Services

The services offered at the User-Network Interface (UNI) of GSM are patterned after the services offered by the Integrated Services Digital Network (ISDN) 7 for fixed terminals tied to telephone lines. GSM services are therefore divided just like ISDN services into three categories bearer services, teleservices, and supplementary services. A bearer service offers the basic technical capability for the transmission of binary data i.e. it offers the data transfer between end terminals at...

F

FACCH (Fast associated control channel), 58 Fading Fast associated control channel, see FACCH Fax, 226 see also Services adaptation protocol, 211 FCAPS (Fault, configuration, accounting, performance, security) management, 233 FCCH (Frequency correction channel), 58, 68 FDD, see Duplex FDMA, see Multiple access Fill bits, 101 Forward error correction, see Channel coding hyperframe, 76 multiframe, 76, 263 number (FN), 72 search frame, 84 superframe, 76 TDMA frame, 15 Frame check sequence, 132...

Optional Frequency Hopping

Mobile radio channels suffer from frequency-selective interferences, e.g. frequency-selective fading due to multipath propagation phenomena. This selective frequency interference can increase with the distance from the base station, especially at the cell boundaries and under unfavorable conditions. Frequency hopping procedures change the transmission frequencies periodically and thus average the interference over the frequencies in one cell. This leads to a further improvement of the...

Internal Error Protection Convolutional Coding

After block coding has supplemented the data with redundancy bits for error detection (parity bits), added fill bits and thus generated sorted blocks, the next stage is calculation of additional redundancy for error correction to correct the transmission errors caused by the radio channel. The internal error correction of GSM is based exclusively on convolutional codes. Convolutional codes 35 can also be defined using shift registers and generator polynomials. Figure 6.9 illustrates a possible...

Characteristics of the Mobile Radio Channel

Figure 2.1 Simplified two-path model of radio propagation Figure 2.1 Simplified two-path model of radio propagation more than with the square of the distance from the transmitter. We can approximate the received power by considering the direct path and only one reflected path (two-path propagation) 42 and we obtain, under the simplified assumptions of the two-path propagation model, from Figure 2.1, a propagation loss of 40 dB per decade In reality, the propagation loss depends on the...

Generating Security Data

At the network side, the 2-tuple (RAND, SRES) need not be calculated each time when authentication has to be done. Rather the AUC can calculate a set of (RAND, SRES) 2-tuples in advance, store them in the HLR, and send them on demand to the requesting VLR. The VLR stores this set (RAND n , SRES n ) and uses a new 2-tuple from this set for each authentication procedure. Each 2-tuple is used only once so new 2-tuples continue to be requested from the HLR AUC. This procedure, to let security data...

Radio Subsystem Link Control

The radio interface is characterized by another set of functions of which only the most important ones are discussed in the following. One of these functions is the control of the radio link Radio Subsystem Link Control, with the main activities of received-signal quality measurement (quality monitoring) for cell selection and handover preparation, and of transmitter power control. If there is no active connection, i.e. if the mobile station is at rest, the BSS has no tasks to perform. The MS,...

Transmission Power Control

Power classes (Table 5.8) are used for classification of base and mobile stations. The transmission power can also be controlled adaptively. As part of the Radio Subsystem Link Control, the mobile station's transmitter power is controlled in steps of 2 dBm. The GSM transmitter power control has the purpose of limiting the mobile station's transmitter power to the minimum necessary level, in such a way that the base station receives signals from different mobile stations at approximately the...

References

1 3GPP (Third Generation Partnership Project), http www.3gpp.org. 2 W. D. Ambrosch, A. Maher, and B. Sassceer. The Intelligent Network. Berlin Springer, 1989. 3 G. Begin and D. Haccoun. Performance of sequential decoding of high-rate punctured convolutional codes. IEEE Transactions on Communications, vol. 42, no. 3, pp. 966987, 1994. 4 D. Bertsekas and R. Gallager. Data Networks. Englewood Cliffs, NJ Prentice Hall, 1987. 5 Ch. Bettstetter, H.-J. V gel, and J. Ebersp cher. GSM phase 2+ General...

Traffic Channels

The carried service (e.g. telephony). For the packet-switched mode, the TCH carries user data of OSI Layers 2 and 3 according to the recommendations of the X.25 standard or similar standard packet protocols. A TCH may either be fully used (full-rate TCH, TCH F) or be split into two half-rate channels (half-rate TCH, TCH H), which can be allocated to different subscribers. Following ISDN terminology, the GSM traffic channels are also designated as Bm channel (mobile B channel) or Lm channel...

Signalling Channels

The control and management of a cellular network demands a very high signaling effort. Even when there is no active connection, signaling information (for example location update information) is permanently transmitted over the air interface. The GSM signaling channels offer a continuous, packet-oriented signaling service to MSs in order to enable them to send and receive messages at any time over the air interface to the BTS. Following ISDN terminology, the GSM signaling channels are also...

Overview of Data Communication

Voice service needs only a switched-through physical connection, which changes its bit rate in the BSS due to the speech transcoding in the TRAU. From the MSC on, the speech Mobile Termination Terminal Equipment, ISDN Interface Terminal Equipment, no I SDN interface (V X, Terminal Adapter Reference Point Radio Interface Reference Points ISDN i norvlSDN Mobile Termination Terminal Equipment, ISDN Interface Terminal Equipment, no I SDN interface (V X, Terminal Adapter Reference Point Radio...

