X.28 Emulation

Description

X.28 emulation is the standard user interface between data terminal equipment (DTE) and a packet assembler/disassembler (PAD). The Cisco IOS software provides an X.28 user emulation mode, which enables you to interact with and control the PAD. During this exchange of control information, messages or commands sent from the terminal to the PAD are called PAD command signals. Messages sent from the PAD to the terminal are called PAD service signals. These signals and any transmitted data take the form of encoded character streams as defined by International Alphabet Number 5.

For asynchronous devices such as terminals or modems to access an X.25 network host, the device's packets must be assembled or disassembled by a PAD device. Using standard X.28 commands from the PAD, calls can be made into an X.25 network, X.3 PAD parameters can be set, or calls can be reset. There are 22 available X.3 PAD parameters to configure. These parameters can also be set by a remote X.25 host using X.29. Figure 30 shows a typical example of an asynchronous device accessing a router; the router's PAD in turn places calls into an X.25 network.

Benefits

Cisco's new X.28 PAD implementation enables users to access X.25 networks or set PAD parameters using the X.28 standard user interface. This standard interface is common in many European countries and adheres to the X.25 International Telecommunication Union Telecommunication (ITU-T) standards.

The new X.28 interface is designed for asynchronous devices that require X.25 transport to access a remote or native asynchronous or synchronous host application. For example, dial-up users can use the X.28 interface to access a remote X.25 host. Banks implement Cisco routers to support back office applications, ATM, point of sales authorization devices, and alarm systems. These alarm devices are connected asynchronously to the same Cisco router and report alarm conditions to a remote alarm host for the dispatch of police. Cisco's X.28 PAD calls can be transported over a public packet network, a private X.25 network, the Internet, a private IP-based network, or a Frame Relay network. With this new service, Cisco now offers the flexibility to use the X.28 interface either directly or over a Cisco IOS application service such as with protocol translation. The protocol translation VTY asynchronous application enables users to bidirectionally access an X.25 application with the PAD service or protocols such as Digital Equipment Corporation (DEC), local-area transport (LAT), and transmission control protocol (TCP).

List of Terms

X.28--The standard user interface between DTE and a PAD.

X.29--The ITU-T recommendation that defines the form for control information from the remote terminal-to-PAD interface used in X.25 networks.

X.3--The ITU-T recommendation that defines various PAD parameters used in X.25 networks.

X.3 PAD parameters--Internal variables that define the operation of a PAD. For example, parameter number 9 is the crpad parameter. It determines the number of bytes to add after a carriage return.

Platforms

The following platforms support X.28 emulation:

• Cisco 2500 series

• Cisco 4000 series (Cisco 4000, 4000-M, 4500, 4500-M, 4700, 4700-M)

• Cisco AS5200

• Cisco 7000 series

• Cisco 7200 series

• Cisco 7500 series

Configuration Tasks

The following optional tasks are described in this section:

• Set X.28 Access and Display Options

• Enter PAD Command Signals for X.25 Connections

• Set X.3 PAD Parameters for X.25 Connections

X.28 mode is initiated with the x28 command from the EXEC level or using the autocommand line configuration command. The default X.28 router prompt is an asterisk (*). Once you enter this mode, the standard X.28 user interface is available. From this interface, you can configure or use the PAD inside a Cisco router with X.3 parameters (see the "Set X.3 PAD Parameters for X.25 Connections" section), or you can access an X.25 network (see the "Enter PAD Command Signals for X.25 Connections" section).

Set X.28 Access and Display Options

To enter X.28 mode and set different access and display parameters, perform any of the following tasks beginning in EXEC mode:

See the "Configuration Examples" section for sample X.28 configurations.

Enter PAD Command Signals for X.25 Connections

Many X.25-related functions can be performed from the PAD in X.28 mode. However, only the following two most common tasks are described in this section:

• Connect to a Remote X.25 Device

• Clear a Connection to a Remote X.25 Device

In X.28 mode, you can set PAD command signals using standard or extended command syntax. A command specified with standard command syntax is merely an abbreviated version of the extended syntax version. Both syntaxes have the same functionality. For a complete list of PAD command signals, see Table 39 under the x28 command.

Connect to a Remote X.25 Device

To call an X.25 device using a local PAD signal command, perform the following steps beginning in EXEC mode:

See the "Configuration Examples" section for a sample connection to a remote X.25 device.

Clear a Connection to a Remote X.25 Device

Once you connect to a remote X.25 device, you can clear the connection by performing the following steps beginning in EXEC mode:

See the "Configuration Examples" section for a sample of how to clear a connection to a remote X.25 device.

