airay PEINeracue
`
`Cenafor
`
`3G Networks
`IP, UMTS, EGPRS and ATM
`
`ERICSSON EXHIBIT 1026, Page 1
`
`ERICSSON EXHIBIT 1026, Page 1
`
`

`

`Convergence Technologies
`for 3G Networks
`IP, UMTS, EGPRS and ATM
`
`Jeffrey Bannister, Paul Mather and Sebastian Coope
`at Orbitage Consultants
`
`ERICSSON EXHIBIT 1026, Page 2
`
`

`

`ERICSSON EXHIBIT 1026, Page 3
`
`ERICSSON EXHIBIT 1026, Page 3
`
`

`

`Convergence Technologies
`for 3G Networks
`
`ERICSSON EXHIBIT 1026, Page 4
`
`

`

`ERICSSON EXHIBIT 1026, Page 5
`
`ERICSSON EXHIBIT 1026, Page 5
`
`

`

`Convergence Technologies
`for 3G Networks
`IP, UMTS, EGPRS and ATM
`
`Jeffrey Bannister, Paul Mather and Sebastian Coope
`at Orbitage Consultants
`
`ERICSSON EXHIBIT 1026, Page 6
`
`

`

`Copyright  2004
`
`John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester,
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`
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`
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`
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`
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`ERICSSON EXHIBIT 1026, Page 7
`
`

`

`1.3 WHY UMTS?
`
`3
`
`are now generating more traffic and revenue from non-voice services, the business case
`for 3G is present. These operators are no longer able to meet the subscriber demand for
`such applications, and have been a major impetus in 3G development, particularly NTT
`DoCoMo, arguably the most successful, and a pioneer in non-voice services. However,
`the situation in Japan and Korea is somewhat different to the rest of the world. There are
`a number of key factors that led to the growth of data services there:
`• low Internet penetration, due largely to language factors;
`• high existing mobile penetration (in Japan, the high cost and low efficiency of fixed-line
`services has partially fuelled this);
`• large urban conurbation with sizeable proportion of the working population commuting
`on public transport, often for a long duration;
`• low relative cost of mobile services.
`
`This is evident in Japan, where the first driving application of DoCoMo’s iMode service
`was provision of email.
`However, the current situation outside of these exceptions is that thus far, consumer
`demand for data services has been limited, even now when there is widespread availability
`of data-capable mobile devices. Cost of new services has been a significant factor in this
`poor uptake as bandwidth charges are unrealistically high when compared to fixed-line
`equivalents, particularly now with the widespread availability of economical consumer
`digital subscriber line (DSL) services.
`
`1.3 WHY UMTS?
`
`The 3G standard proposed by the European Telecommunications Standards Institute
`(ETSI) with much joint work with Japanese standardization bodies is referred to as
`the universal mobile telecommunications system (UMTS). UMTS is one of a number
`of standards ratified by the International Telecommunications Union–Telecommunication
`Standardization Sector (ITU-T) under the umbrella of International Mobile Telephony
`2000 (IMT2000), as discussed in the next section. It is currently the dominant standard,
`with the US CDMA2000 standard gaining ground, particularly with operators that have
`deployed cdmaOne as their 2G technology. At the time of writing, Japan is the most
`advanced in terms of 3G network deployment. The three incumbent operators there
`have implemented three different technologies: J-Phone is using UMTS, KDDI has a
`CDMA2000 network, and the largest operator NTT DoCoMo is using a system branded
`as FOMA (Freedom of Multimedia Access). FOMA is based around the original UMTS
`proposal, prior to its harmonization and standardization.
`The UMTS standard is specified as a migration from the 2G GSM standard to UMTS
`via the general packet radio service (GPRS) and enhanced data rates for global evolution
`(EDGE), as shown in Figure 1.1. This is a sound rationale since as of December 2002,
`there were over 780 million GSM subscribers worldwide,1 accounting for 71% of the
`
`1Source: GSM Association, www.gsmworld.com.
`
`ERICSSON EXHIBIT 1026, Page 8
`
`