Protection of Subscriber Identity

The intent of this function is to prevent disclosing which subscriber is using which resources in the network, by listening to the signaling traffic on the radio channel. On one hand this should ensure the confidentiality of user data and signaling traffic, on the other hand it should also prevent localizing and tracking of a mobile station. This means above all that the International Mobile Subscriber Identity (IMSI) should not be transmitted as clear text, i.e. unencrypted. Instead of the...

Supplementary Services of Phase

In the course of further evolution of the GSM standard, the menu of services known from ISDN is being made available in stages 7 and supplemented by some new GSM-specific performance characteristics. In Phase 2, which was standardized in 1996, there are some supplementary services (Table 4.5), such as Call Waiting (CW) or hold (HOLD), which enable performing brokerage functions. Two very powerful supplementary services are Conference Calling (CONF) allowing the interconnection of several...

Transport of User Data in the Signaling Plane

In the signaling plane (control plane) of the GSM architecture, one can also transport packet-oriented user data from or to mobile stations. This occurs for the point-to-point SMS (see Section 4.2). Short messages are always transmitted in store-and-forward mode through a Short 'Message Service Center (SMS-SC). The service center accepts these messages, which can be up to 160 characters long, and forwards them to the recipients (other mobile stations or fax, email, etc.). In principle, GSM...

Bearer Services and Supplementary Services

The bearer services of GPRS offer end-to-end packet switched data transfer to mobile subscribers. Currently, a Point-to-Point (PTP) service is specified, which comes in two variants a connectionless mode (PTP Connectionless Network Service (PTP-CLNS), e.g. for IP) and a connection-oriented mode (PTP Connection Oriented Network Service (PTP-CONS), e.g. for X.25). For future releases it is planned to implement a Point-to-Multipoint (PTM) service. It will offer transfer of data packets from one...

Signaling at the Air Interface Um

Signaling at the user-network interface in GSM is essentially concentrated in Layer 3. Layers 1 and 2 provide the mechanisms for the protected transmission of signaling messages across the air interface. Besides the local interface, they contain functionality and procedures for the interface to the BTS. The signaling of Layer 3 at the user-network interface is very complex and comprises protocol entities in the mobile station and in all functional entities of the GSM network (BTS, BSC, and...

Logical Channels

Table 11.4 lists the packet data logical channels defined in GPRS. As with logical channels in conventional GSM, they can be divided up into two categories traffic channels and signaling (control) channels. The signaling channels can further be divided into Packet Broadcast Control, Packet Common Control, and Packet Dedicated Control channels. The Packet Data Traffic Channel (PDTCH) is employed for the transfer of user data. It is assigned to one mobile station (or in case of PTM to multiple...

Protocol Architecture of the Signaling Plane 731 Overview of the Signaling Architecture

Figure 7.11 shows the essential protocol entities of the GSM signaling architecture (control plane or signaling plane). Three connection elements are distinguished the radio-interface connection element, the BSS-interface connection element, and the Ainterface connection element. This control plane protocol architecture consists of a GSM-specific part with the interfaces Um and Abis and a part based on Signaling System Number 7 (SS 7) with the interfaces A, B, C, E (Figure 7.11). This change of...

Objectives of GSM Network Management

International operation of network management Cost limitation of GSM systems with regard to short-term as well as long-term aspects Achievement of service quality which at least matches the competing analog mobile radio systems The international operation of a GSM system includes among others the interoperability with other GSM networks (including different countries) and with ISDN networks, as well as the information exchange among network operators (billing, statistical data, subscriber...

Connection Establishment and Termination 831 Routing Calls to Mobile Stations

The number dialed to reach a mobile subscriber (MSISDN) contains no information at all about the current location of the subscriber. In order to establish a complete connection to a mobile subscriber, however, one must determine the current location and the locally responsible switch (MSC). In order to be able to route the call to this switch, the routing address to this subscriber (MSRN) has to be obtained. This routing address is assigned temporarily to a subscriber by its currently...

Subscriber Identity Confidentiality

As in GSM, the identity of the subscriber is held confidential. This is done by using temporary identities on the radio channel. In particular, the user's IMSI is not transmitted unencrypted, but a Packet Temporary Mobile Subscriber Identity (P-TMSI) is assigned to each user by the SGSN. This address is temporary and is only valid and unique in the service area of this SGSN. From the P-TMSI, a Temporary Logical Link Identity (TLLI) can be derived. The mapping between these temporary identities...

Call Establishment and Corresponding MAP Procedures

Call establishment in GSM at the air interface is similar to ISDN call establishment at the user network interface (Q.931) 7 . The procedure is supplemented by several functions random access to establish a signaling channel (SDCCH) for call setup signaling, the authentication part, the start of ciphering, and the assignment of a radio channel. The establishment of a connection always contains a verification of user identity (authentication) independent of whether it is a mobile-originated call...

Supplementary Services in GSM Phase 2 1241 Supplementary Services for Speech

By far the largest part of the supplementary service characteristics known from ISDN have in one way or another already been implemented in GSM (see Section 4.3). The mobility of the users, however, creates the need for new supplementary services. Examples of supplementary services known from ISDN or newly defined are mobile access hunting, short message forwarding, multiple subscriber profile, call transfer, or Completion of Calls to Busy Subscribers (CCBS). The example of the CCBS service...

