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Home » Eclipse Projects » Eclipse Titan » Decoding NAS PDUs
Decoding NAS PDUs [message #1787575] Tue, 29 May 2018 11:12 Go to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hi,

I am facing an issue in decoding NAS PDUs that are piggybacked in RRC messages in Titan. I believe there is an issue with the codec parametrization for those NAS PDU types but I seem to be unable to figure out the correct settings.

testcase nas_decoding_tests() runs on MTC {
  // connection request original
  var bitstring v_NasPduBitstring := oct2bit('07410108091010000000001002E06000040201D011'O);
	
  log(v_NasPduBitstring);
	
  var NAS_UL_Message_Type v_NAS_UL_Message;
  var NasEmu_DecodedNasPduUL_Type v_DecodedNasPduUL;
    
  if (f_NasEmu_Decvalue(v_NasPduBitstring, v_NAS_UL_Message) != 0) {
      setverdict(fail);
  } else {
    v_DecodedNasPduUL.Msg := v_NAS_UL_Message;
  }  
  log(v_DecodedNasPduUL);
  setverdict(pass);
}



Below are the logs for the test and it seems like the first two nibbles are actually swapped, i.e. the securityHeaderType should be 0000 and the protocolDiscriminator 0111. Any idea how to correctly setup and configure the NAS decoding in Titan?

12:43:15.315968 EncodingTest.ttcn:157 Component type MTC_Component.MTC was initialized.
12:43:15.315998 EncodingTest.ttcn:162 '000001110100000100000001000010000000100100010000000100000000000000000000000000000000000000010000000000101110000001100000000000000000010000000010000000011101000000010001'B
12:43:15.316447 EncodingTest.ttcn:173 { Msg := { aTTACH_COMPLETE := { securityHeaderType := '0111'B, protocolDiscriminator := '0000'B, messageType := '01000001'B, esmMessage := { iei := '01'O, iel := '0809'O ("\b\t"), esmPdu := '1010000000001002E06000040201D011'O } } } }
12:43:15.316526 EncodingTest.ttcn:182 { securityHeaderType := '0000'B, protocolDiscriminator := '0111'B, messageType := <unbound>, esmMessage := <unbound> }


Thanks
Andre
Re: Decoding NAS PDUs [message #1787578 is a reply to message #1787575] Tue, 29 May 2018 11:48 Go to previous messageGo to next message
Gábor Szalai is currently offline Gábor SzalaiFriend
Messages: 26
Registered: December 2015
Junior Member
How the definition of the NAS_UL_Message_Type looks like?
Re: Decoding NAS PDUs [message #1787579 is a reply to message #1787578] Tue, 29 May 2018 11:54 Go to previous messageGo to next message
Gábor Szalai is currently offline Gábor SzalaiFriend
Messages: 26
Registered: December 2015
Junior Member
Just replace the order of the fields in the type definition

The RAW encoder, by default, fills the octets from right to left.
So the first 4 bit fields in the type definition will be in the right side of the first octet, which is the place of the protocol discriminator.
Re: Decoding NAS PDUs [message #1787585 is a reply to message #1787579] Tue, 29 May 2018 15:51 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hey Gabor,

thanks for that but unfortunately reordering the fields in the messages (e.g. ATTACH_ACCEPT , ATTACH_COMPLETE) wont work because all the templates, etc need to be changed there as well. It's probably possible but I'd really like to avoid that effort.. I've tried to attach a "variant "HEXORDER(high)" to NAS_UL_Message_Type/ATTACH_REQUEST etc. but that doesn't seem to work.

Thanks
Andre
Re: Decoding NAS PDUs [message #1787594 is a reply to message #1787585] Tue, 29 May 2018 19:02 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hi again,

just checked the code in NasEmu.ttcn again and saw that f_NasEmu_Decvalue() uses the implicit decoding with decvalue(). Is there any way to parameterize that?

Thanks
Andre
Re: Decoding NAS PDUs [message #1787622 is a reply to message #1787594] Wed, 30 May 2018 08:54 Go to previous messageGo to next message
Gábor Szalai is currently offline Gábor SzalaiFriend
Messages: 26
Registered: December 2015
Junior Member
The HEXORDER is applicable only for hexstring.

Add the following variant to the type definition of the messages:
variant (securityHeaderType, protocolDiscriminator) "FIELDORDER(msb)"

The FIELDORDER(msb) instructs the TITAN to use left to right order of the fields within the bytes. So it will swap the fields within the first byte.
Re: Decoding NAS PDUs [message #1787628 is a reply to message #1787622] Wed, 30 May 2018 09:53 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hi Gabor,

just tried your suggestion but it still doesn't work. Interestingly, the securityHeaderType is decoded fine now but the protocolDiscriminator is also 0000'B instead of 0111'B. I've added a simple testcase to demonstrate the issue [1]. A log is also attached, line #88 is the original PDU as octetstring, #92 in bitstring and #103 the decoded NAS_PDU.

Let me know if you have any other idea to try.

Thanks
Andre

11:34:10.878280 SRSLTE_RLC_Test.ttcn:83 Component type MTC_Component.MTC was initialized.
11:34:10.878292 SRSLTE_RLC_Test.ttcn:88 '07417208991007000000994605F070C040180005025AD011D15C0A003103E5E0349011035758A65D0100C1'O
11:34:10.878345 SRSLTE_RLC_Test.ttcn:92 '00000111010000010111001000001000100110010001000000000111000000000000000000000000100110010100011000000101111100000111000011000000010000000001100000000000000001010000001001011010110100000001000111010001010111000000101000000000001100010000001111100101111000000011010010010000000100010000001101010111010110001010011001011101000000010000000011000001'B
11:34:10.878519 SRSLTE_RLC_Test.ttcn:103 { Msg := { aTTACH_COMPLETE := { securityHeaderType := '0000'B, protocolDiscriminator := '0000'B, messageType := '01000001'B, 




[1] https://github.com/andrepuschmann/ttcn3_rlc
Re: Decoding NAS PDUs [message #1787630 is a reply to message #1787628] Wed, 30 May 2018 10:04 Go to previous messageGo to next message
Gábor Szalai is currently offline Gábor SzalaiFriend
Messages: 26
Registered: December 2015
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Where is the type definition of the NAS?
Re: Decoding NAS PDUs [message #1787836 is a reply to message #1787630] Wed, 30 May 2018 14:18 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
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Hi Gabor,

the type of the message is defined in the 3gpp testsuite. I am a bit unsure as to whether I am supposed to reproduce that code in some github repo or not and therefore decided to only make the patch available. For that to compile you would need to follow the instructions in ue_testcases/README, download the testsuite from the ETSI ftp servers and apply the patch thereafter. If you are experiencing difficulties just let me know and I provide you an alternative approach.

