Asynchronous Rotary Line Queueing

This document describes the Asynchronous Rotary Line Queueing feature. It includes information on the benefits of the new feature, supported platforms, related documents, and so on.

This document includes the following sections:

Feature Overview

The Cisco IOS software Asynchronous Rotary Line Queueing feature allows Telnet connection requests to busy asynchronous rotary groups to be queued so that users automatically obtain the next available line, rather than needing to try repeatedly to open a Telnet connection. The Cisco IOS software sends a periodic message to the user to update progress in the connection queue.

Connections are authenticated using the method specified for the line configurations for the asynchronous rotary group. If a connection is queued, authentication is done prior to queueing and no authentication is done when the connection is later established.

Benefits

Effective Use of Limited Resources in High Demand

This feature allows users to make effective use of the asynchronous rotary groups on a Cisco router to access legacy mainframes or other serial devices with a limited number of asynchronous ports that might be used by a large number of users.

Eliminate Manual Connection Retries

Users that are unable to make a Telnet connection on the first attempt are assured of eventual success in an orderly process. They are no longer required to guess when a line might be available and to retry manually again and again. This feature allows users to make more effective use of their valuable time.

Supported Platforms

Asynchronous rotary line queueing is supported on any Cisco router that has an asynchronous port, but has been tested on the following platforms:

Cisco 2500 series routers
Cisco 2600 series routers
Cisco 3600 series routers

Asynchronous rotary line queueing was designed to operate on routers with software that contains the communications server subsystem and that have multiple asynchronous interfaces. See the section "Prerequisites" later in this document for more information about system prerequisites.

Supported Standards, MIBs, and RFCs

Standards

No new or modified standards are supported by this feature.

MIBs

No new or modified MIBs are supported by this feature

RFCs

No new or modified RFCs are supported by this feature.

Prerequisites

The router must have operational and successfully configured asynchronous interfaces, and asynchronous rotary groups must be enabled.

Configuration Tasks

See the following sections for configuration tasks for the Asynchronous Rotary Line Queueing feature. Each task in the list indicates if the task is optional or required.

Configuring Asynchronous Rotary Line Queueing (Required)
Verifying Asynchronous Rotary Line Queueing (Optional but Recommended)

Configuring Asynchronous Rotary Line Queueing

Make sure you comply with the following requirements when configuring asynchronous rotary line queueing:

Configure more virtual terminal lines than will ever be used by waiting asynchronous rotary connection attempts. Even when the queue is at its maximum, there must be at least one virtual terminal line available so that system operators or network administrators can use Telnet to access the router to show, debug, or configure system performance.
When adding lines to a rotary group, all lines must be either queued or not queued. A mixture of queued and unenqueued lines in the same rotary group is not supported and can result in unexpected behavior.
All lines within a queued rotary group need to use the same authentication method. Using different authentication methods within the same rotary group can result in unexpected behavior.

To configure asynchronous rotary line queueing, use the following commands beginning in global configuration mode:

Command Purpose

Step 1

Router (config)# enable Router# configure terminal
Enters configuration mode.

Step 2

Router (config)# line [aux | console | tty | vty] line-number [ending-line-number]
Starts line configuration.

Step 3

Router(config-line)# rotary group [queued]
Enables asynchronous rotary line queueing on the designated line or group of lines.

	Command	Purpose
Step 1	Router (config)# enable Router# configure terminal	Enters configuration mode.
Step 2	Router (config)# line [aux \| console \| tty \| vty] line-number [ending-line-number]	Starts line configuration.
Step 3	Router(config-line)# rotary group [queued]	Enables asynchronous rotary line queueing on the designated line or group of lines.

Additional information about configuring asynchronous lines and rotary groups can be found in the Cisco IOS Dial Services Configuration Guide: Terminal Services; see the chapters "Interfaces, Controllers, and Lines Used for Dial Access Overview," "Preparing Asynchronous Interfaces," and "Configuring Modems and Chat Scripts."

