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Information in this chapter will help you understand the X Window system and how to configure your protocol translator to support XRemote connections.
For a complete description of the commands mentioned in this chapter, refer to the chapter "XRemote Configuration Commands" later in this publication. For information about establishing XRemote connections, refer to the Remote Access Server Connection Guide.
The X Window System, also called X, is a network-based graphics window system originally developed for workstations running UNIX. Cisco Systems has developed an XRemote application that allows the XRemote capabilities of X terminals to run on the protocol translator.
Previous window systems for terminals were kernel-based and thereby closely linked to the operating system running on the workstation itself. They typically ran only on discrete systems, such as a single workstation. The X Window System is not part of any operating system, but instead, is composed of application programs. Thus, the X Window System enables flexible, graphics-based network computing across a wide range of operating systems and hardware platforms.
The underlying architecture of the X Window System is based on a client-server model. The system is split into two parts: clients and display servers. Clients are application programs that perform specific tasks, and display servers provide specific display capabilities and track user input. These two parts can reside on the same computer, or can be separated over a network. In an X terminal environment, such as in NCD terminal implementations, the display server resides on the display station and the client resides on a host computer.
Because X employs this functional partitioning and is independent of both hardware and operating environment, X terminal users can access different types of computers to simultaneously access several applications and resources in a multivendor environment. A user at an X terminal can run and display a calendar program on a VAX, a spreadsheet program on a PC, and a compiler on a workstation concurrently.
XRemote is a protocol developed specifically to optimize support for X over a serial communications link. Its compression and decompression algorithms are designed to handle bit-mapped displays and windowing systems.
There are two basic parts to XRemote:
These two helper processes communicate with each other using the optimized XRemote protocol. The client-side helper communicates with X clients using the standard X protocol. The server-side helper communicates with the server using standard X. The server-side helper might operate as part of the X server or it might be external and accessed across the network; for example, the server-side helper can operate in a router at your house or work site. If the server-side helper is in the X terminal, it must have XRemote PROMs installed.
XRemote enables a user of a display station to run the X Window System via 9600 baud (and faster) modem connections with performance that is superior to using conventional serial protocols, such as Serial Line Internet Protocol (SLIP). An X display station must either implement XRemote or be connected to a network configuration that includes a protocol translator.
Cisco's implementation of XRemote is fully compatible with the NCD XRemote protocol.
Figure 4-1 illustrates an XRemote connection between an X terminal and a protocol translator. In Figure 4-1, the server-side helper is running on the X terminal and the client-side helper is running on the protocol translator.
Remote access to fonts is provided in the following ways:
A single XRemote user can use any combination of TCP/IP and LAT client connections, and any combination of TFTP and LAT font access.
To make a host connection using NCD's XRemote feature and the protocol translator, complete the basic configuration steps in the following sections, as needed:
See the end of this chapter for an XRemote configuration file example.
In general, you can use any modem that provides acceptable performance for your application. The following guidelines apply to an XRemote operation using a modem (refer to the user manual for your modem for specific connection procedures):
Refer to the Router Products Configuration Guide for more information about configuring modems.
The X Server for the X terminal and the Network and Serial parameters for the X terminal must be configured as described in the publications for the specific X terminal you are using. In general, the X terminal configuration determines the mode of operation for the terminal, the source of font information, and the source of remote configuration information (when applicable).
If you intend to download fonts to the X terminal, you must set the font loader host identification. To do this, perform the following global configuration task:
| Task | Command |
|---|---|
| Specify a TFTP font server as the source for fonts. | xremote tftp host [host-name] |
The NCD terminal contains a small set of built-in fonts in local ROM. You should use these fonts because loading fonts over a serial line can increase application startup time. The default for an NCD terminal is to use built-in fonts, unless you log in using DECwindows over LAT. When using DECwindows over LAT, the standard DECwindows fonts are used automatically.
Perform the tasks in the following sections to select fonts:
When an X terminal application requests a font that is not stored in the terminal's ROM, the X terminal makes a request for a font file from the protocol translator. The protocol translator uses the TFTP to load the font from the font server, and then passes the font to the X terminal using the XRemote protocol. The process of loading fonts from the protocol translator to the X terminal can take 30 to 45 seconds, depending on the size of the font file.
An X server can display only the fonts it finds in the directories in its font path. The X server's default font path includes only the built-in fonts. To access fonts stored on a host, you must add the host's font directories to the X server's font path. To do this, use the UNIX command xset with the fp+ argument to add fonts to the end of the server's font path.
For example, to allow your display station to access the 100 dots per inch (dpi) fonts found in the standard font directory, run the following command at the host system prompt:
host_prompt% xset fp+ /usr/lib/x11/ncd/fonts/100dpi
For more information, refer to the NCDware XRemote User's Manual.
Downloading of fonts occurs automatically when you initiate a remote DECwindows login session using the EXEC xremote lat command. Instead of relying on TFTP to download the fonts, the fonts are read in via the LAT protocol.
If you want to use DECwindows fonts while running standard X applications on a UNIX host, you need to use the UNIX xset command or an application that issues an XSetFontPath request to set a font path. You might want to do this if you are primarily a TCP/IP user, but also run some DECwindows applications.
Execute xset, or the application to issue an XSetFontPath request, to set the following path:
In this path, SERVICE is a LAT service name with DECwindows support; case is not significant.
When the protocol translator sees a request for font files in that directory, it uses LAT instead of TFTP to access the specified service.
When the X terminal requests that a font file be loaded, the protocol translator must first load the font file into an internal buffer before passing it to the X terminal. The default value for this buffer is 70,000 bytes, which is adequate for most font files, but the size can be increased as necessary for nonstandard font files.
To change the buffer size, perform the following global configuration task:
| Task | Command |
|---|---|
| Set the buffer size used for loading font files. | xremote tftp buffersize [buffersize] |
This task can be performed for both TFTP and LAT font access.
You might need to increase the number of times that the font loader will try to load the fonts. This is particularly important when the font servers are known to be heavily loaded.
To set the TFTP font loader retries, perform the following global configuration task:
| Task | Command |
|---|---|
| Set the number of retries by the TFTP font loader. | xremote tftp retries [retries] |
To check the status of XRemote connections, perform one or more of the following tasks at the EXEC prompt:
| Task | Command |
|---|---|
| Display current connections and monitor traffic. | show xremote |
| Display traffic and line statistics. | show xremote line number |
The following example illustrates how to specify IBM-1 as the host name of the TFTP font server, specify 7 retry attempts at accessing the server, and reduce the buffer size to 20,000 bytes.
xremote tftp host IBM-1
xremote tftp retries 7
xremote tftp buffersize 20000
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