Chapter 4 Wireless Networking

transceiver (pg 182)

A transmit/receive unit

NLOS

Non-line-of-sight

pseudorandom

Pseudorandom means the sequence appears to be random but in fact does repeat, typically after some lengthy period of time.

Why does the access point have two antennas?"

The answer is that the two antennas implement what is called spatial diversity. This antenna arrangement improves received signal gain and performance.

hopping sequence

The order of frequency changes

WPA

WPA stands for Wi-Fi Protected Access, and it supports the user authentication provided by 802.lx and replaces WEP as the primary way for securing wireless transfers. WPA2 is an improved version of WPA. WPA is considered to be a higher level of security for wireless systems.

pairing

When a Bluetooth device is set up to connect to another Bluetooth device

last mile

1. The last mile is basically the last part of the connection from the telecommunications provider to the customer. 2. The cost of the last mile connection can be expensive, which makes a wireless alternative attractive to the customer.

Basic Service Set (BSS) (pg 182)

Term used to describe an independent network The problem with the Basic Service Set is that mobile users can travel outside the radio range of a station's wireless link with one access point.

hand-off

When the user's computer establishes an association with another access point

Passkey

The Passkey is used in Bluetooth Security to limit outsider access to the pairing.

BLuetooth

The information normally carried by a cable is transmitted over the 2.4GHz ISM frequency band, which is the same frequency band used by 802.lIb/g/n. There are three output power classes for Bluetooth.

OFDM (pg. 185)

1. Another technique used in the 802.11 standard is orthogonal frequency division multiplexing (OFDM). 2. The basic idea behind this technique is to divide the signal bandwidth into smaller subchannels and to transmit the data over these subchannels in parallel. 3. These sub channels can be overlapping, but they will not interfere with each other. 4. The subchannels are mathematically orthogonal, which yields uncorrelated or independent signals.

CONFIGURING A POINT-TO-MULTIPOINT WIRELESS LAN:

1. Antenna Site Survey The proposed antenna site (see Figure 4-26) is on top of a hill approximately 1 kilometer (km) from the home network. A site survey provides the following information: • The site has a tower that can be used to mount the wireless antenna. • The site has a small building and available rack space for setting up the wireless networking equipment. • There is a clear view of the surrounding area for 6 km in every direction. • There is not an available wired network connection back to the home network. The decision is made to use the proposed antenna site and set up an l l Mbps wireless link back to the home network 2. Establishing a Point-to-Point Wireless link to the Home Network The cost is too high to install a wired connection back to the home network; therefore, it is decided to use a point-to-point 802.11 wireless link for the interconnection. This requires that antennas be placed at both the home network and the antenna site. A wireless bridge is used at each end of the point-to-point wireless link to interconnect the networks. The bridge will connect to the wired home network and to the multipoint distribution on the antenna site. Also each antenna will be outfitted with lightning arrestors to protect the electronics from any possible lightning strikes. 3-4. Configuring the MuLtipoint Distribution/Conducting an RF Site Survey At this point, an I1Mbps wireless data link has been established with the home network. The next task is to configure the antenna site for multipoint distribution. It was previously decided that a 2Mbps link would be adequate for the remote users, based on the data rate to be supported for the planned coverage area. 5. Configuring the Remote Installations The last task is to develop a configuration for the remote users. The antenna for each remote user needs to be able to see only the multipoint distribution antenna site. The requirements for the remote client are as follows: • 2Mbps data rate connection • Directional antenna (Yagi) plus mount, lightning arrestor, wireless bridge

sharekey

1. IEEE 802.11 supports two ways to authenticate clients: open and sharekey. Open authentication basically means that the correct SSID is being used. 2.authentication, a packet of text is sent by the access point to the client with the instruction to encrypt the text and return it to the access point.

Access Point Example: (pg 183) (fig. 4-2)

1. If data is being sent from PC-A to PC-D, the data is first sent to the access point and then relayed to PC-D. 2. Data sent from a wireless client to a client in the wired LAN also passes through the access point. 3. The users (clients) in the wireless LAN can communicate with other members of the network as long as a link is established with the access point. 4. For example, data traffic from PC-A to PC-E will first pass through the access point and then to PC-E in the wired LAN.

MIMO (pg 187)

1. MIMO uses a technique called space-division multiplexing, where the data stream is split into multiple parts called spatial streams. 2. The different spatial streams are transmitted using separate antennas. 3. With MIMO, doubling the spatial streams doubles the effective data rate. The downside of this is the possibility of increased power consumption.

wireless misconceptions (pg 190)

1. One of the biggest misconceptions about wireless is that it does not require a wired connection. 2. This is not quite correct. The connection to a wired LAN is provided by a wireless access point, which provides a bridge between the wireless LAN and the wired network. 3. A physical cable connection (typically CAT6/5e) ties the access point to the wired network's switch or hub (typically Ethernet).

