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Causes of SS7 Signaling Link Problems

Purpose

This section describes common causes that prevent SS7 signaling links from coming into service or alignment.

Point Code Mismatch

The OPC (Originating Point Code) as defined in the SS7 Signaling Stack Configure message must match the value that the distant end signaling point expects. Also, the distant end's point code must match the APC (Adjacent Point Code) and DPC (Destination Point Code) values defined in the SS7 Signaling Link Set Configure message and SS7 Signaling Route Configure message.

Signaling Link Code Mismatch

The Signaling Link Code (SLC) is a number (0-15) which is assigned by both ends to identify a specific link within a link set. The SLC defined in the SS7 Signaling Link Configure message must match the SLC value assigned to the link by the distant end.

Network Indicator Mismatch

The Network Indicator (NI) value is defined by two bits (therefore values 0-3 are possible). The default value of the Network Indicator is set to National (0x02) for both ANSI and ITU. Some networks may require the Network Indicator to be set to International (0x00) or one of the spare values (0x01 or 0x03). To change the NI value, PPL Configure Messages need to be sent to components MTP3 HMRT and MTP3 HMDT. See the API Reference for complete information on configuration byte locations and values.

Link Status Signaling Unit Size Mismatch

By default, the CSP transmit a Link Status Signaling Unit (LSSU) with a 1-octet status field. Some signaling points may require a LSSU size of 2-octet. To change the LSSU size, a PPL Configure Message needs to be sent to component MTP2 TXC. Consult the API Reference for complete information on configuration byte locations and values.

Path and Rate Problem

The span carrying the signaling link must be defined for clear channel operation, in service, and not experiencing slips. Both parties must agree upon the timeslot used to carry the signaling link. Additionally, the data rate of the signaling link must be the same on both sides. The Service State Configure message for signaling links is different than the Service State Configure message used for channels. The signaling link timeslot and data rate are defined in the SS7 Signaling Link Configure message.

No Route Defined

A valid SS7 route must be defined to the destination to enable the CSP to send messages. This is typically indicated by received Signaling Link Testing Message (SLTM) with no SLTMs being sent by the CSP.

See Signaling System Number Seven.
A number that addresses a node in a SS7 network.
The point code of the node adjacent to “own node” (SS7)
Destination Point Code
Link that connects to the same node
American National Standards Institute. ANSI administers and coordinates the U.S. voluntary standardization and conformity assessment system for the
telecommunications industry. More details on these standards may be
viewed at www.ansi.org.
International Telecommunications Union (UN)
See Programmable Protocol Language.
Message Transfer Part level 3 - network level
Message Transfer Part level 2 - data link level
The condition of a component at a given instant. The current "context" of a PPL object, such as Idle, Seizing, Answered. In PPL files, a State is represented by a circle.