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In case of Radio Access Protocol of Cellular Technology, usually (practically for every technology), 3GPP/3GPP2 specfication comes first and then real UE comes out and those UE should be tested based on 3GPP/3GPP2 before it hits market. However, in case of IMS we didn't have any official 3GPP specification for severa years after various UEs came out with its own IMS implementation. Based on my experience, I think I saw UEs with early IMS implementation since early 2012 but the initial 3GPP IMS specification came out around mid 2016 (Ref 12) and I think the wide range implementation of conformance system was out early/mid 2017(Ref 13). Before the 3GPP conformace, most of the IMS implementation was based on RFC specification. As you may know, RFC specification is not as clearly described as 3GPP (at least to me) and it allows wide range of variations by the specification itself. This had been causing a lot of issues in terms of testing, because there are many cases where test equipment implemented a feature in a certain way described in RFC and UE implmented the same feature in a slightly different way that is also allowed in RFC. In this case, even though we get some test that failed we couldn't blame the equipment or UE since both of them might be correctly implemented in terms of RFC point of view. Anyway, now we have clearer common specification and hope our life as an engineer would go a little bit easier :)

 

In this page, I will write things about 3GPP test specification for IMS, but I would not describe on each and every test cases in the specification. It is not possible and not meaningful either. What I am trying to do in this page is just to give you some high level guidelines about the specification and some tips on how to navigate through the specifications to understand the details about the test case and hope to help with troubleshooting as well.

 

 

 

Specification to look into

 

Specifiction

Comments

34.229-1

This is the main document that specifies all the IMS test case procedure. If you are involved in IMS conformance testing, this is the document you should look into everyday.

34.229-2

This is a kind of supplimentary document for 34.229-1. This documents would specifies the detailed condition for test verdict and related PIXIT parameters. You would see various tables which are very dry, boring, confusing. But you should learn how to interpret these tables in your own live understanding for the detailed troubleshooting.

34.229-3

This is a kind of high level architecture document for IMS stack. You would not look into this document very often, but I would suggest you to go through this to get some big picture of IMS stack implementation.

36.523-1

As you may know, this is not the main document for IMS testing. It is mainly for protocols for radio access protocol stack. But there are some IMS feature that requires tight interplay with radio access protocol such as SRVCC, IMS SMS over SG, IMS Emergency Call, eCall over IMS etc.

 

 

 

Test Case Framework

 

Followings are the brief summary of each chapter in IMS Conformance test specified in 34.229-1 at the level of each chapter.

 

Test Case Group

Description

6. PDP Context Activation

  As you know, IMS is a type of communication going on through IP layer. So before initiating any IMS related procedure, it should be guaranteed that the PDP with required information(e.g, UE IP allocation and server IP information etc) should be completed first. In LTE, this procedure is done by PDN Connectity Procedure and in WCDMA this procedure is done by PDP Activation procedure. In 34.229-1 the test procedure is described in terms of PDP Activation procedure, but the real sequence and message would vary a little bit depending on whether it is for UMTS, LTE or ePDG etc. See here, here and here for overall procedure and look into 34.229-1 section 6 for the conformance specific parameters.

7. P-CSCF Discovery

 

This is to test the procedure of how UE get the information for P-CSCF(i.e, IP address of P-CSCF). Usually this procedure is done at the same time of PDP Context Activation through a specific Information element in the message. This procedure also varies a little bit depending on what kind of radion access the UE use. For high level description, see here and look into 34.229-1 section 7 for the conformance specific parameters.

8 Registration

 

This is to check whether UE can complete the very basic IMS registration with the proper IP and CSCF allocated by section 6 and 7. For high level description, see (Registration + Subscription) and look into 34.229-1 section 8 for the conformance specific parameters

9. Authentication
 

This is the abnormal case (negative test) test for Athentication process.  Basic idea is to see how UE react when the CSCF responds with an invalid AKAv1-MD5 authentication challenge with an invalid MAC value. Would UE accept it without any complain ? or try additional request to get the valid information.

10. Subscription
 

This is the abnormal case(negative test) test for SUBSCRIBE message. Basic idea is to see how UE react when it gets 503 Service Unavailable.  

11. Notification
  This is to verify that UE do propfer behavior when it gets NOTIFY message with a certain event state attribute or even attributes.
12. Call Control
  This is to test how UE respond to a certain error message (503, 504), to verify with Precondition and Codecs (AMR, AMR-WB, EVS etc)
13. Signaling Compression (SigComp)
  This is to verify that UE preforms the required procedure when SigComp is enabled.
14. Emergency Service
  VOID as of v14.02
15. Supplimentary Service
 

This is to test Supplimentary Service such as OIP, OIR, TIP, TIR, Communication Forwarding, Call Hod, Communication Barring, MWI, Conference Call, Communication Waiting, GBA Authentication.

16. Codec Selecting
  This is to test on Codec selection for AMR, AMR-WB with all codec modes and selective codec modes
17. Media Use Case
  This is to test whether UE can add and remove Video Call while in Voice Call
18. SMS Over IMS
  It as said in the title, i.e, to test whether UE can successfully send and receive SMS using IMS.
19. Emergency Service over IMS
  Is as said in the title, i.e, to test whether UE can perform Emergency Call with IMS (PSAP)

20. Customized Alerting Tones (CAT)

  This is to test on Early Media/Ring back tone.
21. eCall Over IMS