wireless LAN

A network requires physical media to connect its nodes. The physical media is where the data flows. You have most likely heard about the OSI reference model, which defines network hardware and services in terms of their functions. The OSI reference model we already discussed in detail in Chapter 1 (“Network and their building blocks.”) Transmission media work at Layer 1(physical layer) of the OSI model.

The physical layer represents bits as voltages, radio frequencies, or light pulses, so various standards organizations have contributed to defining the physical, electrical, and mechanical properties of the media available for different data communications. These characteristics guarantee that cables and connectors will function as expected with other data link layer implementations. There are three main categories of physical media:

Copper cable Media

Types of cable include unshielded twisted-pair (UTP), shielded twisted-pair (STP), and coaxial cable. Copper-based cables are inexpensive and easy to work with compared to fiber-optic cables. Still, as you’ll learn when we get into the particulars, the main disadvantage of copper cable is that it offers a limited range that cannot handle advanced applications.

The most used physical media for data communications is cabling (copper media), which uses copper wires to send data and control bits between network devices. Cables used for data communications generally consist of individual copper wires from circuits dedicated to specific signaling purposes. There are three main types of copper media used in networking:

• Unshielded Twisted-Pair (UTP)
• Shielded Twisted-Pair (STP)
• Coaxial

The above cables interconnect computers on a LAN and other devices such as switches, routers, and wireless access points. Each type of connection and the associated devices have cabling requirements specified by physical layer standards. The physical layer standards also specify the use of different connectors for different types, the mechanical dimensions of the connectors, and the acceptable electrical properties of each type.

Unshielded Twisted-Pair Cable (UTP)

Unshielded twisted-pair (UTP) cabling is the most common networking media for voice and data communications. UTP cable consists of four pairs of color-coded wires that have been twisted

Together, they are encased in a flexible plastic sheath that protects them from minor physical damage. Twisting wires helps decrease electromagnetic and radio-frequency interference induced from one wire to the other.

UTP cabling is terminated with RJ-45 connectors for interconnecting network hosts with intermediate networking devices, such as switches and routers. In the figure, the color codes identify the individual pairs and wires and help in cable termination.

Shielded Twisted-Pair Cable(STP)

Shielded twisted-pair (STP) cabling provides better noise protection than UTP cabling. However, STP cables are more expensive and difficult to install. Like UTP cables, STP uses an RJ-45 connector.

The extra covering in shielded twisted pair wiring protects the transmission line from electromagnetic interference leaking into or out of the cable. STP cabling is often used in Ethernet networks, speedy data rate Ethernet.

Shielded twisted-pair (STP) cables also combine shielding to counter EMI and RFI and wire twisting to counter crosstalk. To take full advantage of the shielding, STP cables are also terminated with special shielded STP data connectors. If the cable is improperly grounded, the shield may act as an antenna and pick up unwanted signals.

Coaxial Cable

Coaxial cable is called “coaxial” because two conductors share the same axis. The outer channel serves as a ground. Many of these cables or pairs of coaxial tubes are placed in a single outer sheathing and, with repeaters, can carry information for a great distance. As shown in the figure, the coaxial cable consists of:

• A copper conductor is used to send the electronic signals.
• A layer of flexible plastic insulation surrounds a copper conductor.
• The insulating material is surrounded by a woven copper braid or metallic foil, which acts as the second wire in the circuit and as a shield for the inner conductor. This second layer or shield also reduces the amount of outside electromagnetic interference.
• A cable jacket covers the entire cable to prevent minor physical damage.

There are different types of connectors used with coax cables.

Although UTP cable has essentially replaced the coaxial cable in modern Ethernet installations, the coaxial cable design:

• We can use many types of coax cables in different ways. Following is the table of different types of coax cable

Fiber Optics Cable Media

Fiber Optic cable is another type of physical media. It offers huge data bandwidth, protection against many types of noise and interference, and enhanced security.

So, fiber provides clear communications and a comparatively noise-free environment. The disadvantage of fiber is that it is costly to purchase and it requires specialized equipment and techniques for installation.

Properties of Fiber-Optic Cabling

Fiber optic cable can send data over long distances with higher bandwidths than any other networking media. It can also send signals with less attenuation and is totally protected from EMI and RFI. OFC is generally used to connect network devices.

Fiber optic cable is flexible but very thin—a transparent strand of very pure glass, not bigger than a human hair. Bits are encoded on the fiber as light impulses. The fiber-optic cable acts as a waveguide or “light pipe” to send light between the two ends with minimal signal loss.

As an analogy, consider an empty paper towel roll with the inside coated like a mirror. It is a thousand meters long, and a small laser pointer sends a Morse code signal at the speed of light. Essentially, that is how a fiber-optic cable operates, except that it is smaller in diameter and uses advanced light technologies.

Fiber-optic cabling is now being used in four types:

• Enterprise Networks: Used for backbone cabling and interconnecting infrastructure devices.
• Fiber-to-the-Home: Used to give always-on broadband services to homes and small businesses.
• Long-Haul Networks: The service providers use this type to connect countries and cities.
• Submarine Networks provide reliable, high-speed, high-capacity solutions that survive in harsh undersea environments up to transoceanic distances.

Fiber Optic Cable Structure

The optical fiber is composed of two kinds of glass (core and cladding) and a protective outer shield (jacket), shown in Figure 3-8.

Core

The core is the light transmission element at the center of the optical fiber. This core is typically silica or glass. Light pulses travel through the fiber core.

