Communication
Networks
Communication
Networks
Web Page created by:
Kuross Amri 99066589
Tom Ceglarek 99066627
Declaration of Originality:
The work contained in this web page and associated files, other than that specifically attributed to another source, is that of the author(s). It is recognised that, should this declaration be found to be false, disciplinary action could be taken and the assignments of all students involved will be given zero marks. In the statement below, I have indicated the extent to which I have collaborated with other students, whom I have named.
1. Outline Of Topis To Be Covered
7. SMS Speak
10. External Short Messaging Entities
11. Short Message Service Centre
13. SMS - Gateway
21. SMS Signalling
22. Wireless Access
23. Dial-up Access
24. MAP Operations
25. Service Elements
27. GSM Signalling Protocol - MS
28. GSM Signalling Protocol - BSS
31. Signalling System No.7 - SCCP
32. Signalling System No.7 - MTP
33. SMS Point to Point Protocol
34. SMS TPDU Types
38. Telecator Alphanumeric Protocol
39. SMS using Telecator Alphanumeric Protocol
41. Protocol for SMS
42. Block Mode
43. Text Mode
44. PDU Mode
45. SEMA SMS2000
48. Compression
49. Concatenation
50. Alphabet
51. Different Alphabet Support
55. Features Under Development
56. Glossary
57. References
1. Outline Of Topis To Be Covered
1. Background
• What is SMS?
• Uses?
• Historical development
• How does it appear to the user?
(Demonstration)
2. Social impacts
• New form of communication
• Rapid uptake by users
• Why?
3. Architecture
• Network required to operate a short
message service
4. Components
• What each part of the network does
5. Signalling
• What signalling in the network is
required to send an SMS
6. Features
7. Modes of operation
• Mobile originated: Sending an SMS
• Mobile terminated: Receiving an SMS
from another mobile, web, network operator etc. (Timelines)
[Back to
Contents]
2. What is SMS?
Definition: 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
(International Engineering Consortium, 2002)
Guaranteed delivery: if a wireless recipient is switched off, out of range or if
there is a network outage, the SMS message will be stored in the network and
delivered when the recipient announces its presence, or when the outage is
rectified. No guarantees existed with previous such services eg. Alphanumeric
paging. This is the basis of the store-and-forward concept.
Send or receive during voice or data calls: SMS messaging makes use of a
separate channel, normally used for transfer of control messaging to transfer
its packets. Being out-of-band, this means voice and data calls will not be
interrupted by SMS transfer. Furthermore, the low-bandwidth requirements of
transmitting short alphanumeric strings allows messaging worldwide with very low
latency. This of course depends upon network operator agreements.
Analogue: the world-wide standard in the late 1980s and
early 1990s had no capability for text messaging
GSM: European networks began development of a digital standard (GSM) in 1991.
Phase 2 of the standard, release in 1993, defined data bearing services over GSM
– SMS was a part of this standard. Vodacom (South Africa) became the first
company in the world to implement fax and data services on its network, later
that year.
CDMA/TDMA: The American networks decided to take an alternative route, using
first TDMA and later, the superior CDMA which integrated text messaging into its
standard. TDMA later gained this capability through Motorola’s iDEN development.
Interoperability: When the buildout of personal communication service (PCN)
networks was complete in 1998, SMS was fully deployed. All that remained was the
agreement between network operators to allow this.
April 2000: Australian networks agree to allow interoperability between SMS
users.
Originally SMS was used for:
- notification purposes: particularly voice mail (eg. Optus)
- 2-way messaging: intended to supersede alphanumeric paging, the capability was
introduced simply to allow general-purpose messaging between wireless entities.
Newer implementations for SMS include:
- E-mail: a number of services now exist that allow you to check a POP3 mail
account on your handset, or employ translation of e-mail into SMS form for
receipt on a handset
- Fax: allows of transfer through handset to a notebook, or translation into
actual SMS messages for viewing on the handset.
- Interactive banking: services such as the Vodafone/Commonwealth Bank
mobileBank service allow account balances, funds transfers and other
transactions to be completed via SMS messaging on a user’s handset.
- Information services: for a fee, a number of service providers will now send
regular updates on share prices, news headlines, the weather and even goings on
at the Big Brother house straight to your handset via SMS.
Web integration:
- a number of forms exist, including the ability to receive web content through
SMS, the sending/receiving of actual WAP datagrams through SMS, as well as
emerging cross-platform approaches such Internet instant messaging services
being combined with SMS sending capabilities – allowing ‘SMS chat’.
5. Using SMS
FlashMX presentation of SMS operation on a mobile handset. The ‘user’s view’ of SMS.
Animation 1
This animation covers typing and sending of messages to another mobile entity.
Select MESSAGES and WRITE MESSAGES from the phone menu. It is of course possible
to select the inbox from your phone to view incoming messages, however this is
not covered in the scope of this animation.
The model used for this animation is based on the NOKIA™ SMS typing system.
Initially the screen shows the available 160 characters that are available for
use in the SMS. It also shows in the top left hand of the screen the style of
text entry. At the present it is on predictive text with the first letter being
a capital.
As the text is being typed in the first thing that is noticed is the
decrementing of the available characters in the message. The style of text has
also changed to indicate that the letters will be in lowercase. The style of
text can be changed via the “#” key which cycles through the available styles,
this includes turning off predictive text.
The predictive text method involves only pressing the button containing the
letter you want once. This is a development over the manual method whereby if
the letter required is 3rd on the button, the button must be pressed 3 times.
Predictive text allows one press per letter and the different possibilities are
presented at the end of the word for selection. This can be seen on the word
“me” in the animation. The phone selects the more commonly used “of” by default
and it is up to the user to select the required word. If the word is unusual, or
not on file in the phone, it can be manually entered via the old method to be
saved into the phone’s memory.
Once the message has been typed in, the user can then choose to send it to the
desired recipient. In this case the number is already available, however it can
be entered manually or selected via the phone or sim card memory. The message is
sent and if received by the SMSC a successful acknowledgement is returned. The
message does not have to be delivered to the MSE immediately as 7 days storage
in the SMSC is available for the message to be sent.
SMS was introduced with GSM network
rollouts across Australia, 1993/4. Not a big selling point initially; marketing
focused upon security and voice call clarity under ‘digital’ systems.
SMS became appreciated for its discreetness; communication was made possible
during meetings, movies and even lectures without disturbing others.
