What is UDH?

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UDH - User Data Header, UDH is a binary structure which may be present at the start of a short message in the Short Message Service in GSM. It is used in case of port bassed or concatenated message.

Sample UDH (In Concatenation) :

05 00 03 0A 02 01

05 is the length of data field in the UDH

00 : Offset to indicate new part of UDH

03 : Concate Header

0A : Message Reference Number

02 : Total Count of message.

01 : Sequence Number.