Thanks
Andre
Re: Decoding NAS PDUs [message #1788104 is a reply to message #1787836] Wed, 30 May 2018 15:45 Go to previous messageGo to next message
Gábor Szalai is currently offline Gábor SzalaiFriend
Messages: 26
Registered: December 2015
Junior Member
OK, I'm going to play with it.
Re: Decoding NAS PDUs [message #1790119 is a reply to message #1788104] Tue, 05 June 2018 13:00 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
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Hey Gabor,

I was just wondering if you had a chance to look into the NAS decoding issue?

Thanks
Andre
Re: Decoding NAS PDUs [message #1790156 is a reply to message #1790119] Wed, 06 June 2018 08:59 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

sorry , Gabor is caught up in an urgent matter.
We are looking into this;let me come back to you.


BR

Elemer
Re: Decoding NAS PDUs [message #1790157 is a reply to message #1790156] Wed, 06 June 2018 09:01 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
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Hey Gabor, Elemer,

no worries and thanks for the update.

Looking to hearing back
Andre
Re: Decoding NAS PDUs [message #1790329 is a reply to message #1790157] Fri, 08 June 2018 11:50 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

could you do a 'make archive' on the project that contains

testcase nas_decoding_tests()

Please verify that the archive is compileable by unzipping it and running make.
If not , add whatever is missing to the Makefile, OTHER_FILES


And upload it here.

If for any reason you'd prefer not to upload, PM me on Twitter

https://twitter.com/jrama00

so we can find another solution.


BR

Elemer








Re: Decoding NAS PDUs [message #1790432 is a reply to message #1790329] Sun, 10 June 2018 20:10 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
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Hi Elemer,

thanks for looking into it. I've prepared the package and uploaded it to private webspace. Do you have a mail address you prefer?

Thanks
Andre
Re: Decoding NAS PDUs [message #1790438 is a reply to message #1790432] Mon, 11 June 2018 06:48 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

thanks; I don't want to make my e-mail public , so if you message me up on Linkedin or Twitter I'll send it to you.

Best regards
Elemer


Re: Decoding NAS PDUs [message #1790441 is a reply to message #1790438] Mon, 11 June 2018 07:16 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
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Hi,

no worries. Just did the same.

Thanks
Andre
Re: Decoding NAS PDUs [message #1790448 is a reply to message #1790438] Mon, 11 June 2018 09:20 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
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Hi,

to add to this, I just learned that there is a NAS testsuite available from ETSI [1]. I wasn't aware of that. Has anybody used this before? Can it be coupled with the UE testsuite in anyform to perform the NAS decoding?

Thanks
Andre



[1] http://oldforge.etsi.org/websvn/listing.php?repname=Evolved+Packet+Core.NAS



Re: Decoding NAS PDUs [message #1790511 is a reply to message #1790448] Tue, 12 June 2018 07:59 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre ,


this module has an assumed codec that is not part of the package; it's referred as below:

module LibNAS_TypesAndValues {
.
.
.
} with {
    encode "LibNAS"
}// End of module LibNAS_TypesAndValues


It can be coupled with the UE test suite but it has to be decorated with Titan -specific RAW codec instructions , which is probably more work than writing the TTCN-3 code from scratch.

I will publish soon some NAS protocol modules that use RAW encoding and have been tested with Titan.

We have several versions, maybe you could tell me which is the one you are aiming for so I can publish the closest.


Best regards
Elemer







Re: Decoding NAS PDUs [message #1790612 is a reply to message #1790511] Wed, 13 June 2018 14:54 Go to previous messageGo to next message
Botond Baranyi is currently offline Botond BaranyiFriend
Messages: 11
Registered: February 2016
Junior Member
Hi Andre,

the problem with the way you used the variant 'FIELDORDER(msb)' is that the field type 'ATTACH_COMPLETE.protocolDiscriminator' uses the user-defined codec 'NAS Types', not the RAW codec, because it has no 'encode' attribute of its own, and the referenced type's (ProtocolDiscriminator) encode "NAS Types" attribute takes precedence over the parent type's (ATTACH_COMPLETE) encode "RAW".
This means that the variant is treated as a user-defined encoding variant, not a RAW encoding variant, and is thus ignored by the compiler (there is even a warning displayed that it will be ignored).

To fix this you need to explicitly set the field's encoding to RAW, like this:

type record ATTACH_COMPLETE { 
...
} with {
  encode (protocolDiscriminator) "RAW";
  variant (securityHeaderType, protocolDiscriminator) "FIELDORDER(msb)"
};



I've also noticed that the test case (nas_decoding_tests) expects the chosen field in the union to be 'aTTACH_REQUEST', but the chosen field after decoding is 'aTTACH_COMPLETE'. This is because the union has no variant attributes, so it has to pass the given data to every field (in the order of their declaration), and the first one to successfully decode it will be the chosen one (in this case 'aTTACH_COMPLETE' successfully decodes the data, so it becomes the chosen field, before decoding it as 'aTTACH_REQUEST' is even attempted).
I'm not familiar with this protocol, but I've noticed that all of the union's fields are records that start with the same 3 fields ('securityHeaderType', 'protocolDiscriminator' and 'messageType'). If the chosen field in the union depends on the values of these fields, then the 3 fields could be moved to a new top-level record, whose 4th field is the union, and the union could be given a 'CROSSTAG' variant attribute (to determine which union field to choose based on the 3 fields).

For example:

type record NAS_UL_Message_Type {
  SecurityHeaderType securityHeaderType,
  ProtocolDiscriminator protocolDiscriminator,
  MessageType messageType,
  NAS_UL_Message_Choice choice
}
with {
  variant (choice) "CROSSTAG(aTTACH_COMPLETE, protocolDiscriminator = '0000'B;
                             aTTACH_REQUEST, protocolDiscriminator = '0001'B;
                             ...
                             )"
}

type union NAS_UL_Message_Choice {
  ATTACH_COMPLETE aTTACH_COMPLETE,
  ATTACH_REQUEST aTTACH_REQUEST,
  ...
}


Hope this helps.
Best regards,
Botond Baranyi

[Updated on: Wed, 13 June 2018 15:43]

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Re: Decoding NAS PDUs [message #1791003 is a reply to message #1790612] Thu, 21 June 2018 10:38 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hey Botond, all,

sorry for the delay and thanks for looking into the issue. I've now played around following your suggestions but still can't decode it properly with the built-in types.

I've followed your suggestions and decorated all union members (that have the fields) with:
type record ATTACH_COMPLETE { 
...
} with {
  encode (protocolDiscriminator) "RAW";
  variant (securityHeaderType, protocolDiscriminator) "FIELDORDER(msb)"
};


That seemed to have worked ok and the fields are extracted ok (although the wrong type is selected).

