WALKE_LAYOUT_Layout 10/21/13 3:47 PM Page 12
`
`SPECIAL SECTION ON TELECOMMUNICATIONS HISTORY
`
`THE ROOTS OF GPRS: THE FIRST SYSTEM FOR
`MOBILE PACKET-BASED GLOBAL INTERNET ACCESS
`
`BERNHARD H. WALKE, RWTH AACHEN UNIVERSITY
`
`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 ran-
`dom 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 sys-
`tem, dynamic placement of control channels to
`the packet data channel and statistical multiplex-
`ing 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.
`INTRODUCTION
`The General Packet Radio Service (GPRS) was
`launched worldwide in 2001 as a service provid-
`ed 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 Univer-
`sal Mobile Telecommunications System (UMTS)
`and 4G system Long Term Evolution (LTE).
`
`EARLY CONCEPTS FOR
`WIDE AREA MOBILE DATA NETWORKS
`The architecture of a Public Land Mobile Net-
`work (PLMN) is shown in Fig. 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 Net-
`work (CN), and comprises multiple Base Sta-
`tions (BSs) each serving a radio cell connected
`star-shaped to a Base Station Controller not
`shown in the figure. In the core network, mobili-
`ty supporting functions are found like Subscriber
`Register (SR) responsible for roaming, authenti-
`cation and billing of MSs, and switching nodes
`dedicated to circuit- and packet-switched ser-
`vices, respectively. Gateway Circuit-/Packet-
`Switched Exchange nodes hosting Interworking
`Functions (IWFs) shown in Fig. 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 cur-
`rent 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 previ-
`ous cell. Advanced PLMNs besides roaming also
`support handover for keeping service quality of a
`MS when communicating on the move. Han-
`dover provides continuation of communication
`within and across cells with small service inter-
`ruption, only.
`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 typical-
`ly do not provide cellular radio coverage, roam-
`ing 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.
`The network elements shown in Fig. 1 have
`its own protocol stack for both control and user
`data exchange. PLMNs differ much in the proto-
`col 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 exis-
`tence or status, management of the mobile ran-
`dom-access to the uplink (UL) channel by
`
`12
`
`1536-1284/13/$25.00 © 2013 IEEE
`
`IEEE Wireless Communications (cid:129) October 2013
`
`Sony, Ex. 1012, p.1
`
`

`

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`
`Access network
`
`Core network
`
`Other networks
`
`Cell 1
`
`MS
`
`..
`
`MS
`
`..
`
`MS
`
`GCSX
`
`PSTN
`o. PLMN
`
`BSS
`
`CSX
`PSC
`
`SR
`
`MS
`
`Cell 2
`
`Radio
`interface
`
`GPSX
`
`PDN
`Internet
`
`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.
`
`BSS = Base station subsystem (base station (BS) plus BS controller);
`CSX/PSX: Circuit-/packet-switched exchange;
`MS = Mobile station;
`GCSX/GPSX = Gateway CSX/PSC;
`SR = Subscriber register;
`PSTN = Public switched telephone network;
`PLMN = Public land mobile network;
`PDN = Public data network
`
`Figure 1. Generic architecture of a cellular mobile radio network (PLMN).
`
`multiple concurrent MSs is a major challenge in
`radio access protocol design. Aloha and slotted
`(S) Aloha are the simplest multiple-access proto-
`cols to a mobile radio channel, but these are
`considered inefficient when used for data trans-
`fer, where MSs contend directly with their data
`messages. In [1] it is shown that radio access
`protocols that combine S-Aloha request chan-
`nels with separate traffic channels can achieve
`very high utilization 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 utiliza-
`tion) then the data channels may be operated at
`high utilization. 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.
`
`Mobile Circuit-Switched Data Networks — Mobile net-
`works 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 kb/s data rate using error correction
`protocols like MNP-10, V.34, and V.42 for reli-
`able 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 pro-
`viding 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 mes-
`sage is transferred. This traffic channel is estab-
`lished between the MS and the Interworking
`Function (IWF) located in the GCSX in Fig. 1.
`Data transmission on top of an underlying
`cellular telephone service has limitations
`imposed by the characteristics of the voice-cir-
`cuit connection. The service might be cost effec-
`tive 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.
`
`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 net-
`works 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.
`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.
`
`IEEE Wireless Communications (cid:129) October 2013
`
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`
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`

