Chapter 16: Short Message and Data Services Section 1: The Early Years from mid-1982 up to the Completion of the First Set of Specifications for Tendering in March 1988 Friedhelm Hillebrand 1 16.1.1 The Mandate by CEPT and the First Action Plan of 1982 The mandate given to the Technical Committee GSM by CEPT in mid-1982 requested the ‘‘harmonisation of a public mobile communication system in the 900 MHz band’’. 2 This decision took place during the very hot promotion phase for ISDN. Therefore it is remarkable to note that GSM was not defined as a ‘‘mobile ISDN’’. Instead the decision leaves the nature of the GSM open, but requests the study of the interconnection with ISDN. The first action plan for the group GSM elaborated by the Nordic and Dutch PTTs was approved at the meeting GSM#1 in December 1982. It mentioned basic requirements for data services 3 It is expected that in addition to normal telephone traffic, other types of traffic (non-speech) will be required in the system. However since such predictions concerning the user requirements will contain a great amount of uncertainty, a modular system structure allowing for a maximum of flexibility will be necessary. The services offered in the public switched telephone networks and in the public data networks at the relevant period of time should be available in the mobile system . The system may also offer additional facilities. These basic requirements regarding data services were very far-sighted. They were nearly forgotten for long periods due to priorities for telephony. 1 The views expressed in this section are those of the author and do not necessarily reflect the views of his affiliation entity. 2 GSM Doc 1/82. 3 GSM Doc 2/82. GSM and UMTS: The Creation of Global Mobile Communication Edited by Friedhelm Hillebrand Copyright q 2001 John Wiley & Sons Ltd ISBNs: 0-470-84322-5 (Hardback); 0-470-845546 (Electronic) 16.1.2 Discussions on Data Services from the Beginning of 1983 to the End of 1984 The focus of the GSM work in the period from the end of 1982 to the end of 1984 was on strategic questions and the requirements for the basic telephony oriented system, e.g. the relationship between GSM and emerging analogue 900 MHz interim systems, radio aspects, speech coding and hand-held viability. There was also a lack of data communication exper- tise in GSM. Therefore the progress was slow in this area during this period. Results were not saved in permanent documents and were often forgotten after some time. During GSM#2 meeting in February/March 1983 a general discussion on ISDN and OSI and their applicability took place without firm conclusions. During the GSM#4 meeting November 1983 regarding ISDN it was clarified, that it was not possible to provide the full capacity of B- and D-channels but only the functions. GSM#6 in November 1984 received a report from a working party on network aspects which had met during the GSM meeting. 4 It proposed to use the ISDN concepts of terminal adaptors and interworking units for data services in the GSM system. 16.1.3 The First Concept for Data Services Agreed in February/March 1985 (GSM#7) During GSM#7 the Working Party 1 ‘‘ Services’’ (WP1) elaborated a document on ‘‘ services and facilities of the GSM system’’ which was endorsed by GSM. 5 This was based in the data services part mainly on an input submitted by Germany and France. 6 The output document contained a reference model for data services, definitions of tele-, bearer and supplementary services, network connections and types of mobile stations. The reference model introduced terminal adaptor functions at the mobile station and an interworking unit between the mobile and the fixed network (the diagram is shown in Chapter 10, Section 1, Fig. 10.1.1). The annexes contained lists of teleservices including the Short Message Service (SMS). SMS had three services: mobile originated, mobile terminated and point to multipoint. It foresaw a maximum message length of, e.g. 128 octets, and an interworking with a message handling system. Other non-voice teleservices mentioned were, e.g. access to message hand- ling systems and to videotex, facsimile, and transmission of still pictures. A comprehensive range of circuit switched bearer services was listed: † asynchronous duplex up to 9600 bit/s end-to-end † synchronous duplex up to 9600 bit/s end-to-end † asynchronous PAD access up to 9600 bit/s The necessary connection types to support the mentioned services were defined by a set of attributes. Another important prerequisite for the work on data services was the emerging consensus on network functions and architecture of the basic GSM system as needed for telephony 7 . This allowed to start work on the reference configuration for data services 8 . GSM and UMTS: The Creation of Global Mobile Communication408 4 GSM Doc 90/84 Annex 3. 5 GSM Doc 28/85 rev. 2. 6 GSM Doc 19/85, for more details see Chapter 10, Section 1, paragraph 10.1.4.1. 7 GSM Doc 43/85. 8 GSM Doc 106/85. 