3.4 Security Sublayer

3.4 Security Sublayer

The MAC Sublayer also contains a separate Security Sublayer (Figure 3.2) providing authentication, secure key exchange, encryption and integrity control across the BWA system. The two main topics of a data network security are data encryption and authentication. Algorithms realising these objectives should prevent all known security attacks whose objectives may be denial of service, theft of service, etc.

In the 802.16 standard, encrypting connections between the SS and the BS is made with a data encryption protocol applied for both ways. This protocol defines a set of supported cryptographic suites, i.e. pairings of data encryption and authentication algorithms. An encapsulation protocol is used for encrypting data packets across the BWA. This protocol defines a set of supported cryptographic suites, i.e. pairings of data encryption and authentication algorithms. The rules for applying those algorithms to an MAC PDU payload are also given.

An authentication protocol, the Privacy Key Management (PKM) protocol is used to provide the secure distribution of keying data from the BS to the SS. Through this secure key exchange, due to the key management protocol the SS and the BS synchronize keying data. The basic privacy mechanisms are strengthened by adding digital-certificate-based SS authentication to the key management protocol. In addition, the BS uses the PKM protocol to guarantee conditional access to network services. The 802.16e amendment defined PKMv2 which has the same framework as PKM, re-entitled PKMvl, with some additions such as new encryption algorithms, mutual authentication between the SS and the BS, support for a handover and a new integrity control algorithm.

3.3 Medium Access Control Common Part Sublayer

3.3 Medium Access Control Common Part Sublayer (MAC CPS)

The Common Part Sublayer (CPS) resides in the middle of the MAC layer. The CPS represents the core of the MAC protocol and is responsible for:

• bandwidth allocation;

• connection establishment;

• maintenance of the connection between the two sides.

The 802.16-2004 standard defines a set of management and transfer messages. The management messages are exchanged between the SS and the BS before and during the establishment of the connection. When the connection is realised, the transfer messages can be exchanged to allow the data transmission.

The CPS receives data from the various CSs, through the MAC SAP, classified to particular MAC connections. The QoS is taken into account for the transmission and scheduling of data over the PHY Layer. The CPS includes many procedures of different types: frame construction, multiple access, bandwidth demands and allocation, scheduling, radio resource management, QoS management, etc. These functions are detailed in Chapters 8 to 11.

3.2 Convergence Sublayer (CS)

3.2 Convergence Sublayer (CS)

The service-specific Convergence Sublayer (CS), often simply known as the CS, is just above the MAC CPS sublayer (see Figure 3.2). The CS uses the services provided by the MAC CPS, via the MAC Service Access Point (SAP). The CS performs the following functions:

• Accepting higher-layer PDUs from the higher layers. In the present version of the standard ^[1], CS specifications for two types of higher layers are provided: the asynchronous transfer mode (ATM) CS and the packet CS. For the packet CS, the higher-layer protocols may be IP v4 (version 4) or v6 (version 6).

• Classifying and mapping the MSDUs into appropriate CIDs (Connection IDentifier). This is a basic function of the Quality of Service (QoS) management mechanism of 802.16 BWA.

• Processing (if required) the higher-layer PDUs based on the classification.

• An optional function of the CS is PHS (Payload Header Suppression), the process of suppressing repetitive parts of payload headers at the sender and restoring these headers at the receiver.

• Delivering CS PDUs to the appropriate MAC SAP and receiving CS PDUs from the peer entity.

Chapter 3: Protocol Layers and Topologies

In this chapter, the protocol layer architecture of WiMAX/802.16 is introduced. The main objectives of each sublayer are given as well as the global functions that they realise. Links are provided to the chapters of this book where each of these sublayers or procedures are described in much more detail.

3.1 The Protocol Layers of WiMAX

The IEEE 802.16 BWA network standard applies the so-called Open Systems Interconnection (OSI) network reference seven-layer model, also called the OSI seven-layer model. This model is very often used to describe the different aspects of a network technology. It starts from the Application Layer, or Layer 7, on the top and ends with the PHYsical (PHY) Layer, or Layer 1, on the bottom (see Figure 3.1).

