BR5.5 - SF10420 V2.1 1/2 Siemens AG 2004 Technical modifications possible. Issued by the Information and Communication Networks Technical specifications and features are binding only insofar as they are Hofmannstrae 51, D- 81359 Mnchen specifically and expressly agreed upon in a written contract.

Mobile Communication System GSM900 GSM -R GSM1800 GSM1900/24 GSM1900/30 Phase 1 Phase 2 Phase 2+

BR5.5 SF10420 V2.1

Base Station Subsystem General Packet Radio Service (GPRS)

Long Descrip tion BTS BSC LMT TRAU OMC-B NMC Tool Set

In General Today a number of wireless data services are available, but none are as innovative as the data service for GSM networks called General Packet Radio Service (GPRS). GPRS refers to a high-speed packet data technology. The most important aspects of GPRS are:

Data transmission speeds of up to over 100 Kbps Packet-based technology

Support of the world's leading Internet communications protocols, Internet Protocol (IP) and X.25

Always online Volume-based billing

Example Packet data technology provides a seamless and immediate connection from a mobile PC

to the Internet or corporate Intranet allowing all existing Internet applications such as E-mail and Web browsing to operate smoothly without even needing to dial into an Internet service provider via a fixed line (see Figure 1).

The advantage of a packet-based approach is that GPRS only uses the medium, in this case the radio link, for the duration of time that data is being sent or received. This means that multiple us-ers can share the same radio channel very efficiently. Since many applications have idle periods during a session, with the packet data technology users will only pay for the amount of data they actually transfer, and not the idle time. In fact, with GPRS, users could be "virtually" connected for hours at a time and only incur modest connection charges.

Figure 1: From a mobile PC to the Internet v ia GPRS

While packet-based communication works well with all types of communications applications, it is especially well-suited for the frequent transmission of small amounts of data ("bursty" data trans-

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fer), such as E-mail. But packet transmission is equally well-suited for large batch operations, and other applications involving large file transfers.

Customer Benefits GPRS is a service for both bursty and bulky data transfer. The main benefits for the operator are as listed below:

new business opportunities on the market with tremendous growth potential

better cost to bandwidth ratio

effective use of radio resources direct access to packet data networks, e.g. the Internet (with faster access)

optimized transfer media for frequent point -to-point transmission of small data volumes

reliability

scalability integrated services, Operation and Management

future-proof technology, GPRS principles as the basis of future networks higher data transfer rates,

cost reduction due to volume-dependent charging, new applications enabling real plug and play.

With the new GPRS, the customer is able to go an evolutionary step towards UMTS, the third generation of mobile communications. Siemens GPRS hardware is suitable for the new UMTS networks.

Improvement of Quality of Service The following features are designed to improve the QoS:

Delay Class Quality profiles varying over a wide range have been defined for data transmission (GSM Rec.02.60). For the QoS, the Delay Class is an important attribute. In BR5.5, the Best Effort class is supported.

Operation and Maintenance The O&M functionalities, as offered for the SBS, are supplemented with the management of the BSS part of the GPRS network. The management principles for switch-oriented GSM services are equally valid for packet-oriented GPRS services.

The O&M functions for GPRS are equally available from an LMT and from the OMC -B. The indi-vidual network elements of the BSS are accessed from the Radio Commander for management purposes via the existing O interface and the BSCs.

With the introduction of GPRS, the network provider is able to:

verify the correct dimensioning of the GPRS network (for short- and long-term planning) check the parameters of the GPRS network planning

provide fine-tuning of the GPRS network configuration parameters determine the QoS and performance of the GPRS network

To this end, new performance measurements have been introduced. This measurement set sup-plies information on the following functionalities and may be used to confirm and optimize the GPRS configuration parameters in the network:

GPRS radio access

radio resource usage radio resource reassignment

dynamic allocation and de-allocation of GPRS radio resources packet queuing

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used coding schemes

Performance measurements and counters GPRS's flexibility concerning transfer rates and radio assignment influenced and improved per-formance measurements. The PPCU (new board for the Gb interface between the BSC and the SGSN) is responsible for all GPRS traffic -related tasks in the BSC, e.g. access control, radio channel management or PDCH scheduling, and is also responsible for carrying out the GPRS performance measurements. The following measurements are available for GPRS:

Dynamic allocation / de-allocation of GPRS radio resources

There is no fixed number of radio resources allocated to GPRS traffic. Furthermore, the distribution of packet -switched and circuit-switched traffic is made dynamically. The num-ber of PDCHs can increase to an operator-defined maximum of 8 and decrease to an op-erator-defined minimum (0 is also possible as minimum). Additional PDCHs can be allo-cated if the number of mobile stations on a single PDCH exceeds a given operator de-fined threshold (two thresholds, one for uplink and one for downlink), or if the number of PDCHs allocated within the cell is not sufficient to fulfill the MS capability in terms of the number of channels that can be handled in uplink and downlink. A PDCH is de-allocated if CS needs resources in order to serve new calls or if the PDCH is not used for an operator defined timer. To provide the operator with information on how to set these thresholds appropriately, the following measurements are available:

NAVPDTCH - Min/max/mean number of available (configured) PDTCHs per cell (3 counters, counter types: real)

AALPDTT - All available PDTCH fully allocated time per cell' (1 counter, counter type: du-ration, unit: seconds)

Initiation of a GPRS connection by a mobile station

To supervise the establishment of a GPRS connection, the following measurements are available:

TASAGPRS - Number of attempted GPRS accesses per cell (1 counter, counter type: in-teger) TASUGPRS - Number of successful GPRS accesses per cell (1 counter, counter type: integer)

Resource reassignment

The BSS can change the radio resources of an existing GPRS connection. This change can be an addition of uplink resources while downlink is running (concurrent TBF) or vice versa. Handling concurrent TBF can result in an addition of PDCHs, ending a concurrent TBF can result in the removal of PDCHs. The resource reassignment is carried out by a message on PACCH. The measurements related to these reassignment procedures are: NATPRRE - Number of attempted packet resource reassignment procedures per cell (1 counter, counter type: integer) NSUPRRE - Number of successful GPRS accesses per cell (1 counter, counter type: in-teger)

Packet retransmission In case a GPRS packet (i.e. Packet Data Unit PDU) is not received correctly (uplink by the BSS or downlink by the mobile station), the sender is notified by a message. The sender is then able to retransmit the failed PDUs. (There is no similar mechanism in circuit-switched connections.) The measurement for counting these retransmissions is:

NRETPDU - Number of retransmitted PDUs (uplink / downlink) (2 counters, counter type: integer)

Paging

In GPRS, paging is possible in three different ways. It can be performed by using sub-channels of CCCH, PCCCH or PACCH. The measurements related to paging are:

NATGPPAG - Number of attempted GPRS paging procedures (1 counter, counter type: integer)

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NSUGPPAG - Number of successful GPRS paging procedures (1 counter, counter type: integer)

Throughput measurements

Throughput measurements provide the operator with the appropriate information transmit-ted through an interface, in Kbytes/s. The result of these measurements can easily be taken to check whether the system is close to its upper level of capacity. The following throughput measurements are available:

MUTHRF - Mean user data throughput (uplink / downlink) per cell on the RF interface (2 counters, counter type: mean throughput)

MSTHRF - Mean signaling data throughput (uplink / downlink) per cell on the RF inter-face (2 counters, counter type: mean throughput)

MUTHBS - Mean user data throughput (uplink / downlink) per cell on the BSSGP inter-face (2 counters, counter type: mean throughput) MSTHBS - Mean signaling data throughput (uplink / downlink) per cell on the BSSGP in-terface (2 counters, counter type: mean throughput)

Allocated PDTCH This measurement gives the mean number of PDTCHs for a GPRS connection per cell. (There is no analogous measurement for TCHs.) MEALPDCO - Mean number of allocated PDTCHs per GPRS connection per cell (1 counter, counter type: calculated mean)

BSC processor load

The existing BSCPRCLD measurement will be extended in order to contain not only the processor load on the MPCC and TDPC boards but also on the PPCU boards. This means that this measurement now contains two more counters for each board (4 new in total), one for the prime time and one for the total time. Just like in the case of the MPCC and the TDPC, the values are provided by the operating system. Just like in the case of the MPCC and the TDPC, the values are provided by the operating system.

Improvement of Resources Management GPRS enables more efficient frequency usage on the air interface: radio resources are used on demand only. It offers shared use of physical radio resources, thus increasing the number of sub-scribers per channel. By channel combining and the use of new coding schemes, GPRS offers higher user data rates.

Timeslot combining GPRS enables high data rates by combining several timeslots. According to the recommenda-tions (GSM Rec. 02.60, 03.60, 03.64) up to 8 timeslots may be combined for one user. The PDCH distribution is dynamically managed depending on instantaneous traffic conditions and service requests, in order to serve traffic spots and traffic peaks when and where necessary. Up to 7 timeslots may be allocated on a BCCH carrier or as well up to 8 timeslots using dif fer-ent carriers than BCCH.