Cladding

It is made from slightly different chemicals than those used to make the core. It behaves like a mirror by reflecting light into the fiber’s core, keeping the light in the core as it travels down the fiber.

Buffer

Used to help shield the core and cladding from damage.

Strengthening Member

The buffer surrounds the fiber cable, preventing it from stretching out when it is pulled. The material used is often the same as that used to manufacture bulletproof vests.

Jacket

Typically, a PVC jacket protects the fiber against abrasion, moisture, and other contaminants. This outer jacket composition can vary depending on cable usage.

Types of Fiber Media

Light pulses instead of the transmitted data as bits on the media generated by either:

• Lasers
• Light-emitting diodes (LEDs)

Electronic semiconductor devices called photodiodes detect the light pulses and convert them to voltages. The laser light transmitted over fiber-optic cabling can damage the human eye. Care must be taken to avoid looking into the end of active optical fiber. Fiber-optic cables are mostly classified into two types:

• Single-mode fiber (SMF): its core is very small and uses very expensive laser technology to send a single ray of light, as shown in Figure Popular, in long-distance situations spanning hundreds of kilometers, such as those required in long-haul telephony and cable TV applications. The following are single-mode cable characteristics.
  • Small core
  • Less dispersion
  • Use laser as the light source
  • Suited for long-distance application
  • Commonly used with campus backbone for the distance of several thousand meters.

• Multimode fiber (MMF): Its core is very large, and this cable type uses LED emitters to send light pulses. Specifically, light from an LED enters the multimode fiber at different angles, as shown in Figure 3-10. They are popular in LANs because they are powered by low-cost LEDs. It provides bandwidth up to 10 Gb/s over link lengths of up to 550 meters. Following are single-mode cable characteristics.
• Larger core than single-mode cable
• Uses LEDs as the light source
• Allows more excellent dispersion and, therefore, loss of signal
• Suited for long-distance applications but shorter than single-mode
• Commonly used with LANs or distances of a couple of hundred meters within a campus network.

Wireless Media

Wireless media include radio frequencies, microwave, satellite, and infrared. The deployment of wireless media is faster and less costly than cable deployment, primarily when there is no existing infrastructure. There are a few disadvantages associated with wireless. It supports much lower data rates than wired media. Wireless is also greatly affected by external environments, such as the impact of weather, and reliability can be difficult to guarantee. It carries data through electromagnetic signals using radio or microwave frequencies.

Wireless media provides the best mobility options, and the number of wireless-enabled devices continues to increase. As network bandwidth options increase, wireless is quickly gaining in popularity in enterprise networks, and it has some important points to consider before planning:-

• Coverage area: Wireless data communication technologies work well in open environments. However, certain construction materials used in buildings, structures, and the local terrain will limit effective coverage.
• Interference: Wireless is at risk of intrusion and can be disrupted by standard devices such as household cordless phones, fluorescent lights, microwave ovens, and other wireless communications.
• Security: Wireless communication coverage requires no access to a physical media strand. Thus, devices and users not authorized to access the network can access the transmission. Network security is the main component of wireless network administration.
• Shared medium: WLAN works in half-duplex, which means just one device can be sent or received at a time. The wireless medium is shared among all wireless users. The more users need to access the WLAN simultaneously, the less bandwidth each user will need.

Types of Wireless Media

The IEEE and telecommunications industry standards for wireless data communications cover both the data link and physical layers. Cellular and satellite communications can also provide data network connectivity. However, we are not discussing these wireless technologies in this chapter. In each of these standards, physical layer specifications are applied to areas that include:

• Transmission Frequency
• The transmission power of the transmission
• Data to radio signal encoding
• Signal reception and decoding requirements
• Antenna design and construction

Wi-Fi is a trademark of the Wi-Fi Alliance. The certified product uses that belong to WLAN devices that are based on the IEEE 802.11 standards. Different standards are the following:-

WI-FI standard IEEE 802.11

WLAN technology is commonly referred to as Wi-Fi. WLAN uses a protocol called Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). The wireless NIC must first listen before transmitting to decide if the radio channel is clear. If another wireless device is transmitting, the NIC must wait until the channel is clear. We will briefly discuss CSMA/CA.

Bluetooth standard IEEE 802.15

Wireless Personal Area Network (WPAN) standard, commonly known as “Bluetooth”, uses a device pairing process to communicate over distances from 1 to 100 meters.

WI-MAX Standard IEEE 802.16

Usually known as Worldwide Interoperability for Microwave Access (WiMAX), a point-to-multipoint topology gives wireless broadband access.

Wireless LAN (WLAN)

General wireless data implementation wireless LAN requires the following network devices:

• Wireless Access Point (AP): In a wireless local area network (WLAN), an access point (AP) is a station that transmits and receives data. An access point also connects users to other users within the network and can serve as the interconnection point between the WLAN and a fixed wire network. Each access point can serve multiple users within a defined network area, so when people move beyond the range of one access point, they are automatically handed over to the next one. A small WLAN may only need a single access point; the number required increases the function of the number of network users and the physical size of the network.
• Wireless NIC adapters: Provide wireless communication ability to each network host.

As technology has developed, several WLAN Ethernet-based standards have emerged. Therefore, more care needs to be taken when purchasing wireless devices to ensure compatibility and interoperability.

The benefits of wireless data communications technologies are clear, notably the savings on costly premises wiring and the convenience of host mobility.