Banyan Asynchronous Terminal Emulation Guide
Chapter 1 - Introduction to Asynchronous Terminal Emulation
The Banyan Asynchronous Terminal Emulation (ATE) option lets users of DOS workstations do the following:
|Use their workstations as terminals connected to host computers|
|Access the development environment through a server development connection|
|Access a server console, using their workstation as a remote server console|
The ATE option extends the usefulness of user workstations into any environment that supports asynchronous terminals. Examples include mainframes, minicomputers, and data services. Users can run the application programs in those environments as if their workstations were a terminal connected to them.
When users use the ATE option, they connect to a host computer through a Banyan server using an asynchronous terminal emulation service that runs on the Banyan server. Their workstation emulates one of several common terminals that the service supports.
In this guide, a host is a computer, usually a mainframe or a minicomputer, that provides a network with resources such as computation, databases, or programming. A server is a computer that provides a particular service, or set of services, across a network. A workstation is a computer that functions as a network client.
This chapter gives an overview of the ATE option.
In describing the ATE option, this guide refers to types of Banyan servers. A Banyan server is not a particular brand of server. Instead it is a server that supports Banyan VINES communications. The types of Banyan servers referred to in this guide are Native VINES servers.
The ATE option supports only DOS workstations. To run the ATE option from an OS/2 workstation or from Windows, you must use a DOS window.
The ATE option does not support Macintosh workstations.
Supported Terminal Types
The ATE option supports the following terminal types:
|TTY - A plain terminal type, also called a glass TTY.|
|VT100 - A DEC® VT100 terminal.|
|VT52 - A DEC VT52 terminal.|
|IBM3101 - An IBM 3101 terminal.|
Chapter 4 describes when to choose which terminal type and the corresponding UNIX terminal type. You set the terminal type for a connection, but can override the terminal type during emulation by using the Action Menu. Connections are described in "Supported Connections," which follows. Chapter 7 describes the Action menu.
For connections to host computers, the ATE option supports three kinds of connections:
|X.29 PAD (over an X.25 line)|
The ATE option also features two types of connections that do not use serial lines, but instead use the networking features of your LAN:
|Remote server console|
The following sections give an overview of all of these connection types. Chapter 4 describes how to create and configure them.
Direct lines connect the server to a local or remote host without an auto-dial modem. Examples of direct lines include leased telephone lines or lines that use a modem eliminator. When using a direct line, the service allocates any available direct line from a list of line numbers specified by a connection name or parameter file. If none of the lines is available, the user must try again later.
Dial-out lines use auto-dial modems to connect to remote hosts. By dialing different phone numbers, the same dial-out line can be used to connect to several host computers. An example of a dial-out line is a switched telephone line.
Regardless of how a user accesses a dial-out line - by dialing out manually, by providing a connection name, or by providing the name of parameter file - after the user initiates the connection, the ATE service examines the dial-out lines for any that match the user's requirements.
In this process, dial-out lines are not specified by number. The dial-out lines serve as a shared resource for all attempts to dial-out through the service. Requirements, such as supporting a specific line speed, can be specified from ATE menus or by the connection name or parameter file. A connection name can use both direct lines and dial-out lines. The ATE service goes through both the direct and dial-out line selection processes to find an available line to the host. If no appropriate line is available, the user must try again later.
X.25 lines connect the server to a local or remote host either over an X.25 Public Data Network (PDN) or directly. X.25 lines support X.29 user sessions.
To establish an X.29 user session with a host, the service selects an X.25 line. Each X.29 user session consumes one switched virtual circuit (SVC) associated with that line. An SVC is analogous to a switched telephone line.
Multiple SVCs can be associated with a single X.25 line, supporting multiple user sessions with hosts. You can use an SVC to connect any server and host at any two sites. For example, once a server in city A and a host in city B are no longer using an SVC, you can use that SVC to connect the server to another host in city C.
When establishing an X.29 user session, the service allocates any available SVC associated with the X.25 line specified by an X.29 connection name or parameter file. If none of those SVCs is available, the user must try again later.
A server can have a maximum of two serial communications cards. For each serial communications card you use for X.25 communications, there are 128 virtual circuits available. (So, if a server contains two serial communications cards, that server will have 256 virtual circuits available.)
