Huawei GPRS Network Planning & Optimization.pdf

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Chapter 10 GPRS Radio Network Planning and

Optimization

10.1 GPRS Basic Principles

General Packet Radio Service (GPRS) is a kind of mobile packet data service developing from the existing GSM mobile communication network. GPRS introduces packet switching functional entities to the GSM digital mobile communication network. In this case, the data can be transmitted in terms of packet in a GPRS system. The GPRS system expands the services provided by the original GSM circuit switching system. Therefore, in a GPRS system, mobile users can use packet data mobile terminals to access the Internet or other packet data networks.

The digital cellular mobile communication based on GSM and CDMA as and the packet data communication based on the Internet are the two industries enjoying the fastest growth in information area. Tendency shows that the two industries are coming to integration. The advent of the GPRS takes the first step towards the integration of the mobile communication and the packet data communication.

Currently, while the voice service keeps developing, the 2G mobile communication gradually supports IP and high-speed data services. Moreover, the 3G mobile communication will be also characterized by IP and high data services.

GPRS provides multiple data services, including PTP (Point-to-Point) service, PTM-M (Point to Multipoint Multicast) service, PTM-G (Point to Multipoint Group Call) service, and IP-M (Internet Protocol Multicast) service.

GPRS can be applied in various areas, including E-mail, WWW browse, WAP service, electronic commerce, information query, remote supervisory, and so on.

10.1.1 Network Structure and Functional Entities

The GPRS network supports packet switching and packet transmission, which enables the GSM network to efficiently support data services. As shown in Error! Reference source not found., the GPRS network is an overlay network of the existing GSM network. In the GPRS network, the functional entities, such as Service GPRS Support

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The GPRS network and the existing GSM network share the same BSS system, but the corresponding hardware and software must be upgraded to meet the requirements of GPRS services. Meanwhile, the interfaces of the functional entities of the GPRS network and the GSM network must be properly defined. In addition, the MS must be required to support the GPRS services.

The GPRS network can connect to PSPDN with the help of GGSN. Either the X.75 or X.25 can work as the interface protocol. Moreover, the GPRS network can connect to the IP network directly.

Figure 10-1 GPRS network structure

The following introduces the functions of the equipments related to the GPRS network in detail.

I. GPRS mobile station

z Terminal equipment

The terminal equipment (TE) is a computer terminal operated by users. In the GPRS system, it transmits and receives the packet data of the terminal users. The TE can be an independent computer, or can be integrated with the mobile terminal (MT). To some extent, all the functions provided by the GPRS network enable a packet data transmission path to be established to connect the TE and the external data networks.

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2/27/2009 All rights reserved Page6 of 94 The mobile terminal can communicate with the TE. In addition, it can communicate with BTS through Um interface and establish logical links to SGSN. In a GPRS network, the ME can enjoy the services provided by the GPRS system only when it is configured with related GPRS functional software. During data communication, the MT connects the TE to the Modem in the GPRS system. The functions of the MT and TE can be integrated into one physical device.

z Mobile station

The mobile station (MS) can be taken as the integration of the MT and TE. Physically, it can be either one entity or two entities (TE + MT).

Three types of MSs are available, including type A, type B, and type C. The MSs of type A can perform packet switched service and packet circuit switched service simultaneously. The MSs of type B can be attached to the GPRS network and the existing GSM network, but they cannot perform packet switched service and packet circuit switched service simultaneously. The MSs of type C cannot be attached to the GPRS network and the existing GSM network.

II. BTS

The base station transceiver (BTS) is the wireless part in BSS system. It is controlled by base station controller (BSC) and serves one or more cells.

The functions of the BTS are as follows:

z Realize radio transmission and related control function between the BTS and the

MS through Um interface.

z Fulfill the functions of the Um interface at the first and second layers and

transparently transmit the messages at the third layer.

z Help the BSC to fulfill the functions of the Um interface at the third layer.

III. BSC

BSC is the core controlling part in the BSS system of the GSM network and the GPRS network. For packet switched service, the BSC undertakes the following responsibilities:

z Configure packet radio channels

z Control the conversion of the radio channel between packet switched service and

packet circuited service.

z Provide necessary packet call control support for the cells with no Packet

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Packet control unit (PCU) helps the BSS support the GPRS. Its functions are as follows:

z Manage the major part of the packet radio resources z Control packet calls

z Transmit packet data

z Support Gb interface and Pb interface

V. SGSN

SGSN is a basic network element in the GPRS network. The SGSN is introduced to the GSM network to enable GPRS service. The main function of the SGSN is to forward the packet data for the MSs within the local SGSN service areas, which is similar to the function of the Visited Mobile Switching Center (VMSC) in the GSM circuit network. The specific functions of the SGSN are as follows:

z Forward the packet data and provide the route for all the GPRD MSs within the

local SGSN service areas.

z Provide encryption and authentication z Manage session

z Manage mobility z Manage logical links

z Provide the interface with GPRS BSS, GGSN, HLR, SMS-GMSC, and

SMS-IWMSC.

z Generate the output bills and collect the information of the utilized radio resources.

In addition, the SGSN contains the function similar to that of the VLR in the GSM network. When subscribers are in GPRS attach state, the SGSN stores the information of the subscribers and their location. Similar to VLR, most information of the SGSN subscribers are obtained from the VLR when the subscribers perform location update. VI. GGSN

The Gateway GPRS Support Node (GGSN) is introduced to the GSM network to support GPRS service. It provides the route and encapsulation for the data packets to be transmitted between the GPRS network and the external data networks. Which GGSN is selected as the gateway is decided according to subscribers’ subscription information and access point name (APN) during the PDP context activation. The GGSN provides the following functions:

z Provide the interface to the external data networks.

z Manage GPRS session and establish the communication between the MS and

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z Generate and output bills (it is mainly applied when subscribers use the external

networks.) Note:

The GGSN must provide the interface for the MS to access external packet data networks. From the perspective of external networks, the GGSN can be compared to the router of the IP of all the subscribers in the GPRS network, so it has to exchange the route information with external networks.

VII. CG

Charging gateway (CG) collects, combines, and preprocesses the GSN bills and keeps the communication at the interfaces between billing centers. This equipment does not exist in earlier GSM networks. The bills of the GPRS subscribers are generated from multiple network elements when the subscribers access the network once. Moreover, each network element will generate multiple bills.

Therefore, the CG is introduced to combine and preprocess the bills before they are sent to billing center. As a result, the load of the billing center is eased. In addition, the SGSN and the GGSN do not have to provide the interface to billing center.

VIII. RADIUS

During non-transparent access, the network will authenticate the subscribers’ identities. The Remote Authentication Dial in User Service Server (RADIUS) stores the information of the authentication and authorization of the subscribers. This functional entity is not exclusive to the GPRS.

