In gprs type a mobile station supports

13.8.2 Security in GPRS

The general packet radio service(GPRS) allows packet data to be sent and received across a mobile network (GSM). GPRS can be considered an extension to the GSM network to provide 3G services. GPRS has been designed to allow users to connect to the Internet, and as such is an essential first step toward 3G networks for all mobile operations. In GPRS, TMSI is replaced by P-TMSI and P-TMSI signature as alternative identities. The HLR GPRS register maps between internet protocol (IP) addresses and IMSI.

GPRS security functionality is equivalent to the existing GSM security. Authentication and encryption setting procedures are based on the same algorithms, keys, and criteria as in GSM systems.

GPRS provides identity confidentiality to make it difficult to identify the user. This is achieved by using a temporary identity where possible. When possible, confidentiality also protects dialed digits and addresses. As in GSM, the device is authenticated by a challenge-response mechanism. This only verifies that the smart card within the device contains the correct key.

GPRS does not provide end-to-end security so there is a point where the data is vulnerable to eavesdropping or attack. If this point can be protected, e.g., in a physically secure location, this is not a problem. However, if end-to-end security is required, there are other standards that can be used over GPRS; such as the wireless application protocol (WAP) and Internet protocol security (IPSec).

In GPRS authentication is performed by serving GPRS support node (SGSN) instead of VLR. The encryption is not limited to radio part, but it is up to SGSN. An IP address is assigned after authentication and ciphering algorithm negotiation.

III.C.1 GPRS

General packet radio service (GPRS) is a “packet mode” wireless data system that has been standardized to operate on GSM infrastructure, by introducing new packet support nodes and associated protocol stacks. A portion of the radio resources (channel frequencies) in an existing GSM system may be dedicated for packet data services using GPRS. Alternatively, GPRS and GSM services may dynamically share the same radio resources. Thus, GSM voice services and GPRS packet data services can coexist in the same GSM system.

GPRS provides IP connectivity to the mobile users. The maximum data rate supported is 171 kbps realized through statistical multiplexing of traffic over-the-air. Point-to-point (e.g., e-mail, Internet access, remote access, road toll) as well as point-to-multipoint (e.g., multicast, financial updates, fleet management, traffic information) applications are envisaged.

The new packet support nodes in GPRS are Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). The SGSN and GGSN enable the mobile data users to connect to the Internet, essentially playing analogous roles of the Serving MSC and Gateway MSC in GSM that connect voice users to the PSTN.

The over-the-air communication between a mobile station (MS) and the GPRS network is defined by the physical layer and the data link layer. The physical layer functions involve modulation, demodulation, channel encoding/decoding, etc. The data link layer consists of two sublayers, namely, logical link control (LLC) layer and the radio link control/media access control (RLC/MAC) layer.

The LLC layer operates between the MS and the SGSN, and provides a logical link between them. The LLC layer supports two modes of operation, namely, asynchronous disconnected mode (ADM) and asynchronous balanced mode (ABM). In ADM, the LLC performs “unacknowledged” operation and does not provide any error recovery procedure to guarantee in-order deliver (such a mode may be applicable for delay-sensitive, error-tolerant applications like voice over IP). In ADM, the LLC performs “acknowledged” operation which includes functionalities like error recovery through ARQ, in-order delivery, and flow control (these functionalities are essentially based on the well-known HDLC protocol). Also, LLC ensures data confidentiality through ciphering functions.

The RLC/MAC layers are primarily responsible for the efficient sharing of common radio resources by several mobiles. The RLC/MAC peers are at the MSC and the BS. Each LLC frame is segmented into several RLC data blocks of fixed size. Each RLC data block occupies a fixed number of slots, depending on the channel coding scheme used. The RLC layer can operate either in acknowledged or unacknoledged mode. In acknowledged mode, RLC provides for the selective retransmission of erroneous RLC data blocks. The MAC operates on a slotted-ALOHA based reservation protocol. The MAC layer requests/reserves resources in terms of number of data slots. The MAC function provides arbitration between multiple mobiles attempting to transmit simultaneously, and provides collision detection and recovery procedures.

