GPRS technical review

GPRS Technical Review By Natalia V Rivera and Dr Belka Kraimeche (Pending for publication) Today the digital systems such as the Global System for Mobile Communication (GSM), Code Division Multiple Access (CDMA based on IS-95), and United States Time Division Multiple Access (US-TDMA based on IS-136) conformed to what is known as second-generation systems All these three systems have made voice communications to go one step ahead in wireless and multimedia networking resulting in a great demand for services such as text messaging and access of data networks through the Internet Hence, Internet have been utilized as the fundamental access for these types of services as well as for more advanced services inciting leading markets and customers with increasingly finding value for services such as streaming audio, http, video, remote banking, and e-commerce Advanced Second generation systems and Third generation systems such General Packet Radio Service (GPRS) and Universal Mobile Telecommunication Services (UMTS) respectively, are based on the concept presented above, enabling enhanced and high quality multimedia communications between end-to-end users at the cost of higher data rates and innovative communications capabilities resulting in the wireless domain a persistent interest in IP technology Such that it is growing intensively since most of the communication capabilities to support ground-breaking communications can be obtained at a low cost with appropriate network architecture and highly efficient and secure protocols The arrival of imminent handset devices packed-based systems such as GPRS or UMTS based will make possible to access the Internet not only by using a fixed connection, but also using a mobile terminal Nevertheless, because of all different technologies and frequency allocation throughout the United States and the world, global roaming will continue to require specific arrangements between operators, such as multi-mode and multi-band handset and roaming gateways between the different core networks Furthermore, in spite of cost for new technology, it is believed that the demand for such technology will be higher and hence a further growth for 3G communication systems will take place especially with the perception of all IP-based core networks, which are currently under standardization As mentioned before, there are currently three Secondgeneration technologies, however two are the most promising to succeed and evolve in Third-generation systems: First, is GSM, which with an improved core network (circuit and packed based integrated) and advanced new features that are not included in GSM phase I or II+ will offer high data rate, flexibility and efficient utilization of scarce bandwidth across the air interface Second, is CDMA, which for Third generation adopts two new concepts concerning multi-carrier transmission for CDMA2000 and wideband CDMA for UMTS, both resulting in high data rates and spectrum efficiency, but differs mainly in physical characteristics Furthermore, an emerging alternative, which lately has been growing, is GPRS with an all IP-based core network As it is know, GPRS is the data network for GSM technology however, its architecture and protocols are slightly different Figure illustrates an example of standardized concept as regards to connections between typical core networks and air interface that are currently considered for 2.5+G and 3G networks Figure Core network relation to the 3G air interface alternatives The growth of all these technologies is based of the evolution and high technology advances on crucial protocols, one of the main widely used is known as Transmission Control Protocol (TCP/IP) The architecture and application of TCP/IP protocol will not be covered in this paper, however a small explanation is given in order to facilitate understanding of packet networks TCP is a connection-oriented transport protocol of the datagram network layer (IP) TCP applies a Selective Repeat Protocol (SRP) with positive acknowledgements and timeouts to provide reliable end-to-end byte transport However, if reliable transmission is not required a different protocol can be applied Such protocol is connectionless transport and is known as User Datagram Protocol (UDP) Note that UDP is used for application requiring a fast transport with low delay, where occasional packet loss is less important An example of such application is stream video History and Evolution of GPRS GSM (Global System Mobile communications) standardized by ETSI (European Telecommunication Institute) is one of today’s largest second generation cellular system GSM functions under the 900 MHz cellular frequency band as well as under the 1800 MHz and 1900 MHz personal communication frequency bands Technology for GMS has evolved rapidly since the introduction of its data services, however in order to support such services GSM adapted a new solution called GPRS (General Packet Radio Service), which is intended to provide actual packet radio for GSM and TDMA users with corresponding enhanced architecture adjustments, new response times and implementation of innovative features The main set of GPRS specification was approved by SMG#25 (Special Mobile Group) in 1997, and was completed by 1999 The purpose of GPRS is to accommodate efficiently data sources that are bursty in nature as well as