Before significant competition brought the costs of voice calls down, SMS was
seen as a significantly cheaper, and in some ways more convenient form of mobile
communication. Whereas simply the flag fall for a voice call could have amounted
to over 20c, SMS was initially a tiny 15c. For this reason, it became popular
amongst the younger users, largely on expensive low-volume or pre-paid plans.
Partly to combat the restriction of only being allowed 160 character messages,
partly due to the appeal of being part of an emerging subculture and partly due
to laziness in having to type through a clumsy telephone keypad, a ‘dialect’
specific to SMS came into usage. It is primarily composed of abbreviations for
commonly used words and phrases; thereby allowing users to fit more into 160
characters.
The popularity of SMS has seen this ‘dialect’ seep into the mainstream somewhat,
through youth-targeted advertising and similar.
SMS did not truly take off, however, until network interoperability was
introduced in April 2000, when it became possible to message any user on any
network.
7. SMS Speak
Various shortcuts used in SMS messages (from AAPT CellularOne)
This data from the GSM Association shows the growth in SMS usage per subscriber, averaged worldwide. It is evident that the volume of SMSs per month doubled approximately every six months, a trend that has continued until now but numbers appear to be levelling off as the market moves towards maturity.
Studies completed for the GSM Association
show the continued upward trend in SMS usage. The results of the previous slide
should be viewed through the context of this information; that is, usage trends
vary greatly among users of different regions.
In the Philippines, for instance, SMS was initially provided as a free service
but incredible usage (upwards of 300 messages/user/month – 1.2 billion messages
in December 2000) meant network operators had to introduce a small tariff to
encourage ‘responsible’ usage of the service. Philippine users are asked to pay
1 peso per message; 8 messages are equivalent in cost to one minute of standard
call time.
Studies have not been completed on the Australian market, however similarities have been noted with the UK telecommunications market, as illustrated here. This data from the UK’s Mobile Data Association shows the marked increase in usage following mobile interoperability agreements (at April 1999), and the introduction of similar agreements for prepaid users (December 1999). SMS has proved particularly popular among prepaid users as the call rates for voice calls on such agreements tend to be exorbitant.
These figures, provided by a leading
Norwegian carrier, depict the changes in usage for SMS. Initially, it was used
largely as a notification system for voicemail messages; while only 2% of
messages were used for person to person messaging.
This greatly contrasts to the later figures that suggest merely 4% of SMSs are
voicemail alerts, and almost 90% of messages are communication-based.
The information SMSs – share price notifications, etc. have not made a
significant impact on SMS usage patterns.
The mobile station is the wireless terminal capable of receiving and originating short messages. These are usually digital cellular phones, but more recently the application of SMS has been extended to other terminals such as point-of-sale (POS), handheld computers and personal digital assistants (PDAs). The wireless infrastructure is based upon signalling system no. 7 (SS7). More specifically, the SS7 mobile applications part (MAP) defines mechanisms and methods of wireless communication, and the transactional capabilities application part (TCAP) in which a SMS service layer makes use of the MAP signalling capabilities and enables the transfer of short messages.
10. External Short Messaging Entities
The ESME is any device that may send or
receive SMSs. They may be fixed within the mobile network, may communicate
through an external network (such as the Internet) or may simply be another
Short Message Service Centre, perhaps from another network.
Examples of ESMEs include:
- Voice mail notification systems (such as Optus’ voice mail service)
- Internet-based clients such as the webSMS interfaces readily available at
BlueSkyFrog.com or freeSMS.com
- E-mail servers: originally only to notify users of incoming messages, this
technology has now extended to actually viewing and sending e-mails from the
keypad of one’s mobile phone
- Others, such as paging systems, operator bureaus and so forth.
11. Short Message Service Centre
The SMSC is a combination of hardware and
software responsible for the relaying and storing and forwarding of a short
message between an SME and a mobile device.
In this way, if one’s phone is switched off or the storage for SMS is full, the
SMSC will retain any messages until the user can receive them.
Of course, the SMSC must be highly reliable, with redundant backups for its
primary functionality in case of failure. It must be able to serve a large
number of subscribers, and thus be able to support a high throughput of
messages. It should also be scalable, to allow expansion for greater capacity or
new developments in messaging, such as EMS or MMS in future.
Manufacturers and networks are increasingly incorporating other forms of access
directly to the SMSC, through modem dialup, X.25 and even the Internet so that
corporate customers can leverage the power of SMS without needing mobile
stations such as mobile phones.
This variant on the implementation of a
Short Message Service Centre places one such unit at every base station,
interacting through, in this example, leased lines. An alternative would be
microwave links between the wireless stations.
This distributed architecture as the advantage of better redundancy in case of a
single failure; all other SMSCs will remain operational throughout the network.
However, load distribution will most likely be uneven through the network and so
some units will be used under capacity and potentially others overloaded.
This alternative implementation for the
Short Message Service Centre has base stations networked through leased lines,
with one centralised location for Short Message Service Centres. This
implementation has a cluster of such NT servers, visible to the network as a
single entity.
This form has the advantage of being better suited to load-sharing as demand in
different areas and times varies in operation. A disadvantage is the requirement
for higher bandwidth links between this SMSC cluster and the rest of the
network; that is, the data distribution will centre upon one part of the
network.
Some of the potential applications of SMS technology, utilizing
both MT-SM and MO-SM where appropriate, include the following:
Notification Services - Notification services are currently the most widely
deployed SMS services. Examples of notification services using SMS include the
following:
Voice/fax message notification, which indicates that voice or fax mail messages
are present in a voice mailbox
E-mail notification, which indicates that e-mail messages are present in an
e-mail mailbox
Reminder/calendar services, which enable reminders for meetings and scheduled
appointment
E-mail Interworking - Existing e-mail services can be easily integrated with SMS
to provide e-mail to short messaging and mobile e-mail and message escalation.
Paging Interworking - Paging services integrated with SMS allow digital wireless
subscribers to be accessible via existing paging interfaces, as well as
escalation of messages.
Information Services - A wide variety of information services can be provided by
the SMS, including weather reports, traffic information, entertainment
information (e.g., cinema, theatre, concerts), financial information (e.g.,
stock quotes, exchange rates, banking, brokerage services), and directory
assistance. SMS can support both push (MT) and pull (MO) approaches to allow not
only delivery under specific conditions but also delivery on demand, as a
response to a request.
WAP Integration - SMS can deliver notifications for new WAP messages to wireless
subscribers but can also be used as the transport mechanism for WAP messages.
These messages can contain diverse information from sources that include
databases, the World Wide Web, e-mail servers, etc.
