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SMS FAQS
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What is SMS?
SMS or Short Messaging Service enables mobile phones to send and receive
alphanumeric messages. It is part of the
GSM (Global System for Mobile
Communications) standard.
How many ways can you send and receive SMS?
Two. You can send and receive SMS by text mode and by PDU mode.
What does SMS PDU mode offer?
The SMS PDU mode offers to send binary information in 7-bit
GSM format
8-bit (manufacturer specific) and 16-bit Unicode format. In PDU mode, it
is possible to send images, ring tones and long SMSes (more than 160
characters) as long as the receiving phone supports it.
What is the difference between text mode and pdu mode in SMS?
Text mode is just an encoding of the bit stream represented by the
PDU mode. Alphabets may differ and there are several encoding alternatives
when displaying an SMS message. The most common options are "PCCP437",
"PCDN", "8859-1", "IRA" and "
GSM". These
are all set by the at-command AT+CSCS, when you read the message in a computer
application. If you read the message on your phone, the phone will choose a proper
encoding. An application capable of reading incoming SMS messages can thus use text
mode or PDU mode. If text mode is used, the application is bound to (or limited by)
the set of preset encoding options. In some cases, that's just not good enough.
If PDU mode is used, any encoding can be implemented.
What does a SMS message in pdu mode contain?
The PDU string contains not only the message, but also a lot of meta-information
about the sender (his SMS service center, the time stamp etc). It is all in the form
of hexa-decimal octets or decimal semi-octets.
How does SMS work?
Each GSM network has a SMS
Center or SMSC, which is in charge of routing SMS messages. When someone sends a SMS
message to another user, this goes to the SMSC, which finds where the other user is.
It adds to the SMS message the date, time and number of the sender and sends it to
recipient. If the recipient's mobile phone off, the message is stored and will be
sent as soon as the recipient turns on the mobile phone.
What is the maximum length of a SMS?
A single SMS can contain up to 160 characters of text. However it is possible to
string together a number of SMSes to contain more than 160 characters, in practice
it is possible to send SMSes with about 400 characters (technically it is possible
to send much longer SMSes but if just one of the messages gets lost, everything is
lost) so in practice about 400 is the limit. Many networks also charge for each PDU
sent, so sending long SMSes becomes prohibitively expensive (this is more of a factor
than the cost) If you need to send really long SMSes maybe you should rethink either
your application or the platform. Anyway nobody wants to read those long SMSes
(they are a pain on a small phone display). One application where long SMSes may be
relevant is in M2M (Machine 2 Machine) communication where two computers are
communicating and transferring for example security data (Nokia
has a few examples on their website (link)) from a "outpost" (with weak connection to the base station)
to a main data center. In those cases you should maybe consider a proprietary two way
radio link to a better location and a data transfer from there.
Do all mobile phones have SMS capability?
No. Only GSM-based mobile
phones and later technologies support SMS. However outside Japan and USA almost all
phones do support it, and in US the networks are converting fast to GSM
-based technology. Some phone manufacturers support SMS sending better than others.
Nokia is probably the best and
SAGEM and Motorola
the worst when it comes to supporting SMS, but they all support SMS nowadays.
Can SMS be sent anywhere?
SMS can be sent to any GSM
-compatible network anywhere in the world, and a few TACS compatible networks also
support SMS. NMT (if they Scandinavians haven't closed that relic down yet) also
support SMS (in fact it started there).
Does SMS support all languages?
No. basic SMS does not support Greek, Cyrillic, Asian and Arabic characters.
However, Some phones (the newer ones) support
Unicode (UCS-16) SMS and then all languages in the world
at least have basic support.
What is GSM?
GSM (Global System for Mobile
Communications) is a digital system with a specified standard for how data is sent
over a wireless network. Visit
ETSI Website for more information.
What is SMSC?
SMSC (Short Message Service Center) enables subscribers to send and receive messages
in a mobile network. When you access a SMSC from the phone it is invisible but when
you program computers the SMSC is very visible. The SMSC is the first step in the
sending of a SMS (and the last step if you are receiving) in the SMS world the SMSC
works very much like your ISP works in the internet world. Different operators has
given different capabilities to their SMSCs. Some SMSCs can't roam and others are
very expensive (and some are both).
What is EMS?
EMS (Enhanced Messaging Service) is an enhancement of the SMS standard. EMS allows
the inclusion of simple melodies, pictures, sounds, animations, modified text and
standard text into the message. EMS is touted at the successor to SMS and we believe
it to be true. Nokia already has most of the capabilities of EMS but if you want to
send a picture message from a Nokia phone to a Alcatel then it wont work. If however
you send a picture message from a EMS capable Ericsson phone to a EMS capable phone
of another brand then it will work, and that is the good thing about EMS is that
like text SMS, it is highly standardized. Visit
3GPP Website for more information.
What is MMS?
MMS (Multimedia Messaging Service) is the next generation upgrade for SMS in 3G
networks. It is intended to provide a rich set of content to subscribers in a
messaging context by enabling text, sounds, images and video to be embedded into
the message. At present and about 3 years from now, don't think too much about MMS.
Very few operators has network infrastructure that supports this new standard.
What is 3G?
3G stands for the third generation of wireless communication technology.
It refers to pending improvements in wireless data and voice communications
through any of a variety of proposed standards. The immediate goal is to raise
transmission speeds from 9.5K to 2M bit/sec. Presently there is only one 3g network
in operation (by Docomo in Japan)
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