`

`4
`
`INTRODUCTION
`
`GSM
`
`GPRS
`
`UMTS
`
`EDGE
`
`Figure 1.1 GSM evolution to UMTS
`
`global cellular subscriber figures. The emphasis is on enabling as much of the GSM
`network as possible to continue to operate with the new system.
`The goal of 3G is to provide a network infrastructure that can support a much broader
`range of services than existing systems so the changes to the network should reflect
`this. However, many of the mechanisms in the existing networks are equally applicable
`to supporting new service models, for example mobility management. For a successful
`migration, the manufacturers and suppliers of new 3G equipment understand that most
`licences granted for 3G network operation will be to existing 2G operators and thus
`the next step must be an evolution rather than a revolution. Operators in the main are
`expected to introduce GPRS functionality before taking the step to 3G. This will allow
`them to educate and develop the consumer market for these new services prior to major
`investment in new technology. This means that the Core Network will comprise the GSM
`circuit switched core and the GPRS packet switched core. The first release (Release 99)
`specification for UMTS networks is focused on changes to the Radio Access Network
`rather than the Core Network. This allows the Core Network to continue in functionality
`although changes will be made in areas of performance due to the higher data rates
`required by subscribers in the future networks. Maintaining this functionality allows the
`mobile network operators to continue using their existing infrastructure and progress to
`3G in steps. The handover between UMTS and GSM offering worldwide coverage has
`been one of the main design criteria for the 3G system.
`
`1.4 IMT2000 PROCESS
`
`The IMT2000 is a global process, coordinated by the ITU-T to develop next generation
`mobile networks, and covers both the technical specifications and the frequency alloca-
`tions. It was started in 1995 under the original heading of Future Plans for Land Mobile
`Telecommunications System (FPLMTS). IMT2000 is not a particular technology, but
`rather a system which should allow seamless, ubiquitous user access to services. The
`task is to develop a next generation network fulfilling criteria of ubiquitous support for
`broadband real-time and non-real-time services. The key criteria are
`• high transmission rates for both indoor and outdoor operational environments;
`• symmetric and asymmetric transmission of data;
`
`ERICSSON EXHIBIT 1026, Page 9
`
`

`

`44
`
`GSM FUNDAMENTALS
`
`However, the popularity of GSM brought to bear the economies of scale and thus PDC
`is only evident in Japan. The success of GSM in Asia is not surprising as many of the
`original ideas in the design of a network that would transcend political borders are also
`relevant in Asia.
`Currently, at time of writing, GSM technology has over 70% global market share of
`second generation cellular systems. As networks evolve to 3G, GSM should not be seen
`as becoming redundant, but rather GSM is an integral part of the 3G UMTS network
`infrastructure as it also evolves to the GSM-EDGE radio access network (GERAN).
`
`3.1 GENERAL ARCHITECTURE
`
`Figure 3.1 shows the general architecture for a GSM network. The various functional
`blocks are explained in the following subsections.
`
`Mobile station (MS)
`The MS consists of the mobile equipment (ME; the actual device) and a smart card called
`the subscriber identity module (SIM). The SIM offers personal mobility since the user
`can remove the SIM card from one mobile device and place it in another device without
`informing the network operator. In contrast, most other 2G systems require a registration
`update to the operator. The SIM contains a globally unique identifier, the international
`mobile subscriber identity (IMSI), as well as a secret key used for authentication and other
`security procedures. The IMSI (or a variation of it for security purposes) is used throughout
`the network as the identifier for the subscriber. This system enables a subscriber to
`change the mobile equipment and still be able to make calls, receive calls and receive
`other subscriber information by simply transferring the SIM card to the new device.
`Any calls made will appear on a single user bill irrespective of changes in the mobile
`device. The mobile equipment is also uniquely identifiable by the international mobile
`equipment identity (IMEI). The IMEI and IMSI are independent, thus providing the user
`flexibility by separating the concept of subscriber from access device. Many operators still
`issue ‘locked’ mobile devices where the equipment is tied for use only on a particular
`operator’s network. A mobile device not equipped with a SIM must also still be able to
`
`Mobile
`Station
`SIM
`
`ME
`
`BSS
`
`NSS
`
`PSTN
`
`Air/Um
`
`Abis
`
`TRAU
`
`MSC/VLR
`
`GMSC
`
`BTS
`
`BSC
`
`Home-PLMN
`
`HLR
`
`AuC
`
`EIR
`
`Figure 3.1 GSM general architecture
`
`ERICSSON EXHIBIT 1026, Page 10
`
`

