How to analyze an SS7 ISUP Trace

Owned by Kelli Higdon
Last updated: Mar 01, 2024
4 min read

 

Introduction:

The Dialogic IMG 1010 Integrated Media Gateway, the Dialogic IMG 1004 Integrated Media Gateway and the Dialogic IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic BorderNetâ„¢ 2020 Session Border Controller support Call Tracing, which allows a user to view various items of information on a per call basis. With the IMG 1010 and IMG 1004, the call trace is saved to a log file in the following directory in the Dialogic Gate Control Element Management System (GCEMS) server: opt/dialogic/common/calltracing (Software 10.5.1+). With the IMG 2020, the call trace is saved to a file at the location specified in the Call Trace object in the WebUI.

Call Trace log files have the following naming convention: syslog_<ChassisSerialNumber>_<YYMMDD>_.log

A Call Trace log includes information such as:
- Call Leg Information
- Call ID Information
- Call Duration
- RTCP Stats
- Codec Information
- Routing Information

This article describes how to analyze an SS7 ISUP trace in an IMG call tracing log.
For information on how to convert a call trace file to a pcap file that can be viewed in Wireshark please refer to the following article:
How to view ISDN & SS7 traces using Wireshark 

Sample Call Flow:

This example uses this sample IMG call tracing log, . 

This is a call from SIP to SS7; the call flow is as follows:

Click on the following image to view it full-size:



Analyzing the SS7 ISUP (ITU) traces : 

Note: Detailed ISUP message decoding is available in this Wireshark file, .

1. IMG sent ISUP Initial Address Message (IAM) to PSTN

11:42:38.284 CALL(SS7) (01:00002:01)
SENT: STK: 2 PRI: 00
DPC: 0-34-1 OPC: 0-35-1
SLS: 0x3d CIC: 00061 (0x003d)
IAM [0048000a03020907031047172653000a070310058826030000]
11:42:38.284 CALL(SS7) (01:00002:01) SENT IAM to (0x119:0x111:61)

This IAM message was sent on SS7 Stack id (2) to DPC: 0-34-1 (0x111) CIC: 61 (0x3d), IMG's OPC is 0-35-1 (0x119).

The ISUP parameters, including the mandatory fixed part, the mandatory variable part and the optional part, are listed between square brackets. 

The IAM ISUP parameters are decoded as follows:

Click on the following image to view it full-size:

Note: More IAM ISUP parameters decoding are included in the Wireshark file isup-itu.pcap, .
 
2. IMG received an ISUP Address Complete Message (ACM) from PSTN
 

11:42:38.644 CALL(SS7) (01:00002:01)

RCVD: STK: 2 PRI: 00

DPC: 0-35-1 OPC: 0-34-1

SLS: 0x0d CIC: 00061 (0x003d)

ACM [000400]

11:42:38.644 CALL(SS7) (01:00002:01) RCVD ACM from (0x111:0x119:61)


This ACM was received on SS7 Stack id (2) from the PSTN, which has OPC: 0-34-1 (0x111), CIC: 61 (0x3d), IMG is its DPC 0-35-1 (0x119)
 
The ACM parameter is decoded as follows:

Click on the following image to display it full-size:

3. IMG received an ISUP Answer Message (ANM) from PSTN 

11:42:39.874 CALL(SS7) (01:00002:01)

RCVD: STK: 2 PRI: 00

DPC: 0-35-1 OPC: 0-34-1

SLS: 0x0d CIC: 00061 (0x003d)

ANM [00]

11:42:39.874 CALL(SS7) (01:00002:01) RCVD ANM from (0x111:0x119:61)


This ANM was received on SS7 Stack id (2) from PSTN, which has OPC: 0-34-1 (0x111), CIC: 61 (0x3d), IMG is its DPC 0-35-1 (0x119)

There are no ISUP parameters in this ANM message.

4. IMG sent an ISUP Release Message (REL) to PSTN 

11:42:58.514 CALL(SS7) (01:00002:01)

SENT: STK: 2 PRI: 00

DPC: 0-34-1 OPC: 0-35-1

SLS: 0x3d CIC: 00061 (0x003d)

REL [0200028090]

11:42:58.514 CALL(SS7) (01:00002:01) SENT REL cause 16 to (0x119:0x111:61)


This REL message was sent on SS7 Stack id (2) to DPC: 0-34-1 (0x111) CIC: 61 (0x3d), IMG's OPC 0-35-1 (0x119).
 
The REL parameter is decoded as follows:

Click on the following image to display it full-size:

5. IMG received an ISUP Release Complete Message (RLC) from PSTN 

11:42:58.574 CALL(SS7) (01:00002:01)

RCVD: STK: 2 PRI: 00

DPC: 0-35-1 OPC: 0-34-1

SLS: 0x0d CIC: 00061 (0x003d)

RLC [00]

11:42:58.574 CALL(SS7) (01:00002:01) RCVD RLC from (0x111:0x119:61)


This RLC was received on SS7 Stack id (2) from PSTN, which has OPC: 0-34-1 (0x111), CIC: 61 (0x3d), IMG is its DPC 0-35-1 (0x119)

There are no ISUP parameters in this RLC message.


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 BorderNetâ„¢ 2020 Session Border Controller

 

Glossary of Acronyms / Terms

ISUP - ISDN User Part
ISUP CIC - Circuit Identification Code
IAM - Initial Address Message
ACM - Address Complete Message
ANM - Answer Message
REL - Release Message
RLC - Release Complete

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