16.1.4 Work in the Period from March 1985 to February 1987, when the Radio and Speech Coding Technologies Were Chosen In the following meetings GSM and its working parties concentrated again on basic telephony aspects. GSM#12 (September/October 1986 in Madrid) discussed, whether the speech codec should be transparent to DTMF signals. It was qualified as desirable, but not as an essential requirement, since other solutions could be found. The priority for telephony left no work resources for data. The situation was very critical in WP3 ‘‘ Network Aspects’’ , which was very busy with system architecture, mobility manage- ment, etc. Also WP2 ‘‘ Radio Aspects’’ was fully loaded with the evaluation of the different radio techniques and had no time or capacity to work, e.g. on channel coding for data services. 16.1.5 Fundamental Decisions on Data Transmission in GSM#13 (February 1987 in Funchal) The catalyst for some fundamental decisions on data services was the discussion of require- ments on the speech codecs with respect to transparency for DTMF and voice band data. During the selection decision of the voice codec at GSM#13 it became clear, that a transpar- ency requirement for DTMF and voice band data would lead to additional complexity and a deterioration of the speech quality. On the other side it was realised, that data would need additional protection, since the system would provide at cell boundaries only a bit error rate of 1 error bit per 100 transmitted bits (compared to less than 1 in 1 000 000 in ISDN). GSM#13 decided that the speech codecs should be optimised for speech only, since GSM was intended to be primarily a mobile telephony system. It was further confirmed that the capability of the system to carry DTMF and voice-band data was an essential requirement. Based on the proposal of an ad-hoc group 9 GSM decided that DTMF should be ‘‘ transmitted as a signalling message over the Dm channel’’ and that the DTMF tones should be ‘‘ injected into the audio path at the receive end’’ . ‘‘ Data services should be supported by the GSM system . The terminal equipment is connected to the mobile station via a terminal adaptor and the transmission is fully digital. Terminal adaptors for the V-series are to be specified.’’ 10 As a consequence of this decision GSM agreed on the necessity of putting extra resources on this task, since WP3 dealing with network aspects was not able to cope with it due to overload and lack of specialised expertise. To start the work, a sub-working party under WP3 was created. I was appointed as an interim chairman, since I was one of the very few GSM members with data communication expertise. 11 Furthermore GSM decided, that interim terms of reference should be agreed between the WP3 chairman and myself and that the group should meet independently of WP3 and should not make use of resources presently used by WP3. Chapter 16: Short Message and Data Services 409 9 GSM Doc 39/87. 10 GSM Doc 41/87. 11 I had been responsible for the setting up of the German national packet switching network DATEX-P. 16.1.6 The Agreement on Strategic Issues and the First Set of Specifications for Tendering from May 1987 and to March 1988 16.1.6.1 Setting Up of the New Group IDEG and Initial Discussions The new group was called the Implementation of Data and Telematic Services Expert Group (IDEG). The first IDEG meeting on 20–22 May 1987 in Bonn was attended by 18 delegates. 12 Draft terms of reference and a set of working assumptions for the work as well as an action plan were elaborated and agreed (see annexes to the meeting report). The creation of IDEG coincided with the time when the rules for participation in CEPT were relaxed. GSM had asked the superior bodies to allow manufacturer’s participation in the detailed technical work after the GSM radio decision. Prior to that time, CEPT participation was limited to representatives of the post and telecommunications authorities only. The new rules allowed industry experts to participate in meetings by the invitation of, and as an advisor to, a CEPT member organisation. They were admitted as experts assisting the CEPT members, not as representatives of their companies. They were also members of the delega- tion of the CEPT member they were assisting. They could not submit documents in the name of their company, but had to hand them to a CEPT member. Industry participation was limited to two experts per committee per country. This restrictive situation was not sustainable. It lead later to the creation of the European Telecommunication Standards Institute (ETSI) and the transfer of all standardisation work from CEPT to ETSI. In the case of IDEG, there was a majority of delegates coming from industry from the beginning. The key tool to start the work was a set of working assumptions. This concept had been used in the decision on the basic parameters of GSM at GSM#13 in February 1987 in Funchal. The working assumptions were agreed as preliminary conclusions. They were seen as open to change, but the proponent of a change would need to prove their case. This is essentially a process of ‘‘ slowly drying cement’’ which allows the chairman of a group to find an agree- ment on a soft consensus conclusion and to start the process which leads to a firm consensus conclusion. Key working assumptions with regard to strategic issues were elaborated in the first meet- ing: † Confirm telephony as the prime system application. † Co-use the telephony optimised system for data services to the maximum possible extent. † Ensure a high quality of service. † Avoid changes to the system architecture and support data services by add-on modules/ functions, which can be implemented as options and can be dimensioned to meet the data traffic needs. † The concept of ‘‘ mobile office’’ lead to the requirement to have identical coverage and velocity requirements from the mobile station as the telephony service. † Limit the additional complexity, since data was assumed as a small share of the system traffic. GSM#14 (June 1987 in Brussels) approved the proposed terms of reference for IDEG and confirmed me as chairman. GSM and UMTS: The Creation of Global Mobile Communication410 12 Report in GSM Doc 70/87. 