The 802.11 family currently includes six over-the-air modulation techniques that all use the same protocol. The most popular (and prolific) techniques are those defined by the b, a, and g amendments to the original standard; security was originally included and was later enhanced via the 802.11i amendment. 802.11n is another modulation technique under development. Other standards in the family (c¡Vf, h, j) are service enhancements and extensions or corrections to previous specifications. 802.11b was the first widely accepted wireless networking standard, followed (somewhat counterintuitively) by 802.11a and 802.11g.
802.11b and 802.11g standards use the 2.4 gigahertz (GHz) band, operating (in the USA) under Part 15 of the FCC Rules and Regulations. Because of this choice of frequency band, 802.11b and 802.11g equipment can incur interference from microwave ovens, cordless telephones, Bluetooth devices, and other appliances using this same band. The 802.11a standard uses the 5 GHz band, and is therefore not affected by products operating on the 2.4 GHz band.
Which part of the radio frequency spectrum may be used varies between countries, with the strictest limitations in the USA. While it is true that in the USA 802.11a and g devices may be legally operated without a license, it is not true that 802.11a and g operate in an unlicensed portion of the radio frequency spectrum. Unlicensed (legal) operation of 802.11 a & g is covered under Part 15 of the FCC Rules and Regulations. Frequencies used by channels one (1) through six (6) (802.11b) fall within the range of the 2.4 gigahertz amateur radio band. Licensed amateur radio operators may operate 802.11b devices under Part 97 of the FCC Rules and Regulations that apply.
|
Protocol |
Release Date |
Frequency |
Bandwidth |
|
IEEE 802.11 |
1997 |
2.4 GHz |
1, 2 Mbps |
|
IEEE 802.11a |
1999 |
5 GHz |
6, 9, 12, 18, 24, 36, 48, 54 Mbps |
|
IEEE 802.11b |
1999 |
2.4 GHz |
5.5, 11 Mbps |
|
IEEE 802.11g |
2003 |
2.4 GHz |
6, 9, 12, 18, 24, 36, 48, 54 Mbps |
|
IEEE 802.11n |
expected mid-2007 |
2.4 GHz |
540 Mbps |
[Router]A router acts as a junction between two or more networks to transfer data packets among them. A router is different from a switch. A switch connects devices to form a Local area network (LAN).
One easy illustration for the different functions of routers and switches is to think of switches as neighborhood streets, and the router as the intersections with the street signs. Each house on the street has an address within a range on the block. In the same way, a switch connects various devices each with their own IP address(es) on a LAN.
However, the switch knows nothing about IP addresses except its own management address. Routers connect networks together the way that on-ramps or major intersections connect streets to both highways and freeways, etc. The street signs at the intersection (routing table) show which way the packets need to flow.
So for example, a router at home connects the Internet Service Provider's (ISP) network (usually on an Internet address) together with the LAN in the home (typically using a range of private IP addresses, see network address translation) and a single broadcast domain. The switch connects devices together to form the LAN. Sometimes the switch and the router are combined together in one single package sold as a multiple port router.
In order to route packets, a router communicates with other routers using routing protocols and using this information creates and maintains a routing table. The routing table stores the best routes to certain network destinations, the "routing metrics" associated with those routes, and the path to the next hop router. See the routing article for a more detailed discussion of how this works.
Routing is most commonly associated with the Internet Protocol, although other less-popular routed protocols are in use.
[WiMax ¡V 802.16d/e]WiMAX is a term coined to describe standard, interoperable implementations of IEEE 802.16 wireless networks, in a rather similar way to Wi-Fi being interoperable implementations of the IEEE 802.11 Wireless LAN standard. However, WiMAX is very different from Wi-Fi in the way it works.
In Wi-Fi, the media access controller ("MAC") uses contention access ¡X all subscriber stations that wish to pass data through a wireless access point ("AP") are competing for the AP's attention on a random interrupt basis. This can cause distant nodes from the AP to be repeatedly interrupted by closer nodes, greatly reducing their throughput. This makes services such as Voice over IP (VoIP) or IPTV, which depend on a predetermined type of "quality of service" (QoS), difficult to maintain for large numbers of users.
In contrast, the 802.16 MAC uses a scheduling algorithm, where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and contract, but it remains assigned to the subscriber station, meaning that other subscribers cannot use it. This scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It can also be more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service parameters by balancing the time-slot assignments among the application needs of the subscriber stations.