`

`3.1 GENERAL ARCHITECTURE
`
`45
`
`25mm
`
`IMEI number
`
`Figure 3.2 GSM IMEI and IMSI
`
`15mm
`
`make emergency calls. To protect the call from undesirable snooping or listening in, the
`IMSI will not always be transmitted over the cell to identify the subscriber. Instead a
`temporary IMSI (T-IMSI) identifier is used and changed at regular intervals. Note that
`for extra security the whole data stream is encrypted over the air interface. Figure 3.2
`shows the 15-digit IMEI number on the left and the SIM card, which incorporates the
`15-digit IMSI.
`
`Base station subsystem (BSS)
`The base station subsystem (BSS) is composed of three parts, the base transceiver station
`(BTS), the base station controller (BSC), which controls the BTSs, and the transcoding
`and rate adaption unit (TRAU).
`
`Base transceiver station (BTS)
`The BTS houses the radio transceivers (TRXs) that define a cell and handle the radio link
`with the mobile station. As was seen, each TRX can handle up to eight full-rate users
`simultaneously. If more than eight full-rate users request resources within the TRX then
`they will receive a busy tone, or a network busy message may be displayed on the mobile
`device. It is possible to increase the number of simultaneous users in a cell by increasing
`the number of TRXs, hence the number of frequencies used. When a mobile device moves
`from one cell to another the BTS may change. Within the GSM system a mobile device
`is connected to only one BTS at a given time. The first TRX in a cell can actually only
`handle a maximum of seven (possibly less) simultaneous users since one channel on the
`downlink is used for broadcasting general system information through what is known as
`the broadcast and control channel (BCCH). The BTS is also responsible for encrypting
`the radio link to the mobile device based on security information it receives from the
`core network.
`
`Base station controller (BSC)
`The BSC manages the radio resources for one or more BTSs. It handles the radio channel
`setup, frequency hopping and handover procedures when a user moves from one cell to
`another. When a handover occurs, the BSC may change; it is a design consideration that
`
`ERICSSON EXHIBIT 1026, Page 11
`
`

`

`46
`
`GSM FUNDAMENTALS
`
`this will not change with the same regularity as a BTS change. A BSC communicates
`with the BTS through time division multiplex (TDM) channels over what is referred to
`as the Abis interface, generally implemented using E1 or T1 lines. If the numerous BTSs
`and the corresponding BSC are in close proximity then this link may be a fibre optic
`or copper cable connection. In some cases, there are a large number of BTSs in close
`proximity but quite some distance away from the controlling BSC. In such cases it may
`be more efficient to relay the calls from each of the BTSs to a single BTS via microwave
`links. This type of link may be very cost effective since generally the running costs of
`a point-to-point microwave link may be free. Of course this has to be weighed against
`the cost of the purchasing and deployment of the equipment. The collector BTS can then
`connect to the BSC via another microwave link or via a landline cable. A problem with
`the above system is that if the collector BTS fails then calls from the other BTSs may
`also fail. To overcome this problem it is possible to have two collector BTSs both sending
`the calls to the BSC. This forms a redundant link and if one collector BTS fails then this
`does not present such a large problem, as is illustrated in Figure 3.3(b).
`
`Transcoding and rate adaption unit (TRAU)
`The central role of the second generation systems is to transfer speech calls and the
`system has been designed and optimized for voice traffic. The human voice is converted
`to binary in a rather complex process. GSM is now quite an old system and as such
`the original encoding method used (LPC-RPE1) is not as efficient as some of the more
`recently developed coding systems such as those used in other cellular systems. There
`have been many developments in digital signal processing (DSP) which have enabled
`good voice quality to be transmitted at lower data rates. Although the TRAU is actually
`
`BTS
`
`BTS
`
`Base
`Station
`Controller
`(BSC)
`
`BTS
`
`BTS
`
`Base
`Station
`Controller
`(BSC)
`
`BTS
`
`BTS
`
`BTS
`
`(a)
`
`BTS
`
`(b)
`
`Figure 3.3 Base station connectivity
`
`1Linear predictive coding with regular pulse excitation (LPC-RPE) provides a digital model of the
`vocal tract and vocal chords, excited by a signal which is air from the lungs.
`
`ERICSSON EXHIBIT 1026, Page 12
`
`

