Bulletproof Wireless Security Elsevier

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Table of Contents,CH 1 Security and Cryptography,CH 2 Network Security Protocols. CH 3 Security and the Layered Architecture,CH 4 Voice Oriented Wireless Networks. CH 5 Data Oriented Wireless Networks,CH 6 Security in Traditional Wireless Networks. CH 7 Security in Wireless Local Area Networks,CH 8 Security in Wireless Ad Hoc Networks. Data Oriented,Wireless Networks, Advanced Mobile Phone System AMPS Global System for Mobile Communica.
tions GSM and Universal Mobile Telecommunications System UMTS were all. technologies geared primarily to transfer voice over a Wide Area Network WAN. With the phenomenal growth in data traf c think Internet there has been a demand. for wireless networks capable of transferring data traf c along with voice traf c. Just as in the wired world the eld of wireless is seeing the integration of voice and. data networks Second generation 2G wireless networks currently the most widely. deployed and used have been enhanced to support data Such networks are some. times referred to as 2 5G in order to distinguish them from voice only 2G wireless. networks Moreover third generation 3G networks the next generation wireless. networks have been designed with inherent support to carry both voice and data. Given the capabilities of 2 5G and 3G to carry data it may not be apparent at rst. why there was a need to design another wireless standard As we would see 802 11. and 3G are more different than they are similar Yes both of them are wireless net. work standards and yes both of them support both voice and data but 802 11 is a. LAN standard meant to connect wireless clients in a small geographical area whereas. 3G aims to provide wide area universal wireless connectivity. The rst widely deployed wireless data network standard has been IEEE s 802 11. standard The 802 11 standard is a suite of protocols de ning an Ethernet like com. munication channel using radios instead of wires Such networks are referred to. as Wireless Local Area Networks WLANs and the technology is more popularly. referred to as Wi Fi WLANs allow users to connect to a network and by extension. to the Internet without the wires Put simply 802 11 is Ethernet 802 3 without the. wires Just as we use 802 3 to form wired local area networks LANs we can use. 802 11 to create WLANs On the positive side since there are no wires to lay down to. create the network setting up WLANs is much easier than setting up LANs On the. other hand due to the nature of the wireless medium the packet loss experienced in. WLANs is much more than that in wired LANs, Another distinguishing feature of the 802 11 standard is that it operates in the. unlicensed frequency spectrum This means that 802 11 service providers popularly. referred to as Wi Fi service providers do not have to pay a spectrum usage fee to. their governments Contrast this with 3G where service providers have spent billions. of dollars in purchasing the 3G spectrum which was auctioned by governments world. wide just a few years ago Operating in the unlicensed frequency spectrum has the. advantage of keeping operating costs low but also means no protection from interfer. ence caused by other users This makes the wireless operating environment even more. dif cult to operate in,OSI Reference,Application,Presentation. Session Model,Transport Upper LLC Service,Layer Access Point. Protocols LSAP,Logical Link Control,Data Link Medium Access. Control Scope,Physical Physical IEEE 802,Medium Medium.
Figure 5 1 802 11 in the OSI Stack, The 802 11 standard speci es protocols for the physical PHY and the media access. control MAC layers of the open systems interconnection OSI stack Multiple. variations of the 802 11 standard de ne different PHY layers The rst release of. 802 11 was made in 1997 It speci ed a uni ed MAC layer and three separate PHY. layers Direct Sequence Spread Spectrum DSSS Frequency Hopping Spread Spec. trum FHSS and infrared that provided for data rates of 1 to 2 Mbps Since then the. Data Oriented Wireless Networks, standards have been enhanced to support higher data rates for example 802 11b uses. DSSS in the 2 4 GHz spectrum to reach data rates up to 11 Mbps whereas 802 11a. uses FHSS in the 5 2 GHz range to reach data rates up to 52 Mbps Figure 5 2 clari. es the 802 11 alphabet soup,supplements,higher 802 11c and 802 11f. supplements,802 11 802 11d 802 11e,MAC 802 11i and 802 11h. supplements,802 11 802 11a 802 11b,PHY and 802 11g.