15.2.2 General Packet Radio Service

The general packet radio service (GPRS) [6, 7] enhances GSM data services significantly by providing end-to-end packet switched data connections. This is particularly efficient in Internet/intranet traffic, where short bursts of intense data communications are actively interspersed with relatively long periods of inactivity. Because there is no real end-to-end connection to be established, setting up a GPRS call is almost instantaneous and users can be continuously on-line. Users have the additional benefits of paying for the actual data transmitted, rather than for connection time. Because GPRS does not require any dedicated end-to-end connection, it only uses network resources and bandwidth when data is actually being transmitted. This means that a given amount of radio bandwidth can be shared efficiently among many users simultaneously.

The next phase in the high-speed road map is the evolution of current short message service (SMS), such as smart messaging and unstructured supplementary service data (USSD), toward the new GPRS, a packet data service using TCP/IP and X.25 to offer speeds up to 115 kbps. GPRS has been standardized to optimally support a wide range of applications ranging from very frequent transmissions of medium to large data volume. Services of GPRS have been developed to reduce connection set-up time and allow an optimum usage of radio resources. GPRS provides a packet data service for GSM where time slots on the air interface can be assigned to GPRS over which packet data from several mobile stations is multiplexed.

A similar evolution strategy, also adopting GPRS, has been developed for DAMPS (IS-136). For operators planning to offer wideband multimedia services, the move to GPRS packet-based data bearer service is significant; it is a relatively small step compared to building a totally new 3G IMT-2000 network. Use of the GPRS network architecture for IS-136+ packet data service enables data subscription roaming with GSM networks around the globe that support GPRS and its evolution. The IS-136+ packet data service standard is known as GPRS-136. GPRS-136 provides the same capabilities as GSM GPRS. The user can access either X.25 or an IP-based data network.

GPRS provides a core network platform for current GSM operators not only to expand the wireless data market in preparation for the introduction of 3G services, but also a platform on which to build IMT-2000 frequencies should they acquire them.

The implementation of GPRS has a limited impact on the GSM core network. It simply requires the addition of new packet data switching and gateway nodes, and an upgrade to existing nodes to provide a routing path for packet data between the wireless terminal and a gateway node. The gateway node provides interworking with external packet data networks for access to the Internet, intranet, and databases.

A GPRS architecture for GSM is shown in Figure 15.2 and network element interfaces in Figure 15.3. GPRS supports all widely used data communications protocols, including IP, so it is possible to connect with any data source from anywhere in the world using a GPRS mobile terminal. GPRS supports applications ranging from low-speed short messages to high-speed corporate LAN communications. However, one of the key benefits of GPRS — that it is connected through the existing GSM air interface modulation scheme — is also a limitation, restricting its potential for delivering higher data rates than 115 kbps. To build even higher rate data capabilities into GSM, a new modulation scheme is needed.

GPRS can be implemented in the existing GSM systems. Changes are required in an existing GSM network to introduce GPRS. The base station subsystem (BSS) consists of a base station controller (BSC) and packet control unit (PCU). The PCU supports all GPRS protocols for communication over the air interface. Its function is to set up, supervise, and disconnect packet switched calls. The packet control unit supports cell change, radio resource configuration, and channel assignment. The base station transceiver (BTS) is a relay station without protocol functions. It performs modulation and demodulation.

The GPRS standard introduces two new nodes, the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN). The home location register (HLR) is enhanced with GPRS subscriber data and routing information. Two types of services are provided by GPRS:

Point-to-point (PTP)

Point-to-multipoint (PTM)

Independent packet routing and transfer within the public land mobile network (PLMN) is supported by a new logical network node called the GPRS support node (GSN). The GGSN acts as a logical interface to external packet data networks. Within the GPRS networks, protocol data units (PDUs) are encapsulated at the originating GSN and decapsulated at the destination GSN. In between the GSNs, IP is used as the backbone to transfer PDUs. This whole process is referred to as tunnelling in GPRS. The GGSN also maintains routing information used to tunnel the PDUs to the SGSN that is currently serving the mobile station (MS). All GPRS user related data required by the SGSN to perform the routing and data transfer functionality is stored within the HLR. In GPRS, a user may have multiple data sessions in operation at one time. These sessions are called packet data protocol (PDP) contexts. The number of PDP contexts that are open for a user is only limited by the user's subscription and any operational constraints of the network.

