`The first System for Mobile Packet based
`Global Internet Access1
`
`
`Walke B H.
`
`Electrical Engineering and Information Technology, RWTH Aachen University, ComNets Research
`Group, Kopernikusstrasse 5, Aachen, 52062, Germany.
`walke@comnets.rwth-aachen.de
`
`
`Keywords: GPRS, General Packet Radio Service, GPRS Fundaments, Enabler of Mobile
`Internet Access, Multiple-Access Protocol, EDGE, Packet-Switched Cellular Radio Network.
`
`Abstract
`
`GPRS, the General Packet Radio Service in GSM was the enabler of the mobile Internet.
`The origins of key radio access functions employed for packet-switching in GPRS are
`identified by reviewing state-of-the-art on random access protocols applied in cellular radio
`data networks existent or proposed before GPRS specification started. A table is provided
`showing the degree of conformance to GPRS of the respective systems. Besides the type of
`demand assigned multiple access protocol used in a system, dynamic placement of control
`channels to the packet data channel and statistical multiplexing of fractions of IP packets of
`simultaneously transmitting mobile stations to the same packet data channel appear to be
`key differentiators, besides others. CELLPAC by comparing its functions to that of GPRS is
`shown to comprise what is called here the Fundaments of the GPRS Radio Interface
`Protocol. The history of ETSI GPRS standard development is described. Although GPRS is a
`result of cooperation of many actors which contributions are valued, it appears possible to
`identify the roots of its radio access protocol and thereby main contributors.
`
`
`
`1. Introduction
`
`The General Packet Radio Service (GPRS) was launched worldwide in 2001 as a service
`provided by the Global System for Mobile (GSM) to provide mobile Internet access. Later,
`adaptive modulation and coding for higher data rate was introduced to GPRS under the
`name Enhanced Data Rate for GSM Evolution (EDGE), leaving the access protocol
`unchanged. Concepts enabling packet data communication in cellular radio networks were
`kept and further developed from GPRS/EDGE when specifying 3G Universal Mobile
`Telecommunications System (UMTS) and 4G system Long Term Evolution (LTE).
`
`1.1 Early Concepts for Wide Area Mobile Data Networks
`
`The architecture of a Public Land Mobile Network (PLMN) is shown in Figure 1, where the
`Access Network (AN) is made-up from Mobile Stations (MSs) connected to the Base Station
`Subsystem (BSS) across the Radio Interface (RI). The BSS is part of both AN and Core
`Network (CN), and comprises multiple Base Stations (BSs) each serving a radio cell
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`1 IEEE Wireless Communications, October 2013 1536-1284/13/$25.00 © 2013 IEEE
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`connected star-shaped to a Base Station Controller not shown in the figure. In the core
`network, mobility supporting functions are found like Subscriber Register (SR) responsible for
`roaming, authentication and billing of MSs, and switching nodes dedicated to circuit- and
`packet-switched services, respectively. Gateway Circuit- / Packet-Switched Exchange nodes
`hosting Interworking Functions (IWFs) shown in Figure 1 interface to external networks to
`connect a MS to MSs of other PLMNs and to fixed subscriber terminals.
`PLMNs support roaming where the MS’s current location is stored in SR so that an incoming
`call can be routed to a MS. Roaming requires the MS to update SR when entering another
`cell not belonging to the location area of the previous cell. Advanced PLMNs besides
`roaming also support handover for keeping service quality of a MS when communicating on
`the move. Handover provides continuation of communication within and across cells with
`small service interruption, only.
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`Roaming of movable wireless terminals (WTs) connected directly by protocol IEEE 802.11
`WLAN to the Internet is provided by Mobile Internet Protocol versions 4 (MIPv4) and MIPv6.
`Since Internet access routers typically do not provide cellular radio coverage, roaming of
`WTs is supported only when associated to an access router and handover of WTs is not
`provided at all. Therefore, wireless networks are not considered to be mobile networks.