Separation of Directions and Duplex Transmission

The most frequent form of communication is the bidirectional communication which allows simultaneous transmitting and receiving. A system capable of doing this is called full-duplex. One can also achieve full-duplex capability, if sending and receiving do not occur simultaneously but switching between both phases is done so fast that it is not noticed by the user, i.e. both directions can be used quasi-simultaneously. Modern digital mobile radio systems are always full-duplex capable....

Appendix C Acronyms

3rd Generation Partnership Project 2 Algebraic Code Excitation Linear Prediction Barring of Incoming Calls when Roaming Outside the Home PLMN Barring of Outgoing International Calls Barring of Outgoing International Calls except those to Home PLMN Base Tranceiver Station Identity Code Base Station System Application Part Base Station System Application Part + Base Station System GPRS Application Protocol Base Station System Management Application Part Customized Applications for Mobile Network...

Call Termination

At the air interface, a given call can be terminated either by the mobile equipment or by the network. The taking down of the connection is initiated at the Um interface by means of the CC messages disconnect, release, and release complete. This is followed by an explicit release of occupied radio resources (channel release). On the network side, the connection between the involved switching centers (MSC, etc.) is terminated using the ISUP messages rel and rlc in the SS 7 network (Figure 8.11)....

Cellular Technology

Reuse Ferequency

Because of the very limited frequency bands, a mobile radio network has only a relatively small number of speech channels available. For example, the GSM system has an allocation of 25 MHz bandwidth in the 900 MHz frequency range, which amounts to a maximum of 125 frequency channels each with a carrier bandwidth of 200 kHz. Within an eightfold time multiplex for each carrier, a maximum of 1000 channels can be realized. This number is further reduced by guardbands in the frequency spectrum and...

Supplementary Services

The supplementary services in GSM correspond to the supplementary services of ISDN with regard to service and performance characteristics. They can be used only in connection with a teleservice, i.e. they modify or supplement the functionality of a GSM telecommunication service (bearer or teleservice). Besides the improved network organization, the introduction of numerous ISDN-like supplementary services is the main feature of GSM Phase 2. Some GSM supplementary services are identical or...

Connection Management

Call Control (CC) is one of the entities of Connection Management (CM) the CM sublayer is shown in Figure 7.12. It comprises procedures to establish, control, and terminate calls. Several parallel CC entities are provided, such that several parallel calls on different MM connections can be processed. For CC, finite state models are defined both on the mobile side as well as on the network side. The two entities at the MS and MSC sites each instantiate a protocol automaton, and these communicate...

General Description

Functional Architecture Gsm

GSM networks are structured hierarchically Figure 3.1 . They substantially consist of at least one administrative region, which is assigned to a Mobile Switching Center MSC . Each administrative region is made up of at least one Location Area LA . Sometimes the LA is also called the visited area. An LA consists of several cell groups. Each cell group is assigned to a Base Station Controller BSC . Therefore for each LA there exists at least one BSC, but cells of one BSC may belong to different...

Signaling Plane

Gprs Attach

The protocol architecture of the signaling plane comprises protocols for control and support of the functions of the transmission plane, e.g., for the execution of GPRS attach and detach, PDP context activation, the control of routing paths, and the allocation of network resources. Between MS and SGSN Figure 11.11 , the GPRS 'Mobility Management and Session Management GMM SM protocol is responsible for mobility and session management. It includes functions for GPRS attach detach, PDP context...

Realization of Short Message Services

The procedures for the transport of point-to-point short messages reside in the CM sublayer, also called the Short 'Message Control Layer SM-CL and in the Short Message Relay Layer SM-RL directly above. Accordingly, the protocol entities are called the Short Message Control entity SMC and the Short Message Relay entity SMR . A complete established MM connection is needed for the transport of short messages, which again presumes an existing RR connection with LAPDm protection on an SDCCH or...

Multiple Access Procedures

The radio channel is a communication medium shared by many subscribers in one cell. Mobile stations compete with one another for the frequency resource to transmit their information streams. Without any other measures to control simultaneous access of several users, collisions can occur multiple access problem . Since collisions are very undesirable for a connection-oriented communication like mobile telephony, the individual subscribers mobile stations must be assigned dedicated channels on...

Frame Multiframe

For the transmission of the control channels which are not associated with a TCH all except FACCH and SACCH , a multiframe is formed consisting of 51 consecutive TDMA frames Figure 5.6 . According to channel configuration Section 5.1 , the multiframe is used differently. In each case, multiframes of 51 TDMA frames serve the purpose of mapping several logical channels onto a physical channel. Furthermore, some of these control channels are unidirectional, which results in different structures...

Routing and Conversion of Addresses

Now we explain the routing example of Section 11.3.3 in detail. Figure 11.9 roughly illustrates the transfer of an incoming IP packet. It arrives at the GGSN, is then routed through the GPRS backbone to the responsible SGSN and finally to the MS. Using the PDP context, the GGSN determines from the IP destination address a Tunnel Identifier TID and the IP address of the relevant SGSN. Between GGSN and the SGSN, the GPRS Tunneling Protocol is employed. The SGSN derives the Temporary Logical Link...

Interleaving

The decoding result of the convolutional code strongly depends on the frequency and grouping of bit errors that occur during transmission. Especially burst errors during long and deep fading periods, i.e. a series of erroneous sequential bits, have negative impact on error correction. In such cases, the channel is not a binary channel without memory, rather the single-bit errors have statistical dependence, which diminishes the result of the error correction procedure of the convolutional code....