SSID

1. Service set identifier 2. The SSID is the wireless service set identifier, basically a password that enables the client to join the wireless network. 3. The access point uses the SSID to determine whether the client is to become a member of the wireless network. 4. The term association is used to describe that a wireless connection has been obtained.

Extended Service Set (ESS) Example: (pg. 183)

1. The mobile computer will establish an authorized connection with the access point that has the strongest signal level (for example, AP-l). As the user moves, the signal strength of the signal from AP-l will decrease. 2. At some point, the signal strength from AP-2 will exceed AP-l, and the wireless bridge will establish a new connection with AP-2. 3. This is called a hand-off. This is an automatic process for the wireless client adapter in 802.11, and the term used to describe this is roaming.

beacon

1. Used to verify the integrity of a wireless link. 2. the beacons are transmitted so that a wireless user can identify an access point to connect to.

WLAN (180)

1. Wireless local area network 2. The WLAN provides increased flexibility and mobility for connecting to a network. 3. A properly designed WLAN for a building provides mobile access for a user from virtually any location in the building.

DSSS-Direct sequence spread spectrum (pg 184)

DSSS is a technique used to spread the transmitted data over a wide bandwidth; in this case it is a 22 MHz bandwidth channel.

Radio Frequency Identification (RFID)

Radio frequency identification (RFID) is a technique that uses radio waves to track and identify people, animal, objects, and shipments. This is done by the principle of modulated backscatter. There are three parameters that define an RFID system. These include the following: • Means of powering the tag • Frequency of operation • Communications protocol (also called the air interface protocol)

"How does the access point know that the wireless data packet is being sent from a client in the wireless LAN?"

The answer is the 802.ll wireless LAN devices use an SSID to identify what wireless data traffic is allowed to connect to the network. The SSID is the wireless service set identifier, basically a password that enables the client to join the wireless network.

backscatter

The term "backscatter" is referring to the reflection of the radio waves striking the RFID tag and reflecting back to the transmitter source with its stored unique identification information

roaming

The term used to describe a user's' ability to maintain network connectivity as he moves through the workplace

inquiry procedure

to determine whether any other Bluetooth devices are available. This procedure is also used to allow itself to be discovered.

wireless adapter (pg 189)(fig 4-6)

1. (wireless LAN adapter) is the device that connects the client to the wireless medium. 2. The medium is typically a radio wave channel in the 2.4GHz or 5GHz ISM band. 3. The wireless medium can also be infrared, although this is not used very often. The following services are provided by the wireless LAN adapter: • Delivery of the data • Authentication • Privacy For example, computer PC-A shown in Figure 4-6 sends a data packet to PCD, a destination in the wired LAN. PC-A first sends a data packet over the wireless link. The access point recognizes the sender of the data packet as a host in the wireless LAN-X and allows the wireless data to enter the access point. At this time, the data is sent out the physical Ethernet connection to the wired LAN. The data packet is then delivered to PC-D in the wired LAN.

RADIUS

1. A Remote Authentication Dial-In User Service (RADIUS) service is sometimes used to provide authentication. 2. This type of authentication helps prevent unauthorized users from connecting to the network. 3. Additionally, this authentication helps to keep authorized users from connecting to rogue or unauthorized access points.

piconet

1. A piconet is an ad hoc network of up to eight Bluetooth devices such as a computer, mouse, headset, earpiece, and so on. 2. In a piconet, one Bluetooth device (the master) is responsible for providing the synchronization clock reference. All other Bluetooth devices are called slaves.

wired network inside the building (fig 4-10)

1. Wireless LANs have a maximum distance the signal can be transmitted. 2. This is a critical issue inside buildings when user mobility is required. 3. Many obstacles can reflect and attenuate the signal, causing reception to suffer. 4. Also, the signal level for mobile users is hampered by the increased distance from the access point. 5. Distance is also a critical issue in outdoor point-to-multipoint wireless networks. A solution is to place multiple wireless access points within the facility, as shown in Figure 4-11.

ad hoc (pg 182)

Another term used to describe an independent network. In this network, the wireless clients (stations) communicate directly with each other. This means the clients have recognized the other stations in the WLAN and have established a wireless data link.

