Wireless Network Components & Standards
WLANs have several components in common, which are:
* stations, or STAs * access points, or APs * a service set, and * a distribution system, or DS
Fast Infrared (FIR)
Fast Infrared is an obsolete term, but is still used to describe data transmission rates of 4 Mbps. FIR is also an informal reference to all speeds above that of the SIR specification.
Broadcast Communication
In broadcast communication, data goes from a source node to all other nodes on a network. Each node receives data and acts on it. Radio communication is an example of broadcast communication.
Name other ways (other than radio) that wireless transmissions can be sent.
Infrared transmissions, Bluetooth transmissions, and microwave transmissions.
What is a wireless antenna?
A wireless antenna is a device that converts high-frequency signals on a cable into electromagnetic waves, and vice versa. In wireless communication, an antenna is used to receive or transmit radio waves. The frequency at which an antenna can send or receive radio waves depends on the physical dimensions of the antenna. The larger the antenna, the lower the frequency of the waves it can transmit.
Wireless antennas can be either - what?
Directional & Omni-Directional
Infrared transmission
Infrared transmission is a form of wireless transmission over unbounded media in which signals are sent as pulses of infrared light. Infrared signals transmit at frequencies between 300 GHz and 300,000 GHz. Infrared frequencies transmit in the range just below visible light in the electromagnetic spectrum. Receivers need an unobstructed view of the sender to receive signals, although the signals can reflect off hard surfaces to reach the recipient. Many infrared-compatible devices follow the standards defined by the Infrared Data Association, or IrDA. Infrared wireless networking offers transmission rates between 10 and 16 Mbps. Infrared-compatible devices, such as a wireless mouse and keyboard, are limited to distances of approximately 3 feet. Direct transmission and short distances between devices virtually eliminate eavesdropping and signal tampering.
Microwave Transmission
Microwave transmission is a form of point-to-point wireless transmission. It sends signals via pulses of electromagnetic energy in the microwave region of the electromagnetic spectrum, at a frequency range of 1 GHz to 300 GHz. Receivers need an unobstructed view of the sender to receive a signal and, depending on the frequency in use, transmissions can be affected by environmental conditions. Signals can be reflected off satellites to increase transmission distance. Microwave transmission technologies are often used in WANs and MANs.
Multipoint Communication
Multipoint communication uses connections between many nodes. Each multipoint connection has more than two endpoints. All devices that share the medium can detect a signal transmitted in the medium, so the signal isn't private. However, not all the devices can receive it. Wireless computer networks use multipoint communication.
Omni-Directional
Omni-directional antennas radiate a signal beam in all directions. They have lower gain than directional antennas but can cover a wider area. The transmission radiates from the antenna in all directions, generally in a single horizontal or vertical plane, so that the sending and receiving stations don't need to be as precisely aligned. However, a wider coverage zone means there are more potential sources of interference, and there is lower gain because the signal power isn't as focused. Omni-directional antennas are used in multipoint and distributed networks. Examples include the ceiling dome or blister antenna, blade antenna, and various rod-shaped antennas.
Serial Infrared (SIR)
With Serial Infrared, discovery and negotiation of data connections are performed at 9.6 Kbps, and speeds vary from 9.6 to 115.2 Kbps.
IrDA Governed Function: Printing
The IR Line Printer, or IrLPT, protocol enables printing between IrDA devices such as laptops and IrDA printers.
What is a wireless network also referred as?
Unbound network media
Basic Service Set (BSS)
A BSS is a set of devices with an AP connected to a wired network and one or more wireless stations or clients. A BSS can extend the supported distance between wireless endpoints by forwarding signals through the wireless access point.
What is a DS?
A distribution system, or DS, is a wired connection between a BSS and a premise-wide network. This system provides mobile access to available network resources.
How do Wireless LAN & Cellular technologies use wireless communication?
Signals are sent via radio frequency, or RF, waves. These networking technologies communicate using RF waves within the ultra-high frequency (between 300 and 3000 MHz) and super high frequency (between 3 and 30 GHz) ranges.
Extended Service Set (ESS)
An ESS is a configuration of multiple BSSs used to support user mobility on a wireless network. The BSSs are connected to a common distribution system such as a wired network. This enables users to move their mobile devices, such as laptop computers, outside of their home BSS while keeping their connections. It also enables data to be forwarded from one BSS to another through the network backbone.
Independent Basic Service Set (IBSS)
An IBSS is a peer-to-peer network in which each wireless station acts as both a client and a wireless AP. Each wireless station can both transmit and receive data.
What is a STA?
An STA is a device that connects an IEEE 802.11-conformant MAC interface to a wireless medium with an Ethernet-like driver interface. A wireless STA contains an adapter card, a PC card, or an embedded device to provide wireless connectivity.
