`
`Abstract
`This tutorial presents an overview of the Global System for Mobile Communications Short Message Service from the viewpoint of implementing
`new tclematic services. SMSoffers the users of GSM networksthe ability to exchange alphanumeric messages up to the limit of 160 characters.
`The tutorial is motivated by an acute absence of research publications in this field. The information gathered in the tutorial was required
`considering the increasing potential SMS offers for integration with existing messaging services andits ability to offer a successful replacement
`for the Transmission Control and Internet Protocols as far as low-bandwidth-demanding applications are concerned. Lnitially, the tutorial gives a
`brie! overview of the building blocks of GSM networks — the mobile station, base station, and network subsystem -
`- and then emphasizes the
`SMSnetwork and protocol architecture, The most widely used protocols for message submission are then introduced (text-based, SMS2000,
`ETSI 0705, TAP) and compared in terms of features provided and flexibility to handle extended alphabets or two-way messaging. Finally the
`tutorial outlines a summary of current and future issues for further development and researchin the light of novel features for submission
`protocols and telematic services.
`
`The Global System for
`Mobile Communications
`Short Message Service
`
`
`
`GUILLAUME PEERSMAN AND SRBA CVETKOVIC,
`THE UNIVERSITY OF SHEFFIELD
`
`PAUL GRIFFITHS AND HUGH SPEAR, DIALOGUE COMMUNICATIONS LTD.
`
`to send and/or reccive alphanumeric messages. The short
`since the first Global System
`messages can be up to 140 bytes in length, and are delivered
`for Mobile Communications (GSM) network started opera-
`within a few seconds where GSM coverageis available, More
`tion ‘in 1991, more than 100 countries have adopted the stan-
`dard. Over20 million subscribers of GSM networks are now
`than a commonpaging service, the delivery of the messageis
`guaranteed even when the cellular terminal is unavailable
`offered worldwide coverage, outstanding voice quality over a
`whole range of operating conditions, and a variety of value-
`(e.g., whenit is switched off or outside the coverage area).
`added services, These services include voice mail, call han-
`The network will hold the message and deliver it shortly after
`the cellular terminal announcesits presence on the network,
`dling facilities, call line identification, and Short Message
`The fact that SMS (through GSM)supports international
`Service (SMS).
`roaming with very low latency makes it particularly suitable
`With SMS, users are able to exchange alphanumeric mes-
`sages (up to 160 characters) with other users ofdigital cellular
`for applications such as paging, e-mail, and voice mail notifi-
`cation, and messaging services for multiple users. However,
`networks, almost anywhere in the world, within seconds of
`the facilities offered to users and the charges for these facili-
`submission, Even if the service was originally conceived as a
`ties still mainly depend on the level of service provided by the
`paging mechanism for notifying the users of voicemail mes-
`network operator.
`sages, SMS is now increasingly used as a messaging service,
`There are two types of SMS available: cell broadcast [1]
`The messages are typically created on mobile phone keypads,
`and point-to-point [2]. In cell broadcast, a message is trans-
`which is somewhat awkward, Fortunately, there are other
`mitted toall the active handsets or mobile stations (MSs) pre-
`ways to access the message centers, as discussedin this article,
`Numerous applications are already available and make short
`sent in a cell that have the capability of receiving short
`messages and have subseribed to this particular information
`message reception and submission possible using a computer.
`service. This service is only one-way, and no confirmation of
`Gateway architectures are also being widely implemented and
`conhect company’s c-mail or yoiccmail systems to the SMS,
`receipt will be sent. It can send up to 93 7-bit character or 82
`The practical implementation of SMS and the different
`8-bit characters, typically used to transmit messages about
`traffic conditions, weather forecast, stock market, and so on.
`protocols for message submission are addressedinthis article.
`In point-to-point service, messages can be sent from one
`The future of SMS anda brief review of the fields currently
`mobile to another or from a PC to a mobile andvice versa.
