You are here: CSP Developer’s Guide: Common Channel Signaling > 8 ISDN > ISDN Redundancy

ISDN Redundancy

Overview

The ISDN PRI Redundant I/O card used with two ISDN PRI cards, or two ISDN Series 3 cards used with two CCS Series 3 I/O cards, provide complete redundancy by enabling all 32 D channels on a card to be replicated on a standby card. You configure redundancy by using the CCS Redundancy Configure message to designate one ISDN card as primary (active) and the other as secondary (standby) prior to configuring the D channels.

A mirror image of the active card’s primary and secondary D channels is copied to the standby card. If the active card fails or you remove it, the standby card takes over and manages call processing. All calls in a connected state are retained while others are purged. If you reset the active card, it switches over to standby.

Configuration

To configure card redundancy, you must designate one ISDN card as primary and the other as secondary. The primary card attempts to become active. You refer to the primary slot number for all subsequent configuration.

Once redundancy is configured and the primary card becomes active, you should refer to the primary slot number only in subsequent configuration messages (D Channel Assign, PPL Audit Configure, PPL Audit Query).

You designate primary and secondary cards by sending the CCS Redundancy Configure message prior to assigning the D channels and completing the rest of a normal configuration.

The prerequisites for using this message are:

• Both ISDN cards (primary and secondary) must be in adjacent slots.

• Both ISDN cards must be in service.

• The ISDN Redundant I/O card must be installed in the appropriate slots, opposite the ISDN cards, in the back of the chassis.

• For each ISDN Series 3 card, you must use a single slot CCS I/O Series 3 card. The two adjacent CCS I/O Series 3 cards are linked with a CCS I/O Series 3 Redundancy Link cable.

After you send the message and a positive acknowledge (ACK) response is returned to the host, the primary card is placed in active mode and the secondary is placed in standby mode. All database information on the active card, including configuration data and active calls, is copied to the standby card. This process enables both the active and standby cards to manage the same information and input.

Important! Dialogic recommends that you send the CCS Redundancy Configure message after resetting the configuration on the whole system. The synchronization of databases on the cards involves intensive processing, so you should send the message when there is little or no call activity on the system. After you send the CCS Redundancy Configure message, all subsequent configuration is distributed to both cards.

Switchover

The CSP transfers control from the active card to the standby card when any of the following occurs:

• You remove the active card.

• You reset the active card by pushing the reset button.

• The active card malfunctions and forces a reset.

• The active card stops communicating with the Matrix Controller.

• The active card is taken out of service from the host.

• The host sends a Reset Configuration message to the active card.

During an ISDN card switchover, the stable calls remain active and the other calls are purged with the switchover purge code 0x18.

When the standby card becomes active, it takes over the management of the D channels. The host is informed by the CCS Redundancy Report messages and is then responsible for reconfiguring redundancy.

The host uses CCS Redundancy Query messages to track the state of both the primary and secondary cards. The Matrix Controller redundancy manager sends an CCS Redundancy Report message with every transition from one state to another.

The possible states reported are:

• 0x01 - Primary Active, Secondary Synchronizing

• 0x02 - Primary Synchronizing, Secondary Active

• 0x03 - Primary Active, Secondary Standby

• 0x04 - Primary Standby, Secondary Active

States 3 and 4 are stable, and the card pair should be in one of these states most of the time.

Constraint

The CCS Redundancy Configure message will fail if the ISDN card in the secondary slot already has D channels assigned to it. A status of 0xF2 "CCS Redundancy: Not the Primary Slot" returns. Only the ISDN card in the primary slot may have D channels assigned prior to the CCS Redundancy Configure message being sent. The host application must keep track of which ISDN cards currently have D channels assigned.

Scenario

CCS Redundancy is configured with the primary ISDN card in slot 6 and the secondary card in slot 7. The primary ISDN card fails, causing a switchover to the secondary card (and card redundancy to be deconfigured). All ISDN D channels are not assigned to the ISDN card in slot 6.

A new ISDN card eventually replaces the failed primary card in slot 6. If the host wishes to re-assign redundancy, it must issue the CCS Redundancy Configure message with the primary slot set to 7, (the card with the D channels currently assigned), and the secondary slot set to 6 (the newly replaced card). Note that this is the opposite way the cards were originally configured.

Disabling Redundancy

The CSP disables redundancy under the following conditions:

• The primary or secondary ISDN card is removed.

• A dead primary or secondary ISDN card is detected.

• The primary or secondary ISDN card is taken out of service.

• The ISDN Redundant I/O card fails, or the card is removed.

• The CCS I/O Series 3 card fails, or the card is removed.

• A Matrix Controller switchover occurs while the ISDN cards are synchronizing.

• A timeout occurs during synchronization. (The default time limit is 120 seconds.)

Important! When you remove an I/O card, the state of the secondary ISDN card changes from standby to single and all D channels on that card are de-assigned.

Always press the STOP button on the ISDN Series 3 line card in a redundant card pair configuration before removing or inserting the corresponding I/O card.

For example, in a redundant ISDN Series 3 card pair configuration, be aware that the redundant line card may reset when removing or inserting the primary I/O card. If this occurs, the system will lose calls.

You can disable the redundancy configuration from the host by sending the CCS Redundancy Configure message and setting the Secondary Slot field to 0xFF. This action changes the active and standby cards to an independent state and de-activates the D channels on both cards. If you do not configure redundancy when you send the message, the system still returns a positive ACK response.

Reconfiguring Redundancy

If you disable card redundancy by removing one of the cards, the remaining ISDN card processes calls as an independent card.

To activate redundancy after replacing the card, send the CCS Redundancy Configure message and designate the active card as primary and the replaced card as secondary. Dialogic recommends sending this message when the system is idle.

Configuring the re-installed card as the primary card resets all configuration and active call information on the active card.

If a switchover occurs when the cards are in state 3 (primary active, secondary standby) and the active card is reset, the following messages are sent to the host in the order indicated:

1. The Alarm message reports an alarm condition for the active card.

2. The CCS Redundancy Report message reports state 2 (primary synchronizing, secondary active).

3. The CCS Redundancy Report message reports state 4 (primary standby, secondary active).

Querying Redundancy

You can query the redundancy information by sending the CCS Redundancy Query message. The CSP returns the state of the redundant pair and identifies the primary, secondary, and active slots.

If a Matrix Controller switchover occurs while the two ISDN cards are synchronizing and they have not reached the active and standby states, the system resets both cards to the default configuration.

If the cards are already in active and standby states and the Matrix Controller becomes active, the Card Status Report and CCS Redundancy Report messages are sent to the host to indicate the state of the redundant cards.

See Integrated Services Digital Network.
See Common Channel Signaling.
Data channel. One of two fundamental components of an ISDN interface, it provides a path (16Kbps for BRI, 64Kbps for PRI) for carrying control signals and call data in a packet-switched mode.
See Programmable Protocol Language.
Positive acknowledgment to a message