12:27:57.444458 NAS_Codec_Test.ttcn:37 dec_3GPP_PDU_NAS_EPS(): Stream before decoding: '07417208991007000000994605F070C040180005025AD011D15C0A003103E5E0349011035758A65D0100C1'O
12:27:57.444484 NAS_Codec_Test.ttcn:37 dec_3GPP_PDU_NAS_EPS(): Decoded @EPS_NAS_MsgContainers.NAS_UL_Message_Type: { aTTACH_COMPLETE := { securityHeaderType := '0000'B, protocolDiscriminator := '0111'B, messageType := '01000001'B, esmMessage := { iei := '72'O ("r"), iel := '0899'O, esmPdu := '1007000000994605F070C040180005025AD011D15C0A003103E5E0349011035758A65D0100C1'O } } }
12:27:57.444507 NAS_Codec_Test.ttcn:38 { aTTACH_COMPLETE := { securityHeaderType := '0000'B, protocolDiscriminator := '0111'B, messageType := '01000001'B, esmMessage := { iei := '72'O ("r"), iel := '0899'O, esmPdu := '1007000000994605F070C040180005025AD011D15C0A003103E5E0349011035758A65D0100C1'O } } }
12:27:57.444546 NAS_Codec_Test.ttcn:49 { Msg := { aTTACH_COMPLETE := { securityHeaderType := '0000'B, protocolDiscriminator := '0111'B, messageType := '01000001'B, esmMessage := { iei := '72'O ("r"), iel := '0899'O, esmPdu := '1007000000994605F070C040180005025AD011D15C0A003103E5E0349011035758A65D0100C1'O } } } }


Your second suggestions, i.e. putting securityHeaderType, protocolDiscriminator and messageType into the parent record wont work for two reasons. First, not all NAS_UL_Message's have them (98% do but not all) and second because I'd really like to keep the types as much as possible like they are because each change also requires changes in the ETSI code which I'd like to avoid as much as possible.

Anyway, I've now carried on and decorated the NAS_UL_Message_Type union with the tag specifier like this (so messageType:='01000001'B shall decode to ATTACH_REQUEST).

  type union NAS_UL_Message_Type {                                              /* NAS message with direction 'UE to network ' or 'both' */
    ATTACH_COMPLETE                                     aTTACH_COMPLETE,
    ATTACH_REQUEST                                      aTTACH_REQUEST,

    AUTHENTICATION_FAILURE                              aUTHENTICATION_FAILURE,
    AUTHENTICATION_RESPONSE                             aUTHENTICATION_RESPONSE,

    DETACH_ACCEPT                                       dETACH_ACCEPT, /* direction: both */
    DETACH_REQUEST_MO                                   dETACH_REQUEST_MO,

    EMM_STATUS                                          eMM_STATUS, /* direction: both */

    EXT_SERVICE_REQUEST                                 eXT_SERVICE_REQUEST,

    GUTI_REALLOCATION_COMPLETE                          gUTI_REALLOCATION_COMPLETE,

    IDENTITY_RESPONSE                                   iDENTITY_RESPONSE,

    SECURITY_MODE_COMPLETE                              sECURITY_MODE_COMPLETE,
    SECURITY_MODE_REJECT                                sECURITY_MODE_REJECT,

    SECURITY_PROTECTED_NAS_MESSAGE                      sECURITY_PROTECTED_NAS_MESSAGE,

    SERVICE_REQUEST                                     sERVICE_REQUEST,

    TRACKING_AREA_UPDATE_COMPLETE                       tRACKING_AREA_UPDATE_COMPLETE,
    TRACKING_AREA_UPDATE_REQUEST                        tRACKING_AREA_UPDATE_REQUEST,

    UL_NAS_TRANSPORT                                    ul_NAS_TRANSPORT,

    ACTIVATE_DEDICATED_EPS_BEARER_CONTEXT_ACCEPT        aCTIVATE_DEDICATED_EPS_BEARER_CONTEXT_ACCEPT,
    ACTIVATE_DEDICATED_EPS_BEARER_CONTEXT_REJECT        aCTIVATE_DEDICATED_EPS_BEARER_CONTEXT_REJECT,

    ACTIVATE_DEFAULT_EPS_BEARER_CONTEXT_ACCEPT          aCTIVATE_DEFAULT_EPS_BEARER_CONTEXT_ACCEPT,
    ACTIVATE_DEFAULT_EPS_BEARER_CONTEXT_REJECT          aCTIVATE_DEFAULT_EPS_BEARER_CONTEXT_REJECT,

    BEARER_RESOURCE_ALLOCATION_REQUEST                  bEARER_RESOURCE_ALLOCATION_REQUEST,
    BEARER_RESOURCE_MODIFICATION_REQUEST                bEARER_RESOURCE_MODIFICATION_REQUEST,

    DEACTIVATE_EPS_BEARER_CONTEXT_ACCEPT                dEACTIVATE_EPS_BEARER_CONTEXT_ACCEPT,

    ESM_INFORMATION_RESPONSE                            eSM_INFORMATION_RESPONSE,

    ESM_STATUS                                          eSM_STATUS, /* direction: both */

    MODIFY_EPS_BEARER_CONTEXT_ACCEPT                    mODIFY_EPS_BEARER_CONTEXT_ACCEPT,
    MODIFY_EPS_BEARER_CONTEXT_REJECT                    mODIFY_EPS_BEARER_CONTEXT_REJECT,

    PDN_CONNECTIVITY_REQUEST                            pDN_CONNECTIVITY_REQUEST,

    PDN_DISCONNECT_REQUEST                              pDN_DISCONNECT_REQUEST,

    ACTIVATE_TEST_MODE_COMPLETE                      aCTIVATE_TEST_MODE_COMPLETE,
    DEACTIVATE_TEST_MODE_COMPLETE                    dEACTIVATE_TEST_MODE_COMPLETE,