The main goal of the GPRS-136 architecture is to integrate IS-136 and GSM GPRS as much as possible with minimum changes to both technologies. In order to provide subscription roaming between GPRS-136 and GSM GPRS networks, a separate functional GSM GPRS HLR is incorporated into the architecture in addition to the IS-41 HLR.

The European Telecommunication Standards Institute (ETSI) has specified GPRS as an overlay to the existing GSM network to provide packet data services. In order to operate a GPRS over a GSM network, new functionality has been introduced into existing GSM network elements (NEs) and new NEs are integrated into the existing service provider's GSM network.

The BSS of GSM is upgraded to support GPRS over the air interface. The BSS works with the GPRS backbone system (GBS) to provide GPRS service in a similar manner to its interaction with the switching subsystem for the circuit-switched services. The GBS manages the GPRS sessions set up between the mobile terminal and the network by providing functions such as admission control, mobility management (MM), and service management (SM). Subscriber and equipment information is shared between GPRS and the switched functions of GSM by the use of a common HLR and coordination of data between the visitor location register (VLR) and the GPRS support nodes of the GBS. The GBS is composed of two new NEs — the SGSN and the GGSN.

The SGSN serves the mobile and performs security and access control functions. The SGSN is connected to the BSS via frame-relay. The SGSN provides packet routing, mobility management, authentication, and ciphering to and from all GPRS subscribers located in the SGSN service area. A GPRS subscriber may be served by any SGSN in the network, depending on location. The traffic is routed from the SGSN to the BSC and to the mobile terminal via a BTS. At GPRS attach, the SGSN establishes a mobility management context containing information about mobility and security for the mobile. At PDP context activation, the SGSN establishes a PDP context which is used for routing purposes with the GGSN that the GPRS subscriber uses. The SGSN may send in some cases location information to the MSC/VLR and receive paging requests.

The GGSN provides the gateway to the external IP network, handling security and accounting functions as well as the dynamic allocation of IP addresses. The GGSN contains routing information for the attached GPRS users. The routing information is used to tunnel PDUs to the mobile's current point of attachment, SGSN. The GGSN may be connected with the HLR via optional interface Gc. The GGSN is the first point of public data network (PDN) interconnection with a GSM PLMN supporting GPRS. From the external IP network's point of view, the GGSN is a host that owns all IP addresses of all subscribers served by the GPRS network.

The PTM-SC handles PTM traffic between the GPRS backbone and the HLR. The nodes are connected by an IP backbone network. The SGSN and GGSN functions may be combined in the same physical node or separated — even residing in different mobile networks.

A special interface (Gs) is provided between MSC/VLR and SGSN to coordinate signaling for mobile terminals that can handle both circuit-switched and packet-switched data.

The HLR contains GPRS subscription data and routing information, and can be accessible from the SGSN. For the roaming mobiles, the HLR may reside in a different PLMN than the current SGSN. The HLR also maps each subscriber to one or more GGSNs.

The objective of the GPRS design is to maximize the use of existing GSM infrastructure while minimizing the changes required within GSM. The GSN contains most of the necessary capabilities to support packet transmission over GSM. The critical part in the GPRS network is the mobile to GSN (MS-SGSN) link which includes the MS-BTS, BTS-BSC, BSC-SGSN, and the SGSN-GGSN link. In particular, the Um interface including the radio channel is the bottleneck of the GPRS network due to the spectrum and channel speed/quality limitations. Since multiple traffic types of varying priorities are supported by the GPRS network, the quality of service criteria as well as resource management is required for performance evaluation.

The BSC will require new capabilities for controlling the packet channels, new hardware in the form of a packet control unit, and new software for GPRS mobility management and paging. The BSC also has a new traffic and signaling interface from the SGSN.

The BTS has new protocols supporting packet data for the air interface, together with new slot and channel resource allocation functions. The utilization of resources is optimized through dynamic sharing between the two traffic types handled by the BSC.

