2. Definition
Short message service (SMS) is a globally accepted
wireless service that enables the transmission of
alphanumeric messages between mobile subscribers
and external systems such as electronic mail, paging,
and voice-mail systems.
3. Introduction
SMS appeared on the wireless scene in 1991 in Europe.
The European standard for digital wireless, now known as
the Global System for Mobile Communications (GSM),
included short messaging services from the outset.
In North America, SMS was made available initially on
digital wireless networks built by early pioneers such as
BellSouth Mobility, PrimeCo, and Nextel, among others.
These digital wireless networks are based on GSM, code
division multiple access (CDMA), and time division
multiple access (TDMA) standards.
4. How it works?
Messages in Short Message Service (SMS) must be no longer than 160 alpha-numeric
characters and contain no images or graphics.
Once a message is sent, it is received by a Short Message Service Center (SMSC),
which must then get it to the appropriate mobile device.
To do this, the SMSC sends a SMS Request to the home location register (HLR) to find
the roaming customer. Once the HLR receives the request, it will respond to the SMSC
with the subscriber's status: 1) inactive or active 2) where subscriber is roaming.
If the response is "inactive", then the SMSC will hold onto the message for a period of
time. When the subscriber accesses his device, the HLR sends a SMS Notification to
the SMSC, and the SMSC will attempt delivery.
The SMSC transfers the message in a Short Message Delivery Point to Point format to
the serving system. The system pages the device, and if it responds, the message gets
delivered.
The SMSC receives verification that the message was received by the end user, then
categorizes the message as "sent" and will not attempt to send again.
The number of mobile-phone users expects to reach 500 million worldwide by 2003, and
with the help of SMS, 75 percent of all cellular phones will be Internet-enabled.
5. Benefits of SMS
At a minimum, SMS benefits include the following:
Delivery of notifications and alerts
Guaranteed message delivery
Reliable, low-cost communication mechanism for concise
information
Ability to screen messages and return calls in a selective way
Increased subscriber productivity
6. Benefits of SMS (cont.)
More sophisticated functionality provides the following
enhanced subscriber benefits:
Delivery of messages to multiple subscribers at a time
Ability to receive diverse information
E-mail generation
Creation of user groups
Integration with other data and Internet-based applications
7. Benefits of SMS (cont.)
The benefits of SMS to the service provider are as follows:
Ability to increment average revenue per user (due to increased number of calls
on wireless and wireline networks by leveraging the notification capabilities of
SMS)
An alternative to alphanumeric paging services, which may replace or
complement an existing paging offer
Ability to enable wireless data access for corporate users
New revenue streams resulting from addition of value-added services such as e-
mail, voice mail, fax, and Web-based application integration, reminder service,
stock and currency quotes, and airline schedules
Provision of key administrative services such as advice of charge, over-the-air
downloading, and over-the-air service provisioning
Protection of important network resources (such as voice channels), due to
SMS’ sparing use of the control and traffic channels
Notification mechanisms for newer services such as those utilizing wireless
application protocol (WAP)
8. Network Elements and Architecture
The basic network structure of the SMS in an IS–41 network.
9. External Short Messaging Entities
An ESME is a device that may receive or send short
messages. The short message entity (SME) may be
located in the fixed network, a mobile device, or another
service center.
VMS—The VMS is responsible for receiving, storing, and playing voice messages
intended for a subscriber that was busy or not available to take a voice call. It is also
responsible for sending voice-mail notifications for those subscribers to the SMSC.
Web—The growth of the Internet has also affected the world of SMS. Therefore, it
is almost mandatory to support interconnections to the World Wide Web for the
submission of messages and notifications. The increasing number of Internet users
has a positive impact on the SMS traffic increment experienced in the last few years.
10. SMSC
SMSC is a combination of hardware and software responsible for the
relaying and storing and forwarding of a short message between an
SME and mobile device.
The SMSC must have high reliability, subscriber capacity, and
message throughput. In addition, the system should be easily scalable
to accommodate growing demand for SMS in the network.
Normally, an IN–based solution will allow for a lower entry cost
compared to point solutions because it can support other applications
on a single hardware platform and share resources, thereby spreading
the deployment cost over several services and applications.
Another factor to be considered is the ease of operation and
maintenance of the application, as well as the flexibility to activate new
services and upgrade to new software releases.
11. External Short Messaging Entities
(cont.)
E-Mail—Probably the most demanded application of SMS is
the ability to deliver e-mail notifications and to support two-way
e-mail, using an SMS–compliant terminal. The SMSC must
support interconnection to e-mail servers acting as message
input/output mechanisms.