Channel coding

Channel coding was strongly modified for GPRS (GSM Rec.03.64). ETSI defined 4 new chan-nel coding schemes (CS1 to CS4).

In BR5.5, the CS1 and CS2 channel coding schemes will be used. Theoretically, CS1 allows the transmission of 9.05 Kbps and CS2 allows 13.4 Kbps. In practice, given excellent radio conditions, CS1 enables data transmission rates of up to 8 Kbps, and CS2 up to 12 Kbps. CS1 is especially suited for safe coding of the RLC / MAC data and control blocks. Channel coding starts with splitting the digital information into blocks to be transferred. These so-called radio blocks, i.e. the blocks before coding, consist of:

MAC header RLC / MAC signaling block or RLC data block

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Block Check Sequence (BCS) Data loss of the radio blocks is prevented with convolutional coding. Furthermore, channel coding comprises interleaving, i.e. that the radio blocks are interleaved to a certain number of bursts / burst blocks.

New logical channel types The packet-switched traffic provided by GPRS is much more suited for data transfer than the circuit-switched traffic. Its flexibility concerning transfer rates and assignment of radio re-sources meets the requirements of the bursty nature of data traffic. In GPRS, the physical radio resource is called PDCH. Each PDCH consists of 52 TDMA frames. A mobile station may use more than one PDCH and there is no exclusive use of a ra-dio resource by a mobile station. Whereas in circuit-switched traffic each connection occupies one TCH, in GPR S downlink traffic up to 16 MS may share one physical radio resource (PDCH), and, in uplink traffic up to 8 mobile stations can be handled at a time, since one TCH is required by the PRACH. This is implemented by the definition of different logical channels (PDTCHs) in one PDCH. Thus, in addition to the existing TCH and SDCCH, GPRS introduces new logical channel types in the connection between the mobile station and the BSS (Um interface):

PBCCH group:

- Packet Broadcast Control Channel (PBCCH) to transmit sy stem information to all mobile stations in a cell (downlink)

PCCCH group:

- Packet Random Access Channel (PRACH) to initiate packet transfer or to an-swer to paging messages (uplink)

- Packet Paging Channel (PPCH) to page an MS prior to downlink packet transfer (downlink)

- Packet Access Grant Channel (PAGCH) to send resource assignment in packet transfer establishment (downlink)

PTCH group:

- Packet Data Traffic Channel (PDTCH) to transfer data (uplink / downlink) - Packet-Associated Control Channel (PACCH) to transfer signaling information

(uplink / downlink)

Additional Business New subscriber groups can be reached, since GPRS allows completely new applications. It opens the way for the operator to participate in the tremendous growth of Internet -based services (Internet access, establishing Intranets). Furthermore, GPRS provides a means for new mobile applications and services (e.g. Telematic, E-commerce, etc.)

Example: For business users, GPRS enables a data connection with the office wherever they go, so

that they can have access to E-mail, the Internet, their files, faxes and other data wher-ever and whenever it is needed, giving them a competitive advantage and more flexible lifestyles.

GPRS is expected to profoundly alter and improve the end-user experience of mobile data com-puting, by making it possible and cost-effective to remain constantly connected, as well as to send and receive data at much higher speeds than today. GPRS will complement rather than replace the current data services available through today s GSM digital cellular networks, such as circuit-switched data and Short Message Service (SMS).

Additional Revenue Additional revenue may be obtained through new applications and new data subscribers.

Functionality

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GPRS is an integral part of GSM Phase 2+. It provides a direct high-speed radio access to Packet Switched Data Networks (PSDN). It defines four new Coding Schemes (CS1 to CS4; in BR5.5, the BSS handles CS1 and CS2) and uses channel combining to enable higher data rates and more network efficiency . As a packet-oriented service, GPRS is suited for all applications requiring both bulky and bursty data transfer. Thus, GPRS is an ideal solution for Internet applications, e.g. E-mail.

GPRS Features The SBS design introducing GPRS, as implemented in the GPRS initial phase (BR5.5), took spe-cial care to:

keep SBS flexible and modular, avoid resource waste,

minimize the operators' investments, provide overnight service, and

ensure good performance. In line with this concept GPRS offers the following features:

New logical channel types In GPRS, the physical radio resource is called Packet Data Channel (PDCH). A mobile station may use more than one PDCH, and there is no exclusive use of a radio resource by a mobile station. Up to 8 mobile stations may share one PDCH. This is implemented by the definition of different logical channels, so-called Packet Data Traffic Channels (PDTCHs) in one PDCH.

Thus, in addition to the existing Traffic Channel (TCH) and Stand-alone Dedicated Control Channel (SDCCH), GPRS introduces new logical channel types in the connection between the mobile station and the BSS (Um interface):

Packet Broadcast Control Channel (PBCCH) group: - PBCCH to transmit system information to all mobile stations in a cell (downlink)

Packet Common Control Channel (PCCCH) group:

- Packet Random Access Channel (PRACH) to initiate packet transfer or to an-swer to paging messages (uplink)

- Packet Paging Channel (PPCH) to page a mobile station prior to downlink packet transfer (downlink)

- Packet Access Grant Channel (PAGCH) to send resource assignments in packet transfer establishment (downlink)

Packet Transfer Channel (PTCH) group:

- Packet Data Traffic Channel (PDTCH) to transfer data (uplink / downlink) - Packet-Associated Control Channel (PACCH) to transfer signaling information

(uplink / downlink) One PACCH is associated with one or more PDTCH(s) concurrently assigned to a mobile station and is allocated to one of the physical channels of the related PDTCH(s). In the case of half duplex / fixed allocation mobile stations, a PACCH block downlink is sent during a three (optionally two) timeslot gap in the uplink allocation on the PACCH; with this type of mobile station no data will be sent downlink in the time-slot preceding (optionally following) and during uplink PACCH timeslots.

Support on CCCH and PCCCH To provide GPRS services, the present GSM radio interface supports new logical and physical channel types. The functionality is similar to that required by normal GSM traffic: GPRS Common Control Channels (CCCHs) are among those logical resources whose similarity to normal GSM CCCHs allows the compatibility with actual physical CCCHs. It is therefore pos-sible to support GPRS common signaling either on already existing CCCHs (shared CCCHs) or on GPRS-dedicated CCCHs (PCCCHs).

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Shared CCCH There are no GPRS-dedicated control signaling channels, so that GPRS common control sig-naling packets access a CCCH in accordance with its mapping rules. This mechanism is mandatory whenever a dedicated CCCH is not allocated. The messages are carried in the LAPD related to the BTSE. The channel is routed via switch-ing matrix to a PPLD where the LAPD protocol is processed. The extracted messages are read by TDPC via Telephonic Bus from the PPLD Dual Port RAM. In the TDPC, the messages are analyzed: GPRS-related messages are written by TDPC via Telephonic Bus to the Dual Port RAM of the Peripheral Packet Control Unit (PPCU), where they are processed. Dedicated CCCH (PCCCH) PCCCH is mapped in the multiframe of a PDCH. In this case the common control signaling is carried on a logical channel dedicated to GPRS traffic. The messages are carried in a TRAU frame of the 16 Kbps timeslot related to the physical PDCH where the dedicated CCCH is mapped. The timeslot is routed via switching matrix di-rectly to the PPCU, where the channel is processed. To avoid GPRS signaling load on "normal" CCCHs, it is recommended to use PCCCHs as soon as GPRS traffic increases, so that GPRS signaling traffic has no influence on normal signaling and the overall traffic capacity is improved. The advantages of using PCCCHs are straightforward:

On the air interface, CCCH performance for normal GSM traffic is not reduced because of GPRS messaging.

On the Abis interface, the capacity of the LAPD link is not shared between GSM and GPRS traffic.

The TDPC does not waste real time to route GPRS messages toward PPCUs and to mul-tiplex in LAPDs the messages received from the PPCUs.

The Telephonic Bus is relieved in both directions from the message exchange between PPLD, PPCU and TDPC.

On the other hand, shared CCCHs are supported to provide the first access when no GPRS channels are allocated. Besides, shared CCCHs are the only way to allow Class B mobile stations attached to GPRS to listen to their Circuit-Switched Paging channel on CCCH.

PDCH handling PDCHs are the physical channels dedicated to GPRS packet data and signaling traffic. They are organized in a multiframe structure carried by a timeslot (see Figure 2).

B 0 B 1 B 2 x B 3 B 4 B 5 x B 6 B 7 B 8 x B 9 B 1 0 B 1 1 x

B 0 - B 1 1 = R L C b l o c k s c o m p o s e d b y 4 b u r s t x = i d l e f r a m e s

5 2 m u l t i f r a m e n u m b e r

Figure 2: PDCH multiframe structure

The radio blocks from B0 to B11 are allocated to PCCCHs and PTCHs according to the fol-lowing rules:

1. The blocks are put in a logical order according to the following list of blocks: B0 B6 B3 B9 B1 B7 B4 B10 B2 B8 B5 B11

2. The BCCH indicates the PDCH containing the PBCCH. The PBCCH is allocated downlink to the first block of the list. The next 1 to 3 blocks of the list can be allocated to additional PBCCHs (the total PBCCH block number reported by BS_PBCCH_BLKS parameter, broadcast in the first PBCCH).