IX. DNS

Two types of Domain Name Servers (DNS) exist in the GPRS network. One connects the GGSN to external networks. Its main function is to resolve the domain name of the external networks, which is completely equivalent to the function of the general DNS fixed on the Internet. The other one is applied in the GPRS backbone network. It functions in two aspects. One is to resolve the IP address of the GGSN according to the determined APN during the PDP context activation. The other one is to resolve the IP address of the original SGSN according to the original routing area number during the routing area update. The DNS is not exclusive to GPRS.

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In fact, the border gateway (BG) is a router. It provides the route between the SGSN and GGSN in the GPRS network and manages the security. It is not exclusive to the GPRS.

XI. HLR

The home location register (HLR) stores the permanent information of GPRS subscribers. It provides the required data of the subscribers to the SGSN. In addition, it can update the information of the subscribers if necessary and notify the update to the corresponding SGSN. The HLR has the following functions:

z Manage the data of GPRS subscribers

z Manage the information of the location of GPRS subscribers z Authenticate subscribers’ identities

z Recover errors

XII. MSC/VLR

The Mobile Switching Center (MSC)/Visitor Location Register (VLR) can combine the GPRS service and the GSM service with the help of Gs interface. In this case, the MSC /VLR store both the information of the International Mobile Subscriber Identity (IMSI) of subscribers and the related SGSN numbers. The MSC/VLR have the following functions:

z Combine attachment and detachment z Combine location update and route update z Page circuit service

z Prompt non-GPRS in associated status z Request subscriber information

z Indicate mobile information

10.1.2 Service Function and Numbering Plan

In a Public Land Mobile Network (PLMN), the GPRS enables subscribers to transmit and receive data under end-to-end packet transfer mode. Two types of bearer services are defined in GPRS. They are PTP service and PTM service. Based on the standard network protocols supported by GPRS bearer services, GPRS carriers can support or provide subscribers with various telecommunication services. The application of the services provided by GPRS has the following characteristics:

z They are applicable in the transmission of the discontinuous non-periodic (burst)

data. The occurrence interval of the burst data is far greater than its mean transmit delay.

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z They can be applied to process the data service shorter than 500 bytes. In this

case, the data service can occur several times in each second and can be frequently transmitted.

z They can be applied to process the data service of thousands of bytes. In this case,

the data service can occur several times in each hour and can be frequently transmitted.

These characteristics prove that the GPRS is favorable to the application of the burst data services and can efficiently use the channel resources. However, the GPRS network must restrict the huge data services. The reasons are as follows:

z A small amount of data traffic is prescribed in the GPRS network.

The GPRS network is developed from the existing GSM network. Currently, GSM networks mainly provide telephony service. The telephony subscribers are of great intensity and the traffic volume of great, but the intensity of the GPRS data subscribers is relatively low, so only a small number of channels can be applied to the GPRS service in a cell.

z The transmission rate of the data on radio channels is low.

Currently, the CS-1 and CS-2 coding schemes are in general use. They can meet the requirement of carrier-to-interference ratio (C/I) is equal to or greater than 9 dB and ensure 100% (CS-1) and 90% (CS-2) of the GPRS coverage. In this case, however, the transmission rate of the data is only 9.05 Kbit/s (CS-1) and 13.4Kbit/s (CS-2) (including the RLC block header). The reason is that half of the bit rate (CS-1) and one third of the bit rate (CS-2) in the radio link control (RLC) blocks is applied to the forward error correction (FEC). Though this reduces the requirement of C/I, it reduces the transmission rate of the data.

Though the transmission rate of the data under the CS-3 (15.6Kbit/s) and CS-4 (21.4Kbit/s) is relatively high (including the RLC block header), it is enhanced through reducing and canceling the error correction bits, so the CS-3 and CS-4 coding schemes require the C/I to be a greater value. In this case, the CS-3 and CS-4 are applicable in the areas with greater C/I value.

In addition, the number of multislot channels supported by the MS is limited at present, so the GPRS network must restrict the huge data services. Generally, the high data is allowed to occur several times in each hour.

z When the GPRS service and GSM service share channels, the telephony service

takes the higher priority if the channels are dynamically allocated. The two times of conversation gapping of any one dynamically allocated channel can be applied to the GPRS service. For the GPRS system, its packet data channel can be shared by multiple GPRS MSs. That is, multiple logical channels can be reused on one physical channel. Therefore, the GPRS can be particularly applied for the burst data. In this case, the utilization rate of the channels can be greatly enhanced.

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1) PTP data service

The PTP service enables the transmission of one or more packets between two subscribers. Two types of PTP service are available. They are PTP Connectionless Network Service (PTP-CLNS) and PTP Connection Orientated Network Service (PTP-CONS).

The PTP-CLNS belongs to the service type of data diagram. It is mainly applied in bursting non-interacting service and it is supported by the Connectionless Network Protocols (CLNP), such as the Internet Protocols (IP).

PTP-CONS is applied in burst events and interacting application service. It is supported by the Connection Orientated Network Protocols (CONP), such as the X.25.

2) PTM data service

The PTM data service enables single information to be sent to multiple subscribers. It includes the following three types of services.

z PTM-M data service

This service enables the information to be sent to all the current subscribers in an area. It is a kind of one-way communication service, so not all subscribers can necessarily receive the information correctly. The time to provide the packet data and the quality of service (QoS) are decided according to the negotiation of the GPRS carriers and the PTM-M providers.

z PTM-G data service

This service enables the information to be sent to current specific sub-group subscribers in an area. It provides both one-way communication and multi-way communication. The PTM-G data service is particularly used to provide the communication to group data subscribers, so it is mainly used in the areas, such as in the dispatching management of group subscribers, taxi dispatch, group classified information, and special news services.

z IP-M data service

This service is one of the services defined in the Internet Protocols. The information of the data is transmitted among the participants of the IP-M data services. The subscribers in an IP group can be both fixed and mobile IP subscribers. The service areas of IP-M are not restricted in terms of geography, so the IP-M subscribers can be either a group of subscribers in a PLMN or in the Internet.

II. GPRS supplementary service

According to the specifications defined in the ETSI GPRS in SMG#28 earlier, most of the supplementary services for the circuit switched service are inapplicable to GPRS. The supplementary services applicable to GPRS include:

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z Call Forwarding Unconditional (CFU)

z Call Forwarding on Mobile Subscriber Not Reachable (CFNRc) z Closed User Group (CUG)

z Advice of Charge (Information) (AoCI) z Advice of Charge (Charging) (AoCC)

In addition, specific GPRS supplementary services are applicable to GPRS subscribers. Currently, the specific GPRS supplementary service is the “barring GPRS interworking files” service. This service restricts subscribers from accessing external networks with the help of the interworking files activated by barring.

