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Note for Data Communication and Computer Network - DCCN By Waseem Abbas

  • Data Communication and Computer Network - DCCN
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• Performance statistics and reporting mechanism. Increased Accountability and Transparency through escalation policies, work orders and maintenance of secure activity logs. Optical Fiber: Fiber is the newest form of transmission cable technology. Instead of transferring data over copper wires, these cables contain optical fibers that transmit data via light, rather than pulses of electricity. Each optical fiber is individually coated with plastic layers and contained in a protective tube, making it extremely resistant to external interference. The result is a very reliable and super fast connection that has 26,000X more transmission capacity than twisted-pair cables, but that also comes with a much higher cost. Types of optical fiber cable Optical fiber cable is available in three forms which are 1. Slotted core cable 2. Loose tube cable 3. Loose tube slotted core cable Application of the optical fiber cables • • • • • • Public and private telecommunication lines Computer network (LAN, WAN ) Television distribution network (CATV) Military network Control, remote control & signalizing network Video supervision lines Advantages of the optical fiber cables: Optical fiber cables are not affected by any interference originated from energy transmission lines. Radio waves and cross talk between the fibers does not exist. No special protection is necessary. 1. Greater capacity: The potential bandwidth, and hence data rate, of optical fiber is immense; data rates of hundreds of Gbps over tens of kilometers have been demonstrated. Compare this to the practical maximum of hundreds of Mbps over about 1 km for coaxial cable and just a few Mbps over 1 km or up to 100 Mbps to 10 Gbps over a few tens of meters for twisted pair. 2. Smaller size and lighter weight: 2

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Optical fibers are considerably thinner than coaxial cable or bundled twisted-pair cable at least an order of magnitude thinner for comparable information transmission capacity. For cramped conduits in buildings and underground along public rights-of-way, the advantage of small size is considerable. The corresponding reduction in weight reduces structural support requirements. 3. Lower attenuation: Attenuation is significantly lower for optical fiber than for coaxial cable or twisted pair (Figure 4.3c) and is constant over a wide range. 4. Electromagnetic isolation: Optical fiber systems are not affected by external electromagnetic fields. Thus the system is not vulnerable to interference, impulse noise, or crosstalk. By the same token, fibers do not radiate energy, so there is little interference with other equipment and there is a high degree of security from eavesdropping. In addition, fiber is inherently difficult to tap. 5. Greater repeater spacing: Fewer repeaters mean lower cost and fewer sources of error. The performance of optical fiber systems from this point of view has been steadily improving. Repeater spacing in the tens of kilometers for optical fiber is common, and repeater spacing’s of hundreds of kilometers have been demonstrated. Coaxial and twisted-pair systems generally have repeaters every few kilometers Optical fiber cable used in Pakistan 1. 2. 3. 4. Olex cable Fujikura cable Siemen cable LT Engineering cable Optical Distribution Frame (ODF): Driven by requirements for high-speed data rate, the deployment of fiber optic has been growing. As the growth of installed fiber optic, the management of optical transmission networks becomes more difficult. Many factors should be considered during fiber optic cabling like; • flexibility • Future • Viability • Cost of the deployment • Management To handle large amounts of fiber optic with lower cost and higher flexibility various optical distribution frames (ODF) are being widely used to connector and schedule optical fiber. An optical distribution frame (ODF) is a frame used to provide cable interconnections between communication facilities which can integrate fiber splicing, fiber termination, fiber optic adapters & connectors and cable connections together in a single unit. It can also work as a protective device to protect fiber optic connections from damage. 3

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Splicing of Optical Fiber: There are two methods of fiber splicing. 1. Fusion Splicing: Preparing the fiber - Strip the protective coatings, jackets, tubes, strength members, etc. leaving only the bare fiber showing. The main concern here is cleanliness. Step 2: Cleave the fiber - Using a good fiber cleaver here is essential to a successful fusion splice. The cleaved end must be mirror-smooth and perpendicular to the fiber axis to obtain a proper splice. 2. Mechanical Splicing: Mechanical splicing is an optical junction where the fibers are precisely aligned and held in place by a self-contained assembly, not a permanent bond. This method aligns the two fiber ends to a common centerline, aligning their cores so the light can pass from one fiber to another. Step 1: Preparing the fiber - Strip the protective coatings, jackets, tubes, strength members, etc. leaving only the bare fiber showing. The main concern here is cleanliness. Step 2: Cleave the fiber - The process is identical to the cleaving for fusion splicing but the cleave precision is not as critical. Ring Topology: Ring topology, also known as Ring network, is a type of network topology where each node is exactly connected to two other nodes, forward and backward, thus forming a single continuous path for signal transmission. There are two types of the Ring Topology based on the data flow: • Unidirectional and, • Bidirectional 4

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A Unidirectional ring topology handles data traffic in either clockwise or anticlockwise direction. This data network, thus, can also be called as a half-duplex network. A Unidirectional ring topology is thus easy to maintain compared to the bidirectional ring topology. Ex: SONET network, SDH network etc. A SONET/ SDH is a standardized network protocol that transfers data streams over optical fibers. Whereas, a bidirectional ring topology handles data traffic in both the direction and can be a full-duplex network. Advantages of Ring topology: • • • • Reduced chances of data collision as each node release a data packet after receiving the token. Token passing makes ring topology perform better than bus topology under heavy traffic No need of server to control connectivity among the nodes Equal access to the resources 5

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