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Configuring the Airline Product Set

Configuring the Airline Product Set

This chapter describes how to configure the Airline Product Set (ALPS). For a complete description of the ALPS commands in this chapter, refer to the "Airline Product Set Configuration Commands" chapter in the Bridging and IBM Networking Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.

ALPS is a tunneling mechanism that transports airline protocol data across a Cisco router-based TCP/IP network to an X.25-attached mainframe. This feature provides connectivity between agent set control units (ASCUs) and a mainframe host that runs the airline reservation system.

Figure 191 shows the basicALPS topology and the protocols implemented in the feature. Three major components provide the end-to-end transportation of airline protocol traffic across the network: the Airline Control (ALC) protocol, the TCP-based transport protocol, and the access to the mainframe, Airline X.25 (AX.25) or exchange of mixed traffic over X.25 (EMTOX).


Figure 191:
ALPS Architecture


Cisco's ALPS feature provides an end-to-end solution for airlines and central reservation systems.

The ALPS feature is integrated in the Cisco IOS software and allows airlines to replace their existing hardware and software with Cisco routers. For customers who already use Cisco routers, this feature allows them to consolidate networking overhead and functionality.

The ALPS feature is supported on the following platforms:


Note The Cisco 4500 and Cisco 4700 platforms must have a high-density, low-speed serial card installed. 16 low-speed ports are usable for performing the remote CPE functions.

ALPS Configuration Task List

Perform the tasks in the following sections to configure and maintain the ALPS feature.

See the end of this chapter for "ALPS Configuration Examples."

Configure the Remote CPE Routers

Perform the tasks in the following sections to configure the ALPS feature on the remote CPE routers:

Specify the ALPS Local Peer IP Address

You must identify an IP address as an ALPS local peer on the remote CPE. Only one ALPS local peer is permitted on a router.

To specify the ALPS local peer IP address, use the following commands in global configuration mode:
Step Command Purpose

1 . 

alps local-peer ipaddress

Specify an IP address to use as the ALPS local peer on the remote CPE.

2 . 

alps keepalive [interval time] [retry count]

Enable TCP keepalives for ALPS TCP peer connections.

Specify the ALPS Remote Peer IP Address

You must also specify in the remote CPE configuration the IP addresses of ALPS peers that exist on the central CPE router. The peer connection may be either permanent or dynamic (established on demand).

To specify the IP addresses that exist on the central CPE, use the following commands in global configuration mode:
Command Purpose

alps remote-peer ip-addr [dynamic [inact-timer]] [tcp-qlen [num]

Specify the IP addresses of ALPS peers that exist on partner CPE routers.

Customize the Service Messages

You can customize the contents of the service message list. To specify the service message number and the content of the message, use the following command in global configuration mode:
Command Purpose

alps service-msg-list list number number msg

Specify service message numbers and content.

Specify the ALPS Circuit

An ALPS circuit is a communication path across a TCP connection for one or more ASCUs. The ALPS circuit must have a configured association with an ALPS remote peer to establish a connection to the host. Additionally, an ALPS circuit configuration may specify a different remote peer as a backup peer to the host. Configuration for an ALPS circuit also includes X.25 connection information to be passed to the central CPE router when the circuit is established. ALPS circuits may be multiplexed across a single TCP connection.

To specify an ALPS circuit, use the following commands, beginning in global configuration mode:
Step Command Purpose

1 . 

alps circuit name

Specify an ALPS circuit at the remote CPE and enter ALPS circuit submode.

2 . 

alps primary-peer ip-addr [backup-peer ip-addr]

Specify the primary TCP peer and an optional backup peer for this ALPS circuit.

3 . 

alps local-hld loc-hld remote-hld rem-hld

Specify the local and remote HLDs for this ALPS circuit.

4 . 

alps connection-type permanent retry-timer

Specify that this circuit should be established when the circuit is enabled.

5 . 

alps lifetime-timer timer

Specify how long messages can be queued in the ALPS circuit queue.

6 . 

alps hostlink number {ax25 lcn | emtox x121-addr} [winout val1] [winin val2] [ops val3] [ips val4]

Specify the information required to establish an X.25 virtual circuit at the central CPE.