Figure 3.1: The seven-layer OSI model for networks. In WiMAX/802.16, only the two first layers are defined

The OSI model separates the functions of different protocols into a series of layers, each layer using only the functions of the layer below and exporting data to the layer above. For example, the IP (Internet Protocol) is in Layer 3, or the Routing Layer. Typically. only the lower layers are implemented in hardware while the higher layers are implemented in software.

The two lowest layers are then the Physical (PHY) Layer, or Layer 1, and the Data Link Layer, or Layer 2. IEEE 802 splits the OSI Data Link Layer into two sublayers named Logical Link Control (LLC) and Media Access Control (MAC). The PHY layer creates the physical connection between the two communicating entities (the peer entities), while the MAC layer is responsible for the establishment and maintenance of the connection (multiple access, scheduling, etc.).

The IEEE 802.16 standard specifies the air interface of a fixed BWA system supporting multimedia services. The Medium Access Control (MAC) Layer supports a primarily point to-multipoint (PMP) architecture, with an optional mesh topology (see Section 3.7). The MAC Layer is structured to support many physical layers (PHY) specified in the same standard. In fact, only two of them are used in WiMAX.

The protocol layers architecture defined in WiMAX/802.16 is shown in Figure 3.2. It can be seen that the 802.16 standard defines only the two lowest layers, the PHYsical Layer and the MAC Layer, which is the main part of the Data Link Layer, with the LLC layer very often applying the IEEE 802.2 standard. The MAC layer is itself made of three sublayers, the CS (Convergence Sublayer), the CPS (Common Part Sublayer) and the Security Sublayer.

Figure 3.2: Protocol layers of the 802.16 BWA standard. (From IEEE Std. 802.16-2004 ^[1]. Copyright IEEE 2004, IEEE. All rights reserved.)

The dialogue between corresponding protocol layers or entities is made as follows. A Layer X addresses an XPDU (Layer X Protocol Data Unit) to a corresponding Layer X (Layer X of the peer entity). This XPDU is received as an (X-1)SDU (Layer X-1 Service Data Unit) by Layer X-1 of the considered equipment. For example, when the MAC Layer of an equipment sends an MPDU (MAC PDU) to a corresponding equipment, this MPDU is received as a PSDU (PHYsical SDU) by the PHYsical Layer (see Figure 3.2).

In this chapter, the different layers are introduced. Each of these layers or sublayers and many of their functions are described in the following sections.

2.6 The Korean Cousin: WiBro

2.6 The Korean Cousin: WiBro

South Korea has definitely an advantage in modern telecommunication networks, whether in ADSL (Asymmetric Digital Subscriber Line) or 3G figures. The TTA PG302 BWA standard was approved in June 2004 by the TTA (Telecommunications Technology Association, the Korean standardisation organisation) and is known as WiBro (Wireless Broadband). This standard has the support of leading people in the Korean telecommunication industry.

Originally sought as a competitor of WiMAX, an agreement was found by the end of 2004, while 802.16e was still under preparation, between 802.16 backers (including Intel) and WiBro backers in order to have WiBro products certified as WiMAX equipments.

WiBro licenses were assigned in Korea in January 2005. The three operators are Korea Telecom (KT), SK Telecom (SKT) and Hanaro Telecom. Pilot networks are already in place (April 2006). Relatively broad coverage public commercial offers should start before the end of 2006. WiBro planned deployments in other countries have been reported (among others. Brazil). This should give WiBro an early large-scale BWA deployment and then provide important field technical and market observations.

2.5 Other 802.16 Standards

2.5 Other 802.16 Standards

In addition to the 802.16e amendment of the 802.16 standard, other amendments have been made or are still in preparation. The goal of these amendments is to improve certain aspects of the system (e.g. have a more efficient handover) or to clarify other aspects (e.g. management information).

The 802.16f amendment, entitled ‘Management Information Base’, was published in December 2005 and provides enhancements to IEEE 802.16-2004, defining a Management Information Base (MIB) for the MAC and PHY and the associated management procedures (see Section 3.6 for more details on 802.16f).

The 802.16g amendment was still at the draft stage in October 2006. The draft is entitled ‘Management Plane Procedures and Services’ and the amendment approval is planned for May 2007 (October 2006 information). It should provide the elements for efficient handover, high-performance QoS (Quality of Service) management and radio resource management procedures.