Source Coding and Speech Processing

Source coding reduces redundancy in the speech signal and thus results in signal compression, which means that a significantly lower bit rate is achieved than needed by the original speech signal. The speech coder decoder is the central part of the GSM speech processing function, both at the transmitter Figure 6.2 as well as at the receiver Figure 6.3 . The functions of the GSM speech coder and decoder are usually combined in one building block called the codec COder DECoder . Figure 6.2...

Basic Packet Mode

Two variants of PSPDN access can be realized with the protocol model in Figure 9.14 PSPDN access according to ITU-T X.32 Access to PSPDN packet handlers according to ITU-T X.31 Case A basic packet mode . PSPDN access according to X.32 has not met much acceptance with the applications the X.31 procedure is used more often. PSPDN access according to X.32 is the simpler variant. The X.25 packets can be trans Figure 9.14 X.25 access at the ISDN S interface Figure 9.14 X.25 access at the ISDN S...

External Error Protection Block Coding

The block coding stage in GSM has the purpose of generating parity bits for a block of data, which allow the detection of errors in this block. In addition, these blocks are supplemented by fill bits tail bits to a block length suitable for further processing. Since block coding is the first or external stage of channel coding, the block code is also known as external protection. Figure 6.7 gives a brief overview showing which codes are used for which channels. In principle, only two kinds of...

Channel Measurement

The task of Radio Subsystem Link Control in the mobile station includes identification of the reachable base stations and measurement of their respective received signal level and channel quality quality monitoring task . In idle mode, these measurements serve to select the current base station, whose PCH is then periodically examined and on whose RACH desired connections can be requested. During a connection, i.e. on a TCH or SDCCH with respective SACCH FACCH, this measurement data is...

Short Message Service SMS

Another teleservice which was assigned high priority in the service implementation strategy - and which is now very successful - is the capability to receive or send short messages at the mobile station Short 'Message Service SMS , TS21 and TS22. This service was supposed to be offered in the third phase E3 at the latest from 1996 on all GSM networks. TS21 is the point-to-point version of the SMS, which allows a single station to be sent a message of up to 160 characters. Conversely, TS22 has...

Channel Coding

Stages Channel Coding

The heavily varying properties of the mobile radio channel see Section 2.1 result in an often very high bit error ratio, on the order of 10 3 to 10_1. The highly compressed, redundancy-reduced source coding makes speech communication with acceptable quality almost impossible moreover, it makes reasonable data communication impossible. Suitable error correction procedures are therefore necessary to reduce the bit error probability into an acceptable range of about 10 5 to 10 6. Channel coding,...

Signaling at the User Interface

Another often neglected but nevertheless very important interface in a mobile system is the user interface of the mobile station equipment. This Man-Machine Interface MMI can be realized freely and therefore in many different ways by the mobile equipment manufacturers. In order to keep a set of standardized service control functions in spite of this variety, the MMI commands have been introduced. These MMI commands define procedures mainly for the control of basic and supplementary services....

Subscriber Data in GSM

Imsi Msisdn Sim

Besides data of the address type, which is the most important subscriber data of any communication network, a whole series of other service- and contract-specific data exists in GSM networks. Addresses serve to identify, authenticate, and localize subscribers, or switch connections to subscribers. Service-specific data is used to parameterize and personalize supplementary services. Finally, contracts with subscribers can define different service levels, e.g. booking of special supplementary...

Appendix A Gsm Standards

1 GSM 01.02, General Description of a GSM PLMN 2 GSM 01.04, Abbreviations and Acronyms 3 GSM 02.02, Bearer services BS supported by a GSM PLMN 4 GSM 02.03, Teleservices supported by a GSM PLMN 5 GSM 02.04, General on supplementary services 6 GSM 02.09, Security aspects 7 GSM 02.16, International MS Equipment Identities 8 GSM 02.17, Subscriber Identity Modules - Functional Characteristics 9 GSM 02.22, Personalisation of GSM Mobile Equipment ME Mobile functionality specification 10 GSM 02.30,...

Coding Authentication and Ciphering

The previous chapter explained the basic functions of the physical layer at the air interface, e.g. the definition of logical and physical channels, modulation, multiple access techniques, duplexing, and the definition of bursts. In this chapter, we discuss several additional functions that are performed to transmit the data in an efficient, reliable, and secure way over the radio channel source coding and speech processing Section 6.1 , channel coding and burst mapping Section 6.2 , and...

Protocol Architecture Planes

Gsm Protocol Architecture

The various physical aspects of radio transmission across the GSM air interface and the realization of physical and logical channels were explained in Chapter 5. According to the terminology of the OSI Reference Model, these logical channels are at the Service Access Point of Layer 1 physical layer , where they are visible to the upper layers as transmission channels of the physical layer. The physical layer also includes the forward error correction and the encryption of user data. The...

Protocol Architecture 1141 Transmission Plane

Figure 11.7 illustrates the protocol architecture of the GPRS transmission plane. The protocols offer transmission of user data and its associated signaling e.g. for flow control, error detection, and error correction . An application running in the GPRS-MS e.g. a browser uses IP or X.25, respectively, in the network layer. As mentioned earlier in this chapter, IP and X.25 packets are transmitted encapsulated within the GPRS backbone network. This is done using the GPRS Tunneling Protocol GTP ,...

