Network + 7

If connections are inconsistent, try changing the channel to another, nonoverlapping channel.

False. Weather conditions can have a huge impact on wireless signal integrity.

Wireless enabled:  Some laptops make it incredibly easy to turn wireless on and off.

Auto transfer rate: By default, wireless devices are configured to use the strongest, fastest signal. If you experience connectivity problems between wireless devices, try using the lower transfer rate in a fixed mode to achieve a more stable connection. For example, you can manually choose the wireless transfer rate. Also, instead of using the highest transfer rate available, try a lesser speed. The higher the transfer rate, the shorter the connection distance.

Router Placement:

Antenna

Building Obstructions

Conflicting Devices

Wireless channels

Protocol issues

SSID


WEP encryption must match

Physical objects

RF.  Shred channels too

Eletctrical interference: computers, fans or motorized devices

Environmental factors:  Weather, rain

c

a

All the 802.11 wireless standards employ the CSMA/CA access method.

Multiple input multiple output (MIMO) antenna technology is the biggest development for 802.11n and the key to the new speeds.

Ethernet protocol and CSMA/CA access method.

There were actually two variations on the initial 802.11wireless standard. Both offered 1 or 2Mbps transmission speeds and the same RF of 2.4GHz. The difference between the two was in how datatraveled through the RF media. One used FHSS, and the other used DSSS. The original 802.11 standards are far too slow for modern networkingneeds and are now no longer deployed.

In terms of speed, the 802.11a standard was far ahead ofthe original 802.11 standards. 802.11a specified speeds of up to 54Mbps in the 5GHz band, but most commonly, communication takes place at6Mbps, 12Mbps, or 24Mbps. 802.11a is incompatible with the 802.11band 802.11g wireless standards.

The 802.11b standard provides for a maximum transmission speed of 11Mbps. However, devices are designed to be backward compatible with previous 802.11 standards that provided for speeds of 1,2, and 5.5Mbps. 802.11b uses a 2.4GHz RF range and is compatible with 802.11g.

802.11g offers wireless transmission over distances of150 feet and speeds up to 54Mbps compared with the 11Mbps of the802.11b standard. Like 802.11b, 802.11g operates in the 2.4GHz range and therefore is compatible with it.

The newest of the wireless standards listed in the Network+ objectives is 802.11n, which is a popular wireless standard today. The goal of the 802.11n standard was to significantly increase through put in both the 2.4GHz and the 5GHz frequency range. The baseline goal of the standard was to reach speeds of 100Mbps, but given the right conditions, it is estimated that the 802.11n speeds can reach a staggering 600Mbps. In practical operation, 802.11n speeds are much slower.

Multiple input Multiple Output.  Essentially, MIMO uses multiplexing to increase the rangeand speed of wireless networking. Multiplexing is a technique that combines multiple signals for transmission over a single line or medium.  MIMO enables the transmission of multiple data streams traveling on different antennas in the same channel at the same time. A receiver reconstructs the streams, which have multiple antennas as well. By using multiple paths, MIMO provides a significant capacity gain over conventional single-antenna systems, along with more reliable communication.

The 802.11b and 802.11g wireless standards use a single channel to send and receive information.  With channel bonding, you can use two channels at the same time. As you might guess, the ability to use two channels at once increases performance. It is expected that bonding can help increase wireless transmission rates from the 54Mbps offered with the 802.11g standards to atheoretical maximum of 600Mbps. 802.11n uses the OFDM transmission strategy.

2.4GHz RF, 1 to 2 Mbps, Ad hoc/infrastructure, 20 Feet, CSMA/CA

2.4GHz, Up to 11Mbps, Ad hoc/infrastructure, Up to 150 feet indoors; range can be affected by building materials, CSMA/CA

5GHz, upto 54Mbps, Ad hoc/structure, 25 to 75 ft indoors materials can affect it, CSMA/CA

2.4 GHz, up to 54Mbps, Ad hoc/Infrastructure, up to 150 feet indoors materials affect, CSMA/CA

2.4Ghz/5Ghz, up to 600mbps, ad hoc/infrastructure, 175+ feet indoors; range can be affected by building materials, CSMA/CA

Yes.  An AP can operate as a bridge, connecting a standard wired network to wireles devices, or as a router, passing data transmissions from one access point toanother.

The infrastructure wireless topology is commonly used to extend a wired LAN to include wireless devices.

—A network name needed to connect toa wireless AP. It is like a workgroup name used with Windows networking.802.11 wireless networks use the SSID to identify all systems belonging to the same network. Client stations must be configured withthe SSID to be authenticated to the AP. The AP might broadcast theSSID, allowing all wireless clients in the area to see the AP’s SSID. For security reasons, APs can be configured not to broadcast the SSID or tocloak it. This means that an administrator needs to give client systems the SSID instead of allowing it to be discovered automatically.

—Refers to a wireless network that uses a singleAP and one or more wireless clients connecting to the AP. Many home offices are an example of a BSS design. The BSS is an example of the infrastructure wireless topology. Chapter 1 discusses wireless topologies and other networks.

—Refers to two or more connected BSSs that use multiple APs. The ESS is used to create WLANs or larger wireless networks and is a collection of APs and clients. Connecting BSS systems enables clients to roam between areas and maintain the wireless connection without having to reconfigure between BSSs.

—Although the termsESSID and SSID are used interchangeably, there is a difference between the two. SSID is the name used with BSS networks. ESSID is the network name used with an ESS wireless network design. With an ESS, not all APs necessarily use the same name.

—The MAC address of the BasicService Set (BSS) AP. The BSSID is not to be confused with the SSID,which is the name of the wireless network.

—When troubleshooting or designing wireless networks, the BSA is an important consideration. The BSA refers tothe AP’s coverage area. The BSA for an AP depends on many factors, including the strength of the AP antenna, interference in the area, andwhether an omni directional or directional antenna is used.

• Increase transmission power
• Relocate the AP
• Adjust or replace antennas
• Signal amplification
• Use a repeater

• . Work around obstacles
• . Minimize the effects of interference
• . Increase signal strength
• . Focus the transmission, which can increase signal speed

To determine an antenna’s strength, refer to its gain value.  The dB in dBi stands for decibels and the i stands for the hypothetical isotropic antenna.  In terms of performance, the rule of thumb is that every 3dB of gain added doubles an antenna’s effective power output.

Directional or Omnidirectional

An omnidirectional antenna is designed to provide a 360-degree dispersed wave pattern. This type of antenna is used when coverage in all directions from the antenna is required. Omnidirectional antennas are advantageous when a broad-based signal is required. For example, if you provide an even signal in all directions, clients can access the antenna and its associated access point from various locations. Because of the dispersed nature of omnidirectional antennas, the signal is weaker overall and therefore accommodates shorter signal distances. Omnidirectional antennas are great in an environment that has a clear line of sight between the senders and receivers.  Power is spread evenly to all points making omni-directional  antennas well suited for home and small office apps.

Omnidirectional antennas provide wide coverage but weaker signal strength in any one direction than a directional antenna.

Directional antennas are designed to focus the signal in a particular direction.This focused signal enables greater distances and a stronger signal between two points. The greater distances enabled by directional antennas give you aviable alternative for connecting locations, such as two offices, in a point-to point configuration.

Directional antennas are also used when you need to tunnel or thread a signal through a series of obstacles. This concentrates the signal power in a specific direction and enables you to use less power for a greater distance than anomnidirectional antenna. Table 7.1 compares omnidirectional and directionalwireless antennas.

Because wireless signals travel through the atmosphere, they are subjected toall sorts of environmental and external factors. This includes storms and thenumber of walls, ceilings, and so on that the signal must pass through. Just how weakened the signal becomes depends on the building material used andthe level of RF interference. All these elements decrease the power of the wireless signal.

Wireless signals degrade depending on the construction material used. Signals passing through concrete and steel are particularly weakened.

• Antenna
• Device placement One factor that can degrade wireless signals is RF interference. Because of this, you need to try to keep wireless devices away from appliances that output RF noise. This includes microwaves, electrical devices, and certain cordless devices using the same frequency, such as phones.
• Network Location
• Boost the signal

Radio frequency (RF) channels are an important part of wireless communication.  A channel is the band of RF used for the wireless communication. Each IEEE wireless standard specifies the channels that can be used. The 802.11astandard specifies radio frequency ranges between 5.15 and 5.875GHz. In contrast, 802.11b and 802.11g standards operate in the 2.4 to 2.497GHz range. IEEE wireless standards are discussed later in this chapter.

As far as channels are concerned, 802.11a has a wider frequency band, enabling more channels and therefore more data throughput. As a result of the wider band, 802.11a supports up to eight non overlapping channels.802.11b/g standards use the smaller band and support only up to three nonoverlapping channels.

Non-overlapping.  Channels 1, 6, and 11.

Yes.

When troubleshooting a wireless problem in Windows, you can use the ipconfig command to see the status of IP configuration. Similarly, the ifconfig commandcan be used in Linux. In addition, Linux users can use the iwconfig command to view the state of your wireless network. Using iwconfig, you can view such important information as the link quality, AP MAC address, data rate, and encryption keys, which can be helpful in ensuring that the parameters in the network are consistent.

IEEE 802.11b/g wireless systems communicate with each other using radio frequency signals in the band between 2.4GHz and 2.5GHz. Neighboring channels are 5MHz apart. Applying two channels that allow the maximum channel separation decreases the amount of channel crosstalk and provides a noticeable performance increase over networks with minimal channel separation.

802.11n

For instance, 802.11n listsa speed of up to 100Mbps. This represents the speed at which devices using this standard can send and receive data.

Throughput represents the actual speed to expect from wireless transmissions. In practical application, wireless transmissions are approximately one-half or less of the data rate. This means that you could hope for about 40 to 50Mbps for 802.11n. Depending on the wireless setup, the transmission rate could be much less.

Throughput refers to the actual speeds achieved after all implementation and interference factors.

Beacons are an important part of the wireless network because it is their job to advertise the presence of the access point so that systems can locate it. Wireless clients automatically detect the beacons and attempt to establish a wireless connection to the access point.

Yes.  Client stations send beacons only if connected in an ad hoc network design.

• Channel information
• supported data rates
• SSID
• Time stamp
• Advertise the AP

Every 10 milliseconds

• Passive Scanning
• Active scanning

The client station transmits another type of management frame known as a probe request. The probe request goes out fromthe client system, looking for a specific SSID or any SSID within its area. After the probe request is sent, all APs in the area with the same SSID reply with another frame, the probe response. The information contained in the probe response is the same information included with the beacon frame. This information enables the client to access thesystem.

The client system listens for the beacon frames to discover the AP. After it is detected, the beacon frame provides the information necessary for the system to access the AP.

Spread spectrum refers to the manner in which data signals travel through a radio frequency. With spread spectrum, data does not travel straight through a single RF band; this type of transmission is known as narrowband transmission.

• Frequency hopping and
• direct sequence

FHSS requires the use of narrowband signals that change frequencies in a predictable pattern. The term frequency hopping refers to data signals hopping between narrow channels. For example, consider the 2.4GHz frequency bandused by 802.11b/g. This range is divided into 70 narrow channels of 1MHz each. Somewhere between 20 and several hundred milliseconds, the signal hops to a new channel following a predetermined cyclical pattern.

Because data signals using FHSS switch between RF bands, they have a strong resistance to interference and environmental factors. The FHSS signal strategy makes it well suited for installations designed to cover a large geographic area and where using directional antennas to minimize the influence of environmental factors is not possible.

FHSS is not the preferred spread-spectrum technology for today's wifi standards.  It is used for lesser-used standards like cellular.

With DSSS transmissions, the signal is spread over a full transmission frequency spectrum. For every bit of data sent, a redundant bit pattern is also sent. This 32-bit pattern is called a chip.  These redundant bits of data provide both security and delivery assurance. The reason transmissions are so safe and reliable is simply because the system sends so many redundant copies of the data, and only a single copy is required to have complete transmission of the data or information.

Orthogonal Frequency Division Multiplexing (OFDM) is a transmission technique that transfers large amounts of data over 52 separate, evenly spaced frequencies.  OFDM splits the radio signal into these separate frequencies and simultaneously transmits them to the receiver.

Infrared wireless networking uses infrared beams to send data transmissions between devices. Infrared wireless networking offers higher transmission rates, reaching 10Mbps to 16Mbps.

LOS is very important.  

Either Directed (LOS) or diffuse technology.

3 feet and typically used for personal networks.

Diffused infrared can travel farther and is more difficult to block with a signal object. Diffused infrared wireless LAN systems do not require line of sight, but usable distance is limited to room distances.

• . It provides adequate speeds—up to 16Mbps.
• . Infrared devices use less power and therefore don’t drain batteries as much.
• . Infrared is a secure medium. Infrared signals typically are a direct-line implementation in a short range and therefore do not travel far outside the immediate connection. This eliminates the problem of eavesdropping or signal tampering.
• . Infrared is a proven technology. Infrared devices have been available for some time and as such are a proven, nonproprietary technology with an established user and support base.
• . It has no radio frequency interference issues or signal conflicts.
• . It replaces cables for many devices, such as keyboards, mice, and other peripherals.
• . It uses a dispersed mode or a direct line-of-sight transmission.
• . Transmissions travel over short distances.

Station (STA)

. Wireless bands: The routers can provide only 2.4 GHz, only 5 GHz, or be either selectable (choosing one of the two) or simultaneous (using both).

. Switch speed: The ports on the switch can usually support either Fast Ethernet (10/100Mbps) or Gigabit Ethernet (10/100/1000Mbps).

• . Security supported: The SSID, security mode, and passphrase may be configurable for each band, and some routers include a push-button feature for accessing setup. Some enable you to configure MAC address filtering
• and Guest access. MAC address filtering enables you to limit access to only those specified hosts. Guest access uses a different password and network name and enables visitors to use the Internet without having access to the rest of the network (thus avoiding your data and computers).

• SSID
• Channel
• SSID Broadcast
• Authentication
• Wireless Mode
• DTIM Period (seconds)
• Maximum Connection Rate
• Network Type

WPA uses a temporal key integrity protocol (TKIP), which scrambles encryption keys using a hashing algorithm.

CCMP uses 128-bit AES encryption with a 48-bit initialization vector.

Wired Equivalent Privacy

Wi-Fi protected access 

Originally, the data packet was combined with a secret 40-bit number key as it passed through an encryption algorithm known as RC4. The packet was scrambled and sent across the airwaves. On the receiving end, the data packet passed through the RC4 backward, and thehost received the data as it was intended. WEP originally used a 40-bit number key, but later it specified 128-bit encryption, making WEP that much more robust.

Static and dynamic.  Dynamic changes keys periodically.

Yes.  WPA was made to be backward compatible with that hardware.

• Enhanced data encryption
• Authentication

WPA uses a temporal key integrity protocol (TKIP) which scrambles encryption keys using a hashing alogrithm.  Then the keys are issued an integrity check to verify that they have not been modified or tampered with during transit.

Using Extensible Authentication Protocol (EAP),WEP regulates access to a wireless network based on a computer’s hardware-specific MAC address, which is relatively simple to be sniffed and stolen. EAP is built on a more secure public-key encryption system to ensure that only authorized network users can access the network.

False.  TKIP provides strong encryption for home users and nonsensitive data. However, itmay not provide the level of security necessary to protect corporate or more sensitive data while in transmission.

802.11i

The difference betweenWPA and WPA2 is that the former implements most—but not all—of 802.11ito communicate with older wireless cards (which might still need an update through their firmware to be compliant) and it used the RC4 encryption algorithm with TKIP, whereas WPA2 implements the full standard and is not compatible with older cards.

Specifies port-based network access control.  Not wireless specific.

. Supplicant: The system or node requesting access and authentication to a network resource.

Authenticator: A control mechanism that allows or denies traffic thatwants to pass through a port.

Authentication server: Validates the credentials of the supplicant that istrying to access the network or resource

yes.  they are synonymous.

• WEP-Open is the simplest of the authentications methods
• because it does not perform any type of client verification.  It is a weak form of authntication because it requires no proof of identity.

WEP-Shared requires that a WEP key be configured on both the client system and the access point. This makes authentication with WEP-Shared mandatory, so it is more secure for wireless transmission.

WPA-psk (Wi-Fi Protected Access with Pre-Shared Key) is a stronger form of encryption in which keys are automatically changed and authenticated between devices after a specified period of time, or after a specified number ofpackets have been transmitted.