Paper
The First Wireless Network Protocol: 802.11
Approval of the IEEE 802.11 standard for wireless local area networking (WLAN) and rapid progress made toward higher data rates have put the promise of truly mobile computing within reach. While wired LANs have been a mainstream technology for at least fifteen years, WLANs are uncharted territory for most networking professionals. Some obvious questions come to mind when considering wireless networking:
+ How can WLANs be integrated with wired network infrastructure?
+ What is the underlying radio technology?
+ How is multiple access handled?
+ What about network security?
IEEE 802.11 is limited in scope to the Physical (PHY) layer and Medium Access Control
(MAC) layer (Lough, 3), but it shares MAC characteristics with the IEEE 802.3 Ethernet standard (3Com, 2). The following overview explains major differences between wired and wireless LANs and should answer some of the questions that arise when evaluating WLAN technology.
Network Topology
WLANs can be used either to replace wired LANs, or as an extension of the wired LAN infrastructure. The basic topology of an 802.11 network is shown in Figure 1. A Basic Service Set (BSS) consists of two or more wireless nodes, or stations, which have recognized each other and have established communications. In the most basic form, stations communicate directly with each other on a peer-to-peer level sharing a given cell coverage area. This type of network is often formed on a temporary basis, and is commonly referred to as an ad hoc network, or Independent Basic Service Set (IBSS) (Geier, 3).
Figure 1 (Intel, 1)
In more structured environments, the BSS contains an Access Point (AP). The main function of an AP is to form a bridge between wireless and wired LANs. The AP is similar to a basestation used in cellular phone networks. When an AP is present, stations do not communicate on a peer-to-peer basis. All communications between stations or between a station and a wired network client go through the AP. AP s are not mobile, and form part of the wired network infrastructure. A BSS in this configuration is said to be operating in the infrastructure mode.
The Extended Service Set (ESS) consists of a series of overlapping BSSs (each containing an AP) connected together by means of a Distribution System (Geier, 3). Although the Distribution System could be any type of network, it is almost invariably an Ethernet LAN. Mobile nodes can roam between APs and seamless campus-wide coverage is possible.
Radio Technology
IEEE 802.11 provides for two variations of the physical layer. These include two RF technologies, namely, Direct Sequence Spread Spectrum (DSSS), and Frequency Hopped Spread Spectrum (FHSS). The DSSS and FHSS physical layer options were designed specifically to conform to FCC regulations for operation in the 2.4 GHz ISM bands, which has worldwide allocation for unlicensed operation (Geier, 3). Both FHSS and DSSS physical layers currently support 1 and 2 Mbps. However, all 11 Mbps radios are DSSS.
Multiple Access
The basic access method for 802.11 is the Distributed Coordination Function (DCF) which uses Carrier Sense Multiple Access / Collision Avoidance (CSMA / CA) (Lough, 4) similar to AppleTalk. This requires each station to listen for other users. If the channel is idle, the station may transmit. However if it is busy, each station waits until transmission stops, and then enters into a random back off procedure. This prevents multiple stations from seizing the medium immediately after completion of the preceding transmission.
Packet reception in DCF requires acknowledgement. The period between completion of packet transmission and start of the acknowledgement (ACK) frame is one Short Inter Frame Space (SIFS) or 28 microseconds (Brenner, 8). ACK frames have a higher priority than other traffic. Fast acknowledgement is one of the significant features of the 802.11 standard, because it requires ACKs to be handled at the MAC sublayer.
Transmissions other than ACKs must wait at least one DCF inter frame space (DIFS) or 128 microseconds before transmitting data (Brenner, 8). If a transmitter senses a busy medium, it determines a random back-off period by setting an internal timer to an integer number of slot times. Upon expiration of a DIFS, the timer begins to decrement. If the timer reaches zero, the station may begin transmission. However, if the channel is seized by another station before the timer reaches zero, the timer setting is retained at the decremented value for later transmission.