MS-SGSN Link

The logical link control (LLC) layer (see Figure 15.4) is responsible for providing a link between the MS and the SGSN. It governs the transport of GPRS signaling and traffic information from the MS to the SGSN. GPRS supports three service access points (SAPs) entities: the layer 3 management, subnet dependent convergence, and short message service (SMS). On the MS-BSS link, the radio link control (RLC), the medium access control (MAC), and GSM RF protocols are supported.

Figure 15.4. Protocol stack in GPRS.

The main drawback in implementing GPRS on an existing GSM infrastructure is that the GSM network is optimized for voice transmission (i.e., the GSM channel quality is designed for voice which can tolerate errors at a predefined level). It is therefore expected that GPRS could have varied transmission performance in a different network or coverage area. To overcome this problem, GPRS supports multiple coding rates at the physical layer.

A GPRS could share radio resources with GSM circuit switched (CS) service. This is governed by a dynamic resource sharing based on the capacity of demand criteria. A GPRS channel is allocated only if an active GPRS terminal exists in the network. Once resources are allocated to GPRS, at least one channel will serve as the master channel to carry all necessary signaling and control information for the operation of the GPRS. All other channels will serve as slave and are only used to carry user and signaling information. If no master channel exists, all the GPRS users will use the GSM common control channel (CCCH) and inform the network to allocate GPRS resources.

A physical channel dedicated to GPRS is called a packet data channel (PDCH). It is mapped into one of the physical channels allocated to GPRS (see Figure 15.5). A PDCH can either be used as a packet common control channel (PCCCH), a packet broadcast control channel (PBCCH), or a packet traffic channel (PTCH).

Figure 15.5. GPRS logical channels.

The PCCCH consists of:

•

Packet random access channel (PRACH) — uplink

•

Packet access grant channel (PAGCH) — downlink

•

Packet notification channel (PNCH) — downlink

On the other hand, the PTCH can either be:

•

Packet data traffic channel (PDTCH)

•

Packet associated control channel (PACCH)

The arrangement of GPRS logical channels for given traffic characteristics also requires the combination of PCCCHs and PTCHs. Fundamental questions such as how many PDTCHs can be supported by a single PCCCH is needed in dimensioning GPRS.

RLC/MAC Layer

The multiframe structure of the PDCH in which GPRS RLC messages are transmitted is composed of 52 TDMA frames organized into RLC blocks of four bursts resulting in 12 blocks per multiframe plus four idle frames located in the 13th, 26th, 39th, and 52nd positions (see Figure 15.6).

Figure 15.6. Idle frame location in GPRS multiframe.

B0 consists of frames 1, 2, 3 and 4, B1 consists of frames 5, 6, 7, and 8 and so on. It is important that the mapping of logical channels onto the radio blocks is done by means of an ordered set of blocks (B0, B6, B9, B1, B7, B4, B10, B2, B8, B5, B11). The advantage of ordering the blocks is mainly to spread the locations of the control channels in each time slot reducing the average waiting time for the users to transmit signaling packets. It also provides an interleaving of the GPRS multiframe.

GPRS uses a reservation protocol at the MAC layer. Users that have packets ready to send request a channel via the PRACHs. The random access burst consists of only one TDMA frame with duration enough to transmit an 11-bit signaling message. Only the PDCHs carrying PCCCHs contain PRACHs. The blocks used as PRACHs are indicated by an uplink state flag (USF = free) by the downlink pair channel.

Alternatively, the first K blocks following the ordered set of blocks can be assigned to PRACH permanently. The access burst is transmitted in one of the four bursts assigned as PRACH. Any packet channel request is returned by a packet immediate assignment on the PRACHs whose locations are broadcast by PBCCH. Optionally, a packet resource request for additional channels is initiated and returned by a packet resource assignment. The persistence of random access is maintained by the traffic load and user class with a back-off algorithm for unsuccessful attempts. In the channel assignment, one or more PTCHs (time slot) will be allocated to a particular user. A user reserves a specific number of blocks on the assigned PTCH as indicated by the USF. It is possible to accommodate more than one user per PTCH. User signaling is also transmitted on the same PTCH using the PAGCH whose usage depends on the necessity of the user.

