SMS Technical Details

SMS TECHNICAL DETAILS

Short Message Service -(SMS-PP) Point to Point has been defined in GSM recommendation 03.40. GSM 03.41 is separate from this which defines the Short Message Service - Cell Broadcast (SMS-CB) which provided messages (public information, advertising etc.) to be broadcasted in a specific geographical area to all mobile users.

Messages sent are forward mechanism-and-via store to a Short Message Service Centre (SMSC), which tries sending message to the recipient and possibly retry if the user at a given time is not reachable. Both Mobile Terminated (MT), for messages which are sent to a mobile handset, and Mobile Originating (MO), for those which are sent from the mobile handset, operations are given support. The best effort is message delivery, so there is no guarantee that a message will really be delivered to its recipient and delay or the message which is of complete loss is not uncommon, specially when it is send between  networks.

Within the standard GSM MAP frame work transmission of the short messages between SMSC and phone is via SS7 . Messages sent with the additional MAP operation forward_short_message, whose payload length is limited through constraints of the signalling protocol to precisely 140 bytes.

In Content which is larger (long SMS or concatenated SMS) can be sent over multiple messages that is segmented, in which case every message will begin with a user data header (UDH) that contains segmentation information. Since UDH in the payload, the number of characters per segment is lower: 153 for 7 bit encoding, 134 for 8 bit encoding and 67 for 16 bit encoding.

While the standard theoretically allows till 255 segments, practically maximum is 3 to 4 messages, messages which long are billed that are equivalent to multiple SMS messages.

Short messages can be send to binary content also such as logos or ring tones, as well as configuration data or OTA programming. Uses like these are a vendor-specific extension of the GSM specification and competing strands which are multiple are there, although Nokia's Smart Messaging is the most common.

Few service providers provide ability  to send the messages to land line telephones not regarding  their capability of receiving text messages by phoning automatically  the recipient and reading the message loudly by using a speech synthesizer also with the number of the sender.