Set X.3 PAD Parameters for X.25 Connections

To set an X.3 PAD parameter from a local terminal, perform the following steps beginning in EXEC mode:

See the "Configuration Examples" section for an example of how to set X.3 parameters for X.25 connections.

Configuration Examples

This section provides the following X.28 configuration examples:

• Enter PAD Command Signals Examples

• Set X.3 PAD Parameters Examples

• Modify and Load an Existing X.25 PAD Parameter Profile Example

• Network User Identification Data Relocation Example

• X.25 Reverse Charge Call Example

• X.25 Call Detail Display Example

Enter PAD Command Signals Examples

The following examples show two ways to make a call to a remote X.25 host over a serial line. The remote host's interface address is 123456. In the first example, Router-A calls Router-B using the pad 123456 EXEC command. The second example shows Router-A calling Router-B using the call 123456 PAD signal command in X.28 mode. Both commands accomplish the same goal.

Router-A# pad 123456
Trying 123456...Open
 
Router-B> exit
 
[Connection to 123456 closed by foreign host]
Router-A# x28
 
* call 123456
COM
 
Router-B>

The following examples show two ways to clear a connection with a remote X.25 host. The first example shows Router-A disconnecting from Router-B using the disconnect command in EXEC mode. The second example shows Router-B disconnecting from Router-A using the clr command in X.28 mode.

Router-A# pad 123456
Trying 123456...Open
 
Router-B> <Enter the escape sequence (for example, press Shift-Ctrl-^-x).>
Router-A# disconnect
Closing connection to 123456 [confirm]
Router-A#
Router-A# x28
 
* call 123456
COM
 
Router-B> <Press Ctrl-p>
* clr
 
CLR CONF 
 
*

Set X.3 PAD Parameters Examples

The following example configures parameter 9 from 0 to 1, which adds one byte after the carriage return. This setting is performed from a local terminal using the set parameter-number:new-value PAD command signal.

Router-A# x28
 
* par
   PAR 1:1 2:1 3:126 4:0 5:1 6:2 7:2 8:0 9:0 10:0 11:14 12:1 13:0 14:0 15:0 16:127 17:24 18:18 19:2 20:0 21:0 22:0 
 
* set 9:1
 
* par
   PAR 1:1 2:1 3:126 4:0 5:1 6:2 7:2 8:0 9:1 10:0 11:14 12:1 13:0 14:0 15:0 16:127 17:24 18:18 19:2 20:0 21:0 22:0 
 
*

The following example shows how to change a local X.3 PAD parameter from a remote X.25 host using X.29 messages, which is a secure way to enable a remote host to gain control of local PAD. The local device is Router-A. The remote host is Router-B. The parameters listed in the ParamsIn field are incoming parameters, which are sent by the remote PAD. The parameters listed in the ParamsOut field are parameters sent by the local PAD.

Router-A# pad 123456
Trying 123456...Open
 
Router-B> x3 2:0
Router-B>
Router-A# show x25 pad 
 
tty0, connection 1 to host 123456
 
Total input: 12, control 3, bytes 35. Queued: 0 of 7 (0 bytes).
Total output: 10, control 3, bytes 64.
Flags: 1,   State: 3,   Last error: 1
 ParamsIn:  1:0, 2:0, 3:0, 4:0, 5:0, 6:0, 7:0,
    8:0, 9:0, 10:0, 11:0, 12:0, 13:0, 14:0, 15:0,
    16:0, 17:0, 18:0, 19:0, 20:0, 21:0, 22:0,
 ParamsOut:  1:1, 2:0, 3:2, 4:1, 5:1, 6:0, 7:21,
    8:0, 9:1, 10:0, 11:14, 12:1, 13:0, 14:0, 15:0,
    16:127, 17:21, 18:18, 19:0, 20:0, 21:0, 22:0,
Router-A#

Modify and Load an Existing X.25 PAD Parameter Profile Example

The following example modifies and loads an existing X.25 PAD parameter profile. It accesses the existing PAD profile ppp, changes its padding parameter (specified as 9) to a value of 2, and displays the new parameters using the par command in X.28 mode.

Router-A# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router-A(config)# x29 profile ppp 9:2
Router-A(config)# end
Router-A#
%SYS-5-CONFIG_I: Configured from console by console
Router-A# x28 profile ppp
 
* par
   PAR 1:1 2:1 3:126 4:0 5:1 6:2 7:2 8:0 9:2 10:0 11:14 12:1 13:0 14:0 15:0 16:127 17:24 18:18 19:2 20:0 21:0 22:0 

Network User Identification Data Relocation Example

The following example sends an authentication message to a remote X.25 host using the x28 nuicud command in X.28 mode followed by the Ncisc-123456 X.28 command. The network identifier is N. The network user password is cisc. The destination address of the remote device is 123456. The ASCII representation of the user password appears in the call user data field, not in the data packet.

