What is SMS?

There are several unique features to Short Message Service (SMS), as defined within the GSM digital mobile phone standard that is popular in Europe, the Middle East, Asia, Africa and some parts of North America:

• A single short message can be up to 160 characters of text in length. Those 160 characters can comprise of words or numbers or an alphanumeric combination. Non-text based short messages (for example, in binary format) are also supported.

• The Short Message Service is a store and forward service, in other words, short messages are not sent directly from sender to recipient, but rather always via an SMS Center. Each mobile telephone network that supports SMS has one or more messaging centres to handle and manage the short messages.

• The Short Message Service features confirmation of message delivery. This means that unlike paging, users do not simply send a short message and trust and hope that it gets delivered. Instead the sender of the short message can receive a return message back notifying them whether the short message has been delivered or not.

• Short messages can be sent and received simultaneously with GSM voice, data and fax calls. This is possible because whereas voice, data and fax calls take over a dedicated radio channel for the duration of the call, short messages travel over and above the radio channel using the signaling path. As such, users of SMS rarely if ever get a busy or engaged signal as they can do during peak network usage times.

• Ways of sending multiple short messages are available. SMS concatenation (stringing several short messages together) and SMS compression (getting more than 160 characters of information within a single short message) have been defined and incorporated in the GSM SMS standards. ·

• To use the Short Message Service, users need the relevant subscriptions and hardware, specifically:

  • a subscription to a mobile telephone network that supports SMS o use of SMS must be enabled for that user (automatic access to the SMS is given by some mobile network operators, others charge a monthly subscription and require a specific opt-in to use the service)
  • a mobile phone that supports SMS
  • knowledge of how to send or read a short message using their specific model of mobile phone
  • a destination to send a short message to, or receive a message from. This is usually another mobile phone but may be a fax machine, PC or Internet address.

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