to obtain high data rate, flexibility and efficient utilization of bandwidth across the air interface that is why GPRS reuses the same infrastructure in order to provided end-to-end packet switched services Thus, to comply with these concepts new radio channels are defined, in where the allocation of these channels is flexible such that one to eight time slots can be allocated to a user or several active users at a giving time This implies that one or more users could share the same time slot resulting different allocation formats for uplink and downlink transmissions Hence, radio resources can be shared dynamically between speech and data services as a function of traffic load or operator preference, which can be accomplished through various radio channel code schemes that have been implemented successively in order to allow bit rates from 9kbps to more than 171.2 kbps per user Furthermore, since GPRS and GSM share the same frequency bands with telephone and circuit switched data traffic and both make use of many physical properties at the physical layer such its TDMA frame structure, modulation technique and structure of GSM time slots, the migration to data services is moving rapidly and optimistically To facilitate a better understating of the evolution of GPRS, a standard GSM architecture is provided as well as its data network implementation i.e GPRS system Figure GSM System Architecture As seen from Figure 2, GSM system architecture includes three standard interfaces; the air interface (Um), the Abis interface, and the A interface The GSM functionalities are divided into the Mobiles Stations (MS), the Base Station Subsystem (BSS), which is composed of two main systems (1) Base Transceiver Station (BTS), which handles the radio interface towards the MS and (2) Base Station Controller (BSC), which manages the radio resources and control handovers The GSM core network contains the (Mobile Switching Center (MSC), which permits access to public networks such as Public Switched Telephone Network (PSTN), Integrated Service Digital (ISDN), Circuit Switched Public Data Network (CSPN), and Packet Switched Public Data network (PSPDN) In addition, three databases, the Home Location Register (HLR), the Visitor Location Register (VLR), and the Authentication Center (AUC) support the MSC All these networks components will be modified at their different level of architecture so that a migration step toward 3G will be accomplished A standardized concept is presented in the Figure Figure GPRS System Architecture What is GPRS? General Packet Radio Services is a new and interesting service to value added in the field of the services that it concurs with the customers to send information using the mobile telephony GPRS is a packet-switched service that provides lots of advantages, but also requires hardware and software changes in the GSM networks GPRS is known for its defined characteristics that can be a continuation of new technological advances, which implies speed, immediacy, and new data features GPRS facilitates the instantaneous logon between various finished networks since it is always connected, thus that as the information reached its destination instantaneously at all times GPRS corresponds to Internet, e-commerce applications amongst others The basic idea of GPRS is to provide a packet-switched bearer in a GSM network in where resources are use more efficiently through bursty data applications and general flexibility In brief from Figure 3, it can be deduced that GPRS can be described as a service providing optimized access to the Internet, while reusing to a large degree existing GSM infrastructure The GPRS network is created to support theoretically a maximum speed of 171.2 kbps; hence the concept of packet-switched network is adopted throughout the infrastructure and implementation of a GPRS network It is foreseeable that its architecture will not contain any MSC, VLR or AUC applications, but instead will enclose two new network GSN (GPRS Support Node) elements: a Gateway GPRS Support Node (SGSN) and a Serving GPRS Support Node (GGSN) The gateway GPRS Support Node (GGSN) as the name implies it serves as the gateway between the GPRS network and other packet networks GGSN is also responsible for routing data to the mobile stations at their current points of attachments to the network In other words, GGSN acts as a logical interface to external packet data networks On the other hand, the Serving GPRS Support Node (SGSN) is responsible for the delivery of packets to the Mobile Systems (MSs) within its particular geographical service area Within the GPRS network, Protocol Data Units (PDUs) are encapsulated at the originating GSN and decapsulated at the destination GSN In between the GSNs, the Internet protocol (IP) is used as the backbone to transfer PDUs This process is known as GPRS tunneling (GTP) The GSNs that make up a GPRS PLMN are interconnected via an IP backbone, in where standards IP routers are employed to help the SGSN to perform the routing and data transfer functionality that is needed concerning the user related data, which is constantly stored within the network Home Location Register (HLR) The GPRS Public Land Mobile Network (PLMN) is made up of a number of network elements and communications links which connections are based on the Internet Protocol (IP) standard stack On the interface the