Concatenation User Data Header
There are 5 octets required in the User Data Header to describe a Concatenated SMS. These are:
Octet Number Value Description 1 00 Information Element Identifier (IEL). Does not change. 2 03 Information Data Length (IEDL). Does not change. 3 AA A unique hexadecimal reference number. Does change for every set of Concatenated SMS. 4 03 Total number of concatenated SMS. Remains the same for each part of a Concatenated SMS. 5 01 Current Concatenated SMS part number. Does change for every SMS part. Example UDH's of a 3 part Concatenated SMS:
0003010301 0003010302 0003010303