The original WiMAX standard (IEEE 802.16) specified WiMAX in the 10 to 66 GHz range. 802.16a, updated in 2004 to 802.16-2004 (also known as 802.16d), added support for the 2 to 11 GHz range. 802.16d was updated to 802.16e in 2005. 802.16e uses scalable orthogonal frequency-division multiplexing (OFDM) as opposed to the non-scalable version in .16d. This brings potential benefits in terms of coverage, self installation, power consumption, frequency re-use and bandwidth efficiency. .16e also adds a capability for full mobility support.
Most interest will probably be in the 802.16d and .16e standards, since the lower frequencies suffer less from signal attenuation and therefore give improved range and in-building penetration.
The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and range and stronger encryption. It provides connectivity between network endpoints without need for direct line of sight in favourable circumstances. The non-line-of-sight propagation (NLOS) performance requires the .16d or .16e variants, since the lower frequencies are needed. It relies upon clever use of multi-path signals.
[UWB]Ultra-Wideband (UWB) is a technology for transmitting information spread over a large bandwidth that should, in theory and under the right circumstances, be able to share spectrum with other users. A February 14, 2002 Report and Order by the Federal Communications Commission (FCC) [1] authorizes the unlicensed use of UWB in 3.1¡V10.6 GHz. This is intended to provide an efficient use of scarce radio bandwidth while enabling both high data rate personal-area network (PAN) wireless connectivity as well as longer-range, low data rate applications as well as radar and imaging systems. More than four dozen devices have been certificated under the FCC UWB rules, the vast majority of which are radar, imaging or positioning systems. Deliberations in the International Telecommunication Union Radiocommunication Sector (ITU-R) have resulted in a Report and Recommendation on UWB in November of 2005. National jurisdictions around the globe are expected to act on national regulations for UWB very soon.
Due to the extremely low emission levels, UWB systems tend to be short-range. However, due to the short duration of the UWB pulses, extremely high data rates are possible, and data rate can be readily traded for range by simply scaling the number of pulses per data bit. Conventional OFDM technology can also be used subject to the minimum bandwidth requirement of the regulations. High data rate UWB can enable wireless monitors, the efficient transfer of data from digital camcorders, wireless printing of digital pictures from a camera without the need for an intervening personal computer, and the transfer of files among cell phone handsets and other handheld devices like personal digital audio and video players.
[HomePlug]HomePlug is a standard body for power line communication. This organization of about 50 companies sets the global HomePlug standard, currently at v 1.0. HomePlug 1.0 is the specification for a technology that connects devices to each other through the power lines in a home. HomePlug certified products connect PCs and other devices that use Ethernet, USB, and 802.11. Many devices made by alliance members have HomePlug built in and to connect them to a network all one has to do is plug the device into the wall in a home with other HomePlug devices. Since surge protectors and similar devices may interfere with the high-frequency signals used by HomePlug, the directions included with HomePlug devices recommend plugging them directly into the wall outlets without using extension cords or outlet strips.
The HomePlug powerline alliance has defined a number of standards:
HomePlug 1.0 ¡X specification for connecting devices via power lines in the home
HomePlug AV ¡X designed for transmitting HDTV and VoIP around the home
HomePlug BPL ¡X a working group to develop a specification for to-the-home connection
Homeplug CC ¡X Command and Control is a low-speed, very low-cost technology intended to complement the alliance's higher-speed powerline communications technologies. The specification will enable advanced, whole-house control of lighting, appliances, climate control, security and other devices.
[DLNA]The Digital Living Network Alliance (DLNA) is a cross-industry organization of leading consumer electronics, computing industry and mobile device companies. We share a vision of a wired and wireless interoperable network of Personal Computers (PC), Consumer Electronics (CE) and mobile devices in the home and on the road, enabling a seamless environment for sharing and growing new digital media and content services. DLNA is focused on delivering interoperability guidelines based on open industry standards to complete the cross industry digital convergence.
In the DLNA digital home, it will be common for consumers to:
• Easily acquire, store and access digital music from almost anywhere in the home
• Effortlessly manage, view, print and share digital photos
• Take favorite content anywhere to share with family and friends
• Enjoy distributed, multi-user content recording and playback
[ViiV]ViiV is a platform marketing initiative from Intel. Like Intel's Centrino and vPro, ViiV is a computer platform certification for a particular combination of Intel products as its primary components. It is an open specification for an Intel-based Media Center PC.
Specifically, ViiV is a particular combination of CPU, mainboard chipset, software, Digital Rights Management and network card. It is intended for primary use as an in-home media and desktop platform with the ability to operate as a normal PC or as a hardware media player/centre - running applications, playing DVDs, CDs, MP3, photographs and games as well as subscription based (partially DRM protected) content such as ILoveFilm, Napster and SKY.