3. Additional PDCHs containing PCCCHs are indicated in the PBCCH: On these PDCHs, the first BS_PBCCH_BLKS blocks of the list are used for PDTCH or PACCH in the downlink.

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4. On any PDCH with PCCCHs the next BS_PAG_BLKS_RES (broadcast in PBCCH, from 0 to (12 - BS_PBCCH_BLKS)) blocks of the list are used downlink for PAGCH, PNCH, PDTCH or PACCH.

5. The remaining blocks of the ordered list can be used to carry PPCH, PAGCH, PNCH, PDTCH or PACCH.

6. On the uplink of a PDCH containing PCCCHs, blocks can be used as PRACH, PDTCH or PACCH (PRACH are identified by the Uplink State Flag USF=FREE).

7. Optionally, the first BS_PRACH_BLKS (broadcast in PBCCH) blocks of the list are used only for RACHs.

8. On PDCHs not containing PCCCHs, all blocks can be used as PDTCH or PACCH. 9. In any case, the current usage of a block is indicated by the message type.

Master / Slave Concept and Capacity on Demand Concept The flexible and dynamic allocation / de-allocation of radio resources allows for efficient radio resource sharing between circuit-switched and packet -switched services. Therefore two basic concepts are used within GPRS:

Master / Slave concept This concept uses a master channel, which is a more or less statically allocated channel containing the GPRS CCCH, and one or more dynamically allocated slave channels carry-ing the user data.

Capacity on Demand concept

With this concept, the network dynamically allocates capacity from the common pool of all radio resources depending on the number of GPRS mobile stations (MS), their data amounts, multislot capabilities and requested Quality of Service (QoS).

An optimized radio resource management mechanism also allows the use of resources due to the gaps between two consecutive circuit-switched connections.

Timeslot combining Timeslot combining allows the use of applications which need more throughput than that achieved by using one timeslot only, and enables the operator to speed up simultaneous data transmission for several users. A maximum of 7 timeslots can be combined using a single BCCH carrier or as well a maximum of 8 timeslots using other carriers than BCCH. Timeslot combining supports all MS multislot classes from 1 up to 29.

Channel Coding CS1 and CS2 on PDTCH The introduction of GPRS into the networks in GSM Phase 2+ requires a modification of cur-rent channel coding. Four channel coding schemes (CS1 to CS4) are specified. For the first GPRS release, the CS1 and CS2 coding schemes are implemented. CS1 and CS2 differ in the number of transmitted data bits. (Please note that CS3 could add only 10 % performance both for throughput and spectrum ef -ficiency, while CS4 works in specific radio environments only.)

CS1 implements the basic coding for the RLC / MAC data and control blocks. The maximum net data throughput performed by CS1 is about 8 Kbps under good radio conditions and changes slowly as function of the C/I ratio. CS2 provides a higher data throughput (a maxi-mum net data throughput of 12 Kbps) in good radio environments, the changes are more de-pendent on the C/I ratio. The initial coding scheme for downlink is based on a default value, which is anchored in the data base of the BSC. This initial value can be handled by O&M commands, and the default value is prescribed by the operator. The initial value in the database works per cell class.

Support of 11 data bit packet random access burst on PDCH In the current GSM, the burst carrying the random access uplink message contains 8 informa-tion bits. Evaluations have shown that this limitation is a bottleneck.

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To avoid this bottleneck, an 11 information bit random access uplink message has been de-fined. The new 11 bit random access request message allows more frequent one phase ac-cess instead of two phase access. In the one phase access procedure, an immediate channel assignment message assigning a suitable channel allocation follows directly after the random request message, whereas in a two phase access procedure an additional signaling step is necessary to find a suitable chan-nel allocation. The 11 information bit random access request message speeds up the call set -up and there-fore decreases the signaling load, which makes the GPRS call duration quite short in com-parison to circuit-switched connections and, enables more frequent call set -ups.

Power Control Power control is important for spectrum efficiency as well as for minimizing power consump-tion in the mobile stations. In order to minimize the impact on the existing frequency plans when introducing GPRS, the amount of interference power generated is kept at a minimum. The present GSM radio interface supports uplink and downlink power control, based on re-ceived signal level and received signal quality measurements during continuous two -way con-nections. This mechanism is not applicable to the unbalanced bursty nature of data communi-cations. Therefore, new power control mechanisms are introduced as standardized by ETSI, which fulfill the GPRS requirements. In BR5.5, MS open loop power control will be supported. The algorithm is based on parameters configured by the customer. The specified algorithm (GSM 5.08, Annex B) is implemented at the MS side as follows:

PMS = G0 GCH - a*(C+48) PMS is the output power at the MS side.

G0 equals 39 dbm for GSM 900 and 36 dbm for DCS 1800.

GCH is an operator-dependent parameter set on the PTPPKF object. Its value is calculated to reach a target value for received uplink signals at the BTS.

a is a constant system parameter broadcast on PBCCH or on BCCH. C is the downlink signal level received at the MS side.

Quality of Service (Best Effort) The GSM standards define a Quality of Service (QoS) for data transmissions over the network for GPRS. The QoS is divided into four Delay Classes, the predictive classes Class1 to Class3 and the non-predictive Class4, the so-called "Best Effort" class. BR5.5 supports Class4 (Best Effort), thus providing an optimum of spectrum efficiency and being best suited for Web access.

Operation and Maintenance Functionality The Operation and Maintenance (O&M) functionality as provided for the SBS system is en-hanced to cover the management of the BSS part of the GPRS network. This means that all general management principles applicable to the GSM circuit-switched connections are also valid for the GPRS packet -switched connections. The O&M functions for GPRS are available from the Local Maintenance Terminal (LMT) as well as from the OMC-B. From there, the ex-isting O interface is used for management purposes. With the introduction of GPRS in the network, the operator is able to:

verify the correct dimensioning of the GPRS network (short - and long-term planning)

examine the GPRS network planning parameters

fine-tune the GPRS network configuration parameters identify the QoS and performance of the GPRS network

Performance Measurements In order to check the GPRS network performance, new performance measurements have been introduced. This set of measurements provides information on the following functional-

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ities and can be used to verify and optimize the GPRS configuration parameters in the net-work:

GPRS radio access Radio resource usage

GPRS radio resource reassignment Dynamic allocation and de-allocation of GPRS radio resources

Packet queuing Used coding schemes

Possible Applications One way the user can benefit from GPRS is by the packet nature of GPRS, which makes a GPRS connection similar in many ways to a local area network (LAN) connection. Just as with a LAN connection, once a GPRS mobile station registers with the network, it is ready to send and receive packets.

Example:

A user with a laptop computer could be working on a document without even thinking about being connected, and then automatically receive new E-mail. The user could decide to continue working on a document, then half an hour later read the E-mail message and reply to it. All this time the user has had a network connection and not once had to dial in (as s/he must today with circuit-switched connections). Furthermore, GPRS allows for si-multaneous voice and data communication, so the user can still receive incoming calls or make outgoing calls while in the midst of a data session.

Since there is almost no delay before sending data, GPRS is ideally suited for applications such as extended communications sessions, E-mail communications, database queries, dispatch, and stock updates to name just a few. In addition, the high throughput of GPRS will overcome many obstacles in the use of graphical Web-based applications in multimedia. For example, mobile users will have easy access to graphically intensive Web-based map applications to get directions while traveling. GPRS meets the needs of most data applications in a wide range. The following point -to-point applications will be possible:

Mobile Internet / Intranet access with corresponding applications Traffic guide and information systems

General information services (e.g. stock exchange, tourist information)

Entertainment

Mobile Office Field sales / service

Group call-based services (e.g. stock information)

Wireless access to databases

Mobile Internet access Electronic commerce

Point of sale

Electronic banking

Electronic cash

Messaging Fleet management

Security / supervisory systems

Telemetry

Reservation systems (e.g. hotel, theater, and flights) Highway charging systems

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Impacts on BSS GPRS is based on the existing GSM network infra structure, i.e. it introduces an overlaying archi-tecture on the existing one with the definition of new entities and new interfaces. In the BSS, the Packet Control Unit (PCU) located in the BSC is a new network component for the BSS. In addition, the Channel Codec Unit (CCU) is a new BTS extension, which is easily in-stalled via software download. In detail, GPRS has the following impacts on the BSS:

BSC The GPRS network structure as standardized in SMG requires a new interface in the BSC to-wards the Serving GPRS Support Node (SGSN) / Gateway GPRS Support Node (GGSN), the so-called Gb interface. This is caused by the fact that with the GPRS functionality packet -oriented data transfer and new protocols have to be handled in the otherwise circuit-switched BSS. In the BSS, this new interface is implemented by so-called Peripheral Packet Control Unit (PPCU) cards, which are plugged into the BSC rack as additional units. The PCU is scalable in steps of 64 channels per PPCU and can handle a maximum of up to 128 GPRS channels per BSC.