16.1.6.2 The Agreement on Fundamental Aspects In the second IDEG meeting (6–8 July 1987 in Heckfield, UK) a number of fundamental aspects were discussed and brought to conclusion for the specification work. An important concept was to use existing data terminals and provide the normal interfaces to them by a terminal adaptor function in the GSM mobile station. This meant that the terminals needed to see a quality of service (bit error rate, delay) which is comparable to the quality of service in fixed networks. Quality of service is a critical issue for data services in a radio network. There are short interruptions of a connection during hand-overs or radio fades. At cell boundaries 1 out of 100 bits is corrupted compared to 1 out of 1 000 000 in modern digital fixed networks. Therefore measures have to be implemented in a GSM network to enhance the basic quality of service. The first measure is a powerful channel coding on the radio interface tailored to data which adds checksums to detect and to correct errors (FEC ¼ Forward Error Correction). This reduces the bit error rate by several orders of magnitude. The short interruptions during handover and radio fades cannot be corrected by forward error correction, since they last too long if normal transmission delay values are requested. This type of problem can be tackled by protocols providing an automatic re-transmission of lost information. For efficiency reasons such a mechanism can be applied only on blocks of data. The protocol provides an additional checksum per block, which allows the detection of whether the received block is erroneous. A sequence number allows the detection of lost blocks. The receiving side confirms blocks received without detected errors and requests re- transmissions of blocks with errors or lost blocks. Such protocols are known in the fixed networks as the High Level Data Link Control (HDLC) family of protocols. They cannot be used in a mobile network due to the bad basic quality of service. Due to the great block size (e.g. 1024 octets in fixed packet switching networks) many blocks would have errors both during the first transmission and the re- transmission. Therefore the throughput would fall to zero. Therefore a special protocol had to be designed which was robust to cope with the difficult radio network environment. This protocol was called Radio Link Protocol (RLP). It was matched to the GSM transmission time slots, had a block length of 240 bits ( ¼ 30 bytes) and other means to secure the highest possible throughput. Services using only FEC were called transparent services. Services using FEC and RLP were called non-transparent services. Both types of services provide a low bit error rate. Transparent services provide a constant throughput and a constant transmission delay. They have however interruptions of service caused by handover and fading. Non-transparent service secure the transmission of all blocks. They re-transmit blocks lost or corrupted by the interruptions caused by handover and radio fades. During such activities the throughput is reduced and the transmission delay time is increased. IDEG refined, added details and agreed the set of working assumptions. 13 They covered all requirements without adding complexity to the basic telephony oriented system. 14 Key detailed working assumptions were: † Data for connection-less bearer capabilities (e.g. for SMS) are transmitted on a control channel. Chapter 16: Short Message and Data Services 411 13 GSM Doc 83/87. 14 GSM#15 Report, Section 7d. † DTMF information is carried on a control channel on the radio interface. † Connection mode bearers are carried on one traffic channel, no multiplexing of low speed bearers on one traffic channel. † A reference configuration for the mobile station was agreed. † Interworking requirements and architecture were agreed. † A rate adaptation mechanism was selected. † One-way transmission delay less or equal 200 ms. † Transparent services use rate adaptation and forward error correction, no ARQ. † Non-transparent services use rate adaptation, FEC and RLP † Bearer services must be capable of transmitting up to 9.6 kbit/s. I recall a very lively discussion on the maximum bit rate on full-rate channels. Several delegates pleaded to limit the bit rate at 4.8.kbit/s in order to have a very good protection by a ‘‘ heavy channel coding’’ . They argued also that such a bit rate is more than sufficient for a single user. It was through the enduring efforts of Alan Cox and Ian Harris (both of Voda- fone), who succeeded in convincing the meeting that 9.6 kbit/s on a full-rate channel was required in order to be future proof. In addition the action plan was revised. The target was to complete the specification for the essential services (E2) which would be needed for a tendering purposes in early 1988 until the end of January 1988. 