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ISUP Continuity Check

Overview

This feature provides the CSP ANSI and ITU SS7 variants with a means to perform a continuity check to verify the integrity of the voice circuit between two exchanges before use of the circuit.

This section provides general information applicable to both ANSI and ITU variants then provides specific information on each as follows:

ITU ISUP Continuity

ANSI ISUP Continuity

Specifications

The requirements for the Continuity Check on the outgoing circuit are provided in the following recommendations for the International Telecommunication Union (ITU):

• ITU-T Q.724

• ITU-T Q.761 Functional Description of the ISDN User Part of Signalling System No. 7

• ITU-T Q.762 General Function of Messages and Signals of the ISDN User Part of Signalling System No. 7

• ITU-T Q.763 Formats and Codes of the ISDN User Part of Signalling System No. 7

• ITU-T Q.764 Signalling System No. 7 - ISDN User Part Signalling Procedures

The requirements for the Continuity Check on the outgoing circuit for the North American variant are provided in the following recommendations:

• ANSI T1.113.4 Signalling System No. 7 (SS7) - Integrated Services Digital Network (ISDN) User Part.

Required DSP Equipment

A Call Progress Tone (CPT) transmitter, and a Call Progress Analysis (CPA) receiver of appropriate PCM encoding are required in order to perform outgoing continuity checks.

Implementation

The ISUP part of the SS7 stack (ANSI and ITU-T) has provisions for a continuity check on the outgoing side of the circuit. A continuity check is initiated with either the Continuity Check Request message to the network side, or the setting of the continuity check indicator bits in the Nature of Connection Indicators mandatory parameter field within the IAM message.

These initial messages allow the network side of the circuit to loop back the chosen circuit, so that continuity testing can be done on that circuit. The CCO component within ISUP executes a continuity test to determine if the circuit to be used has continuity before it is used.

A COT message containing the Continuity Indication is sent to the network side when testing is complete. This indication determines whether continuity exists on the circuit or whether more continuity testing is required.

If a Continuity Recheck procedure is running (CRO for ANSI, CRCS for ITU), outgoing calls on the circuit are rejected with an error code of 0x0A.

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 Signaling System Number Seven.
International Telephone Union – Telecommunications sector (UN)
ITU-TSS Publication on Signaling Procedures (TUP)
ITU-TSS Publication on Functional Description of ISUP
See Integrated Services Digital Network.
ITU-TSS Publication on General Function of Messages and Signals (ISUP)
ITU-TSS Publication on Formats and Codes (ISUP)
ITU-TSS Publication on Signaling Procedures (ISUP)
Digital communications link - voice, data, and video at a 1.544 Mbps rate (24 64 Kbps channels)
ISDN. Network architecture based on digital transmission, switching, and common channel signaling. Basic configurations include 2B+D called a Basic Rate Interface, and 23+D called a Primary Rate Interface. Outside North America, PRI is 30B+D.
Digital Signal Processor
A tone sent to the caller indicating the progress of the call. Examples include dial tone, busy tone, ringback tone, and comfort noise (digital cellular).
See Pulse Code Modulation.
See Integrated Services Digital Network User Part.