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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.