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Circuit Validation Test and Response

Overview

This feature provides a method by which the host can request the CSP to send a Circuit Validation Test (CVT) message to the far end and process the Circuit Validation Response (CVR). The circuit validation test procedures follow the recommendations of ANSI-ISUP T1.113.

The CVT and CVR messages are used to test and ascertain the consistency in circuit translation data on both the ends of a circuit, typically during circuit turn-up procedures to make sure that the circuit characteristics match. Maintenance personnel may also execute these tests on a routine basis.

The CVT/CVR procedure may also be invoked when a User Part Unavailable message with a cause value of Remote User Part Inaccessible is received by MTP.

Implementation

To initiate a Circuit Validation Test, send a PPL Event Request of CVT (0x002F) to the L3P CIC component (0x000F). After formatting the CVT message, ISUP passes the message on to the CVT component, which passes it to MTP3, which passes it on to the destination.

The destination node collects the required circuit information and returns a CVR message to the originating CVS component, which sends a PPL event to the host. The table below shows the PPL event sent to the host depending on the CVR contents.

CVR Indicator | Circuit Group Characteristics | CIN Parameters | CLLI Parameters | Indication to Host | PPL Event
--- | --- | --- | --- | --- | ---
Success | Match | Match | Don’t Care | CVT Successful | 0x01
Success | Match | No CIN | Don’t Care | CVT Successful | 0x01
Success | No Match | Match | Don’t Care | CVT Successful | 0x03*
Success | Don’t Care | CIN Mismatch | Don’t Care | CIN Mismatch Indication (near-end and far-end CIN sent to host) | 0x02*
Success | Don’t Care | CIN Not Supported | Don’t Care | CVT successful | 0x01
Failure | Don’t Care | Don’t Care | CLLI Exists | CVT Failure indication with CLLI | 0x05*
Failure | Don’t Care | Don’t Care | CLLI Does Not Exist | CVT Failure indication with no CLLI | 0x04
Failure | Don’t Care | Don’t Care | CLLI Not Supported | CVT Failure indication with no CLLI | 0x04
Local Circuit Translation Unavailable | 0x07
Received CVR Not Processed – Pass Through to Host | 0x08**
CVR Not Received After Maximum CVT Retry | 0x06
* Data passed in Raw SS7 Data Parameters ICB (0x22) ** Data passed in SS7 Unformatted Raw Parameters ICB (0x1F)

PPL Events

The PPL events are sent to the host in the PPL Event Indication message. Event data, if any, is sent in an ICB. The ICB subtype and data for those events that include data are shown below. Events 1, 4, 6, and 7 do not include data.

0x02 | CVT Successful - CIN Mismatch ICB Subtype: SS7 Raw Data Parameters (0x22) Data[0–25] - Local CIN Data[26–51] - Remote CIN
0x03 | CVT Successful - CGC Data Inconsistent ICB Subtype: SS7 Raw Data Parameters (0x22) Data[0] - Remote CGC Parameter Data[1–26] - Local CIN
0x05 | CVT Failure - CLLI Received ICB Subtype: SS7 Raw Data Parameters (0x22) Data[0–10] - Remote CLLI
0x08 | CVR Received - CVR in TLV Format ICB Subtype: Formatted SS7 Parameters (0x12) Data [0] - Message Type [CVR] Data [1] - Number of Parameters Data [2] - CVR Indicator Parameters Code Data [3] - CVR Indicator Length Data [4] - CVR Indicator Value Data [5] - CGC Parameters Code Data [6] - CGC Parameters Length Data [7] - CGC Parameters Value Data [8-n] - Optional Parameters [TLV]

User Part Unavailable Message Handling

A CVT may also be initiated when a User Part Unavailable (UPU) indication is received from the far-end. This is configurable with PPL Configuration Byte 14 of the L3P CIC component.

When a UPU message with an appropriate cause value is received from the far end, a CVT message is sent and timer T37 (typically 30 s) is started. On receipt of a CVR or any other ISUP message, the timer is stopped and normalcy is restored. On expiry of T37 without the receipt of any response from the remote end, the CVT procedure is restarted.

The CVR received from the far end will contain the mandatory Circuit Validation Response indicator and Circuit Group characteristic indicator parameters and may also contain other optional parameters (CLLI and CIN code). CLLI/CIN can be enabled/disabled as required and the CLLI/CIN code parameters are configurable.

On receiving a CVT, a CVR with an appropriate CVR indicator of Pass or Fail is sent, depending on the state of the CIC. The CVR contains the configured Circuit Group Characteristics (CGC) parameter and may also contain the optional CLLI if the test fails or CIN if the test passes. For undefined CICs, no optional parameters are sent.

On receipt of an MTP Status primitive with a cause of User part unavailability – Remote user inaccessible, depending on the configuration, the CVT may be generated automatically. On receipt of a CVR or any other ISUP message, the CVT/CVR procedures are stopped and a PPL Event Indication of 0x04 is sent from SPRC to the host.

Error Condition

When the CVT component sends a CVT message to SPRC it starts a TCVT timer. If a CVR is not received before the expiration of the timer, a second CVT is sent. If the timer expires a second time, the CVT attempt is cancelled and a PPL Event Indication (0x06 - CVR Receive Failed after Re-attempt) is sent to the host.

If a CVT procedure is started with Remote User Part Unavailable, the number of CVT re-attempts is determined by the value in Configuration Byte 8 of the CVS component. The default value is 8. The maximum value is 255.

Customization

Use the PPL Configuration Bytes (using the PPL Configure message) of the CVT and CVR components to modify CVT/CVR configuration. The CIN, CLLI, and circuit group characteristics configuration should be same for a given circuit for both the CVT and CVR components. See SS7 PPL Information for the Configuration Byte values.

Circuit Validation Test Call Flows

CVT to Network/CVR Received from Far-end

CVT to Network/No CVR from Far-end

CVT to Network during Active Call

Remote User Part Unavailable

This call flow shows a CVT sent to the network as a result of a Remote User Part Unavailable indication received from the far-end.

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.
See Integrated Services Digital Network User Part.
Digital communications link - voice, data, and video at a 1.544 Mbps rate (24 64 Kbps channels)
See Message Transfer Part.
See Programmable Protocol Language.
See Circuit Identification Codes.
Message Transfer Part level 3 - network level
In PPL, a condition that, when met, drives a state machine (PPL Component) from one state to another, by invoking an associated Primitive. In PPL files, an Event is marked by an arrow and text.
A computer, attached to the Excel platform through an RS-232 or Ethernet link, from which you run the telecommunications application that controls the Excel platform.
See Signaling System Number Seven.
See Information Control Block.
A condition that, when met, drives a state machine from one state to another. A condition that drives a Component out of its current state by invoking an associated primitive.
Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.