Bài giảng Mạng máy tính căn bản: Chương 7 - Phan Vĩnh Thuần

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Bài giảng Mạng máy tính căn bản - Chương 7: Các công nghệ Ethernet (Ethernet technologies) nhằm giúp người học mô tả sự khác biệt và tương đồng trong 10BASE5, 10Base2, và 10BASE-T Ethernet, xác định mã hóa Manchester, liệt kê các yếu tố ảnh hưởng Ethernet,...

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Nội dung Text: Bài giảng Mạng máy tính căn bản: Chương 7 - Phan Vĩnh Thuần

CHƯƠNG 7 CÁC CÔNG NGHỆ ETHERNET ETHERNET TECHNOLOGIES Phan Vĩnh Thuần Computer Network 1
Overview • Ethernet has been the most successful LAN technology largely because of its simplicity of implementation compared to other technologies. Ethernet has also been successful because it has been a flexible technology that has evolved to meet changing needs and media capabilities. This module introduces the specifics of the most important varieties of Ethernet. The goal is not to convey all the facts about each type of Ethernet, but rather to develop a sense of what is common to all forms of Ethernet. Phan Vĩnh Thuần Computer Network 2
• Changes in Ethernet have resulted in major improvements over the 10-Mbps Ethernet of the early 1980s. The 10-Mbps Ethernet standard remained virtually unchanged until 1995 when IEEE announced a standard for a 100 Mbps Fast Ethernet. In recent years, an even more rapid growth in media speed has moved the transition from Fast Ethernet to Gigabit Ethernet. The standards for Gigabit Ethernet emerged in only three years. An even faster Ethernet version, 10 Gigabit Ethernet, is now widely available and still faster versions are being developed. Phan Vĩnh Thuần Computer Network 3
• In these faster versions of Ethernet, MAC addressing, CSMA/CD, and the frame format have not been changed from earlier versions of Ethernet. However, other aspects of the MAC sublayer, physical layer, and medium have changed. Copper- based network interface card (NICs) capable of 10/100/1000 operation are now common. Gigabit switch and router ports are becoming the standard for wiring closets. Optical fiber to support Gigabit Ethernet is considered a standard for backbone cabling in most new installations. Phan Vĩnh Thuần Computer Network 4
• Students completing this module should be able to: – Describe the differences and similarities among 10BASE5, 10BASE2, and 10BASE-T Ethernet. – Define Manchester encoding. – List the factors affecting Ethernet timing limits. – List 10BASE-T wiring parameters. – Describe the key characteristics and varieties of 100-Mbps Ethernet Phan Vĩnh Thuần Computer Network 5
– Describe the evolution of Ethernet. – Explain the MAC methods, frame formats, and transmission process of Gigabit Ethernet. – Describe the uses of specific media and encoding with Gigabit Ethernet. – Identify the pinouts and wiring typical to the various implementations of Gigabit Ethernet. – Describe the similarities and differences between Gigabit and 10 Gigabit Ethernet. – Describe the basic architectural considerations of Gigabit and 10 Gigabit Ethernet. Phan Vĩnh Thuần Computer Network 6
7.1.10-Mbps and 100-Mbps Ethernet 7.1.1. 10Mbps Ethernet • 10BASE5, 10BASE2, and 10BASE-T Ethernet are considered Legacy Ethernet. The four common features of Legacy Ethernet are timing parameters, frame format, transmission process, and a basic design rule Phan Vĩnh Thuần Computer Network 7
Phan Vĩnh Thuần Computer Network 8
• 10BASE5, 10BASE2, and 10BASE-T all share the same timing parameters, as shown in the figure (1 bit time at 10 Mbps = 100 nsec = 0.1 µsec = 1 ten-millionth of a second.) Phan Vĩnh Thuần Computer Network 9
• 10BASE5, 10BASE2, and 10BASE-T also have a common frame format. Phan Vĩnh Thuần Computer Network 10
Phan Vĩnh Thuần Computer Network 11
• The Legacy Ethernet transmission process is identical until the lower part of the OSI physical layer. The Layer 2 frame data is converted from hex to binary. As the frame passes from the MAC sublayer to the physical layer, further processes occur prior to the bits being placed from the physical layer onto the medium. One important process is the signal quality error (SQE) signal. SQE is always used in half-duplex. SQE can be used in full-duplex operation but is not required. Phan Vĩnh Thuần Computer Network 12
• SQE is active: – Within 4 to 8 microseconds following a normal transmission to indicate that the outbound frame was successfully transmitted – Whenever there is a collision on the medium – Whenever there is an improper signal on the medium. Improper signals might include jabber, or reflections that result from a cable short. – Whenever a transmission has been interrupted Phan Vĩnh Thuần Computer Network 13
• All 10 Mbps forms of Ethernet take octets received from the MAC sublayer and perform a process called line encoding. Line encoding describes how the bits are actually signaled on the wire. The simplest encodings have undesirable timing and electrical characteristics. So line codes have been designed to have desirable transmission properties. This form of encoding used in 10 Mbps systems is called “Manchester.” Phan Vĩnh Thuần Computer Network 14
• Manchester encoding relies on the direction of the edge transition in the middle of the timing window to determine the binary value for that bit period. The top waveform has a falling edge, so it is interpreted as a binary 0. The second waveform shows a rising edge, which is interpreted as a binary 1. In the third waveform, there is an alternating binary sequence. With alternating binary data, there is no need to return to the previous voltage level. Phan Vĩnh Thuần Computer Network 15
• As can be seen from the third and fourth wave forms in the graphic, the binary bit values are indicated by the direction of change during any given bit period. The waveform voltage levels at the beginning or end of any bit period are not factors when determining binary values. Phan Vĩnh Thuần Computer Network 16
Phan Vĩnh Thuần Computer Network 17
• Legacy Ethernet has common architectural features. Networks usually contain multiple types of media. The standard ensures that interoperability is maintained. The overall architectural design is of the utmost importance when implementing a mixed- media network. It becomes easier to violate maximum delay limits as the network grows. Phan Vĩnh Thuần Computer Network 18
• The timing limits are based on parameters such as: – Cable length and its propagation delay – Delay of repeaters – Delay of transceivers – Interframe gap shrinkage – Delays within the station Phan Vĩnh Thuần Computer Network 19
• 10-Mbps Ethernet operates within the timing limits offered by a series of not more than five segments separated by no more than four repeaters. This is known as the 5- 4-3 rule. No more than four repeaters may be connected in series between any two distant stations. There can also be no more than three populated segments between any two distant stations. Phan Vĩnh Thuần Computer Network 20