15 A list of the planned specifications was elaborated. Major specifica- tions under IDEG’s prime responsibility were: † GSM PLMN connection types † Technical realisation of the SMS † Transcoding for data and telematic services † Rate adaptation (on several interfaces) † Radio link protocol (on several interfaces) † Terminal adapters (several specs) † Interworking with circuit and packet switching data networks † Service interworking † In addition contributions to the work of several other WPs were needed: † WP1 specifications on teleservices, bearer services and charging † WP3 specifications on network architecture, interworking with PSTN/ISDN, numbering/ routing/identification † WP2 specifications on channel coding GSM#15 in October 1987 confirmed the working assumptions and the action plan and ‘‘ promoted’’ IDEG from a WP3 sub-group to a working party reporting directly to GSM. IDEG was renamed Working Party 4 ‘‘ Data and Telematic Services’’ (WP4). 16.1.6.3 The Production of Specifications Needed for Tendering In the following period WP4 concentrated its effort on producing draft specifications in accordance with the action plan. Two WP4 meetings were held on 26–30 October and on 23–27 November 1987 in Bonn. 16 These meetings elaborated the first draft specifications. GSM and UMTS: The Creation of Global Mobile Communication412 15 GSM Doc 84/87. 16 Report in GSM Doc 144/87. Each meeting week had short opening and closing plenaries on Monday Friday morning, respectively. From Monday afternoon to Thursday evening six drafting groups worked on † SMS † architecture and connection types † terminal adaptor functions † radio link protocol and coding † interworking † numbering and routing Four specifications were completed for examination by GSM#16 in December 1987. These were the most urgent ones, identified by GSM as particularly important for the tendering activities: 03.10, 03.41 (deleted later), 04.21, 07.02. Twelve specifications reached the status ‘‘ preliminary’’ . There was another WP4 meeting in Paris on 22–25 February to complete the first draft specifications. 17 GSM#17 in February 1988 approved the first set of specifications needed for the tendering on 29 February 1988 18 : † 03.10 GSM PLMN connection types † 04.21 rate adaptation at the MS/BS interface † 07.01 principles on terminal adapters † 07.02 terminal adapters for asynchronous bearer services † 08.20 rate adaptation on the A interface 16.1.6.4 The Specification of the SMS WP1 had produced a service description for the three SMSs: 19 † Mobile originated/point to point † Mobile terminated/point to point † Cell broadcast An additional input with a concept proposal for the technical realisation of the ‘‘ mobile terminated/point to point’’ service came from France. 20 It contained a proposal for the func- tional architecture. It proposed a new entity, the service centre in charge of: † Dialogue with the user for message submission and status requests † Handling of messages: storage, status, transmission † Operation and maintenance functions It proposed a layered function split between a message application subsystem and a message transmission subsystem as well as several protocols.WP4 created a Drafting Group Message Handling (DGMH) under the leadership of Finn Trosby (Telenor) in July Chapter 16: Short Message and Data Services 413 17 GSM Doc 93/88. 18 GSM Doc 31/88 rev. 1 19 See Chapter 10, Section 1, Paragraph 10.1.5.1.3. 20 IDEG 16/87. 1987. 21 This group was given the responsibility to deal with message handling access services (MHS) 22 and SMS and also to look for a common architecture for both groups of services. Great efforts and priority were put in the beginning to the MHS access services. But over time they eroded. They were downgraded from teleservices to bearer services and completely deleted in spring 1988, since normal bearer services were seen as providing sufficient func- tions to support this application. In the background was also a development in the market, that MHS according to CCITT X.400 were not a tremendous success. But the group produced an initial draft specification GSM 03.40 ‘‘ Technical realisation of the short message service’’ in November 1987. 