How SMS Works

Science & Technology

It suddenly seems like no one is talking at all. Instead, they're typing away on tiny numerical pads, using their cellphones to send quick messages. SMS, or text messaging, stands for short message service. Simply put, it is a method of communication that sends text between cellphones or from a computer to a cellphone.

The "short" part refers to the maximum size of the text messages: 160 characters. Even if you are not talking on your cellphone, your phone is constantly sending and receiving information. It is talking to its cellphone tower over a pathway called a control channel. The reason for this chatter is so that the cellphone system knows which sub-region or cell your phone is in.

Your phone will change cells or sub-regions as you move around. Your phone and the tower will exchange a packet of data regularly that lets both of them know that everything is okay. The control channel also provides the pathway for SMS messages. When a friend sends you an SMS, the message flows through the SMSC, then to the tower. The tower then sends the message to your phone as a little packet of data on the control channel. In the same way, when you send a message, your phone sends it to the tower on the control channel and it goes from the tower to the SMSC and from there to its destination.

Why 160?

SMS was designed to deliver short bursts of data such as numerical pages. To avoid overloading the system with more than the standard forward-and-response operation, the inventors of SMS agreed on a 160-character maximum message size. However, the 160-character limit is not absolute. Length limitations may vary depending on the network, phone model and wireless carrier. Some phones don't allow you to type anymore once the 160-character limit is reached. You must send your message before continuing. However, some services will automatically break any message you send into chunks of 160 characters or less. So you can type and send a long message, but it will be delivered as several messages. Most sources agree that the first SMS message was sent in the UK in 1992.

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