Abstract
`This tutorial presents an overview of the Global Systcin for Mobile Communications Short Message Service from the viewpoint of iniplerricnling
`new tclcmalic services. SMS offers the risers of GSM networks the ability to exchange alphanumeric nIcssa_i\;i:.s up to the limit of mu Ch:lfil('.ll.:]'5.
`The tutorial is niotivaleii hy an aortic absence of rcsearcli pllblications in this field. The lnfornlalion gatllcrcii iii the Iulorial was T(:t]lllIlC(l
`cotlsidcring Ilic in:.'re:tRing potential SMS offers for integration with existing Incssaging services and its ability to after H successful replaccntenl
`for the 'l‘ransmis5ion Control and Internet Protocrila as far as low-hanrlwirlth-dcmanrling applicatioiis are concerned. Initially. the tuto1'ial gives a
`bricl‘ overview of the building blocks of GSM uclwnrlrs ——- the mohili‘. station, base station, and network siihsystcm -— and then einpltasizcs the
`SMS network and protocol ancliitcctiirc. The most widely used protocols for message suhmisi-'.ion are then introiiuceii (text—l1ased, Sl\-132000,
`l-.'l'S[ T.l".l't'I5. TAP) and compared in terms of features provided and flexibility to handle cstcndcd alphalicts or two—way mcsselging, Finally the
`tutorial outlines a snminary of current and future issues for further development and research in the light of novel fcatllrcs for suhmimion
`protocols and telcmatic 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.
`
`since the first Global System
`for Mobile Colllltllinications (GEM) Iietwork started opera-
`tionin I99], more than lllll countries have adopted the stan-
`dard. Over 20 Inillion sulascrilicrs ol' (‘ISM networks are now
`ollcrcrl worldwide coverage, outstanding voice quality over a
`whole range of operating conditions, and it vatiety of value-
`added services. Tlicsc services include voice mail. call han-
`dling facilities. call line identification. and Short Message
`Service (SMS).
`With SMS, users are able to cxcltangc alphanumeric mes-
`sages [up to 160 characters) with other users of digital cellular
`networks, almost anywhere iii the world, within socoiids ol'
`subrnission. F‘ on if lhc service was originally conceived as a
`paging tticisltnnisrn l'or Imllfyirlg the risers of voiccmail mes-
`sages, SMS is now incrca.<.-ingly used as a messaging service.
`'l'he messages aI'c typically created on Inobilc phone kcypads,
`which is somewhat awkward. Fortunately, there are other
`ways to access the message centers, as discussed in this article.
`Numerous applications are already availahlc and make short
`message reception and submission possilile using a computer.
`tlalcwriy arcliiteclures are also being wiilcly irnplornenled and
`connect con1p:lny’s e—mail or voice.-mail systems to thc SMS.
`'1'hcpr:iclical irnplctlicrllation ol'SMS and the tliffcrcnt
`protocols for rnussagc slilttnissiort are }1(l(.ll'l'.:.‘s':iE‘.'d in this article.
`'l‘hc |'ulurc of SMS and a brief review of the fields currently
`being studied will conclude this article.
`
`The Short Message Service
`Dcvelopcil as part of the GSM Phase 2 specification, the
`Short Message Service, or SMS as it is more commonly
`kttm-VII, is based on the capability of a Lligiial ccllulztr terminal
`
`to send andfor rcccivc alphanumeric mcssagcs. The short
`messages can be up to I40 bytes in length, and are delivered
`within it low sctxnicis where GSM coverage is available. More
`than a common paging service, the delivery of the message is
`guaranteed even when the cellular terminal is unavailable
`{e.g., when it is switched off or outside the coverage area).
`The network will hold the message and deliver it shortly after
`the cellular terminal announces its presence on the network.
`The fact that SNIS (through (JSM) supports international
`roaming with very low latency makes it particularly suitable
`for applications such as paging, e—mail, and voice mail notifi-
`cation, and messaging services for multiple risers. llowevcr,
`the facilities offered to users and the charges l'or these facili-
`ties still mainly depcnd on the level of service provided by the
`network operator.
`There are two types of SMS available: cell broadcast [1]
`and point-to-point [2]. In cell broadcast. a message is trans-
`mitted to all the active handsets or mohilc stations (M85) pre-
`sent in a cell that have the capability of receiving short
`messages and have subscribed to this particular information
`service. This service is only onc—way, and no confirmation of
`receipt will he sent. lt can send up to 93 ?-bit character or 82
`8-hit characters, typically used to transmit Incssagcs l1l.')0|.l'l.