23 It contained a first description of † Service elements † Network architecture † Service centre functions and service centre network † Functions in other network elements † Routing principles for the message transfer between the mobile station and the service centre † Protocols and protocol architecture The SMS was defined between mobile stations roaming in a GSM network or roaming internationally and a service centre, which had store and forward functions. Both Point to point services and the cell broadcast service were treated within this scope. I tried to interest the ISDN community to work with us on a compatible SMS service in the ISDN. This would have provided a standardised access to and from ISDN users. But the initiatives did not fall on fertile ground. Therefore the SMS did not provide a standard for the access from and to fixed subscribers. A close co-operation with the Layer 3 Expert Group responsible for the layer 3 protocols on the radio interface between the mobile and the base station was necessary, since the SMS related messages could be transmitted on normal signalling channels of the GSM system with lower priority than the signalling messages. This would ensure, that short messages could be transmitted to mobile stations in idle mode or involved in a call. The message length was given a ceiling of 180 octets. Later the final value was fixed at 160. The detailed technical work lead also to a proposal to refine the service descriptions 24 in February 1988. This document covered also the international operation of the point to point services. The initial technical specification and the revised services description contained the initial results achieved in the first year. They provided a firm basis and framework for the later detailed work, 25 which is the basis of the tremendous success in the market. 16.1.6.5 Achievements of the Data Group in its First Year from May 1987 to March 1988 IDEG/WP4 had despite the very late establishment after GSM#13 in February 87 met the first important target: to complete the work needed for the planned tendering of ten operators on GSM and UMTS: The Creation of Global Mobile Communication414 21 Minutes of second IDEG meeting on 6–8 July 1987 in Heckfield, UK, IDEG Doc. 58/87. 22 See Chapter 10, Section 1, Fig. 10.1.2. 23 WP4 Doc. 152/87. 24 WP4 Doc. 85/88 rev. 1. 25 See Chapter 16, Section 2. 29 February 1988, contributions to WP1, 2 and 3 as well as the specifications under WP4 prime responsibility. These documents cover the architecture and all functions needed for the asynchronous bearer services. A broad stream of work in other areas was started and initial results were reached. This included SMS. 26 WP4 had become a committed community of data communication experts who were new to the GSM group. WP4 had grown from 18 participants in the first meeting to more than 50 participants in this period. A very efficient and effective working and co-operation spirit has been developed by the group. There were many valuable contributions to the work in this early period. Key contributors were, e.g.: Chritian Be ´ nard-Dende ´ (France Telecom), Alan Clapton (BT), Alan Cox (Voda- fone), Graham Crisp (GPT), Alfons Eizenho ¨ fer (Philips), Ian Harris (Vodafone), Michael Krumpe (Siemens), Thomas Schro ¨ der (GMD), Paul Simmons (Nortel), Finn Trosby (Tele- nor) and Hans Wozny (Alcatel SEL). 16.1.6.6 Continuation of the Work Since I only took on the chairmanship of IDEG/WP4 on a temporary basis and had become responsible for the implementation of the GSM network for Deutsche Bundespost Telekom in Germany (D1), I had to find a replacement chairman. During the creation of IDEG and its conversion to WP4, Graham Crisp had been particularly active in the development of the GSM architecture to support the wide variety of data and telematic services and interworking scenarios that had been identified in the requirements. As a result, I proposed Graham Crisp as my successor. However, the idea of an industry representative chairing a CEPT body was not welcomed with open arms by the GSM membership 27 . I, therefore, had a significant task in convincing the members that an industry representative could be entrusted with the chair- manship of a CEPT working party. As a result, Graham was elected Chairman of WP4 by GSM#17bis in March 1988. He was the first colleague employed by a manufacturer to become a working party chairman in CEPT. The first WP4 meeting to be chaired by Graham was held in Florence in Italy on 5–8 April 1988. Those early years of GSM data standardisation saw some significant changes in the standardisation process, i.e. from CEPT as an organisation open only to PTTs, via industry participation, to ETSI. In 1989 the GSM work was transferred to ETSI and WP4 became GSM4. The GSM phase 1 standards for service opening in 1991 were ‘‘ frozen’’ in 1990. The Chapter 16: Short Message and Data Services 415 26 An interesting snapshot of the state of the GSM standardisation in 1988 is contained in the proceedings of the ‘‘ Third Nordic Seminar on Digital Land Mobile Radio Communication’’ , Copenhagen, September 12–15 1988. During that seminar, a GSM day was held. The GSM day and the rest of the seminar included a number of papers and presentations on the data and telematic aspects of GSM. These included: Implementation of telematic and data services in a GSM PLMN, F. Hillebrand; Architectural aspects of data and telematic services in a GSM PLMN, G. Crisp, A. Eizenho ¨ fer; The Radio Link Protocol (RLP) – a recommendation for the transmission of data in the CEPT GSM Public land mobile network, T. Schroeder, I. Harris, H. Madadi; Rate adaptation and interworking functions for the support of data communication services by a GSM PLMN, A. Clapton, C. Gentile, S. Thomas, G. Ponte, P. Simmons; Support of data transmission services in the European digital cellular 900 MHz mobile communication system, J.C. Benard-Dende; Message communication within the GSM system, B. Kvarnstrom, J. Reidar Rornes, F. Trosby. 