The performance of the MAC layer depends on the logical arrangement of the GPRS channels (i.e., allocation of random access channels, access grant channels, broadcast channels, etc.) for given traffic statistics. This is determined by the amount of resources allocated for control and signaling compared to data traffic. A degree of flexibility of logical channels is also achieved as the traffic varies. The arrangement of logical channels is determined through the PBCCH.

Data Packet Routing in the GPRS Network

The following discusses data packet routing for the mobile originated and mobile terminated data call scenarios. In mobile originated data routing, the mobile gets an IP packet from an application and requests a channel reservation. The mobile transmits data in the reserved time slots. The packet switched public data network (PSPDN) PDU is encapsulated into a sub-network dependent convergence protocol (SNDCP) unit that is sent via LLC protocol over the air interface to the SGSN currently serving the mobile (see Figure 15.7).

Figure 15.7. Data call routing in GPRS network.

For mobile terminated data routing (see Figure 15.7), we have two cases: routing to the home GPRS network, and routing to a visited GPRS network. In the first case, a user sends a data packet to a mobile. The packet goes through the local area network (LAN) via a router out on the GPRS context for the mobile. If the mobile is in a GPRS idle state, the packet is rejected. If the mobile is in standby or active mode, the GGSN routes the packet in an encapsulated format to SGSN.

In the second case, the home GPRS network sends the data packet over the inter-operator backbone network to the visiting GPRS network. The visiting GPRS network routes the packet to the appropriate SGSN.

The PTP and PTM applications of GPRS are listed below:

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Point-to-point

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Messaging (e.g., e-mail)

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Remote access to corporate networks

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Access to the Internet

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Credit card validation (point-of-sales)

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Utility meter readings

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Road toll applications

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Automatic train control

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Point-to-multipoint

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PTM-multicast (send to all)

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News

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Traffic information

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Weather forecasts

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Financial updates

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PTM-group call (send to some)

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Taxi fleet management

•

Conferencing

GPRS provides a service for bursty and bulky data transfer, radio resources on demand, shared use of physical radio resources, existing GSM functionality, mobile applications for a mass application market, volume dependent charging, and integrated services, operation and management.

2.4.2 MI2-SI2 (electricity meter-CAS)

MI2-SI2 is the interface directly linking the electricity meter with the CAS. Due to cost constraints, this will usually be cellular. If a large number of nodes are installed using the network of a telecom provider, operation costs may become significant. In this case, data exchange with the meter has to be kept to a minimum.

A large number of nodes to be managed by the CAS imply this interface does not usually have high bandwidths from the electricity meter perspective. GPRS (General Packet Radio Service)/UMTS (Universal Mobile Telecommunications System) wireless technology was considered to be the most suitable technology for this interface. A protocol architecture will be studied for DLMS/COSEM. Fig. 14 illustrates this interface communication architecture.

GPRS is a mobile data service offered in GSM systems, in addition to GSM service (it is integrated into GSM Release 97 and newer releases). It was originally standardized by the European Telecommunications Standards Institute (ETSI) and now by the 3rd Generation Partnership Project (3GPP). It is nowadays globally available in nearly all countries (except South Korea and Japan). In general terms, GPRS coverage is readily available in populated areas in most countries.

GPRS is widely used in IP networks today as a WAN wireless (cellular) technology. Each GPRS subscriber obtains an IP address, which can be public or private and at the same time fixed or dynamic, depending on the contracted service features and operator capabilities. GPRS service is provided in the GSM licensed frequency bands of 800, 900, 1800, and 1900 MHz.

The GPRS Access network is divided into two sections:

GERAN (for GSM Radio Access Network) which comprises all the layers 1, 2, and 3 for the radio access network, plus all the normalized interfaces between them.

The GSM core network, comprising the GSM network switching subsystem, the Gateway GSM support nodes (GGSN), and the Service GSM support nodes (SGSN).

An electricity meter would function as an MS (Mobile Station) from a GPRS perspective.