Others—There are several other mechanisms to submit short
messages to the SMSC that include, but are not limited to,
paging networks, specialized software for PC–based messaging
and operator bureaus.
12. STP and HLR
Signal Transfer Point
The STP is a network element normally available on IN
deployments that allows IS–41 interconnections over signaling
system 7 (SS7) links with multiple network elements.
HLR
The HLR is a database used for permanent storage and
management of subscriptions and service profiles. Upon
interrogation by the SMSC, the HLR provides the routing
information for the indicated subscriber. Also, if the destination
station was not available when the message delivery was
attempted, the HLR informs the SMSC that the station is now
recognized by the mobile network to be accessible, and thus the
message can be delivered.
13. VLR and MSC
Visitor Location Register (VLR)
The visitor location register is a database that contains
temporary information about subscribers homed in one HLR
who are roaming into another HLR. This information is needed
by the MSC to service visiting subscribers.
MSC
The MSC performs the switching functions of the system and
controls calls to and from other telephone and data systems.
The MSC will deliver the short message to the specific mobile
subscriber through the proper base station.
14. Air Interface and The Base Station
System
Air Interface
The air interface is defined in each one of the different wireless
technologies (GSM, TDMA, and CDMA). These standards specify how
the voice or data signals are transferred from the MSC to the handset
and back, as well as the utilization of transmission frequencies,
considering the available bandwidth and the system’s capacity
constraints.
The Base Station System
All functions related to the transmission of electromagnetic radio signals
between the MSC and the mobile devices are performed in the base
station (BS). The BS consists of base station controllers (BSCs) and
the base transceiver stations (BTSs), also known as cell sites or simply
“cells.” The BSC may control one or more BTSs and is in charge of the
proper resource assignment when a subscriber moves from one sector
of one BTS to another, regardless of whether the next sector lies within
the same BTS or in a different one.
15. The Mobile Device
The mobile device is the wireless terminal capable of receiving and
originating short messages. Commonly, these devices have been
digital cellular phones, but more recently the application of SMS
has been extended to other terminals such as POS, handheld
computers, and personal digital assistants (PDAs). The wireless
network signaling infrastructure is based on SS7. SMS makes use
of the mobile application part (MAP), which defines the methods
and mechanisms of communication in wireless networks and
employs the services of the SS7 transactional capabilities
application part (TCAP). An SMS service layer makes use of the
MAP signaling capabilities and enables the transfer of short
messages between the peer entities.
16. Signaling Elements
The MAP layer defines the operations necessary to support
SMS. The following basic MAP operations are necessary to
provide the end-to-end SMS:
Routing Information Request
Point-to-Point Short Message Delivery
Short Message Waiting Indication
Service Center Alert
17. Service Elements
SMS is comprised of several service elements relevant
to the reception and submission of short messages:
Message Expiration
Priority
Message Escalation
In addition, SMS provides a time stamp reporting the time of
submission of the message to the SMSC and an indication to the
handset of whether or not there are more messages to send (GSM)
or the number of additional messages to send (IS–41).
18. Subscriber Services
SMS comprises two basic point-to-
point services:
• Mobile-originated short message (MO–SM)
• Mobile-terminated short message (MT–SM)
21. MT–SM Scenario (GSM)
1. The short message is submitted from the ESME to the SMSC.
2. After completing its internal processing, the SMSC interrogates the
HLR and receives the routing information for the mobile subscriber.
3. The SMSC sends the short message to the MSC using the forward
short message operation.
4. The MSC retrieves the subscriber information from the VLR. This
operation may include an authentication procedure.
5. The MSC transfers the short message to the MS.
6. The MSC returns to the SMSC the outcome of the
forwardShortMessage operation.
7. If requested by the ESME, the SMSC returns a status report
indicating delivery of the short message.
23. MT Short Message Scenario (IS–41)
1. The short message is submitted from the ESME to the SMSC.
2. The SMSC sends an acknowledgement to the ESME, indicating
reception of the short message.
3. After completing its internal processing, the SMSC interrogates the
HLR.
4. The HLR sends the routing information for the mobile subscriber to
the SMSC.
5. The SMSC sends the short message to the MSC using the
SMSDPP Invoke operation.
6. The MSC transfers the short message to the MS.
7. The MS returns an acknowledgement to the MSC.
8. The MSC returns to the SMSC the outcome of the SMSDPP
operation.
9. If requested by the ESME, the SMSC returns a delivery receipt
indicating successful delivery of the short message.
25. MO–SM Scenario (GSM)
1. The MS is powered on and registered with the network.
2. The MS transfers the SM to the MSC.
3. The MSC interrogates the VLR to verify that the message
transfer does not violate the supplementary services invoked
or the restrictions imposed.