Mobile Data Services
The SMSC can also be used to provide short wireless data. The wireless data may
be in interactive services where voice calls are involved.
Some examples of this type of service include fleet dispatch, inventory
management, itinerary confirmation, sales order processing, asset tracking,
automatic vehicle location, and customer contact management. Other examples may
be interactive gaming, instant messaging, mobile chat, query services, mobile
banking, etc.
13. SMS - Gateway
Linking the SMSC to the network are two
gateways, the SMS-gateway mobile switching centre (SMS-GMSC) and SMS
interworking mobile switching centre. These are typically integrated into the
SMSC.
Essentially, data in mobile networks is routed through a series of mobile
switching centres (MSCs). If a SMSC needs to send a message to a mobile
recipient, the SMS-GMSC interface will interrogate a Home Location Register (HLR)
for the appropriate routing information and pass the message with this. If, on
the other hand, the recipient is within the network, the SMS-IWMSC simply routes
the message to the appropriate SMSC.
The Home Location Register (HLR), an
integral part of any cellular network, contains the data relevant to network
subscribers: their status, location and thus routing information on how to
access them.
The SMSC will interrogate the HLR in order to obtain routing information for
SMSs submitted, destined for mobile recipients.
The HLR will also inform the SMSC if previously unavailable subscribers have now
registered on the network, allowing the delivery of messages that were buffered
in the SMSC for those users.
Depending upon the structure of the
network, subscribers in one HLR may visit another cell or network; the Visitor
Location Register will then maintain the information on these subscribers while
they roam.
If the destined subscriber is not within their homed HLR, the information in the
VLR of the cell or network they are in will provide the routing information to
ensure they receive their calls or messages.
It works by caching the information required to route calls and messages, as
well as provide subscriber services to users that fall within that VLR’s region
of control, geographically.
Generally integrated into the Mobile Switching Centre, examined next.
The Mobile Switching Centre acts like a
switching hub in an Ethernet network. Essentially, it will switch data between
users on the network, in accordance with the routing information provided by the
HLR/VLR.
In addition to the switching functionality, the MSC handles all the tasks needed
to manage mobile subscribers:
Registration
Authentication
Location updating
Handovers
Routing to roaming subscribers
The MSC also acts as the gateway to regular fixed-line networks, be they PSTN,
ISDN or otherwise.
The Base Station System (BSS) transmits
the voice and data traffic between mobile stations; they are the interface
between mobile subscribers and the mobile network.
Generally consisting two parts, the Base Station Transceiver and Base Station
Controller, these generally exist as the mobile phone towers seen throughout
cities.
Houses the radio transceivers that define
a cell
Handles radio protocols with mobile stations
GSM900, GSM1800, GSM1900 (IS-41), CDMA, iDEN types
The Base Station Controller handles the operation of the BTS. Among tasks such as radio channel setup, frequency hopping and handovers of subscribers between cells, the BSC also handles the conversion of the 13kb/s voice channel over the radio link to the 64kb/s standard used in the PSTN.
This diagram gives an appreciation of how
the components of the digital mobile network relevant to short messaging fit
together.
Apparent on the left are the External Short Messaging Entities as inputs to the
network. These feed directly into the Short Messaging Service Centre.
This example has the SMSC connected to two separate base stations. Two signal
transfer points link the SMSC to the mobile switching centre. The home location
register is accessed through the signal transfer point, and the visitor location
register feeds directly into the MSC.
Finally, the MSC transmits to the base station. The base station then provides
the wireless link to all mobile stations – mobile phones, PDAs, POS systems and
handheld computers.
Animation 4
Step 1: The Mobile Station (MS) is powered on and registered with the network.
Step 2: The MS transfers the SM to the MSC
Step 3: The MSC interrogates the Visitor Location Register (VLR) to verify that
the message transfer does not violate the supplementary services invoked or the
restrictions imposed.
Step 4: The MSC send the short message to the SMSC using the ‘forward short
message’ operation.
Step 5: The SMSC delivers the short message to the SME (acknowledgement is
optional).
Step 6: The short message is submitted from the ESME (External Short Message
Entity) to the SMSC.
Step 7: After completing its internal processing, the SMSC interrogates the Home
Location Register (HLR)
Step 8: The SMSC sends the short message to the MSC using the ‘forward short
message’ operation.
Step 9: The MSC retrieves the subscriber information from the VLR. This
operation may include an authentication procedure.
Step 10: The MSC transfers the short message to the Mobile Station
Step 11: The MSC returns to the SMSC the outcome of the ‘forward short message’
operation.
Step 12: If requested by the ESME, the SMSC returns a status report indicating
delivery of the short message.
Step 13: The SMSC acknowledges to the MSC the successful outcome of the ‘forward
short message’ operation.
Step 14: The MSC returns to the MSC the outcome of the MO-SM operation
21. SMS Signalling
As mentioned in the mobile station slide,
the wireless infrastructure that supports SMS is based on the signalling system
no. 7 (SS7) transactional capabilities application part (TCAP).
Regional authorities have devised MAP (mobile application part) layers using the
services of SS7 TCAP for SMS; the American Telecommunications Industry
Association (TIA) standard is referred to as IS-41 and the International
standard, published by the European Telecommunications Standards Institute (ETSI)
is known as GSM MAP.
22. Wireless Access
This solution provides access via a
mobile handset (or GSM modem) and a computer. The handset is required to be
interfaced with a computer equipped with handset compatible software. This
solution is suited for organisations with a minimal throughput requirement.
Billing is levied to the originating party’s chargeable number. The system
requirements include:
Mobile (or GSM modem) with PC interface via PCMCIA card or RS232 adaptor.
PC to mobile specific communications software
A connection is initiated by the computer and associated mobile handset. The message sending process is equivalent to sending messages via a handset. The retrieval is via a computer.
23. Dial-up Access
Dial up access provides a direct
connection to the SMS network via a PSTN dial-up service. Access is enabled via
a computer terminal employing message sending software. A customer can choose
between two levels of access: single message dial up (one at a time) and
multi-message dial up. Both levels of access are designed for customers wishing
to develop their own message sending software based on the TAP protocol.
Single Message Dial-Up
To utilise this solution, a system terminal software and a PSTN modem capable of
2,400 bps is required. The standard message throughput per modem service is one
message. This solution is obviously suited to organisations with minimal
throughput requirements that do not require reply path capability.
Multi Message Dial-Up
Multiple messages are able to be sent in the one dial-up session with the multi
message solution. Suited to organisations with minimal throughput requirements
that do not require reply path capability.