`

`3.1 GENERAL ARCHITECTURE
`
`47
`
`seen as being logically part of the BSS, it usually resides close to the MSC since this
`has significant impact on reducing the transmission costs. The voice data is sent in a
`16 kbps channel through to the TRAU from the mobile device via the BTS and BSC.
`The TRAU will convert this speech to the standard 64 kbps for transfer over the PSTN
`or ISDN network. This process is illustrated in Figure 3.4, where over the air interface,
`speech uses 13 kbps (full-rate) and data 9.6 or 14.4 kbps, with each of these requiring a
`16 kbps link through the BSS.
`As has been mentioned, digital voice data is robust in the face of errors, and can han-
`dle substantial bit error rates before the user begins to notice signal degradation. This
`is in stark contrast to data such as IP packets, which is extremely error intolerant and
`a checksum is generally used to drop a packet which contains an error. Table 3.1 lists
`the adaptive multirate (AMR) speech CODECS which are implemented in UMTS. Also
`indicated on the diagram are the enhanced full-rate (EFR) bit rates for the second gener-
`ation GSM, TDMA and PDC systems for comparison. The GSM EFR uses the algebraic
`code excited linear prediction (ACELP) algorithm and gives better quality speech than
`full-rate (FR) using 12.2 kbps. A half-rate (HR) method of speech coding has also been
`introduced in to the standards, which is known as code excited linear prediction-vector
`sum excited linear prediction (CELP-VSELP). This method will enable two subscribers
`to share a single time slot.
`
`Network switching subsystem (NSS)
`The NSS comprises the circuit switched core network part of the GSM system. The main
`element is the mobile switching centre (MSC) switch and a number of databases referred
`
`BSS
`
`Mobile
`Station
`
`SIM
`
`ME
`
`9.6, 13,
`14.4 kbps
`
`NSS
`
`16kbps
`
`16kbps
`
`64kbps
`
`64kbps
`
`PSTN
`
`BTS
`
`BSC
`
`TRAU
`
`MSC/VLR
`
`Figure 3.4 Transcoding
`
`Table 3.1 CODEC bit rates
`
`CODEC
`
`AMR 12.20
`AMR 10.20
`AMR 7.95
`AMR 7.40
`AMR 6.70
`AMR 5.90
`AMR 5.15
`AMR 4.75
`
`Bit rate (kbps)
`
`12.2 (GSM EFR)
`10.2
`7.95
`7.4 (TDMA EFR)
`6.7 (PDC EFR)
`5.9
`5.15
`4.75
`
`ERICSSON EXHIBIT 1026, Page 13
`
`

`

`48
`
`GSM FUNDAMENTALS
`
`to as the visitor location register (VLR) and home location register (HLR). The HLR is
`always in the home network for roaming subscribers and thus any data exchange may
`have to cross international boundaries. The MSC and VLR are usually combined and are
`located in the visited network.
`
`Mobile switching centre (MSC)
`This acts like a normal switching node for a PSTN or ISDN network. It also takes care
`of all the additional functionality required to support a mobile subscriber. It therefore has
`the dual role of both switching and management. When a mobile device is switched on
`and requests a connection to a mobile network, it is principally the MSC that processes
`this request, with the BSS merely providing the access to facilitate this request. If the
`request is successful then the MSC registers the mobile device within its associated VLR
`(see below; most manufacturers tend to combine the VLR functionality with the MSC).
`The VLR will update the HLR with the location of this mobile device, and the HLR
`may be either in the same network, or a different network in the case of a roaming user.
`The MSC deals with registration, authentication (the MSC requests information from the
`authentication centre but it is the MSC which actually does the authentication), mobile
`device location updating and routing of calls to and from a mobile user. An MSC which
`provides the connectivity from the mobile network to the fixed network, e.g. ISDN or
`PSTN, is known as a gateway-MSC (G-MSC).
`
`Home location register (HLR)
`When a subscriber registers with an operator, they enter into what is known as a service
`level agreement (SLA). This operator’s mobile network is known as the home network or
`home public land mobile network (H-PLMN). The HLR is a huge database located within
`this home network which stores administrative information about the mobile subscriber.
`The information stored for a user in the HLR will include their IMSI, service subscription
`information, service restrictions and supplementary services. The HLR is also expected
`to know the location of its mobile users. It actually knows their location only to the VLR
`with which the mobile device is registered. The HLR also only knows the location of
`a mobile device which is switched on and has registered with some mobile operator’s
`network. This is the case even if the mobile is in a different country connected to another
`mobile operator’s network, as long as a roaming agreement exists between the two mobile
`operators. The GSM system provides all the technical capabilities to support roaming;
`however, this roaming agreement is also required so that both operators can settle billing
`issues arising from calls made by visiting mobile subscribers.
`
`Visitor location register (VLR)
`The VLR is another database of users and is commonly integrated with an MSC. Unlike
`the HLR, where most information is of a permanent nature, the VLR only holds temporary
`information on subscribers currently registered within its vicinity. This vicinity covers the
`subscribers in the serving area of its associated MSC. When a mobile device enters a new
`area, the mobile device may wish to connect to this network and if so informs the MSC of
`its arrival. Once the MSC checks are complete, the MSC will update the VLR. A message
`
`ERICSSON EXHIBIT 1026, Page 14
`
`

