SMS basics

What is SMS?

SMS stands for Short Message Service. The term is also used to refer to a short message itself. It is a technology that enables the sending and receiving of messages between mobile phones in the mobile network. SMS first appeared in Europe in 1992. It was included in the GSM (Global System for Mobile Communications) standards right at the beginning. Thanks to it's success it was introduced to other wireless networks like CDMA networks.

Originally SMS was used in mobile phone to mobile phone communication only. Currently it is also often used in computer to mobile phone communication, as well.

As suggested by the name "Short Message Service", the data that can be held by an SMS message is very limited. One SMS message can contain at most 140 bytes (1120 bits) of data, so one SMS message can contain the following information:

  • 160 characters if 7-bit character encoding is used. (7-bit SMS character encoding is suitable for encoding Latin characters like English alphabets.)
  • 70 characters if 16-bit Unicode UCS2 character encoding is used. (SMS text messages containing non-Latin characters like Arabic, Cyril, Japanese, Chinese or other International characters or symbols, should use 16-bit character encoding.)
  • 140 obtects of binary data, that can hold ringtones, operator logos, mobile phone configuration, wallpapers, animations, business cards (e.g. VCards) and other useful data.

    SMS text messaging supports languages internationally. It works fine with all languages supported thanks to it's support of the Unicode character set.

    One major advantage of SMS is that it is supported by 100% GSM mobile phones. Almost all subscription plans provided by wireless carriers include inexpensive SMS messaging service. Unlike SMS, mobile technologies such as EMS, MMS, WAP and Java (J2ME) are not supported on many mobile phone models.

    Which standardization body is responsible for the SMS standard?


    The GSM and SMS standards were originally developed by the European Telecommunications Standards Institute (ETSI), then it was taken over by The Third Generation Partnership Project (3GPP). Currently 3GPP is responsible for the development and maintenance of the GSM and SMS standards.

    Why use SMS?

    SMS allows applications to directly transmit messages to mobile devices. It is the simplest way to send information. All that is needed is a telephone number and the message text. It is also convenient to receive SMS messages. You can collect information from mobile users this way.

    Is it possible to send a single message to multiple recipients?

    In the SMS standard, there are Point-to-Point and Point-to-Multipoint (cell broadcast) messages.

    For the average user only point-to-point messages are available. Cell broadcast messages are used by mobile network operators to broadcast network information, such as time, location, etc.

    How can I send longer text? What are concatenated SMS messages?

    The SMS technology allows you to send longer data by splitting data into segments and transmitting the segments as multiple SMS messages.

    Although one SMS message can only carry a very limited amount of data (140 bytes), a technology called concatenated SMS (also known as long SMS or multipart SMS technology), makes it possible to send longer text or data. A concatenated SMS text message can contain more than 160 English characters. Concatenated SMS works like this: The sender's mobile phone breaks down a long message into smaller parts and sends each of them as a single SMS message. When these SMS messages reach the destination, the recipient mobile phone will combine them back to one long message.

    Concatenated messages are supported by Ozeki NG SMS Gateway. It does the SMS segmentation and reassembly seamlessly.

    What happens if an SMS message is sent to a mobile phone that is offline?

    The SMS messages is stored in the SMSC until the destination phone becomes online.

    In standard SMS communication when an SMS is submitted by a mobile phone it is submitted to an SMSC. This message submission is called Mobile originated (MO) message submission. After the SMSC receives the message it stores it and looks for the recipient mobile phone. If the recipient mobile phone is available in the mobile network it sends the message as a Mobile terminated (MT) message. The format of the MO and MT messages are different.

    If a computer sends a message to a mobile phone it submits it to an SMSC. This message submission is called Application originated (AO) message submission and it is often done through an IP SMS protocol.

    What is SM-MT (short message - mobile terminated)?

    SM-MT denotes the capability of the GSM system to send a message from the SC to a mobile phone where the message is either received, or, if the recipient device is unavailable, stored for later delivery. A delivery report or failure report is then sent back to the SC. These messages may be input to the Service center by other mobile users (via a mobile originated short message) or by a variety of other sources, for example, speech, telex, or facsimile.

    What is SM-MO (short message - mobile originated)?

    SM-MO denotes the capability of the GSM system to send a message from an M to an SME via an SC and to provide information to the mobile phone about the delivery or failure of that message. These messages may be destined for other mobile users, or for subscribers on a fixed network.

    What are the classes of SM-MT (mobile terminated) messages?

    Classes identify the importance of the message importance and the location where it should be stored. There are four message classes.

    Class 0 SMS: This message is displayed on the mobile phone immediately and a message delivery report is sent back to the SC. The message does not have to be saved in the mobile phone or on the SIM card (unless selected to do so by the mobile user). This type is also referred to as Flash SMS.
    Class 1 SMS: This message is stored in the memory of the mobile phone or the SIM card (depending on memory availability).
    Class 2 SMS: This message class is Phase 2-specific and carries SIM card data. The SIM card data must be successfully transferred prior to sending acknowledgment to the SC. An error message is sent to the SC if this transmission is not possible.
    Class 3 SMS: This message is forwarded from the receiving entity to an external device. The delivery acknowledgment is sent to the SC regardless of whether or not the message was forwarded to the external device.

    I have one issue. If we send SMS through ozeki s/w and receiver number does not exists then what happen?

    In this case the SMS service provider might reject the message when you try to send it, or it might accept it and later return a delivery report, that indicates that the message could not be delivered. In the first case the SMS will end up in the not sent folder. In the second case it will end up in the sent folder, and when an "undelivered" delivery report comes in it will be marked undelivered.

    If you use an SQL to SMS configuration, the status in the first case will be set to notsent, in the second case it will be first set to sent, then to undelivered.

    I have one issue. If we send SMS through ozeki s/w and receiver has switched off his mobile. Will updated value of status field of ozekimessageout table show the status?

    In this case the message will be accepted by the SMS service provider for delivery and the message will be saved into the sent folder. While the recipient mobile phone is switched off, the SMS service provider's SMSC will store the message. When the phone is switched on, it will be delivered to it and your system will receive a delivery report.

    If you use an SQL to SMS configuration, the status will be set to sent after the SMS is accepted by the SMSC, and after the delivery report is received it will be changed to delivered.

    It might be possible that the recipient will never switch his mobile phone on. In this case after a while (message validity time, which is usually 1 week), the SMS will be deleted from the SMSC of the service provider and you will receive an "undelivered" status report.

    If you use an SQL to SMS configuration, the status will be set to sent after the SMS is accepted by the SMSC, and after the delivery report is received it will be changed to undelivered.

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