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7.0

Decoding SMS PDUs

Asked by bmatumbura in Global System for Mobile Communications (GSM), Cellular Phones & Carriers, Microsoft Visual Basic.Net

Tags: GSM, VB, Mobile, PDU

Dear experts,

I am developing a library that can be used to encode and decode SMS text messages. I have attached a debug log from the DLL.

The DLL works perfectly for plain text SMSs (with no EMS content), including concatenated/multi-part SMSs. My challenge is when the SMS has an EMS attachement like a SmallPicture, PredefinedSound, or Formated Text. It fails to decode the User Data part (SM) when the Default 7Bit Alphabet has been used... see the attached log for details. However, if you remove some bytes from the beginning of the User Data, you will be able to decode part of the message correctly.

For example, in the log there is the PDU message (the very last message in the log as received from the GSM modem):

07916277010120F4440B916277640266F300009040210145908031090003FC02020B022505907683E8F737081E96D3E72E90CC4D06C1C3723A081D9E83C2A07699FD26E77520

All details (MTI, Addresses, Time Stamp, User Data Header, Short Message) are correct, but I am failing to decode the User Data (i.e. Short Message):

907683E8F737081E96D3E72E90CC4D06C1C3723A081D9E83C2A07699FD26E77520

When I try to decode this message using my DLL I am getting garbage like this:

"Hvù"?àù$å?'Éw$Fs&ù$å?'ìBÅßì
ùj.fü&NW¥"

whereas I should be getting the text:

"in two parts. 2nd part has a melody: "

If I remove the first 6 characters from the beginning of the user data, I am able to get part of the text like so:

E8F737081E96D3E72E90CC4D06C1C3723A081D9E83C2A07699FD26E77520

gives me this:

"two parts. 2nd part has a melody: "

Any Idea where I could be getting it all wrong?

View the Solution FREE for 30 Days

Attachments:

SM-Debug.txt (10 KB) (File Type Details)

GSM Decoder Log

20091111-EE-VQP-91 - Hierarchy / EE_QW_3_20080625

1. lherrou9,800
2. mrjoltcola5,000
3. JohnGerh...4,900
4. imarshad4,000
5. Meff3,755
6. Mikal6133,750
7. angelIII3,500
7. jpg5263,500
7. logic_cho...3,500
10. aman07112,543
11. sparkmaker2,500
11. game-ma...2,500
13. Darr2472,360
14. upul0072,300
15. tbsgadi2,000
15. objects2,000
15. shellgrip2,000
15. hottroc2,000
15. RDAdams2,000
15. PUNKY2,000
15. avivshabo2,000
15. rindi2,000
15. Ivanov_G2,000
15. garycutri2,000
15. 65td2,000
15. jdera2,000
15. dethbylt2,000
15. thiyaguk2,000
15. shobinsun2,000
15. netskyb02,000
15. xSuperioRx2,000

1. Meff92,128
2. imarshad64,125
3. BigRat32,397
4. Mikal61317,048
5. Fisman16,183
6. upul00716,002
7. lherrou13,800
8. SimonTay13,742
9. keyurkarnik12,600
10. anupvijay10,780
11. jenmir9,310
12. amir226...8,832
13. _nn_8,169
14. SergeiKo8,152
15. Darr2478,110
16. drelectro7,600
17. trinety6,264
18. joghurt5,490
19. bhpr5,448
20. Mamtha1...5,300
21. edin_el_...5,235
22. ALogvin5,150
23. garycutri5,000
23. mrjoltcola5,000
25. JohnGerh...4,900

Decoding SMS PDUs

Asked by bmatumbura in Global System for Mobile Communications (GSM), Cellular Phones & Carriers, Microsoft Visual Basic.Net

Tags: GSM, VB, Mobile, PDU

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