`being studicd will conclude this article.
`These messages are maintained and transmitted by an SMS
`The Short Message Service
`Center (SMSC). The SMSC is an electronic form of ordinary
`mail postal service that stores and then forwards the messages
`when they can be delivered, Each GSM network must support
`Developedas part of the GSM Phase 2 specification, the
`Short Message Service, or SMS as it is more commonly
`one or more SMSCsto sort and route the messages. Each
`SMSCchecks, organizes, and sends the message to the opera-
`known, is based on the capability of a digital cellular terminal
`
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`TEEE Personal Communications * June 2000
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`1070-991 6/00/$10,00 @ 2000 IEEE
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`15
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`Facebook Ex. 1012
`Facebook Ex. 1012
`U.S. Pat. 8,243,723
`USS. Pat. 8,243,723
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`1'!'''''''''1'''
`+''"''1''1'
`_PSTNISDN :
`Base transceiver station
`BTS:
`ithentication ecintre
`o
`Base station controller —
`BSC:
`tain
`uipmentidentity register
`
`——
`Subscriberidentity module
`SIM:
`Home
`location. register: os:
`ME:—Mobile equipment
`.- Visitorlocation register
`:
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`a ‘Operation ‘an
`: “maintenance center :
`
`Datacommu
`'
`“network
`
`B figure 1, The basic GSM network architecture.
`
`GSM Network Architecture
`
`tor. [t also receives and passes on any confirmation messages to
`any GSM mobile on any network, However, in practice, there
`are no agreements to allow SMSto travel between networks.
`There are several ways in which a short message can be
`submitted, depending onthe interfaces supported by the GSM
`network SMSC. Users can call a central paging bureay(i.c.,
`an operator), or directly create the message on the keypad of
`their handset. ‘Typing the messages is made casicr whenusing
`a personal digital assistant (PDA) or a laptop connectedLo
`the handsct. A few SMSCequipment manufacturers and com-
`panies have also developed their own protocols for short mes-
`sage submission, Consequently, more and moce GSM
`networks now olfer access to their SMSC using these proto-
`cols over a variety of hardwareinterfaces: modem dialup,
`X25, and even the Internet.
`
`SIM. Because the [MEI and IMST are independent, personal
`mobility is possible. The SIM canbe protected against unau-
`thorized use by a personal identity number(PIN).
`The Base Station Subsystem
`The base station subsystem is composedof two parts, the
`pase transceiver station (BTS) and base station controller
`(BSC). They communicate across the specified Abis inter-
`face, thus allowing network operators to use components
`made by different suppliers. The BTS houses the radio
`transceivers that define a cell and handle the radio link pro-
`tocols with the MS. Depending on the density of the area,
`more or fewer BTSs are needed to provide the appropriate
`capacity to the cell. Digital communications system (DCS)
`networks working at 1800 MHz need twice the number of
`BTSsto cover the same arca as GSM networks, but provide
`twice the capacity.
`The BSC managesthe radio resources for one or more
`BTSsvia the standardized Abis interface, It handles radio
`The layout of a generic GSM networkwith its severa) func-
`channel setup, frequency hopping, and handovers. The BSC is
`tional entities is shown in Fig.
`1 [3]. The architecture can be
`the connection between the MS and the mobile switching cen-
`divided in three main components;
`ter (MSC). The BSC also takes care of converting the 13 kb/s
`* The subscriber holds the MS, namely the GSM terminal
`yoice channel used over the radio link (Um interface) to the
`» The base station subsystem controls the radio link with the
`MS
`standardized 64 kb/s channel used by the public switched tele-
`phone network (PSTN).
`* The network subsystem performs the switching of calls and
`other management tasks such as authentication.
`The Network Subsystem
`The Mohile Station
`The MSCis the main component of the network subsystem.