7 . 

alps service-msg-interval seconds

Specify the interval between the transmission of a service message to an ASCU and the transmission of a "PLEASE RETRY' message. The "PLEASE RETRY" message is transmitted only to ASCUs that use circuits with a dynamic connection type.

8 . 

alps service-msg-list list

Define the service message list to be used for this circuit.

9 . 

alps enable-circuit

Enable the circuit to be activated.

Specify Each ASCU

Each ASCU must be configured within the context of the serial interface configuration. ASCU addressing information and association with an ASCU circuit must be configured. Timers, maximum frame sizes, and retry values are optional configuration parameters for each ASCU. Appropriate default parameters are used for unspecified parameters.

To specify an ASCU, use the following commands, beginning in global configuration mode:
Step Command Purpose

1 . 

interface type number

Configure an interface and enter interface configuration mode.

2 . 

encapsulation alc

Specify that the ALC protocol will be used on the serial interface.

3 . 

alps t1 delay

Specify the timeout delay between the transmission of an ALC poll message and the receipt of the first character of the poll message response.

4 . 

alps t2 delay

Specify the timeout delay between receipt of the first character of the response to a poll message and the receipt of a Go Ahead message.

5 . 

alps n1 errors

Specify the threshold of consecutive errors logged before an ASCU is declared to be down.

6 . 

alps n2 polls

Specify the number of polls that must be correctly replied to before an ASCU is declared to be up.

7 . 

alps servlim polls

Specify the number of polls of the ASCU UP list allowed between two successive polls of the ASCU DOWN list.

8 . 

alps ascu id

Specify a physical ASCU identity (the ASCU interchange address value for ALC) and enter ALPS ASCU submode.

9 . 

alps default-ckt name

Specify the ALPS circuit that this ASCU uses.

10 . 

alps a1-map a1-value a2-map a2-value

Specify the A1 and A2 logical ASCU identification information.

11 . 

alps retry-option [resend | reenter]

Specify the retry option when an ALC message with a bad cyclic check character (CCC) is received.

12 . 

alps max-msg-length value

Specify maximum input message length.

13 . 

alps error-display number1 number2

Specify where error messages are displayed.

14 . 

alps enable-ascu

Begin polling the ASCU.

Configure the Central CPE Router

Perform the tasks in the following sections to configure the ALPS feature on the central CPE router:

Specify the ALPS Host Local Peer Address

You must identify an IP address to use as the ALPS local peer IP address. Only one ALPS host local peer is permitted on a router. The promiscuous option, which allows any remote CPE to connect, is recommended at the remote CPE.

To specify the ALPS host local peer address, use the following command in global configuration mode:
Command Purpose

alps local-peer ip-address [promiscuous]

Specify the IP address of the local peer.

Specify AX.25

For AX.25 to be enabled on an X.25 interface, the ALPS host high-level designator (HLD) and hostlink number must be configured and AX.25 must be specified on an X.25 serial interface. At circuit-establishment time, the remote CPE router forwards the host HLD, the logical channel number (LCN), and the hostlink number for the permanent virtual circuit (PVC), to be used for the ASCU group.

To configure AX.25 on an X.25 interface, use the following commands, beginning in global configuration mode:
Step Command Purpose

1 . 

interface type number

Configure an interface and enter interface configuration mode.

2 . 

encapsulation x25 ax25

Specify a serial interface as an X.25 device.

3 . 

alps host-hld num host-link num ax25 [damp-tmr value] [life-tmr value]

Enable ALPS on the X.25 interface.

Specify EMTOX

For EMTOX to be enabled on an X.25 interface, the host HLD and the hostlink number must be configured and EMTOX must be specified on an X.25 serial interface. At circuit-establishment time, the remote CPE router forwards the X.121 address to be used as the calling address in the X.25 call and the host HLD and the hostlink number. If the host performs a call out, a correlation between the X.121 called address and a remote CPE peer IP address must be configured.

To configure EMTOX on an X.25 interface, use the following commands, beginning in global configuration mode:
Step Command Purpose

1 . 

interface type number

Configure an interface and enter interface configuration mode.

