![]()
Part I
GSM/EDGE Standardization
![]()
1
GSM Standardization History
Guillaume Sébire
1.1 Introduction
GSM, the Global System for Mobile communications, owes its worldwide success to the continued progressive and backward-compatible evolution of its open industry standard and to visionary yet simple ideas such as global roaming – enabling, thanks to a harmonized spectrum, the use of a device with the same number outside its home network, multivendor environment – enabling different vendors to implement with sufficient freedom compatible products based on the same standard, SMS1 –enabling people to text each other, etc.
First aimed at providing mobile voice communications, GSM developed early on into a rich system offering supplementary services and other data communications, well ahead of the analogue systems then sporadically deployed in several regions of the world and which were incompatible. GSM has been and is by far the most widely used and most successful communications system of all time, enabling, at the time of writing, over four billion subscribers [1] to communicate in just about every single country of the world, just about everywhere (including airplanes) and with virtually everyone. The success of GSM is, simply put, staggering. Of all the active digital mobile subscriptions worldwide, more than 80% are GSM [2].
This chapter relates the history of GSM standardization from the early 1980s to the late 2000s and lists the main features and functionalities that have gradually been introduced in GSM specifications.
1.2 History
Initially launched as a European initiative in 1982 by CEPT,2 the Groupe Spécial Mobile (Special Mobile Group) was tasked to develop a standard for mobile telephony across Europe in the 900 MHz band. Five years later in 1987, the signature by thirteen countries3 of a Memorandum of Understanding to develop a pan-European common cellular telephony system in the 900 MHz band marked the official birth of GSM, set for service launch in 1991. ETSI, the European Telecommunications Standards Institute, created in 1988 by CEPT to handle all telecommunication standardization activities, became in 1989 the sole entity responsible for the GSM standard.
By 1990, the first set of specifications, GSM Phase 1, was frozen and published. By 1995, GSM Phase 2 was available, followed a couple of years later by GSM Phase 2+ which also introduced the concept of “yearly” release. The publication of the specifications into backward-compatible phases/releases has been a cornerstone of the evolution of the GSM standard and a model for future standards. It has ensured the availability in the specifications of a same phase/release of a consistent set of services, functionalities and features on both network and terminal sides and the inherent compatibility between equipment of different phases/releases. Since the first “release” in Phase 2+, known as Release 96 (or R96), nine others have been published (or are being developed): R97, R98, R99, Release 2000 later renamed Rel-4, Rel-5, Rel-6, Rel-7, Rel-8 and Rel-9. Release 9 is still in the making at the time of writing while stage 1 requirements for Release 10 are being laid out. Release 4 marked the transfer of GSM specifications within the Third Generation Partnership Project or 3GPP in the year 2000.
3GPP was established in December 1998 as a collaboration project between ETSI (Europe), ARIB4 (Japan), TTC5 (Japan), ATIS6 (North America), TTA7 (South Korea) and CCSA8 (China) to develop a global third generation mobile phone system specification, that is UMTS commonly referred to as “3G”. Though originating from GSM concepts and seen as part of the GSM family, UMTS is not as such an evolution of GSM. It was developed as a new system using GSM as a model. UMTS requires a new radio interface and the deployment of brand new radio networks, and thus is not backward-compatible with GSM – a UMTS phone cannot work in a GSM system nor can a GSM phone work in a UMTS system. The UMTS core network and architecture, however, though requiring new IP-based interfaces, were largely based on the GSM core network and architecture.
In the following sub-sections, non-exhaustive lists of services, features and functionalities characterizing each GSM phase/release are provided.
1.3 Phase 1
GSM Phase 1 contains the following items:
- Basic telephony using full-rate speech codec (FR) at 13 kbit/s [3] with a speech quality comparable to that of POTS9 wireline.
- Emergency calls using a single number (“112”) even if the SIM10 is not present or the PIN11 is not entered. The growing deployment of GSM outside Europe led to the introduction in Phase 2+ (R96) of additional numbers (in the SIM) to be regarded as emergency numbers.