`traffic conditions, weather forecast, stock market, and so on.
`In point-to-point service, nicssngcs can be sent from one
`mobile to another or from a PC to a mobile and vice versa.
`These messages are maintained and transmitted by an SMS
`Center (SMSC). The SMSC is an electronic form of ordinary
`mail postal service that stores and then fonvards the messages
`when they can he delivered. Each GSM network must support
`one or more SNISCS to sort and route the nicssages. Each
`SMSC checks, organizes, and sends the message to the opera-
`
`IEEE Personal Communications - Junc 2fl(ll.".i
`
`ltl"r‘[l—991(if0ll;'$ lllflil ® Zflilll IEEE
`
`15
`
`Apple 1026
`U.S. Pat. 7,535,890
`
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`i l:l]_',lI|—‘t—! "I. Tito ba.rrr.' GSM network rtt'cItirec.t—ur'c.
`
`tor. IL also rcccitrcs tutti passes on any 00llflI'lt‘lilfi(}fl mc.‘is:1g.;-,5 to
`any GSM mohilc on any network. I lowr.:vc1', in practice. thcrc
`art: no i1g,rt:L'.ItIL:-nl's to allow SMS to travel hctwcon ttctwtirlos.
`'l‘hot'o are several ways in which :1 short Lnossagc can he
`submitted, dcpctlrling on the interfaces supportctl by the (‘ISM
`[lt_’.lW<lI'l( SMSC. Uscrs can call at central paging l‘lllI't‘.!«l1] (to,
`an opcrotor). or directly croittc tho tncsstagc on the ltcypotl of
`tlnoi r limclsot. Typitig tho messages is made cutsiot whctt tisitig
`at pcI':mtIal digital assistant (FDA) or in laptop colmcctetl to
`tho |I:1nLisL:t. A few SMSC C{|lIl|1I'liCI’II. m:trmfar:turt:I's and com-
`puiiios havc also tlcvclopetl their own protocols for short mos-
`imgo 5tib1r1'|s.<:io|1. Cmiscqucntly, more and more GSM
`nctworlos now ol'l‘cr access to tlicir SMSC using tltcsc ]’Jl'()lI(l—
`colt; over ii vziricty of lt:1r'I.lwaIrc ititcrfocosz inoclclil tlialttp,
`.‘(2_‘:', send t:'l-‘C-I'l thc lntcrnct.
`
`C5/l/l Network Architecture
`
`Tho loyotit of‘ El gom:t'ic GSM rictworlr with its xcvcml func-
`tiomrtl entities is .‘il‘l0WI1 in Fig.
`l [3].Tl|oarcl1itccturc cant be
`tlivitlcti in lll.l'CL=1T1£\lIl components:
`' The s:ult:;cribcr holds thc MS, narnoly the GSM terniitial
`' 'l'|1el1asn station sitllsyslcm controls the radio link with the
`MS
`- The network .*illl‘l.'iy.‘ilClI1 pcriorms tho swil'chin}!, of calls and
`other‘ tnamtgcmcnl irlslts 8110]] as authcnticatiorl.
`
`l'l1t=M0l1ile Siotiriri
`The N15 and l'JE1SC station sllbsysttcnt oomntttnicalc across the
`Um intcrl'act:, also known as the fliL’i1ttI:3rfzt(.‘c or radio link.
`The base station tlubsyslcnt L:I’.!1TI1”n.l.lI]lL‘-E1103 with Iihc network
`stlltsystoiti (across the A iIltL‘.1'l:i.(.'t‘.'. Tltc MS |:U|1‘.5l‘:‘u'lS of the
`physical terminal and coiltains this radio lroltsccivor. the dis-
`play mid tligitatl signal pI'0CLlSl5(Jl'S, and tlic Subscrilicl‘ identity
`Motlule (SIM The SI M p1'ovidcs lhc 1.15:1’ with the ability to
`access their s:L1hs::r_ibc:l sci-vices rcgurtllcss of the location and
`the terminal tr.-;cd.
`'l‘llc insertion of the SIM in any GSM cel-
`lular phone allows: the tisor to EICCCSS :I network, make and
`l'CCClVc phone culls, and us:-. all the subscribed .'tci'ViGcei.