In this diagram, the computer terminal is able to send messages via the Dial up connection described previously. The diagram shows the TAP protocol being used to transfer the message(s) into the network. The message is then directed to the handset of choice. If the handset belongs to the originating network, then it is able (if permission is given) to send a short message back to the originating computer. If it is not, for example, an Optus phone on a Telstra network, then the handset will be unable to send a message back to the originating computer.
24. MAP Operations
While MAP
layers may differ between systems, the following basic operations must be
supported by any digital network supporting short messaging:
Routing Information Request: Before attempting delivery of a short message, the
SMSC must receive routing information to determine the serving MSC for the
mobile device at the time of the delivery attempt. This is accomplished by
interrogating the destination HLR. This mechanism takes the form of SMSrequest
for IS-41 and SendRoutingInfoForShortMsg in GSM.
Point-To-Point Short Message Delivery: This mechanism provides a means for the
SMSC to transfer a short message to the MSC that is serving the addressed mobile
device. After the address of the MSC has been obtained from the station’s HLR,
the short message delivery operation provides a confirmed delivery service. The
operation works in conjunction with the base station subsystem while the message
is being forwarded from the MSC to the MS. Therefore, the outcome of the
operation comprises either success (such as delivery to the mobile) or failure
caused by one of several possible reasons. The point-to-point short message
delivery is accomplished via the use of the short message
delivery-point-to-point (SMD-PP) and forwardShortMessage mechanisms in IS-41 and
GSM, respectively.
Short Message Waiting Indication: This
operation becomes active when a Point-To-Point Short Message Delivery operation
fails due to temporary factors such as an unregistered station, and also
provides a mechanism for notification of the SMSC when that MS becomes available
again. Uses SMS_notification indicator in IS-41 and set_message_waiting_data
mechanism in GSM.
Service Centre Alert: This is the mechanism that the HLR uses to inform the SMSC
when a previously unavailable MS registers on the network, and is thus available
to receive an SMS. Accomplished via SMS_notification in IS-41 and
alert_service_center mechanisms in GSM.
25. Service Elements
The Short Message Service utilises a
range of service elements to enact the reception and transmission of short
messages:
Message expiration: an SMSC will store and attempt to retransmit messages for
unregistered users until it is successful or the expiration time is exceeded.
This can be message-specific or set for an entire platform by the network
operator.
Priority: messages can be denoted as ‘urgent’ and thus allow them to take
precedence over ‘normal’ priority messages for delivery. This is irrespective of
the message’s time of arrival at the SMSC.
A message may be escalated to another
form of delivery if this mechanism is supported by the network. After a set
‘escalation time’, undelivered messages are forwarded to alternative means of
delivery such as E-mail or paging systems, specified by the user.
It should be noted that escalation time is smaller than expiration time because
if the alternative systems are also unavailable, the message will be returned to
the SMSC which will attempt to retransmit them – until expiration.
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).
The GSM protocol architecture features
three levels; physical (light purple), data link (dark purple) and message
(blue). Only parts relevant to short messaging will be examined here.
The mobile station utilises all three layers, as does the mobile switching
centre, however the base station is concerned primarily with the bottom two;
like a bridge or router it does little interpretation of data, serving mainly to
transmit it between ‘networks’.
27. GSM Signalling Protocol - MS
The mobile station message layer features
three sublayers, namely connection management (CM), mobility management (MM) and
resource management (RM). The Connection Management sublayer controls
call-related and call-independent supplementary services as well as SMS. The
mobility management layer handles connection establishment, maintenance and
termination with an MSC, over which the CM layer communicates with a peer entity
in the MSC.
It can be noted that data link operations are handled through a mobile-oriented
version of LAPD between the MS and BSS. It allows for the concerns of the radio
path.
Finally, the information is transmitted over the wireless link using a
combination of FDMA and TDMA.
28. GSM Signalling Protocol - BSS
As for a bridge or router, either side of
the protocol diagram will resemble the network it is connected to; this allows
passing of data between dissimilar networks. In this case they are the wireless
link and mobile network infrastructure.
The MSC side of the base station features both message and data link layers. The
Base Substation System Application Part (BSSAP) provides channel switching,
radio resource management and internetworking functions. The Message Transfer
Part (MTP) and Signalling Connection Control Part (SCCP) together implement the
data link layer as well as layer 3 transport functions to allow the transfer of
call control, mobility management and SMS data. You may recall from the
introduction that SMS operates out-of-band from voice calls; it uses SCCP
packets on the control signalling channel instead.
The mobile switching centre is in effect the interface between the BSS and the rest of the mobile network. The signalling from here takes the form of the International Telecommunications Union (ITU) Signalling System No. 7 (SS7). This is the only part of the GSM infrastructure capable of packet and circuit switching; GPRS allows packet switching but is actually independent of GSM. SS7 is examined next.
SS7 is a general purpose signalling
system widely used in ISDN and other public networks.
Examining each layer, the TUP and ISUP parts support telephone operations. The
Transaction Capability Application Part (TCAP), as mentioned before, is an
application layer protocol. It allows an application at one node to invoke
execution of a procedure at another and facilitates the exchange of the results.
It effectively shields the user from the complexity of the transaction layers by
automatically handling transaction and state changes, as well as generating
‘abort’ or ‘reject’ messages fully compatible with ITU and American (ANSI)
standards.
The Mobile Application Part (MAP) thus uses the services of TCAP to provide the
signalling capabilities for mobile applications.
31. Signalling System No.7 - SCCP
The Signalling Connection Control Part (SCCP), together with MTP, correspond to the lower three layers of the OSI model. SCCP allows for connection-oriented and connectionless services for data transfer. It is reliable and independent of the underlying hardware and transparent to users. Logical signalling connections within SS7 are used to ensure reliability and integrity of data transferred.
32. Signalling System No.7 - MTP
The Message Transfer Partis split into
three sublayers;
Level 3: provides congestion control, signalling management, message
discrimination (priority), distribution and routing much like the network layer
in OSI.
Level 2: provides a reliable, sequenced delivery of packets over level 1
connections, like the OSI data link layer
Level 1: defines characteristics of the digital signalling link and is
equivalent to the OSI physical layer
33. SMS Point to Point Protocol
The above diagram illustrates the
protocol layer for SMS. The short-message transfer layer (SM-TL) services the
short-message application layer (SM-AL) and enables it to transfer messages
between peer entities as well as receive confirmation of reception reports from
previous requests.
