SS7 Host Link Failure Detection

Overview

The SS7 host link failure detection and handling feature is based on the existing SS7 local host TCP/Ethernet connection feature. The SS7 host link failure detection and handling feature enables the SS7 card to monitor its TCP/Ethernet connection to its local host by checking the messages received from the local host. If the SS7 card has not received any message from its local host for a certain amount of time, the SS7 card will assume a host link failure has occurred. SCCP/TCAP uses an SS7- to-host Ethernet connection to communicate with a application.

When a single card (or both of a redundant pair of SS7 cards) detects a host link failure, the SS7 card can take the corresponding subsystem out-of-service, abort TCAP transactions, and update the SS7 network with the subsystem out-of-service condition. This will prevent the SCCP/TCAP module from receiving new TCAP transactions from the network when the SS7 card cannot deliver messages to the host application.

The SCCP/TCAP subsystem out-of-service procedure also applies for those subsystems on the matrix host when the matrix host link fails.

This feature is supported for both the SS7 PQ card and SS7 HP Series 3 card.

Poll Messages

Polling has to be enabled to enable host link failure detection. See SS7 Polling and Host Link Failure.

API Messages Used for this Feature

The following APIs, listed in alphabetical order, support the host link failure detection feature for SS7 cards. The format of only three of the messages have been modified to support the feature; they are: Poll (0xAB), System Configuration (0xAF), and System Configuration Query (0xB4). For more details, see the API Reference.

• Alarm (0xB9)

A minor card alarm type, Host link Error, is used to report the receiving host message timeout for the SS7 card. A major card alarm type Host Link Failure is used to report that the SS7 detects a host link failure after four polls.

If the SS7 card does not receive any message from its local host, a minor alarm is sent to the matrix host. The relevant data is:

If the SS7 card detects a host link failure to its local host, a major alarm is sent to the matrix host. The relevant data is:

• Alarm Cleared (0xC1)

If the SS7 card receives a local host message before the host link failure timer expires, an Alarm Cleared for the minor alarm is sent to the matrix host. The relevant data is:

If the SS7 card detects that the local host link recovers, an Alarm Cleared for the major alarm is sent to the matrix host. The relevant data is:

• Poll (0xAB)

The SS7 card supports sending this message to its local host. The third least significant bit of the Card Status field indicates whether the link is up between the mate SS7 card and the local host, and whether the mate SS7 card is receiving messages from the host. The default value is 1, which specifies that host link failure detection is not enabled.

• Poll Interval Configuration (0x9F)

The format of this message does not change. The host send this message directly to the SS7 card through the local host. The SS7 card processes this message from the SS7 local host. The poll interval can be user-defined within a range of valid values: 0-25 seconds. The default value is 2 seconds. The SS7 card stops polling if the interval timer is 0.

• Poll Request (0x9E)

The format of this message does not change. The host sends this message to the SS7 card from the SS7 direct connection. The SS7 card processes this message from the SS7 local host, and initiates polling after receiving this message. Note: The host can re-initiate by default after the SS7 card sends a poll to the local host.

• PPL Event Indication (0x43)

- The format of this message does not change. An SCCP N-State indication is not sent to the host when a host link failure occurs. Normally, when SCCP takes subsystems out-of-service, an N-State is sent to the host.

- A TCAP TC-U-Abort indication is reported in the PPL Event Indication message. Typically when a TCAP restart is initiated, the host will receive a TC-U-Abort for the aborted TCAP transactions. Note that in the case HLF, no TC-U-Abort indications are sent to the host.

• PPL Event Request (0x44)

- The format of this message does not change. After an SS7 card has recovered from a host link failure, SCCP brings those subsystems in-service that were configured in-service before the host link failure occurred.

• System Configuration (0xAF)

The Matrix Controller card already supports this message to enable/disable host link failure detection. The meaning of the Response to Host link failure field has been extended to allow configuring whether to take a SCCP/TCAP subsystem out-of-service when a host link failure occurs.

This message now supports the SS7 card. When the Slot AIB is used for an SS7 card, an internal message is sent from the Matrix Controller card to the SS7 card to enable/disable the SS7 local host link failure detection feature, as well as, configure the host link failure detection timer for the SS7 card.

• System Configuration Query (0xB4)

The matrix already supports this message. Changes to this message reflect changes to the System Configuration message.

Configuration Byte

Use configuration byte, 0x03, of the PPL component TCAP TUSI (0x70), to configure whether to initiate the TCAP restart procedure when a subsystem is out-of-service. See TCAP TUSI (0x0070).