    CLOSE_UE_TEST_LOOP_COMPLETE                         cLOSE_UE_TEST_LOOP_COMPLETE,
    OPEN_UE_TEST_LOOP_COMPLETE                          oPEN_UE_TEST_LOOP_COMPLETE
  } with {
    variant "TAG(
    sERVICE_REQUEST, 								securityHeaderType= '1100'B; 
  	sERVICE_REQUEST,                				securityHeaderType= '1101'B;  
  	sERVICE_REQUEST,                   	  		    securityHeaderType= '1110'B;  
  	sERVICE_REQUEST,          				        securityHeaderType= '1111'B;  
    sECURITY_PROTECTED_NAS_MESSAGE,					securityHeaderType= '0001'B;
    sECURITY_PROTECTED_NAS_MESSAGE,   				securityHeaderType= '0010'B;
    sECURITY_PROTECTED_NAS_MESSAGE,    				securityHeaderType= '0011'B;
    sECURITY_PROTECTED_NAS_MESSAGE,    				securityHeaderType= '0100'B; 
    sECURITY_PROTECTED_NAS_MESSAGE,    				securityHeaderType= '0101'B;
    aTTACH_COMPLETE, 								messageType = '01000011'B;
	aTTACH_REQUEST, 								messageType = '01000001'B;
    aUTHENTICATION_FAILURE, 						messageType = '01011100'B;
	aUTHENTICATION_RESPONSE, 						messageType = '01010011'B;
 	dETACH_ACCEPT,  								messageType = '01000110'B;
	dETACH_REQUEST_MO, 								messageType = '01000101'B;
	eMM_STATUS, 									messageType = '01100000'B;
	eXT_SERVICE_REQUEST, 							messageType = '01001100'B;
	gUTI_REALLOCATION_COMPLETE, 					messageType = '01010001'B;
	iDENTITY_RESPONSE,								messageType = '01010110'B;
	sECURITY_MODE_COMPLETE, 						messageType = '01011110'B;
	sECURITY_MODE_REJECT, 							messageType = '01011111'B;	
	tRACKING_AREA_UPDATE_COMPLETE, 					messageType = '01001010'B;
	tRACKING_AREA_UPDATE_REQUEST, 					messageType = '01001000'B;
	ul_NAS_TRANSPORT,								messageType = '01100011'B;
	aCTIVATE_DEDICATED_EPS_BEARER_CONTEXT_ACCEPT,	messageType = '11000110'B;
	aCTIVATE_DEDICATED_EPS_BEARER_CONTEXT_REJECT, 	messageType = '11000111'B;
	aCTIVATE_DEFAULT_EPS_BEARER_CONTEXT_ACCEPT, 	messageType = '11000010'B;
	aCTIVATE_DEFAULT_EPS_BEARER_CONTEXT_REJECT, 	messageType = '11000011'B;
	bEARER_RESOURCE_ALLOCATION_REQUEST,				messageType = '11010100'B;
	bEARER_RESOURCE_MODIFICATION_REQUEST, 			messageType = '11010110'B;
	dEACTIVATE_EPS_BEARER_CONTEXT_ACCEPT, 			messageType = '11001110'B;
	eSM_INFORMATION_RESPONSE, 						messageType = '11011010'B;
	eSM_STATUS, 									messageType = '11101000'B;
	mODIFY_EPS_BEARER_CONTEXT_ACCEPT, 				messageType = '11001010'B;
	mODIFY_EPS_BEARER_CONTEXT_REJECT,			    messageType = '11001011'B;
	pDN_CONNECTIVITY_REQUEST, 						messageType = '11010000'B;
	pDN_DISCONNECT_REQUEST, 						messageType = '11010010'B;
	aCTIVATE_TEST_MODE_COMPLETE, 					messageType = '11111111'B;
	dEACTIVATE_TEST_MODE_COMPLETE, 					messageType = '11111101'B;
	cLOSE_UE_TEST_LOOP_COMPLETE, 					messageType = '11111110'B;
	oPEN_UE_TEST_LOOP_COMPLETE,						messageType = '11111100'B;
	aTTACH_REQUEST, 								OTHERWISE
    )"
  };


With this tag, however, the decoder isn't decoding anything and complains with:
12:17:35.833370 NAS_Codec_Test.ttcn:37 dec_3GPP_PDU_NAS_EPS(): Stream before decoding: '07417208991007000000994605F070C040180005025AD011D15C0A003103E5E0349011035758A65D0100C1'O
12:17:35.833429 NAS_Codec_Test.ttcn:37 Dynamic test case error: While RAW-decoding type '@EPS_NAS_MsgContainers.NAS_UL_Message_Type': Can not decode type '@EPS_NAS_MsgContainers.NAS_UL_Message_Type', because invalid message was received
12:17:35.833445 NAS_Codec_Test.ttcn:37 setverdict(error): none -> error
12:17:35.833459 NAS_Codec_Test.ttcn:37 Performing error recovery.


Any idea why this happens?

If I comment out any of the fields in the TAG it will decode the union to exactly this type (i.e. the first it finds not specified and therefore valid). Are there any restirctions on which element (and in which order) can serve as identifier for the choice of a union? Can I somehow make the RAW decoder a bit more verbose to follow the decision it makes?

Thanks
Andre
Re: Decoding NAS PDUs [message #1791022 is a reply to message #1791003] Thu, 21 June 2018 14:51 Go to previous messageGo to next message
Botond Baranyi is currently offline Botond BaranyiFriend
Messages: 11
Registered: February 2016
Junior Member
Hi Andre,

With the 'TAG' coding instruction the RAW codec now correctly identifies 'aTTACH_REQUEST' as the selected field, but it fails to decode the field.

The decoded field looks like this, when the decoder runs out of bits:

aTTACH_REQUEST := {
  securityHeaderType := '0000'B,
  protocolDiscriminator := '0111'B,
  messageType := '01000001'B,
  nasKeySetId := {
    iei := '2'H,
    tsc := '1'B,
    nasKeySetId := '011'B
  },
  epsAttachType := {
    spare := '0'B,
    typeValue := '100'B
  },
  oldGutiOrImsi := {
    iei := '90'O,
    iel := '09'O ("	"),
    idDigit1 := '0001'B,
    oddEvenInd := '1'B,
    typeOfId := '011'B,
    otherDigits := '000000906954000F070C84015020A0051D11CDA5001033500E4E031931708565DA150010'O
  },
  ueNetworkCapability := <unbound>,
  esmMessage := <unbound>,
  oldPtmsiSignature := <unbound>,
  additionalGuti := <unbound>,
  lastVisitedRegisteredTai := <unbound>,
  drxParameter := <unbound>,
  msNetworkCapability := <unbound>,
  oldLai := <unbound>,
  tmsiStatus := <unbound>,
  msClassmark2 := <unbound>,
  msClassmark3 := <unbound>,
  supportedCodecList := <unbound>,
  addUpdateType := <unbound>
}


It seems that the octetstring field 'aTTACH_REQUEST.oldGutiOrImsi.otherDigits' decodes everything until the buffer's end, since it has no coding instructions or a fixed length restriction (its length is restricted to 0..10, but the RAW codec only takes fixed length restrictions into consideration). I'm assuming this is not intentional.

As for the 'TAG' coding instruction: you can't have an 'OTHERWISE' condition and other conditions (with fixed values) for the same field. This causes the 'OTHERWISE' condition to be ignored. Since the 'OTHERWISE' condition covers both cases anyway, the fixed condition should simply be removed.
The other conditions look fine to me (you can have multiple conditions with fixed values for a field, these will be treated as if there was an 'or' operator between them).

To my knowledge there is no way to make the decoder more verbose (I've managed to extract the mentioned partially decoded data by modifying the generated C++ code).