TRAU In the BSS, no change of the TRAUs, neither in hardware nor in software, is necessary for the use of GPRS.

BTS In the BSS, GPRS requires no hardware upgrade at all for the BTSs: The GPRS-relevant CCU components can be introduced by simple software download.

Therefore, upgrade of a complete network for GPRS capability does not require any service staff at BTS sites, which constitutes an enormous advantage in terms of time, cost and man-power.

Implementation GPRS includes certain BSS modifications:

linking of the BSS to the new GPRS Support Nodes (GSN) via the Gb interface, that is the installation of a PCU

transmission of the packet data through the BSS

the new channel coding schemes, i.e. the implementation of the CCU

combining of physical channels to achieve high transmission rates via the Um radio inter-face

BSC Due to the packet -oriented data transfer as well as the appropriate protocols that are now also handled in the BSS, the GPRS network structure has been provided with a new interface to the SGSN / GGSN. In the SBS, this interface is implemented with the PCU, i.e. PCU cards are inserted into the BSC rack.

BTSE No hardware modification is required for the BTSE. This way, GPRS is supplemented with the CCU by simple software download.

TRAU The TRAU requires neither hardware nor software changes.

LMT The terminal assigned to the SBS for the local operation and maintenance of the SBS network elements gets O&M functions added to manage the new HW and SW elements.

Entity Implementat ion Impact

MS Must support GPRS by providing the respective protocols and functions

TRAU No impact

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BSC Must be extended by adding the PCU, which handles the GPRS protocol stack and functions

BTS Must be extended for GPRS by software download

OMC Must support GPRS

LMT Must support GPRS

Table 1: Implementation impacts on network entities

Network Compatibility One of the major aspects defining the GPRS standard was to minimize possible effects on the ex-isting GSM network infrastructure. With BR5.5, the effects could be reduced to the extension of only two network elements:

PCU for the BSS to reflect the new GPRS Gb interface onto the Abis interface, and the

CCU in the BTS.

Performance Through the use of GPRS, the existing GSM network will be enhanced by packet data services. These services rely on new network elements that will be particularly suited for specific packet switching needs. Since these new network elements are additionally assigned to the GSM network they will relieve the existing circuit-switched GSM data services. This will not only affect the traffic connections but also the signaling channels.

Functional Split between BTS (CCU) and BSC (PCU) The management of GPRS radio channels and the protocol stack conversion between the Gb and Abis interfaces is carried out by the PCU. The PCU is implemented in the BSC and is inter-faced to several CCUs located in the BTSs, as outlined in Figure 3:

GPRS functions implemented in the BTS (CCU) are:

Channel Coding, including Forward Error Correction (FEC) and interleaving Radio Channel Measurement, including received quality level, received signal level, and

timing advance measurement information Mapping of GPRS data and signaling on the Abis interface toward the BSC

BSC

SGSNPCU

GbAbisBTS

CCU

CCU

BTS

CCU

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CCU

CCU

Figure 3: CCU and PCU location

GPRS functions implemented in the BSC (PCU) are:

Mapping of GPRS data and signaling on the Abis interface towards the BTS MAC and RLC layer handling

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Packet Data Unit (PDU) assembly and segmentation

PDCH RLC Automatic Request (ARQ) functions (i.e. based on MS request ACK / NACK), including buffering and re-transmission of RLC blocks

Scheduling functions for PDCH data transfer

BSS GPRS Protocol (BSSGP) support

Layer 1 (Frame Relay) protocol support on the Gb interface toward SGSN via dedicated link or embedded via Asub interface

Setup and release of GPRS resources on the Abis (Um) interface upon request

PCU MAC layer functions

PDCH multiframe management

Multiframe synchronism (via bit in the PCU frame) Data and control signaling multiplexing based on a scheduling mechanism and on users'

demand The USF sent in the PCU frame allows one MS to transmit in the next uplink radio block. On PCCCHs 7 MSs can be multiplexed, the eighth USF value means that the uplink radio block is free to be used as a RACH burst. On PDCHs not carrying PCCCHs up to 8 MSs can be multi-plexed.

Timing Advance (TA) management

When the BTS receives a Packet Channel Request message in a (P)RACH, it computes the TA and sends both the result and the request to the BSC in a PCU frame or in an LAPD mes-sage. The relevant Packet Resource (Immediate) Assignment will notify the MS of the proper TA.

After this initial TA estimation, the TA will be updated continuously by the BTS. The BTS is able to control the TA of the MSs without the intervention of the BSC. Broadcast information on PBCCH

If PBCCH exists, GPRS cell parameters will be broadcast on it. Power Control

MS Power Control uplink is implemented. Coding Scheme selection

The Coding Scheme applied in a cell is an O&M condition. CS-1 will always be used for PACCH, PBCCH, PAGCH, PPCH, and PNCH. The information about the Coding Scheme to be used is reported in the PCU frame.

Dynamic GPRS channel allocation

Active MSs are associated dynamically with one Temporary Frame Identifier (TFI) and one USF upon resource assignment. Downlink packets are accepted by an MS if the MS TFI and the packet TFI match. The USF contained in downlink packets identifies the MS allowed to transmit in the relevant uplink packet.

PCU RLC layer functions Segmentation and re-assembly of LLC-PDUs into RLC data blocks

Backwards Error Corrections (BEC) procedures to allow selective re-transmission of un-correctable errored frames (Automatic Retransmission Request, ARQ)

Packet acknowledge / not acknowledge (ACK / NACK)

The transfer of RLC data blocks can take place both in a reliable Acknowledged Mode and in a faster Unacknowledged Mode. When the Acknowledged Mode is used, temporary / final Packet ACK / NACK messages are transmitted on the PACCH to the remote peer to report the status of the reception process. Transmitted RLC blocks are numbered through a Block Se-quence Number (BSN).

Temporary Frame Identifier (TFI) management In the PACKET DOWNLINK ASSIGNMENT message, the PCU assigns a TFI to an MS, the assigned TFI identifying the Temporary Block Flow (TBF) on a direction. The same TFI value may be used concurrently for TBFs in opposite directions. Upon reception of a final PACKET

BR5.5 - SF10420 V2.1 14/33

ACKNOWLEDGMENT message from the MS (last data block received successfully), the TFI may be used for other users.

PCU LLC layer functions

The PCU has the responsibility of relaying the LLC layer between the RLC and the BSSGP. A buffering function is able to compensate LLC-PDU frame peaks.

In LLC, for every cell queues are allocated for 4 QoS priority levels and one queue for signal-ing (in BR5.5, no QoS classes are supported, the transmission is of "Best Effort" type).

PCU BSSGP layer functions Bi-directional data flow control One LLC-PDU is mapped in one UL-UNITDATA PDU and vice versa one DL-UNITDATA PDU is mapped in one LLC-PDU.

Downlink queues are managed via flow control procedures.

Paging request handling At this level, paging requests issued by the SGSN through a PAGING PS PDU are managed in the PCU.

Flushing of old data queues (e.g. when an MS changes the BSS) In case a link with an MS is interrupted (e.g. because the MS goes Out of Coverage), the

reception of a FLUSH-LL PDU from an SGSN shall f lush all LLC-PDUs stored in the PCU. Queued BSSGP signaling (e.g. Pages) is not affected.

Multiple level 2 link management

Use of RLC/MAC level information to build BSSGP PDUs and invoke RLC / MAC opera-tions using BSSGP information.

PCU Frame Relay (Network Service) functions Permanent Virtual Connections (PVC) management

A PVC is identified via a Bearer Channel Identifier (corresponding to the physical link, e.g. a 64 Kbps timeslot in a 2Mbps PCM link) and a Data Link Control Identifier (DLCI, addressing f ield in the header of an FR frame).

Load sharing management Network Service-Service Data Units (NS-SDU) are distributed over NSVC on the Gb interface, in order to distribute traffic load and reorganize the traffic after of a failure. Frame Relay support

Protocols and Interfaces In the BSS, GPRS data are carried from the BTS to the SGSN over the Abis and Gb interfaces according to the stack protocol described in Figure 4.

Um interface The PDCH is the physical radio interface within GPRS. It differs in channel coding, multi-frame structure and MS multiplexing mechanisms from a circuit-switched traffic channel. On the Um interface, the common channels Random Access Channel (RACH), Paging Channel (PCH), and Access Grant Channel (AGCH) can be shared for channel requests, paging and assign-ment commands between GPRS and circuit-switched connection services. GPRS traffic is transferred over timeslots taken from the common TCH pool.

Abis interface On the Abis interface, GPRS data and RLC / MAC-associated signaling are mainly transferred via 16 Kbps channels in frames of a fixed length of 320 bits, i. e. in so-called PCU frames (an extension of the existing TRAU frames). RLC / MAC signaling sent over shared control channels is logically multiplexed in the LAPDs between the BTSs and the BSCs. Inband signaling and GPRS traffic are encapsulated in PCU frames by the BTS.