ISM (PG 185)

Industrial, scientific, and medical

Extended Service Set (ESS) (fig. 4-3)

Multiple access points extend the range of mobility of a wireless client in the LAN.

site survey

Performed to determine the best location(s) for placing the access point( s) to provide maximum RF coverage for the wireless clients A site survey for indoor and outdoor installations should obtain the following key information: • Indoor • Electrical power • Wired network connection point(s) • Access point placement • RF coverage-user mobility • Bandwidth supported • Identify any significant RF interference • Outdoor • Electrical power (base access point) • Connection back to the home network • Antenna selection • Bandwidth supported • RF coverage • Identify any significant RF interference

RFID tags are classified

RFID tags are classified in three ways based on how they obtain their operating power. The three classifications are passive, semi-active, and active:

Frequency of Operation

The RFID tags must be tuned to the reader's transmit frequency to turn on. RFID systems typically use three frequency bands for operation, LF, HF, and UHF as shown in Figure 4-24:

paging procedure

The paging procedure is used to establish and synchronize a connection between two Bluetooth devices. When the procedure for establishing the connection has been completed, the Bluetooth devices will have established a piconet.

wireless standards: (pg 187-188)

• 802.11a (Wireless-A): This standard can provide data transfer rates up to 54Mbps and an operating range up to 75 feet. It operates at 5GHz. (Modulation-OFDM) • 802.11b (Wireless-B): This standard can provide data transfer rates up to 11Mbps with ranges of 100-150 feet. It operates at 2.4GHz. (Modulation-DSSS) • 802.11g (Wireless-G): This standard can provide data transfer rates up to 54Mbps up to 150 feet. It operates at 2.4GHz. (Modulation-DSSS or OFDM) • 802.11n (Wireless-N): This is the next generation of high-speed wireless connectivity promising data transfer rates over 200+ Mbps. It operates at 2.4GHz and 5GHz. (Modulation-DSSS or OFDM) • 802.11i: This standard for WLANs provides improved data encryption for networks that use the 802.11 a, 802.11 b, and 802.11 g standards • 802.11r: This standard is designed to speed hand-offs between access points or cells in a WLAN. This standard is a critical addition to 802.11 WLAN s if voice traffic is to become widely deployed

wireless bridge (fig 4-9)

1. A wireless bridge is a popular choice for connecting LANs (running similar network protocols) even if the LANs are miles apart. 2. The wireless bridge then connects to an antenna placed on the roof. 3. A clear (line-of-sight) transmission path must exist between the two buildings; otherwise, signal attenuation (loss) or signal disruption can result. 4. Antenna selection is also critical when configuring the connection. 5. Figure 4-9(b) shows how a wireless bridge can be used to connect multiple remote sites to the main transmitting facility. 6. The bridge connects to its respective LAN. In this case, Bld-A uses an antenna that has a wide coverage area (radiation pattern). 7. The key objective with antenna selection is that the antenna must provide coverage for all receiving sites (in this case, Bld-B and BId-C).

Slotted Aloha

1. A wireless network communications protocol technique similar to the Ethernet protocol. 2. In a Slotted Aloha protocol, the tags are only allowed to transmit at predetermined times after being energized. 3.This technique reduces the chance of data collisions between RFID tag transmissions and allows for the reading of up to 1000 tags per second. (Note: This is for high-frequency tags.) 4. The operating range for RFID tags can be up to 30 meters. 5. This means that multiple tags can be energized at the same time, and a possible RF data collision can occur. 6. If a collision occurs, the tag will transmit again after a random back-off time.

association (pg 190)

1. Access points use the association to build a table of users (clients) on the wireless network. 2. The association table lists the MAC addresses for each networking device connected to the wireless network. 3. The access point then uses this table to forward data packets between the access point and the wireless network. 4. The wireless client adapter will also notify the user if the client has lost an association with the access point.

EAP

1. EAP is the Extensible Authentication Protocol and is used in both WPA and WPA2 by the client computer and the access point. 2. The access point sends an EAP message requesting the user's identity. 3. The user (client computer) returns the identity information that is sent by the access point to an authentication server. 4. The server will then accept or reject the user's request to join the network. 5. If the client is authorized, the access point will change the user's (client's) state to authorized.

IEEE 802.11a (fig 4-3,4-4)

1. IEEE 802.11a equipment is not compatible with 802.11b, 802.11g, or 802.11n. 2. The good aspect of this is that 802.11 a equipment will not interfere with 802.11 b, g, or n; therefore, 802.11a and 802.lIb/g/n links can run next to each other without causing any interference. Figure 4-5 illustrates an example of the two links operating together. 3. The downside of 802.11 a is the increased cost of the equipment and increased power consumption because of the OFDM technology. 4. This is of particular concern with mobile users because of the effect it can have on battery life. 5. However, the maximum usable distance (RF range) for 802.11 a is about the same or even greater than that of 802.11 b/g/n.