Best regards,
Botond Baranyi
Re: Decoding NAS PDUs [message #1791023 is a reply to message #1791022] Thu, 21 June 2018 15:06 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hey Botond,

Quote:

With the 'TAG' coding instruction the RAW codec now correctly identifies 'aTTACH_REQUEST' as the selected field, but it fails to decode the field.


Where do you see that, have you done any other modifications? It doesn't do for me?

Thanks
Andre
Re: Decoding NAS PDUs [message #1791024 is a reply to message #1791023] Thu, 21 June 2018 15:12 Go to previous messageGo to next message
Botond Baranyi is currently offline Botond BaranyiFriend
Messages: 11
Registered: February 2016
Junior Member
Hi,

I've simply added the 'TAG' coding instruction you posted to the code you sent us last time. Plus the 'encode "RAW"' attributes to the 'protocolDiscriminator' fields.
Sorry, forgot to mention that part...

Best regards,
Botond Baranyi
Re: Decoding NAS PDUs [message #1791025 is a reply to message #1791024] Thu, 21 June 2018 15:16 Go to previous messageGo to next message
Botond Baranyi is currently offline Botond BaranyiFriend
Messages: 11
Registered: February 2016
Junior Member
Hi Andre,

To clarify: I get the same error message as you. I've simply added some extra code to the RAW decoders in the generated C++ code to display partial results (which are erased when decoding is finished, so you only see an <unbound> in the log file).

Best regards,
Botond Baranyi
Re: Decoding NAS PDUs [message #1791029 is a reply to message #1791025] Thu, 21 June 2018 15:57 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hi Botond,

I understand the 'unbound' issue is because one of the fields consumes all bits but I am actually not even getting to this point.

With the TAG field that I posted, the decoder doesn't pick up any message and complains with
MTC@andre-xps13: Dynamic test case error: While RAW-decoding type '@EPS_NAS_MsgContainers.NAS_UL_Message_Type': Can not decode type '@EPS_NAS_MsgContainers.NAS_UL_Message_Type', because invalid message was received


Do you mind posting your exact definitions that lead to the RAW decoder picking up the attach_request type?

Thanks
Andre
Re: Decoding NAS PDUs [message #1791036 is a reply to message #1791022] Thu, 21 June 2018 17:00 Go to previous messageGo to next message
Gábor Szalai is currently offline Gábor SzalaiFriend
Messages: 26
Registered: December 2015
Junior Member
I think the otherDigits fields eat all of the octets, because missing length calculation.

The RAW codec uses only the fixed length restriction only. The length field should be specified explicitly using the "LENGTHTO" attribute.

It should be done for all variable length IE. Also either the crostag, tag, or presence attribute should be added to identify the optional IEs
Re: Decoding NAS PDUs [message #1791046 is a reply to message #1791036] Fri, 22 June 2018 06:17 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

what Gabor wrote is very important: you may need to augment the existing TTCN-3 structures to add fields to determine absence /presence of certain fields, length of payload fields etc.
These extra fields will be calculated automatically when encoding end returned by the decoder when decoding.


Also , don't trust the result to work at once, it has to be verified.
Typical test cycle consists of:

-writing a number of representative sample templates and encode/ decode them in a loop
-encode the above templates and decode them with an independent decoder, if available
-get some encoded samples and decode them

Assembling a large RAW coded protocol module may take a couple of days or even one or two weeks for an experienced developer..
However this is still considerably less then writing the codec e.g. in C/C++.



Best regards

Elemer
Re: Decoding NAS PDUs [message #1791245 is a reply to message #1791046] Tue, 26 June 2018 15:37 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hey guys,

thanks again for the input. I admit that making the NAS types work with the RAW codec seems to be a bit more effort than I actually expected but at the same time I agree it probably still easier than writing one from scratch.

Regarding Gabor's suggestion it actually turns out that I even need to decorate some of the mandatory fields, for example in a ATTACH_REQUEST, with PRESENCE or similar tags, because they use types, like the nasKeySetId that itself has an optional IEI, but is always present in an ATTACH_REQUEST type.

My approach for doing that is like this. Because there is no explicit keyword to define that a field is NOT present, I made its presence depend on a value that will not be set, i.e.
variant (nasKeySetId.iei) "PRESENCE(securityHeaderType = '1111'B)"
.
That works ok but with the optional fields within the ATTACH_REQUEST it's a bit more difficult because it depends on the parent type and the value of the IEI whether the field is present or not. For example, the oldPtmsiSignature in the ATTACH_REQUEST: it's optional in an ATTACH_REQUEST and is present if the value of the first decoded octet is '19'O (oldPtmsiSignature.iei). How can I express this?

Further, I found debugging the RAW decoder very cumbersome because all modifications that I do in the generated C++ code are gone after recompilation. It would actually be very helpful to have the intermediate decoded output like in Botond's post generated on request.

type record ATTACH_REQUEST {                                  /* 24.301 cl. 8.2.4
                                                                 Significance:  dual
                                                                 Direction:     UE to network */
  SecurityHeaderType                  securityHeaderType,                     /* cl. 9.3.1    M V 1/2 */
  ProtocolDiscriminator               protocolDiscriminator,                  /* cl. 9.2      M V 1/2 */
  MessageType                         messageType,                            /* cl. 9.8      M V 1   */
  NAS_KeySetIdentifier                nasKeySetId,                            /* cl. 9.9.3.21 M V 1/2 */
  EPS_AttachType                      epsAttachType,                          /* cl. 9.9.3.11  M V 1/2 */
  MobileIdentity                      oldGutiOrImsi,                          /* cl. 9.9.3.12 M LV 5-12 */
  UE_NetworkCap                       ueNetworkCapability,                    /* cl. 9.9.3.34 M LV 3-14  */
  ESM_MessageContainer                esmMessage,                             /* cl. 9.9.3.15 M LV-E 2-n */
  PTMSI_Signature                     oldPtmsiSignature             optional, /* cl 10.5.5.8 of 24.008 O TV 4 IEI=Ox19*/
  MobileIdentity                      additionalGuti                optional, /* cl 9.9.3.12 O TLV 13 IEI=Ox50*/
  TrackingAreaId                      lastVisitedRegisteredTai      optional, /* cl. 9.9.3.32 O TV 6 IEI=0x52 */
  DRXparameter                        drxParameter                  optional, /* cl. 9.9.3.8  O TV 3 IEI=Ox5c */
  MS_NetworkCap                       msNetworkCapability           optional, /* cl. 9.9.3.20 O TLV 4-10 IEI=Ox31 */
  LocAreaId                           oldLai                        optional, /* cl. 9.9.2.2  O TV 6 IEI=0x13 */
  TMSI_Status                         tmsiStatus                    optional, /* cl. 9.9.2.31 O TV 1 IEI=0x9- */
  MS_Clsmk2                           msClassmark2                  optional, /* cl. 9.9.2.4  O TLV 5 IEI=0x11 */
  MS_Clsmk3                           msClassmark3                  optional, /* cl. 9.9.2.5  O TLV 2-34 IEI=0x20 */
  CodecList                           supportedCodecList            optional, /* cl. 9.9.2.10  O TLV 5-n IEI=0x40 */
  AdditionalUpdateType                addUpdateType                 optional  /* cl.9.9.3.0B O TV 1    IEI=0xF @sic R5s100135 sic@ */
} with {
  encode (protocolDiscriminator) "RAW";
  variant (securityHeaderType, protocolDiscriminator) "FIELDORDER(msb)"
  variant (nasKeySetId.iei) "PRESENCE(securityHeaderType = '1111'B)"
  variant (oldGutiOrImsi.iei) "PRESENCE(securityHeaderType = '1111'B)"
  variant (ueNetworkCapability.iei) "PRESENCE(securityHeaderType = '1111'B)"
  variant (esmMessage.iei) "PRESENCE(securityHeaderType = '1111'B)"
  variant (oldPtmsiSignature) "PRESENCE(oldPtmsiSignature.iei = '19'O)"
};