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`
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`BSS = Base Station Subsystem (Base Station (BS) plus BS Controller);
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`CSX/PSX = Circuit-/Packet-Switched Exchange; MS = Mobile Station;
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`GCSX/GPSX = Gateway CSX/PSX;
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`SR = Subscriber Register;
`PSTN = Public Switched Telephone Network;
`PLMN = Public Land Mobile Network;
`PDN = Public Data Network;
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`Figure 1: Generic architecture of a cellular mobile radio network (PLMN)
`
`The network elements shown in Figure 1 have its own protocol stack for both control and
`user data exchange. PLMNs differ much in the protocol stacks used at the RI but extensively
`rely on fixed network protocol stacks known from PDNs. What is PLMN specific are network
`elements for mobility management in the core network and the protocol stack at the RI. The
`focus in this study is mainly on the protocols applied at the RI in the access network.
`
`Mobile stations having data to send will request transmission at random times. Since MSs
`have no knowledge of each other’s existence or status, management of the mobile random-
`access to the uplink (UL) channel by multiple concurrent MSs is a major challenge in radio
`access protocol design. Aloha and slotted (S) Aloha are the simplest multiple-access
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`protocols to a mobile radio channel, but these are considered inefficient when used for data
`transfer, where MSs contend directly with their data messages. In [1] it is shown that radio
`access protocols that combine S-Aloha request channels with separate traffic channels can
`achieve very high utilisation in a stable way. Typically, a request channel has only to transmit
`small amounts of control data and so requires a small bandwidth compared to the user data
`channels. If sufficient bandwidth is allocated to the request channel for it to operate stable (at
`low utilisation) then the data channels may be operated at high utilisation. This is the reason
`why modern mobile radio networks provide random access control channels besides traffic
`channels (TCHs) to carry speech and user data transfer.
`
`1.1.1 Mobile circuit-switched data networks
`
`Mobile networks originally were designed for circuit-switched speech communication and
`later offered data as an add-on. A simple form of mobile data communication is data
`transmission using modems over analog cellular
`telephone
`links.
`In
`this
`form of
`communication, the mobile user accesses a cellular channel just as he would in making a
`standard voice call over the cellular network. Mobile terminals typically operate at 9.6 – 14.4
`kbit/s data rate using error correction protocols like MNP-10, V.34 and V.42 for reliable data
`transmission. Modem based circuit-switched transparent data service was provided by
`analog and digital cellular networks, e.g., EIA-553 AMPS and ETSI GSM shortly after start of
`the respective network. The user then operates the modem just as would be done from office
`to office over the PSTN. In this form of communication the network is not actually providing a
`data service but simply a voice link over which the mobile data modem can interoperate with
`a corresponding data modem in an office or computer center.
`
`A data modem uses a traffic channel on the RI in the same way as the voice service. A traffic
`channel for exclusive use for the data transfer of one mobile user is reserved when the data
`arrives. It will be released when the data message is transferred. This traffic channel is
`established between the MS and the Interworking Function (IWF) located in the GCSX in
`Figure 1.
`
`Data transmission on top of an underlying cellular telephone service has limitations imposed
`by the characteristics of the voice-circuit connection. The service might be cost effective if
`long data files are transmitted on a connection. However, the service is costly if only short
`messages are exchanged over the network during a (long) session supporting an interactive
`service, where the circuit-mode connection is mostly unused but charged by the operator.
`This is the reason for development of mobile data networks that apply end-to-end packet
`switching based on, e.g., X.25, IP or proprietary protocols.
`
`1.1.2 Mobile packet-switched data networks
`
`Mobile packet-switched networks enable MSs to exchange packet data over radio. Besides
`stand-alone networks there exist packet-switched networks integrated to circuit-switched
`networks occupying some of its radio channels.
`
`Before work started to specify GPRS in 1993, a number of concepts were known for packet
`or message switching in a mobile radio network as discussed in the following. But first,
`multiple-access (MA) protocols to a request channel are introduced.
`
`1.2 ALOHA, S-ALOHA, DAMA
`
`The birth of mobile radio and MA to a radio channel dates back to 1897 when Marconi was
`credited with the patent for wireless telegraph. Marconi MSs mounted on ships, sharing the
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`same radio channel were the first to contend to a shared channel for transmitting a sequence
`of Morse coded telegraphy characters. Like with the Aloha protocol Marconi MSs repeat
`transmission if no response is received to a message sent.