`Its provides the same functionality as a switching node ina
`The MS and base station subsystem communicate across the
`PSTN or integrated services digital network (ISDN), but also
`Unminterface, also known as the air interface or radio link,
`takes care of all the functionality needed to bandle a mobile
`‘The base station subsystem communicates with the network
`subscribersuch as registration, authentication, location updat-
`subsystem across the A interface. The MS consists of the
`ing, handovers, and routing to a roaming subscriber. The
`physical terminal and contains the radio transceiver, the dis-
`MSC also acts as a gateway to the PSTN or ISDN, and pro-
`play and digital signal processors, and the Subscriber Identity
`videsthe interface to the SMSC.
`Madule (SIM), The 51M provides the user with the ability to
`The international roaming andcall routing capabilities of
`aceess their subscribed services regardless of the location and
`GSM networks are provided by the home location register
`the termina! used, The insertion of the SIM in any GSM cel-
`(HLR)and visitor lacation register (VLR) together with the
`lular phone allows the user to access a network, make and
`MSC. The HLR database contains all the administrative infor-
`receive phone calls, and useall the subseribed services,
`mation about ¢ach registered user of a GSM network along
`The International Mobile Equipment Identity (IMFI)
`with the current location of the MS. The current location of
`uniquely identifies the mobile terminal according to the Inter-
`an MSis in the form of a Mobile Station Roaming Number
`national Mobile Subscriber Identity (MSI) contained in the
`
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`Um air interface
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`MS
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`Ainterface ©).
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`000°.) MSC_
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`Aigeees gue)
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`@ Figure 2.TheGSM protocol architecture.
`
`TUP
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`MAP
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`TCAP
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`SUP
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`:
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`SCCP
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`a ESaees ae 3a
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`The GSM Signaling Protocol
`The exchange of signaling messages regarding mobility, radio
`resources, and connection management between the different
`entities of a GSM network is handled through the protocol
`architecture, as shown on Fig. 2.
`The architecture consists of three layers: physical, dala
`link, and message. The physical layer and channel structure
`arc described in detail by M. Mouly and M. Pautet [4]. Layer
`2 implements the data link layer using a modified tlavor of the
`Link Aceess Protocol (-APID) to operate within the con-
`straints set by the radio path. On the MS side, the message
`laycr consists of three sublayers: connection management
`(CM), mobility management (MM), and resource manage-
`ment (RR). The CM sublayer manages call-rclated supple-
`mentary services, SMS, and call-independent supplementary
`services support. The MM sublayerprovides functions to
`establish, maintain, and release a connection between the MS
`and the MSC, over which an instance of the CM sublayer can
`oxchange information with its peer. It also performs location
`updating, IMSI management, and Temporary Mobile Sub-
`scriber [dentity (TMSI) identification, authentication, and
`reallocation. The RR sublayerestablishes the physical connec-
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`TEER. Personal Communications ¢ June 2000
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`7
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`(MSRN), typically the $87 number of
`the visited MSC, and used to route a
`eall to the MSC where the mobile is
`actually located.
`The VLR is usually located within
`the MSC to speed up acecss to the
`information required during a call and
`simplify the signaling. The cantent of
`the VLRis a selection of the informa- .
`tion from the HLR,basically all neces-
`sary information for call control and
`provision of the subscribed services,
`for cach single mobile currently locat-
`ed in the geographical area controlled
`by the VLR.
`The network subsystem uscs two
`other databases for authentication and
`sccurity purposes. The Equipment
`Identity Register (ERTR) contains alist
`of cach MS IMEI allowed on the network. The authentication
`center (AuC) database contains cach single PIN stored in the
`MS SIM.
`
`MTPlevel 1
`
`MIP level
`
`
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`Figure 3. ‘fhe SS7protocol stack.
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`tion over the radio link to transmit
`call-related signaling information such
`as the establishment of the signaling
`and traffic channel between the MS
`and the BSS.