4. The MSC sends the short message to the SMSC using the
forwardShortMessage operation.
5. The SMSC delivers the short message to the SME (and
optionally receives acknowledgment).
6. The SMSC acknowledges to the MSC the successful
outcome of the forwardShortMessage operation.
7. The MSC returns to the MS the outcome of the MO-SM
operation.
27. MO–SM Scenario (IS–41)
1. The MS transfers the SM to the MSC.
2. The MSC interrogates the home SMSC to verify that the message transfer
does not violate the supplementary services invoked or the restrictions
imposed. The MSC sends the short message to the home SMSC using the
SMSPP Invoke operation
3. The SMSC delivers an acknowledgment to the MSC.
4. The MSC returns order release to the MS.
5. The SMSC queries the HLR for the location of the destination MS.
6. The HLR returns the destination (MSC) serving the destination MS.
7. The SMSC delivers SM to the MSC serving the destination MS.
8. The SMSC delivers the short message to the MS.
9. The MS acknowledges to the MSC the successful outcome of the SMSDPP
operation.
10. The MSC returns to the SMSC the outcome of the MO–SM operation
(delivery successful).
28. Glossary
ATM asynchronous transfer mode
BS base station
BSC base station controller
BTS base transceiver station
CDMA code division multiple access
CMT cellular messaging teleservice
CPT cellular paging teleservice
ERMES European Radio Messaging System
ESME external short message entities
ETSI European Telecommunications
Standards Institute
GSM Global System for Mobile
Communications
HLR home location register
IN intelligent network
IP Internet protocol
LAN local-area network
MAP mobile application part
MO mobile originated
MO–SM mobile-originated short message
MSC mobile switching center
MT mobile terminated
MT–SM mobile-terminated short message
PDA personal digital assistant
POS point of sale
PP point to point
SIM subscriber identity module
SM short message
SMD short message delivery
SMD–PP short message delivery–point to
point
SME short messaging entity
SMS short message service
SMSC short message service center
SS7 signaling system 7
STP signal transfer point
TCAP transactional capabilities application
part
TDMA time division multiple access
VLR visitor location register
VMN voice-mail notification
VMS voice-mail system
WAN wide-area network
WAP wireless application protocol
29. FAQs (1)
1. What is it?
The Short Message Service (SMS) allows people to send and receive short
( up to 160 characters ) written messages using their GSM telephones.
2. How does it work? Every GSM network has a Message Centre, which is
responsible for the managment of the messages. When someone sends an
message to another user, this goes to the Message Centre, which finds where
the other user is. It adds to the message the date, time and number of the
sender and sends it to receiptient. If his telephone is deactivated, then the
message is stored and will be send as soon as the receiptient connects to the
network.
3. What is SMS-MT, SMS-MO and SMS-CB ?
When a telephone supports SMS-MT means that it can receive short messges.
When a telephone supports SMS-MO means that it can send short messges.
When a telephone supports SMS-CB means that it can receive short messges
send by the network (Cell Broadcasting).
30. FAQs (2)
4. Do all telephones support SMS ?
All telephones are capable of receiving short messages (SMS-MT).
However, many of the older telephones do not support message sending (SMS-MO).
All the new ones, (according to Phase II ) support receiving-sending of messages.
5. What should be done in order to be able of receiving short messages ?
Nothing. You do not need to configure anything on your phone. As soon as you
receive a message, you will be aple to read it on the sceen of your telephone.
6. What should be done in order to be able of sending short messages ?
Before you send a message for the first time, you have to enter into the telephone, the
number of the SMS centre of your network. This number is entered once, and saved
so that you don't have to write it ever time you want to send a message. If you don't
know this number then you should contact your network.
7. How do you send a message ?
From the menus of your telephone, select "write message". Then type in, using the
keypad of your telephone, the message (which should be maximum 160 characters).
Then you will be asked the number of the receiptient. Enter it and press send.
31. FAQs (3)
8. How much does this service cost?
Most networks allow you to use this service without having to make a special
subscription. You only pay for the messages you send. However, some
networks will charge you even if you receive a message.
9.Why use this service ?
Using SMS you can send important information and numbers to someone else
(ex. bank account numbers, telephone numbers etc) with secure. He will have
them saved into his phone and will be able to read them as many times as he
wants. Even more, many companies can send you your e-mail to your mobile
phone, or even give you information you have requested via SMS.
10. Anything else ?
You can use the short message service while you are talking on your mobile
phone. This means, while you talk you are able to receive and send
messages.