27 Based on a proposal of GSM CEPT had allowed the participation of colleagues from industry in technical working groups. But they were seen as part of a delegation of an administration (see guidelines in GSM Doc 3/87 not available on the CD ROM). This showed clearly the need to open a path for full participation, which was achieved in ETSI. last GSM4 meeting chaired by Graham Crisp was GSM4#22 held in Vienna, Austria on 13– 17 May 1991. All quoted GSM Plenary documents can be found on the attached CD ROM. The quoted GSM WP4 documents are not copied on the CD ROM. They can be retrieved from the ETSI archive. GSM and UMTS: The Creation of Global Mobile Communication416 [...]... the MS and the network to offer a hook for later implementations and standardisation activities 428 GSM and UMTS: The Creation of Global Mobile Communication 16.3.4 Main Standardisation Work The first progress was noted on the service description in July 1995 and the stage 1 specification was presented for information But in February 1996 it was obvious that the completion date could not be met and the... controlling modems In 1995, Nokia, Ericsson and Hewlett Packard developed their own specification for AT commands for controlling GSM equipment In discussions with these companies inside GSM4 , they were persuaded that it would be better to have a GSM standard for this, to ensure that it would be compatible with all GSM features After a couple of intensive ad-hoc meetings and largely due to the very hard work... standard for control of modems from a terminal called V.25bis Since this was the only standard available when GSM data was first developed, GSM4 extended this standard to be applicable to control of a mobile modem, with all of the extended facilities However, due to the popularity of the Hayes AT command set, V.25bis was never widely implemented and everyone in the industry became used to AT commands... ‘‘Terminal Services and Capabilities’’, a working group under TSG terminals The combined SMG4/T2 group continued to report into TSG terminals and SMG until the close of SMG in July 2000 GSM and UMTS: The Creation of Global Mobile Communication Edited by Friedhelm Hillebrand Copyright q 2001 John Wiley & Sons Ltd ISBNs: 0-470-84322-5 (Hardback); 0-470-845546 (Electronic) Chapter 16: Short Message and Data Services... Eastern Europe, and even omitted some Northern European characters Coupling that with the expansion of GSM into the middle east and far east, it was clear that some major enhancement was needed One option would be to add several code pages to the GSM system, but this would mean that GSM4 would have to define all the characters Code page switching would result in large tables in the mobile memory, and of course... addition to GSM allowing faster perceived data transmission speeds 16.2.13 High Speed Circuit Switched Data During the early years of GSM development, modems at speeds of 300–1200 bits per second were the norm, and 2400 (2.4 K) modems were only just becoming available So GSM s speed of 9600 (9.6 K) seemed high enough and even a little future proof at that time Of course with the growth in demand for data... speed by a factor between 2 and 8 With 2 £ 14.4 K Chapter 16: Short Message and Data Services 423 channels this began to look like fixed modem speeds of 28.8 K, and devoting two channels to one user was not a big overhead (certainly compared with devoting eight channels to one user) HSCSD has now been implemented by several operators and is in a few mobile handsets 16.2.14 AT Commands When modems first started...Chapter 16: Short Message and Data Services Section 2: The Development from Mid-1988 to 2000 Kevin Holley 1 16.2.1 Short Message and Data Services in 1988 In 1988, Graham Crisp of GPT took over the role of GSM WP4 chairman from Friedhelm Hillebrand and continued the good work progressing towards the completion of phase 1 I started to attend GSM WP4 at the same time It was a small but... bits more than once, and also using predictive Viterbi techniques just as for the speech encoding For the ‘‘non-transparent’’ services it was necessary to detect errors in the transmission path and retransmit packets which were received in error 1 The views expressed in this section are those of the author and do not necessarily reflect the views of his affiliation entity 418 GSM and UMTS: The Creation... that operators and manufacturers could be confident of adding value to the terminals in a flexible but secure way This has resulted in the Release 98, Release 99 and Release 4 issues of the MExE specification 16.2.17 SMS Icons and Tones During 1998, the subject of downloaded images and sounds caught the interest of the industry, and it was recognised that it would be useful to have a standard way to convey . are those of the author and do not necessarily reflect the views of his affiliation entity. 2 GSM Doc 1/82. 3 GSM Doc 2/82. GSM and UMTS: The Creation of Global. papers and presentations on the data and telematic aspects of GSM. These included: Implementation of telematic and data services in a GSM PLMN, F. Hillebrand;