`The ll'll.'t.'-l'l‘IE1l.l()l‘lil.l Mobile Equiprncnl ldctltiiy UMFII]
`uniqtlcly l(lI3lllifil.:.'s' the mobile torminol according to the litter-
`nolionatl Mohilc Subscriber ldoiility (IMSI) contained in the
`
`SIM. Bccausc thc 1Ml".I and IMSI are independent, personal
`mobility is possible. The SIM can bc protcctecl against unau-
`thorizcd use by re personal identity number (PIN).
`
`The Base Station .S'ubsysi'ent
`The base station slibsystem is composetl of two parts, the
`basic transacoivcr station (HTS) and base station controller
`{BSC).'1‘hey communicate across thc spccificd Abis inter-
`face, thus allowing network operators to use cotrlponcrits
`mad; by tlifferent sttppliers, The HTS houses the radio
`trmisceivcrs that di:l'irJo at cell and handle the radio link pro-
`tocols wilh the MS. Dcpending on the density of tho area,
`more or fowcr H'['Ssa are needed to provide the appropriate
`capacity to the cell. Digital comnmnications system (DCS)
`networks working at liltltl Ml-IV. need twice the number of
`IZTS5 to cover the same ztrca as GSM rtctworksi, but provide
`twice thc capacity.
`_
`The BSC1nanzLgos the radio wstturces for one or more
`BT33 via lhc Staitdttrtlized Abifi interface. It handles radio
`channel setup, frequency hopping, and ltatldov-::.I's. The BSC is
`the connection between the MS and the mobile switching cen-
`ter (MSG). The BSC also takes care of convcrting the 13 kbfs
`voice chnnncl used over this radio liolc (Um interface) to the
`stttndardiued 64 kltfs Clianncl used by the public switched Lola-
`phonc network‘ (PSTN).
`
`'l'h.=r Network 5l1lJ5ySl8HI
`The M513 is the rrmin component of the network subsystem.
`lts provides the same l"uncI.iot1alily as :1 switching nodc in a
`l’S'l'l‘*l or integrated services digital network (ISDN), but. also
`takes care of all the functionality needed to handle :1 mobile
`5l1l'fS(,‘l'lhe1‘ such as rcgistratiolt, ituthcnticatiori, location updat-
`ing, ltandovcrs, and routing to a roaming subscriber. Tho
`MSC also acts as El gateway to the PSTN 0:‘ ISBN, and pro-
`vides the interface to thc SMSC.
`'l‘i'Lc intcmatiomtl roaming and call muting capabilities of
`GSM networks are provided by the. home location register
`(HLR) and visitor location register {VLRJ together with the
`MSC. Tlic HLR database contains all the administrative infor-
`mation about cach I't:gisl.orCd user of a GSMi1ctwork along
`with the current lt‘IC'd.tlO!‘l of the MS. 'l‘i1c current location of
`an MS ii: in the form of at Mobile Station Roaming Ntlmbor
`
`"I6
`
`]EI::l:‘ I"a1~sona| Cumtnuriications ' June Ztlllll
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`

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`

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`

`
` SMS—GMSC/
`
`SMS-IWMSC
`
`igure 6. Inrotocol layerfor ;)r)i7nf-tcqioint.
`
`The SM-TL exchanges PDUS with its peer entity. The
`art message relay layer (SM-RL) conveys the PDUs via the
`.iort message link layer (SM-LL). Refer to GSM 03.40 [2] for
`further details.
`
`Sfl/l5 Protocol Data Unit B/pes
`There are six types of TPDU at the SM—TL, as listed in Table
`'l. The elements of the SMS-Deliver and SMS-Submit TPDU
`are shown in Fig. 7 [2]. The main fields of the TPDU are
`described in this document however for a complete descrip-
`tion of the TPDU please refer to GSM 03.40 [2].
`
`clement data (IED) that follows. Each of
`these fields is 1 oetet long.
`In the user data, the message can be 7 bits,
`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 can still display the message properly.
`Using the IE] allows sending and receiving
`of concatenated short messages. The IED field
`contains all the necessary information for the
`receiving entity to reassemble the messages in
`the correct order, and is coded as follows:
`- First octet: short message reference num-
`bcr identifying the message within the same
`transaction
`0 Second octct: specifies the maximum number of short mes-
`sages in the concatenated short message, which will not
`exceed 255
`0 Third octet: identifies the sequence number of the short
`message within the concatenated message
`The minimum header length for concatenated message is 7
`octets for 8-bit and I6-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*l52), 33,915 (255*l33), or 16,830
`(255*66) depending on the character coding scheme used.