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`
`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 communica-
`tion to the MS via a DL
`control channel. The
`PDCH typically is then
`different from the
`contention channel.
`
`Marconi MSs mounted on ships, sharing the
`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 trans-
`mission if no response is received to a message
`sent.
`In 1970 the ALOHANET was opened to con-
`nect 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 sta-
`tion having a data packet ready transmits it on
`the channel to the central host without consider-
`ing any synchronisation or access rule. The pack-
`et also contains identification, control and parity
`check information. Packets sent by different sta-
`tions may partly overlap and collide at the receiv-
`er. A station waits for a time-out to happen or
`for receiving an acknowledgement from the cen-
`tral host. After time-out the packet is retransmit-
`ted 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 over-
`lap of packet transmission of different stations is
`avoided.
`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.
`With the DAMA protocol, user data on UL
`may be transmitted outband (Uo) on a TDMA
`channel different from the shared request chan-
`nel, or inband (Ui) on the shared channel.
`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 chan-
`nel 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 pack-
`et 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 acknowl-
`
`edged by the BS on the corresponding DL chan-
`nel. 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.
`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 realiza-
`tion, respectively, of the implicit reservation
`channel.
`
`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 cellu-
`lar 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 broad-
`cast 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 con-
`firmed by the BS to use the slot that it had used
`for MA for data transmission as a TDMA chan-
`nel in the next and subsequent frames until the
`MS’s data expire.
`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 respec-
`tive region/country.
`The Advanced Radio Data Information Ser-
`vice (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 ser-
`vice connects MSs by radio under control of the
`proprietary Radio Data (RD) Link Access Pro-
`cedure (LAP) offering 8kb/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 man-
`agement 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
`
`14
`
`IEEE Wireless Communications (cid:129) October 2013
`
`Sony, Ex. 1012, p.3
`
`

`

`IWF
`
`Common control
`
`Common traffic channel
`
`Common traffic channel
`
`MS
`
`MS
`
`Figure 2. Packet channel (PCH) reserved for the duration of a packet transfer
`of a single user.
`
`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 intro-
`duced 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 chan-
`nel one by one, see Fig. 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 pro-
`tocol is then not MA at all.
`Improvements to PRMA are proposed in [11]
`by Mitrou (MLP) for an integrated system sup-
`porting both circuit- and message-switching
`voice and data. Slots of a TDMA-frame are ded-
`icated 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 Fig. 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 kb/s data rate.
`Some FDM channels of AMPS carry the connec-
`tion-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
`
`WALKE_LAYOUT_Layout 10/21/13 3:47 PM Page 15
`
`status symbol (CSS) indicating whether the slot-
`ted UL channel is idle or busy. Free UL chan-
`nels 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 trans-
`mits CSS = busy information on DL. DSMA is a
`DAMA (Ui, Dei) protocol. Packet data is trans-
`mitted by concurrent MSs one-by-one (Fig. 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 system was
`introduced by RAM Mobile Data in 1990 it is
`also known as RAM Packet Data Network. The
`RI data rate is 8 kb/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 pro-
`tocol 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 trans-
`mit 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 transmis-
`sion of data of concurrent MSs (Fig. 2).
`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 min-
`islots (four to a slot). 64 byte user data are car-
`ried 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 con-
`trol or data channels. Random access is by S-
`Aloha to a control channel and collisions are
`detected by MSs from absence of an acknowl-
`edgement. 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 Fig. 2.
`
`CELLULAR RADIO INTEGRATING
`CIRCUIT AND PACKET SWITCHING
`Concepts Not Implemented — Local Cellular Radio
`Network (LCRN) [9] is the first to integrate cir-
`cuit-switched digital speech/data and packet-
`
`IEEE Wireless Communications (cid:129) October 2013
`
`15
`
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`

