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Personal Communications.

ABSTRACT

 

This tutorial presents an overview of the Global System for Mobile Communications Short Message Service from the viewpoint of implementing new telematic services. SMS offers the users of GSM networks the 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 and its ability to offer a successful replacement for the Transmission Control and Internet Protocols as far as low-bandwidth-demanding applications are concerned. Initially, the tutorial gives a brief overview of the building blocks of GSM networks -- the mobile station, base station, and network subsystem -- and then emphasizes the SMS network 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 research in 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.

 

Since the first Global System for Mobile Communications (GSM) network started operation in 1991, more than 100 countries have adopted the standard. Over 20 million subscribers of GSM networks are now offered worldwide coverage, outstanding voice quality over a whole range of operating conditions, and a variety of value-added services. These services include voice mail, call handling facilities, call line identification, and Short Message Service (SMS).

With SMS, users are able to exchange alphanumeric messages (up to 160 characters) with other users of digital cellular networks, almost anywhere in the world, within seconds of submission. Even if the service was originally conceived as a paging mechanism for notifying the users of voicemail messages, SMS is now increasingly used as a messaging service. The messages are typically created on mobile phone keypads, which is somewhat awkward. Fortunately, there are other ways to access the message centers, as discussed in this article.

Numerous applications are already available and make short message reception and submission possible using a computer. Gateway architectures are also being widely implemented and connect company's e-mail or voicemail systems to the SMS.

The practical implementation of SMS and the different protocols for message submission are addressed in this article. The future of SMS and a brief review of the fields currently being studied will conclude this article.

The Short Message Service

Developed as part of the GSM Phase 2 specification, the Short Message Service, or SMS as it is more commonly known, is based on the capability of a digital cellular terminal to send and/or receive alphanumeric messages. The short messages can be up to 140 bytes in length, and are delivered within a few seconds 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 SMS (through GSM) supports international roaming with very low latency makes it particularly suitable for applications such as paging, e-mail, and voice mail notification, and messaging services for multiple users. However, the facilities offered to users and the charges for these facilities still mainly depend 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 transmitted to all the active handsets or mobile stations (MSs) present in a cell that have the capability of receiving short messages and have subscribed to this particular information service. This service is only one-way, and no confirmation of receipt will be sent. It can send up to 93 7-bit character or 82 8-bit characters, typically used to transmit messages about traffic conditions, weather forecast, stock market, and so on.

In point-to-point service, messages 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 forwards the messages when they can be delivered. Each GSM network must support one or more SMSCs to sort and route the messages. Each SMSC checks, organizes, and sends the message to the operator. It also receives and passes on any confirmation messages to any GSM mobile on any network. However, in practice, there are no agreements to allow SMS to travel between networks.

There are several ways in which a short message can be submitted, depending on the interfaces supported by the GSM network SMSC. Users can call a central paging bureau (i.e., an operator), or directly create the message on the keypad of their handset. Typing the messages is made easier when using a personal digital assistant (PDA) or a laptop connected to the handset. A few SMSC equipment manufacturers and companies have also developed their own protocols for short message submission. Consequently, more and more GSM networks now offer access to their SMSC using these protocols over a variety of hardware interfaces: modem dialup, X25, and even the Internet.

GSM Network Architecture

The layout of a generic GSM network with its several functional entities is shown in Fig. 1 [3]. The architecture can be divided in three main components:

The Mobile Station

The MS and base station subsystem communicate across the Um interface, also known as the air interface or radio link. The base station subsystem communicates with the network subsystem across the A interface. The MS consists of the physical terminal and contains the radio transceiver, the display and digital signal processors, and the Subscriber Identity Module (SIM). The SIM provides the user with the ability to access their subscribed services regardless of the location and the terminal used. The insertion of the SIM in any GSM cellular phone allows the user to access a network, make and receive phone calls, and use all the subscribed services.

The International Mobile Equipment Identity (IMEI) uniquely identifies the mobile terminal according to the International Mobile Subscriber Identity (IMSI) contained in the SIM. Because the IMEI and IMSI are independent, personal mobility is possible. The SIM can be protected against unauthorized use by a personal identity number (PIN).

