A network required physical media to connect its nodes. The physical media is where the data actually flows. You have most likely heard about the OSI reference model, which defines network hardware and services in terms of the functions they perform. 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 the definition of 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 different 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, but 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 the advanced applications.
The most used physical media for data communications is cabling (copper media); that uses copper wires to send data and also control bits between network devices. Cables use for data communications generally consists of a series of individual copper wires; that from circuits dedicated to specific signalling purposes. There are three main types of copper media used in networking:
- Unshielded Twisted-Pair (UTP)
- Shielded Twisted-Pair (STP)
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 has cabling requirements specified by physical layer standards. The physical layer standards also specify the use of different connectors for different. Physical layer standards also specify 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 as well as for data communications. UTP cable consists of four pairs of colour-coded wires that have been twisted
Together and then encased in a flexible plastic sheath that protects from minor physical damage. The twisting of wires helps to decrease electromagnetic and also radio-frequency interference induced from one wire to the other.
UTP cabling terminated with RJ-45 connectors for interconnecting network hosts with intermediate networking devices Just like switches and routers. In the figure, you can see that the colour codes find the individual pairs and wires and help in cable termination.
Shielded Twisted-Pair Cable(STP)
Shielded twisted-pair (STP) provides better noise protection than UTP cabling. However, compared to UTP cable, STP cable is more expensive and difficult to install. Like UTP cable, 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 often used in Ethernet networks, especially fast data rate Ethernet.
Shielded twisted-pair (STP) cables also combine the techniques of shielding to counter EMI and RFI, and wire twisting to counter crosstalk. To put on the full advantage of the shielding STP cables 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 is called “coaxial” because of the fact that there are two conductors that share the same axis. The outer channel serves as a ground. Many of these cables or pairs of coaxial tubes 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 used to send the electronic signals.
- A layer of flexible plastic insulation surrounding a copper conductor.
- The insulating material surrounded in a woven copper braid or metallic foil; that 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.
- The entire cable has covered with a cable jacket to prevent minor physical damage.
There are different types of connectors uses with coax cable.
Although, UTP cable has essentially replaced the coaxial cable in modern Ethernet installations, the coaxial cable design:
- There are many types of coax cable that we can use 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 to 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. Optic fiber cable can send signals with less attenuation and it’s totally protected from EMI and RFI. OFC is generally used to connect network devices.
Fiber optic cable is a 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 the minimal loss of signal.
As an analogy, consider an empty paper towel roll with the inside coated like a mirror. It is a thousand meters in length, 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: Used to give reliable high-speed; high-capacity solutions capable of surviving 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) shows that figure 3-8.
The core is actually 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.
Made from little different chemicals than those used to make the core. It tends to do like a mirror by reflecting light back into the core of the fiber. This keeps the light in the core as it travels down the fiber.
Used to help shield the core and cladding from damage.
Surrounds the buffer, prevents the fiber cable from being stretched out when it is being pulled. The material used is often the same material uses to manufacture bulletproof vests.
Typically a PVC jacket that protects the fiber against abrasion; moisture, and other contaminants. This outer jacket composition can vary depending on the cable usage.
Types of Fiber Media
Light pulses in lieu of the transmitted data as bits on the media generated by either:
- Light emitting diodes (LEDs)
Electronic semiconductor devices called photodiodes detect the light pulses and then 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 uses very expensive laser technology to send a single ray of light; as shown in Figure Popular in long-distance situations spanning hundreds of kilometres; such as those required in long-haul telephony and cable TV applications. Following is 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 type of cable uses LED emitters to send light pulses. Specifically, light from a LED enters the multimode fiber at different angles; as shown in Figure 3-10. Popular in LANs because they powered by low-cost LEDs. It provides bandwidth up to 10 Gb/s over link lengths of up to 550 meters. Following is single mode cable characteristics.
- Larger core than single-mode cable
- Uses LEDs as the light source
- Allows greater dispersion and therefore, loss of signal
- Suited for long distance application; but shorter than single mode
- Commonly used with LANs or distances of a couple of hundred meters within a campus network.
Wireless media include radio frequencies, microwave, satellite, and infrared. Deployment of wireless media is faster and less costly than the deployment of cable, mostly where there is no existing infrastructure. There are a few disadvantages associated with wireless. It supports much lower data rates than do wired media. Wireless is also greatly affected by external environments, such as the impact of weather, as a result, reliability can be difficult to guarantee. It carries data in the form of 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 point to consider before planning:-
- Coverage area: Wireless data communication technologies work well in open environments. However, certain construction materials used in buildings and structures, and the local terrain, will limit the effective coverage.
- Interference: Wireless is at risk to intrusion and can be disrupted by such common devices as household cordless phones, some types of fluorescent lights, microwave ovens, and other wireless communications.
- Security: Wireless communication coverage requires no access to a physical strand of media. thus, devices and users, not authorized for access to the network, can gain access to the transmission. Network security is the main component of wireless network administration.
- Shared medium: WLAN work in half-duplex, which means just one device can send or receive at a time. The wireless medium is shared among all wireless users. The more users need to access the WLAN simultaneously, results in less bandwidth for each user.
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. But, we are not discussing these wireless technologies here in this chapter. In each of these standards, physical layer specifications applied to areas that include:
- Transmission Frequency
- The transmission power of 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 commonly referred to as Wi-Fi. WLAN uses a protocol known as 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, then the NIC must wait until the channel is clear. We discuss CSMA/CA later briefly.
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), uses a point-to-multipoint topology to give 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 point of interconnection 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, a number of WLAN Ethernet-based standards have emerged. So, more care needs to be taken in purchasing wireless devices to make sure compatibility and interoperability.
The benefits of wireless data communications technologies are clear, particularly the savings on costly premises wiring and the convenience of host mobility