This number of virtual circuits can include SVCs and permanent virtual circuits (PVCs). A PVC is analogous to a leased telephone line and is used by the X.25 option software for server-to-server communications only. If a card is connected to two X.25 lines, you can distribute the 128 virtual circuits between them as you see fit.
Note: Regardless of how many virtual circuits you configure, the ATE service is limited to a maximum of 32 concurrent sessions per service on Banyan servers. (There can be only one ATE service per server). These sessions can be X.29, asynchronous, server development, or remote server console sessions, or any combination of these types of sessions.
A server can establish X.29 user sessions with hosts either over a PDN or without one. The following discussion describes these alternatives.
For X.25 communications over a PDN, it is the contract with the PDN that determines the exact number of PVCs and SVCs available. The PDN usually installs a dedicated private line that connects your server to its network.
Alternatively, some PDNs provide dial-in service. If your connection to the PDN is through a switched telephone line, you must dial the proper number before attempting to make the connection. Users cannot dial this number manually through the ATE menus. X.29 user sessions can be established once the connection to the PDN is active.
If a modem is used on each end of the line, you need to know the speed of the modems, and whether the line you are using is switched or dedicated.
You can use X.25 without a PDN by obtaining a communications line from some other source, such as the local telephone company. In this case, the line can be either switched or dedicated to one host. Examples of dedicated lines include leased telephone lines or lines that use modem eliminators.
For an X.25 line that does not involve a PDN, you must assign the X.25 line as if it were a line to a PDN. You then supply all the necessary information about SVCs. If your connection to the host is through a switched telephone line, you must dial in to the host to make a physical connection. You cannot dial the host through the ATE menus.
Once you have dialed in to the host, the X.25 connection is active. You can then establish X.29 user sessions.
If you are using a dedicated line, the connection to the host is active as soon as you meet all the hardware and software requirements and assign the communications line. You can then establish X.29 user sessions to connect with the host.
Note: With a single X.25 line, you can establish multiple concurrent X.29 user sessions with more than one host without using a PDN. However, the X.25 line must be connected to special switching equipment that you purchase from a third party.
Server Development Connections
Server development connections provide the access to the development environment on the server. This type of connection is necessary if you plan to develop applications to run on a Banyan network. A server development connection enables users to access a server to develop Banyan applications.
A server development connection enables you to use Banyan transport mechanisms to access the Banyan server. When you create the connection, you do not have to specify any line information.
Remote Server Console Connections
Remote server console connections allow you to use the Banyan network to gain access to the server console from a workstation. The workstation becomes a server console. With the remote server console feature, it appears as if you are working at a server console. The remote server console feature provides more than just server console emulation; when you use the remote server console feature, your workstation becomes the server console. Any commands you enter, any screens you display on the remote server console simultaneously appear on the server console.
How the ATE Option Works
The ATE service communicates with client software in the user's workstation to establish and manage communications with the host. To enter terminal emulation, the user runs this client software at the workstation.
Network administrators provide terminal emulation to users by creating a service that runs on a Banyan server. The ATE service may use serial communications cards and communications lines to connect to one or more host computers.
Figure 1-1 illustrates this.
The ATE service uses a character asynchronous protocol to move data between the host and the server over direct lines and dial-out lines. This type of protocol has no retransmission mechanism. If users lose characters during sessions with the host, follow the procedures in "Troubleshooting" in Chapter 7.
How the Service Uses Communications Lines
As part of the installation process, you assign the communications lines that the ATE service uses. When a user attempts to connect to a host, the service must select a communications line to use for the session. The ATE service supports are direct lines, dial-out lines, and X.25 lines to a host computer. For more information on these connection types, see "Supported Connections" earlier in this chapter.
How a User Initiates Connections
To initiate the connection, the user provides a connection name or the name of a parameter file, or dials out manually. For end users, these functions are supported through menus and a command line interface.
Once an asynchronous connection is made, the workstation emulates an asynchronous terminal. A user can use applications and programs running on the host computer directly through the workstation. ATE menus available during terminal emulation support special features such as transferring files, loading parameter files, and dialing out manually. Chapter 7 and Chapter 8 provide complete information on features available to users on the network.