The Base Station Subsystem

The base station subsystem is composed of two parts, the base transceiver station (BTS) and base station controller (BSC). They communicate across the specified Abis interface, 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 protocols 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 BTSs to cover the same area as GSM networks, but provide twice the capacity.

The BSC manages the radio resources for one or more BTSs via the standardized Abis interface. It handles radio channel setup, frequency hopping, and handovers. The BSC is the connection between the MS and the mobile switching center (MSC). The BSC also takes care of converting the 13 kb/s voice channel used over the radio link (Um interface) to the standardized 64 kb/s channel used by the public switched telephone network (PSTN).

The Network Subsystem

The MSC is the main component of the network subsystem. Its provides the same functionality as a switching node in a PSTN or integrated services digital network (ISDN), but also takes care of all the functionality needed to handle a mobile subscriber such as registration, authentication, location updating, handovers, and routing to a roaming subscriber. The MSC also acts as a gateway to the PSTN or ISDN, and provides the interface to the SMSC.

The international roaming and call routing capabilities of GSM networks are provided by the home location register (HLR) and visitor location register (VLR) together with the MSC. The HLR database contains all the administrative information about each registered user of a GSM network along with the current location of the MS. The current location of an MS is in the form of a Mobile Station Roaming Number (MSRN), typically the SS7 number of the visited MSC, and used to route a call to the MSC where the mobile is actually located.

The VLR is usually located within the MSC to speed up access to the information required during a call and simplify the signaling. The content of the VLR is a selection of the information from the HLR, basically all necessary information for call control and provision of the subscribed services, for each single mobile currently located in the geographical area controlled by the VLR.

The network subsystem uses two other databases for authentication and security purposes. The Equipment Identity Register (EIR) contains a list of each MS IMEI allowed on the network. The authentication center (AuC) database contains each single PIN stored in the MS SIM.

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, data link, and message. The physical layer and channel structure are described in detail by M. Mouly and M. Pautet [4]. Layer 2 implements the data link layer using a modified flavor of the Link Access Protocol (LAPD) to operate within the constraints set by the radio path. On the MS side, the message layer consists of three sublayers: connection management (CM), mobility management (MM), and resource management (RR). The CM sublayer manages call-related supplementary services, SMS, and call-independent supplementary services support. The MM sublayer provides functions to establish, maintain, and release a connection between the MS and the MSC, over which an instance of the CM sublayer can exchange information with its peer. It also performs location updating, IMSI management, and Temporary Mobile Subscriber Identity (TMSI) identification, authentication, and reallocation. The RR sublayer establishes the physical connection 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 MSC side, 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 internetworking functions. The Message Transfer Part (MTP) and Signaling Connection Control Part (SCCP) protocols are used to implement the data link layer and layer 3 transport functions for carrying the call control and mobility management signaling messages across the A interface. SCCP packets are also used to carry the messages for SMS.

Signaling between the different entity uses the International Telecommunication Union (ITU) SS7, widely used in ISDN and current public networks. SS7 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 protocol stack.

The ISUP provides the signaling functions needed to support switched voice and data applications in the ISDN environment. The TUP provides the basic functionality for call control functions for ordinary national and international telephone calls. The TCAP is 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 capabilities required to support the mobile capabilities.

The MTP and SCCP (Fig. 4). The SCCP sublayer supports connectionless and connection-oriented services to transfer data and Global Title Translation (GTT) above MTP level 3 for voice, data, ISDN, and GSM services. The data transfer is reliable, independent of the underlying hardware, and transparent to users. The protocol employs logical signaling connections within the SS7 network to ensure reliability and integrity of the ongoing data transfer. The MTP is divided into three levels:

Practical Implementation

SMS uses the SS7 signaling channel to transmit the data packet [5], thus allowing a text message to be received when the user is 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 there is a speech or data call in progress. A confirmation will always be returned to the SMSC 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 successfully. The software within the MS must be able to decode and store the messages.

SMS Mobile Terminated (SMS-MT) is the ability to 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 deliver it shortly after the phone comes back into range or there is space in memory.

The SMS Basic Network Architecture The main components of the SMS network architecture are shown in Fig. 5.