Advanced Speech Call Items ASCI

Gsm System Using Anchor

GSM systems of Phase 2 offer inadequate features for group communications. For example, group call or push-to-talk services with fast connection setup as known from private radio or digital trunked radio systems e.g. TETRA , are not offered. However, such services are indispensable for most closed user groups e.g. police, airport staff, railroad or taxi companies . In particular railroad operators had a strong request for such features. In 1992, their international organization, the Union...

Modulation

Gauss Modulation Pulse Spectrum Gsm

The modulation technique used on the radio channel is Gaussian Minimum Shift Keying GMSK . GMSK belongs to a family of continuous-phase modulation procedures, which have the special advantages of a narrow transmitter power spectrum with low adjacent channel interference on the one hand and a constant amplitude envelope on the other hand, which allows use of simple amplifiers in the transmitters without special linearity requirements class C amplifiers . Such amplifiers are especially...

Cell Selection and Operation in Power Conservation Mode 5541 Cell Selection and Cell Reselection

A mobile station in idle mode must periodically measure the receivable BCCH carriers of the base stations in the area and calculate mean values RXLEV n from this data see Section 5.5.1.1 . Based on these measurements, the mobile station selects a cell, namely the one with the best reception, i.e. the mobile station is committed to this cell. This is called camping on this cell. In this state, accessing a service becomes possible, and the mobile station listens periodically to the PCH. Two...

Dedicated Packet Mode

As in the case of asynchronous PAD access to packet data networks see Section 9.5.3 , the synchronous case of the X.25 access protocol also offers an alternative, which allows the most immediate transition to the PSPDN, even if the mobile station is in a foreign network international roaming . For this purpose, a dedicated mode is also defined with each PLMN having its own packet handler. Figure 9.15 shows the principle of this Dedicated Packet Mode. It essentially includes the functions of the...

Protocol Architecture

Gprs Protocol Architecture

The WAP protocol architecture is shown in Figure 12.12. As mentioned before, WAP is based on the WWW protocol stack and adjusts those protocols to the requirements of wireless transmission and small portable devices. For applications, a uniform microbrowser environment has been specified the Wireless Application Environment WAE . It comprises the following functionality and formats the Wireless Markup Language WML , a simple script language WMLScript, which is based on JavaScript, programming...

System Architecture

Wap System Architecture

Figure 12.14 gives a schematic illustration of a typical WAP system architecture. The principle how content is stored in a distributed way within the network and finally offered to the user is similar to the principle of the WWW. Servers store content directly as a WML document or content is generated with scripts. Mobile stations download these contents from the server to their microbrowser, which then presents them to the user. In theory, it is possible to store content in HTML and...

Addresses and Identifiers

GSM distinguishes explicitly between user and equipment and deals with them separately. According to this concept, which was introduced with digital mobile networks, mobile equipment and users each receive their own internationally unique identifiers. The user identity is associated with a mobile station by means of a personal chip card, the Subscriber Identity Module SIM . This SIM usually comes in the form of a chip card, which is transferable between mobile stations. It allows to distinguish...

Teleservices

On top of the bearer services, which can be used by themselves, a number of teleservices have been defined. The most important categories are Table 4.3 speech, SMS, access to Message Handling Systems MHSs and to videotext, teletext, and facsimile transfer. Voice services had to be implemented by each operator in the start-up phase E1 by 1991. In this category, two teleservices were distinguished regular telephone service TS11 and emergency service TS12 . For transmission of the digitally coded...

Radio Resource Management

The procedures for Radio Resource Management RR are the basic signaling and control procedures at the air interface. They handle the assignment, allocation and administration Figure 7.21 Format of a Um signaling message Layer 3 Figure 7.21 Format of a Um signaling message Layer 3 of radio resources, the acquisition of system information from broadcast channels BCCH and the selection of the cell with the best signal reception see cell selection in Section 5.5.4.1 . Accordingly, the RR procedures...

Multiple Access Duplexing and Bursts

Gmsk Frame

On the physical layer OSI Layer 1 , GSM uses a combination of FDMA and TDMA for multiple access. Two frequency bands 45 MHz apart have been reserved for GSM operation Figure 5.5 890-915 MHz for transmission from the mobile station, i.e. uplink, and 935-960 MHz for transmission from the base station, i.e. downlink. Each of these bands of 25 MHz width is divided into 124 single carrier channels of 200 kHz width. This variant of FDMA is also called Multi-Carrier MC . In each of the uplink downlink...

Speech Transmission

The digital, source-coded speech signal of the mobile station is transmitted across the air interface in error-protected and encrypted form. The signal is then deciphered in the BTS, and the error protection is removed before the signal is passed on. This specially protected speech transmission occurs transparently between mobile station and a Transcoding and Rate Adaptation Unit TRAU which serves to transform the GSM speech-coded signals to the ISDN standard format ITU-T A-law . A possible...

New Data Services and Higher Data Rates Hscsd Gprs and EDGE

Gmsk Constellation Extra Points

Development also continues with data services. The maximal data rate of 9600 bit s for data services in conventional GSM is rather low compared to fixed networks. The desire for higher data rates in GSM networks is therefore quite obvious. Two prominent trends can be recognized integration of packet services into GSM networks and high-bit-rate bearer services with data transmission rates up to some 10 kbit s. Accordingly, one of the GSM standardization groups specified the High Speed Circuit...

Adaptive Frame Synchronization

The mobile station can be anywhere within a cell, which means the distance between mobile and base station may vary. Thus the signal propagation times between mobile and base station vary. Due to the mobility of the subscribers, the bursts received at the base would be offset. The TDMA procedure cannot tolerate such time shifts, since it is based on the exact synchronization of transmitted and received data bursts. Bursts transmitted by different mobile stations in adjacent time slots must not...