2 . 

encapsulation x25

Specify a serial interface as an X.25 device.

3 . 

alps host-hld num host-link num emtox [life-tmr  value]

Enable ALPS on the X.25 interface.

4 . 

alps translate x.121-addr ip-addr

Map an X.121 address to an IP address on a remote peer.

Monitor the ALPS Feature

To monitor the status of the ALPS feature, use the following commands in EXEC mode:
Command Purpose

show alps ascu [interface id] [detail]

Display the status of the ALPS ASCU.

show alps circuits [name name] [detail]

Display the status of the ALPS circuits.

show alps peers [ipaddress addr] [detail]

Display the status of the ALPS remote peers.

show interfaces type number

Display P1024B information.

ALPS Configuration Examples

Figure 192 shows a simple router topology for the ALPS feature. The configuration for this topology follows.


Figure 192: Router Topology for ALPS


Remote CPE Configuration Example

alps local-peer 172.22.0.90
alps keepalive interval 60
alps remote-peer 172.22.0.91 
alps remote-peer 172.22.0.92 dynamic 60
alps service-msg-list 1 number 2 NETWORK DOWN
!
alps circuit CKT1
alps primary-peer 172.22.0.91 backup-peer 172.22.0.92
alps local-hld 4B10 remote-hld 5C00
alps connection-type permanent 30
alps lifetime-timer 3
alps hostlink 3 ax25 120 winout 3 winin 3
alps service-msg-interval 3
alps service-msg-list 1
alps enable-circuit
!
alps circuit CKT2
alps primary-peer 172.22.0.91 backup-peer 172.22.0.92
alps local-hld 4B10 remote-hld 5C00
alps hostlink 3 ax25 1500 winout 4 winin 5
alps enable-circuit
!
alps circuit CKT3
alps primary-peer 172.22.0.91
alps local-hld 4B10 remote-hld 5C00
alps connection-type permanent 30
alps lifetime-timer 6
alps hostlink 3 ax25 905 
alps enable-circuit
!
interface serial 1
ip address 172.22.0.90 255.255.255.0
!
interface serial 2
encapsulation alc
alps t1 3
alps t2 6
alps n1 3
alps n2 2
alps servlim 20
!
alps ascu 51
alps default-ckt CKT1
alps a1-map 40 a2-map 2D
alps retry-option resend
alps max-msg-length 1950
alps error-display 6d 78
alps enable-ascu
!
alps ascu 44
alps default-ckt CKT1
alps a1-map 40 a2-map 2E
alps max-msg-length 590
alps error-display 6d 78
alps enable-ascu
!
alps ascu 7E
alps default-ckt CKT2
alps a1-map 40 a2-map 2F
alps retry-option re-send
alps max-msg-length 2000
alps error-display 6d 78
alps enable-ascu
interface serial 3
encapsulation alc
alps t1 5
alps t2 6
alps n1 1
alps n2 2
alps servlim 20
!
alps ascu 4B
alps default-ckt CKT3
alps a1-map 63 a2-map 41
alps retry-option re-send
alps max-msg-length 1960
alps error-display 6d 78
alps enable-ascu
alps ascu 66 
alps default-ckt CKT2 
alps a1-map 40 a2-map 21
alps max-msg-length 3800
alps error-display 6d 78
alps enable-ascu

Central CPE Configuration (Main) Example

AX.25 Host
alps local-peer 172.22.0.91 promiscuous
interface serial 0
encapsulation x25 ax25
x25 ltc 1600
alps host-hld 4B10 host-link 3 ax25
EMTOX Host
alps local-peer 172.22.0.91 promiscuous
interface serial 0
encapsulation x25
alps host-hld 4B20 host-link 3 emtox 1114235
alps translate 88845* 172.22.0.90

Central CPE Configuration (Backup) Example

AX.25 Host
alps local-peer 172.22.0.92 promiscuous
interface serial 0
encapsulation x25 ax25
x25 ltc 1600
alps host-hld 4B10 host-link 3 ax25 nonstd-ps 240
EMTOX Host
alps local-peer 172.22.0.92 promiscuous
interface serial 0
encapsulation x25 
alps host-hld 4B20 host-link 3 emtox 1114235


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