A Study on Multi Wireless Technologies – Architectures and Security Mechanisms

 

Dr.Hari Ramakrishna

Professor, Department of CSE,

Chaitanya Bharathi Institute of technology

Gandipet -500 075, Hyderabad,

dr.hariramakrishna@rediffmail.com

K.Ravi

Asst. Professor

Dept. of Informatics

Alluri Institute of Management Sciences

kolipakaravi@yahoo.co.in

ABSTRACT

Years are going and the Wireless Communication medium is changing its structure is also changing. In this paper, we focus four types of wireless communication technologies. This paper describes the architectures of these four technologies with there security issues.

All these four models have there different structures and have different mechanisms to handle the data communication between the stations. In this paper we also defined the IEEE 802.1X standards for the four different models and there mechanisms.

Keywords: Wi-Fi, Bluetooth, ZigBee, WiMAX, Networks, IEEE 802.1X, Security, Architecture

1. INTRODUCTION

Today wireless is becoming the leader in communication choices among users. It is not anymore a backup solution for nomadic travelers but really a new mood naturally used everywhere even when the wired communications are possible. Many technologies evolve then continuously, changing the telecommunication world. In this paper we consider four wireless technologies with there architectures and security aspects. The four wireless technologies are:

 

1)       Wi-Fi

2)       Bluetooth

3)       ZigBee

4)       WiMAX

In this paper we can see the IEE 802.1X standard wireless communication models for these wireless technologies. There are many models but we can few of them. We can also see the advantages over the previous technologies in different aspects. Final this paper cover the security issues in these technologies

2. IEEE 802.11 ARCHITECTURE FOR Wi-Fi

 

The IEEE 802.11 standard defines three modes for Wi-Fi wireless Technology

 

1)       Infrastructure Mode

2)       Ad hoc Mode

3)       Mesh Mode

2.1 INFRASTRUCTURE MODE

Within the infrastructure mode, the wireless network consists of at least an access point (AP) connected to the fixed network infrastructure and a set of wireless client stations. This configuration is based on a cellular architecture where the system is subdivided into cells. Each cell in the IEEE 802.11.

 

The stations within a base stations (BSS) execute the same MAC protocol and compete for access to the same shared wireless medium. We can refer to it in the following sections as a cell. Although a WLAN may be formed by a single cell, the maximum distance between stations is limited by many factors like RF output power and the propagation conditions of the indoor/outdoor environments. To provide for an extended coverage area, multiple BSSs are used where the APs are connected through a backbone called a distribution system (DS).

 

The whole interconnected WLAN including at least two different BSSs (with respect to their APs) and the DS, is seen as a single logical IEEE 802 network to the logical link control (LLC) level and is called an Extended Service Set (ESS). The majority of WLANs should be able to reach the fixed LAN services (file servers, printers and Internet access). The DS is responsible of transporting the packets between various cells within the ESS area. Data transfers occur between stations within a BSS and the DS via an AP. DS handles address mapping and networking functions.

 

 

 

Figure 1: Infrastructure mode in IEEE 802.11 for Wi-Fi

BSSs may partially overlap. This is commonly used to cover an extended area. BSSs could be physically disjointed or collocated. To provide flexibility to the WLAN architecture, IEEE 802.11 logically separates the wireless medium from the DS medium. The DS can correspond to an Ethernet network, Token Ring, FDDI or any other communication network such as a wireless IEEE 802.11 point to point.A wide zone ESS can also provide to the various client stations an access towards a fixed network, such as Internet. Before any communication can be set within a BSS, the wireless client stations must execute an association with the AP.

2.2 AD HOC MODE:

The ad hoc mode (Figure 2.6) simply represents a group of IEEE 802.11 wireless stations that communicate directly between them without having a connection with an AP or a connection to a fixed network through the DS. This configuration is sometimes referred as a peer-to-peer configuration. Each station can establish a communication with any other station in the cell which is called an independent cell Independent Basic Service Set (IBSS). These networks have been studied at the beginning of the 1970s and were named packet radio networks (PRNET).

 

 

 

Figure 2: Ad hoc mode

This mode allows to create quickly and simply a wireless network where there is not fixed infrastructure or where such an infrastructure is not necessary for the required services (hotel room, conference centers or airport), or finally when the access to the fixed network is prohibited or difficult.

 

Ad hoc wireless networks have emerged as a category of wireless networks that utilize multihop radio relays and are capable of operating in a self-organizing and self-configuring manner without the support of any fixed infrastructure. The principle behind ad hoc networking is multihop relaying, which was studied in the past under the name of PRNET in relation to defence research carried by the Defense Advanced Research Projects Agency (DARPA).