Transparent Data Transmission

The digital mobile radio channel is subject to severe quality variations and generates burst errors, which one tries to correct through interleaving and convolutional codes see Section 6.2 . However, if the signal quality is too low due to fading breaks or interference, the resulting errors cannot be corrected. For data transmission across the air interface Um, a residual bit error ratio varying between 10 2 and 10 according to channel conditions can be observed 58 . This kind of variable...

Disconnection due to Radio Channel Failure

Radio Link Timeout

The quality of a radio channel can vary considerably during an existing connection, or it can even fail in the case of shadowing. This should not lead to immediate disconnection, since such failures are often of short duration. For this reason GSM has a special algorithm within the Radio Subsystem Link Control which continuously checks for connectivity. It consists of recognizing a radio link failure by the inability to decode signaling information on the SACCH. This connectivity check is done...

Effect of the MSRN Assignment on Routing

Msrn Assignment

There are two ways to obtain the MSRN obtaining the MSRN at location update obtaining the MSRN on a per call basis For the first variant, an MSRN for the mobile station is assigned at the time of each location update which is stored in the HLR. This way the HLR is in a position to supply immediately the routing information needed to switch a call through to the local MSC. The second variant requires that the HLR has at least an identification for the currently responsible VLR. In this case,...

Handover 841 Overview

What The Role The Handovers

Handover is the transfer of an existing voice connection to a new base station. There are different reasons for the handover to become necessary. In GSM, a handover decision is made by the network, not the mobile station, and it is based on BSS criteria received signal level, channel quality, distance between MS and BTS and on network operation criteria e.g. current traffic load of the cell and ongoing maintenance work . The functions for preparation of handover are part of the Radio Subsystem...

Decision Algorithm for Handover Timing

Who Makes The Handover Decisions Gsm

The basis for processing a successful handover is a decision algorithm which uses measurement results from mobile and base station to identify possible other base stations as targets for handovers and which determines the optimal moment to execute the handover. The objective is to keep the number of handovers per cell change as small as possible. Ideally, there should not be more than one handover per cell change. In reality, this is often not achievable. When a mobile station leaves the radio...

Multiple Access and Radio Resource Management

Ondemand Gprs Physical Channel

On the physical layer, GPRS uses the GSM combination of FDMA and TDMA with 8 time slots per TDMA frame as explained in Section 5.2.2 . However, several new methods are used for channel allocation and multiple access. They have significant impact on the performance of GPRS. In circuit switched GSM, a physical channel i.e. one time slot of successive TDMA Figure ll.l3 GPRS-Internet interconnection frames is permanently allocated for a particular MS during the entire call period no matter whether...

Signaling at the A and Abis Interfaces

Location Update Signaling Flow Diagram

Whereas the transport of user data between MSC and BSC occurs across standard connections of the fixed network with 64 kbit s or 2048 kbit s or 1544 kbit s , the transport of signaling messages between MSC and BSC runs over the SS 7 network. The MTP and SCCP parts of SS 7 are used for this purpose. A protocol function using the services of the SCCP is defined at the A interface. This is the Base Station Application Part BSSAP , which is further subdivided into Direct Transfer Application Part...

Camel Gsm and Intelligent Networks

Msc Cap Inap

Essentially, CAMEL represents a convergence of GSM and Intelligent Network IN technologies. The fundamental concept of IN is to enable flexible implementation, introduction and control of services in public networks and to use the idea of dividing the switching functionality into basic switching functionality, residing in Service Switching Points SSPs and centralized service control functionality, residing in Service Control Points SCPs . Both network components communicate with each other over...

PLMN Configurations and Interfaces

Plmn Interface Gsm

The fixed connections for transport of signaling and user data in a GSM PLMN Figure 3.8 are standard transmission lines. Within the SMSS, lines with a transmission rate of 2 Mbit s or 1.544 Mbit s in North America are typically used fixed lines, mostly microwave links or leased lines . The BSS uses mostly 64 kbit s lines. Signaling has two fundamentally different parts GSM-specific signaling within the BSS, including the air interface, and signaling within the SMSS and with other PLMN in...

Improved Codecs for Speech Services Half Rate Codec EFR Codec and AMR Codec

Codage Efr Gsm 244 Bits

One of the most important services in GSM is of course voice service. Thus it is obvious, that voice service has to be further improved. In first place is the development of new speech codecs with two competing objectives better utilization of the frequency bands assigned to GSM and improvement of speech quality in the direction of the quality offered by ISDN networks, which is primarily requested by professional users. Half-Rate codec - The reason for improved bandwidth utilization is to...

Mapping of Logical Channels onto Physical Channels

The mapping of logical channels onto physical channels has two components mapping in frequency and mapping in time. The mapping of a logical channel onto a physical channel in the frequency domain is based on the TDMA frame number FN , the frequencies allocated to base and mobile stations - CA and MA - and the rules for the optional frequency hopping see Section 5.2.3 . In the time domain, logical channels are transported in the corresponding time slots of the physical channel. They are mapped...

