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Use of octetstring in LENGTHTO [message #1842035]

Tue, 08 June 2021 00:31

Anton Kozhemyachenko

Messages: 15
Registered: June 2021

Junior Member

Hello,

I'm currently implementing a NAS encoder based on 3GPP TTCN files. However it specifies length fields as octetstrings, such as Type4Length_Type and Type6Length_Type (which are the typedefs of octetstrings).

For example in the following structure:

  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 */
    Type6Length_Type            iel,
    octetstring                 esmPdu                            /* ESM PDU without NAS security header*/
  };

Here the field 'iel' specifies the length of 'esmPdu'.

But, Titan doesn't allow to use non-integer field in LENGTHTO variant with the following error:

error: The LENGTHTO field must be an integer or union type instead of 'octetstring'

Is there any chance to have a fix for this issue (to be able to use octetstring in LENGTHTO) ?

Thanks

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Re: Use of octetstring in LENGTHTO [message #1842057 is a reply to message #1842035]

Tue, 08 June 2021 09:21

Adam Knapp

Messages: 54
Registered: November 2020

Member

Hi Anton,

I created an issue for that in GitLab: https://gitlab.eclipse.org/eclipse/titan/titan.core/-/issues/554

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Re: Use of octetstring in LENGTHTO [message #1842062 is a reply to message #1842057]

Tue, 08 June 2021 10:18

Anton Kozhemyachenko

Messages: 15
Registered: June 2021

Junior Member

Hi Adam,

Thank you

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Re: Use of octetstring in LENGTHTO [message #1842129 is a reply to message #1842062]

Wed, 09 June 2021 20:08

Anton Kozhemyachenko

Messages: 15
Registered: June 2021

Junior Member

Hello,

I found, that 3GPP TTCN also uses bitstrings for length.

So, it would be super if LENGHTO parameter accepts octetstring and bitstring.

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Re: Use of octetstring in LENGTHTO [message #1842240 is a reply to message #1842129]

Mon, 14 June 2021 08:15

Andre Puschmann

Messages: 57
Registered: March 2018

Member

Hey Anton,

I don't recall the orignal ETSI code but this is what I use for NAS encoding with Titan, works well.

type integer INT16b (0..65535) with { variant "FIELDLENGTH(16), BYTEORDER(last)" };

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 {
  encode "RAW"
  variant (iel) "LENGTHTO(esmPdu)";
};

Cheers
Andre

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Re: Use of octetstring in LENGTHTO [message #1842246 is a reply to message #1842240]

Mon, 14 June 2021 11:12

Anton Kozhemyachenko

Messages: 15
Registered: June 2021

Junior Member

Hello Andre,

On my side I use the similar technique to temporary resolve the issue, I just redeclare the required types, something like this:

type integer Type4Length_Type (0..255) with { variant "FIELDLENGTH(8)" }

However, I would like to avoid additional changes to ETSI code. Probably it shouldn't be a big deal to allow using octetstring/bitstring in LENGTHTO specification.

Regards,
Anton

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