are these bugs when sending concatenated SMSs

Andreas Fink afink at list.fink.org
Wed Jan 31 11:40:02 CET 2007


Here's the exact calculation of the PDU splitting borders.

On the wire and in the air, a SMS PDU always contains a maximum of  
140 octets.
Thats why you can pack 140*8/7 = 160 characters into an SMS.

If a UDH header is used (udh indicator bit is set), then the  
beginning of the SMS-PDU contains the UDH (universal data header).  
The UDH is 6 octets for a splitted text sms. This leaves us with 134  
octets remaining.
134 octets are 1072 bits. in 1072 bits you can pack 153 septets and  
you are left over with one spare bit.
This is where the 153 character limits for split SMS comes from.



On 31.01.2007, at 10:16, Alexander Malysh wrote:

> Hi,
>
> for 7bit (text message) kannel send 154 octets of text + 6 octets  
> udh that give you 160 Octets together. SMPP doesn't pack because  
> it's not necessary following the spec but SMSC packs then those.
>
> Am 31.01.2007, 09:41 Uhr, schrieb Hillel <hillel at ecommunicate.biz>:
>
>> Hi,
>>
>> I've been looking at the spec 03.40 and I've also tested and 154  
>> is the max
>> amount of chars you can use before becoming another SMS.
>>
>> If I re-read the spec below with this information, can I assume  
>> Kannel is
>> using compressed GSM Default alphabet 7 bit data and you always  
>> lose 6
>> octets to give you 134 octets left which translates into 154 chars.?
>> (If it was using uncompressed GSM Default 7 bit data then you  
>> would only
>> have 153 chars per concatenated SMS.)
>>
>> Is my understanding correct?
>>
>> 9.2.3.24.1	Concatenated Short Messages
>> This facility allows short messages to be concatenated to form a  
>> longer
>> message.
>> In the case of uncompressed 8?bit data, the maximum length of the  
>> short
>> message within the TP?UD field is 134 (140?6) octets.
>> In the case of uncompressed GSM Default 7 bit data, the maximum  
>> length of
>> the short message within the TP?UD field is 153 (160?7) characters.
>>
>> In the case of 16 bit uncompressed USC2 data, the maximum length  
>> of the
>> short message within the TP?UD field is 67 ((140?6)/2) characters.  
>> A UCS2
>> character must not be split in the middle; if the length of the  
>> User Data
>> Header is odd, the maximum length of the whole TP-UD field is 139  
>> octets.
>>
>> In the case of compressed GSM Default alphabet 7 bit data, 8 bit  
>> data or
>> UCS2 the maximum length of the compressed short message within the  
>> TP-UD
>> field is 134 ( 140-6) octets including the Compression Header and
>> Compression Footer, both or either of which may be present ( See  
>> subclause
>> 3.9).
>>
>> 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.
>>
>> Thanks for your great response.
>>
>> Rgds
>>
>>
>>
>
>
>
> -- 
> Thanks,
> Alex
>



Andreas Fink

Fink Consulting GmbH
Global Networks Schweiz AG
BebbiCell AG

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