resources are assigned mobile-tomobile stations only temporarily on a per-packet basis thus radio resources are only assigned for the duration of one or few IP packets Generally, it is believed that the idea if introducing GPRS will enable the following features: • Circuit and packet switched services in one mobile radio network • Efficient use of the scarce radio resources • Fast setup/access times • Connectivity to other external packet data network, based on IP and X.25 A visual example of an ideal GPRS network is giving in Figure BTS BTS BSC BSC IP GPRS PLMN X.25 GGSN SGSN Intra PLMN IP SGSN GGS GGSN SS7 HL Figure GPRS Network Additionally, the GPRS mobile stations are known to operate in four modes in order to provide access: Class A: Simultaneous use of GPRS/EDGE other GSM services Class B: Alternate use of GPRS/GPRS and other GSM services Class B136: Alternate use of EDGE and there is-136 services Class C: GPRS/EDGE only (data service only) Thus to use GPRS services, users will need the following: ! ! ! ! A mobile phone or terminal that supports GPRS since existing GSM mobile phones not support GPRS A subscription to a mobile phone network that support GPRS Use of GPRS must be always enabled for the user Some mobile networks operator may allow automatic access to GPRS, others will require a specific opt-in Knowledge of how to send /received GPRS information using their specific mobile phone, including software and hardware configuration resulting in a customer service requirement ! A destination to send/receive information through GPRS Whereas with SMS this was often another mobile phone, in the case of GPRS, it is likely to be an Internet address, since GPRS is designed to make the Internet fully available to mobile users from the first time This implies that it provides an immediate critical mass of uses to all its subscribers From the points mentioned above, it is embedded that GSM MS design must be enhanced in several ways so as to support GPRS First, new protocol layers must be added These include MAC, RLC, LLC, and SNDCP It must also be modified to operate on shared traffic channels with the adoption of new modulation schemes such Gausssian Minimum Shift Keying (GMSK) applicable to GPRS, and Eight level Phase Shift Keying (8-PSK) adopted to the Enhanced GPRS (EGPRS), both occupying a channel width of 200 kHz An additional feature is that GSM BSS have been modified such that GPRS software capability was added to BTS and BSC with minima BSC hardware changes in order to support packet data services, thus that the BSS must interface with the SGSN via frame relay and also several new protocols which will be discusses further in detailed Applications of GPRS GPRS can act as a mobile access network to the Internet Its purpose is to enable a variety of new and unique services to the mobile wireless subscriber such offered services contained several unique characteristics that enhance the values to the customer First among them is mobility, which is the ability to maintain constant voice and data communications while roaming Second, is immediacy, which allows subscribers to obtain connectivity when needed, regardless of location and without a lengthy login session This is why GPRS users sometimes referred to be as being “always connected” Immediacy is one of the advantages of GPRS and SMS when compared to Circuit Switched Data High immediacy is a very important feature for critical time applications Finally, third is localization, which allows subscribers to obtain information relevant to their current location As a consequence, the combination of all these three major characteristics integrates possible applications that can be offered to mobile user in two different categories: corporate and consumer In addition, due to its efficient support of bursty traffic, GPRS is expected for application areas such as: ! Communications, i.e email, fax, unified messaging (SMS), intranet and Internet access ! Values added Services (VAS), i.e Information services, games ! E-Commerce i.e retail, ticket purchasing, financial trading ! Location based application i.e Navigation, traffic condition, airline Rail schedules, location finder ! Vertical application i.e Freight delivery, flee management, sale force automation ! Advertising A graphical example of GPRS is given below Figure Web Applications FAX Email Multimedia Credit card Transactions Text messaging File Transfer Telemetry Figure GPRS common applications Conceptually, GPRS achieves theoretical maximum speeds of up to 171.2 kbps using all eight time-slots as described earlier This is about three times as fast as the data transmission speed possible over today’s network fixed communications networks and ten times as fast as current circuit switched data devices on GSM networks Likewise, GPRS provides a point-to point and point-to- multipont connections to facilitate wide range of applications As a result GPRS uses the scarce radio resources more efficiently and supports a number of applications with different requirements, which are accomplished by a set of several preferences Such preferences are commonly known as Quality of Service (Qos) classes This concept allows network operators to change data transmission schemes for different operations according to its applicable fee charges QoS classes of GPRS phase are provided by its standard specification, which can be found in [2] In phase 2, GPRS’ objective is to create the QoS applications comparable to third generations systems such Universal Mobile Telecommunications Service (UMTS) and adaptable to further generations Hence, today many GPRS operators are either planning to deploy or are investigating 3G while GPRS is shaping under its standards Effectively, GPRS can be seen as a migration step toward several 3G technologies as the innovations of GPRS terminals and infrastructures are driving factors A standard QoS classes are specified in Table Parameter Values Precedence High, Normal, Low Reliability Packet loss probability, e.g 10 −9 ,10 −4 ,10 −2 Delay for packets of Class 128 octets Mean(s) [...]