When routing a mobile originated short message, the SMSC forwards the short message to the SMS-GMSC. The SMS-GMSC interrogates the HLR for 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 terminated short message, the MS addresses the required SMSC according to its global title. If roaming abroad the visited public limited mobile network (PLMN) will route the short message to the appropriate SMS-IWMSC.

The SMSC identifies each short message uniquely by adding a time stamp in the SMS-DELIVER TP-SCTS field. The short message arrival at the SMSC is accurate to the second. It is the SMSC's responsibility to assure that if two or more short message arrive within the same second their time-stamps will be different.

The MS has to be able to receive/submit a short message TPDU, and then return a delivery report upon successful reception. It is also responsible for notifying the network when it has memory capacity available to receive one or more messages, if it had previously rejected a short message because its memory capacity was exceeded.

Protocol Architecture

The protocol layer for SMS is shown in Fig. 6. The short message transfer layer (SM-TL) services the short message application layer (SM-AL) and enables it to exchange short messages with a peer as well as receive confirmation of reception reports from earlier requests.

The SM-TL exchanges PDUs with its peer entity. The short message relay layer (SM-RL) conveys the PDUs via the short message link layer (SM-LL). Refer to GSM 03.40 [2] for further 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 main fields of the TPDU are described in this document however for a complete description of the TPDU please refer to GSM 03.40 [2].

TP-Data-Coding-Scheme

The data coding scheme field (TP-DCS) is used to identify 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-Validity-Period

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-Message-To-Send

The SMSC uses the TP-MMS field to inform the MS that one or more short messages are waiting to be delivered.

TP-User-Data-Header-Indicator

The 1-bit TP-UDHI field indicates whether the TP-UD includes an additional header as well as the short message.

TP-Protocol Identifier

The 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-User-Data (TP-UD)

The TP-UD field is used 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-UDHI field. The amount of space taken by the header reduces the amount of data the PDU can carry. Figure 8 shows a representation of the layout of the TP-UD for 7- and 8-bit data schemes.

The header has at least three fields. The first field, the information element identifier, is used to identify concatenated short messages. Information data length (IDL) is used to indicate the length of the information element data (IED) that follows. Each of these fields is 1 octet 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 IEI 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:

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.

Short Message Routing Considerations

In Fig. 9, user A in network is sending a short message to 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 E.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 SCCP packet 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 has to access the HLR database of his home network. A location request SCCP packet, based on user B's mobile number, is sent by the SMSC (3).

This international SCCP network then routes the location request SCCP packet to the appropriate HLR. When the HLR receives the request, it will return the location information in another SCCP packet to the SMSC (4).

The SMSC then sends the message to the VMSC of user B, based on the information received from the HLR (5). Finally, this VMSC interrogates the VLR (6, 7), and delivers the message to user B (8). Upon successful delivery a confirmation SCCP packet is sent back to the SMSC (9).

Throughout these routing procedures, the SCCP packets can get lost if one of the cellular exchanges along the route does not know where to forward the SCCP packet. SCCP routing is based on the global title used for switches and the SMSC. The routing information has to be in place in the international SCCP transit switches for the messages to successfully reach their destination. Some international switches only check the country code prefix (e.g., 44 for the United Kingdom) and forward the packet to the next exchange, while others also check for the network prefix (e.g., 447976 for Orange). If the exchange routing table does not include all the prefixes allocated to the subscribers, some messages will be rejected. Incompatible implementation of the SMSC can 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 consequences:

Even if Fig. 9 shows the most complicated routing scenario there is still much that can go wrong with short message routing, and a lot of research is currently underway to overcome these.

Protocols for Short Message Submission

The European Telecommunications Standards Institute (ETSI) specified a protocol for short message submission as part of the overall GSM standard [10]. This specification defines three interface protocols for the transfer of SMS short messages between an MS and terminal equipment (TE) via an asynchronous interface. The protocols clearly overlap in functions, and it is not clear why three have been defined.

Block Mode

The block mode is a binary protocol which encapsulates the SMS PDU used for short message transfer between an MS and the SMSC defined in GSM 03.40 [2]. This protocol includes error detection and is suitable for use where the link between the application and the phone is subject to errors. It will be of particular use where control of remote devices is required. The application has to construct a binary string including a header and the short message PDU (SMS-TPDU).