`

`WALKE_LAYOUT_Layout 10/21/13 3:47 PM Page 16
`
`Packet-
`switching
`protocol
`suite
`
`PS
`service
`in CS
`TDMA
`network
`
`DAMA
`protocol
`type
`
`Context
`estab.
`before
`data trx
`
`Dynamic
`placement
`of UL/DL
`control on
`data channel
`
`USF
`function
`
`TA and PC
`for MSs
`sharing a
`TDMA
`channel
`
`Statistical
`mux of
`MSs to
`TDMA
`channel
`
`> 1 MS
`simula-
`tion con-
`trolled
`
`Short ID
`carried in
`control
`and data
`channel
`
`PRMA
`
`ARDIS/
`DSMA
`
`–
`
`(+)
`
`Mobitex
`
`(+)
`
`Cognito
`
`0
`
`LCRN
`
`(+)
`
`–
`
`–
`
`–
`
`–
`
`+
`
`Ui, Dii
`
`Ui, Dei
`
`Ui, Deo
`
`+
`
`+
`
`+
`
`Uo, Deo +
`
`Uo, Deo +
`
`+
`
`–
`
`(+)
`
`+
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`–
`
`0
`
`0
`
`0
`
`+
`
`0
`
`0
`
`Felix [10] 0
`
`MLP [11]
`
`CDPD
`
`(+)
`
`(+)
`
`IS–54/95 +
`
`[17]
`
`(+)
`
`CELLPAC +
`
`GPRS
`
`+
`
`+
`
`+
`
`–
`
`–
`
`+
`
`+
`
`+
`
`–
`
`Uo, Deo +
`
`–
`
`+
`
`Uo, Deo +
`
`Uo, Deo +
`
`Ui, Dei
`
`Ui, Dei
`
`+
`
`+
`
`–
`
`–
`
`–
`
`–
`
`+
`
`+
`
`–
`
`–
`
`–
`
`–
`
`(+)
`
`+
`
`–
`
`–
`
`–
`
`–
`
`+
`
`+
`
`–
`
`–
`
`–
`
`–
`
`+
`
`+
`
`–
`
`–
`
`–
`
`–
`
`+
`
`+
`
`(+)
`
`0
`
`0
`
`(+)
`
`+
`
`+
`
`– : not applicable; 0: not fulfilled; +: fulfilled.
`Table 1. Comparison of proposed/implemented packet-switched data networks.
`
`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.
`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 271kb/s resulting
`in 22.8kb/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 69kb/s.
`It appears that most GPRS Fundaments have
`been first proposed for CELLPAC [13–15] intro-
`ducing packet-switching in GSM. In what follows
`the CELLPAC functions are explained and com-
`pared to GPRS and to other systems known ear-
`lier. 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 intro-
`duce
`
`(cid:129) Packet radio access of GPRS enabled MSs
`without changing GSM layer-1 functions
`implemented in hardware.
`(cid:129) A protocol suite for the network elements of
`the access and core networks to support pack-
`et-switching.
`
`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 proto-
`col stack per network element as introduced in
`[15], which is close to GPRS, see Fig. 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 Fig. 3b, called “Packet Access” in Fig. 3a, and
`Radio Link control (RLC) in Fig. 3b called
`Radio Link Protocol (RLP) in Fig. 3a. In Figure
`3a the MS is split into data terminal equipment
`(DTE) and mobile terminal (MT).
`“Packet Access” protocol data units are trans-
`mitted across the RI in Fig. 3a called RLC/MAC
`data block in GPRS, see Fig. 8. The GPRS stack
`compared to that of CELLPAC is further opti-
`mized to contain the Logical Link Control (LLC)
`protocol, and the Sub-network-Dependent Con-
`vergence 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 estab-
`lished 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 connec-
`
`16
`
`IEEE Wireless Communications (cid:129) October 2013
`
`Sony, Ex. 1012, p.5
`
`

`

`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.
`
`WALKE_LAYOUT_Layout 10/21/13 3:47 PM Page 17
`
`DTE
`
`X.25
`layer 3
`
`LAP-B
`
`LAP-B
`
`X.21
`
`X.21
`
`MT
`L2R
`
`RLP’
`Packet
`access
`GSM
`layer 1
`
`MSC/IWF
`
`X.25
`layer 3
`
`L2R
`
`RLP’
`Packet
`access
`GSM
`layer 1
`
`LAP-B
`
`LAP-B
`
`LAP-B
`
`X.21
`
`X.21
`
`X.21
`
`Application
`IP/X.25
`
`SNDCP
`
`LLC
`
`RLC
`
`MAC
`
`GSM RF
`
`MS
`
`Relay
`BSSGP
`
`RLC
`
`MAC
`
`Network
`service
`
`GSM RF
`
`L1bis
`
`BSS
`
`Um
`
`Scope of GPRS
`
`Um
`
`a)
`
`ISDN/PSDN
`
`SNDCP
`
`LLC
`
`BSSGP
`
`Network
`service
`L1bis
`
`GTP
`
`UCP/
`TCP
`
`IP
`
`L2
`
`L1
`
`SGSN
`
`Gn
`
`Gb
`
`b)
`
`IP/X.25
`
`GTP
`
`UDP/
`TCP
`
`IP
`
`L2
`
`L1
`
`GGSN
`
`Gi
`
`Figure 3. Protocol Suites for a) CELLPAC; b) GPRS.
`
`tion 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.
`Since the packet data rate in early GPRS is
`small (12 kb/s) but Internet application protocols
`like SMPT, HTTP, etc. should be supported, the
`Wireless Application Protocol (WAP) was speci-
`fied 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]. GSM/EDGE with its data
`rate of up to 384kb/s on smart communications
`devices enables Internet application protocols
`more comfortable.
`
`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 real-
`ize a packet radio service. Eight physical TDMA
`radio channels per FDM channel are provided in
`GSM per transmit direction, see Fig. 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 dedi-
`cated TCH. Thereby the GPRS Packet Data Chan-
`nel (PDCH) is anticipated.
`Dedication of some TDMA channels of a cir-
`cuit-switched cellular network for packet-switch-
`ing is known from [9, 10, 12, 18] of which [9] was
`the first to propose this.
`PDCH SHARED BY CONTROL AND USER DATA
`Multi-frames as known from GSM but with dif-
`ferent 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 Fig. 5. The CELLPAC multi-
`frame comprises 26 GSM TDMA frames. In ver-
`tical direction slots 0 to 7 represent the respective
`TDMA frame. TDMA frames 13 and 26 of DL
`and UL, respectively, carry the fixed packet con-
`trol channel (PCCH) on DL and the packet ran-
`dom 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 ran-
`dom access. GPRS specifies a 52 multi-frame.
`Both the GSM control channels for virtual
`connection setup and the CELLPAC dedicated
`TCH are shown in Fig. 6 [15]. The latter com-
`
`IEEE Wireless Communications (cid:129) October 2013
`
`17
`
`Sony, Ex. 1012, p.6
`
`