CSMA/CA (pg 183)

1. In CSMAlCA, the client station listens for other users of the wireless network. 2. If the channel is quiet (no data transmission), the client station can transmit. 3. If the channel is busy, the station(s) must wait until transmission stops. 4. Each client station uses a unique random back-off time. 5. This technique prevents client stations from trying to gain access to the wireless channel as soon as it becomes quiet. 6. Currently four physical layer technologies are being used in 802.11 wireless networking.

FHSS

1. In frequency hopping spread spectrum (FUSS), the transmit signal frequency changes based on a pseudorandom sequence. 2. FHSS uses 79 channels (each IMHz wide) in the ISM 2.4GHz band. 3. FHSS requires that the transmitting and receiving units know the hopping sequence (the order of frequency changes) so that a communication link can be established and synchronized. 4. FHSS data rates are typically IMbps and 2Mbps. FHSS is not commonly used anymore for wireless LANs.

U-NII (pg 185)

1. The 802.11 a standard transports the data over 12 possible channels in the Unlicensed National Information Infrastructure (U-NII). 2. U-NII was set aside by the FCC to support short-range, high-speed wireless data communications.

access point (pg 182)

1. The access point is a transmit/receive unit (transceiver) that interconnects data from the wireless LAN to the wired network. 2. Additionally, the access point provides 802.11 MAC layer functions and supports bridge protocols. 3. The access point typically uses an RJ-45 jack for connecting to the wired network. 4. If an access point is being used, users establish a wireless communications link through it to communicate with other users in the WLAN or the wired network, as shown in Figure 4-2.

802.11b wireless devices (PG 185)

1. The maximum transmit power of 802.11b wireless devices is 1000 mW; however, the nominal transmit power level is 100 mW. 2. The 2.4GHz frequency range used by 802.11 b/g is shared by many technologies, including Bluetooth, cordless telephones, and microwave ovens.

802.11n

1. This wireless technology operates in the same ISM frequency as 802.11b/g (2.4GHz) and can also operate in the 5GHz band. 2. A significant improvement with 802.11n is Multiple Input Multiple Output (MIMO).

Wi-Fi (pg 187)

1. Wi-Fi, which is the abbreviated name for the Wi-Fi Alliance (Wi-Fi stands for wireless fidelity). 2. The Wi-Fi Alliance is an organization whose function is to test and certify wireless equipment for compliance with the 802.11x standards, the group of wireless standards developed under the IEEE 802.11 standard.

WiMAX

1. WiMAX (Worldwide Interoperability for Microwave Access) is a broadband wireless system that has been developed for use as broadband wireless access (BWA) for fixed and mobile stations and can provide a wireless alternative for last mile broadband access in the 2GHz-66GHz frequency range. 2. Internationally, the WiMAX frequency standard is 3.5GHz, while the United States uses both the unlicensed 5.8GHz and the licensed 2.5GHz spectrum. 3. WiMAX has a range of up to 31 miles, and it operates in both point-to-point and point-to-multipoint configurations. 4. The WiMAX system uses time division multiplexing (TDM) data streams on the downlink and time-division multiple access (TDMA) on the uplink and centralized channel management to ensure time-sensitive data is delivered on time.

packet sniffing

1. is a technique used to scan through unencrypted data packets to extract information. 2. In this case, an attacker uses packet sniffing to extract the SSID from data packets. 3. Disabling SSID broadcasting will make it so that most client devices (such as Windows PCs and laptops) won't notice that the wireless LAN is present.

802.11g

1. standard supports the higher data transmission rates of 54Mbps but operates in the same 2.4GHz range as 802.11 b. 2. The 802.11g equipment is also backward compatible with 802.11b equipment. 3. This means that 802.11b wireless clients will be able to communicate with the 802.11g access points and the 802.l1g wireless client equipment will communicate with the 802.11b access points.

BWA

1.Broadband wireless access 2.BWA access for fixed stations can be up to 30 miles, whereas mobile BWA access is 3-10 miles.

IEEE 802.11 WIRELESS LAN (pg 181)

1. A typical computer network uses twisted-pair and fiber-optic cable to interconnect LANs. 2. Another media competing for use in higher data-rate LANs is wireless, based on the IEEE 802.11 wireless standard. 3. defines the physical (PHY) layer 4. the medium access control (MAC) layer, and the media access control (MAC) management protocols and services. The PHY (physical) layer defines the following: • The method of transmitting the data, which can be either RF or infrared (although infrared is rarely used) • The MAC layer defined • The reliability of the data service • Access control to the shared wireless medium • Protecting the privacy of the transmitted data The advantages of wireless include • A cost-effective networking media for use in areas that are difficult or too costly to wire • User mobility in the workplace