SHORT MESSAGE SERVICE.

GSM SHORT MESSAGE SERVICE

Contents
Introduction Sms length Channels used SMS architecture Mobile originated sms Mobile terminated sms

•What is sms???

introduction
 SMS stands for “short message service”  Used to exchange short text messages between short message entities  Originally designed for gsm, but is used in cdma as well as 3g  Maximum length per message is 160 characters  Map protocol used to transfer messages

why max length of 160 characters?

 Transfer of messages via map has limitation of 140 octets (140*8=1120 bits)  Character codes used:
7-bit alphabet 8-bit alphabet 16-bit alphabet

 characters in languages such as Arabic, Chinese, Korean, Japanese, etc, alphabet must be encoded using the 16-bit coding scheme

Concatenated sms/long sms
Used when sms size is >160 characters Sms is split and sent as separate messages Message length is lower:
153 for 7-bit encoding 134 for 8-bit encoding 67 for 16-bit encoding

Udh size of 48-49 bits

Gsm channels used for transfer

 in idle mode
SDCCH

During a voice call
 sacch

architecture

Mobile terminated call flow

Mobile originated call flow

Mt sms during active call

MO SMS during active call