Figure 5 2 The 802 11 Alphabet Soup, However the MAC layer used by all variations of 802 11 is always the same It is this. MAC layer which forms the heart of the 802 11 standard. A typical 802 11 network consists of four major physical components First we have. the station STA A STA is an end point of the connection with a wireless interface. used to access the 802 11 network Typical examples of stations are laptops palmtops. and other hand held computers Figure 5 3 shows laptops as stations. Wired network,Access Point,Basic Service Set,Extended Service Set. Figure 5 3 802 11 System Components, Second we have the Access Point AP An access point is basically a Layer 2 bridge. which has one wireless interface and one wired interface It is therefore the AP which. connects the wireless LAN or rather the stations in the WLAN to the wired LAN. As we saw in Section 4 2 radio propagation effects limit the range of wireless trans. missions In effect this means that the geographical range served by the base station1. is limited This range can be increased by increasing the transmission power level at. the base station However 802 11 has an additional constraint it operates in an unli. censed band in the spectrum By law the transmission power level in the unlicensed. band is restricted This restricts the range of an access point in 802 11 networks to. about 100 300 feet This area is called the Basic Service Area BSA Figure 5 3. shows the BSA of an AP circled While a STA is within the range of an AP it has ac. cess to the wired network and other stations in this BSA 2 The set of stations within a. BSA which can communicate with each other are called the Basic Service Set BSS. Third we have the wireless medium which actually carries the data between the STAs. and the AP The use of radio waves to carry data signi cantly complicates the design. of the physical layer since the wireless medium presents a much bigger set of chal. lenges than any other medium To deal with these complications several physical. layer solutions have been proposed and incorporated into the 802 11 standard Dif. ferent physical layers satisfy different requirements in different environments Which. physical layer is being used by in an 802 11 WLAN can usually be determined by the. letter that follows 802 11 for example 802 11b uses DSSS 802 11a uses Orthogonal. Frequency Division Multiplexing OFDM and so on To deal with multiple physical. layers all of which use the single 802 11 MAC layer the 802 11 standard splits the. physical layer into two components the PLCP and the PMD The Physical Medium. Dependent PMD is responsible for actually transmitting the frames onto the wireless. medium As is obvious from the name this layer is different for each physical layer. DSSS OFDM FHSS and so on The Physical Layer Convergence Protocol PLCP. is responsible for providing a uniform interface of the various physical layers and the. PMDs to the 802 11 MAC layer The position of the PLCP in the OSI model is hazy. The PLCP sits between Layers 1 and 2 and abstracts the variations of the physical lay. ers so that the 802 11 MAC can function independently of the physical layer in use. BTS in GSM Node B in 3G and so on, 802 11 infrastructure networks require even the inter STA communication in a BSA to go through the AP. 802 11e does allow STAs to bypass the AP for communicating with each other. Data Oriented Wireless Networks, Finally we have the Distribution System DS The DS refers to the wired network.
that the AP connects to on its wired interface When a packet frame destined for the. wired network arrives over the wireless interface at the AP the AP forwards it on its. wired interface to the DS The DS is responsible for delivering it to the right node. which may be a STA on the wired network another AP or a router Also if the STA is. mobile and if it moves out of the range of the AP and enters into the range of another. AP this station expects its session to be uninterrupted Obviously this requires that the. two APs be able to communicate with each other The APs communicate with each. other using the DS In other words the DS connects various APs to form an Extended. Service Set ESS The existence of a DS and hence the existence of an ESS allows. for the possibility of transparent handoff when a STA is mobile The 802 11 standard. does not specify any particular technology for the distribution systems However. most commercial implementations of 802 11 use Ethernet as the distribution system. Wireless Client,Basic Service Set BSS,Wireless Client. Wireless Client,Wireless Client,Basic Service Set BSS. Extended Service Set ESS,Figure 5 4 802 11 System Overview. 5 1 1 Addresses in 802 11, There are two important addresses in traditional wired data networks the IP address. and the MAC address IP addresses are used at Layer 3 for routing packets and MAC. addresses are used at Layer 2 Each STA in an 802 11 network is uniquely identi. ed by its MAC This is similar to how end points are identi ed in traditional wired. 5 1 2 Connection Setup in 802 11,mobile terminal,infrastructure.