Verifying Asynchronous Rotary Line Queueing

To verify operation of asynchronous rotary line queueing, perform the following tasks:

Use the show line command in EXEC mode to check the status of the virtual terminal lines (VTYs).
Use the show line async-queue command in EXEC mode to check the status of queued connection requests.

Troubleshooting Tips

In the event that asynchronous rotary line queueing is not operating correctly, use the following debug commands in privileged EXEC mode to determine where the problem may lie:

debug async async-queue
debug ip tcp transactions
debug modem

See the Cisco IOS Debug Command Reference publication for information about the debug modem and debug ip tcp transactions commands. The debug async async-queue command is described later in this document.

Monitoring and Maintaining Asynchronous Rotary Line Queues

To display queued lines and to remove lines from the queue, use the following commands in EXEC mode, as needed:

Command Purpose

Router# show line async-queue rotary-group
Displays which lines are queued.

Router# clear line async-queue rotary-group
Clears all rotary queues or the specified rotary queue. If the rotary-group argument is not specified, all rotary queues are removed.

Command	Purpose
Router# show line async-queue rotary-group	Displays which lines are queued.
Router# clear line async-queue rotary-group	Clears all rotary queues or the specified rotary queue. If the rotary-group argument is not specified, all rotary queues are removed.

Configuration Example

The following example enables asynchronous rotary line queueing on lines 1 and 2 on rotary group 1:

line 1 2
  rotary 1 queued

Command Reference

This section documents the following new and modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.

clear line async-queue

To reset the connections currently waiting to use a rotary line in the queue, use the clear line async-queue command in EXEC mode.

clear line async-queue [rotary-group]

Syntax Description

rotary-group

(Optional) Specifies a rotary group. Unless this argument is entered, all connection requests currently waiting in the queue are reset.

rotary-group	(Optional) Specifies a rotary group. Unless this argument is entered, all connection requests currently waiting in the queue are reset.

Defaults

There is no default condition for this command.

Command Modes

EXEC

Command History

Release Modification

12.1(1)T

This command was introduced.

Release	Modification
12.1(1)T	This command was introduced.

Usage Guidelines

Use this command without any argument to remove all rotary line queues and terminate the asynchronous queue manager.

Examples

The following example clears all the rotary queues and shows the resulting output:

Router# clear line async-queue

Clearing queued connections for ALL rotary groups ! [confirm]
Clearing rotary group 1
  Clearing line 69
  Clearing line 70
Clearing rotary group 2
  Clearing line 66
  Clearing line 67
  Clearing line 68

rotary

To define a group of lines consisting of one or more virtual terminal lines or one auxiliary port line, use the rotary command in line configuration mode. To remove a group of lines from a rotary group, use the no form of this command.

rotary group [queued]

no rotary

Syntax Description

group

Rotary group number.

queued

(Optional) Specifies queueing a connection request to a rotary group.

group	Rotary group number.
queued	(Optional) Specifies queueing a connection request to a rotary group.

Defaults

No group of lines is defined.

Command Modes

Line configuration

Command History

Release Modification

10.0

This command was introduced.

12.1(1)T

The queued keyword was added.

Release	Modification
10.0	This command was introduced.
12.1(1)T	The queued keyword was added.

Usage Guidelines

Connections to a rotary group can take advantage of the following features:

Clear To Send (CTS)---If a line in a rotary group is configured to require CTS, the Cisco IOS software ignores that line if CTS from the attached device is low. This feature enables the software to avoid inactive host ports automatically. To enable this feature, use the modem bad line configuration command.
EIA/TIA-232 handshaking---Rotary groups are often associated with large terminal switches that require an EIA/TIA-232 handshake before forming a connection. In this case, use the modem callout line configuration command to configure the lines in the group. If the EIA/TIA-232 handshake fails on a line, the Cisco IOS software steps to the next free line in the rotary group and restarts the negotiation.
Access control---You can use access lists for groups of virtual terminal lines.
Session timeout---Use the session-timeout line configuration command to set an interval for a line so that if no activity occurs on a remotely initiated connection for that interval the Cisco IOS software closes the connection. The software assumes that the host has crashed or is otherwise inaccessible.