The specifications in the ETSI GPRS in SMG#29 later clearly indicate that the supplementary services are not defined for GPRS.

III. Other service relationships of GPRS and GSM 1) PTP SMS

In the GPRS network, the MS can receive and send short messages.

If the MS is in GPRS attach and IMSI detach state, the short message service (SMS) is provided by the GPRS channel. If the MS is in GPRS attach and IMSI attach state, short messages can be sent both on the GPRS channel and the CS control channel. In this case, the channel priority is decided by carriers. Generally, the radio resources will be more efficiently used if the short messages are sent on the GPRS channel. If the CS control channel is in use, the SGSN will page the MS, and the short messages are sent in this way.

2) Circuit switched service

If both the SGSN and the MSC/VLR supports the Gs interface, and when the SGSN stores the corresponding VLR number and the VLR stores the corresponding SGSN number, a correlation will be established between the SGSN and the MSC/VLR. The correlation functions to coordinate the MSs in GPRS attach and IMSI attach state, and the operation mode is related to the operation mode of the network and the type of the MS. If a GPRS-attached MS enters the circuit switched mode (dedicated mode), it can request the network to suspend the GPRS service. After finishing the circuit switched service, however, it can recover the suspended GPRS service.

IV. GPRS QoS

QoS stands for quality of service. Each PDP context has an independent QoS script related to itself. The GPRS QoS has several attributes, including priority class, delay class, reliability class, peak throughput class, and mean throughput class, and each attribute can be divided into multiple levels. These classes can form multiple GPRS

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Upon subscription, the subscriber subscribes to the defaulted QoS script. During PDP context activation, the MS and the network side renegotiate the QoS script. The MS can request a different QoS from the subscribed one.

Because all the attributes cannot be exclusive to the end-to-end transmission of the packet data, especially because many factors, such as the radio resources at the Um interface, the frame relay link resources at the Gb interface, and bandwidth of the GPRS backbone network, and the processing capability of various GPRS equipments, are related to the transmission, the best effort class is required to be the QoS at present. That is, the data must be transmitted as fast and accurate as possible while the most efficient utilization of the resources is ensured.

Because the system resources needed by various services vary with the grade of service (GoS), the QoS enjoyed by subscribers varies. As a result, carriers can tell the classes of subscribers according to the subscribers’ GoS and adopt flexible charging strategies. And this is helpful for carriers to popularize the GPRS service.

1) Priority class

The priority class ensures subscribers to enjoy the basic or important services in abnormal cases. When network resources are scarce or congested, the network side and the MS decide which data packet must be discarded and which data packet must be sent according to their priority classes.

A priority class is a 3-bit binary code. Currently, three priority classes are defined. They are priority class 1, 2, and 3. For uplink transmission, the three priority classes maps the radio priority classes 2, 3, and 4. For the transmission of the signaling at radio interfaces, the high priority classes must be adopted. The priority class is defined in Table 10-1.

Table 10-1 Definition of the priority class in GPRS QoS

Coding Priority class Meaning Corresponding radio priority class _{for uplink transmission}

001 1 Highest priority class 2

010 2 Normal priority class 3

011 3 Lowest priority class 4

2) Reliability class

The reliability class is defined by together by the GTP, LLC, and RLC transmission modes. The reliability class in the QoS script indicates the transmission features

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Table 10-2 Definition of the reliability class in GPRS QoS Priority

class GTP mode LLC frame mode LLC data mode RLC mode Applicable service type

1 Acknowle_dged Acknowle_dged Protecte_d Acknowle_dged

Non-real time service, great error sensitivity, applicable to the service that cannot process the loss of data

2 Unacknow_ledged Acknowle_dged Protecte_d Protected

Non-real time service, general error sensitivity, applicable to the service that can process a little loss the data

3 Unacknow_ledged Unacknow_ledged Protecte_d Acknowle_dged

Non-real times service, poor error sensitivity, applicable to the service that can process the loss of the data and the GMM/SM service

4 Unacknow_ledged Unacknow_ledged Protecte_d Unacknow_ledged

Real-time service, poor

error sensitivity, applicable to the service

that can process the loss of the data

5 Unacknow_ledged Unacknow_ledged Unprotec_ted Unacknow_ledged

Real-time service, no error sensitivity, applicable to the service

that can process the loss of the data

Note:

For real-time services, proper delay and throughput are required to be configured for QoS script.

3) Delay class

The delay classes defined in the QoS script are the mean delay of the service data units and the maximum delay of the 99% of the service data units that are involved in the end-to-end transmission of the data in the GPRS network. In the GPRS system, four delay classes are defined. The lowest requirement is that the network must support the delay class 4 (best effort). Currently, most carriers support the delay class 4 only. The delay class is defined in Table 10-3.

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Length of the service data unit

128 bytes 1024 bytes

Coding Delay class

Mean delay/s 95% _delay/s Mean delay/s 95% _delay/s 001 1 (predicted) < 0.5 < 1.5 < 2 < 7 010 2 (predicted) < 5 < 25 < 15 < 75 011 3 (predicted) < 0.5 < 250 < 75 < 375

100 4 (best effort) Not defined

4) Peak throughput class

The peak throughput class defines the maximum transmission rate that each PDP context can reach in the network. The peak throughput class is decided by the data transmission capability of the MS and the allocation of the radio resources. The peak throughput is measured at the Gi interface and the R reference point. The peak throughput class is defined in Table 10-4.

Table 10-4 Definition of the peak throughput class in GPRS QoS

Coding Peak throughput class Peak throughput (byte/s)

0001 1 1000 (8kbit/s) 0010 2 2000 (16kbit/s) 0011 3 4000 (32kbit/s) 0100 4 8000 (64kbit/s) 0101 5 16000 (128kbit/s) 0110 6 32000 (256kbit/s) 0111 7 64000 (512kbit/s) 1000 8 128000 (1024kbit/s) 1001 9 256000 (2048kbit/s)

5) Mean throughput class

The mean throughout class defines the mean transmission rate that the PDP context is expected to reach during the PDP context activation in the GPRS network. The mean throughput is measured at the Gi interface and the R reference point, and the measurement time does not include the data transmission time. If the mean throughput class is the best effort, it means that the network must provide subscribers with

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2/27/2009 All rights reserved Page16 of 94 negotiable throughput class according to the requests of the subscribers and the allocation of the network resources. The mean throughput class is defined in Table 10-5.