`On the MSCside, the message layer
`is divided into four sublayers, The
`Base System Substation Application
`Part (BSSAP) of the MSC provides
`the channel switching functions, radio
`resources management, and internet-
`working functions. The Message
`Transfer Part (MTP) and Signaling
`Connection Control Part (SCCP) pro-
`tocols are used te implement the data
`link layer and layer 3 transport func-
`tions for carrying the call control and
`mobility management signaling mes-
`sages across the A interface. SCCP
`packets are also used to carry the messages for SMS.
`Signaling between the different entity uses the Internation-
`al Tclecommunication Union (ITU) 857, widely used in ISDN
`and current public networks. $87 is currently the only element
`of the GSM infrastructure capable of packet switching as well
`as circuit switching. It is used to transport control signals and
`short message packets for SMS. The protocol consists of the
`Mobile Application Part (MAP), Transaction Capability
`Application Part (TCAP}, SCCP, MTP, and ISDN-User Part
`(ISUP) or Telephone User Part (TUP). Figure 3 depicts the
`SS7 protocolstack.
`The ISUPprovides the signaling functions needed to sup-
`port switched voice and data applications in the ISDN cnvi-
`ronment, The TUP provides the basic functionality for call
`control functions for ordinary national and international tele-
`phonecalls. The TCAPis an application layer protocol. It
`allows an application at one node to invoke an execution of a
`procedure at another node and exchange the results of such
`invocation. It isolates the user application from the complexity
`of the transaction layer by automatically handling transaction
`and invocation state changes, and generating the abort or
`reject messages in full accordance with ITU and American
`National Standards Institute (ANSI) standards, The MAP
`uses the TCAP services to provide the signaling capabilitics
`required to support the mobile capabilities.
`The MTP and SCCP(Fig. 4) correspond to the lower three
`
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` wee,
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` mation will always be returned to the SMSC
`
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`: TCAPASUP/TUP
`ttt
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`“SCCP
`
`MrP
`level 3
`
`MTP
`level 2
`
`MTP
`level 1
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`:Figure 5. TheSMS network architecture.
`
`indicating whether the MS has received the short
`message or not. A confirmation will also-be
`returned to the MS from an SMSC indicating
`whether the TPDU has been received successful-
`ly. The software within the MS must be able to
`decode and store the messages.
`SMS Mobile Terminated (SMS-MT)is the
`ability fo receive an SMS message from an
`SMSC and is more ubiquitous, while SMS
`Mobile Originated (SMS-MO) is the ability to
`send short messages to an SMSC, Messages can
`also be stored on the SIM, which can be
`retrieved at a later time. When the phone is not
`within coverage or the SIM is full, the SMSC
`will hold the message and deliverit shortly after
`the phone comes back inte range orthere is
`space in memory.
`The SMS Basic Network Architecture
`The main components of the SMS network archi-
`tecture are shownin Fig. 5.
`When routing a mobile originated short mes-
`sage, the SMSC forwards the short message to
`the SMS-GMSC. The SMS-GMSC interrogates
`the HLRfor routing information and sends the
`short message to the appropriate MSC, The
`MSC delivers the short message to the MS. On
`the other hand, when, routing a mobile terminat-
`ed short message, the MS addresses the required
`SMSC according to its globaltitle. If roaming
`abroadthe visited public limited mobile nctwork
`(PLMN) will route the short message to the
`appropriate SMS-IWMSC.,
`The SMSCidentifies cach short message unique-
`ty by adding a time stamp in the SMS-DELIVER
`TP-SCTSfield. The short message arrival at the
`SMSC is accurate to the second. It is the SMSC’s
`responsibility to assure that if wo or more short
`message arrive within the same secondtheir time-stamps will be
`different.
`The MS hasto be able to reccive/submit a short message
`TPDU, and then return a delivery report upon successful
`reception. It is also responsible for notifying the nctwork
`when it has memory capacity available to reccive one or more
`messages,if it had previously rejected a short message because
`its memory capacity was exceeded.