`

`3.2 MOBILITY MANAGEMENT
`
`49
`
`is sent to the HLR informing it of the VLR which contains the location of the mobile.
`If the mobile device is making or has recently made a call, then the VLR will know the
`location of the mobile device down to a single cell. If the mobile device has requested
`and been granted attachment to a mobile network, but not made any calls recently, then
`the location of the mobile device will be known by the VLR to a location area, i.e. a
`group of cells and not a single cell. A mobile device that is attached to a mobile network
`where a roaming agreement is in force, i.e. is not in its H-PLMN, is said to be in a visited
`PLMN (V-PLMN).
`
`Equipment identity register (EIR)
`The EIR is a list of all valid mobiles on the network. If a terminal has been reported
`stolen or the equipment is not type approved then it may not be allowed to operate in the
`network. The terminals are identified by their unique IMEI identifier.
`
`Authentication centre (AuC)
`The AuC is a database containing a copy of the secret key present in each of the users’
`SIM cards. This is used to enable authentication and encryption over the radio link. The
`AuC uses a challenge–response mechanism, where it will send a random number to the
`mobile station; the mobile station encrypts this and returns it. The AuC will now decrypt
`the received number and if it is successfully decrypted to the number originally sent, then
`the mobile station is authenticated and admitted to the network.
`
`3.2 MOBILITY MANAGEMENT
`
`To make and receive calls, the location of the mobile device has to be known by the
`network. It would be extremely inefficient if a user needed to be paged across an entire
`network, and almost impossible to support roaming to other networks. Each cell broad-
`casts its globally unique identity on its broadcast channel, which is used by the mobile
`device for location purposes. Mobility management is the mechanism that the network
`uses for keeping a dynamic record of the location of all of the mobile devices currently
`active in the network. In this context, location does not refer specifically to the geo-
`graphical location of the mobile device, but rather its location with respect to a cell in
`which it is currently located. However, for the development of cellular towards third
`generation, geographical location becomes important as an enabler for location-based
`services (LBS).
`The major benefit of the cellular telephone over a fixed landline is the mobility that it
`presents to the subscriber. Initially, this mobility was merely allowing the user to move
`around and be tracked within a certain area; however, now mobility extends to cover the
`concept of roaming. Unfortunately, the provision of mobility makes the network much
`more complex to design and operate. As a subscriber moves from one location to another,
`the strength of the signal it receives from the base station to which it is currently listening
`will fluctuate, and, conversely, the signal received by the base station from the mobile
`device will also vary. Both the network and the mobile device must constantly monitor
`
`ERICSSON EXHIBIT 1026, Page 15
`
`

