CAT6

Definition: CAT6 is an Ethernet cable standard defined by the Electronic Industries Association and Telecommunications Industry Association (commonly known as EIA/TIA). CAT6 is the 6th generation of twisted pair Ethernet cabling.
CAT6 cable contains four pairs of copper wire and unlike CAT5, utilizes all four pairs. CAT6 supports Gigabit (1000 Mbps) Ethernet and supports communications at more than twice the speed of CAT5e, the other popular standard for Gigabit Ethernet cabling.
As with all other types of twisted pair EIA/TIA cabling, CAT6 cable runs are limited to a maximum recommended run rate of 100m (328 feet).
Twisted pair cable like CAT6 comes in two main varieties, solid and stranded. Solid CAT6 cable supports longer runs and works best in fixed wiring configurations like office buildings. Stranded CAT6 cable, on the other hand, is more pliable and better suited for shorter-distance, movable cabling such as "patch" cables.
CAT6 comes at a significantly higher price tag than CAT5 or CAT5e, and today's applications simply can't take advantage of CAT6's better performance. However, if wiring a home or building for the long term, one may still consider using CAT6.

CAT5

Definition: CAT6 is an Ethernet cable standard defined by the Electronic Industries Association and Telecommunications Industry Association (commonly known as EIA/TIA). CAT6 is the 6th generation of twisted pair Ethernet cabling.
CAT6 cable contains four pairs of copper wire and unlike CAT5, utilizes all four pairs. CAT6 supports Gigabit (1000 Mbps) Ethernet and supports communications at more than twice the speed of CAT5e, the other popular standard for Gigabit Ethernet cabling.
As with all other types of twisted pair EIA/TIA cabling, CAT6 cable runs are limited to a maximum recommended run rate of 100m (328 feet).
Twisted pair cable like CAT6 comes in two main varieties, solid and stranded. Solid CAT6 cable supports longer runs and works best in fixed wiring configurations like office buildings. Stranded CAT6 cable, on the other hand, is more pliable and better suited for shorter-distance, movable cabling such as "patch" cables.
CAT6 comes at a significantly higher price tag than CAT5 or CAT5e, and today's applications simply can't take advantage of CAT6's better performance. However, if wiring a home or building for the long term, one may still consider using CAT6.

Category 5
The original specification for category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95. These documents specified performance characteristics and test requirements for frequencies of up to 100 MHz.
Category 5 cable includes four twisted pairs in a single cable jacket. This use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and other pairs (this latter form of interference is called crosstalk). It is most commonly used for 100 Mbit/s networks, such as 100BASE-TX Ethernet, although IEEE 802.3ab defines standards for 1000BASE-T - Gigabit Ethernet over category 5 cable. Cat 5 cable typically has three twists per inch of each twisted pair of 24 gauge copper wires within the cable. May be unsuitable for 1000BASE-T gigabit ethernet.

Category 5e
Cat 5e cable is an enhanced version of Cat 5 that adds specifications for far end crosstalk. It was formally defined in 2001 in the TIA/EIA-568-B standard, which no longer recognizes the original Cat 5 specification. Although 1000BASE-T was designed for use with Cat 5 cable, the tighter specifications associated with Cat 5e cable and connectors make it an excellent choice for use with 1000BASE-T. Despite the stricter performance specifications, Cat 5e cable does not enable longer cable distances for Ethernet networks: cables are still limited to a maximum of 100 m (328 ft) in length (normal practice is to limit fixed ("horizontal") cables to 90 m to allow for up to 5 m of patch cable at each end). Cat 5e cable performance characteristics and test methods are defined in TIA/EIA-568-B.2-2001.

Atmosphere: The Wireless Medium

Wireless signals are electromagnetic waves, which can travel through space. No physical medium is necessary for wireless signals, which travel as well in the vacuum of space as they do through the air in an office building. The ability of radio waves to pass through walls and cover great distances makes wireless a versatile way to build a network. Figure shows wireless technologies and features.

The waves differ only in their frequency. Power waves, radio waves, microwaves, Infrared light waves, visible light waves, ultraviolet light waves, x-rays, and gamma rays share some very important characteristics:

-All of these waves have an energy pattern.
-All of these waves travel at the speed of light, c = 299,792,458 meters per second, in a vacuum. This speed might more accurately be called the speed of electromagnetic waves.
-All of these waves obey the equation (frequency) x (wavelength) = c.
-All of these waves will travel through a vacuum. However, they have very different interactions with various materials.
-The primary difference among different electromagnetic waves is their frequency. Low frequency electromagnetic waves have a long wavelength, while high frequency electromagnetic waves have a short wavelength. Wavelength represents the distance from one peak to the next on the sine wave.