`
`—
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`~
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`Protocol Architecture
`The protocol layer for SMSis shown in Fig. 6. The short mes-
`sage transfer layer (SM-TL,) services the short message appli-
`cation layer (SM-AL) and enables it to exchange short
`messages with a peer as well as reccive confirmation of recep-
`tion reports from earlier requests.
`
`layers of the open system interconnection (OST) model (Fig. 4).
`The SCCPsublaycr supports connectionless and connection-
`oriented services to transfer data and Global Title Translation
`(GTT) above MTPlevel 3 for voice, data, ISDN, and GSM ser-
`vices. The data transfer is reliable, independent of the underly-
`ing hardware, and transparent to users. The protocol employs
`logical signaling connections within the $87 network to ensure
`reliability and integrity of the ongoing data transfer, The MTP
`is divided into three levels:
`* MTPlevel 7 defines the characteristics of the digital signal-
`ing link and is equivalent to the OSI physical layer.
`* MTP level 2 is equivalent to the OSI data link layer and
`provides a reliable sequenced delivery of data packets
`across MTP Icvel1.
`* MTPlevel 3 provides congestion control, signaling manage-
`ment, and message discrimination, distribution,
`and routing in a similar way as the OSI network
`layer,
`Practical Implementation
`SMSuses the $87 signaling channel to transmit the
`data packet [5], thus allowing a text message to be
`reecived when the useris making a voice or data
`call. An active MS should be able to send and
`receive a short message Transport Protocol Data
`Unit (TPDU) at any time regardless of whether
`MTable 1. 7PDU types.
`there is a speech or data call in progress. A contir-
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`sheetpeeggee
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`SMS-GMSC /
`SMS-IWMSC
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`‘igure 6. Theprotocol layerfor SMSpoint-to-point.
`
`
`
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`
`
`clement data (IED) that follows. Each of
`these fields is t octet long.
`Tn the user data, the message can be7bits,
`8 bits, or 16 bits. If 7-bit data is used and the
`header does not end on a 7-bit boundary,
`padding bits are used. This is to ensure that
`older mobiles which do not support the TP-UD
`header canstill display the message properly.
`Using the TEI allows sending and receiving
`of concatenated short messages. The IED field
`contains all the necessary information for the
`recciving cntity to reassemble the messages it
`the correct order, and is coded as follows:
`* First octet: short message references num-
`ber identifying the message within the same
`transaction
`* Second octet: specifics the maximum number of short mes-
`sages in the concatenated short message, which will not
`execed 255
`* Third octet: identifies the sequence numberof the short
`message within the concatenated message
`The minimum header length for concatenated message is 7
`octets for 8-bit and 16-bit data and 8 for 7-bit data; leaving 133
`(140 - 7), 152 (160 — 8), and 66 ((140 — 7)/2) characters for the
`short message. The maximum length of the message is then
`increased to 38,760 (255*152), 33,915 (255*133), or 16,830
`(255*66) depending on the character coding scheme used,
`
`TP-Validity-Period
`The TP-VP field contains an information element
`cnabling an MSto specify a validity period for the short
`message it is submitting. The value specifies how long an
`SMSC will guarantee the existence of a short message
`before delivery to the recipient has been carried out.
`TP-More-Message-To-Send
`
`’|TP-user-data-header-indicator TP-user-data-header-indicator
`
`‘The SMSC uses the TP-MMSfield to inform the MS that
`
`one or more shorl messages are waiting to be delivered.
`
`
`TP-message reference
`TP-User-Data-Header-Indtcator
`
`“he 1-bit TP-UDHIfield indicates whether the ‘(P-UD
`
`cludes an additional header as well as the short message.
