Network Fundamentals: Transmission Media Lecture PDF

Network Fundamental LECTURE 2 : Transmission Media Lecturer: Kanar R. Tariq Sulaimani Polytechnic University @2024  Outline What is Transmission Media? Transmission Media Types Guided Media Twisted Pair Cables Coaxial Cable...

Network Fundamental LECTURE 2 : Transmission Media Lecturer: Kanar R. Tariq Sulaimani Polytechnic University @2024  Outline What is Transmission Media? Transmission Media Types Guided Media Twisted Pair Cables Coaxial Cables Fiber Optic Cables What is Transmission Media ? A Transmission medium can be broadly defined as Anything that can carry information from a source to a destination. For example, the transmission medium for two people having a dinner conversation is the air. For a written message, the transmission medium might be a mail carrier, a truck, or an airplane. In data communications the definition of the information and the transmission medium is more specific. The transmission medium is usually free space, metallic cable, or fiber-optic cable. Transmission Media Data after that convert it to information. Figure 4.1 Transmission medium and physical layer Transmission media are actually located below the physical layer and are directly controlled by the physical layer. Transmission Media Types Figure 4.2 Classes of transmission media 5 Guided Media Guided media, which are those that provide a channel from one device to another, include Twisted-pair cable Coaxial cable Fiber-optic cable. ▪ Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current. ▪ Optical fiber is a cable that accepts and transports signals in the form of light. 6  Twisted Pair cable A twisted pair consists of two conductors (normally copper), each with its own plastic insulation, twisted together, as shown in Figure 4.3. Figure 4.3 Twisted Pair Cable 7  Twisted Pair Cable Types The most common twisted-pair cable used in communications is referred to as: 1. Unshielded Twisted-Pair (UTP). 2. Shielded Twisted-Pair (STP). Although metal casing improves the quality of cable by preventing the penetration of noise or crosstalk, it is bulkier and more expensive. 8 UTP Categories Table 4.1 UTP Categories 9  Performance One way to measure the performance of twisted-pair cable is to compare attenuation versus frequency and distance. A twisted-pair cable can pass a wide range of frequencies. Figure 4.5 shows that with increasing frequency, the attenuation, measured in decibels per kilometer (dB/km). Note that gauge is a measure of the thickness of the wire. Figure 4.5 UTP performance 10  Coaxial Cable Coaxial cable (or coax) carries signals of higher frequency ranges than those in twisted-pair cable, in part because the two media are constructed quite differently. Figure 4.6 Coaxial Cable 11 Coaxial cable and Conectors 12 Coaxial Cable Standards Coaxial cables are categorized by their Radio Government (RG) ratings. Each RG number denotes a unique set of physical specifications, including the wire gauge of the inner conductor, the thickness and type of the inner insulator, the construction of the shield, and the size and type of the outer casing. Each cable defined by an RG rating is adapted for a specialized function, as shown in Table 4.2. Table 4.2 Categories of coaxial cables 13  performance We notice in Figure 4.8 that the attenuation is much higher in coaxial cables than in twisted-pair cable. Why? Figure 4.8 Coaxial Cable performance 14 Fiber Optic Cable A fiber-optic cable is made of glass or plastic and transmits signals in the form of light. To understand optical fiber, we first need to explore several aspects of the nature of light. Note: That the critical angle is a property of the substance, and its value differs from one substance to another. Figure 4.9 shows how a ray of light changes direction when going from a more dense to a less dense substance. 15  Angle of Incidence Angle of incidence (I) : is the angle the ray makes with the line perpendicular to the interface between the two substances. If I < critical angle, the ray refracts and moves closer to the surface. If I = critical angle, the light bends along the interface. If I > critical angle, the ray reflects (makes a turn) and travels again in the denser substance. Figure 4.9 Bending of Light ray 16  Optical Fiber Figure 4.10 Optical Fiber Reflections Optical fibers use reflection to guide light through a channel. The difference in density of the two materials must be such that a beam of light moving through the core is reflected off the cladding instead of being refracted into it. See Figure 4.10. Cladding: Glass or plastic surrounding the core of an optical fiber; the optical density of the cladding must be less than that of the core. Core: The glass or plastic center of an optical fiber. 17  Propagation Mode Current technology supports two modes (multimode and single mode) for propagating light along optical channels, each requiring fiber with different physical characteristics. 18  Propagation Mode (Cont.) Multimode: is so named because multiple beams from a light source move through the core in different paths. How these beams move within the cable depends on the structure of the core. In multimode step-index fiber, the density of the core remains constant from the center to the edges. A beam of light moves through this constant density in a straight line until it reaches the interface of the core and the cladding. At the interface, there is an abrupt change due to a lower density, this alters the angle of the beam's motion. 19  Propagation Mode (Cont.) The term step index refers to the suddenness of this change, which contributes to the distortion of the signal as it passes through the fiber. A graded-index fiber, therefore, is one with varying densities. Density is highest at the center of the core and decreases gradually to its lowest at the edge. Figure bellow shows the impact of this variable density on the propagation of light beams. 20  Propagation Mode (Cont.) Single-Mode: uses step-index fiber (lower constant density) and a highly focused source of light that limits beams to a small range of angles, all close to the horizontal. The single mode fiber itself is manufactured with a much smaller diameter than that of multimode fiber, and with substantially lower density. The decrease in density results in a critical angle that is close enough to 90° to make the propagation of beams almost horizontal. In this case, propagation of different beams is almost identical, and delays are negligible. 21  Fiber Sizes Optical fibers are defined by the ratio of the diameter of their core to the diameter of their cladding, both expressed in micrometers (µm). Table 4.3 Fiber Types 22  Cable Composition Figure 4.14 shows the composition of a typical fiber-optic cable. The outer jacket is made of either PVC or Teflon. Inside the jacket are Kevlar strands to strengthen the cable. Kevlar is a strong material used in the fabrication of bulletproof vests. Below the Kevlar is another plastic coating to cushion the fiber. The fiber is at the center of the cable, and it consists of cladding and core. Figure 4.14 Fiber Composition 23 Advantages & disadvantages of Fiber optic Cables 24 Thank you for your Attention!!! Any Questions? 25