The interactive calculator can be used for the following activities:
-Enter a frequency and notice that the calculator displays the wavelength.
-Enter a wavelength and notice that the calculator displays the frequency.
-In either case, the calculator displays the electromagnetic wave associated with the calculation.

Wireless ApplicationsA common application of wireless data communication is for mobile use. Some examples of mobile use include the following:
-Person-to-person communications from moving cars or airplanes
-Satellite communication relays
-Telemetry signals to remote space probes
-Communication links to space shuttles and space stations
-Communications without reliance on copper or optical fiber tethers
-Any-to-any communications to exchange network data

Optical Fibre

Fiber-optic cable is a networking medium that uses modulated light transmissions. It can be costlier than other networking media, depending on the purity and the size of the fiber used. The connectors that terminate fiber also tend to be more expensive. Fiber is not susceptible to electromagnetic or radio frequency interference. It is capable of higher data rates than any of the other types of current networking media. As the diameter of the fiber gets smaller, the maximum transmission rate increases.
Data for fiber-optic cable are converted into pulses of light and this light is allowed to propagate down the fiber.

The light-guiding parts of an optical fiber are referred to as the core and the cladding. The core is usually very pure glass with a lower index of refraction. When a cladding layer of glass or plastic with a low index of refraction surrounds the core glass, light can be trapped in the fiber core. This process is called total internal reflection, and it allows the optical fiber to act like a light pipe that guides light for tremendous distances, even around bends.
Fiber-optic communication is rooted in a number of inventions made in the 19th century. It was not until the 1960s, when solid-state laser light sources and high-quality impurity-free glasses were introduced, that fiber-optic communication became practical. Telephone companies, who saw its benefits for long-distance communication, pioneered its use on a widespread basis

Coaxial Cable

Coaxial cable consists of a center conductor, either stranded or solid, which is surrounded by a layer of insulating material called the dielectric. The dielectric is surrounded by a shield made of foil, braided wire strands, or both. Outside of the shield is a protective insulating sheath that forms the cable jacket.
All of the elements of the coaxial cable encircle the center conductor, as the growth rings in a tree surround the core. Because they all share the same axis, this construction is called coaxial, or coax for short. Coax is the most widely used media for transporting high radio frequency signals over wire, especially cable television signals. The cables leading to most external antennas are coax. The video cables that connect a VCR to a TV are coax. Miles of coax are found in most video production facilities.
In the past, coaxial cable offered significant advantages for LANs. Its frequency response allowed it to carry signals with less degradation over longer distances than the twisted pair media available at the time. Improved manufacturing techniques and better electronics have long made twisted pair or optical fibers the preferred choice for network cabling.
Originally, Ethernet LANs used a thick coaxial cable that was 1.27 cm (0.5 inches) in diameter. The industry began to refer to this cable as Thicknet . The large coax used for 10Base5 networks was particularly difficult to work with and required great care to prevent bends and kinks. When Ethernet was standardized, Thicknet became IEEE 802.3 10Base5.
Later, the 802.3 committee standardized 10Base2, a version that used a much thinner coaxial cable, with an outside diameter of only 0.635 cm (0.25 in.). 10Base2 is sometimes referred to as Thinnet. Because of its low cost and ease of installation, it is also sometimes referred to as cheapernet.

Unshieled Twisted Paid (UTP)

Unshielded twisted-pair cable (UTP) is a four-pair wire medium that is used in a variety of networks. The eight individual copper wires in the UTP cable are each covered by insulating material. Two wires are twisted around each other to form pairs. This type of cable relies on the cancellation effect, produced by the twisted-wire pairs, to limit signal degradation caused by crosstalk and external EMI and RFI. To further reduce crosstalk between pairs in the UTP cable, the number of twists in the wire pairs is increased. Like STP cable, UTP cable must follow precise specifications as to how many twists there are for every 30 cm (1 ft) of cable.
The four pairs used in UTP cable for networking are usually 22 or 24 American Wire Gauge (AWG) copper wire. This differentiates it from the twisted-pair used for telephone wiring, which is typically 19, 22, 24, or 26 AWG. Because UTP has an external diameter of approximately 0.64 cm (0.25 inches), its small size can be advantageous during installation. Since UTP can be used with most of the major networking architectures, it continues to grow in popularity.

UTP cable has many advantages. It is easy to install and is less expensive than other types of networking media. Since it has a small external diameter, UTP does not fill up wiring ducts as rapidly as other types of cable, with the exception of fiber-optic cable, which costs more to purchase and install. This can be an extremely important factor to consider, particularly when installing a network in an older building. Another advantage of UTP is related to the hub-based or switch-based star topology that is used on UTP-based Ethernet LANs.