`
`TP-message-type-indicator
`
`m
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`TP-reject-duplicate
` TP-reply-path
`
`
`
`The SM-TL cxchanges PDUs withits peer entity. The
`«art message relay layer (SM-RL) conveys the PDUsvia the
`ort message link layer (SM-LL), Refer to GSM 03.40[2] for
`turther details.
`
`SMS Protocol Data Unit Types
`There are six types of TPDU at the SM-TL,as listed in Table
`1, The elements of the SMS-Deliver and SMS-Submit TPDU
`are shown in Fig. 7 [2]. The mainficlds of the TPDU are
`describedin this document however for a complete descrip-
`tion of the TPDU please refer ta GSM 03.40 J2].
`TP-Data-Coding-Scheme
`The data coding scheme field (TP-DCS) is usedto iden-
`tify the coding scheme used by the user data, which can
`be 7- or 8-bit or even Unicode [6], as defined in GSM
`03,38 [7].
`
`
`
`.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`:
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`TP-message-type-indicator
`
`TP-more-message-to-send
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`TP-reply-path
`
`TP-status-report
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`TP-originating-address
`
`TP-protocol-|D
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`TP-data-coding-scheme
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`TP-service-center-time-stamp
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`TP-user-data-length
`
`
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`.
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`TP-user-data
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`" SMS<deliver
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`
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`TP-Protocol Identifier
`She TP-PID is used by the MS or SMSC to identify the
`higher-layer protocol being used for internetworking
`with a certain type of telematic device (Telefax group 3
`or 4, Ermes,ete.)
`TP-User-Data (TP-UD)
`The TP-UDficld is uscd to carry the short message. It
`can store up to 140 octets of data for point-to-point SMS,
`together with a header depending on the setting of the
`‘TP-UDHIfield, The amount of space taken by the header
`icduces the amountof data the PDU can carry. Figure &
`:fows a representation of the layout of the TP-UD for 7-
`ind 8-bit data schemes,
`The header has at least three ficlds. The first field,
`the information clement identifier, is used to identify
`‘oncatenated short messages. Information data length
`(IDL) is used to indicate the length of the information
`
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`“EE Personal Communications * June 2000
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`TP-destination-addressoeTP-data-coding-scheme
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`TP-validity-period format
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`|
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`:
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`SMS-submit =
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`@Figure 7.An SMS TL-PDU.
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` Octets
`Octets
`
`Paypayeeeg ae
`
`
`Pre oee
`Poee tae
`‘ea caERD:
`
`
`
`Padding.” PEERSESM)yebit dataic:
`
`
`Septet boundary
`
`
`Total number of octets
`
`
`
` Total numberof septets
`
`
`
`Octet boundary
`
` : Total numberof octets
`
`
`2 Length Indicator ;
`
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`:“lengthindicator
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`
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`a Figure 8, SMS-TPDUformatsfor 7.bit and 8-bit data content,
`
`also lead to the short message not being understood and
`being rejected. All the above-mentioned problems can lead to
`packets getting lost along the way with different conse-
`quences:
`* A negative acknowledgment received by the sender (phone
`displaying “message failed” or a similar message) although
`the short message reachesits destination (loss of packet (13)
`* Reception of duplicate short messages by user B (loss of
`packet (3) or2); could also be due to the timeout valuc
`being set too low in the SMSC
`* Or, in the worst case the message might not be delivered at
`all (loss of packet (12,3, 03, {93}
`Evenif Fig. 9 shows the most complicated routing scenario
`there is still much that can go wrong with short message rout-
`ing, and a lot of research is currently underway to overcome
`these.
`
`Short Message Routing Considerattons
`Tn Fig, 9, user A in network ©) is sending a short messageto
`user B in network () roaming in network “). User A is using
`the SMSC in network @)
`to submit his short message [8].