The SM-TL exchanges PDUs with its peer entity. The short message relay layer
(SM-RL) conveys the PDUs via the short message link layer (SM-LL).
34. SMS TPDU Types
Six types of PDUs exist at the SM-TL
layer:
SMS-Deliver: conveys a short message from an SMSC to the MS
SMS-Deliver-Report: conveys the cause of a failure to deliver
SMS-Submit: conveys a short message from an MS to the SMSC
SMS-Submit-Report: conveys the cause of a failure to submit
SMS-Status-Report: status report from SMSC to MS
SMS-Command: conveys command from MS to SMSC
The main elements of the TPDUs will be
explained below; a complete list can be obtained from the GSM standard GSM
03.40.
TP-Data-Encoding-Scheme
Used to identify the encoding scheme used by the user data; can be 7-bit, 8-bit
or Unicode
TP-Validity-Period
Enables an MS to specify a validity period for the short message it is
submitting; how long the SMSC should guarantee the existence of the submitted
short message before delivery can occur.
TP-More-Messages-To-Send
SMSC uses this to inform the MS that one or more short messages are still to be
delivered. IS-41 will actually specify the number yet to be delivered.
TP-User-Data-Header-Indicator
A 1-bit field that indicates whether the user data has its own header included
TP-Protocol-Identifier
Used by the MS or SMSC in GSM to identify which high-layer protocol is being
used for interworking with another device (such as a fax machine). IS-41
instead uses a teleservice identifier, classing the teleservices in groups such
as Cellular Messaging Teleservice (CMT), Cellular Paging Service (CPT) or Voice
Mail Notification Service (VMN).
TP-User-Data
Used to carry the short message. This is examined in more detail next.
The user data field within the TDPU can
carry up to 140 octets of data for point-to-point SMS, with an optional header.
The longer the header, the less space for the short message.
The first two fields, each 1 octet in length, specify the number of septets and
octets within the message for 7-bit user data in the short message field. If
8-bit data is used, both fields specify a number of octets (header and total
length respectively).
The header has at least three fields. The first, an Information Element
Identifier (IEI) is used to identify concatenated short messages. Newer
telephones such as the Nokia 33x and 55x series allow sending of longer SMS
messages by concatenating regular SMS messages together.
The Information Element Length (IEL) is used to indicate the length of the
Information Element Data (IED) that follows it. Again, each of these elements
are 1 octet in length. These allow the destination to correctly reassemble
concatenated messages.
If the format of the user data is 7-bit and the header does not conclude on a
7-bit boundary, padding digits are used to ensure older mobiles that do not
recognise user data headers can still display the message properly.
For concatenated messages:
8/16-BIT DATA: minimum 7-octet header, thus (140 – 7) 133 characters
7-BIT USER DATA: minimum 8-octet header, thus (160 – 8) 152 characters
Length is then increased based upon the character encoding scheme used.
38. Telecator Alphanumeric Protocol
Developed by Telecom Securocor Cellular Radio Limited, the Telecator Alphanumeric Protocol (TAP) provides greater flexibility and more features than text-based protocols. The overall performance is also significantly more efficient [IEEE, 2000]. At present Telstra is utilising TAP v1.2 August 20 1992 The Personal Communications Industry Association. The latest version available is v1.8 developed in 1997.
In order to decrease holding times on
input lines to alphanumeric systems, it is desirable to promote input devices
which will allow off-line entry paging information and dump this data quickly
after connection to the central paging terminal.
This protocol is compatible with special versions of small input devices
available from numerous sources. There are several options within the protocol:
1. It may be used for paging with fields per transaction or other services with
a different number of fields per transaction.
2. The use of manual input devices is provided in the log on procedure
3. Optional messages to the remote entry device may be added to control
responses from the central terminal.
39. SMS using Telecator Alphanumeric Protocol
Explanation
of Diagram
This diagram shows data transfer using the TAP method. There are millions of
systems worldwide that are capable of accepting alphanumeric messages in the TAP
format. It has not been until recently that these systems have begun to adhere
to a single accepted standard (TAP v1.8). The following is some brief notes
regarding differences in different implementations. There are a great deal of
differences within implementations and not all will be covered in this slide.
Anomalies such as these cannot be determined without sending messages into a
system.
The <CR> Character is used as an end of line marker. Other terminals have used
other end of line markers such as <LF> or a combination of both.
Some systems send “ID=” followed by an end of line marker while others do not.
Also some older systems precede this message with and end of line marker.
Prior to V1.6 of the TAP specification messages sequences were optional. Older
implementations may not send message sequences.
Many implementations send <CR><Control-Code><CR> with no message text if a
message sequence is not included in the response while some systems send the
sequence <Control-Code><CR> without the preceding <CR>.
The interpretation of, and reaction to, non-printable ASCII control characters
sent to a receiver is specific to the receiver in use.
A brief explanation of the Protocol.
<ESC> <EOT> = Begin disconnect
<NAK> <CR> = Checksum error, send latest block again.
<RS> <CR> = Abandon current transaction and go to next.
<ACK> <CR> = OK, send next block
<ESC> [p <CR> = Message go ahead is sent when paging central is ready for new
information
The standard protocol will be ASCII with
X-ON, X-OFF either direction using a 10 bit code (1 start, 7 data, 1 parity, 1
stop) with even parity
Each checksum is computed by performing the simple arithmetic sum of the 7-bit
values of all characters preceding it in that block. (This means that STX and
ETB/ETX are included in the sum.) The checksum is then the least significant 12
bits of this resulting sum.
The checksum is transmitted as 3 printable ASCII characters having values from
Hex 30 to Hex 3F (the characters 0123456789:;<=>?). The most significant 4 bits
of the sum are encoded in the 4 LSBs of the first character and the least
significant 4 bits of the sum are encoded as the 4 LSBs of the third character.
41. Protocol for SMS
There were 3 ways to implement SMS control - the original Block Mode, AT commands-based Text Mode, and AT commands-based PDU Mode. These fought it out in the market place, and although the SMS Block Mode was included in Nokia's Cellular Data Card for the 2110 in 1994, the Block Mode has now faded away and been replaced by PDU Mode.