Gb interface The Gb interface connects the BSS, i.e. the PCU, to the GSN via Frame Relay protocol (FR), allowing the exchange of signaling information and user data, also in a multi-vendor environ-ment. In contrast to the A interface, where a user is provided with a certain physical resource

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for the duration of the entire connection, a resource on Gb is only assigned when active (while data are being sent or received).

The Gb interface is implemented as either a dedicated PCM link towards the SGSN or as an embedded bundle of timeslots of the Asub interface, which are transparently routed via the TRAU to the SGSN. Figure 4 shows the protocol stack that is used for data transmission in the GPRS network.

GSM RF

MAC

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IP/X.25/CLNP

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Figure 4: GPRS protocol stack

Data packetData packet

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Hdr HdrFCS FCS Hdr FCSInfo Field Info Field Info Field

Data packet (encrypted & compressed)

Hdr HdrFCS FCS Hdr FCSInfo Field Info Field Info Field

Burst Burst Burst Burst Burst Burst Figure 5: Data Flow between several protocol layers on the MS and SGSN.

The layers carry out the following functions:

GSM RF The GSM RF is the physical radio channel used to transfer packet data.

MAC The Medium Access Control provides the access to the physical radio resources. It is respon-sible for the physical allocation of a PDTCH.

RLC The RLC layer provides a reliable link over the air interface that fits the block structure of the physical channel. Therefore it segments and re-assembles the LLC frames. Additionally, it performs sub-multiplexing to support more than one mobile station by one physical channel, and channel combining to provide up to 8 physical channels to one mobile station.

LLC The Logical Link Control (LLC) layer provides a logical connection between the mobile station and the SGSN even if no physical connection is established. The physical connection is set up by the RLC / MAC layer when there are data to be transmitted.

BSSGP The BSSGP is used to transfer the LLC frames together with related information between the SGSN and the PCU. Such information includes QoS and routing information.

SNDCF The Sub-Network Dependent Convergence Function (SNDCF) performs the following tasks:

BR5.5 - SF10420 V2.1 16/33

Encryption

Compression

Segmentation / re-assembling

Multiplexing / de-multiplexing of signaling information and data packets. The encryption function is used to support data privacy, whereas the compression and seg-mentation functions are performed to limit the amount of data transferred by the LLC layer.

Higher layers The higher layers are not within the scope of GPRS because these layers are independent of the underlying network.

Functional Description GPRS provides the mobile subscribers with means for services like point -to-point data transfer. In detail, these are:

High system availability because of an extensive and improved system maintenance con-cept and maintenance functions

Support of the standardized Gb interface Support of subscriber mobility including Routing Area update and cell update

Support of the paging function to find subscribers at unknown locations

Support of GSM security functions (authentication) for protection against misuse and fraud

Support of the acknowledged and unacknowledged logical link control operation mode, which allows the usage of multi-purpose applications

For the operator, GPRS offers the following functionality:

High system availability because of an extensive and improved system maintenance con-cept and maintenance functions:

- The consistency of data within the system is checked by audit programs which will be running periodically or on demand. By detecting errors, the applications will be re-quested to correct the data and audit symptom data will be collected.

- Collecting of symptom data in the case of error detection in software applica-tions.

- Escalation to higher recovery levels in the case of frequent software errors. - Different recovery levels are defined. A recovery can also be requested manually

by the operating personnel. Depending on the recovery level, data are initialized and OS resources are released.

- The start -up info service holds information about the software state of the proc-essors within the system.

The operator is able to manage - the network resources and network changes,

- the data specific for the GPRS network nodes, - the parameters of the different protocols that are used for GPRS. The list below gives an overview of the data that are managed by the configuration manage-ment:

- Management of connections to other entities (e.g. from SGSN to the PCUs)

- Management of internal connections between components

- Management of office and project data - Own entity functions and own entity address

Standardized Gb interface according to GSM Support of GSM security functions to prevent misuse and fraud

Support of two LLC modes (acknowledged and unacknowledged), hence the adaptation to different applications.

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Support of a reliable transmission via the logical link.

Support of the simultaneous use of up to 4 different independent data links. Support of the transport of the L3 signaling data packets.

Implementation

PCU and CCU The GPRS features within the BSS are implemented in two functional units:

The PCU located in the BSC provides resource allocation and protocol conversion be-tween the BTS and the SGSN. The PCU acts (just like the BSC) as a statistical multi-plexer and router (see Figure 6). It receives RLC packets from the Abis channel related to more than one mobile station and packs them into LLC frames. These LLC frames are then routed to the SGSN and vice versa together with other LLC frames coming from other Abis channels.

The PCU is one unit composed of two cards named Peripheral Packet Control Unit (PPCU). While the first card provides service, the second one is in cold standby. Each BSC can include two PCU units. In this case, the traffic is divided statically to both units by means of configuration settings. The CCU performs channel coding functions and channel measurement functions.

PCU The PCU is a functional unit within the BSC that provides resource allocation and protocol conversion between the BTS and the SGSN. Looking at the protocol stack, the PCU is re-sponsible for:

Channel Access Control functions, e.g. access requests and grants PDCH scheduling functions for uplink and downlink data transfer

Radio Channel Management functions, e.g. power control, congestion control, broadcast control information, etc.

PDCH RLC ARQ functions, including buffering and re -transmission of RLC blocks

LLC layer PDU segmentation into RLC blocks for downlink transmission RLC layer PDU re-assembly into LLC blocks for uplink transmission

BSSGP protocol provides PCU SGSN communication in terms of BVCI (BSSGP Virtual Connection Identifier)

Network Service functions provide PCU SGSN communication in terms of Virtual Chan-nel (Network Service Virtual Channel NSVC)

CCU The functions inside the CCU are:

Channel coding functions, including FEC and interleaving

Radio channel measurement functions, including received quality level, received signal level and information related to timing advance

Continuous Timing Advance PCU frames are transferred across the Abis interface every 20 ms (fixed length of 320 bits).

TDPC

PCU

PCU Frame PCU Frame

PCU Frame PCU Frame

Abis Gb

LAPD

Frame Relay

SGSN BSC

BR5.5 - SF10420 V2.1 18/33

Figure 6: PCU as multiplexer and router

PCU and PPCU Internal Structure In order to introduce the GPRS service in the SBS, a new unit has been designed to support packet data interworking between the Gb and the Abis interfaces. The evaluation of the feasibility study phase has revealed that the amount of messages exchanged between the Gb and the Abis interfaces needs a dedicated processing resource in order to avoid capability losses in normal GSM traffic. The new PPCU unit will be inserted in the BSC rack instead of PPLDs, as can be seen in Figure 7. The internal physical connections are represented in Figure 8. The BSC can be configured with a maximum of two PCUs (each one redounded).

PCU-0 PPCU-0 replaces PPLD-15 (not used on the BSC) in the frame. PPCU-1 substitutes

PPLD-12. PPLD-14, PPLD-13, and PPLD-11 are removed from the frame.

PCU-1 PPCU-0 substitutes PPLD-8 in the frame, and PPCU-1 replaces PPLD-9.

PPLD-10 and PPLD-7 are removed from the frame. The new layout of the BSC module can be seen in Figure 8. The capacity of each PCU is se-lected via O&M commands in terms of bandwidth reserved on the Abis and Gb interfaces. The minimum bandwidth allowed, the sum of the Abis and Gb interfaces, is 32 * 64 Kbps which means that 4 PPLDs are removed from the system and replaced with two PPCU (0/1) cards.

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Figure 7: The BSC module without GPRS (left) and ready for GPRS (right)

BR5.5 - SF10420 V2.1 19/33

S N

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LICD 0 PPLD 3 PPLD 4 PPLD 5 PPLD 6

PPCC 0 PPCC 1 PPLD 0 PPLD 1 PPLD 2

PPLD 11 PPLD 12 PPLD 13 PPLD 14

PPLD 7 PPLD 8 PPLD 9 PPLD 10

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PPLD 11 PPLD 12 PPLD 13 PPLD 14

PPLD 7 PPLD 8 PPLD 9 PPLD 10 PCU 1

PCU 0

Figure 8: Internal BSC physical connections

Table 2 shows the capacity reduction in terms of LAPD channels with GPRS introduction, both for the SN16 and SN64 network cards.

Card No. of PCU No. of LAPD channel

SN 16 0 112

o r 1 80

SN 64 2 48

Table 2: Number of LAPD channels

The maximum number of LAPD channels is obtained by retaining the PPLD-11 frame. The amount of data traffic handled by the PCU depends on the number of Kbps reserved for the PCU unit on the internal connection between SN16 (or SN64) and the PCU.

Access On the air interface, the cell structure organization remains the same as in the actual implementa-tion. An additional identifier is introduced to group the cells supporting GPRS service in the Loca-tion Area (LA). This information is named Routing Area (RA) which can be less than or equal to the LA. One LA can include more than one RAs. The mobile stations with access to GPRS service receive information on the service in the Sy s-tem Information (SI) messages on the BCCH channel. SIs 3 and 4 are modified in order to insert parameters for GPRS. The new SI 13 is sent on the air interface carrying all parameters for GPRS network access.