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`In 1970 the ALOHANET was opened to connect multiple low data rate stations through a
`single radio channel to a central host. For that purpose the MA-protocol Aloha [2] was
`designed, where stations transmit their data packets at random times. Under Aloha the
`station having a data packet ready transmits it on the channel to the central host without
`considering any synchronisation or access rule. The packet also contains identification,
`control and parity check information. Packets sent by different stations may partly overlap
`and collide at the receiver. A station waits for a time-out to happen or for receiving an
`acknowledgement from the central host. After time-out the packet is retransmitted after a
`random pause interval. This process is repeated until successful transmission or until the
`process is terminated by the station. The randomly transmitted Aloha packet is a user data
`message. It is not a signalling message to prepare for packet data exchange. In [2] it is
`shown that the effective channel capacity is 1/(2e).
`
`The S-Aloha protocol proposed 1972 is applied to a time-slotted channel and thereby
`doubles channel capacity [3]. Stations apply the Aloha protocol but in addition are required to
`synchronise their packet transmissions into fixed length channel time slots. Thereby, partial
`overlap of packet transmission of different stations is avoided.
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`Most cellular radio data networks assign radio channels to MSs based on a demand-
`assigned multiple-access (DAMA) protocol [1] where an UL request channel is shared by
`many MSs through contention based on S-Aloha. A data channel is assigned by the BS in
`response to a successful request and the requesting MS will start to use the channel
`assigned for the duration of its data communication.
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`With the DAMA protocol, user data on UL may be transmitted outband (Uo) on a TDMA
`channel different from the shared request channel, or inband (Ui) on the shared channel.
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`Cellular systems based on DAMA protocol require, besides time-slotting, the channel to be
`organised in TDMA frames so that slots can be identified by their position in a frame. If the
`frame length is longer than the maximum channel propagation delay, each MS can be
`informed of the status of each time slot of the preceding frame. A slot in the frame provides a
`TDMA channel which may be used as a control or packet data channel (PDCH).
`
`DAMA based systems with explicit reservation in response to a request sent on a contention
`channel assign an UL TDMA channel for packet data transmission by explicit communication
`to the MS via a DL control channel. The PDCH typically is then different from the contention
`channel.
`
`With implicit reservation a successful request by an MS on a contention channel is
`acknowledged by the BS on the corresponding DL channel. This results in an automatic
`reservation of the same channel used for the request to be used also for user packet data
`transmission on UL. Accordingly, two DAMA types on DL are to differ: De and Di for explicit
`(e) and implicit (i) realization, respectively, of the DL control channel granting a MS a data
`channel. Further, the DL control channel used to grant a MS a channel for UL packet data
`transmission may be realized outband or inband to the DL packet data channel
`corresponding to the potential UL data channel.
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`Therefore, four DAMA types on DL are to differ: Deo and Dei for explicit outband and explicit
`inband realization, respectively, of the explicit reservation channel. Dio and Dii for implicit
`outband and implicit inband realization, respectively, of the implicit reservation channel.
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`1.2.1 R-ALOHA and PRMA
`
`R-Aloha [4] and PRMA [5] are DAMA protocols type (Ui, Dii). The R-Aloha protocol was
`designed to connect MSs generating long multi-packet messages via transponder based
`satellite systems to a central host. The channel is operated without central control since MSs
`can hear each other. In cellular radio networks where MSs cannot hear the UL channel
`central control by the BS is required to inform MSs via a broadcast control channel on the
`status of each slot of the forthcoming UL frame.
`
`The PRMA protocol is widely known, although not implemented in a real system. There the
`DL control channel is assumed able to immediately broadcast to all MSs the status of an UL
`slot in a preceding frame. UL slots broadcast by the BS to be “available” for random access
`in a frame may be accessed by an MS. Collisions of MSs are resolved by back-off and
`repeated transmission. A successful MS is confirmed by the BS to use the slot that it had
`used for MA for data transmission as a TDMA channel in the next and subsequent frames
`until the MS’s data expire.
`
`1.3 Early Mobile Packet Data Networks
`
`The most important early packet data networks discussed in the following were closed after
`GSM/GPRS started its operation in the respective region/country.
`
`The Advanced Radio Data Information Service (ARDIS) full-duplex wide area packet-
`switched cellular radio service of Motorola and IBM that is based on Motorola DataTAC was
`launched in 1983 in large US cities [6]. The service connects MSs by radio under control of
`the proprietary Radio Data (RD) Link Access Procedure (LAP) offering 8kbit/s user data rate.