Thanks
Andre
Re: Decoding NAS PDUs [message #1791544 is a reply to message #1791245] Mon, 02 July 2018 11:00 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

regarding your first question I looked into a similar NAS_EPS_Types file that has been written for RAW:
 
//Reference:          3GPP 24.301 v15.0.0 (24.008 v15.0.0, 24.011 v14.0.0, 24.161 v14.0.0  

// 9.9.3.26 - 10.5.5.8/24.008
type record P_TMSISignatureTV
{
  OCT1               elementIdentifier,
  OCT3               valueField
} with { variant "PRESENCE (elementIdentifier = '19'O)"; }
 
:
type record DevicePropertiesTV
{
  BIT1             lowPriority,
  BIT3             spare,
  BIT4             elementIdentifier
}
 :
 type record GPRSTimer2TLV 
{
 OCT1          elementIdentifier,
 LIN1          lengthIndicator,
 GPRSTimer2V   gprsTimer2
} with { 
  variant (lengthIndicator) "LENGTHTO (gprsTimer2)"
}
 
 :
:
 
 
 type record PDU_NAS_EPS_AttachRequest
{
  BIT4                           securityHeaderType,
  BIT8                           messageType,
  EPS_AttachTypeV                ePS_attachType,
  NAS_KeySetIdentifierV          nasKeySetId,
  EPS_MobileIdentityLV           ePSMobileId,
  UENetworkCapabilityLV          uENetworkCapability,
  ESM_MessageContainerLVE        eSM_MessageContainer,
  P_TMSISignatureTV              old_P_TMSISignature           optional,
  EPS_MobileIdentityTLV          additionalGUTI                optional,
  TrackingAreaIdentityTV         lastVisitedRegisteredTAI      optional,
  DRXParameterTV                 dRXParameter                  optional,
  MSNetworkCapabilityTLV         mSNetworkCapability           optional,
  LocationAreaIdentificationTV   oldLocationAreaIdentification optional,
  TMSIStatusTV                   tMSIStatusTV                  optional,
  MobileStationClassmark2_TLV    mobileStationClassmark2       optional,
  MobileStationClassmark3_TLV    mobileStationClassmark3       optional,
  SupportedCodecListTLV          supportedCodecList            optional, 
  AdditionalUpdateTypeTV         additionalUpdateType          optional,
  VoiceDomainPrefandUEsettingsTLV voiceDomainPrefandUEsettings optional,
  DevicePropertiesTV             deviceProperties              optional,
  GUTI_TypeTV                    oldGUTI_Type                  optional,
  MS_NetworkFeatureSupportTV     mS_NetworkFeatureSupport      optional,
  NetworkResourceIdentifierContainerTLV tMSIBasedNRIContainer  optional,
  GPRSTimer2TLV                  t3324                         optional,
  GPRSTimer3TLV                  t3412_Extended                optional,
  ExtendedDRXParametersTLV       extendedDRXParameters         optional
} with {  
  variant "TAG (mS_NetworkFeatureSupport, elementIdentifier = '1100'B;
                deviceProperties, elementIdentifier = '1101'B; 
                t3324, elementIdentifier = '6A'O;
                t3412_Extended, elementIdentifier = '5E'O;)";
} 





As you see, the PRESENCE variant appears one level lower, at
P_TMSISignatureTV. so you don't have to reiterate it in every restructure that contains a field of this type.


Regarding your second issue, your wish is noted, in fact it's since long time on our to-do list to have a debugger for RAW.

Two things stopped us from doing it so far:
it needs quite an amount of invested effort and, as soon as users get the hang of the codec, they don't feel it's so urgently needed anymore.
In general, for codecs we aim for speed and simplicity as opposed to sophistication and user friendliness. It pays at performance testing, where
encoding/decoding cycles are the most resource consuming.




Best regards
Elemer


Re: Decoding NAS PDUs [message #1791653 is a reply to message #1791544] Tue, 03 July 2018 10:45 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hey guys,

the problem is that the UE testsuite doesn't define different types for the MobileIdentity for example that can may or may not contain the IEI. In the attach request, for example, the first occurrence is MobileIdentity in LV mode only, so without T but with length and values. Then the second occurrence is MobileIdentity in TLV mode. Here is the record definition:

type record MobileIdentity {
  IEI8_Type            iei optional,                   // '00100011'B
  Type4Length_Type     iel,
  BcdDigit_Bit         idDigit1,                // 1st identitity digit
  B1_Type              oddEvenInd,              // Odd/even indicator
  NAS_IdType           typeOfId,                // Type of identity
  octetstring          otherDigits length(0..10)// Other identity digits (10 octets rather than 8 to cover Guti as well)
};


I guess there are two possibilities, one is defining a second type called MobileIdentityV that doesn't have the iei. I tried that with the NAS_KeySetIdentifierV which has the same issue and can confirm that it works. The drawback is that there are a lot of changes needed in all templates etc.

The second option is to somehow tell the RAW decoder to not decode the iei field in case some condition is met. But I wasn't successfull in doing so, at least something like this
variant (oldGutiOrImsi.iei) "PRESENCE(securityHeaderType = '1111'B)"

didn't work. Any idea how to achieve this, i.e. telling the RAW decoder _not_ to decode a field, without rewriting the types themselves?