`The local cellular exchange routes the short message in an
`SCCP packet according to the SMSC global title as defined by
`the £.164 numbering plan [9]. The SCCP packet is forwarded
`from exchange to exchange until it reaches the destination
`SMSC(1). The routing has to be set up in all the SCCP switches
`along the route for the message to successfully reach the SMSC
`in network ©),
`Once the SCCPpacket carrying the message arrives at the
`destination SMSC, a confirmation message is sent back to the
`handset using another SCCP packet(2).
`To deliver the short message to user B, the SMSC hasto
`access the HLR database of his home network. A location
`request SCCP packet, based on user B’s mobile number, is
`Protocols for
`sent by the SMSC (3).
`Short Message Submission
`This international SCCP network then routes the location
`request SCCP packet to the appropriate HLR. Whenthe
`The European Telecommunications Standards Institute
`HLRreceives the request, it will return the location informa-
`(ETSI) specified a protocol for short message submission as
`tion in another SCCP packet to the SMSC (4).
`part of the overall GSM standard [10]. This specification
`The SMSC then sends the message to the VMSC of user
`defines three interface protocols for the transfer of SMS short
`B, based on the information reccived from the HLR (5).
`messages between an MS and terminal equipment (TE) via an -
`Finally, this VMSC interrogates the VLR (6, 7), and delivers
`asynchronous interface. The protocols clearly overlap in func-
`the message to user B (8), Upon successful delivery a confir-
`tions, and it is not clear why three have been defined.
`mation SCCP packet is sent back to the SMSC (9).
`Throughoutthese routing procedures, the SCCP packets
`Block Mode
`can get lost if one of the cellular exchanges along the route
`The block mode is a binary protocol which encapsulates the
`does not know where to forward the SCCP packet. SCCP
`SMS PDU used for short message transfer between an MS
`routing is based on the globaltitle used for switches and the
`and the SMSC defined in GSM 03.40 [2]. This protocol
`SMSC. The routing information has to be in place in the
`includes error detection and is suitable for use where the
`international SCCP transit switches for the messages to suc-
`link between the application and the phone is subject to
`cessfully reach their destination. Some international switches
`errors. It will be of particular use where control of remote
`only check the country code prefix (e.g., 44 for the United
`devices is required. The application has to construct a bina-
`Kingdom) and forward the packet to the next exchange, while
`ry string including a header and the short message PDU
`others also check for the network prefix (c.g., 447976 for
`(SMS-TPDU).
`Orange). If the exchange routing table does not include all
`the prefixes allocated to the subscribers, some messages will
`Once the application has requested the phone to cnter
`block mode a group of functionsis available:
`be rejected. Incompatible implementation of the SMSC can
`
`20
`
`IEEE Personal Communications * June 2000
`
`

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`a Figure «9. Internationalshort message routing.
`
`
`
`* Submit a short message
`* Delete messages from the phone
`* List messages in the phone
`* Transferall messages or one from the phone to the application
`* Set the phone so that the application is notified cvery time
`a new short message is received
`Each of these commands contains a number of predefined
`‘elements as described in the specification. For example, the
`Insert Message command format used to submit a short mes-
`sage is depicted in Table 2.
`
`Text Mode
`Text mode is a character-based protocol based on the AT
`command set modified for GSM. This mode is suitable for
`unintelligent terminals or terminal emulators, and for applica-
`tion software built on command structures like those defined
`in ITU V25ter. The application passes the message in plain
`text to the phone that constructs the TPDU (Table 3), This
`meansthat text mode offers a lot less functionality than block
`
`SCEesti
`
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`ot PDU mode. The text mode docs not support or automati-
`cally pass incoming messages to the application (only notily it).
`
`PDU Mode
`PDU mode is very similar to text mode, except that it leaves to
`the application the responsibility to build the short message
`TPDU. This mode adds to the convenience of the AT command
`set the possibility to construct more sophisticated PDUs (i.e.,
`allowing binary data to be transmitted, not just characters).