. This topology is considered much easier to troubleshoot than the bus topology of coaxial-based LANs.
There are also disadvantages to using UTP cabling. UTP cable is more prone to electrical noise and interference than other types of networking media, and the distance between signal boosts is shorter for UTP than it is for coaxial and fiber-optic cables.
UTP was once considered to be slower at transmitting data than other types of cable. UTP can currently reach transmission rates up to 1000 Mbps (1 Gbps). A 10-Gbps standard is being considered.

STP (Shielded Twisted Pair)

Shielded twisted-pair cable (STP) combines the techniques of shielding and twisting wires. Each pair of wires is twisted and then wrapped in metallic foil. All four pairs of wires are wrapped in an overall metallic braid or foil. STP is usually 150-ohm cable. As specified for use in Ethernet network installations, STP reduces electrical noise. This includes pair-to-pair coupling, or crosstalk, from within the cable, and electromagnetic interference (EMI) and radio frequency interference (RFI) from outside the cable. STP cable must follow precise specifications as to how many twists or braids exist for every 30 cm (1 ft) of cable. Shielded twisted-pair cable shares many of the advantages and disadvantages of unshielded twisted-pair cable (UTP). Properly installed STP offers greater protection from all types of external interference, but is more expensive and difficult to install than UTP. A hybrid of UTP and STP is screened UTP (ScTP), also known as foil twisted pair (FTP), or pairs in metal foil (PiMF). ScTP is essentially UTP wrapped in a metallic foil shield, or screen. It is usually 100-ohm cable.

If improperly grounded, or if any discontinuities exist in the entire length of the shielding material, (for example, due to poor installation) STP and ScTP become susceptible to major noise problems. This is because noise problems cause the shield to act like an antenna picking up unwanted signals. This effect works both ways. Not only does the foil prevent incoming electromagnetic waves from causing noise on the data wires, but it also minimizes the outgoing radiated electromagnetic waves, which could cause noise in other devices. STP and ScTP cables cannot be run as far as some networking media, such as coaxial cable or optical fiber, without the signal being repeated. Also, more insulation and shielding combine to considerably increase the size, weight, and cost of the cables. The shielding materials make terminations more difficult and susceptible to poor workmanship. Despite their shortcomings, STP and ScTP cables are still useful in high electrical or RF noise environments, such as near an airport radar installation. These cables are also popular in Europe.

Physical Layer Media

A solid foundation must be used for building either a wired or wireless LAN. As shown Figure , this foundation is referred to as Layer 1 or the physical layer in the OSI reference model. The physical layer is the layer that defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems.
This section introduces different types of networking media that are used at the physical layer, including:
-shielded twisted-pair cable
-unshielded twisted-pair cable
-coaxial cable
-fiber-optic cable
-propagated radio waves
Radio waves are the medium used by wireless technologies. When designing and building networks, it is important to comply with all applicable fire codes, building codes, and safety standards. Established performance standards should be followed to ensure optimal network operation. Because of the wide variety of options that are currently available in networking media, compatibility and interoperability should also be considered.

The Future of Wireless Local-Area Networking

Current WLAN technologies offer increasing data rates, better reliability and dependability, and decreasing costs. Data rates have increased from 1 Mbps to 54 Mbps, interoperability has become a reality with the introduction of the IEEE 802.11 family of standards, and prices have dramatically decreased. As WLANs become more popular, manufacturers can increasingly leverage economies of scale.
There will be many improvements to come. For example, many weaknesses have been found in the basic security settings of WLANs, and stronger security in all future products is a priority. Versions such as 802.11g will offer 54 Mbps like 802.11a, but also will be backward compatible with 802.11b.
This course will cover the general technologies behind 802.11a and 802.11b WLANs, including radio technologies, WLAN design, site preparation, and antenna theory. Detailed coverage of the Cisco Aironet products and accessories will also be presented. Students should be able to apply their knowledge at the completion of the course to design WLANs using products from one or multiple vendors.

Evolution of Wireless LAN

The first wireless LAN technologies defined by the 802.11 standard were low-speed proprietary offerings of 1 to 2 Mbps. Despite these shortcomings, the freedom and flexibility of wireless allowed these early products to find a place in technology markets. Mobile workers used hand-held devices for inventory management and data collection in retail and warehousing. Later, hospitals applied wireless technology to gather and deliver patient information. As computers made their way into the classrooms, schools and universities began installing wireless networks to avoid cabling costs, while enabling shared Internet access. Realizing the need for an Ethernet-like standard, wireless vendors joined together in 1991 and formed the wireless Ethernet Compatibility Alliance (WECA). WECA proposed and built a standard based on contributed technologies. WECA later changed its name to Wi-Fi. In June 1997 the IEEE released the 802.11 standard for wireless local-area networking.
Just as the 802.3 Ethernet standard allows for data transmission over twisted-pair and coaxial cable, the 802.11 WLAN standard allows for transmission over different media. Specified media include the following:

-Infrared light
-Three types of radio transmission within the unlicensed 2.4-GHz frequency bands:
Frequency hopping spread spectrum (FHSS)
Direct sequence spread spectrum (DSSS)
Orthogonal frequency-division multiplexing (OFDM) 802.11g
-One type of radio transmission within the unlicensed 5-GHz frequency bands:
Orthogonal frequency-division multiplexing (OFDM) 802.11a

Spread spectrum is a modulation technique that was developed in the 1940s. It spreads a transmission signal over a broad range of radio frequencies. This technique is ideal for data communications because it is less susceptible to radio noise and creates little interference.