Bluetooth
Bluetooth is a wireless technology that facilitates short-range wireless communication between devices such as personal computers, laptops, cellular phones, and gaming consoles. It's often used in a wireless personal area network, or WPAN. However, you can connect devices point-to-point. The original working version of Bluetooth was 1.1. A maximum of eight Bluetooth devices can be connected to each other at one time, and the devices must generally be less than 30 feet apart. Bluetooth can be used to establish both point-to-point and multipoint connections. Bluetooth establishes a link using a radio frequency-based medium. It doesn't need devices to be within line of sight of each other to make connections. Bluetooth 1.1 uses the 2.4 GHz spectrum to communicate a 1 Mbps connection between two devices, for both a 232 Kbps voice channel and a 768 Kbps data channel. A more recent version of Bluetooth - version 2.0 - supports an overall data rate of 2.1 to 3 Mbps, and allows for communicating devices to be as far as 100 feet - or about 30 meters - apart.
Broadcast Radio
Broadcast radio is a form of RF networking that's non-directional, uses a single frequency for transmissions, and comes in low- and high-power versions. Low-power RF transmissions can travel over only a short distance, often no more than 70 meters. However, low-RF systems are inexpensive and relatively easy to install. High-power RF transmissions can travel over longer distances. However, specially trained technicians are often required to install this type of system, which is also more expensive.
Spread Spectrum Technique: Direct Sequence Spread Spectrum (DSSS)
DSSS uses multiple channels simultaneously to send data. In addition, it uses Error Detection And Correction, or EDAC, techniques to reduce data transmission errors. In DSSS, a single data signal is converted into multiple data signals called chips. The set of chips is sent across a wide band of adjacent channels. Upon receiving the data, the receiver combines and converts the signals back into the original. Because of the included EDAC information, the signal can often be reconstructed even if only some of the channels are received clearly.
Directional
Directional antennas concentrate the signal beam in a single direction. They have a relatively narrow, focused transmission beam and relatively high gain. Because they transmit primarily in a single direction, the sending and receiving stations must be precisely aligned. The high gain provides for good signal quality, and the narrow beam ensures that only a narrow transmission area needs to be clear of interference. Directional antennas are used in a point-to-point network to connect one station to another. Examples include parabolic dish, backfire, yagi, and panel antennas.
Spread Spectrum technique: Frequency Hopping Spread Spectrum (FHSS)
FHSS sends signals on one channel at a time, while the channel changes at fixed predetermined intervals. Both the sender and receiver use the same selection and order of frequencies to keep connected as the frequency changes. FHSS doesn't significantly reduce noise or improve the signal-to-noise ratio. Eavesdroppers are less likely to be successful at listening in on an FHSS transmission than a normal radio transmission. It's not likely that parties other than the sender and receiver would know the selection and order of frequencies being used to communicate.
What is information transmitted as, & why?
Information is transmitted as electromagnetic waves, such as radio waves or microwaves, or as light pulses. This enables users to move around while remaining connected to a network.
Where can IrDA functions be supported?
It's included with, or can be added, to many commonly used OSs, including Windows, Mac OS X, & Linux
Medium Infrared (MIR)
Medium Infrared is an unofficial reference to data transmission speeds between 0.576 and 1.152 Mbps.
Name a disadvantage of radio networking.
One of the disadvantages of radio networking is that it's subject to electrical interference from power lines, metal structural components in buildings, and atmospheric conditions.
Point-To-Point Communication
Point-to-point communication is a direct connection between two nodes. Data transmitted by one node goes directly to the other. For example, a cell phone connected to a cell tower is a point-to-point connection. Point-to-point wireless connections are typically used to link distant buildings or networks as part of a controller area network, a metropolitan area network, or a wide area network.
IrDA Governed Function: Dial-Up Networking
The IR Communications, or IrCOMM, protocol enables dial-up Internet access through IR-enabled cell phones.
IrDA Governed Function: LAN Access & Peer-To-Peer Networking
The IR Network, or IrNET, protocol enables network access through IR-enabled access points.
IrDA Governed Function: Image Transfer
The IR Transfer Picture, or IrTran-P, protocol enables easy image transfer between digital cameras and Windows devices.
IrDA Governed Function: File Transfer
The IrDA Object Exchange, or IrOBEX, protocol enables file transfer between IrDA devices.
Spread Spectrum
The spread spectrum is a form of radio transmission in which a signal can be sent over more than one frequency. Because signals are transmitted over different frequencies, it's difficult to eavesdrop on them or to capture the signals. In addition, it's generally easier to distinguish between a signal and any background noise than with broadcast radio signals.
What is meant by the term "gain"?
The term "gain" is used to refer to the ratio between the input and output power of a radio antenna. Gain can occur due to external amplifiers. Typically a high degree of gain is seen as an advantage. However, there may be situations in which the power of a transmitter is already very close to the legal value, so added power could be a serious problem.
Very Fast Infrared (vFIR)
Very Fast Infrared supports data transmission speeds of up to 16 Mbps.
