SS7 MTP2-MTP3 Troubleshooting

This article describes SS7 MTP2/MTP3 troubleshooting on the Dialogic Integrated Media Gateways, including the Dialogic IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic BorderNet™ 2020 Session Border Controller.

The procedure describes how to troubleshoot Link ID 0 for SS7 stack ID 0 on an IMG Gateway using the SS7 MTP2/MTP3 diagnostics in the Command Line Interface (CLI) of the device.

Screenshots in this article have been taken from an IMG 1010 but the procedure applies equally to the IMG 2020, though some screens might look different on the IMG 2020.

This procedure should only be used after reviewing the section Troubleshooting: SS7 Signaling Links in the documentation.

Procedure: 

Establish a telnet session (IMG 1010) or ssh session (IMG 2020) to the device. Log in with admin / password (IMG 1010) or dialogic / Dial0gic (IMG 2020).
If the IMG 1010 is using software version 10.5.0 and above, or the device is an IMG 2020, enter the Advanced Debug menu by typing d. When prompted for the username / password, enter admin / password.

For IMG 1010s using software version 10.3.3 or below you will not have to enter the advanced debug menu. 

MTP2 Diagnostics: 

Enter the SS7 diagnostics menu by typing  3 s.

Please click on the following image to view it full-size

Open

 
Now you can enable MTP2 tracing. This will show whether or not messages such as SIO, SIOS, FISU, and MSU are being transferred between both signalling points. In order to enable MTP2 tracing you need to know the Link ID of the link that is currently down or being investigated. This can be found in the SS7 link configuration under the SS7 Stack in ClientView (IMG 1010) or the WebUI (IMG 2020). 

The following image shows MTP2 being enabled for Link ID 0 using the following commands: b (Link ID), 000 being the link ID, which is 3 digits in Hexadecimal. 
In this case no MTP2 messages were received from the terminating signalling point. The IMG Gateway is transmitting SIO and SIOS but is not receiving any messages in return:

Please click on the following image to view it full-size

Open

The following image shows that proper messaging was sent between both SS7 signalling points and the Link came In Service. 

Please click on the following image to view it full-size

MTP2 diagnostics can then be disabled by typing B 000 , again 000 being the Link ID that is currently being investigated. 

MTP3 Diagnostics: 

On some occasions MTP2 messaging is being passed correctly but MTP3 is failing, showing messages such as SLTM and SLTA.

This can be a result of the Network Indicator being configured incorrectly, an SLC mismatch, incorrect point codes or missing SS7 routes, and so on. 

There are 2 ways to enable MTP3 messaging: for a whole SS7 stack or for an individual SS7 link.

If necessary, enter the SS7 diagnostic menu as above by typing 3 s from the home menu. 

To enable MTP3 tracing, enter the command f followed by either the Stack ID or the Link ID. So, to enable MTP3 diagnostics for Link ID 000, you would type f L000.  Or, to enable it for Stack ID 0, you would type f S0 .

To disable MTP3 tracing, type F L000 or F S0.

Please click on the following image to view it full-size
 

The following image shows that MTP3 is failing with the message 'signaling link test failure'.

Please click on the following image to view it full-size
 

To determine the cause of the issue, examine the detail of the messages:

18:11:51.060 MTP3(U) XMT 2/00: SNT 3 2 010203 010204 00 1160000102030405

18:11:51.150 MTP3(U) RCV 2/00: SNT 3 0 010204 010203 01 2161010102030405

^ ^ ^ ^ ^ ^ ^

| | | | | | |

Stack/LinkID MP NI DPC OPC SLC 0x11=SLTM 0x21=SLTA

The first byte labeled MP is the Message Priority. There is a mismatch in the NI (Network Indicator) and the SLC (Signaling Link Code). The values for the NI are mentioned below and the SLCs can be any digit as long as both signalling points are configured the same. This information can be configured on the SS7 Stack object in ClientView (IMG 1010) or the WebUI (IMG 2020).

Please click on the following image to view it full-size

The network indicator codes are allocated as follows: 

bits D C

0 0 (1) International network

0 1 (2) Spare (for international use only)

1 0 (3) National network

1 1 (4) Reserved for national use

The following image shows both MTP2 and MTP3 with the Link ID 00 coming In Service.

Please click on the following image to view it full-size
 

For more information please refer to the IMG Gateway documentation.

IMG 1010 :

IMG 1010 Documentation

IMG 2020:

IMG 2020 Documentation

Product List:

Dialogic IMG 1010 Integrated Media Gateway
Dialogic IMG 1004 Integrated Media Gateway
Dialogic IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic BorderNet™ 2020 Session Border Controller