UMTS, also known as 3G or third generation mobile technology, is an evolution of existing 2G/GPRS networks using WCDMA modulation techniques in the air interface. It is specified by 3GPP and is part of the global ITU IMT-2000 standard. There have been different releases of UMTS issued by 3GPP. The UMTS lower layer networks are owned by the mobile operator. This network can be further subdivided into two different sections:

UTRAN (UMTS Terrestrial Radio Access Network), which contains the nodes B (Base Stations) and RNCs that comprise the Radio Access Network. This network provides the coverage area, linking the electricity meter with the UMTS core network. Each of the different network sections in UTRAN contains standard interfaces to the others, so the technology can be easily upgraded while maintaining full compatibility. All this is specified in the 25 series of 3GPP specifications.

The Core Network, linking all the RNCs. The UMTS core network is an evolution of the previous 2G (GSM) core networks. It is an access-agnostic network where some services can be directly connected to the core network.

22.8.1 Authentication

An authentication similar to GPRS may occur within the WLAN, depending on the implementation. Where the GPRS operator owns the WLAN, it is likely that the operator will reuse SIM-based authentication or 3GPP-based USIM authentication for UMTS subscribers within the WLAN environment. Similarly, for a subscriber to access services provided by a GPRS operator over any WLAN access network, regardless of whether the WLAN is owned by a GPRS operator, (U)SIM-based authentication can be used. To reuse 3GPP subscription, 3GPP interworking WLAN terminals will need access to UICC smart cards with SIM/USIM applications. A WLAN equipped with a SIM/USIM smart card is called WLAN UE. Given the need for dual-mode (WLAN-cellular) UEs, SIM/USIM will be available in those UEs. The architecture of interworking WLAN access reusing 3GPP USIM/SIM and HSS is shown in Figure 22.12.

The authentication procedure shown in Figure 22.13 is based on the deployment of IEEE 802.1X with 802.11. The cellular access gateway provides the AAA server functionality in the cellular operator's IP core. The access gateway interworks with the home location register (HLR) to obtain the authentication parameters used to create the authentication challenge to the UE and validate the response to the challenge. The EAP is used in the WLAN to perform authentication of the UE, passing the subscriber identity, SIM-based authentication data, and encrypted session key(s) to be used for encryption for the life of the session [3, 4].

The authentication process starts after the UE has associated with an AP. The UE sends an EAP-Over-WLAN (EAPOW) Start message to trigger the initiation of 802.1X authentication. In steps 2 and 3 the identity of the UE is obtained with standard EAP-Request/Response messages (see Figure 22.13). Next, the AP initiates a RADIUS dialog with the access gateway by sending an Access-Request message that contains the identity reported by UE. In the SIM-based authentication, this identity typically includes the IMSI value stored in the SIM card. The access gateway uses IMSI and other information included in the identity (i.e., a domain name) to derive the address of the HLR/HSS that contains subscription data for that particular UE. In steps 5 and 6, the access gateway retrieves one or more authentication vectors from the HLR/HSS. These could be either UMTS authentication vectors (if the UE is equipped with a USIM) or GSM authentication vectors. In both cases, a random challenge, RAND, and an expected response, XRES, is included in every authentication vector. In steps 7 and 8, the random challenges sent to the UE, which runs the authentication algorithm implemented in the (U)SIM card and generates a challenge response value (SRES). In steps 9 and 10, SRES is transferred to the access gateway and compared against the corresponding XRES value received from the HSS. If these values match, a RADIUS Access-Accept is generated in step 11 (otherwise, a RADIUS Access-Reject is generated). This instructs AP to authorize the 802.1X port and allow subsequent data packets from the UE. Note that the RADIUS Access-Accept message may also include authorization attributes, such as packet filters, which are used for controlling the user's access rights in the specific WLAN environment. In step 12, the AP transmits a standard EAP-Success message and subsequently an EAPOW-Key message for configuring the session key in the UE.