Table 10-5 Definition of the mean throughput in GPRS QoS

Coding Mean throughput class Mean throughput (byte/h)

00001 1 100 (about 0.22bit/s) 00010 2 200 (about 0.44bit/s) 00011 3 500 (about 1.1bit/s) 00100 4 1000 (about 2.2bit/s) 00101 5 2000 (about 4.4bit/s) 00110 6 5000 (about 11bit/s) 00111 7 10000 (about 22bit/s) 01000 8 20000 (about 44bit/s) 01001 9 50000 (about 111bit/s) 01010 10 100000 (about 222bit/s) 01011 11 200000 (about 444bit/s) 01100 12 500000 (about 1.1kbit/s) 01101 13 1000000 (about 2.2kbit/s) 01110 14 2000000 (about 4.4kbit/s) 01111 15 5000000 (about 11kbit/s) 10000 16 10000000 (about 22kbit/s) 10001 17 20000000 (about 44kbit/s) 10010 18 50000000 (about 111kbit/s) 11111 31 Best effort

V. GPRS upper layer function

For the application of the GPRS upper layer functions in network entities, see Table 10-6.

Table 10-6 Application of the GPRS upper layer functions in network entities

Function MS BSS SGSN GGSN HLR

1. Network access control function

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Authentication X X X

License control X X X

Message screening X

Packet terminal adaptation X

Charging Data Collection X X

2. Packet routing and transfer function

Forward (relay) X X X X

Routing X X X X

Address translation and mapping X X X

Encapsulation X X X

Tunneling X X

Compression X X

Encryption X X X

3. Mobility management function X X X X

4. Logical link management function

Logical link establishment X X

Logical ink maintenance X X

Logical link release X X

5. Radio resource management function

Um management X X

Cell reselection X X

Um-Tranx X X

Path management X X

Note:

X indicates that an entity has the function listed in the left column.

The following introduces the network access control function, packet routing and transfer function, mobility management function, logical link management function, and radio resource management function respectively.

1) Network access control function

This function controls the MS to access the network so as to make the MS use the related network resource to fulfill data service. For GPRS network, subscribers can access the network from the MT and the fixed network side (including the Internet and

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The GPRS network access function consists of the following:

z Registration function z Authentication function z License function

z Message screening function z Packet terminal adaptation function z Charging Data Collection function

2) Packet routing and transfer function

This function ensures the packet data to be sent to the destination according to the best path. This function consists of the following:

z Forward (relay) function z Routing function

z Address translation and mapping function z Encapsulation function

z Tunneling function z Compression function z Encryption function z DNS function

3) Mobility management function

This function is applied to monitor the current location of the MS in the PLMN. The mobility management function of GPRS is similar to that of GSM. That is, one or more cells constitute a routing area (RA) or a RA subset, and the SGSN provides services for several RAs.

The mobility management (MM) of subscribers can be described according to three types of MM state. Each type of state describes a certain level of function and information allocation. All the information is stored in the MM context of the MS and the SGSN.

The three types of MM state are idle state, standby state and ready state. The network monitors the MS location according to the MM state of the MS. If the MS is in standby state, the network only knows the RA of the MS. When the MS is in ready state, the network can know which cell the MS is in.

The following introduces the three types of state respectively. a) Idle state

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2/27/2009 All rights reserved Page19 of 94 When the MS is in idle state, the MM context of the MS and the SGSN does not contain the valid location and routing information of the subscriber. The MS can receive the PTM-M service information, but it cannot carry out the PTM-G service. If the MM context is to be established between the MS and the SGSN, the MS must perform PLMN selection, cell selection and reselection, and GPRS attach program.

b) Standby state

When the MS is in standby state, the subscriber attaches the GPRS network, and MM context identified by the IMSI of the subscriber is established in the MS and the SGSN. The MS can receive both the PTM-M service data and the PTM-G service data. In addition, it can also receive the circuit switched pages passing the SGSN. However, the MS can neither receive the PTP service in this state, nor can it send the PTP service and the PTM-G data.

The MS can select and reselect the GPRS RAs and cells. When the MS enters a new RA, it notifies its current location to the SGSN with the help of the MM procedure. When the MS is in standby state, it can initiate the procedures to activate and deactivate the PDP context. Before the receiving and sending data, the PDP context must be activated.

When the network needs to send data or signaling to the standby MS, the SGSN will send a paging request in the RA where the MS is in. If the MS receives the paging request and makes a response, the MM state of the MS will change from standby state to ready state. Meanwhile, when the SGSN receives the response from the MS, the MM state of the SGSN will change from standby state to ready state. When the MS needs to send data and signaling to the network, the MM state of the MS will change from standby state to ready state after the MS sends the data and the signaling. When the SGSN receives the data and the signaling from the MS, its MM state will change from standby state to ready state.

Either the MS or the SGSN can initiate the GPRS detach procedure to change the MM state to idle state. When the MS leaves the ready state for standby state, the SGSN will start the MS reachable timer. After receiving the PTP PDU from the MS, the SGSN will stop this timer. If this timer expires, the SGSN will initiates the implicit GPRS detach procedure. In this case, the MM context of the MS and the SGSN will be deleted and the MS will enter the idle state.

c) Ready state

When the MS is in ready state, the information of the cell that the MS has camped on is added to the MM context corresponding to MS in the SGSN. The MS provides the information to the network through initiating the procedure to activate the PDP context.

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2/27/2009 All rights reserved Page20 of 94 When the MS is in ready state, the MS can both receive and send PTP PDU. The network does not start the PS page for the MS, and the page for other services can be realized by the SGSN.

Before the MM ready timer (T3314) expires, the MM state keeps in ready state regardless that the MS should be allocated with radio resource. After the T3314 expires, the MM state will change to standby state. If the MM state will change from standby state back to idle state, the MS must initiate the procedure to deactivate the PDP context.

Figure 10-2 shows the transition of the three types of MM state.

Figure 10-2 MM state transition model 4) Logical link management function

The logical links indicate the links established between the MS and the GPRS network and needed for the transmission of packet data. The logical link management function keeps channel for the communication between the MS and the PLMN. After logical links are established, the MSs and the logical links are one-to-one matched. The logical management function consists of the following:

z Logical link establishment function z Logical ink maintenance function z Logical link release function

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The radio resource management function involves the allocation and management of the radio communication channels. For the GPRS radio resource management function, it must enable the GPRS service and GSM service to share the radio channels. The radio resource management function consists of the following:

z Um management function z Cell reselection function z Um-tranx function

6) Network management function

It is the operation and maintenance function of the GPRS system. The realization of this function varies with carriers.

VI. GPRS numbering plan

The distribution of the addresses, numbers, and identities involved in the GPRS are shown in Figure 10-3.

