question for concatenated message

[Denis Kenzior]

Hi Zhigang,

> According to 23.040:
> The maximum length of an uncompressed concatenated short message is 39015
> (255*153) default alphabet characters, 34170 (255*134) octets or 17085
> (255*67) UCS2 characters.

The structure of UD when concatentation is used is like this:

[UDH length][IEI1][IEI1LEN][IEI1DATA]PAYLOAD

One can use two header types for concatenation.  16 bit sequence and 8 bit 
sequence.  16 Bit sequence uses 4 bytes while 8 bit sequence uses 3 bytes.  So 
the total overhead is:
1 byte for udhl + 1 byte for iei + 1 byte for length + 3|4 bytes = 7 for 16 
bit header and 6 bytes for 8 bit header.

So the you provide above numbers are correct for the 8bit case, but not 
correct for 16 bit case.

In 16 bit case we can encode 255 * 152 GSM characters and 255 * 66 UCS2 
characters (the UCS2 characters cannot be split in the middle).

>
> But in oFono didn't match above:
> For UCS2 is (255 * 66), default alphabet is (253* 153)

oFono uses 16 bit sequence by default, so at least in the case of UCS2 it is 
correct.  For 7bit case you need to limit the payload to 255 * 152 characters.  
253*153 will in fact result in 255 segments when using 16 bit headers.

Regards,
-Denis