In GPRS service, there is no handover: When the mobile station leaves one cell, it starts a cell re -selection procedure. The RR links are disconnected and a new access operation is started. The integrity and sequence of data is handled in the RLC layer.

BR5.5 - SF10420 V2.1 20/33

Channel Configuration The packet data logical channels are mapped onto the physical channels that are dedicated to packet data. The physical channel dedicated to packet data traffic is called PDCH. For GPRS, three types of channels have to be considered:

Packet Data Traffic Channel (PDTCH)

Packet Broadcast Control Channel (PBCCH)

Packet Common Control Channel (PCCCH) All channels described above are allocated on the BCCH TRX. This ensures that radio planning allows maximum cell power.

PDCH channels are "normal" TCH channels allocated, on demand, to a GPRS service. Up to 8 mobile stations can be multiplexed on one PDTCH channel. If a service requires more bandwidth, it is possible to allocate to it up to 7 PDTCHs. This way, these channels are allocated to the same mobile station and they have the same ARFCN, MAIO, HSN, and TSC. PBCCH and PCCCH are semi-permanent channels configured with O&M commands. The PDTCH allocation is handled by LV3 Radio, i.e. the master in the radio resource allocation. For each PDTCH, a network connection must be set up in order to connect one 16 Kbps on the Abis interface with one 16 Kbps PDT on the PCU unit. By request of the PCU, the TDPC releases the PDTCH channel.

The PBCCH and PCCCH have a semi-permanent connection between one Abis 16 Kbps and one PDT. The radio channels allocated to the PCCCH and PBCCH can no longer be used for normal speech traffic. The BCCH information is also replicated in the PBCCH if it is active in the cell to allow circuit-switched operation, even if the mobile station is monitoring the PBCCH only. In other words, the PBCCH works like a second BCCH for mobile stations supporting GPRS.

The PCCCH works like the CCCH in normal operation and as PBCCH - if it is active in the cell - it also carries the information about circuit-switched operation.

Network Service Control The Sub-Network Service ent ity provides communications service to Network Service Control peer entities. The peer-to-peer communication across the Gb interface between remote Network Service Control entities is performed over Network Service Virtual Connections (NSVC). The Network Service Control takes care of the end-t o-end NSVCs communication between the PCU and the SGSN. The Network Service Control entity is responsible for the following functions:

NSDU transmission The Network Service Data Units (NSDUs) are transmitted on the NSVCs. The NSDUs are en-capsulated in the Network Service Control PDUs, which in turn are encapsulated in the Sub-Network Service PDUs. On each NSVC, data are transferred in order.

Load sharing

The load sharing function distributes the NSDU traffic among the available (i.e. unblocked) NSVCs.

NSVC management A blocking procedure is used by an NS entity to inform an NS peer entity when an NSVC be-comes unavailable for NS user traffic. An unblocking procedure is used for the reverse opera-tion. A reset procedure is used between peer NS entities in order to set an NSVC to a deter-mined state, after events resulting in possibly inconsistent states of the NSVC on both sides of the Gb interface. A test procedure is used to check whether an NSVC is operating properly be-tween peer NS entities.

When the Sub-Network Service entity detects that an NSVC becomes unavailable (e.g. DLCI fail-ure detection) or when the NSVC becomes available again (e.g. DLCI failure recovery), the Net-work Service Control entity is informed.

Quality of Service

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GSM 03.60 currently specifies five different attributes within the QoS profile associated with each PDP context. These attributes are:

Precedence class Delay class

Reliability class Peak throughput class

Mean throughput class During the QoS profile negotiation between the mobile station and the network, the mobile station can request a value for each QoS attribute; the network always attempts to provide adequate re-sources to support the negotiated QoS profile.

For an uplink data transfer, the QoS profile is communicated by the mobile station as priority in-formation in the PACKET_CHANNEL_REQUEST message. For a downlink data transfer, the BSSGP provides the means to transfer the full QoS profile together with each downlink LLC PDU from the SGSN to the BSS, which is the controller of the media utilization on the radio interface. In the lat -ter case, the following QoS parameters are included in each LLC-PDU transferred to the BSS:

Precedence class

Peak throughput

LLC-PDU lifetime Taking into account the available radio resources and the multislot capabilities of the mobile sta-tion, the PCU decides if and how the requested QoS may be satisfied. This means that the core algorithm of the PCU would try to satisfy the requested QoS by acting on many factors , for exam-ple changing the coding scheme on the air interface (CS2 has more transfer capacity than CS1), allocating more radio resources (capacity on demand), reshuffling subscribers in the available PDCHs according to the mobile station multislot capabilities, delay of the subscriber according to the subscriber priority, etc. In the first phase of GPRS, the QoS supported is the so-called Best Effort. This means that the PCU main scheduler queues the mobile stations requests without considering the QoS attributes.

PCCCH and PBCCH Channel Allocation To introduce GPRS in the GSM network, new channel types have been specified. The PBCCH works like a secondary BCCH in the supporting GPRS cell. The PCCCH works like a secondary CCCH in the supporting GPRS cell. Both the PBCCH and PCCCH are recognized only by mobile stations supporting GPRS. These two channel types are allocated on the BCCH carrier, and no hopping is admitted for these channels in the SBS. To create these channels means to create a semi-permanent connection between the Abis 16 Kbps channels and one 16 Kbps PDT in one PCU.

These channel types can be handled by adding a new parameter to the CHAN creation command in order to specify the combination used for the GPRS channel. The PBCCH or PCCCH creat ion can be allowed only if the PTPPKF object is created. The PDT is selected automatically by the system. Since, from the BTS point of view, these channels are managed in a completely different way than the other common control channels, the BTS is notified of the creation of these channels.

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Create ChannelPBCCH/PCCCH

Update Data Baseof MPCC / TDPC

Request NetworkConnection

between Abis /PDT

Send Data Baseto PCU

AllocationPossible

No

Yes

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No

Yes

Choose PDT onserving PCU

CREATENACK

PDTAvailable

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CREATENACK

Send Data Baseto BTS

Request to sendSystem Information

to TL3RD

Figure 9: Logical flow chart of a CREATE PBCCH / BCCCH command

The framing of these channels is managed by the PCU directly. The mobile stations are notified via a SI message on the BCCH channel that these channels are active in a cell. Special SI called Packet System Information (PSI) is sent on the PBCCH and PCCCH. When mobile stations that support GPRS mode are in a cell supporting GPRS service and where these kinds of channels are allocated, they listen to the information broadcast on these channels in-stead of to the one broadcast on the BCCH. Figure 9 represents the logical operational flow to be performed for the allocation of the PCCCH / PBCCH. These channels are created in the "Locked" state, that means that no power can be sent on them until the UNLOCK command is performed. The PCU is informed of the availability of the channels because it needs to know when they can be used. When the channel is working, the channel is transmitting at the power of the BCCH TRX. Locking the PBCCH or PCCCH means to switch off the power at the BTS side and stop using it for paging and access grant on the PCU side. Framing of channel and SI transmission is continued. The GPRS service in the cell can be pro-vided, even if no PBCCHs or PCCCHs are configured or available.

PDCH Channel Allocation Strategy PDCHs are normal channels dynamically allocated for GPRS service. The allocation of a PDCH channel is performed on the BCCH TRX carrier or a different one. The resource allocation / de-allocation is driven by the PPCU software; the channel chosen and the channel activation / re-lease to the BTS is a TL3RD task. The rules for the PDTCH allocation in the multislot configura-tion are as follows:

same frequency hopping law

same training sequence code

same MAIO adjacent timeslot number

a maximum of 8 timeslots allocated per mobile station

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The first three rules must be observed during configuration, which means that all TCHs on the BCCH carrier must abide by the same hopping law and the same training sequence code. The fourth law is observed dynamically for the timeslot selection. If a request for a new PDCH comes from the PCU, the TL3RD tries to allocate a new PDCH adjacent to the previous one. In the case of no free timeslots adjacent to the busy one, the adjacent timeslots are in a stable call state, and there is at least one free channel in the cell, a forced intracell handover is initiated in order to move the call camped in the adjacent timeslot to another one (see Figure 10) using the same rule as the HSCSD. It must be taken into account that HSCSD calls cannot be forced. Because the in-tracell handover procedure doesn't need more than 0.4 sec., no packet queuing notification is sent to the PCU software in order to keep the channel allocation in the standby state. In the case of channel locking (PBCCH, PCCCH, and PDTCH) the PDT and the corresponding radio channels are released to the idle state.