Once the application has requested the phone to enter block mode a group of functions is available:

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 message 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 application 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 means that text mode offers a lot less functionality than block or PDU mode. The text mode does not support or automatically pass incoming messages to the application (only notify 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 implementation of a GSM SMSC [11]. The specification mainly describes the delivery of short messages to MSs, but also specifies the protocols for short message submission. The protocol has been designed to operate over a variety of interfaces such as X25, DECnet, and SS7. The SMS2000 SMSC is usually accessed via the general X25 access gateway -either 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 SMS2000 SMSC can also send the commands listed in Table 5 to an SME.

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 and is being processed. Upon delivery 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. However a login facility is still provided in order to access the SMSC from a different location (i.e., PAD).

Text-Based Protocols

Usually these protocols are proprietary and developed as an interface to the SMSC of a digital cellular network operator. The advantage of a text-based protocol is that the user does not need any special client software to submit a short message; 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, key disadvantages with text-based protocols: they offer limited support for extended character sets, and only work one way, to name a few. The user is only able to send messages and receive confirmation of submission. The SMSC is unable to notify the end user of successful delivery.

Telocator Alphanumeric Protocol

Developed by Telecom Securicor Cellular Radio Limited, the Telocator Alphanumeric Protocol [12] provides greater flexibility and 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 acceptance.
  2. Submit a short message and receive status of the first delivery 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 number of 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 can be classified as dumb or smart based on whether they provide notification of delivery and/or advanced functionality (message deletion, replacement, etc.). We chose to discuss the protocols used in the United Kingdom as an example of the different possibilities offered to subscribers and software developers.

Current Issues

SMS is increasingly popular; the barrier of 100 million messages in a month was recently reached in the United Kingdom. As growing numbers of users start to realize that GSM has more to offer than crystal clear voice calls, the services offered are likely to evolve even more rapidly, and it is quite likely that data calls and short messages will soon represent an important part of the overall GSM traffic.

New protocols are now being designed that will allow even more advanced functionality to be implemented in client software. Some of the features under development include:

Last but not least, some research projects are studying the possibility 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 Wireless 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.

[4] M. Mouly and M. Pautet, "The GSM System for Mobile Communications," 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 language-specific information," v. 5.2, May. 1996.

[8] K. Holley, http:/ftp.labs.bt.com/people/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; Equipment (DTE - DCE) interface for Short Message Service (SMS) and Cell Broadcast Service (CBS)," draft, May 1996.

[11] SEMA Group Telecommunications, "SMS2000 v. 4.0, Open Interface Specification," INS/FS/28.

[12] Telocator Alphanumeric Protocol (PCIA) v. 1.2 Functional Spec for TAP-AIM ver 2.6 (Aldiscon)

Additional Reading
[1] M. Rahnema, "Overview of the GSM System and Protocol Architecture," IEEE Commun. Mag., vol. 3, no. 4, Apr. 1993, pp. 92–100.

Biographies
 Guillaume Peersman graduated from the Institut Superieur d'Electronique 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 Science Department. His research interests focus on the development and performance 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 completed his B.Sc. (with First Class Honours) and Ph.D. degrees in electronic and electrical engineering at City University, London (1983) and University College London (1987), respectively. In June 1987, he joined the Department of Electronic and Electrical Engineering at the University of Surrey as a lecturer in telecommunications 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 September 1995 he took up the post of senior lecturer in multimedia communications 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 Communications and Distributed Systems (CDSRG), which he co-founded in October 1997 with Prof. Colin Smythe. CDSRG (including CREDO) is currently involved in projects of value in excess of US$8.5million 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 electromagnetic 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.dcs.shef.ac.uk/~srba

Paul Griffiths graduated from Sheffield City Polytechnic 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 Dialogue 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 Communications Ltd., a specialist SMS software manufacturer which has recorded an average growth rate of 70 percent for the last three years.

Hugh Spear 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 Fretwell-Downing Data Systems in Sheffield. In 1995 he co-founded Dialogue Communications Limited, a mobile messaging business which develops 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.