Figure 10-3 GPRS address and numbering diagram

In a GPRS backbone network, each SGSN had an internal IP address, which is used for the communication within the backbone network. In addition, the SGSN has a SGSN SS7 number, which is used for the communication with MSC/VLR, HLR, and EIR. Each GGSN also has an internal IP address, which is used for the communication within the backbone network. If the GGSN connects to the HLR through Gc interface, it should also have a GGSN SS7 number. Moreover, as the gateway connecting to external data networks, the GGSN has an address used for the connection with the external data networks.

The GPRS MS has an exclusive IMSI. When it is attached to the GPRS, the SGSN will allocate a temporary P-TMSI to the MS. If the MS intends to access an external PDN, it must have an address (it is called PDP address) corresponding to the PDN. For example, if the MS accesses the X.25/X.75 network, the type of the PDP address is

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2/27/2009 All rights reserved Page22 of 94 X.121 address. If the MS accesses an IP network, the type of the PDP address is the IP address of the IP network. The IP address can be either a static address or a dynamic address, among which the dynamic address is allocated by the GGSN. When starting the packet data service, the MS must provide an APN to the SGSN; otherwise the network cannot know which external network the MS intends to access.

When the GPRS packet data service is being processed, the logical link between the MS and the SGSN is identified by the TLLI only, and the logical link between the SGSN and the GGSN is identified by the TID only.

1) IMSI

Compared with the original GSM subscribers, GPRS subscribers also have an IMSI except anonymous subscribers. The anonymous access means that a subscriber accesses the network anonymously without the IMSI or IMEI authentication. In this case, the call cost is paid by the called party. Carriers can decide whether to allow the anonymous access according to actual service needs.

2) P-TMSI

The SGSN will allocate a P-TMSI used for packet call to the GPRS-attached subscribers. The P-TMSI is related to the subscriber IMSI. Both the P-TMSI and TMSI consist of are 32-bit codes, but the most significant bit of P-TMSI is 11, and the most significant bit of TMSI is 00, 01, and 10.

3) NSAPI

As shown in Figure 10-4, the network layer service access point identifier (NSAPI) is the address used for application layer of the packet data protocol (PDP) to access the sub-network dependent convergence protocol (SNDCP). For the X.25 and IP, they have their own NSAPI. The value of NSAPI ranges from 0 to 15. Currently, the NSAPI whose value ranges from 5 to 15 are used for dynamic allocation.

Figure 10-4 NSAPI numbering diagram 4) TLLI

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2/27/2009 All rights reserved Page23 of 94 The TLLI stands for temporary logical link identity. When the MS has just accessed the GPRS network and the GPRS network has not allocated the P-TMSI to the MS, the TLLI identifies the exchanged signaling between the MS and the SGSN. The TLLI identifies a solar logical link between the MS and the SGSN in an RA. If the MM context does not know which RA the TLLI belongs to, the TLLI and the routing area identifier (RAI) should be used together. In a RA, the TLLI and the IMSI are one-to-one matched. The TLLI consists of 32-bit codes. In the GPRS system, there are four types of TLLI, and they are introduced hereunder.

a) Local TLLI

The most significant bit of the local TLLI is 11. The other bits come from the P-TMSI allocated by the SGSN to the MS. The local TLLI is valid only in the RAs related to the P-TMSI.

b) Foreign TLLI

The most significant bit of the foreign TLLI is 10. The other bits come from the P-TMSI allocated by the other RA. When the subscriber performs RA update, the MS will report the RA update to the SGSN.

c) Random TLLI

If no P-TMSI is attached to the MS, the MS must provide a random TLLI. The most five significant bit of the random TLLI is 01111. The others are random bits.

d) Assisted TLLI

The assisted TLLI provides the identities to the anonymously-accessed MSs. The most five significant bit of the assisted TLLI is 01110. The others are allocated by the SGSN. e) NSAPI/TLLI pair

The NSAPI/TLLI pair is used to select the route of the network layer. The TLLI can identify the logical links between the MS and the SGSN. The NSAPI and the TLLI are used as the route of the network layer. There is only one NSAPI/TLLI pair in a RA. f) PDP address

The PDP address is the address of the packet protocol. The MS is identified by the IMSI. For different external networks, however, they must have the PDP address if they intend to fulfill the packet data function; because the PDP address helps the external data networks identify the PDP context of the MS. The PDP address can be divided into IP address (IP4 address or IP6 address) and X.121 address (for the X.25 service). The previous types of addresses can be either statically or dynamically allocated. When they are statically allocated, the MS must be subscribe to the network first, and

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2/27/2009 All rights reserved Page24 of 94 then the network will allocate a corresponding address to the MS. Meanwhile, the network will record the fixed address in the SIM card and the database of the subscriber. The type of PDP address must be made clear during subscription; otherwise the system will reject the PDP address that has not been subscribed.

g) TID

Tunnel identifier (TID) consists of IMSI and NSAPI. It lies in the GTP header and identifies the solar PDP context between GSNs (between SGSN and GGSN, or between SGSN and the original SGSN). The TID consists of 8 bytes. For the specific format, see Table 10-7.

Table 10-7 TID format

Bit

8 7 6 5 4 3 2 1 IMSI the 2nd digit IMSI the 1st digit

IMSI the 4th digit IMSI the 3rd digit IMSI the 6th digit IMSI the 5th digit IMSI the 8th digit IMSI the 7th digit IMSI the 10th digit IMSI the 9th digit IMSI the 12th digit IMSI the 11th digit IMSI the 14th digit IMSI the 13th digit

NSAPI IMSI the 15th digit

h) RAI

The RAI stands for routing area identifier. The carriers define the RA. A RA can contain one or more cells, or it can be a location area, or a subset of a location area. A location area is controlled by a SGSN. As a kind of system information, the RA information will be broadcast on common control channels.

RAI = MCC + MNC + LAC + RAC (The RAC has a maximum of 16 bits.)

CGI = LAI + {RAC} + CI (If the cell supports GPRS, the CGI contains the RAC; otherwise it does not contain the RAC.)

i) CI

The CI stands for cell identity. The CI of the GPRS network is the same as that of the original GSM network.

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To communicate with the GPRS backbone network and other GSNs, each SGSN and each GGSN have an IP address (IPv4/IPv6) of their own. These addressed are the internal addresses of the GPRS network, and each address has one or more corresponding domain names. The GSN address consists of address type (2 bits), address length (6 bits), and address (a maximum of 16 bits). When the address type is 0, the address is IPv4 address. When the address type is 1, the address is IPv6 address.

To communicate with the HLR and the EIR, each SGSN must still have a SGSN SS7 number. If the GGSN connects to the HLR through Gc interface, it must have a GGSN SS7 number.

k) APN

The APN identifies the GGSN that is to be used in the GPRS backbone network. In the GGSN, the APN is used to characterize the external data networks.

