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VINES X.25 Guide

Chapter 1 - Overview of VINES X.25

Introduction

Calculating the number of virtual circuits that you need
Meeting data networks and ISDN service requirements
Installing X.25 hardware and software
Assigning the X.25 communications line

VINES Implementation

Note: In this document, the term "ICA card" is used to refer to an ICA, ICA mC, or ICAplus card.

Figure 1-1. VINES X.25 Implementation

Facilities Supported

Table 1-1. VINES X.25 Facilities

Prerequisites and Limitations

Prerequisites

VINES ICA, ICA plus, or ICAmc card
A synchronous modem for servers connected to a public data network (PDN) or AT&T 7500 Data Module for servers connected to an ISDN network
VINES X.29 option if X.29 dial-in communications are required
VINES X.29 option and the VINES Asynchronous Terminal Emulation (ATE) option if terminal emulation to a host computer is required

Limitations

A VINES server supports a maximum of 256 virtual circuits. This limit applies to all server platforms.
An ICA card supports a maximum of 128 virtual circuits. Note that the ICA card is the only serial communications card that the option supports.
An ICA card has a maximum of two X.25 lines.
An X.25 line supports a maximum of 32 Permanent Virtual Circuits (PVCs).

Network Connections

Connections Create a VINES Network

Server-to-Server Communications

Servers Connected Through a PDN

Figure 1-2. Servers Connected Through a PDN

Servers Directly Connected

Figure 1-3. Servers Directly Connected

Workstation-to-Server Communications

Accepts asynchronous characters from the workstation and assembles them into an X.25 packet for transmission to the server through the PDN or switched telephone line
Accepts X.25 packets from the PDN or switched telephone company line and disassembles them into asynchronous characters to be passed to the DOS workstation

Connections Through a PDN

Figure 1-4. Workstations Connected to a Server Through a PDN

Connections Through an ISDN Network

Figure 1-5. Workstations Connected to a Server Through an ISDN Network

Connections over a Switched Line

Figure 1-6. Workstations Connected to a Server Over a Switched Line

Set-up Procedures

1. Subscribe to a PDN, an ISDN network, or arrange for lines to connect the two servers or the workstations and server.

2. Install the X.25 hardware and software. The X.25 option uses a serial communications card and attached lines to communicate with remote sites.

3. Assign communications lines at both sites.

4. Make the proper modems and lines available to connect the X.25 hardware to the PDN, ISDN network or to other lines.

Servers Connected to a Host

Figure 1-7. Server Directly Connected to a Host

Set-up Procedure

1. Subscribe to a PDN or arrange for lines to connect the server and host.

2. Install the X.25 hardware and software. The X.25 option uses a serial communications card and attached lines to communicate with hosts.

3. Assign a communications line at the server. Chapter 2 describes how you do this. Pay close attention to the configuration. If you have questions about the configuration, contact your PDN.

4. Make the proper modems and lines available to connect the X.25 hardware to the PDN or to other lines.

5. Verify that the X.29 and Asynchronous Terminal Emulation options are installed on the server, and that an asynchronous terminal emulation service is created and properly configured. See the Banyan Asynchronous Terminal Emulation Guide for details on both these options.

Virtual Circuits

Permanent Virtual Circuits

Example PVCs Connecting Two Cities

Figure 1-8. Permanent Virtual Circuit Connecting Servers in Two Cities

Switched Virtual Circuits

Types of SVCs

Incoming virtual circuits (IVCs) - Used to receive an incoming call, but not to place an outgoing call. A host with only IVCs can answer calls, but cannot place any calls. IVCs are used for X.29 dial-in communications, X.25 server-to-server connections, and applications developed with the Banyan Applications Toolkit. When IVCs are used with X.25 server-to-server connections, the remote server places the call.
Two-way virtual circuits (TVCs) - Used to receive an incoming call and place an outgoing call. A host with only two-way virtual circuits can call remote hosts and answer any calls. TVCs are used for X.25 server-to-server communications, X.29 dial-in communications, X.29 host communications, and applications developed with the Banyan Applications Toolkit.
Outgoing virtual circuits (OVCs) - Used to place outgoing calls, but cannot receive incoming calls. A host with only outgoing virtual circuits can call other hosts but cannot answer calls from other hosts. OVCs are used for X.29 host communications, X.25 server-to-server connections, and applications developed with the Banyan Applications Toolkit

Using SVCs

Example SVCs Connecting Two Cities

Figure 1-9. Switched Virtual Circuit Connecting Servers in Two Cities

Summary

Table 1-2 Types of SVCs

Table 1-3. Using PVCs and SVCs

Number of Circuits Available

Figure 1-10. Virtual Circuits Distributed Between Two ICA Cards

Figure 1-11. Virtual Circuits Distributed Among Four ICA Cards

Lines per Card

Example Vines Server With Two ICA Cards

Figure 1-12. VCs Distributed Between Serial Lines

Subscribing for Virtual Circuits

Exceeding the Maximum

If you receive an incoming call, you lose one of your listening circuits.
If you place an outgoing call, the attempt is unsuccessful and you receive a COM162 error message (no buffer space available).

What Kinds of Virtual Circuits

Number of Virtual Circuits

How many servers will your server be communicating with over the PDN or ISDN network?
How many concurrent X.29 asynchronous terminal emulation sessions with host computers do you need to support?
How many X.29 dial-in sessions do you need to support between DOS workstations and a server?

How Many SVCs

Total SVCs = Total Servers + Total X.29 ATE Sessions + Total X.29 Dial-in Sessions + Other Connections

SVCs for ATE Sessions

Note: Keep in mind that as you reserve more virtual circuits per card for server-to-server communications or X.29 dial-in sessions, you may decrease the number of virtual circuits available for server-to-host communications, and vice versa. You may adversely affect performance as you increase the number of configured SVCs. Performance is affected even when all virtual circuits are not in use. Do not configure virtual circuits unless you need them.

How Many PVCs

Total Number of Virtual Circuits

Total VCs = Total SVCs + Total PVCs

PDNs Supported

Table 1-4. PDNs Supported by VINES X.25

PDN and ISDN Network Requirements

Modem requirements
Facilities information
PVC information
SVC information

Modems

Facilities Information

Note: Facilities information does not apply to X.29 dial-in sessions.

When you assign the communications line
When you define a remote server connection
When you define an X.29 connection

Note: Invalid facilities information causes a call to fail. Be careful to obtain and supply the correct information.

PVC Information

PVC Worksheet

Table 1-5. PVC Worksheet

SVC Information

SVC Worksheet

Table 1-6. SVC Worksheet

Using the X.25 Option without a PDN

Connecting Two VINES Servers

Designating a DTE and DCE

PVCs or SVCs

Switched and Leased Lines

1. Dial in to the other server to make a physical connection.

2. Establish a logical connection.

Connecting a Server to a Host

1. Assign the X.25 line as if it were a line to a PDN.

2. Supply all the necessary information about SVCs.

1. Dial in to the host to make a physical connection.

2. Establish X.29 asynchronous terminal emulation sessions.

Note: With a single X.25 line, you can establish multiple concurrent X.29 asynchronous terminal emulation 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.

Connecting DOS Workstations to a Server

1. Assign the X.25 line as if it were not connected to a PDN.

2. Specify "switched line" when assigning the line. You cannot use a dedicated line to support X.29 dial-in sessions without a PDN or ISDN network.

3. Specify that the server acts as the DCE when you assign the line.

4. Supply the server' s telephone number to the administrator responsible for the PAD that makes the telephone call.

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