Ch 11 Wireless networks
wireless network categories
1 - 802.11b, 802.11g (100 ft) 2 - Bluetooth (10 ft) 802.15 3 - metropolitan area networks(Wi-max) 802.16 (20 miles)
What is a basic service set? A basic service area?
To facilitate mobility, the designers of wireless LAN technologies planned wireless LANs in such a way that larger wireless LANs can be built from smaller wireless LANs. The smallest component unit of a wireless LAN is the area of covered by a single access point. This area is called a basic service area (BSA). The basic service area and the access point covering that area together are called a basic service set (BSS). Large WLANs are built from small blocks -Basic service set (BSS) covering a basic service area (BSA) -BSSs are connected through distribution system (DS) to create larger WLAN (extended service set)
What are the common wireless LAN categories?
802.11a, 802.11b, 802.11g, and 802.11n
What is 802.11 n? What are some likely advantages of 802.11 n over traditional wireless LANs? How does 802.11 n obtain these advantages?
802.11n is the latest wireless LAN technology to be introduced. It provides higher rate than other traditional wireless LANs with speeds up to 600 Mbps. 802.11n also aims to provide wider coverage than traditional wireless LANs. 802.11n obtains these advantages by using a multiple input, output signal transmission. 802.11n access points and receivers user multiple antennas. Each antenna creates and independent data channel
What is the Federal Communications Commission (FCC)?
Beginning in 1994, the Federal Communications Commissions (FCC) realized that operators of cell phones and other services would be willing to pay for access to specific frequencies. The Federal Communications Commissions then began to auction off frequency bands for specific services to the highest bidders offering theses services. The single largest revenue-generating auction was for cell-phone services in the 700 MHz band and was completed in March 2008. The auction generated over $18 billion
What are wireless networks? Why are they useful?
Wireless networks are access points for the internet can be gotten from a wireless router. These access points are useful because a computer does not have to be connected to an Ethernet cable and this can be a much cheaper way for a business to connect computers to the internet.
QAM (Quadrature amplitude modulation)
used in 802.16 WiMAX for stations closer to the base station
Encryption
The transformation of data into a form that mkes it unreadable by anyone except authorized users.
802.15 Personal area networks
-Blue tooth which has communication over short distances (<10m) and are also called personal operating space (POS); Focus on small, power-efficient, inexpensive solutions
Wireless MAN
-IEEE 802.16 -Worldwide interoperability for Microwave access (WIMAX) > popular in developing countries for rural phone connectivity -Original design > High-speed alternative to cable and DSL > Fixed base and subscriber stations > 20+ Mbps up to 10+ miles
802.11b
-Operates in 2.4GHz radio spectrum -Speed: Up to 11 Mbps -Range: 100 feet -Prone to interference (it shares airspace with cell phones, Bluetooth, security radios, and other devices -Least expensive LAN specification -The Wireless Ethernet Compatibility Alliance (WECA) has done its part by certifying hundreds of products to make sure they work together.
802.11n
-Operates in the 2.4 or 5GHz radio spectrum -Speed Up to 700 Mbs -Range: 50 feet -Because 802.11b and 802.11g use the same radio technologies and portions of the spectrum, they are compatible with one another. But becasue the 802.11n standard has yet to be ratified by WECA, it may not be completely compatible with 802.11b and 802.11g.
802.11g
-Operates in the 2.4GHz radio Spectrum -Speed: Up to 54Mbps -Range: 100 feet -Prone to interference (it shares airspace with cell phones, Bluetooth, security radios, and other devices.
802.11a
-Operates in the 5.15 GHz to 5.35 GHz radio spectrum -Speed: Up to 54 Mbps (actual throughput is closer to 22Mbps) -Range: 50 feet -Less prone to interference -More expensive -Because 802.11b and 802.11a use different radio technologies and portions of the spectrum, they are incapatible with one another
WPA (Wi-Fi protected access)
-WPA 1 is TKIP (temporal key integrity protocol) -WPA 2 is CCMP (counter-mode with Cipher-block chaining message authentication code protocol). WPA 2 is what is currently recommended.
