Bài giảng Mạng máy tính căn bản: Chương 3 - Phan Vĩnh Thuần

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Bài giảng Mạng máy tính căn bản - Chương 3: Môi trường truyền dẫn cho networking giúp người học mô tả chi tiết kỹ thuật và màn trình diễn của các loại cáp, mô tả cáp đồng trục, ưu điểm và nhược điểm của các loại cáp, mô tả được bảo vệ xoắn đôi (STP) truyền hình cáp và ứng dụng của nó,...

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Nội dung Text: Bài giảng Mạng máy tính căn bản: Chương 3 - Phan Vĩnh Thuần

Chương 3: MÔI TRƯỜNG TRUYỀN DẪN CHO NETWORKING Overview • Copper cable is used in almost every LAN. Many different types of copper cable are available, with each type having advantages and disadvantages. Proper selection of cabling is key to efficient network operation. Phan Vĩnh Thuần Computer Network 1
• Optical fiber is the most frequently used medium for the longer, high bandwidth, point-to- point transmissions required on LAN backbones and on WANs. Using optical media, light is used to transmit data through thin glass or plastic fiber. Electrical signals cause a fiber- optic transmitter to generate the light signals sent down the fiber. The receiving host receives the light signals and converts them to electrical signals at the far end of the fiber. However, there is no electricity in the fiber-optic cable itself. In fact, the glass used in fiber-optic cable is a very good electrical insulator. Phan Vĩnh Thuần Computer Network 2
• Physical connectivity allowed an increase in productivity by allowing the sharing of printers, servers, and software. Traditional networked systems require that the workstation remains stationary permitting moves only within the limits of the media and office area. • The introduction of wireless technology removes these restraints and brings true portability to the computing world. Currently, wireless technology does not provide the high- speed transfers, security, or uptime reliability of cabled networks. However, flexibility of wireless has justified the trade off. Phan Vĩnh Thuần Computer Network 3
• Administrators often consider wireless when installing a new network or when upgrading an existing network. A simple wireless network could be working just a few minutes after the workstations are turned on. Connectivity to the Internet is provided through a wired connection, router, cable or DSL modem and a wireless access point that acts as a hub for the wireless nodes. In a residential or small office environment these devices may be combined into a single unit Phan Vĩnh Thuần Computer Network 4
• Students completing this module should be able to: – Describe the specifications and performances of different types of cable. – Describe coaxial cable and its advantages and disadvantages over other types of cable. – Describe shielded twisted-pair (STP) cable and its uses. – Describe unshielded twisted-pair cable (UTP) and its uses. Phan Vĩnh Thuần Computer Network 5
– Discuss the characteristics of straight- through, crossover, and rollover cables and where each is used. – Explain the basics of fiber-optic cable. – Describe how fibers can guide light for long distances. – Describe multimode and single-mode fiber. – Describe the type of connectors and equipment used with fiber-optic cable. Phan Vĩnh Thuần Computer Network 6
3.1. Đường truyền cáp đồng 3.1.1. Các đặc tả cáp Cables have different specifications and expectations pertaining to performance: Phan Vĩnh Thuần Computer Network 7
• What speeds for data transmission can be achieved using a particular type of cable? The speed of bit transmission through the cable is extremely important. The speed of transmission is affected by the kind of conduit used. • What kind of transmission is being considered? Will the transmissions be digital or will they be analog-based? Digital or baseband transmission and analog-based or broadband transmission are the two choices. Phan Vĩnh Thuần Computer Network 8
• How far can a signal travel through a particular type of cable before attenuation of that signal becomes a concern? In other words, will the signal become so degraded that the recipient device might not be able to accurately receive and interpret the signal by the time the signal reaches that device? The distance the signal travels through the cable directly affects attenuation of the signal. Degradation of the signal is directly related to the distance the signal travels and the type of cable used. Phan Vĩnh Thuần Computer Network 9
• Some examples of Ethernet specifications which relate to cable type include: – 10BASE-T – 10BASE5 – 10BASE2 • 10BASE-T refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The T stands for twisted pair. Phan Vĩnh Thuần Computer Network 10
• 10BASE5 refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The 5 represents the capability of the cable to allow the signal to travel for approximately 500 meters before attenuation could disrupt the ability of the receiver to appropriately interpret the signal being received. 10BASE5 is often referred to as Thicknet. Phan Vĩnh Thuần Computer Network 11
• 10BASE2 refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The 2, in 10BASE2, represents the capability of the cable to allow the signal to travel for approximately 200 meters, before attenuation could disrupt the ability of the receiver to appropriately interpret the signal being received. 10BASE2 is often referred to as Thinnet Phan Vĩnh Thuần Computer Network 12
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3.1.2. Cáp đồng trục (Coaxial cable ) Phan Vĩnh Thuần Computer Network 14
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• Coaxial cable consists of a hollow outer cylindrical conductor that surrounds a single inner wire made of two conducting elements. One of these elements, located in the center of the cable, is a copper conductor. Surrounding the copper conductor is a layer of flexible insulation. Over this insulating material is 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 reduces the amount of outside electro-magnetic interference. Covering this shield is the cable jacket. Phan Vĩnh Thuần Computer Network 16
• For LANs, coaxial cable offers several advantages. It can be run longer distances than shielded twisted pair, STP, and unshielded twisted pair, UTP, cable without the need for repeaters. Repeaters regenerate the signals in a network so that they can cover greater distances. Coaxial cable is less expensive than fiber-optic cable, and the technology is well known. It has been used for many years for many types of data communication, including cable television. Phan Vĩnh Thuần Computer Network 17
• Coaxial cable comes in a variety of sizes. The largest diameter was specified for use as Ethernet backbone cable, because it has a greater transmission length and noise rejection characteristics. This type of coaxial cable is frequently referred to as thicknet. As its nickname suggests, this type of cable can be too rigid to install easily in some situations. Generally, the more difficult the network media is to install, the more expensive it is to install. Coaxial cable is more expensive to install than twisted-pair cable. Thicknet cable is almost never used anymore, except for special purpose installations. Phan Vĩnh Thuần Computer Network 18
• In the past, ‘thinnet’ coaxial cable with an outside diameter of only 0.35 cm was used in Ethernet networks. It was especially useful for cable installations that required the cable to make many twists and turns. Since thinnet was easier to install, it was also cheaper to install. This led some people to refer to it as cheapernet. Phan Vĩnh Thuần Computer Network 19
• The outer copper or metallic braid in coaxial cable comprises half the electric circuit and special care must be taken to ensure a solid electrical connection at both ends resulting in proper grounding. Poor shield connection is one of the biggest sources of connection problems in the installation of coaxial cable. Connection problems result in electrical noise that interferes with signal transmittal on the networking media. For this reason thinnet is no longer commonly used nor supported by latest standards (100 Mbps and higher) for Ethernet networks. Phan Vĩnh Thuần Computer Network 20