GSM and UMTS (P16)

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.