The APN consists of two parts. One is APN network identification. It is mandatory. The carriers allocate the APN network identification to the Internet service providers (ISP) and companies and it is the same as the fixed Internet domain name. The other one is APN carrier identification. It is optional and identifies the home network. It is expresses as “xxx.yyy.gprs”. For example, MNC.MCC.gprs.

Generally, the APN network identification can be stored as the subscription data in the HLR. Subscribers can provide the APN to SGSN when initiating packet services, because the APN helps the SGSN select the GGSN that the subscribers should access and helps the GGSN judge which external network should be selected. In addition, the APN can be stored as a wildcard (*). In this case, the subscribers and the SGSN can choose to access an APN that is not stored in the HLR. The subscribers can select the GGSN according to different APNs. That is, the subscribers can activate multiple PDP contexts (each PDP context is related to one APN only). The reason for the subscribers to select different APNs is that they can select an external network to access through different GGSNs.

The APN cannot obtain the real IP address of the GGSN or the external network node until the DNS successfully resolve their domain names.

An APN consists of one or more labels, and each label consists of an octet indicating the length and multiple octets coded by the 8-bit ASCII. The maximum length of an APN is 100 octets. The value of an octet can be expressed by English letters, Arabic numbers, and the mark “-“.

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2/27/2009 All rights reserved Page26 of 94 The APN network identification contains at least one label, and the maximum length of the label is 63 octets. The label of the APN network identification cannot be a “*”, the first label cannot be “rac”, “lac”, and “sgsn”, and the last label cannot be “gprs”. The APN network identification is exclusively allocated by each GPRS PLMN. The APN carrier identification identifies one GPRS PLMN only, including three labels. They are “carrier name”, carrier group”, and “gprs” according to the front-to-back sequence. The defaulted APN carrier identification is “MNC.MCC.gprs”.

10.1.3 Main Interfaces and Related Protocols

I. Main Interfaces

Various interfaces exist among the entities in the GPRS network. Equipments of different carriers cooperate with each other if these interfaces are properly defined. Figure 10-5 shows the main interfaces in the GPRS system.

Figure 10-5 Main interfaces in the GPRS system

The following introduces the interfaces shown in Figure 10-5. 1) R reference point

The R reference point is the interface connecting the TE to MT. Subscribers can perform packet data services at the TE.

2) Um interface

The Um interface connects the MS to the GPRS network side. It maintains the communication between the MS and the network side. In addition, it helps the

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2/27/2009 All rights reserved Page27 of 94 realization of multiple functions, including the packet data transmission, mobility management, session management, and radio resource management, between the MS and the GPRS network side. The RF part of the Um interface utilizes the timeslot of the GSM carrier, but it must be configured with PDCH. The coding schemes on the PDCH can be divided into CS1, CS2, CS3, and CS4 corresponding to the data transfer rate. The PDCH supports multislot transmission. The number of transmitted timeslots is decided by the multislot level of the MS.

3) Gb interface

The Gb interface connects the SGSN to the BSS. The SGSN maintains the communication with the BSS and the MS with the help of Gb interface so that the functions, including packet data transmission, mobile management, and session management, can be realized between them. Moreover, the Gb interface provides flow control function.

This interface is a must in the GPRS networking. Currently, the standard GPRS protocols define that the Gb interface adopts frame relay as the transfer protocols at the lower layer. In addition, the standard GPRS protocols also define that either frame relay or PTP frame relay can be used for communication between the SGSN and the BSS. 4) Gi reference point

The Gi reference point connects the GPRS network to the external packet data networks. It lies between the GGSN and the external packet data networks. The GPRS network connects communicates with various PDNs (such as the Internet) or ISDNs through the Gi reference point. The operations, including the encapsulation/decapsulation of the protocols, the conversion of the addresses (such as the conversion between IP address of a private network and that of a public network), the authentication and authorization of the subscriber access, must be performed at the Gi reference point.

5) Gn interface

The Gn interface connects the GPRS support nodes (GSN) with each other. That is, the Gn interface connects the SGSNs to each other and connects the SGSN to the GGSN within the PLMN. Based on the TCP/UDP protocols, the Gn interface bears the GTP to carry out the communication and manage the packet data transmission and mobility. 6) Gs interface

The Gs interface connects the SGSN to the MSC/VLR. It adopts the BSSAP+ protocols bearing on the No.7 signaling. The cooperation of the Gs interface and the MSC helps the SGSN manage the mobility of the MS. In addition, the Gs interface enables the SGSN to receive the circuit switched paging messages from the MSC and deliver them to the MS through PCU. If no Gs interface is provided, the SGSN cannot perform paging coordination, so the network can work under the network mode of operation II (NMO II) and NMO III only, and this will prevent the enhancement of the call connected

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2/27/2009 All rights reserved Page28 of 94 ratio. In addition, if no Gs interface is provided, the RAs of the combined locations cannot be updated, and this will results in heavy signaling load in the system.

7) Gr interface

The Gr interface connects the SGSN to the HLR. It adopts the MA+ protocols bearing on the No. 7 signaling. The SGSN obtains the data relative to the MS through the Gr interface. The HLR stores the data and the routing information for the GPRS subscribers. When any RA updates in the SGSN, the SGSN will update the corresponding information in the HLR. When the data in the HLR changes, the HLR will notifies the change to the SGSN.

8) Gd interface

The Gd interface connects the SGSN to the SMS-GMSC and SMS-IWMSC. The SGSN, SMS-GMSC, SMS-IWMSC, and SMC cooperate with each other at the Gd interface to fulfill the SMS in the GPRS system. The Gd interface enables the SGSN to receive short messages and forward them to the MS. If no Gd interface is provided, the Class C MSs cannot receive and send short messages when attached to the GPRS network. 9) Gp interface

The Gp interface connects GPRS networks with each other, so it is used between the GSNs that belong to different PLMNs. The Gp interface is similar to the Gn interface in telecommunication protocols except that the border gateway and fire wall are added to the Gp interface. Because the BG provides the routing protocols for the border gateways, the Gp interface enables the GSNs belonging to different PLMNs to communicate with each other normally.

10) Gc interface

The Gc interface connects the GGSN to the HLR. When the network side initiates the PDP context activation, the GGSN uses the IMSI to request the address of the current SGSN where the subscriber is in from the HLR. In current mobile data services, this kind of situation is seldom seen.

11) Gf interface

The Gf interface connects the SGSN to EIR. Generally, the EIR is not configured with the networks at present, so the Gf interface cannot be necessarily emphasized. II. Related protocols

The data and signaling in the GPRS system are transmitted in an integrated platform, as shown in Figure 10-6.

