial communications controllers and the 2110 workstations to the VS community in the early 1980s, it was not viewed by most users as a significant event. Since then, dial-up access to VS systems has become an important part of many shops, and demand has boomed recently due to interest in telecommuting and other remote business needs.

This month and next we'll look at some of the choices available for dialup access to the Wang VS and how to meet the challenge of additional connectivity to enterprise applications - Wang-based or not.

Communications Design

Several asynchronous connection types are available to VS systems. VS async controllers fall into three categories: standard terminal ports (ADC, MLTC, etc.) for 2110 and industry standard VT100 terminals, enhanced terminal ports for using Wang Word Processing and other applications that load microcode to the port and high-speed specialty communications ports such TC IOP.

The first category is of most interest for dial-in terminal communications since it has a significantly lower cost per port. Both MLTC and ADC ports have speed limitations (19,200 baud); MLTC ports can be assigned as terminal ports or general communications ports. However, all of the ports on the controller have to be the same type.

After you have determined the type of connection consider how the dial-in user teaches those connections.

A simple method is to purchase a new telephone line and modem for each user you support - a point-to-point design (Figure 1). However, since each user dials into a specific modem, this approach is costly and makes it difficult to work around malfunctioning modems or lines.

A more cost-effective method is to employ a rotary switching system (Figure 2), in which a number of users share a smaller pool of modems and a switching device sends each user to the next connection point as they connect. Rotary arrangements can be set up using specialty switch equipment, through local telephone equipment or provided as a service by the telephone company.

An alternative point-to-point connection (Figure 3) uses a locally-attached PC to interact with the VS and then communicates with a remote PC. This approach requires the local PC to be ready to communicate through an outside line and uses PC "remote control" products to link the two systems.

While providing all of the functionality of a local terminal - including multiple VS terminal windows, access to Wang Word Processing, etc. - this approach is expensive and response may be slow.

Selecting A Workstation Type

Once the communications design is complete, the type of terminal should be considered. There are two major categories of remote terminals: actual terminals (such as the Wane 2110) and personal computers emulating such terminals.

Dedicated terminals are inexpensive, but in most analyses the functionality and flexibility of PC terminal emulation wins out. The presence of local computing power can be a real benefit to remote users, allowing them to work on other tasks (word processing, etc.) without connecting to the host system.

Traditionally, most of us have purchased software to emulate the Wang 2110 terminal, but industry-standard VT 00 terminal emulation software Is more commonly available and may be used for other purposes, such as access to other systems. Advantages of using 2110 software include faster screen updates and better overall performance; Wang's 2110 terminal protocol is optimized for VS block-mode screen transfers.

Here are some considerations when evaluating terminal emulators:

• Keyboard support: Developers of 2110 terminal emulation products understand the expectations of Wang keyboard users and provide reasonable approximations using standard keyboards. If a VT100 emulation is considered, the software must let changes to the keyboard operation support Wang function keys and other special key definitions.
  
  Most VT100 terminal emulation software provides this, allowing you to tailor the workstation to individual preferences and add special functions (macros, etc.) to improve your productivity.

• File transfer: Transferring files requires matching host and workstation software. PC terminal packages and online services offer several industry- standard communications protocols (XMODEM, YMODEM, ZMODEM, Kermit, etc.), but vendors for VS communications products typically support only their own proprietary protocols.
  
  While these protocols are adequate for occasional use by VS users, they are not robust enough for frequent file transfers and have no application in other environments.

• Screen characteristics: Many Wang applications make use of screen characteristics such as underlining, blinking, etc. Some terminal emulation packages translate these screen attributes to alternate colors rather than showing them in their intended form, resulting in a confusing display. Flexibility: With the right choice, you can use the same terminal program to connect to other hosts, including online services and Internet providers.

• Protocol support: 2110 packages provide support for only one communications protocol: asynchronous communications with a VS host. Industry standard terminal products can also be used for connections to a network (dial-up or direct).

Setting Up Remote Terminals

Once the terminal type and connectivity issues are settled, it's time to set up the remote workstation and test. This experience ranges from the simple (a Wang 2110 terminal and a modem) to the complex (installing industry-standard software; modifying the keyboard definition).

For our VT100 emulation package, we use a keyboard script to set up our emulation package, Reflections 2 from Walker Richer & Quinn. A similar approach may be used with other terminal packages. As written, this script assigns normal PF key values to Fl through F12 and adds 10 to the value of the key with a SHIFT key and 20 to the value with the CTRL key. Some examples: the value of PF16 would be SHIFT plus F6; the value of PF32 would be CTRL plus F12. For a sample keyboard script contact me care of Access to Wang.

Connectivity To Other Applications?

In many cases, it is not just a VS system that typically holds out interest: we are now interested in PC applications (electronic mail, word processing, etc.) and access to shared drives. How can we gain access to these network applications from outside the office? And how can we do that while simultaneously using VS terminal access? More on that next month.

Figure 1: Model of Simple Host/Terminal Communications

Figure 2: Model of Rotary Host/Terminal Communications

Figure 3: Model of Alternative Point-to-Point Host/Terminal Communications