`

`WALKE_LAYOUT_Layout 10/21/13 3:47 PM Page 18
`
`Frequency/MHz
`
`0
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`7
`
`0
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`7
`
`TDMA frame
`
`4.615 ms
`
`960
`
`935
`
`915
`
`890
`
`0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 ...
`
`Duplex distance
`
`Gap between uplink and
`downlink
`
`3 tail bits
`
`0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 ...
`
`Time slot
`
`Data bits
`
`Training
`
`Data bits
`
`57 bit
`
`26
`
`57 bit
`
`3 tail bits
`
`1 toggle bit
`
`Burst (148 bit)
`
`Time slot (156.25 bit)
`0.577 ms
`
`Figure 4. FDM and TDMA channels in GSM.
`
`Time/ms
`
`1
`
`11
`
`24
`
`26
`
`Frame
`number
`
`Packet control channel
`
`Random access only
`
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`
`13
`
`Packet control channel
`
`Random access only
`
`1 2
`
`3
`
`4 5 6
`7 8
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`Reserved or idle
`
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`Reserved or random access
`
`0
`1
`2
`3
`4
`5
`6
`7
`
`0
`1
`2
`3
`4
`5
`6
`7
`
`Downlink
`
`Uplink
`
`Slot
`number
`
`60 ms
`
`60 ms
`
`Figure 5. CELLPAC multi-frame. “Reserved” means a slot is dedicated as PDTCH.
`
`prises logical control channels (“Access” and
`“Control”) and voice/data channels for packet
`data transmission. The logical channels men-
`tioned 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.
`PACKET DATA CONTEXT ESTABLISHMENT
`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 associa-
`
`tion 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 (Fig. 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.
`Virtual connections based on X.25 are intro-
`duced by CELLPAC [14, 15] to connect MS and
`IWF, see Fig. 3a using GSM signaling, before data
`packets are transmitted on the packet dedicated
`TCH assigned. Context establishment before data
`transmission was known before GPRS.
`
`CONTROL OF
`TWO MSS BY ONE DL CONTROL BURST
`The logical link between MS and BSS operated
`by the RLC/MAC protocol in Figs. 3b carries
`RLC/MAC blocks, see Fig. 8 and is known as
`
`18
`
`IEEE Wireless Communications (cid:129) October 2013
`
`Sony, Ex. 1012, p.7
`
`

`

`Base station
`
`DCCH/RACH
`
`Dedicated TCH(S)
`
`Virtual call setup
`
`Voice/data
`
`Voice/data
`
`Access
`
`Control
`
`DCCH/RACH
`
`Dedicated TCH(S)
`
`Mobile station
`
`Figure 6. GSM dedicated control channel (DCCH) and random access chan-
`nel (RACH) used for virtual call set-up, and dedicated traffic channel (TCH)
`for data transmission in CELLPAC [15]. No cellular packet-switched system
`besides GPRS applies a multiframe for mapping logical control and data
`channels to one TDMA channel as introduced in [15].
`
`Temporary Block Flow (TBF) as a temporary
`MS address to assign it on UL one Radio Block
`to communicate either