Chapter 3 LAN principles

Chapter 3 LAN principles
LAN technology mainly corresponds to the physical layer and data link layer of the OSI reference model, that is, the network interface layer of the TCP/IP model. The physical layer of a LAN specifies the physical and electrical properties, mechanical properties, and connection labels of devices, cables, and interfaces that provide services to the LAN. Common such standards include: For 10BASE5 coaxial coarse cable and transceiver (transceiver); For 10BASE2 coaxial fine cable and BNC connector; For 10BASE-T, 100BASE-TX and 1000BASE-T twisted pair and RJ-45 connector; optical fiber used for various Ethernet transmission; used for WLAN radio waves. IEEE divides the data link layer of a LAN into two sub-layers, LLC, and MAC. The LLC sub-layer above enables the data link layer to be hardware-independent, such as traffic control and error recovery. The lower MAC layer provides interfaces between the LLC and the physical layer. Different lan mac layers are different, and the LLC layer is the same. One of the main functions of the data link layer is to encapsulate and identify upper-layer data, which is implemented by the LLC sublayer in the LAN. 802.2 defines the LLC sub-layer, which is shared by the 802 series standard. Another major function of the data link layer is to adapt to a variety of transmission media and process channel occupation, site identification, and addressing issues on any specific media. In the LAN, this function is implemented by the MAC Sub-layer. Because MAC Sub-layers have different physical layer media, they are defined by multiple standards. For example, 802.3 defines the MAC Sub-layer of Ethernet, 802.4 defines the MAC Sub-layer of the general network of tokens, and 802.5 defines the MAC Sub-layer of the Ring Network. In addition, the MAC layer is responsible for verifying the integrity of inbound data frames. Common LAN technologies include Ethernet, Token Ring, and FDDI (Fiber Distributed Data Interface) the main difference between the Ethernet standard and the 802.3 standard is that the Ethernet standard only describes the bus LAN with a 50 ohm coaxial cable and a data transmission rate of 10 Mbps, the Ethernet standard includes all the content of the ISO data link layer and physical layer. The standard describes the data transmission rate from 1 Mbps ~ 10 Mbps all use the CSMA/CD Protocol LAN, and the standard only defines the MAC Sub-layer and the physical layer of the data link layer in the ISO Reference Model, while the LLC sub-layer of the data link layer is described. Ethernet Technology Basic Ethernet unicast and broadcast Ethernet throttling 802.3 also specifies the method of using PAUSE for traffic control in full duplex environments. In a full-duplex environment, when the receiver cannot process data, it can send a 64-byte PAUSE frame to the reserved multicast address 0180. c200.0001 to notify the sender to suspend sending. Back pressure (back pressure) is used for traffic control over half-duplex Ethernet. When the receiver is too late to process data, it can send a voltage signal to the line, so that the sender can temporarily escape, so that the receiver can process the data accumulated in its buffer. Modern Ethernet Technology Optical fiber for data transmission has the following advantages: high bandwidth: Long Distance: High Reliability: good security: Wide Band: multi-mode fiber uses coarse fiber cores, light Emitting Diode is used as the light source. The incident light is transmitted in the optical fiber using the principle of total reflection. Due to the scattered angle of incident light, LAN technology mainly corresponds to the physical layer and data link layer of the OSI reference model, that is, the network interface layer of the TCP/IP model. The physical layer of a LAN specifies the physical and electrical properties, mechanical properties, and connection standards of devices, cables, and interfaces that provide services to the LAN. Common such standards include: For 10BASE5 coaxial coarse cable and transceiver (transceiver); For 10BASE2 coaxial fine cable and BNC connector; For 10BASE-T, 100BASE-TX and 1000BASE-T twisted pair and RJ-45 connector; optical fiber used for various Ethernet transmission; used for WLAN radio waves. IEEE divides the data link layer of a LAN into two sub-layers, LLC, and MAC. The LLC sub-layer above implements hardware-independent functions of the data link layer, such as traffic control and error recovery. The lower MAC layer provides interfaces between the LLC and the physical layer. Different lan mac layers are different, and the LLC layer is the same. One of the main functions of the data link layer is to encapsulate and identify upper-layer data, which is implemented by the LLC sublayer in the LAN. 802.2 defines the LLC sub-layer, which is shared by the 802 series standard. Another major function of the data link layer is to adapt to a variety of transmission media and process channel occupation, site identification, and addressing issues on any specific media. In the LAN, this function is implemented by the MAC Sub-layer. Because MAC Sub-layers have different physical layer media, they are defined by multiple standards. For example, 802.3 defines the MAC Sub-layer of Ethernet, 802.4 defines the MAC Sub-layer of the general network of tokens, and 802.5 defines the MAC Sub-layer of the Ring Network. In addition, the MAC layer is responsible for verifying the integrity of inbound data frames. Common LAN technologies include Ethernet, Token Ring, and FDDI (Fiber Distributed Data Interface) the main difference between the Ethernet standard and the 802.3 standard is that the Ethernet standard only describes the bus LAN with a 50 ohm coaxial cable and a data transmission rate of 10 Mbps, the Ethernet standard includes all the content of the ISO data link layer and physical layer. The standard describes the data transmission rate from 1 Mbps ~ 10 Mbps all use the CSMA/CD Protocol LAN, and the standard only defines the MAC Sub-layer and the physical layer of the data link layer in the ISO Reference Model, while the LLC sub-layer of the data link layer is described. Ethernet Technology Basic Ethernet unicast and broadcast Ethernet throttling 802.3 also specifies the method of using PAUSE for traffic control in full duplex environments. In a full-duplex environment, when the receiver cannot process data, it can send a 64-byte PAUSE frame to the reserved multicast address 0180. c200.0001 to notify the sender to suspend sending. Back pressure (back pressure) is used for traffic control over half-duplex Ethernet. When the receiver is too late to process data, it can send a voltage signal to the line, so that the sender can temporarily escape, so that the receiver can process the data accumulated in its buffer. Modern Ethernet Technology Optical fiber for data transmission has the following advantages: high bandwidth: Long Distance: High Reliability: good security: Wide Band: multi-mode fiber uses coarse fiber cores, light Emitting Diode is used as the light source. The incident light is transmitted in the optical fiber using the principle of total reflection. Due to the scattered angle of the incident light, the pulse peaks and valleys after long-distance transmission will gradually blur, resulting in distortion. Therefore, it is suitable for close distance, usually within kilometers. However, the optical fiber and light source have low manufacturing requirements and low costs. The diameter of a single-mode fiber core is usually micron, which is equal to the wavelength of the optical wave. At this time, the light can forward directly along the optical fiber without multiple total reflection. Therefore, the distortion is small, the transmission distance is tens of thousands of meters. However, a single-mode optical fiber requires a single-wavelength laser to be sent by the light source, and the manufacturing process of the optical fiber is demanding, so the cost is also relatively high. Common optical fiber connectors: Fast Ethernet and Gigabit Ethernet