Words of today are nixer and nix, brought to you by the letters N and X , unrelated to knack or nack or knackered (except, perhaps in an onomatopaeic, no, alliterative ? way).
https://www.etymonline.com/word/nixnixer is an Irish slang term for a casual,, often "off-the-books" or part-time, job, .. The term originates from " nix " (meaning "nothing" or "no") .. implying work done for cash with no tax or insurance declared. Origin: The term is derived from "nix," which stems from the German nichts or colloquial nix (meaning nothing).
https://www.etymonline.com/word/knackknack "a deception, trick, device," a word of uncertain origin. .. "a sharp sounding blow" .. knak, .. German knacken "to crack;" also knap) .. Sense of "special skill" .. is first recorded 1580s. In old slang (mid-18c. to mid-19c.) nacky meant "full of knacks; ingenious, dexterous."
https://www.etymonline.com/search?q=knackeredknackered "worn out, tired," .. knacker/nacker "harness-maker" (1570s) .. Old Norse hnakkur "saddle," related to hnakki "back of the neck,"
[15:33, 04/02/2026] James Coleman: 😀 possibly sign of light headedness just cycled back up the road after donating a pint of blood
nix sounds latin, doesn't it ? .. nix means snow in latin
Brought to you by the surprising gap in knowledge of someone on family whatsapp group (not knowing what a nixer is).
Cheat: we know this should contain a 120 char message, 120 same e-grave chars.
e-grave char encoding in GSM is 4.
so we think in this string we have 120 chars value 4 repeated
and we think each char is using 7bits
Note, Wireshark .. unfortunately this was not SCTP encapsulated but TCP/IP encapsulated. I had an older wireshark with a change in decoding plugins hand built that could decode SS7, but, on an old machine now :-(. See below found an online docoder that worked BUT it doesn't explain how it is done.
Gemini .. gave some good pointers on decoding and referenced the right specs but this was a hard task for it and it was hallucinating and making up[ decodings more often than giving good info.
ETSI 3GPP standards 3GPP TS 23.040 and 3GPP TS 23.038
We can decode the PDU with info in these 2 standards.
SM-RP-UI AVP:3301 6.3.3.3 OctetString M, V No 6.3.3.3 SM-RP-UI The SM-RP-UI is of type OctetString and it shall contain a short message transfer protocol data unit (TPDU) which is defined in 3GPP TS 23.040 [3] and represents the user data field carried by the short message service relay sub-layer protocol. Its maximum length is of 200 octets.
9.2.2.1 SMS‑DELIVER type Basic elements of the SMS‑DELIVER type:
..
TP‑DCS TP‑Data‑Coding‑Scheme M o
Parameter identifying the coding scheme within the TP‑User‑Data.
..
TP‑UDL TP‑User‑Data‑Length M I Parameter indicating the length of the TP‑User‑Data field to follow.
TP‑UD TP‑User‑Data O 3)
1) Provision; Mandatory (M) or Optional (O). 2) Representation; Integer (I), bit (b), 2 bits (2b), Octet (o), 7 octets (7o), 2‑12 octets (2‑12o). 3) Dependent on the TP‑DCS.
9.2.3 Definition of the TPDU parameters 9.2.3.1 TP‑Message‑Type‑Indicator (TP‑MTI)
0x78= 120 decimal, 120 septets in sequence == TP‑User‑Data‑Length (TP‑UDL)
TP‑User‑Data‑Length (TP‑UDL) If the TP‑User‑Data is coded using the GSM 7 bit default alphabet, the TP‑User‑Data‑Length field gives an integer representation of the number of septets within the TP‑User‑Data field to follow.
9.1.2.4 Alphanumeric representation A field which uses alphanumeric representation shall consist of a number of 7‑bit characters represented as the default alphabet defined in 3GPP TS 23.038 [9].