`RD-LAP covers ISO/OSI network (layer-3) and link layer (layer-2). Connectionless and
`connection-oriented communication based on virtual circuits is supported. Mobility and radio
`resource management is provided covering roaming but not handover. RD-LAP layer-2
`provides ARQ and access control at the RI by the Digital Sense Multiple Access (DSMA)
`protocol. With DSMA the BS provides in each DL slot, besides user data for a MS addressed
`in a slot, the channel status symbol (CSS) indicating whether the slotted UL channel is idle or
`busy. Free UL channels are used in contention mode to transmit a request packet. If a MS
`has data to transmit, it randomly waits up to 50 ms before it reads out the CSS. If CSS
`signals an idle UL channel, the MS transmits immediately its data as RD-LAP blocks, 12 byte
`each, resulting in a message of up to 512 byte transmitted. If the channel was detected busy,
`the MS waits for a random time-duration and then again looks for the value of the CSS. A
`collision during contention to the UL is resolved by a random back-off time until the MS
`retries again. During transmission of RD-LAP blocks by a MS the receiving BS transmits
`CSS=busy information on DL. DSMA is a DAMA (Ui, Dei) protocol. Packet data is transmitted
`by concurrent MSs one-by-one (see Figure 2) where one common traffic channel of a cellular
`radio system is alternatingly used as a PDCH by two MSs to transmit data packets with some
`idle gaps in between. The other common traffic channels may also be used as PDCHs or
`may be used for circuit-switched services.
`
`The MOBITEX packet data service for digital speech and data communication developed by
`Swedish operator Telia and Ericsson was first launched in 1986 in Sweden providing
`country-wide cellular data services supporting roaming but not handover. Since in US the
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`system was introduced by RAM Mobile Data in 1990 it is also known as RAM Packet Data
`Network. The RI data rate is 8 kbit/s half-duplex supporting files of up to 20 kByte. The
`network layer supports datagram transfer by the proprietary protocol MPAK and the link layer
`provides ARQ. Access to the shared radio channel is by a DAMA protocol type (Ui, Deo)
`called Reservation TDMA. The BS on DL of the RI provides the number of slots of the FDMA
`channel available for random access [7]. A MS randomly picks a slot to transmit an access
`request on UL while the BS may send DL traffic. At the end of the period reserved for
`random access, the BS grants permissions to MSs one-by-one resulting in sequential
`transmission of data of concurrent MSs, see Figure 2.
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`IWF
`
`Common control
`channel
`Common traffic channel
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`Common traffic channel
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`MS
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`MS
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`Figure 2: Packet channel (PCH) reserved for duration of packet transfer of single user
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`The COGNITO cellular mobile packet switching network was operated until 2003 in UK for
`datagram transfer before it was replaced by GPRS [8]. MSs may transmit in slots or minislots
`(four to a slot). 64 byte user data are carried in a slot. Minislots are used for contention on UL
`and acknowledgement on DL. Periodic slots in the TDMA frame on UL and DL are dedicated
`by means of the Slot Map to be control or data channels. Random access is by S-Aloha to a
`control channel and collisions are detected by MSs from absence of an acknowledgement.
`The BS will acknowledge a request on UL and direct the MS to a free UL slot (TDMA channel
`to transmit its user data. This DAMA protocol is type (Uo, Deo). MS are served one-by-one,
`see Figure 2.
`
`1.4 Cellular Radio integrating circuit- and packet-switching
`
`1.4.1 Concepts not implemented
`
`Local Cellular Radio Network (LCRN) [9] is the first to integrate circuit-switched digital
`speech/data and packet-switched services in a mobile radio system based on FDMA/TDMA
`channels. Virtual connection and datagram service are supported. Some TDMA channels are
`provided for control and others for packet data transfer. S-Aloha is used for MA in a DAMA
`(Uo, Deo) protocol. The trunk of TDMA channels is dynamically assigned according to needs
`to circuit- and packet-switched services.
`
`A cellular radio system integrating circuit- and packet-switched data transmission is
`introduced by Ken Felix [10] where channels can be used for voice, dedicated data or
`packet-switched data. Extensions to the signaling standard of US digital cellular phone
`standard (1993) TIA IS-54 are proposed to enable a mobile packet service. MSs transmit on
`a packet-switched radio channel one by one, see Figure 2. Access to the UL channel is
`either through polling MSs by the BS, or by a MA protocol not specified in detail in [10], which
`appears to be DSMA. If polling is used, random access is switched off and the protocol is
`then not MA at all.