PDT 1

PDT 0TS 0

PBCCH timeslots 0 - 7

BCCH

Busy 1 Busy 2 Busy 3 Busy 4 Free 0 Busy 5

PDT 0TS 0

BCCH

Busy 1 Busy 2 Busy 3 Busy 4 Free 0 Busy 5

Busy 6

OtherChannels

Free 1 Busy 7 Busy 8 Busy 9 Free 3 Busy 0Free 2

Intracell HO tried & successful for busy 3 stable state call

PDT 0TS 0

BCCH

Busy 1 Busy 2 Free 4 Busy 4 Free 0 Busy 5

Busy 6

OtherChannels

Busy 3 Busy 7 Busy 8 Busy 9 Free 3 Busy 0Free 2

PDT 0TS 0

BCCH

Busy 1 Busy 2 Busy 4 Free 0 Busy 5

Busyx : TS allocated to some callFree x: TS not allocatedPDT x: TS used by GPRS-MS

Figure 10: PDTCH multislot strategy allocation when a new PDTCH is requested for the same MS and no adjacent PDTs adjacent to the one in use are free

A maximum of 8 PDCHs can be allocated for each cell; this parameter can be set by an O&M command for each PTPPKF (object PTPPKF, parameter GMANPAL).

The PCU tries to schedule the MS with its maximum TS usage depending on MS multislot class. If there is no PDTCH allocated in one cell and the MS needs to establish a TBF, the PCU must al-locate the maximum number of TSs supported by the MS, if there is at least one TS free on the cell the TBF is accepted; otherwise the TBF is rejected. If another MS needs to setup a TBF and the number of TSs supported are the same or less than those used by the previous MS, the new mobile is allocated to the already allocated TS. If the MS requires more TSs then additional re-quests are sent to the TDPC in order to satisfy the maximum MS capacity and the MS is shared between the already existing TS and the new time slot. In the case of an incoming CS (Circuit Switch) call (Normal Assignment or External Incoming HO, single slot) the following algorithm applies to the cell having no free channel:

If the incoming CS call finds the cell congested, the first thing attempted is to preempt one vulnerable CS call.

If preemption cannot be started for whatever reason (feature not enabled, the incoming CS call has a PCI set to 0, ...) a directed retry is started.

If not even the directed retry can be started (because the feature is not enabled or the fea-ture is enabled but the BTS is sending a condition for an Intercell HO message without a cell list) GPRS preemption is attempted. The GPRS TS having the highest TS number (except some very special cases that only occur when the incoming CS call is half rate

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and GPRS TSs are mixed FULL_RATE_ONLY or FULL_AND_HALF) is selected to be preempted.

If the GPRS preemption cannot be started because no GPRS TS are available (or be-cause of very special cases due to Half Rate CS), the queuing procedure is started.

The following algorithm applies to the case of an incoming circuit switch call (Normal Assignment or External Incoming HO, HSCSD 1+1) to a cell having no free channel:

If the incoming CS call finds the cell congested, the first thing attempted is to preempt one vulnerable CS call.

If preemption cannot be started for whatever reason (feature not enabled, incoming CS call having the PCI set to 0, ...) then a directed retry is started.

If not even the directed retry can be started (because the feature is not enabled) GPRS preemption is attempted. The GPRS TS to be preempted is selected choosing the one with the highest TS number of GPRS assigned TSs (except some very special cases that occurs when the incoming CS call is Half Rate and GPRS TSs are mixed FULL_RATE_ONLY or FULL_AND_HALF).

If not even the directed retry can be started (feature enabled but the BTS sending condi-tion is for an intercell HO without a cell) it is assigned to a normal phase 2 data call (if necessary the GPRS preemption is started for this call).

If the GPRS preemption cannot be started because no GPRS TS are available (or be-cause of very special cases due to Half Rate CS), the queuing procedure is started.

The following behavior applies to normal assignments or external incoming HOs; no GPRS pre-emption is executed in the case of CS internal intercell/intracell HOs because the BTS, when the HO is not managed, repeats the HO indication (same rule used in the existing CS preemption).

System Information Management SIs are regularly broadcast by the network on the BCCH and the busy TCH. SI broadcasts can be grouped in 6 classes as described in GSM 04.07 based on the information they contain. On the basis of this information, the mobile station is able to decide whether and how it may gain ac-cess to the network via the current cell. With the introduction of GPRS, the SI 3 and 4 rest octets are modified, while SI 13 is added. In addition, if the PBCCH is allocated to the cell, new System Information called Packet System In-formation (PSI), required by GPRS, is broadcast on this new logical channel. All mobile stations camping in a GPRS-supporting service cell in which PCCH is allocated, listen to the PSI instead of to the traditional SIs. A GPRS mobile station reading the PCCH can receive non-GPRS paging incoming from the network, because on this GPRS broadcast channel tradi-tional SI is also sent to guarantee this event.

When a mobile station moves to a new cell, it switches to the BCCH. The mobile station listens to the SIs 3, 4, 7 or 8. If the cell does not support GPRS, the mobile station cannot perform packet access to the network. If the cell supports GPRS, the mobile station reads SI 13. A mobile station that has read SI 13 but without first having read SIs 3, 4, 7 or 8 may assume that the current cell supports GPRS service.

System Information 3 and 4 These messages are broadcast on the BCCH. They contain new additional information about supporting GPRS service in the cell.

System Information 13 This message is broadcast on the BCCH only if GPRS is supported in the cell. It indicates:

If the PBCCH is active in the cell: If the PBCCH is not configured, the mobile station in idle packet mode reads SI 13 accord-ing to GSM 05.08. In case the PBCCH is active in the cell, additional SI related to GPRS is sent on the PBCCH.

If SI 1 is necessary for packet access in the cell:

Here, the mobile station is not allowed to initiate packet access until it has obtained SI 1. The availability of SI 13 is sent on the BCCH using the SIs 3, 4 and, if sent, 7 or 8.

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Packet System Information 1 PSI 1 is sent by the network on the PBCCH or PACCH giving information for cell selection, for control of the PRACH, for the description of the control channel(s) and optional global power control parameters. Special requirements for the transmission of this message apply on the PBCCH (GSM 05.02).

Packet System Information 2

PSI 2 is sent by the network on the PBCCH or PACCH giving information on reference fre-quency lists, mobile station allocations and PCCCH channel descriptions applicable for packet access in the cell. A consistent set of these messages is required to completely decode the in-formation.

Packet System Information 3

PSI 3 is sent by the network on the PBCCH or PACCH giving information on the BCCH alloca-tion in the adjacent cells and cell selection parameters for serving cells and non-serving cells. Special requirements for the transmission of this message apply on the PBCCH (GSM 05.02).

Packet System Information 3 bis This optional message is sent by the network on the PBCCH and PACCH giving information on the BCCH allocation in the adjacent cells and cell selection parameters for non-serving cells. If the entire information does not fit into one PSI 3 bis message, the PSI 3 bis message can be repeated. Special requirements for the transmission of this message apply on the PBCCH (GSM 05.02).

Packet System Information 4

PSI 4 is optionally sent by the network on the PBCCH and PACCH giving information for di-recting the mobile station to make measurements on a list of serving cell PDCHs, during the idle frame of those PDCHs. Special requirements for the transmission of this message apply on the PBCCH (GSM 05.02).

Packet System Information 5

This optional message is sent by the network on the PBCCH or PACCH giving information for measurement reporting and network -controlled cell reselection. If the entire information does not fit into one message, the remaining information will be sent in the PSI 5 bis message. The message is sent on PBCCH only if so indicated in PSI 1.

Packet System Information 5 bis This optional message is sent by the network on the PBCCH or PACCH giving information for measurement reporting and network -controlled cell reselection. If the entire information does not fit into one message, the remaining information will be sent in the PSI 5 bis message. The message is sent on PBCCH only if so indicated in PSI 5.

Packet System Information 6 PSI 6 is sent by the network on the PBCCH giving information for scheduling of the PBCCH messages.

In GSM networks, SI formatting is carried out by the TDPC, which sends them to the BTS to be broadcast on the cells after having updated all SIs. In GPRS / GSM networks, PSI, with the PCCCH active in the BSS area, must also be broadcast, again supported by the TDPC.

For this reason, the TDPC reads all parameters needed by SI 1 to SI 13 and by PSI 1 to PSI 6 from its own database. After having formatted all / only -modified PSI, the TDPC sends them to the PCU which broadcasts the PSI on the air.

Paging Management If in packet idle mode for mobile stations supporting GPRS the PCCCH is active in the serving cell, the mobile station listens to the PBCCH and to the corresponding paging sub-channels. If the PCCCH is not active in the considered cell, the mobile station listens to the BCCH and to the corresponding paging sub-channels.

Paging sub-channels are, in any case, monitored according to the paging groups determined for the mobile station in packet idle mode (defined in GSM 05.02) and its current DRX mode (defined in GSM

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04.60 and GSM 05.02). Paging for GPRS is performed in the Routing Area (RA) instead of in the LA as in standard GSM (A RA is defined for a GPRS cell and represents a cluster of cells; it is contained in an LA). Moreover, if a mobile station is in transfer mode, it can be paged in the cell where it is camping.

