Performing COT Test

When you finish an SS7 installation and bring the signaling/CICS active, depending on the telco involved, they may be required to perform testing on the bearer channels before doing any call testing (since the signaling path is different than the bearer path).  This testing is what is called a  COT test.

COT testing is a diagnostic procedure that is performed to ensure that circuits are in service and without excessive loss (ITU Q704 Section 1.4.X).

This is done by having the originator of the  COT test send tones across the bearer channel (i.e. the CICS)

A  COT test can be initiated as either an IAM message or CCR message (Continuity Check Request).

The two different types of  COT are:

Loopback -The destination is put into loopback mode.  In this case, when the telco performs a  COT test it sends a 2010 Hz tone down the line, lands at NSG which is looped back, which sends back to the telco the same 2010 Hz tone. This type is used on 4-wire trunks

Transponder Mode - The originator of the  COT test will send a 2010 Hz tone down the bearer channel, where the destination (ie. NSG, if telco sends  COT) will respond with a 1780 Hz frequency tone.

If a  COT test fails, the originator will receive errors/alarms.

When working with ITU SS7, there are no preparation procedures required, but to simply watch telco perform COT test

When working with ANSI SS7 Networks, if the telco is required to perform  COT tests (they will tell you), we must enable 'loopback mode' in NSG configuration.

To do this, toggle the " Loop Back Acknowledge COT/CCR Request", found under " Advanced Options" under  Channel configuration

If the telco's  COT test is successful, in a wireshark trace, you will see the Telco sending a CCR message to NSG, where NSG replies with LPA (Loop back acknowledge).

Following that you will see further Release and unblock messages, along with respective acks for that CIC.

Below is an example of Telco performing a  COT test for CIC 2001 (ANSI)

Feature Update:

Up until today (august 12 2015) NSG only supported receiving of  COT tests, however, R&D have now enabled ability for NSG to also initiate  COT tests.

If telco requires us (NSG) to initiate a  COT test, use the below nsg_cli commands 

->  ftdm ss7 cot span X chan Y

->  ftdm ss7 ccr span X chan Y

Use the first command for ITU installations

Use the second command for ANSI installation.

If you take a wirshark trace when initiating a  COT test from NSG, you will see the same messages, but in the reverse direction.