802 11 NETWORKS Prepared for Information Systems 311 California State University Northridge Prepared by Olga Agnew Bryant Likes Daewon Seo November 19 2002 Table of Contents Introduction 1 802 11 Overview 1 802 11 Components 2 802 11 Topologies 2 802 11 Media Access Control 3 802 11 Network Operations 4 802 11b 6 Data Transmission 6 802 11a 7 Data Transmission 7 Comparing 802 11b and 802 11a 8 802 11 Security 9 Security Issues 9 802 11 Security Mechanisms 9 Future of Wireless Security 12 Works Sited 13 Questions 14 ii Introduction Just like the cell phone revolution of the 90 s there is a wireless revolution going on all around us Traditional networks are going wireless Wireless networks free users from the cables of traditional networks allowing them to become fully mobile There are many wireless standards being proposed from Bluetooth to Third generation 3G mobile telephony networks But the 802 11 networking standards are the only standards that have gained mainstream acceptance and use For less than 100 home users can add wireless access to their home networks saving them from the hassle of running wires through out their house Products using the original 802 11 standard were initially released in 1997 and were limited to 2 Mbps Gast 2002 The Institute of Electrical and Electronics Engineers IEEE 802 11 working group which is responsible for the 802 11 standards quickly began working on faster standards They produced both 802 11a and 802 11b which were released in 1999 Products based on 802 11b were released in 1999 and have been widely successful while products based on 802 11a were not released until 2000 and are just now starting to become available 802 11b networks run at speeds up to 11 Mbps 802 11a networks run at speeds up to 54 Mbps Gast 2002 However wireless networks also have some drawbacks Security is the biggest issue when implementing wireless networks With traditional networks cables can be hidden in the walls and access to them can be controlled In contrast wireless networks broadcast their traffic across the air allowing anyone in range to listen in on the transmission The current versions of 802 11 allow for some basic encryption to solve this problem but it has been demonstrated that it can be broken with only a small amount of effort This report will look how 802 11 networks work the details of 802 11a and 802 11b how they differ and what type of security issues exist 802 11 Overview In order to understand wireless networks it is helpful to first have a basic understanding of how traditional wired networks work Almost 95 percent of all local area networks LAN installed today use some form of Ethernet Dennis 2002 Ethernet networks consist of network interface cards NIC network cables and hubs or switches Each computer on the network will have a NIC which is connected to a central hub using a network cable Inside the hub is a bus that connects the hub s ports into which the network cables are plugged Data can then travel between computers by being broadcast from the NIC across the cable and into the hub which then broadcasts the data back to all the computers connected to it 1 1 When a switch is used instead of a hub the network works in a different matter However switched networks are beyond the scope of the report 1 802 11 wireless networks are built on the already successful Ethernet standard In an 802 11 network each computer must also have a NIC However there are no cables plugged into it 802 11 networks also have something similar to a hub which is called an access point AP Since there are no cables each computer on the network sends its message from its NIC to the AP through the air using radio 2 802 11 Components 802 11 networks can be broken down into four main components Figure 1 shows these four components Figure 1 Gast 2002 Distribution System The distribution system is made up of one or more access points This system is also responsible for communication between access points which enables users to move from one access point to another if more than one access point is used Access Points An access point is a device that accepts messages that are sent from 802 11 NICs and can broadcast those messages back out The AP is connected to the distribution system and acts as a bridge between the wired and wireless networks Wireless Medium 802 11 network devices communicate using radio frequencies that travel through the air The air is the medium that replaces the cables in Ethernet networks However the wireless communication can also pass through walls and floors which can also be considered part of the medium Stations Each computer on a 802 11 wireless network is called a station A station consists of the computer as well as the NIC which is used to transmit the signal 802 11 Topologies There are two basic types of network topologies that 802 11 networks can use Both of these types of networks are shown in figure 2 Independent networks 802 11 networks can be formed without using access points These types of networks are called independent networks or ad hoc networks In this type of topology each station connects directly to the other stations in the network This means that a station can only send messages to other stations that are in that stations range 2 The 802 11 standard also supports sending message using infrared IR light instead of radio however because of the limitations of IR it has never been used 2 Figure 2 Gast 2002 Infrastructure networks 802 11 networks can also be structured with an access point that acts much like the hub of an Ethernet network This type of topology is advantageous for several reasons First stations can communicate with other stations that may be out of their range As long as each station can connect to the access point then each station can communicate with all the other stations Secondly the access point can serve as a centralized control unit which controls access to the network Of the two topologies infrastructure networks are by far the most common Independent networks are usually used more for group meetings rather than permanent solutions Infrastructure networks can also have multiple access points which allows them to span over larger areas Wireless Bridging In addition to the two main topologies of wireless networks 802 11 wireless networking can also be used to bridge two sections of a network together This is done by using two access points as bridges Instead of the normal antenna which has a circular range of