Communication NetworksSMS: How Does It Work?


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.


Contents:

1. Outline Of Topis To Be Covered

2 What is SMS?

3 History of SMS

4 Applications of SMS

5 Using SMS

6. SMS in Society

7. SMS Speak

8. The Growth of SMS

9. Mobile Station

10. External Short Messaging Entities

11. Short Message Service Centre

12. SMSC Implementation

13. SMS - Gateway

14. Home Location Register

15. Visitor Location Register

16. Mobile Switching Centre

17. Base Station System

18. Base Transceiver Station

19. Base Station Controller

20. Network Architecture

21. SMS Signalling

22. Wireless Access

23. Dial-up Access

24. MAP Operations

25. Service Elements

26. GSM Signalling Protocol

27. GSM Signalling Protocol - MS

28. GSM Signalling Protocol - BSS

29. GSM Signalling - MSC

30. Signalling System No.7

31. Signalling System No.7 - SCCP

32. Signalling System No.7 - MTP

33. SMS Point to Point Protocol

34. SMS TPDU Types

35. SMS TPDU Examples

36. SMS TPDU User Data

37. SMS Message Length

38. Telecator Alphanumeric Protocol

39. SMS using Telecator Alphanumeric Protocol

40. TAP Functionality

41. Protocol for SMS

42. Block Mode

43. Text Mode

44. PDU Mode

45. SEMA SMS2000

46. SMS2000 Functionality

47. Message Delivery Failure

48. Compression

49. Concatenation

50. Alphabet

51. Different Alphabet Support

52. Security & Encryption

53. Mobile Originated SMS

54. Mobile Terminated SMS

55. Features Under Development

56. Glossary

57. References

58. Key Learning Points

59. Multiple Choice Questions


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)
 
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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.


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3. History of SMS

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.

 

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4. Applications of SMS

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’.


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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.

 

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6. SMS in Society

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.

 

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7. SMS Speak

Various shortcuts used in SMS messages (from AAPT CellularOne)

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8. The Growth of SMS

 

 

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.

 

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9. Mobile Station

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.

 

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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.

 

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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.

 

 

 

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12. SMSC Implementation

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.

 

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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.

 

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14. Home Location Register

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.

 

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15. Visitor Location Register

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.

 

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16. Mobile Switching Centre

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.

 

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17. Base Station System

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.

 

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18. Base Transceiver Station

Houses the radio transceivers that define a cell

Handles radio protocols with mobile stations

GSM900, GSM1800, GSM1900 (IS-41), CDMA, iDEN types

 

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19. Base Station Controller

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.

 

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20. Network Architecture

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

 

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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.

 

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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.

 

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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.

 

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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.

 

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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).

 

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26. GSM Signalling Protocol

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’.

 

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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.

 

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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.

 

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29. GSM Signalling - MSC

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.

 

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30. Signalling System No.7

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.

 

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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.

 

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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

 

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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).

 

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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

 

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35. SMS TPDU Examples

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.

 

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36. SMS TPDU User Data

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.

 

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37. SMS Message Length

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.

 

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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.

 

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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

 

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40. TAP Functionality

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.

 

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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.

 

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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).

 

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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.

 

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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.

 

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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.

 

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46. SMS2000 Functionality

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.

 

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47. Message Delivery Failure

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

 

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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.

 

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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.

 

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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.

 


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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.

 

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52. Security & Encryption

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.

 

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53. Mobile Originated SMS

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.

 

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54. Mobile Terminated SMS

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.

 

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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.

 

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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

 

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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

 

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58. Key Learning Points

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

 

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59. Multiple Choice Questions

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

 

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