42. Block Mode
Block Mode is a binary synchronous
protocol for text with a defined end and a defined beginning. Block Mode
constructs TPDUs within block markers and is entered be sending the AT command
AT+CESP. The application can then request groups of operations such as:
List all short messages held in the mobile phone
Transfer all or specified short messages from the mobile phone
Set the mobile phone so that all new incoming short messages are passed
immediately to the application
Submit short messages for transmission
Delete short messages from the mobile phone
Block mode commands and responses are generated by constructing a pre-defined
set of components or information elements in binary. For example, an ‘Insert
SMS’ command, used to transfer a short message to the mobile phone, is
constructed by stringing together the information elements “Message Type”,
“Insert Type”, “RP-Destination Address” and “SMS-TPDU”. The SMS-TPDU consists of
the user data itself along with other parameters such as the Data Coding Scheme.
Advantages:
Because of its built-in error correction in the form of a block check sum, Block
Mode is highly suited to applications where the GSM radio link may not be
completely reliable
Allows the control of remote terminals
A long established and proven standard
Allows the efficient transfer of binary encoded user data because AT commands do
not need to be repeated for each instruction. In fact, Block Mode is effectively
a string of Protocol Data Units (PDUs) without the AT commands
Disadvantages:
A PC or some other intelligent device is required to implement the Block Mode
protocol
Block Mode is used exclusively for SMS- when an application commands the mobile
phone to enter Block Mode, the mobile phone is not available for voice or Data
calls until this mode is terminated. Neither Text Mode nor PDU Mode impose this
restriction
Poor support among hardware manufacturers
Block Mode characters can conflict with flow control at serial ports (for
example, the Xon/ Xoff characters).
43. Text Mode
Text Mode allows the transfer of text one
character at a time based on AT commands. Unlike Block Mode, with Text mode, the
application first sets up fixed parameters such as the SMS Centre address. The
mobile phone then uses those parameters to construct a PDU when the application
requests it to send a short message.
Advantages:
Simple enough to be suitable for terminal emulators and dumb terminals
Inexpensive to implement a solution or test proof a concept before commencing
more serious development work
The only mode which has an interface readily understood by non-technical people
Disadvantages:
Not widely implemented by manufacturers
Message header information has to be input separately. In PDU Mode and Block
Mode, parameters such as Validity period can be set in the TPDU
Both Text Mode and PDU Mode are capable of responding to AT+CNMI settings to
forward the full message. However, phone manufacturers have implemented an
inconsistent set of responses which makes it seem like there is a Text Mode
limitation here.
44. PDU Mode
PDU Mode shares some characteristics with
each of the other two modes. In common with Block Mode, it uses a TPDU, but
rather than using raw binary, each character is encoded using HEX (the
characters 0...9,A..F). In fact, if you encode a Block Mode TPDU as HEX, you
have a PDU. In common with Text Mode, PDU Mode is implemented through an
identical series of AT commands.
Advantages:
-
Suitable for AT command-based software drivers that do not understand the
content of the message blocks
-
Can be automated
-
Binary coded data can be sent as well as characters
-
Fullest manufacturer support
-
Allows hardware to interact with Data and Fax as well as SMS
-
No flow control issues as characters transferred at the serial port are A..F,
0..9.
Disadvantages:
-
Manufacturers have interpreted the ETSI specification inconsistently. Thus we
have around nine different implementations of PDU Mode, all of which conform to
the specification. For example, Nokia alone has three different versions in its
product range.
-
Not as suitable as Block Mode for binary data or continuous SMS operation
-
Inefficient because of the need to repeat the “AT=” command. However, this is
not a rate determining factor in the submission of short messages.
45. SEMA SMS2000
Sema Group Telecoms developed SMS2000 as an implementation of GSM SMSC. The specification mainly describes the delivery of the short messages to the MSs, but also specifies the protocols for short message submission. The protocol has been designed to operate over a variety of interfaces such as X25, DECnet and SS7. The SMS2000 SMSC is usually accessed via the general X25 access gateway – either using a Radio Packet Disassembler (PAD) or a dedicated link to the message centre.
Explanation of SMS2000 functionality:
Submit SM – Send an SM to an MS.
Delete SM – Delete a previously submitted SM.
Replace SM – Replace a previously submitted SM to an MS.
Delete all SM – Delete all previously submitted and undelivered SM to an MS.
Enquire SM – Request status of a previously submitted SM.
Cancel SM – Cancel all status report requests (SRR) about a previously submitted
SM.
Alert SME Request – Request to be alerted when a specified SME becomes registered.
Retrieve Request – Request transmission from the SMS2000 SMSC to any pending SM
or SR.
Login – For X25 general access when accessing from a different location.
Change Password – For X25 general access when accessing from a different
location.
Once connected to the SMSC, an SME can request any of the operations listed. The
SMS2000 SMSC can also send commands such as:
Alert SME – indicates a MS has registered with the GSM network
Status Report – Indicates a successful delivery or failure of a previously
submitted SM
Incoming SM – Indicates an incoming SM is being held by the SMS2000 SMSC
A transaction between the SME and the SMSC involves one party sending a request
with a status report sent back on completion or failure of the request. The
transaction is initiated by the SME when a submit SM invoke is sent to the SMSC.
The SMSC responds with a result messages indicating that the short message has
been accepted and is being processed. Upon delivery the SMSC notifies the SME
(if requested). The SME then acknowledges the SR.
Since the SME’s connected to the SMS2000 SMSC are assumed to be trusted
transactions, a basic transaction will not include any exchange of login and
password between the SME and SMSC. However a login facility is still provided in
order to access the SMSC from a different location.
Undeliverable
The system will not attempt a delivery retry for a message failure categorised
as “undeliverable”. An “undeliverable” message is likely to arise when a phone
does not support the receipt of short messages or the message is incorrectly
addressed. “undeliverable” messages are marked as “done” and purged from the
message file.
Absent
For a message failure categorised as “absent”, the system will retry delivery
based on both a trigger from the mobile switch and a retry algorithm. A message
is held in the retry state, until the mobile phone registers. That is, it is
turned on and signals back to the mobile network.
Temporary fail
For a message failure categorised as “temporary fail”, the system will retry
delivery but the delivery algorithm is varied according to the configuration
parameters associated with the particular reason for the failure. For each type
of “temporary fail” there can be up to 8 levels of retry, and each retry levels
can be repeated numerous times.
Specific handset failures include:
The phone is powered off or is temporarily out of radio range
The mobile phone memory is full
The mobile phone does not have short message capability
There has been a signalling or system failure in the mobile network
The customer’s mobile service is barred for the receipt of SMS messages
48. Compression
Compressing short messages involves
getting more than 160 characters of information into a single short message. SMS
compression has been defined within GSM 03:42. The extent to which extra
characters can be fitted in a short message depends upon the level of
compression used:
Raw untrained dynamic Huffman algorithm. Use of this algorithm allows short
message lengths to be increased to about 200 characters. This algorithm means
that there does not need to be any preconceived notion that the short message is
compressed at either the sending or receiving end.