`

`3.3 GSM AIR INTERFACE
`
`55
`
`890.2Mhz
`
`0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0
`
`1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
`
`TDM frame
`
`Mobile Station Transmission
`
`TDM frame
`
`935.2Mhz
`
`5 6 7 0 1 2 3 4
`
`5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4
`
`Base Station Transmission
`
`Figure 3.9 TDM channels in GSM
`
`T/slot 0
`T/slot 1
`Broadcast Voice Call
`
`T/slot 2
`Free
`
`T/slot 3
`Voice Call
`
`T/slot 4
`Free
`
`T/slot 5
`Voice Call
`
`T/slot 6
`Voice Call
`
`T/slot 7
`GPRS Call
`
`SMS
`
`Location
`Update
`
`Broadcast
`
`Voice Call
`
`Free
`
`Voice Call
`
`Voice Call
`
`Free
`
`Free
`
`Free
`
`Voice Call
`
`Figure 3.10 Example use of time slots
`
`to make telephone calls (voice or data). The duration of these obviously depends on the
`call itself.
`The network selects which band to use, whether there is an option, for example
`900 MHz or 1800 MHz, the frequency, if there is more than one available in this cell,
`and the time slot the subscriber will use. This selection is completely transparent to the
`subscriber; in fact, the frequency and time slot will normally change throughout the call,
`with the user perhaps noticing a small amount of interference or possibly nothing at all.
`The ability to change the frequency of a subscriber is required when a subscriber roams
`from one cell into another since adjacent cells cannot use the same frequency.
`Within a cell, most GSM systems implement frequency hopping, where the BTS and
`mobile unit transmit consecutive frames on different carrier frequencies across the radio
`channels. Frequency hopping is a key part of the GSM system and is used to alleviate
`some of the inherent problems with radio links such as multipath fading by avoiding
`prolonged use of one frequency. The BCCH channel is not part of the frequency-hopping
`scheme since it needs to be located by mobile devices wishing to connect to the cell.
`Figure 3.11 below shows a simplified example of the frequency hopping process. In a
`practical situation each individual time slot can hop independently to the TDMA frame.
`
`3.3.1 GSM multiframes
`
`The above eight time slot framing structure as shown in Figure 3.9 is part of a much
`larger multiframe. There are two types of multiframe: the traffic channel and control
`
`ERICSSON EXHIBIT 1026, Page 16
`
`

`

`56
`
`GSM FUNDAMENTALS
`
`Subscriber
`timeslots
`
`BCCH remains
`
`on t/slot 0
`
`BCCH
`
`time
`
`BCCH
`
`BCCH
`
`TDMA
`block 1
`
`TDMA
`block 2
`
`TDMA
`block 3
`
`BCCH
`
`TRX3
`
`TRX2
`
`TRX1
`
`frequency
`
`Figure 3.11 Frequency hopping in GSM
`
`channel multiframes. The traffic channel multiframe consists of 26 groups of 8 TDM
`frames whereas the control multiframe consists of 51 groups of frames.
`
`3.3.2 Traffic channel multiframe
`
`Although this is a designated traffic channel consisting of 26 frames, at most only 24 of
`these are used for TCH user data such as voice. The frame is also used to carry two logical
`control channels, the slow associated control channel (SACCH) and the fast associated
`control channel (FACCH). Time slots 12 and 25 are specifically used for SACCH. In fact,
`the SACCH may actually alternate between these on different multiframes and so there is
`only one SACCH channel transmitted per multiframe. During the frame that the mobile
`device is not transmitting or receiving on its dedicated TCH, it is constantly monitoring
`the strength of the received signals from the cell it is attached to as well as other cells
`in the area. The mobile station can actually monitor up to six surrounding cells. The
`SACCH is then used for sending these measurement results to the network. A SACCH
`message is 456 bits long (4 bursts × 114 bits per burst); it therefore has a time interval
`of 480 ms before repeating itself. This information can be used to increase or decrease
`the transmitted power levels of both the mobile device and the network every 480 ms, or
`just a little over twice a second. The mobile device uses this information it receives but
`actually alters its power in steps every 60 ms. Enhanced circuit switched data (ECSD)
`can also use a fast power (FP) method which is sent within the data stream every 20 ms.
`Figure 3.12 illustrates the SACCH power control mechanisms: both the mobile device
`and the BTS send measurement reports to the BSC, which makes the decision to increase
`or decrease power.
`The SACCH may also be used for sending SMS messages to and from the mobile
`device while a call is in progress. User data frames 0–11 and 13–24 also carry control
`information in the form of the FACCH channel, as described below. A single user voice
`
`ERICSSON EXHIBIT 1026, Page 17
`
`