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The following introduces the protocols shown in Figure 10-6. 1) GTP

The GTP stands for GPRS tunneling protocol. It is used for the tunneling transmission of the data and signaling between GSNs in the GPRS backbone network. The GTP is applicable to the Gn interface and the Gp interface.

The GTP consists of GTP signaling and data transmission program. In the signaling platform, the GTP defines the tunneling control and management protocols for the MS to access the GPRS network. In the transfer platform, the GTP utilizes the tunnels established between the GSNs to transmit subscriber data.

All PDP PDUs transmitted between GSNs must be encapsulated with the GTP header. The format of the GTP header is fixed to 20 bytes, the last 8 of which identify the TIDs for specific subscribers.

In addition, the GTP provides the flow control function. 2) UDP/TCP

The UDP/TCP is the transport layer protocol used to establish the reliable link from end-to-end. The TCP orients to connection. It can discard and protect the errors and controls flow. In addition, it ensures the data to be accurately transmitted and can used to bear the GTP PDUs that require reliable transmission.

Compared with the TCP, the UDP orients to non-connection. It neither recovers errors nor cares about whether receives the messages correctly or not. Instead, it transmits and receives the data only. It is used to bear the GTP PDUs that do not require reliable transmission.

3) IP

The IP stands for the Internet protocols. It is used to select the route for the subscriber data and control signaling in the GPRS backbone network. Currently the IPv4 is widely used, but it will gradually develop into IPv6.

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The BSSGP (BSS GPRS protocols) includes the functions of the network layer and parts of the transport layers. It provides a radio link that is used to transmit the unacknowledged data between the BSS and the SGSN. The primary function of the BSSGP is to explain the routing information and the QoS information. On downlinks, the SGSN provides the radio information to be used by the RLC/MAC to the BSS. On uplinks, the BSS provides the radio information obtained from the RLC/MAC from the SGSN. In addition, the BSSGP also manages and controls the nodes between the SGSN and the BSS.

The BSSGP entity uses BSSGP virtual circuit (BVC) to transmit BSSGP packet data units (BSSGP PDU). The BVC consists of a group of network service virtual circuits (NS-VC) and is only identified by the BSSGP virtual circuit identification (BVCI) and network service entity identification (NSEI) in the SGSN. In the BSSGP layer, the BVCI identifies a cell.

The BSSGP has three users. They are relay (RL), GPRS mobility management (GMM), and network management (NM).

The function of flow control is available is the BSSGP layer. This function controls the load for the QoS delay class queues between the SGSN and the BSS so as to optimize the buffer area. Because the physical mediums and transmission protocols at the Gb interface are different from that at the Um interface, the data transfer rate at the Gb interface is higher that that at the Um interface. In addition, when the data is transferred on the downlink, the transfer will receive the restriction from multiple factors, such as the multislot capability of the MS, the radio quality, and the unavailability of the radio channels in cells, at the Um interface. Therefore, the data transmission rate is unstable. In this case, you must control the flow of the data transmitted on the downlink, while the control of the flow of the data transmitted on the uplink is unnecessary.

The BSSGP layer manages two types of buffers. One buffer of the MS and the other is the buffer of the BVC. First the BSSGP puts each LLC-PDU, with TLLI as identification, received by each LLC-PDU into the buffer of the corresponding MS, and then put the data, with BVCI as identification, into the buffer of the BVC.

When the cell works normally, the PCU must start the flow control procedure. In this case, the PCU reports the size and rate of the buckets in the cell to the SGSN periodically according to the radio packet channels. In addition, it must also report the size and the rate of the MS to the SGSN according to the radio resource seized by the MS. Upon receiving the reports, the SGSN adjusts the downlink data rate for the cell and the MS according to the reported parameters in needed time. And this is how the downlink data flow is controlled. The SGSN controls the flow according to one principle.

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Note:

z The bucket of the cell is the maximum of packet data that the cell can store. That is,

it is the maximum amount of the packet data of that the buffer of the BVC can store. The bucket varies with the number of packet channel in the cell.

z The bucket of the MS is the maximum amount of the packet data that the MS can

store. That is, it is the maximum amount of the packet data that the buffer of the MS can store. The bucket varies with the number of channels allocated to the MS.

z The bucket rate is the data transmission rate.

5) NS

The NS stands for network service. The primary functions of the NS layer include the transmission of the network service packet data units (NS-PDU), the indication of network congestion, and the indication of NS layer state.

The NS layer consists of the NS sub-network and the NS control part. Currently, the NS sub-network adopts the frame relay. The NS control part transmits the NS-PDU, shares the load, and manages the NS-VC. The NS-VC is the frame-relay permanent virtual circuit (PVC) and it is only identified by the NS-VCI in the SGSN. The NS-VCI is an end-to-end identification at the Gb interface.

6) SNDCP

The SNDCP stands for Sub-Network Dependent Convergence Protocol. The SNDCP layer is the transition between the network layer and the link layer. It mainly contributes to the transparent transmission of the network layer PDU (N-PDU) and the enhancement of the channel utilization. The SNDCP can reuse the date (it is from various service source) to be transmitted. The PDP type of the data varies with its service source and the PDP context is identified by different NSAPIs. A type of PDP can contain several PDP contexts and NSAPIs and different PDPs can use a NSAPI. The SNDCP layer packet data unit (SN-PDU) includes header and data. One SN-PDU contains the data of one N-PDU only. The SN-PDU has two formats, SN-DATA PDU and SN-UNITDATA PDU, the first of which is used to transmit the data of the acknowledged mode, and the second of which is used to transmit the data of the unacknowledged mode.

The SNDCP has two compression types, data header compression and data compression.

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The LLC stands for logical link control. The LLC protocol is the radio link protocol used at the transport layer and based on high-speed digital subscriber line (HDSL). It provides the logical link between the MS and the SGSN, with end-to-end encryption and no error. The LLC layer supports point-to-multipoint addressing, data retransmission and multiple QoS delay class. The intact LLC frame can be generated through adding the LLC address and frame field to the LLC based on the PDU. An LLC frame (LLC PDU) consists of address field (1 byte), control field (a maximum of 32 bytes), information field (a maximum of N201 bytes, and frame correction sequence (FCS) field (3 bytes). Under acknowledged mode, the parameter N201-I will indicate that the maximum valid bytes of SN-DATA PDU are 1520. Under unacknowledged mode, the parameter N201-U will indicate that the maximum valid bytes of the SN-UNITDATA PDU are 500.

The LLC layer has set different service access points (SAP) for different upper layer subscribers. Each SAP is identified by one service access point identifier. A SAPI consists of 4 bytes and locates in the least-4 digits of the field address of the LLC frame. Currently 6 values are adopted, in which the SAPI = 1 matches the GPRS mobility management/session management (GMM/SM) service, the SAPI = 7 matches the short message service, and the SAPI = 3, 5, 9, and 11 match data service of the subscribers whose QoS is 1, 2, 3, and 4.

