Home » 2011 » March » 7 » Why SMS text message limited to 160 characters ?
12:06 PMWhy SMS text message limited to 160 characters ?
SMS text message is sent by SMSC ( SMS Center ) handset using SS7 protocol. If you see more in SS7, we need application layer called Mobile Application Part ( MAP ) which send SMS text message using application module Message Originating ( MO ) and Message Terminating ( MT ).
In this protocol we can answer that limitation is in SMS development. When it was built, SMS just have Digital Coding Scheme ( DCS ) signalling protocol limited 140 octets, which means 140 * 8 bits = 1120 bits.
For default alphabet, we use 7 bit / characters, and for another purpose like smart messaging like images and ringing tones or chinese and japanese we user 8 bit. For other purposes 16 bit characters encoding will be used like for Flash SMS which show blinking or alerting SMS. So for default alphabet we have 1120 bits / 7 bits = 160 characters. In same we way, we have 140 characters in 8 bit, and 70 characters in 16 bit.
So we can see now that for one SMS text messages we have limited 160 characters for 7 bit alphabet, 140 characters for 8 bit alphabet and 70 characters for 16 bit characters.
In the next innovation and improvement you can adjust maximum Digital Code Scheme upper 140 octets, so we can expand maximum characters for one SMS text message.
Even your mobile phone has capabilities to write more than 160 characters, the SMS system just see that in several messages. You can see the indicator in your text messaging that your long SMS based on phone capabilities only the way to write SMS. SMS system only see it in several messages. For example if you can write until 400 characters, the system only see it in 3 SMS text messages and you will be charged for 3 messages by the mobile operators.But you have alternative way to send long messages to your mobile operators. To increase the maximum characters in one SMS text message we can concatenate SMS in larger content, it is called as long SMS. It is configured in your mobile operator not in your handset.
In concatenated SMS, you will have additional User Data Header ( UDH ) contains segmentation information. Because of that the maximum capacity will decrease becomes 153 for 7 bit, 133 for 8 bit and 67 for 16 bit. Here some mobile operators have tariff scheme for this implementation. Most of them will charge additional UDH bits, because they uses system resources.
Next I will explain about SMS tariff scheme from Bakrie Telecom which apply tariff scheme SMS for characters you sent, not based on how many messages you sent. So here, I hope you clear about the maximum of SMS characters you have in one SMS text message.
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