Basic Handover between two MSCs

Fast Handover

The principal sequence of operations for a basic handover between two MSCs is shown in Figure 8.20. The MS has indicated the conditions for the handover, and the BSS requests the handover from MSC-A handover required . MSC-A decides positively for a handover and sends a message perform handover to MSC-B. This message contains the necessary data to enable MSC-B to reserve a radio channel for the MS. Above all, it identifies the BSS which is to receive the connection. MSC-B assigns a handover...

Services and Applications

Wrc 2000 Wrc 1992 Umts

The first specification of WAP has been released by the WAP Forum in April 1998. Version 1.1 followed in June 1999 and Version 1.2 in December 1999. WAP terminals have been introduced around February 1999 for the first time, and today there exists a broad variety of WAP products mobile equipment, gateways, development tools, WML browsers and editors. Besides the technical implementation in the network and the development of new WAP-capable mobile equipment, innovative WAP services are in...

Mobility Management

Implicit Imsi Detach

The main task of 'Mobility Management MM is to support the mobility of the mobile station for example, by reporting the current location to the network or verifying the subscriber identity. Another task of the MM sublayer is to offer MM connections and associated services to the CM sublayer above. The message format for MM messages is the uniform Layer 3 signaling message format Figure 7.21 . MM has its own protocol discriminator, and the MM messages are marked with a type code MT, Table 7.5 ....

Mapping of packet data logical channels onto physical channels

Gprs Multi Frame Ptcch

From Section 5.4 we know that the mapping of logical GSM channels onto physical channels has two components mapping in frequency and mapping in time. The mapping in frequency is based on the TDMA frame number and the frequencies allocated to the BTS and the mobile station. The mapping in time is based on the definition of complex multiframe structures on top of the TDMA frames. A multiframe structure for PDCHs consisting of 52 TDMA frames each with 8 time slots is shown in Figure 11.16. The...

Bearer Services

The basic services of a GSM network are the foundation for data transmission, i.e. a basic service provides the fundamental technical facilities at the end terminal interface reference point R to transport user payloads. The basic services are called transport services 7 or bearer services in ISDN - and therefore in GSM, too. The GSM bearer services offer asynchronous or synchronous data transport capabilities with circuit-switched or packet-switched data rates of 300-9600 bit s, with a 13 kbit...

Session Management and PDP Context

To exchange data packets with external PDNs after a successful GPRS attach, a mobile station must apply for an address used in the PDN. In general, this address is called PDP address Packet Data Protocol address . In case the PDN is an IP network, this will be an IP address. For each session, a so-called PDP context is created, which describes the characteristics of the session. It contains the PDP type e.g. IPv4 , the PDP address assigned to the mobile station e.g. an IP address , the...

Telecommunication Management Network TMN

Tmn Architecture

TMN was standardized within ITU-T ETSI CEPT almost simultaneously with the pan-European mobile radio system GSM. The guidelines of the M. series of the ITU-T M.20, M.30 serve as a framework. TMN defines an open system with standardized interfaces. This standardization enables a platform-independent multivendor environment for management of all components of a telecommunication network. Essentially it realizes the communication of a management system with network elements it administers, which...

TMN Realization in GSM Networks

Tmn Architecture

TMN and GSM were standardized approximately at the same time, so that there was a good opportunity to apply TMN principles and methods in a complete TMN system for network management in GSM from the beginning and from ground up. For this purpose, specific working groups were founded for the five TMN categories Figure 10.1 as well as for architecture and protocol questions which were supposed to develop as much as possible of the TMN system and its services, while following the top-down...

Lll System Architecture

Gprs Backbone Arsitektur

In order to integrate GPRS into the existing GSM architecture see e.g. Figure 3.9 , a new class of network nodes, called GPRS Support Nodes GSNs , has been introduced. GSNs are responsible for the delivery and routing of data packets between the mobile stations and external packet data networks PDNs . Figure 11.1 illustrates the resulting system architecture. Figure 11.1 GPRS system architecture and interfaces Figure 11.1 GPRS system architecture and interfaces A Serving GPRS Support Node SGSN...

Some GSM History and Statistics

In 1982 the development of a pan-European standard for digital cellular mobile radio was started by the Groupe Sp cial Mobile of the CEPT Conf rence Europ enne des Administrations des Postes et des T l communications . Initially, the acronym GSM was derived from the name of this group. After the founding of the European standardization institute ETSI European Telecommunication Standards Institute , the GSM group became a Technical Committee of ETSI in 1989. After the rapid worldwide...

Mapping onto the Burst Plane

After block encoding, convolutional encoding, and interleaving, the data are available in form of 114-bit interleaving blocks. This corresponds exactly to the amount of data which can be carried by a normal burst Figure 5.6 . Each interleaving block is mapped directly onto one burst Figure 6.17 . After setting the stealing flags, the bursts can be composed and passed to the modulator. The stealing flags indicate whether high-priority signaling messages are present FACCH messages , which must be...

Location Registration and Location Update

Tmsi Reallocation Procedure

Before a mobile station can be called or gets access to services, the subscriber has to register with the mobile network PLMN . This is usually the home network where the subscriber has a service contract. However, the subscriber can equally register with a foreign network provider in whose service area he or she is currently visiting, provided there is a roaming agreement between the two network operators. Registration is only required if there is a change of networks, and therefore a VLR of...

Bit Rate Adaptation

Five basic traffic channels are available in GSM for the realization of bearer services TCHH2.4, TCH H4.8, TCH F2.4, TCH F4.8, TCH F9.6 see Tables 5.2 and 6.2 with bit rates of 3.6 kbit s, 6 kbit s, and 12 kbit s. In recent standardization efforts, a TCH F14.4 has also been defined. The bearer services Table 4.2 with bit rates from 300 bit s up to 9.6 kbit s must be realized on these traffic channels. Furthermore, on the fixed connections of the GSM network, the data signals are transmitted...