... transmission in GPRS Note that the A interface is used for both signaling and voice transmission in GSM Interfaces Um, Gb, Gn, Gp, and Gi are used for both signaling and transmission in GPRS of gaining efficient resources sharing between packets and circuit switches GPRS Protocols On the network level, GPRS supports IP and X.25 protocols to be used by an end-to-end application The GPRS packet delivery... decapsulated for routing Figure 7 illustrates the GPRS signaling plane, which gives a more detailed concept of the functionalities and internetworking applications between GSM and GPRS network elements Figure 7 GPRS signaling plane GPRS signaling plane consists of protocols for control and support of the transmission plane functions Among these protocols, the GPRS- specific protocols include SNDCP, LLC,... carrying RLC data blocks Table 2 GPRS Coding Schemes Figure 10 presents a more general and sophisticated graphical representation of GPRS architecture with respect to the OSI model Figure 10 GPRS in relation to the OSI model It is also necessary to mention that there are three essential applications that are used interchangeably throughout the GPRS network in order to facilitate GPRS service These applications... controls GPRS services in a particular geographical coverage area This may also be considered similar to routers with additional functionality for GPRS Gateway GSN (GGSN) ! Serves as a gateway between the GPRS network and other packet networks (i.e IP/ X.25) ! ! ! ! It is responsible for routing data to the MS at their current points of attachment to the network Stores SGSN routing info for each GPRS user... same suite of protocols Figure 6 GPRS transmission plane Figure 6 illustrates the GPRS transmission plane, which consists of a layered protocol structure for user information transfer and the associated control procedures mentioned above As seen from Figure 6, the IP or X.25 packets are forwarded through the GPRS PLMN network using dedicated protocols Albeit, the GPRS network seems to have different... rate Within this class there are 19 classes ranging from best effort to 111 kbps in order to meet GPRS transmission standards GPRS Air-Interface Protocol The air interface known as the Um interface is considered as one of the most important aspects of GPRS because it mainly determines that performance of GPRS Here, the air interface protocol is concerned with applications related to the physical, Medium... other mentioned earlier in this paper GPRS conclusion In this article it has been examined the concept, evolution, challenges and future views that concerns GPRS development and its considerations for 3G systems It is captured that GPRS is an evolutionary path chosen by the Universal Wireless Communication Consortium (UWCC) among many others with the purpose to let GPRS evolve to the next step, which... [3] MOBILE Lifestreams Limited Data on GPRS www.mobileGPRS.com [4] GSM world Topic on GPRS www.gsmworld.com [5] Seybold, Andrew “Wireless Data Opportunities.” www.wirelessknowledge.com [6] Advances in Packet Switching, Routing in Optical Networks, QoS and Resources Allocation in the 3G Wireless Networks IEEE Communication Magazine February 2001 [7] GSM 01.61 GPRS Ciphering algorithm requirements [8]... path, General description [14] GSM 05.02 Multiplexing and multiple accesses on the radio path [15] GSM 08.18 General Packet Radio, (GPRS) ; Base Station System (BSS) – Serving GPRS Support node (SGSN); BSS GPRS Protocol (BSSGP) [16] TS.24.008 “3rd Generation Partnership Project; Technical Specification Group Core Network; Mobile Radio Interface layer 3 specification; Core Network Protocol – stage 3 ... Idle state, if the MS is not attached to the GPRS MM ! Standby state, if the MS is attached to the GPRS MM ! Ready state, if the location information for the MS has been identified of cell level The PDP contexts are stored in the MS, HLR, SGSN and GGSN, which contain mapping and routing information packet transmission between the MS and GGSN Note that for each GPRS communication made on a MS, a PDP context ... example of an ideal GPRS network is giving in Figure BTS BTS BSC BSC IP GPRS PLMN X.25 GGSN SGSN Intra PLMN IP SGSN GGS GGSN SS7 HL Figure GPRS Network Additionally, the GPRS mobile stations... Simultaneous use of GPRS/ EDGE other GSM services Class B: Alternate use of GPRS/ GPRS and other GSM services Class B136: Alternate use of EDGE and there is-136 services Class C: GPRS/ EDGE only (data... illustrates the GPRS signaling plane, which gives a more detailed concept of the functionalities and internetworking applications between GSM and GPRS network elements Figure GPRS signaling plane GPRS