`
`
`
`TP-Validity-period format
`
`TP-reply-path
`
`TP-use-r~o|ata-heacler-indicator
`
`TP-message reference
`
`TP-destination-address
`
`
`
`
`
`19
`
`TP-data-coding-scheme
`
`SMS-subrriit
`
`g
`
`.
`
`
`
`
`
`
`
`TP-message-typeindicator
`
`TP—reject—dup|icate
`
`TP-message-type-indicator
`
`TP-more-message-to-send
`
`TP-reply-path
`
`TP-user-data-header-indicator
`
`TP-status-report
`
`TP-originating-address
`TP-protocol-ID
`TP-data-coding-scheme
`
`TP-service-center-time-stamp
`
`
`
`
`
`TP-user-data-length
`
`
`
`TP—user—data
`
`SIVlS—de|iver
`
`I_ Figure 7./In SMS TL-PDU. "
`
`TP-Dota—Coo‘ing—Srheme
`The data coding scheme field (TP-DCS) is used to 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].
`
`TP-l/alitlii}/—Per1otl
`The TP-VP field contains an information element
`
`enabling an MS to 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-/l/lessoge-To-Send
`The SMSC uses the TP-MMS field to inform the MS that
`.-«he or more short messages are waiting to be delivered.
`
`TP—U5cr—Dato—l-leader-indicator
`' he 1-bit Tl’-UDHI field indicates whether the 'l‘P-UD
`l .r‘ludes an additional header as well as the short message.
`
`TP—Protocol identifier
`"he 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, etc.)
`
`TP—lJser—Data {TP—UD)
`The TP-UD field is used to carry the short message. It
`ran store up to 140 octets of data for point-to-point SMS,
`together with a header depending on the setting of the
`Tl’-UDHI field, The amount of space taken by the header
`reduces the amount of data the PDU can carry. Figure 8
`: hows a representation of the layout of the TI’-UD for 7-
`.-nd 8-bit data schemes.
`The header has at least three fields. The first field,
`the information element identifier, is used to identify
`roncatenated short messages. Information data length
`(IDL) is used to indicate the length of the information
`
`= a;‘.EE Personal Communications ' June 2tJUt]
`
`

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`

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`

`
`

`
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`
`I Figure 12. Short message submission using 1211".
`
`.
`same transaction
`- Support for distribution list creation and modification with-
`in tlic SMSC to greatly increase short message throughput
`last but not least, some research projects are studying the pos-
`sibility of using SMS as an alternative layer to TCP/IP, thus
`adding mobility to low-bandwidth applications. Intel’s Narrow
`Band Socket specification first tried to define how applications
`could benefit by using SMS as an alternative to TCP/IP; however,
`this work is now in the process of being superseded by the Wire-
`less Application Protocol (WAP).
`
`References
`1] ETSI GSM 3.41, “Digital Cellular Telecommunication System (Phase 2);
`Technical Realisation of Short Message Service Cell Broadcast (SMSCB),"
`v. 5.2.0, May. 1996.
`2] ETSI GSM 3.40, "Digital Cellular Telecommunications System (Phase 2+)
`Technical Realisation of the Short Message Service Point-to-Point," v.
`4.13.0, May. 1996.
`3] J. Scourias, "A Brief Overview of GSM," Univ. of Waterloo; http://ccngaf
`uwaterloo.ca/~jscouriar'GSMrgsmreport.htm|
`4] M. Mouly and M. Pautet. "The GSM System for Mobile Communica-
`tions," 1992.
`5] W. Roth, "Data Service on the GSM Platform," GSM Summit Hong
`Kong. Mar. 1993.
`6] ISO/IEC10646, "Universal Multiple Octet Coded Character Set (USC),
`UCS2, 16 Bit Coding."
`7] ETSI GSM 3.38, "Digital Cellular Telecommunications System (Phase 2+):
`Alphabets and languagespecific information," v. 5.2, May. 1996.
`B] K. Holley, http:.lftp.labs.bt.comlpeople/holleyka
`9] CCITT E.164, "Numbering Plan of the International Telephone Service,"
`v. 5, 1997.
