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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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Transmission: Transmission (abbreviation: Tx) is the process of sending and propagating an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless. Transmission Technology Transmission technologies and schemes typically refer to physical layer protocol duties such as modulation, demodulation, line coding, equalization, error control, bit synchronization and multiplexing, but the term may also involve higher-layer protocol duties, for example, digitizing an analog message signal, and source coding (compression). Transmission of a digital message, or of a digitized analog signal, is known as data transmission or digital communication. One transmission is the sending of a signal with limited duration, for example a block or packet of data, a phone call, or an email. There are three types of medias/carrier are used in Pakistan by PTCL. • Copper • WLL (Wireless Local Loop) • Optical Fiber Using Copper as media of transferring of data, there is a local exchange (LE) the setup of LE is installed on ground floor and the data is transferred from MDF (Main Distribution Frame) from the front side we access via cable while back side is switching box. Benefits: • Proactive identification and resolution faults of through Real-time Network Monitoring & status visibility. • Increase network availability through Enhanced Quality of Service and centralized 1

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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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