The method described above relies on the assumption that every station can hear all other stations. This is not always the case. Referring to Figure 2, the access point is within range of the Station A, but Station B is out of range. Station B would not be able to detect transmissions from Station A, and the probability of collision is greatly increased. This is known as the Hidden Node (Lough, 4).
Figure 2 (Intel, 3)
To combat this problem, a second carrier sense mechanism is available. Virtual Carrier Sense enables a station to reserve the medium for a specified period of time through the use of RTS/CTS frames. In the case described above, Station A sends an RTS (ready to send) frame to the AP. Station B will not hear the RTS. The RTS frame contains a duration/ID field, which specifies the period of time for which the medium is reserved for a subsequent transmission. The reservation information is stored in the all stations detecting the RTS frame (Brenner, 6).
Upon receipt of the RTS, the AP responds with a CTS (clear to send) frame, which also contains a duration/ID field specifying the period of time for which the medium is reserved. While Station B did not detect the RTS, it will detect the CTS and update itself accordingly. Thus, collision is avoided even though some nodes are hidden from other stations. The RTS/CTS procedure is invoked according to a user specified parameter. It can be used always, never, or for packets that exceed an arbitrarily defined length (Brenner, 6).
As mentioned above, DCF is the basic media access control method for 802.11 and it is mandatory for all stations. The Point Coordination Function (PCF) is an optional extension to DCF. PCF provides a time division duplexing capability to accommodate time bounded, connection-oriented services such as cordless telephony.
Logical Addressing
The authors of the 802.11 standard allowed for the possibility that the wireless media, distribution system, and wired LAN infrastructure would all use different address spaces. IEEE 802.11 only specifies addressing for over the wireless medium, though it was intended specifically to facilitate integration with IEEE 802.3 wired Ethernet LANs. The IEEE802 48-bit addressing scheme was therefore adopted for 802.11, thereby maintaining address compatibility with the entire family of IEEE 802 standards. In the vast majority of installations, the distribution system is an IEEE 802 wired LAN and all three logical addressing spaces are identical.
Security
IEEE 802.11 provides for security via two methods: authentication and encryption (Brenner, 13). Authentication is the means by which one station is verified to have authorization to communicate with a second station in a given coverage area. In the infrastructure mode, authentication is established between an AP and each station.
Authentication can be either Open System or Shared Key. In an Open System, any station may request authentication. The station receiving the request may grant authentication to any request, or only those from stations on a user-defined list. In a Shared Key system, only stations which possess a secret encrypted key can be authenticated. Shared Key authentication is available only to systems having the optional encryption capability.
Encryption is intended to provide a level of security comparable to that of a wired LAN. The Wired Equivalent Privacy (WEP) feature uses the RC4 PRNG algorithm from RSA Data Security, Inc. (Brenner, 13). The WEP algorithm was selected to meet the following criteria:
+ Reasonably strong
+ Self-synchronizing
+ Computationally efficient
+ Exportable
+ Optional
Works Cited
Brenner, Pablo. A Technical Tutorial on the IEEE 802.11 Protocol. SSS-Online. February 25, 2001. .
Geier, Jim. Overview of the IEEE.11 Standard. Wireless-Nets. February 24, 2001. .
Lough, Blankenship, and Krizman. A Short Tutorial on Wireless LANs and IEEE 802.11. Computer. February 24, 2001. .
What is Wireless Networking? Intel. February 24, 2001. .
What s New in Wireless LANs: The IEEE 802.11b Standard. 3Com. February 24, 2001. .
Другие работы по теме:
Bridges Essay Research Paper Bridges are used
Bridges Essay, Research Paper Bridges are used to interconnect LANs using one or more of the IEEE 802.x standards, that is Ethernet or Token Ring LAN environments and also others. Bridges are devices with two or more ports, which connect LANs at the Data Link layer of the OSI Model. The purpose of bridges is to allow nodes connected to different LANs to communicate as if they were located on the same LAN.
Wap Essay Research Paper What is WAPWAP
Wap Essay, Research Paper What is WAP? WAP stands for Wireless Application Protocol. The idea has been developed by some of the wireless telecommunications giants such as Nokia and Ericsson.