Regarding the second issue, for now I've simply extended the RAW code-generator to log partially decoded types, works well and can be turned off at compile-time without performance penalties.

diff --git a/compiler2/record.c b/compiler2/record.c
index 22ce77e6..3cca0261 100644
--- a/compiler2/record.c
+++ b/compiler2/record.c
@@ -5361,6 +5361,14 @@ static char *genRawDecodeRecordField(char *src, const struct_def *sdef,
     }
   }
   src = mputstr(src, ");\n");
+
+  // log partially decoded message
+  src = mputprintf(src, "  TTCN_Logger::begin_event(TTCN_DEBUG);\n");
+  src = mputprintf(src, "  TTCN_Logger::log_event_str(\"{ %s := \");\n", sdef->elements[i].name);
+  src = mputprintf(src, "  field_%s%s.log();\n", sdef->elements[i].name, sdef->elements[i].isOptional ? "()" : "");
+  src = mputprintf(src, "  TTCN_Logger::log_event_str(\" }\");\n");
+  src = mputprintf(src, "  TTCN_Logger::end_event();\n");
+
   if (delayed_decode) {
     src = mputprintf(src, "  if (decoded_field_length != %d) return -1;\n",
       sdef->elements[i].raw.length);


Thanks
Andre
Re: Decoding NAS PDUs [message #1791661 is a reply to message #1791653] Tue, 03 July 2018 12:54 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

"The second option is to somehow tell the RAW decoder to not decode the iei field in case some condition is met. "

Sorry, this is not currently supported, although it might be a good idea.

Although it sounds painful, I'd recommend you take the first route.

As for RAW decode logger, yes, this is the way to go, but of course for all types simple and structured.

Best regards

Elemer




Re: Decoding NAS PDUs [message #1791703 is a reply to message #1791661] Wed, 04 July 2018 12:09 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hey again,

I went through the process adopting a few more types and now the MobileIdentity decodes ok and isn't consuming the entire bits. I took the next field which is of type UE_NetworkCap, again the same with an optional IEI field that should not be decoded in the AttachRequest message. Looking at the generated RAW decoder it was rather simple to just comment the IEI decoding and set the field to omit to achieve what I wanted.

So if there was an option to have a keyword to tell the RAW decoder not to decode a specific optional field, it would save a lot of work modifying the 3GPP TTCN3 code. Can someone please confirm again that this cannot be expressed with the current keywords for the RAW coder?

I then went to see what is needed to extend the RAW-AST to include a new keyword like NOT_PRESENT to have that available in the RAW code-generator as a boolean and extended the parser accordingly. It's not working yet but would that be the preferred way to go? Also, is there a timeline for a feature like this to be added officially? If so, I'd rather wait before further going in this direction.

Cheers
Andre
Re: Decoding NAS PDUs [message #1791767 is a reply to message #1791703] Thu, 05 July 2018 06:59 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

can you please write a proposal with a simple but complete example
demonstrating how this should work?

I don't think a new keyword should be necessary , we have OTHERWISE which works with TAG for instance,
semantically that should be equivalent.


Thank you and best regards
Elemer




Re: Decoding NAS PDUs [message #1791793 is a reply to message #1791767] Thu, 05 July 2018 11:33 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hey,

sure, I am happy to explain and document what would be needed. Just to make sure again, this is only needed if one wants to use the ETSI defined TTCN3 typedefs for NAS decoding. Needless to say that your approach with having separate types for "type" and "length and value" obviously works with the current RAW coded (as shown in the example you sent). But let's try to get the ETSI code work as well

Let's take this type for example:
type record ESM_MessageContainer {                            /* 24.301 cl. 9.9.3.15 */
  IEI8_Type                   iei                   optional, /* present in case of TLV; omit in case of LV */
  INT16b                      iel,
  octetstring                 esmPdu                optional  /* ESM PDU without NAS security header;
                                                                 type is FFS */
} with {
  variant (iel) "LENGTHTO(esmPdu)";
};


This type contains the element identifier in some messages and in some not (in those in which this field is mandatory like in the attach request for example). So what happens is that the RAW decoder _always_ decodes the iei field.

What would be ideal, semantically, would be to express that condition, i.e. if the IEI is present or not, in the parent type, e.g. the attach request. I've made up something using the PRESENCE tag, trying to negate it.

type record ATTACH_REQUEST {                                  /* 24.301 cl. 8.2.4
                                                                 Significance:  dual
                                                                 Direction:     UE to network */
  SecurityHeaderType                  securityHeaderType,                     /* cl. 9.3.1    M V 1/2 */
  ProtocolDiscriminator               protocolDiscriminator,                  /* cl. 9.2      M V 1/2 */
  MessageType                         messageType,                            /* cl. 9.8      M V 1   */
  NAS_KeySetIdentifierV               nasKeySetId,                            /* cl. 9.9.3.21 M V 1/2 */
  EPS_AttachType                      epsAttachType,                          /* cl. 9.9.3.11  M V 1/2 */
  MobileIdentityV                     oldGutiOrImsi,                          /* cl. 9.9.3.12 M LV 5-12 */
  UE_NetworkCap                       ueNetworkCapability,                    /* cl. 9.9.3.34 M LV 3-14  */
  ESM_MessageContainer                esmMessage,                             /* cl. 9.9.3.15 M LV-E 2-n */
  PTMSI_Signature                     oldPtmsiSignature             optional, /* cl 10.5.5.8 of 24.008 O TV 4 IEI=Ox19*/
  MobileIdentity                      additionalGuti                optional, /* cl 9.9.3.12 O TLV 13 IEI=Ox50*/
  TrackingAreaId                      lastVisitedRegisteredTai      optional, /* cl. 9.9.3.32 O TV 6 IEI=0x52 */
  DRXparameter                        drxParameter                  optional, /* cl. 9.9.3.8  O TV 3 IEI=Ox5c */
  MS_NetworkCap                       msNetworkCapability           optional, /* cl. 9.9.3.20 O TLV 4-10 IEI=Ox31 */
  LocAreaId                           oldLai                        optional, /* cl. 9.9.2.2  O TV 6 IEI=0x13 */
  TMSI_Status                         tmsiStatus                    optional, /* cl. 9.9.2.31 O TV 1 IEI=0x9- */
  MS_Clsmk2                           msClassmark2                  optional, /* cl. 9.9.2.4  O TLV 5 IEI=0x11 */
  MS_Clsmk3                           msClassmark3                  optional, /* cl. 9.9.2.5  O TLV 2-34 IEI=0x20 */
  CodecList                           supportedCodecList            optional, /* cl. 9.9.2.10  O TLV 5-n IEI=0x40 */
  AdditionalUpdateType                addUpdateType                 optional  /* cl.9.9.3.0B O TV 1    IEI=0xF @sic R5s100135 sic@ */
} with {
  encode (protocolDiscriminator, nasKeySetId, epsAttachType) "RAW";
  variant (securityHeaderType, protocolDiscriminator, nasKeySetId,epsAttachType,oldGutiOrImsi,ueNetworkCapability) "FIELDORDER(msb)"
  variant (esmMessage.iei) "PRESENCE(NULL)"
  variant "TAG (oldPtmsiSignature, iei = '19'O;
                additionalGuti, iei = '50'O; 
                lastVisitedRegisteredTai, iei = '52'O;
                drxParameter, iei = '5c'O;)";
  
};


So basically don't decode esmMessage.iei in case it's an attach_accept.