8) RLC

The RLC protocol is applied between the link layer and the network layer. It controls the radio links. The primary function of RLC layer is to disassemble and assemble LLC-PDU. The application of the sliding window mechanism enables the RLC layer to ensure the data transmission between the MS and the BSS through adopting the acknowledged mode or unacknowledged mode. The size of the GPRS RLC sliding window is 64.

a) RLC acknowledged mode

Under this mode, each RLC data blocks sent by the sending end must be acknowledged by the receiving end; otherwise the sending end must select the automatic repeat request (ARQ) mechanism to resend the data. Only after all the data are sent and acknowledged by the receiving end, the temporary block flow (TBF) can be released.

The TBF is a kind of physical connection used for the transmission of the data between the MS RR entity and the BSS RR entity. It exists during data transmission only. b) RLC unacknowledged mode

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2/27/2009 All rights reserved Page33 of 94 Under unacknowledged mode, the data sent by the sending end do not have to be acknowledged by the receiving end and the discarded data blocks do not have to be resent either. The TBF can be released after the data is completely sent.

Note:

At present, all GPRS networks adopt the RLC acknowledged mode. 9) MAC

The MAC stands for medium access control. The MAC protocol is applied to the link layer. Its primary functions are to define the GPRS logical channels at the Um interface and make coordination to enable multiple MSs to share these channels or enable one MS to use the physical channels of different timeslots. Therefore, the MAC must fulfill the following tasks:

z Fully reuse the uplink and downlink

z Perform the contention and decision during uplink access

z Transmit the downlink data according to access attempt sequence z Process the radio priority class

z Match the LLC-PDU to the corresponding physical channels

There are three MAC modes, including fixed allocation, dynamic allocation, and extended dynamic allocation, which are detailed in the following.

a) Fixed allocation

Under this mode, the BSS allocates the radio blocks to be used by the MS in advance. If there is still data needs to be transmitted after all the radio blocks have been used, the BSS will reallocates radio blocks to the MS.

b) Dynamic allocation

Under this mode, the BSS allocates the radio blocks to be used by the MS when MS needs them. When assigning radio resources to the MS, the BSS will assign several radio channels and the corresponding uplink state flag (USF) for the MS. Upon receiving an assignment message, the MS begins to listen the downlink radio blocks in the assigned channel to obtain the USF. If this USF is the same as the assigned USF, the MS will transmit the data on the corresponding uplink radio block.

c) Extended dynamic allocation

Under this mode, the resource allocation mechanism is the same as that under the dynamic allocation mode except that greater uplink throughput is provided under the dynamic allocation mode. According to extended dynamic allocation, the multislots are allocated to the MS according to its multislot capability. Upon receiving a USF on one

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10.1.4 Radio Channels and Their Importance

I. Radio Chnnels

1) Types of packet data logical channels

Packet data logical channels can be divided into four types. They are packet data traffic channel (PDTCH), packet broadcast control channel (PBCCH), packet common control channel (PCCCH), and packet dedicated control channel (PDCCH). The following details the four types of channels respectively.

a) PDTCH

The PDCH is used to transmit the subscriber data under packet transfer mode and the transfer rate ranges from 0 to 22.8 kbit/s. All the PDCCHs are unidirectional. The PDTCH uplink (PDTCH/U) helps the MS to transmit the data to the GPRS network. The PDTCH downlink (PDTCH/D) helps the GPRS network to transmit the data to the MS. b) PBCCH

The PBCCH broadcasts the parameters needed by the MS to access the network for packet service. In addition, it also broadcasts the parameters used for circuit switched service. The GPRS-attached MSs monitor the PBCCH only.

If a cell has the PBCCH, corresponding prompt is present in the BCCH. That is, the MS will be told that this cell is configured with the PBCCH through SI13. If there is no PBCCH is the cell, the BCCH will broadcast the parameters used for packet service. c) PCCCH

The PCCH can be divided into the following types:

z Packet paging channel (PPCH)

It is applied to the downlink only and used to page the MS.

z Packet random access channel (PRACH)

It is applied to the uplink only and used to request one or more PDTCH for the MS.

z Packet access grant channel (PAGCH)

It is applied to the downlink only and used to allocate one or more PDTCH.

z Packet notification channel (PNCH)

It is applied to the downlink only and used to notify the MS that the PTM-M call exists. If there is no PCCCH in a cell, the information of the packet service is transmitted on the CCCH. If there is PCCCH, the information of the packet service is transmitted on the

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d) PDCCH

The PDCCH can be divided into the following types:

z Packet associated control channel (PACCH)

It is bi-directional and used to transmit the packet signaling.

z Packet timing advance control channel uplink (PTCCH/U)

It is used to transmit the random access burst so that the BSS side can estimate the timing advance for the MS performing the packet service.

z Packet timing advance control channel downlink (PTCCH/D)

It is used to provide the information of timing advance for multiple MSs. A PTCCH/D matches multiple PTCH/Us.

2) Combination of the packet data logical channels There are the following combinations:

z PBCCH + PCCCH + PDTCH + PACCH + PTCCH z PCCCH + PDTCH + PACCH + PTCCH

z PDTCH + PACCH + PTCCH

If the cell needs the PBCCH, the first combination is used. A cell needs only one group of the combination only.

If a great number of MSs are present in a cell, one or more groups of the second combination can be configured when the PCCCH is busy. The second combination cannot be configured with a cell unless the first combination is configured.

The third combination is used to transmit the uplink and downlink packet data only. A cell can be configured with one or more groups of this combination.

3) Mapping transformation between logical channels and physical channels The GPRS channel adopts 52-multiframe structure. Each packet channel has 52 multiframes in total, four of which form a radio block. Therefore, a radio block consists of 12 radio blocks and 4 idle frames. Figure 10-7 shows the structure.

B0 B1 B2 X B3 B4 B5 X B6 B7 B8 X B9 B10 B11 X

B0-B11: 12 radio blocks X: idle frame

Figure 10-7 Structure of a radio channel

In a GPRS system, the packet logical channel has a mapping relationship with the PDCH physical channel according to the radio block sequence. That is, B0, B6, B3, B9, B1, B7, B4, B10, B2, B8, B5, B1.

Huawei GPRS Network Planning & Optimization.pdf

Table of Contents

List of Figures

List of Tables

Chapter 10 GPRS Radio Network Planning and

Optimization

10.1 GPRS Basic Principles

10.1.1 Network Structure and Functional Entities

10.1.2 Service Function and Numbering Plan

10.1.3 Main Interfaces and Related Protocols

10.1.4 Radio Channels and Their Importance