Router-A# debug x25 event
X.25 special event debugging is on
Router-A# x28 nuicud
 
* Ncisc-123456
COM
 
Router-B>
02:02:58: Serial1: X.25 O P1 Call (16) 8 lci 20
02:02:58:   From(3): 222 To(3): 123456
02:02:58:   Facilities: (0)
02:02:58:   Call User Data (8): 0x01000000xxxxxxxx (pad)
02:02:58: Serial1: X.25 I P2 Call Confirm (5) 8 lci 20
02:02:58:   From(0):  To(0): 
02:02:58:   Facilities: (0)

X.25 Reverse Charge Call Example

The charges for all outgoing calls made from the local router can be reversed to the destination device using the x28 reverse command. To reverse the charges for only one outgoing call, use the R-address command, which is the standard X.28 reverse charge facility command.

Router-A# x28 reverse 
 
* exit
Router-A# x28
 
* R-123456 
COM 

X.25 Call Detail Display Example

Each time a call is made to a remote device, you can specify that detailed information be displayed about the call and the destination device by entering the x28 verbose command. The following example shows reverse charging configured and call user data represented as userdata:

Router# x28 verbose
 
* R-111*userdata
 
Called DTE Address : 3001
Facility Block     : R 
Call User Data     :userdata
COM

Command Reference

This section documents the new x28 command. All other commands used with this feature are documented in the Cisco IOS Release 11.2 Wide-Area Networking Command Reference.

x28

To enter X.28 mode and access an X.25 network or set X.3 PAD parameters, use the x28 EXEC command.

Syntax Description

Default

Disabled. X.28 mode uses standard X.28 command syntax.

Command Mode

EXEC

Usage Guidelines

This command first appeared in Cisco IOS Release 11.2 F.

If both the escape and noescape options are not set, the default escape sequence is used (exit command).

X.28 mode is identified with an asterisk (*) router prompt. Once you enter this mode, the standard X.28 user interface (with the exception of the escape sequence) is available. From this interface, you can configure a PAD device using X.3 parameters, or you can access an X.25 network.

In X.28 mode, you can set PAD command signals using standard or extended command syntax. For example, you can enter the clr command or clear command to clear a virtual call. A command specified with standard command syntax is merely an abbreviated version of the extended syntax version.

Table 39 lists the commands available in both standard and extended command syntax.

Table 40 lists the different types of parameters you can set using the set parameter-number: new-value PAD command signal from X.28 mode.

Several methods can be used to connect to the X.28 pad mode of a router. Refer to the "Making Connections to Network Devices" chapter of the Cisco IOS Release 11.2 Access Services Configuration Guide for more information.

Table 41 lists the options for the X.28 help command.

Table 42 shows examples of parsed call requests.

Examples

The following example shows how to place a virtual call using the call PAD command signal in X.28 mode:

Router# x28
* call 123456

The following example enters X.28 mode with the x28 EXEC command and configures a PAD with the set X.3 parameter command. The set command sets the idle time delay to 40 seconds.

Router# x28
* set 4:40

Related Command

pad

Debug Command

This section describes the debug x28 command.

debug x28

To monitor error information and X.28 connection activity, use the debug x28 privileged EXEC command. The no form of this command disables the debugging function.

Sample Display

Figure 31 shows sample output while the PAD initiates an X.28 outgoing call:

Router# debug x28
X28 MODE debugging is on
Router# x28
*
03:30:43: X.28 mode session started
03:30:43: X28 escape is exit
03:30:43: Speed for console & vty lines :9600 
*call 123456
COM
03:39:04: address ="123456", cud="[none]" 03:39:04: Setting X.3 Parameters for this call...1:1 2:1 3:126 4:0 5:1 6:2 7:2 8:0 9:0 10:0 11:14 12:1 13:0 14:0 15:0 16:127 17:24 18:18 19:2 20:0 21:0 22:0 
Router> exit
CLR CONF
*
*03:40:50: Session ended
* exit
Router#
*03:40:51: Exiting X.28 mode

What to Do Next

Refer to the "Configuring X.25 and LAPB" chapter in the Cisco IOS Release 11.2 Wide-Area Networking Configuration Guide for more information about configuring X.25.