1. Introduction to
SMS Messaging
1.1. What is SMS
(Short Message Service)?
SMS
stands for Short Message Service. It is a technology that enables the
sending and receiving of messages between mobile phones. SMS first
appeared in Europe in 1992. It was included in the GSM (Global System
for Mobile Communications) standards right at the beginning. Later it
was ported to wireless technologies like CDMA and TDMA. The GSM and
SMS standards were originally developed by ETSI.
ETSI is the abbreviation for European Telecommunications Standards
Institute. Now the 3GPP (Third
Generation Partnership Project) is responsible for the development
and maintenance of the GSM and SMS standards.
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 up to:
160
characters if 7-bit character encoding is used. (7-bit 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 Chinese
characters should use 16-bit character encoding.)
SMS
text messaging supports languages internationally. It works fine with
all languages supported by Unicode, including Arabic, Chinese,
Japanese and Korean.
Besides
text, SMS messages can also carry binary data. It is possible to send
ringtones, pictures, operator logos, wallpapers, animations, business
cards (e.g. VCards) and WAP configurations to a mobile phone with SMS
messages.
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 WAP and mobile Java are not supported on many
old mobile phone models.
1.2. Concatenated
SMS Messages / Long SMS Messages
One
drawback of the SMS technology is that one SMS message can only carry
a very limited amount of data. To overcome this drawback, an
extension called concatenated SMS (also known as long SMS) was
developed. 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.
The
drawback of concatenated SMS is that it is less widely supported than
SMS on wireless devices.
1.3. EMS (Enhanced
Messaging Service)
Besides
the data size limitation, SMS has another major drawback -- an SMS
message cannot include rich-media content such as pictures,
animations and melodies. EMS (Enhanced Messaging Service) was
developed in response to this. It is an application-level extension
of SMS. An EMS message can include pictures, animations and melodies.
Also, the formatting of the text inside an EMS message is changeable.
For example, the message sender can specify whether the text in an
EMS message should be displayed in bold or italic, with a large font
or a small font.
The
drawback of EMS is that it is less widely supported than SMS on
wireless devices. Also, many EMS-enabled wireless devices only
support a subset of the features defined in the EMS specification. A
certain EMS feature may be supported on one wireless device but not
on the other.
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