This gonna be a long post!
USSD stands for Unstructured Supplementary Service
Data. In a nutshell, they are application where a user dials *a number
#, for example *144# for balance inquiry for Safaricom (a Kenyan Telco). It
is a capability built into the GSM standard for support of transmitting
information over the signaling channels of the GSM network. However
gateways can be built (API) to help developers. USSD provides
session-based
communication, enabling a variety of applications. Imagine how to
build the menu you interact with when you dail *188# on a safaricom
network?
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| USSD System architecture |
USSD is not a mobile phone software!
Well, USSD (Unstructured Supplementary Service Data) is a
Global System for Mobile(GSM) communication technology that is used to send text
between a mobile phone and an application program in the network.
USSD text
messages can be up to 182 bytes (unlike sms, which is 160 bytes) in
length (Bytes; I simply mean characters). Messages
are transferred directly over the network signaling channels.
USSD
is session-oriented, which means that when a user
accesses a service with USSD, a session is established and the radio connection
stays open until the user, application, or time out releases it. You may have noticed that when you run a USSD code in you phone, and become idle, the menu disappears and you are forced to start all over again. This provides
faster response times for interactive
applications.
USSD applications are
accessed by user request, and make use of short codes or text strings to trigger certain
services in a session-based communication.
These codes could
perform a function, request a snippet of information, or lead the user into a series
of textual menus
which are navigated through the corresponding menu numbers.
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| USSD Menu |
How does it differ from SMS (Short Message Service) ?
1. SMS uses a “store and forward” technique to
deliver text messages:
A text message is first sent to a sender’s Short Message Service Center
(SMSC) before the SMSC tries to deliver the text message to the recipient.
The sender receives an indication of whether the text
was successfully received by
the SMSC; however, the text message is not guaranteed to
reach the recipient instantly.
USSD on the other hand is session oriented, unlike SMS, which is a
store-and-forward, USSD is transaction-oriented technology.
2. Turnaround response times for interactive applications
are shorter for USSD than SMS because of the session-based feature of USSD, and
because it is NOT a store and forward service.
3. USSD is also not a point-to-point bearer such as SMS.
One subscriber cannot send another text using USSD unless there is a special
network application offering such an application.
4. One can send 182 characters using USSD, but SMS only
allows for 140 x 8-bit, or 160 x 7-bit characters.
A USSD gateway is usually equipped with session
management capabilities, that can handle cell switching, to make sure an USSD
Session is preserved even when the subscriber changes cells.
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