`-
`[10] GSM 07.05, "Digital Cellular Telecommunications System (Phase 2};
`Use of Data Terminal Equipment — Data Circuit terminating; Equip-
`ment (DTE - DCE) interface for Short Message Service (SMS) and Cell
`Broadcast Service (CBS)," draft, May 1996.
`[11] SEMA Group Telecommunications, "SMS2D00 v. 4.0, Open Interface
`Specification," INS/F5/28.
`
`[12] Telocaior Alphanumeric Protocol -(PCIA) v. 1.2 Functional Spec for TAP-
`AIM ver 2.6 (Aldisconl
`
`Additional Reading
`[1] M. Rahnema, "Overview of the GSM System and Protocol Architecture,"
`IEEE Common. Mag., vol. 3, no. 4, Apr. 1993, pp. 92-100.
`
`Biographies
`GUILLAUME PEERSMAN (G.Peersman@dcs.shef.ac.uk) graduated from the Insti-
`tut Superieur d'E|ectronique de Paris (ISEP) in 1996 with a double M.Eng.
`in electronics and computer networks. He then joined the University of
`Sheffield, and is currently reading for a Ph.D. degree in the Computer Sci-
`ence Department. His research interests focus on the development and per-
`formance analysis of two-way messaging gateways for the GSM Short
`Message Service. He also recently extended his field of research to the
`Wireless Application Protocol gateway design.
`
`SRBA R. CVETKOVIC (S.Cvetkovic@dcs.shef.ac.uk) completed his B.Sc. (with
`First Class Honours) and Ph.D. degrees in electronic and electrical engineer-
`ing at City University, London (1983) and University College London (1987),
`respectively. In June 1987, he joined the Department of Electronic and Elec-
`trical Engineering at the University of Surrey as a lecturer in telecommuni-
`cations and satellite systems. In September 1992 he moved to the
`Department of Electrical Engineering and Electronics, Brunel University,
`West London, to a senior lectureship in data communications. In Septem-
`ber 1995 he took up the _post of senior lecturer in multimedia communica-
`tions systems in the Department of Computer Science at the University of
`Sheffield. In January 1996 he established the Centre for Research, Education
`and Development Online (CREDO). He now leads the Research Group in Com-
`munications and Distributed Systems (CDSRG), which he co-founded in Octo-
`ber 1997 with Prof.-Colin Smythe. CDSRG (including CREDO) is currently
`involved in projects of value in excess of US$8.5mi||ion and has over 35 full-
`time members of academic, research, and support staff. In October 1997 he
`was promoted to reader (in telematics) and in June 1999 to a personal chair
`in mobile systems, a joint position between the Departments of Electronic and
`Electrical Engineering, and Computer Science. His research interests include
`multimedia/broadband communication systems, satellite communications and
`DSP systems. as well as numerical modeling and measurements of electro-
`magnetic fields. More recently, his focus has been on protocols for supporting
`mobile systems (Mobile IPv6, GSM/SMS) and knowledge management. For
`further information visit http://www.cIcs.shef.ac.uk/-srba
`
`PAUL GRIFHTHS (P.Ciriffiths@dialogue.co.uk) graduated from Sheffield City Poly-
`technic in 1986 with a B.Sc. Hons. in business studies. He then joined
`Fretwell Downing Data Systems as a software developer where he worked on
`various projects between 1998 and 1991. Between 1991 and 1994 he
`worked on secondment with Sheffield Hallam University to conduct research
`into the development of GUI environments. In 1994 he helped to.found Dia-
`logue Communications Limited who developed a product for GSM short
`messaging called pagemail which has since sold over 500,000 copies. He has
`since been involved with both business and technical aspects of developing
`server products for GSM SMS. He is now co-director of Dialogue Communica-
`tions Ltd., a specialist SMS software manufacturer which has recorded an
`average growth rate of 70 percent for the last three years.
`
`HUGH SPEAR (H.Spear@dialogue.co.uk) received an M.Sc. with distinction in
`Software Systems Technology from Sheffield University in 1991. Between
`1991 and 1995 he worked as a systems analyst and project leader with
`Fretweil-Downing Data Systems in Sheffield. In 1995 he co-founded Dia-
`Iogue Communications Limited, a mobile messaging business which devel-
`ops and markets products and services for messaging over GSM SMSand
`paging services. By the end of 1999 Dialogue had over 250,000 customers
`and products in over 20 countries.
`
`IEEE Personal Communications - June 2000
`
`25