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`Improvements to PRMA are proposed in [11] by Mitrou (MLP) for an integrated system
`supporting both circuit- and message-switching voice and data. Slots of a TDMA-frame are
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`dedicated to be control or data channels as known from PRMA and COGNITO. UL control
`slots used for MA are subdivided into minislots to each carry a miniburst request message.
`Once a request miniburst was successful, the MS is assigned by the BS a periodic packet
`data slot for the duration of its data transmission. The protocol is DAMA (Uo, Deo). MSs are
`served one by one as shown in Figure 2.
`
`1.4.2 Systems Implemented
`
`The cellular digital packet data (CDPD) service was specified in 1993 as an overlay to the
`advanced mobile phone service (AMPS) [12] to provide 19.2 kbit/s data rate. Some FDM
`channels of AMPS carry the connection-less CDPD service. MA at the RI by DSMA protocol
`prepares transmission of up to 64 blocks each 54 Byte without multiplexing data blocks of
`concurrent stations.
`
`Standards TIA IS-54 and TIA IS-95 specify a three-slot per TDMA frame and a CDMA (code
`division multiple access cellular radio system, respectively. Like ETSI GSM, around 1992
`these networks were prepared to carry circuit-switched data services besides speech. Data
`services were offered from about 1993/94 on, where a channel is dedicated to a point-to-
`point connection. Since many mobile data applications generate bursty traffic, market
`acceptance of the service was low. In all these systems a channel is shared by MSs on a call
`by call basis. A DAMA (Uo, Deo) protocol is used to provide circuit-switched data service.
`
`2. CELLPAC a first Version of GPRS
`
`To ease understanding of GPRS, the Fundaments of the GPRS Radio Interface Protocol
`(“GPRS Fundaments”) are introduced in the following with reference to the roots where the
`respective functions were proposed first. The first full GPRS specification Release ’99
`provided in 200 kHz bandwidth a symbol rate of 271kbit/s resulting in 22.8kbit/s data rate of a
`full-rate TDMA traffic channel (TCH). Multi-slot operation is an option. In a later GPRS
`Release (EDGE) the data rate of a TCH increased to 69kbit/s.
`
`It appears that most GPRS Fundaments have been first proposed for CELLPAC [13] - [15]
`introducing packet-switching in GSM. In what follows the CELLPAC functions are explained
`and compared to GPRS and to other systems known earlier. Table 1 (discussed later)
`summarizes the results.
`
`GPRS is based on a new protocol for radio access and on provisions introduced to the GSM
`core network to enable packet data transmission [16]. Since packet-switched data networks
`and IP tunneling were known when GPRS was designed, the hardest part in designing
`GPRS was to introduce
`
`(1) Packet radio access of GPRS enabled MSs without changing GSM layer-1
`functions implemented in hardware.
`
`(2) A protocol suite for the network elements of the access and core networks to
`support packet-switching.
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`2.1 Protocol Suite
`
`Protocol stacks for network elements required for packet-switching did not exist in GSM [18].
`Figure 3a shows the protocol suite with a protocol stack per network element as introduced
`in [15], which is close to GPRS, see Figure 3b. It is worth noting that layer-2 at the radio
`interface (RI) Um running on top of GSM physical layer (layer-1), in both protocol stacks
`shows two sub-layers, namely Medium Access Control (MAC) in Figure 3b, called ‘Packet
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`Access’ in Figure 3a, and Radio Link control (RLC) in Figure 3b called Radio Link Protocol
`(RLP) in Figure 3a. There the MS is split into data terminal equipment (DTE) and mobile
`terminal (MT).
`‘Packet Access’ protocol data units are transmitted across the RI in Figure 3a called
`RLC/MAC data block in GPRS, see Figure 8. The GPRS stack compared to that of
`CELLPAC is further optimized to contain the Logical Link Control (LLC) protocol, and the
`Sub-network-Dependent Convergence Protocol (SNDCP), both operating between MS and
`SGSN, not affecting the RI. In network layer (layer-3) ITU-T protocol X.25 is used in both
`CELLPAC and GPRS, besides IP. During specification of GPRS Rel.’99 it turned out that IP
`would be the major network layer protocol. An X.25 like virtual connection established during
`association of a MS to GPRS was kept to allow for fast link establishment of a MS having
`data ready to send. The virtual connection later was specified as semi-permanent, thereby
`providing the ‘Always On’ property of GPRS.