Future Of Wireless Networking Essay Research Paper
For each of the past five years, industry pundits have been convinced it would be the year of wireless data in the wide-area environment. And every year it was for a different reason: support for IP protocols; phones with microbrowsers; support from industry giants, such as Microsoft and IBM; and new platforms, such as handheld computers.
Internet Tv Essay Research Paper ZENITH TO
Internet Tv Essay, Research Paper ZENITH TO LAUNCH INTERNET TV PRODUCTS BASED ON NC TECHNOLOGY FROM ORACLE LAS VEGAS, Jan. 8, 1997 — Zenith Electronics Corporation (NYSE:ZE) has joined forces with Network
Atandt Essay Research Paper The dominant economic
Atandt Essay, Research Paper The dominant economic traits of this industry start with having an enormous amount of capital required for staying competitive. One is also required to spend lots of money on research and development, as the telecommunications industry seems to be the vision of the future. More and more companies like AT&T are trying very hard to combine their network services of phone line, video and data transfer, high speed internet access, and television cable via one line in the consumers homes.
Links 2000 Essay Research Paper OK Now
Links 2000 Essay, Research Paper O.K. Now you have an account what do you do now? You need to setup Web folders in My Network Places. Not in Network neighborhood. This is only in WinME.If you are not using WinME you might not have this option. In that case you need to download & install Internet Explorer 5.5 from microsofts website here.After you install IE 5.5 come back here.
Telecommunications Act Of 1996 Essay Research Paper
This paper analyzes the effects on the implementation of the Telecommunications Act of 1996 (”Act”) on US telecommunications markets and is based on my forthcoming book with the same title. The Act is a milestone in the history of telecommunications in the United States. Coming 12 years after the breakup of AT&T, the Act attempts to move all telecommunications markets toward competition.
Network Debate Essay Research Paper It was
Network Debate Essay, Research Paper It was a brutal race. They interrupted our daily scheduled shows with boisterous promises they could never fulfill. They invaded our towns and cities with their advertisements; their faces defaced our buses and benches. And still, no one has emerged as the clean victor.
E911 Essay Research Paper The FCC E911
E911 Essay, Research Paper The FCC E911 Regulation is Essential for Consumers and Telecommunications Industry In June of 1996, the FCC proposed a mandate for E-911 services. The wireless E911 order provides value-added service for all cellular phone users and consumers.
Nervous System Adaptation Essay Research Paper Nervous
Nervous System Adaptation Essay, Research Paper Nervous System Adaptation plays a significant role in exercise development as seen by mental imagery, cross education, and coactivation. The body must establish and modify it?s own neural network before it can strengthen. A weight lifter can improve his workouts by understanding the fundamentals of NSA.
Market Power In The Deregulation Of Electicity
Essay, Research Paper Market power, which is at the heart of the debate over ownership and control of the electricity transmission network, has been identified by the FERC (Federal Energy Regulatory Commission) as a potential impediment to the development of an unencumbered competitive market for electricity.
Wireless Application Protocol Essay Research Paper Wireless
Wireless Application Protocol Essay, Research Paper Wireless Application Protocol (WAP) Background Market study has shown that the number of mobile users is exceeding the number of PC users. Some of the industry leaders have created a forum to evolve an industry standard for providing internet access to users over wireless access.
Cable Essay Research Paper CableRoad RunnerRoad Runner
Cable Essay, Research Paper Cable-Road Runner Road Runner is a software program that works for cable. The first commercial broadband online service was delivered to customers through a broadband fiber coaxial cable network in 1996. After 15 months after these initial launches, Time Warner Inc. and MediaOne announced their intention to create the nations largest broadband online business.
Internet PC
’s: Next Wave Or Nonsense? Essay, Research Paper Internet PC’s: Next Wave or Nonsense? Call them what you will: Internet appliances. Network terminals. The whole
Wireless Communications Essay Research Paper INTRODUCTION
Wireless Communications Essay, Research Paper INTRODUCTION Wireless communications are becoming increasingly popular in today?s fast paced world. Mobility, portability, and instant access (via the Internet) to unlimited information have become the mantra of businesses and individuals alike. The evolution of wireless communications has been incredibly quick and the future of this technology is unlimited.