Placement of the Protocol Entities for HLR Interrogation

Call Routing Foreign Hlr

Depending on the capabilities of the associated switches and the called target national or international MSISDN , there are different routing procedures. In general, the local switching center analyzes the MSISDN. Due to the NDC, this analysis of the MSISDN allows the separation of the mobile traffic from other traffic. The case that mobile call numbers are integrated into the numbering plan of the fixed network is currently not provided. In the case of a national number, the local exchange...

Layer 2 Signaling

Layer Signaling

The LAPDm protocol is the data link protocol for signaling channels at the air interface. It is similar to HDLC. It provides two operational modes In the unacknowledged operation mode, data is transmitted in UI frames unnumbered information without acknowledgement there is no flow control or L2 error correction. This operational mode is allowed for all signaling channels, except for the RACH which is accessed in multiple access mode without reservation or protection. The acknowledged operation...

Dedicated PAD Access in GSM

However, direct access to packet data networks through the asynchronous GSM data services has disadvantages One needs another subscription to a packet data network operator besides to GSM. Independent of the current mobile subscriber's location, a circuit-switched connection to a PAD of a packet service provider is needed. Sometimes the packet network access is only allowed to specific PADs. This is a particular disadvantage if the mobile subscriber is currently in a foreign GSM network and...

Encryption of Signaling and Payload Data

The encryption of transmitted data is a special characteristic of GSM networks that distinguishes the offered service from analog cellular and fixed ISDN networks. This encryption is performed at the transmitting side after channel coding and interleaving and immediately preceding modulation Figure 6.25 . On the receiving side, decryption directly follows the demodulation of the data stream. A Cipher Key Kc for the encryption of user data is generated at each side using the generator algorithm...

Subsequent Handover

After a first basic handover of a connection from MSC-A to MSC-B, a mobile station can move on freely. Further intra-MSC handovers can occur Figure 8.15 , which are processed by MSC-B. If, however, the mobile station leaves the area of MSC-B during this connection, a Subsequent Handover becomes necessary. Two cases are distinguished in the first case, the mobile station returns to the area of MSC-A, whereas in the second case it enters the area of a new MSC, now called MSC-B'. In both cases,...

Frequency and Clock Synchronization

Spektrum Bcch Fcch

A GSM base station transmits signals on the frequency carrier of the BCCH which allow a mobile station to synchronize with the base station. Synchronization means on the one hand the time-wise synchronization of mobile station and base with regard to bits and frames, and on the other hand tuning the mobile station to the correct transmitter and receiver frequencies. For this purpose, the BTS provides the following signals Figure 5.6 Synchronization Channel SCH with extra long Synchronization...

IntraMSC Handover

The basic structure for an external handover is the handover between two cells of the same MSC Figure 8.15 . The mobile station continually transmits measurement reports with channel monitoring data on its SACCH to the current base station BSS 1 . Based on these measurement results, the BSS decides when to perform a handover and requests this handover from the MSC message handover required . The respective measurement results can be transmitted in this message to the MSC, to enable its...

Attachment and Detachment Procedure

Before a mobile station can use GPRS services, it must attach to the network similar to the IMSI Attach used for circuit switched GSM services . The mobile station's attach request message is sent to the SGSN. The network then checks if the user is authorized, copies the user profile from the HLR to the SGSN, and assigns a Packet Temporary Mobile Subscriber Identity P-TMSI to the user. This procedure is called GPRS Attach. For mobile stations using both circuit switched and packet switched...

Location Management

Routing Area Update Gprs

As in circuit switched GSM, the main task of location management is to keep track of the user's current location, so that incoming packets can be routed to his or her MS. For this purpose, the MS frequently sends location update messages to its SGSN. How often should a mobile station send such a message If it updates its current location e.g. its cell rather seldom, the network must perform a paging process in order to search the MS when packets are coming in. This will result in a significant...

Nontransparent Data Transmission

Compared to the bit error ratio of the fixed network, which is on the order of 10 6 to 109, the quality of transparent data service is often insufficient for many applications, especially under adverse conditions. To provide more protection against transmission errors, more redundancy has to be added to the data stream. Since this redundancy is not always required, but only when there are residual errors in the data stream, forward error correction is inappropriate. Rather, an error detection...

Layer 1 of the Msbts Interface

Radio Channel Access

Layer 1 of the OSI Reference Model physical layer contains all the functions necessary for the transmission of bit streams over the physical medium, in this case the radio channel. GSM Layer 1 defines a series of logical channels based on the channel access Figure 7.16 Layer 1 service interfaces Figure 7.16 Layer 1 service interfaces procedures with their physical channels. The higher layer protocols access these services at the Layer 1 service interface. The three interfaces of Layer 1 are...

Classification of Mobile Communication Systems

Mobile Communication Classification

This book deals almost exclusively with GSM however, GSM is only one of many facets of modern mobile communication. Figure 1.1 shows the whole spectrum of today's and -as far as can be seen - future mobile communication systems. For the bidirectional - and hence genuine - communication systems, the simplest variant is the cordless telephone with very limited mobility in Europe especially the DECT standard . This technology is also employed for the expansion of digital PBXs with mobile...