`The protocol suite proposed in [15] was followed by the GPRS standard at the RI and in part
`in the core network.
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`a) PSDN = Packet Switched Data Network, MSC/IWF = Mobile Switching Center/Interworking
`Function
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`b) BSS = BS Subsystem, SGSN = Serving GPRS Support Node, GGSN = Gateway GPRS SN
`Figure 3: Protocol Suites for CELLPAC (a) and GPRS (b)
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`Since the packet data rate in early GPRS is small (12 kbit/s) but Internet application
`protocols like SMPT, HTTP, etc. should be supported, the Wireless Application Protocol
`(WAP) was specified by the WAP Forum to enable ‘Thin Clients’ with small screens to run
`Internet applications on MSs with low processing power across low rate data links [20].
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`GSM/EDGE with its data rate of up to 384kbit/s on smart communications devices enables
`Internet application protocols more comfortable.
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`2.2 GPRS as a Service in the Circuit-Switched GSM Network
`GSM with its voice and data services was deployed when discussion started on how to
`realize a packet radio service. Eight physical TDMA radio channels per FDM channel are
`provided in GSM per transmit direction, see Figure 4. A time-slot may carry a Normal Burst
`(NB) as used by GSM control and TCHs, or may carry a Random Access Burst (RAB) or
`other burst type. In [13] - [15] one (or more) time slot of the GSM TDMA-frame representing
`in GSM a physical TDMA channel is dedicated as a combined packet data and control
`channel, called the CELLPAC dedicated TCH. Thereby the GPRS Packet Data Channel
`(PDCH) is anticipated.
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`Dedication of some TDMA channels of a circuit-switched cellular network for packet-
`switching is known from [9], [10], [12], and [18] of which [9] was the first to propose this.
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`Figure 4: FDM and TDMA channels in GSM
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`2.3 PDCH Shared by Control and User Data
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`Multi-frames as known from GSM but with different structure are introduced in [15] for both
`UL and DL of the slot used as a CELLPAC TCH. A CELLPAC multi-frame specifies the roles
`of a slot of a TDMA-frame over time to be either control channel or packet data traffic
`channel (PDTCH), see Figure 5. The CELLPAC multi-frame comprises 26 GSM TDMA
`frames. In vertical direction slots 0 to 7 represent the respective TDMA frame. TDMA frames
`13 and 26 of DL and UL, respectively, carry the fixed packet control channel (PCCH) on DL
`and the packet random access channel on UL. Slots on the DL may carry the PDTCH or the
`dynamic packet control channel (PCCH). UL slots may be reserved by the BS as PDTCH for
`a MS to transmit packet data or may be dynamically be dedicated for random access. GPRS
`specifies a 52 multi-frame.
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`Figure 5: CELLPAC multi-frame. ‘Reserved’ means a slot is dedicated as PDTCH
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`Both the GSM control channels for virtual connection setup and the CELLPAC dedicated
`TCH are shown in Figure 6 [15]. The latter comprises logical control channels (‘Access’ and
`‘Control’) and voice/data channels for packet data transmission. The logical channels
`mentioned correspond to Packet Random Access Channel (PRACH), Packet Common
`Control Channel (PCCCH) and Packet Data Traffic Channel (PDTCH) specified by the GPRS
`multi-frame to be carried on the Packet Data Channel (PDCH) that is a frame-periodic slot.
`
`Figure 6: GSM Dedicated Control Channel
`(DCCH) and Random Access Channel
`(RACH) used for virtual call set-up, and
`dedicated Traffic Channel (TCH) for data
`transmission in CELLPAC [15].
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`No cellular packet-switched system besides
`GPRS applies a multi-frame for mapping
`logical control and data channels to one
`TDMA channel as introduced in [15].