- Support for multiple data services (up to 9.6 kbit/s) allowing, for example interconnection with ISDN,12 modem connection through PSTN.13
- Security through authentication and confidentiality in order to protect operators and subscribers against malicious actions by third parties. Authentication to verify and confirm a subscriber's identity. Confidentiality to preserve the privacy of a given piece of information [4]. See Chapter 4 for more details on the evolution of GSM security.
- Short message service (SMS) either point-to-point or using cell broadcast [5,6].
- Supplementary services pertaining to call barring and call forwarding such as barring of all incoming calls, barring of incoming calls when roaming outside the home network, call forwarding on no reply, call forwarding on mobile subscriber busy, etc.
- Support for facsimile (fax) communications (Group 3: the most widely used) [7,8].
1.4 Phase 2
GSM Phase 2 contains the following items:
- Half-rate speech codec (HR) at 5.6 kbit/s allowing a higher maximum number of voice users compared to FR speech, at the expense of speech quality [9].
- Enhanced Full-Rate speech codec (EFR) at 12.2 kbit/s. EFR provides a considerable speech quality improvement over FR [10].
- Half-rate data services allowing a higher maximum number of data users.
- SMS enhancements such as SMS concatenation, replacement.
- Supplementary services such as enhancements to call barring and forwarding, calling line identification presentation and restriction, multiparty calls, etc.
- Fax enhancements.
- Support of GSM in the 1800 MHz band that is DCS14 1800 as well as interworking between GSM 900 and DCS 1800, and multi-band operation by a single operator.
1.5 Phase 2+
1.5.1 Phase 2+, R96
Release 96 contains the following items:
- Data services at 14.4 kbit/s.
- High-Speed Circuit-Switched Data (HSCSD) allowing the use of multiple 9.6 kbit/s or 14.4 kbit/s channels in one direction for considerably faster data transfers. HSCSD offers data rates up to 38.4 kbit/s (four times 9.6 kbit/s) or 57.6 kbit/s (four times 14.4 kbit/s) for Type 1 mobile stations that is mobile stations not required to transmit and receive at the same time [11].
- ASCI (Advanced Speech Call Items) Phase 1 for GSM railway systems (GSM-R) containing for example Voice Broadcast Service (VBS) calls supporting one talker and several listeners and Voice Group Call Service (VGCS) allowing calls supporting several talkers and listeners [12,13].
- CAMEL (Customized Applications for Mobile networks Enhanced Logic) Phase 1. CAMEL enables the definition of services on top of existing GSM services such as allowing using the same phone number when roaming outside one's home network. CAMEL Phase 1 offers call control related functionalities.
- SIM Application Toolkit (SIM ATK) which provides standardized means for applications (e.g. banking, weather) residing on the SIM to interact proactively with the mobile station.
- Support of additional call set-up MMI procedures allowing emergency calls to be placed with emergency numbers stored in the SIM thus catering for the expansion of GSM in countries using other numbers than “112” for emergencies.
1.5.2 Phase 2+, R97
Release 97 contains the following items:
- GPRS (General Packet Radio Service) allowing packet-switched data connections down to the GSM radio interface thus providing a more efficient use of network and radio resources compared to circuit-switched data. Resources are assigned when data are transmitted, and released otherwise thus creating packet transmissions. Four coding schemes, CS-1 to CS-4 using GMSK15 modulation, and link adaptation allow adaption of the channel coding to the channel conditions thus enabling an efficient use of radio resources. Data rates up to 20 kbit/s per time slot per direction are possible [13].
- GPRS encryption using the GPRS-A5 algorithm (GEA16). See Chapter 4 for more details on the evolution of GSM security.
- Security mechanisms for SIM ATK.
- ASCI Phase 2.
- CAMEL Phase 2.
1.5.3 Phase 2+, R98
Release 98 contains the following items:
- AMR (Adaptive Multi-Rate speech codec): Definition of mechanisms to support AMR speech (narrow-band or AMR-NB) in GSM enabling the adaptation of the speech ...