Higher level compression algorithms use compression criteria such as
punctuation, keywords, case shifts and character frequency tables (listing the
most commonly used characters in the language being used). This requires the
receiving entity to hold character frequency tables to decipher the intended
text. Several hundred characters can be sent as a single short message when such
compression criteria are used.
Mobile phone manufacturers have been reluctant to incorporate language-specific
compression criteria into their phones. As such, Huffman is the most widely
deployed means of compression. The incorporation of character frequency tables
alone into mobile phones would allow a gain of about 80 additional characters.
Mobile phone manufacturers have shown themselves to be more inclined to use the
limited mobile phone memory for additional ringing tones and games (for example,
recent Nokia mobile phones include three games as standard). The majority of
mobile phone users also prefer having ringing tones and games to SMS features-
the ringing tones let them differentiate the calls they receive from other
people who have the same model of mobile phone. Although the presence of SMS
compression is indicated by the Data Coding Scheme, many mobile phones do not
support the setting of this parameter. Hence, mobile network operators need to
assign a specific value to another special bit called the Protocol Identifier
(PID) which can be transferred to and from Terminal Equipment connected to the
mobile phone.
49. Concatenation
Concatenation is the process of stringing
several short messages together as a group. SMS concatenation has been defined
and incorporated into the GSM 03:40 specification. Up to 255 short messages can
be concatenated.
Every short message contains additional information outside the short message
text itself. One of these information fields, the User Data Header Indicator, is
used to indicate that concatenation is being used, which set the concatenated
short message belongs to, how many concatenated short messages are in that set
and where the concatenated short message belongs in the complete sequence. This
enables the receiving application to put the concatenated short messages back
together in the right order and determine whether all the short messages have
been received. The concatenation standard does NOT incorporate a recovery
mechanism if one concatenated short message in the sequence is lost- there is no
automatic retransmission of missing short messages. Mechanisms for handling such
errors are determined by the specific application software. Whilst the presence
of concatenation is indicated in the User Data Header Indicator, many mobile
phones do not support this bit. Hence, mobile network operators may need to
assign a special value to the Protocol Identifier (PID) to indicate that
concatenation is present. A mobile phone can pass this PID value to and from
Terminal Equipment connected to the mobile phone.
Concatenation can in theory be used for any application that requires more than
160 characters of information transfer. However, SMS was not designed for high
volume information transfer. As such, concatenation of more than three or four
short messages is impractical because it is often cost ineffective when mobile
network operators do not offer special tariffs for concatenated short messages
and inefficient because of the possibility of losing some short messages in the
sequence. For information transfer beyond a few hundred characters, Data should
be used.
50. Alphabet
The GSM 03:38 specification defines the
alphabets that SMS supports. This standard is called UCS2 and incorporates all
of the major languages from around the world such as Chinese and Arabic
characters. UCS2 stands for Universal Multiple Octet Coded Character Set 2, and
is derived from the ISO standard ISO/IEC10646-1.
In addition to UCS2 and the default 7-bit alphabet, GSM 03.38 also specifies the
way that eight bit data, i.e. binary, is sent.
51. Different Alphabet Support
There are two different GSM SMS
alphabets: UCS2 and the GSM 7-bit Default Alphabet, which is derived from the
CCITT IA5 Alphabet, and more commonly known as the ASCII character set. The main
difference between the GSM and CCITT versions is that the control characters
(except for carriage return and line feed) have been replaced with other
European language variants such as umlauts and accents. Because only 7-bits are
sent to the mobile phone, this allows 160 7-bit characters to be packed into the
140 octet limit of available capacity for the user data (i.e. short message
text) itself.
Whilst the default Latin GSM alphabet uses 7 bits per character, the non-Latin
characters are complex, such that they each require 16 bits to code. This means
that each non-Latin short message has a maximum length of 70 characters and such
applications may need to use compression or concatenation for greater
information transfer. Currently, all mobile phones support the default GSM 7-bit
alphabet but not necessarily UCS2.
Clearly, the extent to which security has
been built into the GSM standard is important for SMS-based applications
generally and banking and other sensitive uses such as stolen vehicle tracking
in particular.
To ensure that short messages do not get corrupted or intercepted, data
integrity is incorporated in the GSM standard. The Short Message Service is
afforded the same high level of security as that used to protect the signalling
channel generally. The SMS information passing across the signalling channel is
split into 23 byte segments, each of which is protected by a 5 byte ‘fire code’
which provides a cyclic redundancy check. Forward error protection is
incorporated using conventional encoding. All of the information inside and
outside of the short message text itself is included in the check. This check is
automatically calculated between the Mobile Station and the BSS (Base Station
Sub-system which is responsible for providing the access between the mobile
phones and the GSM core network) and between the BSS and the SMS Centre. Short
messages are routinely encrypted over the radio path between the Mobile Station
and BSS using the IA5 encryption algorithm. Because of this high level of
security, no short message is ever known to have been intercepted and read.
Whilst IA5 is sufficient for most routine short messaging requirements, for
optimal security in applications such as mobile banking, end-to-end encryption
is advisable between the sending Short Message Entity and the receiving Short
Message Entity. This means that there should be encryption at the host- banks,
for example, typically use their own encryption and this is outside of- and does
not affect- the mobile network. Some Terminal Equipment such as mobile Point of
Sale terminals also includes mechanisms to encrypt outbound short messages and
decrypt inbound short messages.
Animation 3
Step 1: The Mobile Station (MS) is powered on and registered with the network.
Step 2: The MS transfers the SM to the MSC
Step 3: The MSC interrogates the Visitor Location Register (VLR) to verify that
the message transfer does not violate the supplementary services invoked or the
restrictions imposed.
Step 4: The MSC send the short message to the SMSC using the ‘forward short
message’ operation.
Step 5: The SMSC delivers the short message to the SME (acknowledgement is
optional).
Step 6: The SMSC acknowledges to the MSC the successful outcome of the ‘forward
short message’ operation.
Step 7: The MSC returns to the MSC the outcome of the MO-SM operation.
Animation 4
Step 1: The short message is submitted from the ESME (External Short Message
Entity) to the SMSC.
Step 2: After completing its internal processing, the SMSC interrogates the Home
Location Register (HLR)
Step 3: The SMSC sends the short message to the MSC using the ‘forward short
message’ operation.