WLAN similarities to LAN
1 - frame structure almost identical of Ethernet 2 - use the 48-bit MAC addresses
WLAN differences to LAN
1 - no defined boundaries; possible overlaps 2 - network experience cannot be specified; dependent on distance of host to access point 3 - inherently unreliable medium 4 - uses multiplexing 5 - stations on two opposite ends may not be able to hear each other; collision detection may be unsuccessful
why are there ISM frequencies that are unregulated?
1 - regulators recognized need for wireless frequencies in experimentation & amateur use 2 - generally not useful for commercial use 3 - poor transmission properties; absorbed by walls, foliage, water 4 - most of the popular ISM bands are not useful for commercial use
What is a portal in a wireless LAN?
A portal acts as a gateway between the extended service set and the rest of the internet. When a message is sent to a host that is not in the extended service set, the distribution system sends the message to the portal. The portal performs all the necessary packet format changes required for the message to be transported on the neighboring network.
Access point (AP)
Acts like a station on the Basic Service Set and enables access to the Distribution System (DS) to associated wireless stations
Extended Service Set
An extended service set (ESS) is one or more interconnected basic service sets (BSSs) and their associated LANs. Each BSS consists of a single access point (AP) together with all wireless client devices (stations, also called STAs) creating a local or enterprise 802.11 wireless LAN (WLAN). To the logical link control layer (part of layer 2 of the 7-layer OSI Reference Model) the ESS appears as a solitary BSS at any one of the STAs.
WIMAX Goals
Delivery of last mile wireless broadband access Fixed, nomadic, portable broadband connectivity Typically, up to 40 Mbps per channel, for fixed and portable access applications up to 6 miles -Enough bandwidth to simultaneously support hundreds of businesses with T-1 speed connectivity and thousands of residences with DSL speed connectivity
Distribution System (DS)
Directs traffic between multiple Basic Service Sets. 802.11 does not specify how DS should distribute messages between APs and can combine multiple Basic Service Sets (BSS) to create a wireless network of arbitrary size which called an Extended Services set (but a DS is not considered part of ESS)
What is an access point? What are some reasons why you would prefer access points to wireless routers to create a wireless network in your organization?
Each access point serves as a router; each BSS would become an independent subset. Each time a user moved from one access point to the next, he would connect to a different subnet. This would potentially give him a different IP address and gateway router address. This address reallocation would stop any ongoing transfers and could also potentially disturb the network connectivity of some applications. With the concept of an extended service set, when users move from one access point to another, there is no change to any network setting, and ongoing network transfers can continue without interruption. Within an organization, basic service sets may be placed as appropriate to deliver the required coverage and reliability. For example, in high traffic area basic service sets may overlap to provide redundancy and to share traffic.
ISM (Industrial, Scientific, and Medical) frequencies
Industrial, Scientific and Medical; can be put to almost any use by anybody without permission from anyone or payments of license fees to anyone; called unregulated frequencies
802.11 Physical layer
MAC layer in wireless LANs is designed to be independent of physical layer technology used Unlike other technologies, wireless LAN physical layer adds a header to account for unreliable transmission
What was the primary innovation of 802.11n
MIMO (multiple input multiple output) which is defined as the use of multiple antennas at both the transmitter and receiver to improve communication performance. It is one of several forms of smart antenna technology.
Bluetooth vs. LAN
Not intended for dedicated computing devices Little or no direct connectivity to the world outside the link No infrastructure necessary (e.g. AP, DS) Focus on long battery life and low cost
What is the Network unit of Bluetooth?
Piconet- One device, master, provided synchroniztion clock; All other devices are piconet slaves; all devices on a piconet share the same physical channel. A piconet is formed when at least two devices, such as a portable PC and a cellular phone, connect. A piconet can support up to eight devices. When a piconet is formed, one device acts as the master while the others act as slaves for the duration of the piconet connection. A piconet is sometimes called a PAN.
What is an extended service set?