Typically, rotary groups are used on devices with multiple modem connections to allow connection to the next free line in a hunt group. In the event that there are no free asynchronous ports, the queued keyword enables outgoing connection requests to be queued until a free port becomes available. Periodic messages are sent to users to update them on the status of their connection request.

For a nonqueued connection request, the remote host must specify a particular TCP port on the router to connect to a rotary group with connections to an individual line. The available services are the same, but the TCP port numbers are different. Table 1 lists the services and port numbers for both rotary groups and individual lines.

Table 1: Services and Port Numbers for Rotary Groups and Lines

Services Provided Base TCP Port for Rotaries Base TCP Port for
Individual Lines

Telnet protocol

3000

2000

Raw TCP protocol (no
Telnet protocol)

5000

4000

Telnet protocol, binary mode

7000

6000

XRemote protocol

10000

9000

Services Provided	Base TCP Port for Rotaries	Base TCP Port for Individual Lines
Telnet protocol	3000	2000
Raw TCP protocol (no Telnet protocol)	5000	4000
Telnet protocol, binary mode	7000	6000
XRemote protocol	10000	9000

For example, if Telnet protocols are required, the remote host connects to the TCP port numbered 3000 (decimal) plus the rotary group number. If the rotary group identifier is 13, the corresponding TCP port is 3013.

If a raw TCP stream is required, the port is 5000 (decimal) plus the rotary group number. If rotary group 5 includes a raw TCP (printer) line, the user connects to port 5005 and is connected to one of the raw printers in the group.

If Telnet binary mode is required, the port is 7000 (decimal) plus the rotary group number.

Examples

The following example establishes a rotary group consisting of virtual terminal lines 2 through 4 and defines a password on those lines. By using Telnet to connect to TCP port 3001, the user gets the next free line in the rotary group. The user needs not remember the range of line numbers associated with the password.

line vty 2 4
 rotary 1
 password letmein
login

The following example enables asynchronous rotary line queueing:

line 1 2 
 rotary 1 queued

Related Commands

Command Description

login (line)

Enables password checking at login and defines the method (local or TACACS+).

modem bad

Removes an integrated modem from service and indicates it as suspect or proven to be inoperable.

modem callout

Configures a line for reverse connections.

modem dialin

Configures a line to enable a modem attached to the router to accept incoming calls only.

session-timeout

Sets the interval for closing the connection when there is no input or output traffic.

Command	Description
login (line)	Enables password checking at login and defines the method (local or TACACS+).
modem bad	Removes an integrated modem from service and indicates it as suspect or proven to be inoperable.
modem callout	Configures a line for reverse connections.
modem dialin	Configures a line to enable a modem attached to the router to accept incoming calls only.
session-timeout	Sets the interval for closing the connection when there is no input or output traffic.

show line async-queue

To display the status of connections currently waiting in the queue, use the show line async-queue command in EXEC mode.

show line async-queue [rotary-group]

Syntax Description

rotary-group

(Optional) Specifies a rotary group.

rotary-group	(Optional) Specifies a rotary group.

Defaults

This command has no defaults.

Command Modes

EXEC

Command History

Release Modification

12.1(1)T

This command was introduced.

Release	Modification
12.1(1)T	This command was introduced.

Usage Guidelines

Use this command to display all rotary line queues.