Step 4: The MSC retrieves the subscriber information from the VLR. This
operation may include an authentication procedure.
Step 5: The MSC transfers the short message to the Mobile Station
Step 6: The MSC returns to the SMSC the outcome of the ‘forward short message’
operation.
Step 7: If requested by the ESME, the SMSC returns a status report indicating
delivery of the short message.
55. Features Under Development
Concatenation is the process of stringing
several short messages together as a group. SMS concatenation has been defined
and incorporated into the GSM 03:40 specification. Up to 255 short messages can
be concatenated.
Every short message contains additional information outside the short message
text itself. One of these information fields, the User Data Header Indicator, is
used to indicate that concatenation is being used, which set the concatenated
short message belongs to, how many concatenated short messages are in that set
and where the concatenated short message belongs in the complete sequence. This
enables the receiving application to put the concatenated short messages back
together in the right order and determine whether all the short messages have
been received. The concatenation standard does NOT incorporate a recovery
mechanism if one concatenated short message in the sequence is lost- there is no
automatic retransmission of missing short messages.
Support for distribution list creation and modification within the SMSC to
greatly increase short message throughput.
56. Glossary
AMPS - Analogue Mobile Phone System
BTS- Base Transceiver Station
BSC - Base Station Controller
BSS - Base Station Subsystem
CMT - Cellular Messaging Teleservice
CPT - Cellular Paging Service
CDMA - Code Division Multiple Access
ETSI - European Telecommunications Standards Institute
ESME - External Short Messaging Entity
FDMA - Frequency Division Multiple Access
GSM - Global System for Mobile Communications
GPRS - General Packet Radio Service
HLR - Home Location Register
Huffman Algorithm - Compression Algorithm for SMS
HTTP - HyperText Transfer Protocol
IMEI - International Mobile Equipment Identity
ISDN - Integrated Digital Services Network
ITU - International Telecommunications Union
IN - Intelligent Network
ISP - Internet Service Provider
IA5 - Encrption Algorithm
LLAPD - Layer Link Access Protocol
MSC - Mobile Switching Centre
MAP - Mobile Application Part
OSI - Open Systems Interconnect
PSTN - Public Switching Telphone Network
PDA - Personal Digital Assistant
PAD - Packet Assembler Disassembler
PCN - Personal Communication Service
PID - Protocol Identifier
QVB - Queen Victoria Building
SMS MO - SMS Mobile Originated
STP - Signalling Transfer Point
SMS - Short Message Service
SMSC - Short Message Switching Centre
SMPP - Short Message Peer to Peer Protocol
SCCP - Signalling Connection Control Part
SS7 - Signalling System No. 7
SM AL - Short Message Application Layer
SM TL - Short Message Transfer Layer
SM RL - Short Message Relay Layer
SM LL - Short Message Link Layer
SMS MT - SMS Mobile Terminated
TAP - Telecator Alphanumeric Protocol
TPDU - Transport Protocol Data Unit
TDMA - Time Division Multiple Access
TAP - Telecator Alphanumeric Protocol
TIA - Telecommunications Industry Association
VPS - Virtual Private Network
VMN - Voice Mail Notification Service
VLR - Visitor Location Register
WAP - Wireless Application Protocol
57. References
UTS Online: Communication Networks Course - Staff Information retrieved via Internet Explorer v5.5
The International Engineering Consortium "Web ProForum Tutorial: Wireless Short Message Service" http://www.iec.org/online/tutorials/wire_sms 24/03/2002 21:09 retrieved via Internet Explorer v6.0
Williamson, John "SMS: An unlikely hit" Global Telephony, Overland Park; Mar 2002, Issue. 3; pg. 16 David Hua Min Tan, Siu Cheung Hui and Chiew Tong Lau "Wireless Messaging Services for Mobile Users" Journal of Network and Computer Applications (2001) 24, 151–166 Guthery, Scott B. Mobile application development with SMS and the SIM toolkit, McGraw-Hill, New York 2002 Gallagher, Michael D., Mobile telecommunications networking with IS-41, McGraw-Hill, New York 1997 Peersman, G. Griffiths, P. Spear, H. Cvetkovic, S. Smythe, C. "Tutorial overview of the short message service within GSM" Computing & Control Engineering Journal. v 11 n 2 2000. p 79-89 Peersman, Guillaume. Cvetkovic, Srba. Griffiths, Paul. Spear, Hugh "Global system for mobile communications short message service" IEEE Personal Communications IEEE Wireless Communications. v 7 n 3 2000. p 15-23 Nortel Networks "Products and Services: Short Message Service" http://www.nortelnetworks.com/products/01/sms/index.html 20/02/2002 15:43 retrieved via Internet Explorer v6.0
Key Learning Outcomes
This project has allowed us to learn about a number of factors.
- The Social issues and background to the SMS as it exists today.
- The components of the SMS network
- The architecture and manner in which the components interact within the
network
- The signalling that occurs at different levels in the network between the
network components
- The features SMS provides
- The protocols of the network
- The modes of operation of the SMS network
1. Which of these is not a general categorisation of message
delivery failure:
a) Undeliverable
b) Absent
c) Terminal
d) Temporary fail
2.
Which of these statements is true:
a) Text mode is a protocol developed by Sema Group Telecoms
b) Block mode is used for synchronous binary transfer
c) PDU mode is equivalent to text mode with characters encoded using HEX
d) TAP encodes the information from end point to end point
3.
Character frequency tables are used for:
a) compression
b) concatenation
c) routing
d) encryption
4.
Why has concatenation of Short messages been adopted more readily into the
market?
a) SMS was not designed for high volume traffic
b) Not cost effective
c) Poor error correction
d) All of the above
5. SMS has the qualities of:
a) transmitting up to 160 characters
b) guaranteed delivery
c) in-band transmission
d) A & B
e) A, B & C
6.
Which networks allow short messaging?
a) AMPS
b) GSM
c) CDMA
d) B & C
e) A, B & C
7.
The short message service centre
a) is a combination of hardware and software
b) performs switching of SM's through the mobile network
c) is only accessible from mobile stations
d) B & C
8.
The roles of the HLR include
a) storing and managing subscriptions and service profiles
b) route voice and data calls
c) supplying routing information to SMSC
d) A & B
e) A & C
9.
The Mobile Application Part (MAP) is derived from
a) LAPDM
b) GSM
c) SS7 TCAP
d) SCCP
10. The SMSC obtains routing information from the:
a) MSC
b) BTS
c) BSS
d) HLR