Other amendments at the draft stage are the following (from the IEEE 802.16 website, July 2006):

• 802.16/Conformance04 – Protocol Implementation Conformance Statement (PICS) proforma for frequencies below 11 GHz;

• 802.16k – Media Access Control (MAC) Bridges – Bridging of 802.16.

Amendments at the pre-draft stage are the following:

• 802.16h – Improved Coexistence Mechanisms for License-Exempt Operation;

• 802.16i – Mobile Management Information Base, where the objective is to add mobility support to the 802.16f fixed MIB standard.

Work on the 802.16j amendment draft has been reported, which concerns the Multi-hop Mobile Radio (MMR). Hence, 802.16j should provide some enhancement for the Mesh mode. The Project Authorization Request (PAR) of 802.16j was approved in March 2006.

2.4 Predicted Products and Deployment Evolution

2.4 Predicted Products and Deployment Evolution

2.4.1 Product Types

Different types of WiMAX products are expected.

First step: CPE products. These CPE products are first outdoor (see Figure 1.5) and then indoor. These are the products already certified (mainly outdoor for the moment). For CPEs WiMAX products, some providers may require that only authorised installers should install the equipment for subscribers. It can be expected that self-installed CPEs will quickly appear.

Second step: devices installed on portable equipments. These portable equipments will first be laptops. It is expected (and probably already realised by the time of publication of this book) that these laptop-installed WiMAX devices may have a USB (Universal Serial Bus) connection, PCMCIA (Personal Computer Memory Card International Association) (less probable), a PCI (Peripheral Component Interconnect) connection or another type of connection. In this case, a WiMAX subscriber can move in a limited area (the one covered by the BS) and then nomadicity will be realised.

Later, a WiMAX internal factory-installed device in laptops will probably appear, as is already the case for WiFi. This will clearly produce a situation where WiMAX will spread widely. The difficulties encountered are of two types:

• manufacturing devices small enough; this do not really seem to be a difficult problem:

• radio engineering and deployment considerations, where the technology and deployment techniques should be mature enough to have a high concentration of subscribers.

Final step: WiMAX devices in PDA and other handheld devices such as a mobile phone. For this, WiMAX devices need to be even smaller. They could take the shape of the SIM (Subscriber Identity Module) cards presently used for cellular systems (second and third generation). Thus WiMAX will be a mobile network and then a competitor for 3G systems.

2.4.2 Products and Deployment Timetable

Once WiMAX evolution is described, we need to know about the timetable of these products. What about the network deployments? As of today a large number of pre-WiMAX networks exist around the world, both in developed and developing countries. These deployments are often on a scale smaller than the whole country, typically limited to a region or an urban zone. For example, in France, Altitude Telecom operator proposes a BWA subscription in four geographic departments: Calvados, Orne, Seine-et-Marne and Vendée. The displayed data rate is 1 Mb/s (June 2006). Many fixed WiMAX networks (then using the recently certified products) are imminent, some of them belonging to pre-WiMAX operators planning to upgrade to certified WiMAX.

Table 2.5 is based on documents and conferences by WiMAX actors. The (e), expected, dates are only assumptions. Some of these previewed dates may be changed in the future.

Table 2.5: WiMAX products and networks timetable: (e), expected
Open table as spreadsheet

	Products	Certification	Networks
2005	Proprietary (pre-WiMAX); outdoor CPE		Fixed
2006	Pre-WiMAX equipments; first use of WiMAX certified products	Since January 2006, certification of fixed WiMAX equipments based on IEEE 802.16-2004 (see Section 2.3.1)	Launch of WiBro service in Korea; (e) first nomadic use of WiMAX?
2007	(e) Indoor, self-installed; (e) first use of mobile WiMAX, wave 1 (no MIMO and AAS, etc.)	(e) Certification of mobile WiMAX equipments based on IEEE 802.16e	(e) Nomadic use of WiMAX
2008	(e) Ramp-up of mobile WiMAX products, wave 1 and wave 2 (MIMO and AAS)		(e) Mobility