Wireless Internet Essay Research Paper Wireless InternetBy
Wireless Internet Essay, Research Paper Wireless Internet By 2004, the wireless subscriber base worldwide is expected to reach 1.4 billion users, and approximately 300 million users will be accessing the Internet from some form of wireless appliance. The race is on, and Nortel Networks have first-mover advantage.
Mobile Alerts Essay Research Paper Mobile Alerts
Mobile Alerts Essay, Research Paper Mobile Alerts – Concept Paper. What is Mobile Alert? Mobile Alert is the text message (SMS) sent to a mobile phone as a result of occurrence of an event for which the mobile user has registered the request for getting the notification.
The Old Man And The See Essay
, Research Paper THE HISTORY OF INTERNET In the beginning of the 1970`s in USA was an older military network called ARPANET converted to Internetvork wish was a network between networks. Accept a few Universities
The Bus Network Essay Research Paper The
The Bus Network Essay, Research Paper The Bus Network The world revolves around technology. Everywhere we go we are affected either directly or indirectly by technology. In fact, almost everything that surrounds us is a product of technology. Cell phones, beepers, television, radio; these are just a few basic examples of technological advancement in our human history.
Cellular Phone Tracking Essay Research Paper On
Cellular Phone Tracking Essay, Research Paper On April 9th of last year, Ellen Kirk from San Jose, California had a tragic car accident, slamming her into tree. Bleeding profusely, she reached into here purse, grabbed her cell phone, and called 911 and tried to give her location as best as possible. She waited, and waited, and waited.
Computer Tech Essay Research Paper Common Network
Computer Tech Essay, Research Paper Common Network Architectures There are many different types of networks used today that could be evaluated. I would like to take a brief look at three main types of networks, the host-based network, the client-based network, and the client-server network. I would like to look at both the advantages and disadvantages of each type.
Home Computer Network Essay Research Paper Have
Home Computer Network Essay, Research Paper Have you ever needed to have more than one home computer for you and your family? Do you have two or more computers, but need to copy and/or share files and/or programs between them, but you don t know how? Do all of your computers need Internet access, but you don t want to have a phone line installed for each of them? Well, you can do all of this.
Network Security And Firewalls Essay Research Paper
Network, in computer science, techniques, physical connections, and computer programs used to link two or more computers. Network users are able to share files, printers, and other resources; send electronic messages; and run programs on other computers.
Network Support Essay Research Paper I have
Network Support Essay, Research Paper I have decided to research the Career path of a Network Support Specialists. I have been looking into this job field for quite sometime now, and still seem to be interested. A Network Support Specialist is responsible for the administration and maintenance of computers, network connection, e-mail, telephones and other IT related tools used by t he client.
What Is A Computer Network Essay Research
Paper What is a computer network? In simple terms, a computer network is a group of connected computers that allow the sharing of information and equipment. The most ordinary network is made up of two computers connected by some kind of cable in order to exchange information more quickly and efficiently. A standalone computer is very useful to many businesses, but without a network, those businesses would have to spend twice the amount of money then they would have to by having a network.
Lucent Technologies Report Essay Research Paper LUCENT
Lucent Technologies Report Essay, Research Paper LUCENT TECHNOLOGY COMPANY OVERVIEW Lucent Technologies is a company that is focused on being a leader in the field of technology in building a broadband and mobile Internet community that will hopefully make a difference in the way people communicate. Lucent also provides the systems, software, silicon, and services for what has been created as the largest networking company built from the ground up in history.
Token Vs Ethernet Essay Research Paper Well
Token Vs Ethernet Essay, Research Paper Well, now I feel confused about this whole situation. I started taking classes part time at BU about five years ago. I took two networking classes, Network hardware and Network management. I didn?t transfer my credits to um because the technology had changed so fast, and I wanted to learn the newest technology.