GPRS-Paging Using Paging Sub-channel on the CCCH

This type of paging is used to send paging information to mobile stations in idle mode and in packet idle mode if the PCCCH is not active in the cell. Three types of paging messages can be broadcast on this channel:

PAGING REQUEST TYPE 1

PAGING REQUEST TYPE 2 PAGING REQUEST TYPE 3

as described in GSM 04.07. Paging request messages can include more than one mobile sta-tion, as well as priority levels related to the mobile station identification.

For GPRS, just as for the well-known standard GSM service, a paging channel in combination with DRX can also be organized. If a mobile station chooses to use the DRX mode (as indi-cated in Classmark), it indicates to the network to which additional paging groups it listens, which allows acceptable access delay and/or acceptable battery consumption and/or the QoS needed by the application. A mobile station using DRX is only required to monitor the PCH blocks belonging to its paging group in the same way as in GSM 05.02. A mobile station not using DRX is required to monitor every PCH block on the same CCCH as for DRX.

Paging reorganization is supported in the same way as for circuit-switched GSM. The internal network message flow is as follows:

The SGSN, knowing how to use the DRX, sends a paging message to all PCUs support-ing the proper RA. This message includes the information whether or not the DRX is used and, through the SPLIT_PG_CYCLE parameter, if the enhanced DRX mechanism is used.

The PCU forwards the PACKET PAGING REQUEST message combined with the re-quested paging parameters over the internal interface to the BSC.

The BSC calculates the proper paging group and forwards, per LAPD connection, the PACKET PAGING REQUEST messages to the paging queues inside the BTS. Addition-ally, the BSC evaluates all needed DRX parameters which have to be broadcast on the BCCH.

The BTS queues all PACKET PAGING REQUEST messages and sends them, sorted by first-in first-out, on the PCHs in the CCCH multiframe.

GPRS-Paging Using Paging Sub-channel on the PCCCH

This type of paging is used to send paging information to mobile stations in packet idle mode if the PCCCH is active in the cell. The initiation procedure and paging request are specified in GSM 04.60. A mobile station using the DRX is required to monitor the PPCH. A mobile station not using the DRX is required to monitor every PPCH block on the same PCCCH as for the DRX.

Paging reorganization may be supported in the same way as for circuit-switched GSM. The internal network message flow is as follows:

The SGSN, knowing how to use the DRX, sends a paging message to all PCUs located in the proper RA. This message includes the information whether or not the DRX is used and, through the SPLIT_PG_CYCLE parameter, if the enhanced DRX mechanism is used.

The PCU calculates the proper paging group and adds all PACKET PAGING REQUEST messages on its paging group queues. Additionally, the PCU evaluates all needed DRX parameters which have to be broadcast on the PBCCH.

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The PCU includes the PACKET PAGING REQUEST messages into the RLC / MAC blocks and schedules the messages into the PDCH multiframes which contain the PCCCH. The RLC / MAC blocks are transferred via TRAU frames to the BTS, which transmits the PACKET REQUEST message immediately.

GPRS-Paging Using Paging Sub-channel on the PACCH

This type of paging is used to send paging information to mobile stations in packet transfer mode, if the PCCCH is active in the cell. The initiation procedure and paging request are specified in GSM 04.60.

GPRS Mobile Classes and Crossed-paging Types Three classes of GPRS mobile stations are defined:

Class A Simultaneous and independent execution for both circuit-switched and GPRS operation is possible. Therefore, the class A mobile station uses two independent receivers / transmit-ters. (The class A mobile station is a typical high-end MS.)

Class B

Simultaneous execution of circuit-switched and GPRS operation is possible, but the qual-ity of service of a GPRS operation may decrease in the case of a pending or established circuit-switched connection. The minimum requirement is sequential support of the ser-vices, whereas the mobile station must be able to monitor the CCCH. (The class B mobile station is a typical all-purpose MS.)

Class C Alternate use of circuit-switched and GPRS operation is possible. The mobile station sup-ports either GPRS operation only or both circuit -switched and GPRS operation. In the lat-ter case, only one service at a time is available by default or manual pre-selection. That means, a class C mobile station is either a GPRS or a non-GPRS mobile station. (The class C mobile station with exclusive GPRS capability is a typical low-cost MS for GPRS supporting a particular application.) Therefore, the introduction of GPRS in the GSM networks introduces a new concept in the management of paging message transmission, because a class A or B mobile station can be paged during data packet transfer for a traditional speech call or vice versa. In the case of a class A mobile station, no problems will arise because the two calls can be managed independently. In the case of a class C mobile station, no problems are ex-pected because it supports only one mode at a time. In the case of a class B mobile station, it is necessary to perform different actions than the ones carried out till now.

GPRS-Paging to Class B Mobile Stations During Speech Calls If, in a BSS, a paging message arrives from an SGSN node for a class B mobile station busy in a circuit-switched (originating / terminated) call, it is necessary that the PCU asks the TDPC to perform paging to the addressed mobile station. Since the mobile stations position in the RA is known, the TDPC scans the list of the cells belonging to the addressed RA and sends a paging message on the PCH channel to each of them.

The addressed mobile station reads the paging message and can decide whether to stop the conversation and start normal procedures for this case,

ignore to read the paging and continue the current speech call, or

put on hold the current conversation, switch to GPRS as long as data are transferred and, afterwards, switch back to non-GPRS mode to retrieve the first call.

Paging a Class B Mobile Station During Data Transfer Mode

If, in a BSS, a paging message arrives from an SGSN node for a class B mobile station busy in a circuit-switched (originating / terminated) call, it is necessary that the PCU asks the TDPC to perform paging to the addressed mobile station. Since the mobile stations position in the

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RA is known, the TDPC scans the list of the cells belonging to the addressed RA and sends a paging message on the PCH channel to each of them. The addressed mobile station reads the paging message and can decide whether to

stop the conversation and start normal procedures for this case,

ignore to read the paging and continue the current speech call, or put on hold the current conversation, switch to GPRS as long as data are transferred and,

afterwards, switch back to non-GPRS mode to retrieve the first call.

Paging a Class B Mobile Station in a GPRS-supporting Cell in Standby State If, in a BSS, a paging arrives from the MSC for a class B mobile station while it camps in a cell supporting GPRS and is in standby state so its LA is known , the TDPC needs to scan the list of the cells belonging to the addressed LA. Then, for each cell belonging to the addressed area and in which a PCCCH is not allocated, the TDPC sends a paging message on the PCH, while for each cell in the addressed area and in which a PCCCH is allocated, it asks the PCU to perform a paging. The PCU then broadcasts a paging message on the PPCH for each of the indicated cells. The addressed mobile station reads on the paging channel, listens to the paging message sent, and can switch back to non-GPRS mode to begin normal procedures to obtain a circuit-switched connection for the time required by the conversation and, finally, switches back to GPRS if the cell where it is located again supports this service.

Uplink Access to the Network by Mobile Stations Access to the GPRS network uses a slotted-aloha protocol and is performed by sending a tradi-tional 8 bit access burst type (GSM 05.01). In line with the ETSI specifications, a new enhanced access burst type with 11 information bits can be sent by the mobile station to attempt access to the GPRS network. It depends on the network whether this one or the other message is used: the capability of the network to receive messages of 8 or 11 bit length is broadcast by the ACCESS_BURST_TYPE SI parameter that indicates the permitted access length; the 8 bit length is called one phase access method and the 11 bit length two phase access method.

In the one phase access, the PACKET CHANNEL REQUEST is answered by the network with the PACKET IMMEDIATE ASSIGNMENT reserving the resources on PDCH(s) for uplink transfer of a number of radio blocks. This reservation is carried out according to the information on the requested resources that is comprised in the PACKET CHANNEL REQUEST. On the RACH, there is only one cause value available for denoting GPRS and the network can only assign uplink resources on 1 or 2 PDCH(s) or two different priorities. One phase ac-cess on PCCCH and CCCH is used in the case of paging response, cell update, and MM procedure, as well as in all cases where the MS need not send more information than the MS class and priority.

In the two phase access, the PACKET CHANNEL REQUEST is answered with the PACKET IMMEDIATE ASSIGNMENT which reserves the uplink resources for transmitting the PACKET RESOURCE REQUEST. The PACKET RESOURCE REQUEST message carries the complete de-scription of the requested resources for the uplink transfer. This message is already sent on the assigned PDCH(s) in the PACKET ASSOCIATED CONTROL CHANNEL (PACCH). This channel is a transparent link between the mobile station and the PCU. If the number of PDCH(s) in the cell needs to be increased, the PCU requests additional channels from the BSC. Afterwards, the PCU responds on the PACCH with the PACKET RESOURCE ASSIGNMENT reserving resources for the uplink transfer. Two phase access on PCCCH and CCCH is used in the case of data transfer in unacknowledged mode as well as in all cases described for one phase access when additional information needs to be carried in the access phase.

The mobile station is always able to override the one phase access by sending the PACKET RESOURCE REQUEST on the assigned resource to initiate the two phase access. The PACKET IMMEDIATE ASSIGNMENT message includes the Timing Advance (TA) and Power Con-trol (PC) information. If there is no response to the PACKET CHANNEL REQUEST within a pre-defined time period, the mo-bile station initiat