Looking at the first part of the generated RAW decoder, we can see that there is only the limit check for the iei field.
int ESM__MessageContainer::RAW_decode(const TTCN_Typedescriptor_t& p_td, TTCN_Buffer& p_buf, int limit, raw_order_t top_bit_ord, boolean no_err, int, boolean)
{ (void)no_err;
  int prepaddlength=p_buf.increase_pos_padd(p_td.raw->prepadding);
  limit-=prepaddlength;
  size_t last_decoded_pos = p_buf.get_pos_bit();
  int decoded_length = 0;
  int decoded_field_length = 0;
  raw_order_t local_top_order;
  if(p_td.raw->top_bit_order==TOP_BIT_INHERITED)local_top_order=top_bit_ord;
  else if(p_td.raw->top_bit_order==TOP_BIT_RIGHT)local_top_order=ORDER_MSB;
  else local_top_order=ORDER_LSB;
  int value_of_length_field1 = 0;
  if (limit > 0){
  size_t fl_start_pos = p_buf.get_pos_bit();
  decoded_field_length = field_iei().RAW_decode(NAS__CommonTypeDefs::IEI8__Type_descr_, p_buf, limit, local_top_order, TRUE);
  TTCN_Logger::begin_event(TTCN_DEBUG);
  TTCN_Logger::log_event_str("{ iei := ");
  field_iei().log();
  TTCN_Logger::log_event_str(" }");
  TTCN_Logger::end_event();
  if (decoded_field_length < 1) {
  field_iei = OMIT_VALUE;
  p_buf.set_pos_bit(fl_start_pos);
  } else {
  decoded_length+=decoded_field_length;
  limit-=decoded_field_length;
  last_decoded_pos=bigger(last_decoded_pos, p_buf.get_pos_bit());
  }
  }
  else field_iei=OMIT_VALUE;


I've checked the decoding is correct by commenting out the decoding in the generated C++.
Basically what would be needed is to have the check expressed above to skip the IEI decoding in case the above mentioned condition is matched. I assume the parent type is available in the AST to verify that PRESENCE condition.

Please let me know if anything is unclear or you need any further example.

Thanks in advance
Andre
Re: Decoding NAS PDUs [message #1791797 is a reply to message #1791793] Thu, 05 July 2018 12:37 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

so if I understand correctly, presence or absence of iei field in ESM_MessageContainer is a user decision, that you wan to indicate with the PRESENCE variant?
And it does not correlate with anything else.?


If this is correct , then why not set it simply to omit when encoding and decode it as it comes ( assuming that the other end encodes it properly in which case it will be set to omit) ?

Any error in encoding this will not be detected on codec or type level but on template level.


Or am I missing something here?


BR

Elemer
Re: Decoding NAS PDUs [message #1791813 is a reply to message #1791797] Thu, 05 July 2018 14:12 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
OK, sorry, that may not work.
Let me think it through once again.

[Updated on: Thu, 05 July 2018 14:12]

Report message to a moderator

Re: Decoding NAS PDUs [message #1791831 is a reply to message #1791813] Thu, 05 July 2018 19:58 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hi Elemer,

Quote:
so if I understand correctly, presence or absence of iei field in ESM_MessageContainer is a user decision, that you wan to indicate with the PRESENCE variant?
And it does not correlate with anything else.?


That's right. Well, this would be one option to model this using the current type definitions. But what is important here is that is must not be per type but per field. This is because some types are actually present as mandatory fields (without IEI) and as optional field (with IEI) in the same record. For example, type MobileIdentity in ATTACH_REQUEST. But also note that it's not the entire record that is absent or present, but only one field inside the nested record.

So semantically, when decoding a field of type X, whether the IEI is decoded or not depends on the actual field and not solely on the type.

Quote:
If this is correct , then why not set it simply to omit when encoding and decode it as it comes ( assuming that the other end encodes it properly in which case it will be set to omit) ?


I've not tried encoding it but I assume this would work, yes. But decoding does not, as you already assumed.

Another option would be to have a keyword to set the value of a field to a specific value if some condition is met or, in a parent record, to explicitly set the content of a nested field. In this case one could do this:

type record ATTACH_REQUEST {                                  /* 24.301 cl. 8.2.4
                                                                 Significance:  dual
                                                                 Direction:     UE to network */
  ...
  ESM_MessageContainer                esmMessage,                             /* cl. 9.9.3.15 M LV-E 2-n */
   ...
} with {
  variant (esmMessage.iei) "SETVALUE(omit)"
};



Thanks
Andre
Re: Decoding NAS PDUs [message #1791853 is a reply to message #1791831] Fri, 06 July 2018 08:45 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

I have a clear picture now;

I can confirm that currently RAW cannot handle this; but we will look into extending PRESENCE accordingly; I don't have an ETA yet, but I'll keep you posted.

Best regards
Elemer



Re: Decoding NAS PDUs [message #1791854 is a reply to message #1791853] Fri, 06 July 2018 08:48 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Hi Elemer,

that sounds great. Much appreciated. Please let me know if you want me to test anything or need any further test vectors.

Thanks
Andre
Re: Decoding NAS PDUs [message #1792944 is a reply to message #1791854] Thu, 26 July 2018 08:40 Go to previous messageGo to next message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

we have committed code for this new RAW encoding variant,

please see https://bugs.eclipse.org/bugs/show_bug.cgi?id=537389

Looking forward to your feedback
Elemer


Re: Decoding NAS PDUs [message #1792996 is a reply to message #1792944] Fri, 27 July 2018 08:51 Go to previous messageGo to next message
Andre Puschmann is currently offline Andre PuschmannFriend
Messages: 48
Registered: March 2018
Member
Elemer, all,

I'll let the logs respond ;-)

Test case nas_decoding_tests finished. Verdict: pass


Thanks a lot for this, I haven't done any encoding tests yet but I'll do that shortly.

Very much appreciated.

Cheers
Andre
Re: Decoding NAS PDUs [message #1793641 is a reply to message #1792996] Mon, 13 August 2018 06:56 Go to previous message
Elemer Lelik is currently offline Elemer LelikFriend
Messages: 807
Registered: January 2015
Senior Member
Hi Andre,

fyi,

I have published NAS_EPS 15.2.0.1 containing declarations that align with the RAW codec.


see

http://git.eclipse.org/c/

git clone ssh://username@git.eclipse.org:29418/titan/titan.ProtocolModules.NAS_EPS_15.2.0.1


Best regards
Elemer
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