Wireless LAN (WLANs)

What is Wireless LAN
In the simplest of terms, a wireless local-area network (WLAN) does exactly what the name implies. It provides all the features and benefits of traditional LAN technologies such as Ethernet and Token Ring, but without the limitations of wires or cables. Thus, WLANs redefine the way the industry views LANs. Connectivity no longer implies attachment. Local areas are measured not in feet or meters, but in miles or kilometers. An infrastructure need not be buried in the ground or hidden behind walls. An infrastructure can move and change based on the needs of an organization.
A WLAN, just like a LAN, requires a physical medium through which transmission signals pass. Instead of using twisted-pair or fiber-optic cable, WLANs use infrared light (IR) or radio frequencies (RFs). The use of RF is far more popular for its longer range, higher bandwidth, and wider coverage. WLANs use the 2.4-gigahertz (GHz) and 5-GHz frequency bands. These portions of the RF spectrum are reserved in most of the world for unlicensed devices. Wireless networking provides the freedom and flexibility to operate within buildings and between buildings.

No More Wires
Wireless systems are not completely wireless. Wireless devices are just one part of the traditional wired LAN. These wireless systems, designed and constructed using standard microprocessors and digital circuits, connect to traditional wired LAN systems. Furthermore, wireless devices must be powered to provide energy to encode, decode, compress, decompress, transmit, and receive wireless signals.
The first generation WLAN devices, with their low speeds and lack of standards, were not popular. Modern standardized systems are now able to transfer data at acceptable speeds. The IEEE 802.11 committee and the Wi-Fi Alliance have diligently worked to make wireless equipment standardized and interoperable.

Wireless technology will now support the data rates and interoperability necessary for LAN operation. Also, the cost of the new wireless devices has decreased greatly. WLANs are now an affordable option to wired LAN connectivity. In most countries these devices do not require special governmental licensing.

Why Wireless ?

Current wired Ethernet LANs operate at speeds around 100 Mbps at the access layer, 1 Gbps at the distribution layer, and up to 10 Gbps at the core level. Most WLANs operate at 11 Mbps to 54 Mbps at the access layer and are not intended to operate at the distribution or core layers. The cost of implementing WLANs is competitive with wired LANs. So why install a system that is at the lower end of the current bandwidth capabilities? One reason is that in many small LAN environments, the slower speeds are adequate to support the application and user needs. With many offices now connected to the Internet by broadband services such as DSL or cable, WLANs can handle the bandwidth demands. Another reason is that WLANs allow users to roam a defined area with freedom and still remain connected. During office reconfigurations, WLANs do not require rewiring and its associated costs.

WLANs have numerous benefits for home offices, small businesses, medium businesses, campus networks, and larger corporations. The environments that are likely to benefit from a WLAN have the following characteristics:
-Require standard Ethernet LAN speeds
-Benefit from roaming users
-Reconfigure the physical layout of the office often
-Expand rapidly
-Utilize a broadband Internet connection
-Face significant difficulties installing wired LANs
-Need connections between two or more LANs in a metropolitan area
-Require temporary offices and LANs

WLANs do not eliminate the need for Internet Service Providers (ISPs). Internet connectivity will still require service agreements with local exchange carriers or ISPs for Internet access. There is a current trend for ISPs to provide wireless Internet service. These ISPs are referred to as Wireless Internet Service Providers (WISPs). Furthermore, WLANs do not replace the need for traditional wired routers, switches, and servers in a typical LAN.
Even though WLANs are primarily designed as LAN devices, they can be used to provide site-to-site connectivity at distances up to 40 km (25 miles). The use of WLAN devices is much more cost effective than using WAN bandwidth or either installing or leasing long fiber runs. For instance, the cost of installing a WLAN between two buildings will incur a one-time cost of several thousand U.S. dollars. A dedicated leased T1 link, which only provides a fraction of the bandwidth of a WLAN, will easily cost hundreds of U.S. dollars per month or more. Installing fiber across a distance of more than 1.6 km (1 mile) is difficult and would cost much more than a wireless solution.