Note that the authentication and authorization in the above procedure is controlled by UE's home environment (i.e., home GPRS network). The AP in the visited WLAN implements 802.1X and RADIUS but relies on the HSS in the home environment to authenticate the user. Figure 22.14 shows the protocol architecture for the authentication process. The UE is ultimately authenticated by HSS by means of either the GSM AKA or the UMTS AKA mechanisms.

The WLAN access network is connected to a 3GPP AAA proxy via the Wr reference point. The Wr reference point is used for authentication and key agreement signaling, and the protocols in this reference point are extensible authentication protocol (EAP) over DIAMETER or RADIUS (see Figure 22.15). 3GPP AAA proxy forwards authentication signaling between the WLAN access network and the 3GPP AAA server over the Ws reference point. The 3GPP AAA server verifies if the subscriber is authorized to use WLAN. The authorization information and authentication vectors needed in the authentication protocols are stored by the HSS. The 3GPP AAA server retrieves this information over the Wx reference point.

After the user has been successfully authenticated and authorized for network access, the WLAN access network grants UE access to an IP network. In the simplest case, the IP network is the public Internet, and the user data is directly routed from the WLAN access network to the Internet.

9.1.1.2 Wireless communication technology

(1)

GPRS (general packet radio service)/EDGE (enhanced data rate for GSM (global system for mobile communication) evolution)/CDMA (code division multiple access)/3G: GPRS and other technologies are regarded as a means of data transmission based on mobile communication network. This kind of technical signal can cover a wide range, adapt to the complex geographical conditions, and install conveniently. However, there are some limitation of an uncertain delay, low transmission rate, and low reliability. The suitable application of GPRS is the system with low real-time requirements.

Wireless local area networks (WLANs): it is the use of radio frequency technology constituting the LAN. IEEE802.11 is the most commonly used transmission protocol in WLAN. With continuous development, transmission rate is improved from the initial 2 to 300 Mbps, even 600 Mbps. WLAN has the advantage of high transmission rate, flexible networking, and wide covering range, which can be applied to small-scale microgrid system.

Worldwide interoperability for microware access system (WiMAX): WiMAX, namely IEEE802.16, is a new type of broadband wireless access technology. The data transmission distance is up to 50 km, with the advantage of large coverage, fast transmission, real time, low cost, and easy maintenance. While spectrum resources, standard, and security of WiMAX should be improved.

Zigbee: Zigbee is synonymous with IEEE802.15.4 protocol, which determines a short-range, low-power wireless communication technology. Zigbee network is established mainly for data transmission in industrial field automation control, having characteristics of simple, low-power consumption, easy to use, reliable, low price, and short delay. It is suitable for a variety of sensor information collection and control, due to its low transmission rate (20–250 kbps). A variety of sensors and household appliances through the Zigbee module communicate with microgrid controller in the WINSmartGrid microgrid project, University of California, Los Angeles (UCLA). At the end of 2007, Zigbee Pro is introduced enhancing scalability and security of complex networks. Therefore, it can meet the requirements of the wireless network for supervisory control and data acquisition (SCADA) system (Franceschinis et al., 2013).

4.5.4 CDMA2000/1xEV

CDMA provides a comparable mechanism to GPRS/EDGE for the IMS UE to obtain IP connectivity. The protocols and methods to set up the data session, however, have differences. The data session is established by the Point-to-Point Protocol (PPP). The UE requests the CDMA entities to assign the IP address and establish the logical connection for IP packet exchange. Once the PPP session is set up, the IP packets can be exchanged. In the CDMA network, the Packet Data Serving Node (PDSN) provides the service access to the P-CSCF, as shown in Figure 4.21. The PDSN also enables the setup of the PPP session with the UE.

CDMA networks utilize the simple IP or Mobile IP Protocol (MIP) for granting IP connectivity. Mobile IP is preferred as it can support seamless handovers. With simple IP protocol, a wireless device needs to obtain a new IP address whenever it changes its point of connection. Since the PDSN is responsible for assigning the IP address, moving from PDSN to another PDSN constitutes a change in packet data session. The IP address will have to be re-assigned. A packet data session and a PPP session are concurrent in simple IP.

