5. Basic Concepts
of SMS Technology
the following sections, we will introduce to you some basic concepts
of the SMS technology.
Period of an SMS Message
SMS message is stored temporarily in the SMS center if the recipient
mobile phone is offline. It is possible to specify the period after
which the SMS message will be deleted from the SMS center so that the
SMS message will not be forwarded to the recipient mobile phone when
it becomes online. This period is called the validity period.
is an example that illustrates how validity period can be used.
Suppose you find a very interesting program that is showing on TV
now. You think your friend may want to watch it. So, you send a text
message to tell your friend about the TV program. Let's say the TV
program lasts for an hour. Your SMS text message will not be useful
to your friend if his mobile phone is not available before the
program finishes. In this situation, you may want to send a text
message with a validity period of one hour to your friend. The
wireless carrier will not deliver the SMS text message to your friend
if his mobile phone is not available before the validity period ends.
mobile phone should have a menu option that can be used to set the
validity period. After setting it, the mobile phone will include the
validity period in the outbound SMS messages automatically.
you may want to know whether an SMS message has reached the recipient
mobile phone successfully. To get this information, you need to set a
flag in the SMS message to notify the SMS center that you want a
status report about the delivery of this SMS message. The status
report is sent to you in the form of an SMS message.
mobile phone should have a menu option that can be used to set
whether the status report feature is on or off. After setting it, the
mobile phone will set the corresponding flag in the outbound SMS
messages for you automatically. The status report feature is turned
off by default on most mobile phones and GSM / GPRS modems.
leaving the mobile phone, an SMS message goes to the SMS center. When
it reaches the SMS center, the SMS center will send back a message
submission report to the mobile phone to inform whether there are any
errors or failures (e.g. incorrect SMS message format, busy SMS
center, etc). If there is no error or failure, the SMS center sends
back a positive submission report to the mobile phone. Otherwise it
sends back a negative submission report to the mobile phone. The
mobile phone may then notify the user that the message submission was
failed and what caused the failure.
the mobile phone does not receive the message submission report after
a period of time, it concludes that the message submission report has
been lost. The mobile phone may then re-send the SMS message to the
SMS center. A flag will be set in the new SMS message to inform the
SMS center that this SMS message has been sent before. If the
previous message submission was successful, the SMS center will
ignore the new SMS message but send back a message submission report
to the mobile phone. This mechanism prevents the sending of the same
SMS message to the recipient multiple times.
the message submission report mechanism is not used and the
acknowledgement of message submission is done in a lower layer.
receiving an SMS message, the recipient mobile phone will send back a
message delivery report to the SMS center to inform whether there are
any errors or failures (example causes: unsupported SMS message
format, not enough storage space, etc). This process is transparent
to the mobile user. If there is no error or failure, the recipient
mobile phone sends back a positive delivery report to the SMS center.
Otherwise it sends back a negative delivery report to the SMS center.
the sender requested a status report earlier, the SMS center sends a
status report to the sender when it receives the message delivery
report from the recipient.
the SMS center does not receive the message delivery report after a
period of time, it concludes that the message delivery report has
been lost. The SMS center then re-sends the SMS message to the
the message delivery report mechanism is not used and the
acknowledgement of message delivery is done in a lower layer.
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