 

2.3 MESH MODE

The third type defines a hybrid configuration combining infrastructure and ad hoc modes

 

2.4 Wi-Fi SERVICES

The IEEE 802.11 standard Wi-Fi technology architecture supports a series of basic services that are:

 

Ø       Association/disassociation  / resuscitation

Ø       Delivery of the MAC/MSDU frames

Ø       Authentication/deauthentication

Ø       Diffusion and broadcast

Ø       Beacon and probing

Ø       Privacy/confidentiality

Ø       Higher-layer timer synchronization/QoS traffic scheduling

Ø       Radio measurements

3. IEEE 802.15.1 ARCHITECTURE FOR BLUETOOTH

Bluetooth communication requires two preliminary things: first we have to know the devices in the neighborhood and second there must be a pre established circuit. Communication is also based on a master–slave principle. A group of equipments forms a cell called piconet.

 

A piconet comprises a master and seven slaves at the maximum. Several piconets can overlap and form a “scatternet” (see Figure 3.3). In a piconet the communication is based on the master to harmonize the frequencies and channels. We know the neighbors through the discovery phase while in a scatternet there is a need to route data between masters and relay nodes.

 

 

 

Figure 3: IEEE 802.15.1 Bluetooth Master/Slave Architecture

Two slave devices cannot talk directly to each other except during the discovery phase. Channel allocation and communication establishment are under the responsibility of the master. Although there was a limitation in earlier versions of Bluetooth on the number of simultaneous channels in a piconet, it is removed from the current version as the cell capacity has increased significantly. The standard supports also broadcast by simply removing the destination from the messages.

The master is responsible of polling nodes and also allocating/blocking new connection  andwidth. It is responsible for setting the piconet synchronization clock and as we will see decides for the frequency hopping sequence (FHS). A slave can be part of several piconets.

 

 

 

Figure 4: Bluetooth Scatternet

One major interesting feature of Bluetooth is that it is not dependent on the IP. This courageous design decision eases the deployment of devices that do not need to worry about upper layer problems such as address allocation, default router, netmask, etc. Auto configuration is hence much easier. In Bluetooth we identify several protocols:

 

Ø      Lower layer protocols: Baseband, LMP, L2CAP, service discovery

Ø      protocol (SDP)

Ø      Interfacing protocols: RFCOMM

Ø      Applicative control specifications: TCS Binary, AT Commands

Ø       Applicative protocols: PPP, TCP/IP, OBEX, WAP, vCard, VCal, WAE

4. IEEE 802.15.4 ARCHITECTURE FOR ZIGBEE

ZigBee is the architecture developed on top of the IEEE 802.15.4 reference stack model and takes full advantage of its powerful physical radio layer. IEEE 802.15.4 and ZigBee Alliance continue to work closely to ensure an integrated and complete solution for the market especially for sensor networking-based applications. ZigBee provides services such as security, discovery, profiling and so on for the two layers specified by the IEEE group.

As shown in Figure 5 the different topologies that can range from a centralized star or a cluster-tree-based architecture to a complete mesh network. In the last case there is a need to have an additional routing protocol.

 

 

 

Figure 5: Basic possible topologies and node categories in IEEE 802.15.4

A possible architecture for mesh network is shown in Figure 6: Mesh networking enables to increase range, reliability (self-healing) and formation of ad hoc networks where redundant  paths are provided.

 

 

 

Figure 6: Mesh Network of ZigBee

 

IEEE 802.15.4 is hence a low-rate wireless personal area network solution. It is designed to be simple for low-power devices and lightweight wireless networks. These devices rely on long-life battery normally measurable in years, but they do not claim any high throughput and should not be used in this field.

 

4.1 THE DATA RATES AND FEATURES

Ø       Data rates from 20 to 250 Kbps

Ø       Different topologies such as conventional star and mesh operation

Ø       Addressing based on short 16 bits or normal MAC (64 bits) addresses

Ø       Support of simple access and slotted allocation with guarantees

Ø       Support of acknowledged data transfer, and an optional beacon structure

Ø       Energy detection (ED)

Ø       Link quality indication (LQI)

Ø       Multilevel security.

5. IEEE802.16 STANDARDS AND WIMAX

The IEEE 802.16 group has started to produce recommendations for a relatively long period. The evolution of the wireless physical layers is seen in the different versions, the same way it can be noticed in IEEE 802.11 standard. That is why we can see a first physical layer implementing plesiochronous digital hierarchy (PDH) like data rates with a line of sight restrictive condition.

 

Few years later, with the familiarization to OFDM, a new version has come up with “line of sight” restriction removed but with lower throughput.We did not see any IEEE 802.16 equipment in the first editions of the standard, not because the lack of products, but because of the unclear legislation in that area together with the wide deployment of fixed asymmetric digital subscriber line (ADSL) wired lines.