`

`3.3 GSM AIR INTERFACE
`
`57
`
`SACCH every 480ms
`
`Base Station Subsystem
`
`Power Control and measurement reporting
`Power Control Decision
`
`Mobile
`Station
`
`SIM
`
`ME
`
`Abis
`
`Power Control and
`measurement reporting
`
`BTS
`
`Power Control
`Decision
`
`BSC
`
`Figure 3.12 SACCH power control
`
`call will be transmitted in frame 0 of the multiframe for a particular amount of time,
`followed by a particular amount of time in frame 1 etc. Eight such calls can be made on
`this carrier frequency. A traffic channel is only assigned when the mobile device is in
`dedicated mode, whereas in idle mode the mobile device does not have a traffic channel
`assigned to it. Figure 3.13 shows the relationship of the TDM frame within a traffic
`channel multiframe.
`Each of the eight time slots in the TDM frame consists of 148 bits lasting 547 µs and
`has the structure shown in Figure 3.14.
`
`0
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`7
`
`8
`
`Multi-frame 32,500 bits in120msec
`16
`15
`14
`13
`12
`11
`10
`9
`18
`17
`
`19
`
`20
`
`21
`
`22
`
`23
`
`24
`
`25
`
`Control
`Frame
`
`Control
`Frame
`
`0 1 2 3 4 5 6 7
`TDM frame
`
`1250 bits in 4.615msec
`
`Figure 3.13 GSM multiframe
`
`0
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`7
`
`000
`
`Information
`
`F1
`
`Training
`
`F1
`
`Information
`
`000
`
`8.25 bit guard band
`
`3 bits
`
`57 bits
`
`1 bit
`
`26 bits
`
`1 bit
`
`57 bits
`
`3 bits
`
`148 bit data frame sent in 547us
`
`Figure 3.14 GSM data burst
`
`ERICSSON EXHIBIT 1026, Page 18
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`

`

`4.2 GENERAL ARCHITECTURE
`
`81
`
`load of the network. Enhanced GPRS (EGPRS) is an enhancement to the system, which
`allows higher bit rates through the use of different modulation techniques and coding
`schemes (see Section 4.11.12).
`The concept of a GPRS handover is referred to as a cell reselection procedure and
`is normally performed by the mobile device. The handover timing for GPRS is not so
`critical when compared to GSM since the traffic is not real time, and can thus be buffered.
`In this cell reselection procedure, the mobile device makes measurement reports, as with
`GSM; however the mobile station (MS) is more involved in the decision process, and can
`even initiate the procedure for handover. It is, nevertheless, still the responsibility of the
`network the serving GPRS support node (SGSN) to allow the handover to occur.
`Security functions are essentially quite similar to those for GSM services. The SGSN
`is responsible for authenticating the subscriber as well as encrypting/decrypting of data
`towards the mobile device (regular GSM encryption is only between the mobile device
`and the base station). The SGSN and mobile device can also compress data to make more
`efficient use of the Gb and air interface. A mobile device containing a standard GSM
`SIM can connect to the GPRS network and use the services, depending on the specifics
`of the operator network settings.
`
`4.2 GENERAL ARCHITECTURE
`
`Figure 4.2 shows the general architecture of a GPRS network and its interface to other
`IP-based networks such as the Internet. The GPRS network makes use of much of the
`existing GSM infrastructure. The HLR, AuC and EIR may require minor modifications to
`support GPRS, generally in the form of a software upgrade. In the diagram, the different
`equipment within the GPRS backbone network is connected together using an Ethernet
`switch. Within the GPRS standard, there is no stipulation as to what Layer 2 technology
`
`BSS
`
`Abis
`
`Mobile
`Station
`
`BTS
`
`BSC
`
`NSS
`
`PSTN
`
`MSC/VLR
`
`GMSC
`
`HLR
`
`AuC
`
`EIR
`
`switch
`
`SGSN
`
`GGSN
`
`External
`Network e.g.
`Internet
`
`GPRS IP
`Backbone
`
`CG
`
`LIG
`
`DNS
`
`Figure 4.2 GPRS General Architecture
`
`ERICSSON EXHIBIT 1026, Page 19
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`

`82
`
`GENERAL PACKET RADIO SERVICE
`
`infrastructure should be used to interconnect the IP backbone, since to support roaming,
`the SGSN and GGSN will be connected through an internetwork. Most current networks
`are using an Ethernet network to implement this local backbone, as it is a cost-effective
`architecture choice. This Ethernet switch can be a weak link as it is a single point of
`failure in the network, so usually it will contain a great deal of redundancy to ensure
`reliability.
`
`4.3 GPRS NETWORK ELEMENTS
`
`To enable GPRS over an existing second generation network such as GSM, a number
`of additional network elements are required in the GPRS backbone network. These are
`described in the