access point,application application,LLC LLC LLC,802 11 MAC 802 11 MAC 802 3 MAC 802 3 MAC. 802 11 PHY 802 11 PHY 802 3 PHY 802 11 PHY,Figure 5 5a 802 11 System Architecture. As we said at the beginning of this section 802 11 is a LAN standard which was. designed primarily for data communication The Traditional Wireless Networks. TWNs were designed primarily for voice and aimed to extend and inter work with. the Public Switched Telephone Network PSTN The TWN model therefore extends. the connection oriented circuit switched model of the PSTN This means that sig. naling is used to establish a connection between the endpoints of communication. Establishing a connection involves reserving circuits in the trunks and the switches. which would carry the voice call, The 802 11 standard on the other hand ts in more closely with the IP network. model than with the PSTN model The IP networking model is a connectionless. Data Oriented Wireless Networks,TWNs WLANs MANETs, Frequency Spectrum Licensed Unlicensed Can use either. Services Primarily Voice Primarily Data Primarily Data. Geographical Coverage WAN LAN PAN, End User Service End to End Last Hop Link Layer End to End.
Legacy PSTN based IP based IP based, Core Infrastructure Circuit Switched Packet Switched Not Used. Air Interface Packet Switched Packet Switched Packet Switched. Connection Connection Oriented Connection Less Connection Less. Signaling SS7 N A N A, Bandwidth Reserved using signaling per packet contention per packet contention. Dominant Standards GSM UMTS 802 11 HIPERLAN In Research phase. Figure 5 5b Wireless Networks Comparisons, packet switched network where each packet is routed independently and there is no. concept of a connection The term connection setup therefore becomes irrelevant in. an 802 11 network Since the 802 11 standard has been designed with the IP network. model in mind there is no concept of an end to end connection between the commu. nicating end points and no resources are reserved in the network Instead each STA. competes to transmit each and every packet There is however a concept of associa. tion between the STA and the AP in 802 11 networks. We will look at the process of association in a moment but before that we need to. understand what association is and why is it used in WLANs Remember that TWNs. used location management to route incoming calls to the end user The exact location. of the mobile station MS the exact cell in which the user currently is is deter. mined only when needed in other words only when there is an incoming call for that. mobile To nd out the exact cell of the MS during call setup the mobile switching. center MSC requests a set of base transceiver stations BTSs to broadcast a page. request in their respective cell The MS is then expected to send a page response back. to the BTS This BTS then informs the MSC that it has located the desired MS This. locate when needed approach works for TWNs because they are connection oriented. networks where the connection establishment is done once at the beginning of a call. and then all voice follows the same path Contrast this with the datagram packet. oriented approach in IP based networks where each packet is routed independently. 802 11 is designed to work in such an environment Using a locate when needed. approach for each packet is obviously too much overhead and therefore not an option. What is needed is for the DS to know the location of the end user at all times so. that it can route the packets destined to that STA whenever such packets arrives This. is achieved by the AP Whenever a STA is within the BSA of an AP it associates with. the AP Think of the association process like a STA registering its location with the. Bulletproof Wireless Security GSM UMTS 802 11 and Ad Hoc Security By Praphul Chandra June 2005 ISBN 978 0 7506 7746 2 Paperback 272 Pages 52 95 Order from Newnes Mail Elsevier Science Order Fulfillment 11830 Westline Industrial Dr St Louis MO 63146

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