The advantage of composing large wireless LANs from multiple basic service areas is that it facilitates mobility. The extended service set appears to end users as one large LAN. Users can move anywhere within an extended service set and still retain the same IP address and subnet membership
What are some differences between wired and wireless LANs? How do they impact the design of the wireless LAN header?
The most important differences is that wireless LANs have no defined boundaries. Wall jacks define the end-points for Ethernet. An Ethernet wall jack is hardwired to a specific port on a specific switch. As results, a network administrator can control every aspect of the network traffic that flows through the wall jack and to the computer connected to the jack. When you connect to the network through a wall jack, you become part of a well-defined network. Typically one area of an office is served by one switch and most users have no choice but to become a member of the Ethernet network that is closest to them. Also, The technical implication is that, whereas the signal strength of a wired connection always meets Ethernet standards, the signal strength, and hence the network experience of wireless connection, cannot be specified. The network performance of a wireless connection depends upon the distance of the host from the access point. A user who is very far from an access point will get very weak signals. -No defined boundaries in wireless LANs; Geographical location does not define LAN membership -Very unreliable medium; boundary is unobservant and can shift
What are some differences between the physical layers in wireless and wired LANs?
The physical layer in the Ethernet adds no header fields to the frame. It simply converts the frame to a signal. The wireless LAN phyical layer does add fields to the frame header. Wired Ethernet uses carrier sense multiple access with collision detextion (CSMA/CD) as its MAC mexhanism. Wireless LAN (802.11), on the other hand, lacks the ability to read and send data at the same time; therefore, it cannot detect collision like its wired counterpart. Hence, WLAN uses carrier sense multiple access with collision avoidance (CSMA/CA) as the MAC mechanism
What are ISM frequency bands? Why are they useful?
The special signal frequencies that enable wireless networking are called ISM frequencies because these frequencies are available for free use for Industrial, Scientific, and Medical applications. The terms industrial and scientific are interpreted very broadly, and ISM frequencies may be put to almost any use by anybody without permission from anyone or payments of license fees to anyone. These frequencies are therefore also called unregulated frequencies. Cordless phones, remote controlled cars, microwave ovens, wireless keyboards, and mice are other applications that use ISM frequencies.
What are the three Encryption techniques?
WEP (Wired equivalent privacy), TKIP (Temporal key integrity protocol), and CCMP (Counter-mode with Cipher-block chaining message authentication code protocol) WEP is extremely insecure and is now considered obsolete
How do WLAN and WPAN coexist?
Wireless LANs and Bluetooth operate at the same ISM frequency band (2.45GHz). Therefore, there is a high possibility that the signals from the two technologies my interfere with each other. Since blue tooth is the more recent of the two technologies, it is only natural that the designers of Bluetooth had the responsibility of ensuring that Bluetooth minimized interference with the existing wireless LAN technology. Use two kinds of co-existence mechanisms to minimize interference -Collaborative (802.12 and 802.11 system communicate with each other) and Non-collaborative (Transmitters sense channel conditions before transmitting, avoid busy frequencies)
What are some of the concerns with using wireless networks?
Wireless networking introduces some important concerns and limitations that users and business should be aware of The most visible concern is information security. Wired networks have wall outlets in specific locations that can only be reached by users with access to the building. By contrast, wireless signals spread out in all directions and can easily bleed outside the organizations boundaries. Without adequate security, malicious users can easily access the organizations computer network through an improperly secured wireless point. Other concerns include health, speed and reliability.
Basic Service Set
a component of the IEEE 802.11 WLAN architecture. This network architecture is built around a Basic Service Set (BSS), which is actually a set of STAs (the component that connects to the wireless medium such as a network adapter or NIC) that communicate with each other. When one access points (AP) is connected to wired network and a set of wireless stations it is referred to as a Basic Service Set (BSS). BSSs are connected through distribution system (DS) to create larger WLAN (extended service set)
Examples of applications using ISM frequencies
cordless phones, remote controlled cars, microwave ovens, wireless keyboards, mice, etc.
QPSK (Quadrature phase shift keying)
user in 802.16 WiMAX for stations that are further from the base station
WLAN
wireless local area networks aka wifi ex: most college campuses