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`2.4 Packet Data Context Establishment
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`Association of a MS to the mobile network and packet data context (PDC) establishment
`before transmitting GPRS packets avoids that radio resources have to be kept reserved in
`circuit-switched mode during transmission gaps. In GPRS radio resources are only assigned
`by the BS when needed to receive/transmit packet data by an MS, whereby the PDC is
`referenced in packets transmitted. GSM control channels and GSM protocols are used in
`GPRS for association of an MS to the network. Before an MS may transmit/receive packet
`data, establishment of the PDC between SNDCP entities of MS and SGSN, see Figure 3b, to
`be extended by the GPRS Tunnel Protocol (GTP) to the GGSN is also required. The PDC
`specifies the functions of a layer-2 logical link and relates it to the route of the respective
`layer-3 virtual connection.
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`Sony, Ex. 1011, p.10
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`Virtual connections based on X.25 are introduced by CELLPAC [14], [15] to connect MS and
`IWF, see Figure 3a using GSM signaling, before data packets are transmitted on the packet
`dedicated TCH assigned. Context establishment before data transmission was known before
`GPRS.
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`2.5 Control of two MSs by one DL Control Burst
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`The logical link between MS and BSS operated by the RLC/MAC protocol in Figures 3b
`carries RLC/MAC blocks, see Figure 8 and is known as GPRS Temporary Block Flow (TBF)
`identified by the TBF Flow Identity (TFI) carried in the block. TFI is unique among concurrent
`TBFs in a cell and replaces the complete GPRS MS identity known as Temporary Logical
`Link Identity (TLLI). Packet Transmission is performed in layer-3. In layer-2 segments of
`packets are transmitted as RLC/MAC blocks that we call packet data here.
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`The control burst (CB) transmitted in CELLPAC on PCCH has two sub-bursts, each
`comprising (1) 1 bit for uplink state indication (USI), (2) 8 bit identification of the packet data
`context by a ‘MS Random Number’ (MRN), (3) 6 bit for time advance info for slot
`synchronization, (4) 5 bit for power level and (5) 1 Paging Bit (PB), see Figure 7 [15]. The
`next and following UL slots for packet data transmission may be assigned to an MS by a
`control sub-burst with {USI=1, PB=1}. An MS may be informed to receive in the next and
`following DL slots packet data by a control sub-burst with {USI=1, PB=0}. Further, a MS may
`be paged to show-up to the BS by setting {USI=0, PB=1} to transmit a random access burst.
`UL channel reservation for packet data in CELLPAC by setting {MRN, USI=1, PB=1}
`functionally corresponds to the Uplink State Flag (USF) in GPRS. DL channel reservation for
`packet data by setting {MRN, USI=1, PB=0} corresponds to TFI in GPRS. RLC/MAC data
`blocks in GPRS carry both USF and TFI, see Figure 8. Data packets destined for MSs are
`queued by the BS.
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`Figure 7: Packet Control Channel (PCCH) on DL of CELLPAC [15]
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`A PCCH CB in CELLPAC may provide control to two different MSs. The RLC/MAC header in
`GPRS, Figure 8, carries USF and TFI that also may address two different MSs.
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`CELLPAC [15] anticipates control of two MSs by one DL control message as used in GPRS.
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`Since the PCCH may be dynamically placed by the BS on any DL time slot of the CELLPAC
`multi-frame not reserved as a fixed DL control channel [15], consecutive DL slots may be
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`Page 11 of 19
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`Sony, Ex. 1011, p.11
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`used to transmit a PCCH message with interleaving depth four as known from GSM control
`messages.
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`Figure 8: GPRS DL radio link control (RLC) data block
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`2.6 Random Access to a Control Channel on the PDCH
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`The GSM RACH is a request channel located by GSM 51-multi-frame at fixed positions in
`time on an UL slot. The GPRS packet random access channel (PRACH) is an UL control
`channel provided on both fixed and dynamically chosen positions of a PDCH. The RAB in
`GSM and GPRS has the same format and channel coding, with small differences in the
`meaning of the information carried.
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`The GSM RAB carries a random number used by the BS as a temporary MS address to
`assign it a bidirectional circuit-switched signaling channel for connection establishment, in
`response. In GPRS during association the random number is used like in GSM, but for
`establishing a virtual connection. In GPRS another random number is used by the BS during
`a Temporary Block Flow (TBF) as a temporary MS address to assign it on UL one Radio
`Block to communicate either its TLLI address and radio resource requirements (in two-phase
`access), or its address and packet data (one-phase access).
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`CELLPAC [14] describes the one-phase access of GPRS where the slot assigned by the BS
`may not be the next slot in time. The access p