Problem decoding MMS PDU internals

Problem decoding MMS PDU internals SearchSearch
Author Message
Vincent
Unregistered guest
Posted on Tuesday, February 24, 2004 - 07:07 pm:   

Hi,

I've been working on decoding MMS PDUs, and have managed to understand almost all of the headers and all of the contents *apart* from the binary encoding of the transitions from bodypart to bodypart, including the transition from the headers to the first bodypart. I've studied all of the MMS and WAP documents, but I cannot find anything specifically relating to this issue.

If anyone could give me an explanation of what I'm missing, I'd be very grateful. The following hex dump is a default message from Nokia's EAIF application, and the bits that I cannot parse have ??? after them.

Regards,

Vin

--------

8C - X-Mms-Message-Type
80 - m-send-req
98 - trans id
30303030303500 - ID
8D - mms version
90 - 1.0
85 - date
043C57FB15
89 - From
19 - length
80 - address present
2B3335383939303030303036362F545950453D504C4D4E00 - address
97 - to
2B3335383939303030303030332F545950453D504C4D4E00 - address
96 - subject
5468697320697320612074657374204D4D53206D657373616765202100
86 - delivery report
81 - no
90 - read reply
81 - no
8A - Message class
81 - Advert
8F - priority
80 - low
84 - Content-Type
A3 - mixed
02 - 2 bodyparts (???)
04 - length of headers
8167 - length of data = 11100111 = C3 = 195 characters
03838183 - ?????
50656F706C65206861766520676F7474656E207573656420746F20646F696E67207468696E677320 6F7665722074686520496E7465726E657420746861742074686579200D0A68617665207072657669 6F75736C7920646F6E65206279206F74686572206D65616E733A20726561642C20636F7272657370 6F6E642C207075626C6973682C200D0A72657365617263682C20646F207465616D776F726B2C206C 697374656E20746F206D757369632C2073686F702C206D616B652074656C6570686F6E652063616C 6C730D0A202D20746865206C697374207365656D7320656E646C6573732E - Text payload
20 - ???
01 - ???
81AC779EFFD8FFE00010 - ???
4A46494600010200006400640000FFFE001241646F626520496D6167655265616479FFEC00114475 636 (JPG datastream, truncated at this point)
yanxh
Unregistered guest
Posted on Wednesday, February 25, 2004 - 05:34 am:   

Hi,Vincent
I think you should see wap-230 about Content-type encode and multipart encode, which are your weakness. now I give you my explaination:
p.s. multipart/* is formed as :
number |body1|body2|....|bodyN
where body* is formed by headerlen|datalen|contenttype|headers|data

1)02 - 2 bodyparts (???)
YES, IT IS The number of entries in the multipart entity. REFER TO WAP-230 8.5.2 Multipart Header.
2) 8167 - length of data = 11100111 = C3 = 195 characters
NO, 11100111 = E7, NOT C3

3)03838183 - ?????
Content-general-form = Value-length Media-type
Media-type = (Well-known-media | Extension-Media) *(Parameter)
03 IS VALUE-LENGTH OF CONTYPE-TYPE
83 IS CONTENT-TYPE, TEXT/PLAIN (03|0x80),
8183 IS PARAMETER, CHARSET = "US-ASCII".
PLEASE REFER TO Table 42. Character Set Assignment Examples IN WAP-230 DOCUMENT.
4)20 - ???
01 - ???
81AC779EFFD8FFE00010 - ???
BECAUSE THE SIZE OF YOUR TEXT FILE IS E7, 20 IS YOUR TEXT CONTENT.
01 -- HEADERS LEN
81AC77-- DATA LEN,22135 BYTES
9E -- CONTENT-TYPE, IMAGE/JPEG (1E|80)