AND, in 3GPP TS 23.038 we can find how septets are packed into bytes:
6.1.2 Character packing 6.1.2.1 SMS Packing 6.1.2.1.1 Packing of 7-bit characters
e.g.eight characters in seven octets:
- bits number:
7 6 5 4 3 2 1 0
2g1a 1b 1c 1d 1e 1f 1g
3f 3g2a 2b 2c 2d 2e 2f
4e 4f 4g3a 3b 3c 3d 3e
5d 5e 5f 5g4a 4b 4c 4d
6c 6d 6e 6f 6g5a 5b 5c
7b 7c 7d 7e 7f 7g6a 6b
8a 8b 8c 8d 8e 8f 8g7a
SO, TP-UD encoding IS NOT ASN.1, it's defined in 3GPP TS 23.040, it depends on the DCS
No, the TP-UD (Transfer Protocol - User Data) field, which contains the actual text of the SMS, is not defined using ASN.1 (Abstract Syntax Notation One).
The TP-UD field is defined directly within the constraints of the SMS-TPDU (3GPP TS 23.040) and its contents are governed by the Data Coding Scheme (TP-DCS).
How the TP-UD is Defined and Encoded
The TP-UD is simply a sequence of bytes. Its structure and meaning are dictated entirely by the preceding fields in the SMS-TPDU:
1. TP-UDL (User Data Length)
The TP-UDL field specifies the length of the TP-UD field.1
If the message uses GSM 7-bit encoding (the default alphabet), the length is measured in 7-bit characters. The length is then packed into the minimum number of bytes required (e.g., 140 characters fit into 160 bytes).
If the message uses UCS-2/UTF-16 encoding, the length is measured in bytes.
2. TP-DCS (Data Coding Scheme)
The TP-DCS is the single most important field for decoding the TP-UD. This byte specifies the alphabet used:
TP-DCS Value
Encoding Standard
Max Characters (Single Segment)
0x00 - 0x03
GSM 7-bit Default Alphabet
160 characters
0x08
UCS-2 (UTF-16)
70 characters (since each character takes two bytes)
0x04
8-bit Data
140 bytes
The TP-UD is simply the raw byte stream of the text, encoded according to the rule set by the TP-DCS.
Contrast with MAP/TCAP (The ASN.1 Layers)
The reason for the confusion is that the protocols surrounding the SMS-TPDU are defined using ASN.1:
TCAP (Transaction Capabilities Application Part): The TCAP dialogue and components are defined entirely in ASN.1.2
MAP (Mobile Application Part): MAP operations (like mo-ForwardSM) and their parameters are defined using ASN.1.
The SMS-TPDU itself is often wrapped in a MAP Parameter:3The entire SMS-TPDU (including the TP-UD) is usually embedded inside a MAP ASN.1 construct as an OCTET STRING parameter. The ASN.1 defines thecontainerbut not the internalcontentof the TP-UD field itself.
This ONLINE Decoder worked:but doesn't breakdown the decode so you cannot rely on it for testing
If the TP‑User‑Data is coded using compressed GSM 7 bit default alphabet or compressed 8 bit data or compressed UCS2 [24] data, the TP‑User‑Data‑Length field gives an integer representation of the number of octets after compression within the TP‑User‑Data field to follow. YEOW
MTP3�(b! MTP3�(b! MTP3�(b! SCCP - there are 3 pointers to CdPa CgPa and ? WHAT is that 0x6c just before tcap part pasted in 0x65etcetc ? wireshark highlights as if it is a length ? CHANGE IT TO AC ??? SCCP \0 �\0r(\0 \0r(`Ale��H 3 POINTERS: CdPa: �\0r(\0 CgPa: \0r(`A HUH: l.... 0x6c = l might be length .. ac is � I think .. 10101100 YEP need another 2 ? ae \256 needed � MAYBE NOT
TCAP 65 81 aa .. otid dtid components:1 item == GSM MAP 01 01 2c opcode 44 81? 8f ? DA 80 06 013011111111 OA 04 07 91020130101030 0x04 0x7c after OA .. 0x7c maybe is length of PDU. We get contained item exceeds length of containing item error message