Examples

The following example shows all lines that are currently queued:

Router# show line async-queue

Showing async-queue for ALL rotary groups
 
Queue for Rotary Group 1:
    Pos    Waiting TTY    Dest Port    Source Host   Waiting Time
      1          tty69         7001       10.2.1.3       00:00:09
      2          tty70         7001       10.2.1.3       00:00:06
 
 
Queue for Rotary Group 2:
    Pos    Waiting TTY    Dest Port    Source Host   Waiting Time
      1          tty66         7002       10.2.1.3       00:00:36
      2          tty67         7002       10.2.1.3       00:00:29
      3          tty68         7002       10.2.1.3       00:00:26
 
 
Lines which have queuing enabled [tty (group)]:
tty33 (1)  tty34 (1)  tty35 (1)  tty36 (1)  tty37 (2)  
tty38 (2)  tty39 (2)  tty40 (2)  tty41 (3)  tty42 (3)  
tty43 (3)  tty44 (3)  tty45 (4)  tty46 (4)  tty47 (4)  
Router#

Note that Waiting TTY may also be displayed as Waiting VTY and is equivalent.

Debug Commands

This section documents the following new debug command. All other commands used with this feature are documented in the Cisco IOS Release 12.1 command reference publications.

debug async async-queue

debug async async-queue

To display debug messages for asynchronous rotary line queueing, use the debug async async-queue command in privileged EXEC mode.

debug async async-queue

Syntax Description

This command has no arguments or keywords.

Defaults

This command has no default settings.

Command Modes

Privileged EXEC

Command History

Release Modification

12.1(1)T

This command was introduced.

Release	Modification
12.1(1)T	This command was introduced.

Examples

The following example starts the asynchronous rotary line queueing debugging display:

Router# debug async async-queue

*Mar  2 03:50:28.377: AsyncQ: First connection to be queued - starting the AsyncQ manager
*Mar  2 03:50:28.377: AsyncQ: Enabling the AsyncQ manager
*Mar  2 03:50:28.377: AsyncQ: Started the AsyncQ manager process with pid 98
*Mar  2 03:50:28.381: AsyncQ: Created a Waiting TTY on TTY66 with pid 99
*Mar  2 03:50:30.164: WaitingTTY66: Did Authentication on waiting TTY (VTY)
*Mar  2 03:50:30.168: AsyncQ: Received ASYNCQ_MSG_ADD
*Mar  2 03:50:30.168: AsyncQ: New queue, adding this connection as the first element
*Mar  2 03:50:34.920: AsyncQ: Created a Waiting TTY on TTY67 with pid 100
*Mar  2 03:50:36.783: WaitingTTY67: Did Authentication on waiting TTY (VTY)
*Mar  2 03:50:36.787: AsyncQ: Received ASYNCQ_MSG_ADD
*Mar  2 03:50:36.787: AsyncQ: Queue exists, adding this connection to the end of the queue

Related Commands

Command Description

debug ip tcp transactions

Enables the IP TCP transactions debugging display to observe significant transactions such as state changes, retransmissions, and duplicate packets.

debug modem

Enables the modem debugging display to observe modem line activity on an access server.

Command	Description
debug ip tcp transactions	Enables the IP TCP transactions debugging display to observe significant transactions such as state changes, retransmissions, and duplicate packets.
debug modem	Enables the modem debugging display to observe modem line activity on an access server.

Glossary

asynchronous transmission---Term describing digital signals that are sent without precise clocking. Such signals generally have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate individual characters in control bits (called start and stop bits) that designate the beginning and end of each character.

EIA/TIA-232---Common physical layer interface standard, developed by the Electronic Industries Association and Telecommunications Industry Association, that supports unbalanced circuits at signal speeds of up to 64 kbps. Closely resembles the V.24 specification. Formerly called RS-232.

rotary groups---Several contiguous lines that allow a connection to be made to the next free line in the group. Also called a hunt group.

TCP---Transmission Control Protocol. Connection-oriented transport layer protocol that provides reliable full-duplex data transmission. TCP is part of the TCP/IP protocol stack.

Telnet---Standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system. Telnet is defined in RFC 854.

Transmission Connection Protocol---See TCP.

TTY---terminal line.

VTY---virtual terminal line.

Table of Contents

Asynchronous Rotary Line Queueing