With mobile IP protocol, the wireless device can maintain the same IP address as it moves between different PDSNs. The packet data session can continue to exist even through multiple PPP sessions. The mobile IP allows the PPP session to be terminated and reestablished without the need to terminate a packet data session. A packet data session can span several PDSNs. This flexibility to retain the IP address spanning across multiple PPP sessions is aided by the Home Agent (HA). The HA is an IP router function that maintains the IP address correlation with the PDSN (also functioning as a Foreign Agent). It can route the messages to the right PDSN that is currently serving the device.

Let’s examine how this works. The UE initiates the PPP session setup to obtain an IP address for the device. The request reaches the PDSN of the visited network (or the home network, if it is serving the mobile). The PDSN requests authentication of the mobile by a request to the AAA server. The UE then requests an IP address, following successful authentication. The PDSN determines the nature of the service required for the device to perform simple IP or mobile IP procedures. For Mobile IP support, the PDSN communicates with the Home Agent to store the IP address and routing information. This information can then be used subsequently to maintain the packet data session, when the UE hands over the session to another PDSN.

The underlying stacks that support this setup and enable the SIP/RTP session are shown in Figure 4.22. The protocol between the Radio Network and the PDSN is referred to as the R-P protocol, and is used to transfer both packet data and signaling messages. The packet data or the media flows are tunneled using the Generic Routing Encapsulation (GRE). The Link Access Control (LAC) layer and the MAC layers perform similar functions to the RLC and MAC in the GPRS/EDGE network. The LAC is responsible for transfer, segmentation, and re-assembly of the PDUs. The MAC layer controls the access signaling across the air interface.

CONCLUSIONS

Simulation shows how different applications operate in varying GPRS conditions. The QoS in GPRS is difficult to apply in applications that would need a guaranteed level of link quality for their operation. Therefore QoS was studied from the point of view of how these applications operate in variable GPRS conditions. The research studied extreme limits for operation and it is natural that the usability of the applications is very poor close to these limits.

MCRS tolerates delays and jitters very well whether VPN is used or not. The difference is that when using VPN the amount of data transferred is considerably higher than without it. The same is valid in situations where the amount of lost packets increases. As the GPRS link quality decreases drastically the system operates in some fashion but usability is lost. The simulated access time from mobile to MGS varies between 30 and 35 seconds depending on whether VPN tunnelling is used. The time is so long because a large of amount of data (>20kB) is transferred during this process compared to the actual page size (0,5kB). From earlier research it can be noted that without the certification phase the access time to the MGS is less than 5 seconds in practice. Thus there is development work to do to attain a highly secure and usable system.

In the future mobile UMTS networks will come in to evermore practical and wider use. The reference [5] presents the evolved QoS properties of UMTS compared to GPRS. This together with enhanced data transfer capacity should help to implement remote control applications even with modest real-time requirements.

3.2.8.3 Improved Channel Coding

The compact protocol implementation of EC-GSM-IoT compared with GPRS/EGPRS opens up for a reduced message size of the control channels. The overall message size of the control channels have, for example, been reduced from 23 octets as defined for GPRS/EGPRS to 8, 10, and 11 octets for EC-PACCH/U, EC-PACCH/D, and EC-CCCH/D, respectively. In addition to, the already mentioned blind transmissions, the improved channel coding from the reduced payload space also contributes to the coverage extensions on these logical channels.

5.1.5.1 Wireless transport technology of information

The communication methods of power line carrier, optical fiber transmission, CDMA, general packet radio service (GPRS), Wi-Fi, and so on are usually used in the power system online monitoring.

For different communication methods, the performance, characteristics, and applications are different. The data transmission power, the network area covered, group network modes, and so on also have differences [2–5]. Comparisons of some communication methods are shown in Table 5.1.

Table 5.1. Comparison of Main Telecommunication Modes

Because the transmission lines are long and wide, communication of information of the transmission lines in the monitoring system is mainly by wireless communication, such as CDMA, GPRS, Wi-Fi, ZigBee. In the region of mobile signals, public network communication platform of GPRS shall be fully exploited, so that to realize the data transmission of center to multipoint. In the region of no mobile signals, the data transmission can be realized through wireless relay with the help of wireless digital radio.