`
`SEMA SMS2000
`Sema Group Telecoms developed SMS2000 as an implemen-
`tation of a GSM SMSC [11]. The specification mainly
`describes the delivery of short messages to MSs, but also spec-
`ifies the protocols for short message submission, The protocol
`has been designedto oneaateovera variety of interfaces such
`as X25, DECnet, and S87, The SMS2000 SMSC is usually
`accessed via the gencral X25 access gateway -cither using a
`radio Packet Assembler Disassembler (PAD) or a dedicated
`link to the message center.
`Once connected to the SMSC, an SME can
`request any of the operations listed in Table 4. The
`§MS$2000 SMSC canalso send the commandslisted
`in Table 5 to an SME.
`
`
`
`
`
`
`
`
`
`
`SME
`|
`" SMSC
`
`Submit SM
`
`
`
`SM submission status
`
`
`SM delivery status report
`
`<-$_—————
`"Invoke {submit SM)
`
`
`
`
`
`B Figure10. Shortmessage submission using
`SMS2000.
`B Table 3. Short message submission using text mode,
`
`
`TEEE Personal Communications * June 2000
`
`21
`
`

`

`
`
`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. Figure 10 depicts the
`submission of a short message from an SME to the SMS2000
`SMSC.
`The transaction is initiated by the SME when a Submit SM
`invoke is sent to the SMSC. The SMSC responds with a result
`message indicating that the short message has been accepted
`andis being processed. Upondelivery the SMSC notifies the
`SME (if a status report has been requested). The SME then
`acknowledges the SR, thus completing the transaction.
`Since the SMEs connected to the SMS2000 SMSC are
`assumed to be trusted systems, a basic transaction will not
`include any exchange of login and password between the SME
`and the SMSC. Howevera login facility is still provided in
`order to access the SMSC from a different location (i.c., PAD).
`
`Text-Based Protocals
`
`Usually these protocols are proprictary and developed as an
`interface to the SMSC ofa digital ccllular network operator.
`The advantage of a text-based protocol is that the user does
`not need any special clicnt software to submit a short mes-
`sage; they can dial the appropriate message center using any
`terminal emulation software and submit short messages
`using the different options offered. Figure 11 describes the
`submission of a short message using the Telenote-text based
`protocol.
`There are, however, kcy disadvantages with text-based pro-
`tocols: they offerlimited support for extended charactersets,
`and only work one way, to name a few. The user is only able
`to send messages andreceive confirmation of submission. The
`SMSC is unable to notify the end user of successful delivery.
`
`
`
`
`
`
`
`
`
`MW Figure 11. Short message submission using Telenote.
`
`Telocator Alphanumeric Protocol
`
`Developed by Telecom Securicor Cellular Radio Limited, the
`Telocator Alphanumeric Protocol [12] provides greater flexi-
`bility ind more features than text-based protocols. The overall
`performance is also significantly more efficient.
`In its fully featured implementation, the protocol allows
`the user to perform the following operations:
`1. Submit a short message and receive confirmation of accep-
`tance,
`2. Submit a short message and receive status of the first deliv-
`ery attempt.
`3, Query the current status of a message submitted by 1 or 2.
`4, Delete a message submitted by 1 or 2.
`5, Replace a message submitted by 1 or 2, unless the message
`has already been delivered to the mobile.
`6, Update a message submitted by 1 or 2. If the message is
`still in the SMSC.it is replaced; otherwise, a new message
`is sent to the mobile,
`TAP is a session-based protocol, as opposed
`to a permanently connected one, Each session
`comprises a logon, a numberof transactions, and
`a logoff, as shown on Fig, 12,
`Other Submission Protocols
`Many others protocols have been designed and
`operate over a wide range of hardware interfaces
`(UCP, CIMD, SMPP,etc.). Most of the protocols
`ean be classified as dumb or smart based on
`whether they provide notification of delivery
`and/or advanced functionality (message deletion,
`replacement, ctc.}, We chase to discuss the pro-
`
`
`in the United Kingdom. As growing numbers of