Dialogic Service Center

Service Contracts

Technical Helpweb

Downloads

Contact Support

Developer Forums

Training

Service Center Logon

Downloads

Product pages

For Developers

Resources

Contact Dialogic Support

Other downloads

Useful links

 

Technical Helpweb

Dialogic® Distributed Signaling Interface (DSI) - Signaling and SS7 Products

MTP3 Signalling Link Test (SLT) failure

Symptom:

When attempting to bring a Dialogic® Distributed Signaling Interface (DSI) SS7 link into service, it is possible to bring the link in to service at the MTP2 layer, but the link is taken out of service every 30 seconds with the following indication:

MTP3 event : id=0 MTP_SLT_FAIL

Reason for the issue:

The  'MTP_SLT_FAIL'  message indicates a signalling link test failure.  The most common cause of signalling link test failure is a mismatch in the configuration for the MTP3 links.

When a link is brought in to service at the MTP2 layer, the MTP3 layer starts the 'signalling link test' process: a signalling link test message (SLTM) is sent by MTP3 on the link to the adjacent node. This message contains the normal MTP3 header information, such as the point codes, the signalling link code value for the link (SLC), as well as a test pattern.

When the adjacent node receives the SLTM, it examines the values contained in this message to ensure that they match those configured for the link, including:

 - The Originating Point Code (OPC) and the Destination Point Code (DPC)
 - The SLC value used in the SLTM
 - The SIO value used in the SLTM

If all of these values match those configured at the adjacent node (with the obvious exception that the OPC and DPC are reversed at the other end of the link), then it responds with a Signaling Link Test Acknowledgement (SLTA), sending back the test pattern it received in the original SLTM message.


Solution:

An easy way to compare the values configured at each of the link is to simply compare the configuration set for the link at both ends and look for a mismatch in the values configured for the point codes, SLC and SIO. 

If the configuration data is only available for one of the systems, then MTP3 tracing can be used to gather the missing information.  MTP3 tracing can be switched on by sending the MTP3 Trace Mask Configuration Request Message (MTP_MSG_TRACE_MASK) into MTP3; see the Dialogic DSI MTP3 Programmer’s Manual for further details.

If you are using a Dialogic® Distributed Signaling Interface (DSI) Signaling Server in Signaling Interface Unit (SIU) mode, then MTP3 tracing can be enabled by issuing the CNTMS:MODULE=MTP, ACTIVE=Y; command at the MMI command prompt. Further information can be found in the Dialogic DSI SIU User Manual for the product you are using.

Because both ends of the link perform their own Signalling Link Tests you can compare the information received in the SLTM from the adacent node with your configuration. The SLTM will be sent by MTP3 to MTP2 in an MTP Transfer request message (API_MSG_TX_REQ). Further information on this message can be found in the Dialogic DSI MTP3 Programmer’s Manual.

This is an example SLTM message:

S7L:I0000 T 000002111 M tcf00 i0000 f22 d71 s00 p816400320011f0112233445566778899aabbccddeeff

81 = Service Information octect, broken down as follows:
8 = Sub Service field (SSF)
1 = Service Indicator

64003200 = Label, which consists of:
First 14 bits transmitted = DPC (0x64)
Second 14 bits transmitted = OPC (0xc8)
Last 4 bits transmitted = SLS (0)

1 = Heading Code H1
1 = Heading Code H0
0 = Spare
F = Length Indicator
112233445566778899aabbccddeeff = Test Pattern.
 

Details on the SLT procedure and the associated messages can be found in the ITU specification Q.707, with further information on the SIO and the Label  in ITU specification Q.704.


Glossary of Acronyms / Terms
MTP – Message Transfer Part
SLT – Signalling Link Test
SLTM – Signalling Link Test Message
SLTA – Signalling Link Test Acknowledgement
OPC – Originating Point Code
DPC – Destination Point Code
SSF – Sub-Service Field
SLC – Signalling Link Code





Feedback

Please rate the usefulness of this page:  
0 - not useful at all
1 - potentially useful
2 - quite useful
3 - very useful
4 - exactly the information I needed     

Please enter a comment about this page: