Wireless

• WiFi

  • Wi-Fi technologies have been around since the late 1990s, supported and standardized under the umbrella IEEE 802.11 standards.
  • The 802.11 standard has been updated continually since then, manifested by a large number of amendments to the standard
  • These amendments have names such as 802.11g and 802.11ac. It’s important for you to understand all of these 802.11 amendments in detail, as well as the original version, 802.11.
• 802.11

  • The 802.11 standard defines both how wireless devices communicate and how to secure that communication.
  • The original 802.11 standard, now often referred to as 802.11-1997, is no longer used, but it established the baseline features common to all subsequent Wi-Fi standards.
  • The 802.11-1997 standard defined certain features, such as a wireless network cards, special configuration software, and the capability to run in multiple styles of networks.
• Hardware

  • Wireless networking hardware serves the same function as hardware used on wired PCs.
  • Wireless Ethernet NICs take data passed down from the upper OSI layers, encapsulate it into frames, send the frames out on the network media in streams of ones and zeroes, and receive frames sent from other computing devices.
  • The only difference is that instead of charging up a network cable with electrical current or firing off pulses of light, these devices transmit and receive radio waves.
• Wireless

  • Wireless networking capabilities of one form or another are built into many modern computing devices. Almost all portable devices have built-in wireless capabilities.
  • Desktop computers can easily go wireless by adding an expansion card. Shows a wireless PCI Express (PCIe) Ethernet card.
  • You can also add wireless network capabilities using USB wireless network adapters

  
• WAP

  • A wireless access point (WAP) is a device designed to interconnect wireless network nodes with wired networks. A basic WAP operates like a hub and works at OSI Layer 1.
  • Many WAP manufacturers combine multiple devices into one box, however, to create a WAP with a built-in switch and/or router, all rolled into one and working at several OSI layers.
• Software Every

  • Every wireless network adapter needs two pieces of software to function with an operating system: a device driver to talk to the wireless NIC and a configuration utility.
  • Installing drivers for wireless networking devices is usually automatic these days, but you should always consult your vendor’s instructions before popping that card into a slot.
  • You also need a utility for configuring how the wireless hardware connects to other wireless devices. Every operating system has built-in wireless clients for configuring these settings.
• Software

  • Client Configuration: Using this utility, you can determine important things like the link state (whether your wireless device is connected) and the signal strength (a measurement of how well your wireless device is connecting to other devices).
  • You can also configure items such as your wireless networking mode, security encryption, power-saving options, and so on
  • You typically configure WAPs through browser-based setup utilities.
• Wireless Network Modes

  • 802.11 networks operate in one of two modes. In the uncommon ad hoc mode, two or more devices communicate directly without any other intermediary hardware.
  • The much more common infrastructure mode uses a WAP that, in essence, acts as a hub for all wireless clients. A WAP also bridges wireless network segments to wired network segments.
• Wireless Network Modes

  Ad Hoc Mode:

  • Ad hoc mode is sometimes called peer-to-peer mode, with each wireless node in direct contact with each other node in a decentralized free-for-all. Ad hoc mode does not use a WAP and instead uses a mesh topology.
  • Two or more wireless nodes communicating in ad hoc mode form an independent basic service set (IBSS). This is a basic unit of organization in wireless networks.
  • Ad hoc mode networks work well for small groups of computers (fewer than a dozen or so) that need to transfer files or share printers.

  
• Wireless Network Modes

  Infrastructure Mode

  • Wireless networks running in infrastructure mode use one or more WAPs to connect the wireless network nodes centrally
  • This configuration is similar to the physical star topology of a wired network. This creates a wireless local area network (WLAN).
  • You also use infrastructure mode to connect wireless network segments to wired segments. If you plan to set up a wireless network for a large number of computing devices, or you need to have centralized control over the wireless network, use infrastructure mode.
• Wireless Network Modes

  Infrastructure Mode

  • A single WAP servicing a given area is called a basic service set (BSS). This service area can be extended by adding more access points. This is called, appropriately, an extended service set (ESS)
  • Wireless networks running in infrastructure mode require a little more planning—such as where you place the WAPs to provide adequate coverage—than ad hoc mode networks, and they provide a stable environment for permanent wireless network installations. Infrastructure mode is better suited to business networks

  
• Range

  • Wireless range is greatly affected by environmental factors. Interference from other wireless devices and solid objects affects range.
  • The maximum ranges listed in the sections that follow are those presented by wireless manufacturers as the theoretical maximum ranges. In the real world, you’ll achieve these ranges only under the most ideal circumstances.
  • Cutting the manufacturer’s listed range in half is often a better estimate of the true effective range.
• BSSID, SSID, and ESSID

  • The basic service set identifier (BSSID) defines the most basic infrastructure mode network—a BSS of one WAP and one or more wireless clients.
  • They made the BSSID the same as the MAC address for the WAP
  • Ah, but what do you do about ad hoc networks that don’t have a WAP? The nodes that connect in an IBSS randomly generate a 48-bit string of numbers that looks and functions just like a MAC address, and that BSSID goes in every frame.
• BSSID, SSID, and ESSID

  • The Wi-Fi folks created another level of naming called a service set identifier (SSID), a standard name applied to the BSS or IBSS to help the connection happen.
  • The SSID—sometimes called a network name—is up to a 32-bit identification string that’s inserted into the header of each frame processed by a WAP.
  • Every Wi-Fi device must share the same SSID to communicate in a single network. By default, a WAP advertises its existence by sending out a continuous SSID broadcast. It’s the SSID broadcast that lets you see the wireless networks that are available
• BSSID, SSID, and ESSID

  • To really see the power of 802.11 in action, let’s take it one step further into a Wi-Fi network that has multiple WAPs: an ESS. How do you determine the network name at this level? You use the SSID, but you apply it to the ESS as an extended service set identifier (ESSID).
  • In ESS, WAPs connects to a central switch or switches to become part of a single broadcast domain. With multiple WAPs in an ESS, clients connect to whichever WAP has the strongest signal. As clients move through the space covered by the broadcast area, they change WAP connections seamlessly: roaming.
• Transmission Frequency

  • One of the biggest issues with wireless communication is the potential for interference from other wireless devices. To solve this, different wireless devices must operate in specific transmission frequencies.
  • Knowing these wireless frequency ranges will assist you in troubleshooting interference issues from other devices operating in the same wireless band. The original 802.11 standards use either 2.4-GHz or 5.0-GHz radio frequencies.
• Transmission Methods

  • The original IEEE 802.11 wireless Ethernet standard defined methods by which devices may communicate using spread- spectrum radio waves.
  • Spread-spectrum transmits data in small, discrete chunks over the different frequencies available within a certain frequency range
  • The 802.11 standard defines three different spread-spectrum transmission methods: direct-sequence spread-spectrum (DSSS), frequency-hopping spread-spectrum (FHSS), and orthogonal frequency-division multiplexing (OFDM)
• Transmission Methods

  • DSSS sends data out on different frequencies at the same time, whereas FHSS sends data on one frequency at a time, constantly shifting (or hopping) frequencies.
  • DSSS uses considerably more bandwidth than FHSS—around 22 MHz as opposed to 1 MHz
  • DSSS is capable of greater data throughput, but it’s also more prone to interference than FHSS. OFDM is the latest of these three methods, better at dealing with interference, and is used on all but the earliest 802.11 networks.
• Channels

  • Every Wi-Fi network communicates on a channel, a portion of the available spectrum.
  • For the 2.4-GHz band, the 802.11 standard defines 14 channels of 20-MHz each (that’s the channel bandwidth), but different countries limit exactly which channels may be used.
  • In the United States, for example, a WAP using the 2.4-GHz band may only use channels 1 through 11. These channels have some overlap, so two nearby WAPs should not use close channels like 6 and 7.
• Channels

  • Many WAPs use channels 1, 6, or 11 because they don’t overlap. You can fine-tune a network by changing the channels on WAPs to avoid overlap with other nearby WAPs.
  • This capability is especially important in environments with many wireless networks sharing the same physical space.
  • Regulatory impact on Wi-Fi channels. This applies rather specifically to the channels in the 2.4-GHz range and more generally to the other ranges. The bottom line is that governments strictly regulate which bands, and which channels within each band, that Wi-Fi systems can use.
• Channels

  • The 5.0-GHz and 6.0-GHz bands offer many more channels than the 2.4-GHz band. In general there are around 40 different channels in the spectrums, and different countries have wildly different rules for which channels may or may not be used.
  • The versions of 802.11 that use the 5.0- and 6.0-GHz bands use automatic channel switching, so from a setup standpoint we don’t worry about channels when we talk about 5.0-GHz and 6.0-GHz 802.11 standards.
• CSMA/CA

  • Because only a single device can use any network at a time in a physical bus topology, network nodes must have a way to access the network media without stepping on each other’s frames
  • Wired Ethernet networks used carrier-sense multiple access with collision detection (CSMA/CD) but Wi-Fi networks use carrier-sense multiple access with collision avoidance (CSMA/CA). L
• CSMA/CA

  • How do multiple devices share network media, such as a cable? Sharing is fairly simple: Each device listens in on the network media by measuring the level of voltage currently on the wire.
  • If the level is below the threshold, the device knows that it’s clear to send data.
  • If the voltage level rises above a preset threshold, the device knows that the line is busy and it must wait before sending data.

  1. Typically, the waiting period is the length of the current frame plus a short, predefined silence period called an interframe gap (IFG).
• CSMA/CA

  • Frames transmitted on the network from two different devices at the same time will corrupt each other’s signals. This is called a collision.
  • With CSMA/CD, each sending node detects the collision and responds by generating a random timeout period for itself, during which it doesn’t try to send any more data on the network—this is called a backoff.
  • Once the backoff period expires, the node goes through the whole process again. This approach may not be very elegant, but it gets the job done.
• CSMA/CA

  • CSMA/CD won’t work for wireless networking because wireless devices simply can’t detect collisions, for two reasons. First, radio is a half-duplex transmission method.
  • Wireless devices cannot listen and send at the same time. Second, wireless node A wanting to communicate with wireless node B can’t hear the third, hidden node (Wi-Fi C) that’s also trying to communicate with B. A collision might occur in that circumstance
• CSMA/CA

  • The CSMA/CA access method, as the name implies, proactively takes steps to avoid collisions, as does CSMA/CD. The difference comes in the collision avoidance.
  • The 802.11 standard defines two methods for collision avoidance: Distributed Coordination Function (DCF) and Point Coordination Function (PCF). Currently, only DCF is implemented. DCF specifies rules for sending data onto the network media
• CSMA/CA: DCF

  • For instance, if a wireless network node detects that the network is busy, DCF defines a backoff period on top of the normal IFG wait period before a node can try to access the network again.
  • DCF also requires that receiving nodes send an acknowledgment (ACK) for every frame that they process. The ACK also includes a value that tells other wireless nodes to wait a certain duration before trying to access the network media
  • This period is calculated to be the time that the data frame takes to reach its destination based on the frame’s length and data rate.
• CSMA/CA: DCF

  • If the sending node doesn’t receive an ACK, it retransmits the same data frame until it gets a confirmation that the packet reached its destination.
  • Current CSMA/CA devices use the Distributed Coordination Function (DCF) method for collision avoidance. Optionally, they can use Request to Send/Clear to Send (RTS/CTS) to avoid collisions.

  
• 802.11b

  • The first widely adopted Wi-Fi standard—802.11b—supported data throughput of up to 11 Mbps and a range of up to 300 feet under ideal conditions.
  • The main downside to using 802.11b was its frequency. The 2.4-GHz frequency is a crowded place, so you were more likely to run into interference from other wireless devices

  
• 802.11a

  • Foremost was that it operated in a different frequency range, 5.0 GHz. The 5.0-GHz range is much less crowded than the 2.4-GHz range, reducing the chance of interference from devices such as telephones and microwave ovens
  • Too much signal interference can increase latency, making the network sluggish and slow to respond. Running in the 5.0-GHz range greatly reduces this problem.
  • The 802.11a standard also offered considerably greater throughput than 802.11b, with speeds up to 54 Mbps. Range, however, suffered somewhat and topped out at about 150 feet.
• 802.11g

  • The 802.11g standard offered data transfer speeds equivalent to 802.11a—up to 54 Mbps—and the wider 300-foot range of 802.11b.
  • More importantly, 802.11g was backward compatible with 802.11b because they both used the 2.4-GHz band, so the same 802.11g WAP could service both 802.11b and 802.11g wireless nodes.
  • If an 802.11g network only had 802.11g devices connected, the network ran in native mode—at up to 54 Mbps—whereas when 802.11b devices connected, the network dropped down to mixed mode—all communication ran up to only 11 Mbps

  
• 802.11g

  • Later 802.11g manufacturers incorporated channel bonding into their devices, enabling the devices to use two channels for transmission.
  • Channel bonding is not part of the 802.11g standard, but rather proprietary technology pushed by various companies to increase the throughput of their wireless networks.
  • Both the NIC and WAP, therefore, had to be from the same company for channel bonding to work.
• 802.11n

  • The 802.11n standard brought several improvements to Wi-Fi networking, including faster speeds and new antenna technology implementations. The Wi-Fi Alliance backnamed 802.11n as Wi-Fi 4.
  • The 802.11n specification requires all but handheld devices to use multiple antennas to implement a feature called multiple input/multiple output (MIMO), which enables the devices to make multiple simultaneous connections called streams
• 802.11n

  • With up to four antennas, 802.11n devices can achieve excellent speeds. They also implement channel bonding, combining two 20-MHz channels into a single 40-MHz channel to increase throughput even more.
  • Many 802.11n WAPs employ transmit beamforming, a multiple antenna technology that helps get rid of dead spots—places where the radio signal just does not penetrate at all—or at least make them not so bad. The antennas adjust the signal once the WAP discovers a client to optimize the radio signal.
• 802.11n

  • Like 802.11g, 802.11n WAPs can support earlier, slower 802.11b/g devices. The problem with supporting these older types of 802.11 is that 802.11n WAPs need to encapsulate 802.11n frames into 802.11b or 802.11g frames.
  • This adds some overhead to the process. Adding any 802.11b devices to the network causes some slowdown overall, primarily because the faster devices have to wait for the slower devices to communicate.
  • To handle these issues, 802.11 WAPs transmit in three different modes: legacy, mixed, and greenfield. These modes are also sometimes known as connection types.
• 802.11n

  • Legacy mode means the 802.11n WAP sends out separate packets just for legacy devices. This is a terrible way to utilize 802.11n, but was added as a stopgap measure if the other modes didn’t work
  • In mixed mode, also often called high-throughput or 802.11a-ht/802.11g-ht, the WAP sends special packets that support the older standards yet also improve the speed of those standards via 802.11n’s wider bandwidth
• 802.11n

  • Greenfield mode is exclusively for 802.11n-only wireless networks. The WAP processes only 802.11n frames. Dropping support for older devices gives greenfield mode the best goodput but removes backward compatibility.
• 802.11ac

  • 802.11ac is a natural expansion of the 802.11n standard, incorporating even more streams, 80-MHz and 160-MHz channels, and higher speed.
  • To avoid device density issues in the 2.4-GHz band, 802.11ac only uses the 5.0-GHz band
  • Current versions of 802.11ac include a version of MIMO called multiuser MIMO (MU-MIMO). MU-MIMO gives a WAP the capability to transmit to multiple users simultaneously.
  • For a transmitting method, the 802.11n and 802.11ac devices use a version of OFDM called quadruple-amplitude modulated (QAM).
• 802.11ax

  • In 2021, IEEE released the 802.11ax standard that brings improvements in high-density areas, like stadiums and conference halls.
  • Marketed as Wi-Fi 6 (operating at the 2.4-GHz and 5-GHz bands) and Wi-Fi 6E (operating at the 6.0-GHz band), 802.11ax implements orthogonal frequency-division multiple access (OFDMA) to increase overall network throughput by as much as 400 percent and decrease latency by 75 percent compared to 802.11ac.
• WPS

  • To make configuration easier, the wireless industry created a special standard called Wi-Fi Protected Setup (WPS). WPS works in two modes: push button method or PIN method.
  • With the push button method, you press a button on one device (all WPScompatible devices have a physical or virtual push button) and then press the WPS button on the other device. That’s it. The two devices automatically configure themselves on an encrypted connection.