思科第一册第九章（CISCO, Volume , ninth）.doc

思科第一册第九章（CISCO, Volume 1, ninth）The difference between the standard Ethernet, fast Ethernet, Gigabit Ethernet and Gigabit Ethernet is usually called Ethernet physical layer, PHY.Comply with the IEEE standard 802.3 ethernet. Now through the cable and twisted pair cable operation defines four data rate:10 - Mbps 10Base-T Ethernet100 - Mbps Fast Ethernet1000 - Gigabit Ethernet Mbps10 - Gigabit Ethernet GbpsAlthough these different data rate will achieve many different Ethernet, but here only introduce more commonly used Ethernet implementation method. The picture shows some features of Ethernet PHY.This section will discuss the Ethernet physical layer operation of the first part, starting from 10Base-T, and then discuss the variant 10 Gbps.10 Mbps Ethernet mainly include:The use of coaxial cable diameter 10BASE5The use of coaxial thinnet 10BASE2The use of 3 kinds of /5 unshielded twisted pair cable 10BASE-TEarly 10BASE5 and 10BASE2 using Ethernet Coaxial Cable in the physical bus. The method is no longer used nowadays, the new 802.3 standard will no longer support them.10 - 10BASE-T Mbps Ethernet10BASE-T uses Manchester encoding, through two UTP cable transmission. The early use of 10BASE-T 3 cable. Cable but now generally use 5 or higher specification.10 Mbps Ethernet is considered traditional Ethernet, using physical star topology. Ethernet link length of 10BASE-T do not need a hub or repeater within 100 meters.Two of the cable four line with 10BASE-T, and in each terminal with 8 pin RJ-45 connector terminal. Connected to pins 1 and 2 on the line for transmitting, connected to pins 3 and 6 on the line for receiving. The picture shows for 10BASE-T Ethernet RJ45 pin.The new LAN generally do not choose 10BASE-T. But there are still many Ethernet 10BASE-T. The hub in the 10BASE-T network to replace the switch, greatly increase the throughput of the network, prolong the life of traditional ethernet. Connect to the 10BASE-T link switch supports half duplex or full duplex operation.100 - Mbps Fast EthernetIn the late 1990s established several new 802.3 Standard Specification for medium with 100 Mbps through the Ethernet data transmission speed. These standards use different encoding requirements to achieve higher data rate.100 Mbps Ethernet also known as fast Ethernet, can be implemented using twisted pair copper or fiber media. The most common are 100 Mbps ethernet:The use of 5 or more high standard UTP cable 100BASE-TXUse the 100BASE-FX cableBecause of the noise generated by the high frequency fast Ethernet signal is easier to use, so 100-Mbps Ethernet uses two independent encoding steps to enhance the signal integrity.100BASE-TX100BASE-TX support by sending two of 5 or two strands of UTP copper cable. 100BASE-TX and 10BASE-T, also use two line pairs and UTP pins. But 100BASE-TX requires the use of 5 or higher specification UTP. 100BASE-T Ethernet using 4B/5B encoding.Like 10BASE-TX, 100Base-TX is also in the physical star topology. As the physical star topology shown in the example in figure. But unlike 10BASE-T, 100BASE-TX network in the star center instead of using the switch hub. Almost in the 100BASE-TX technology has become the mainstream technology at the same time, LAN switches are widely used. Common development makes them naturally into the design of 100BASE-TX network.100BASE-FXCommunication steps using 100BASE-FX standard with the same 100BASE-TX, but it is not the medium through the optical fiber to transmit UTP copper.Although these two media encoding and decoding and clock recovery steps are the same, but the signal is send different - copper electrical pulses, and the cable is light pulse. 100BASE-FX using low cost fiber optic connector (usually called duplex SC connector).The fiber is a point-to-point connection, which is used to connect two devices. These connections may be between two computers or two switches, may also be between a computer and a switch in a.1000 - Gigabit Ethernet MbpsThe development of Gigabit Ethernet standard produced UTP copper, and single-mode fiber optic cable multimode cable specifications. In Gigabit Ethernet, the transmission of the same data bit time is a fraction of a 100 Mbps 10 network and Mbps network. Due to shorter transmission time, a bit more prone to clutter to signal, so the timing is very important. The performance depends on the network adapter or interface to change the level of speed, and the reliability of the receiving network card or interface 100 meters outside the detection voltage change.In these faster Ethernet, data encoding and decoding is more complex. Gigabit Ethernet using two separate encoding steps. When the code is used to represent the binary bit stream, data transmission efficiency is higher. For encoding data synchronization and improve the bandwidth utilization efficiency and improving the signal-to-noise ratio characteristics.1000BASE-T Ethernet1000BASE-T Ethernet uses all four to 5 or more high standard UTP cable provides full duplex transmission. Gigabit Ethernet using copper wire can make each line of speed increased from 100 Mbps to 125 Mbps, four of the total line speed will rise to 500 Mbps. Because each line of the signal is full duplex, so 500 Mbps doubled again and up to 1000 Mbps.The data throughput of 1000BASE-T using 4D-PAM5 encoding to obtain 1 Gbps lines. This encoding scheme allows the four line to send signals. It will be 8 bytes of data into the four code symbol (4D), as the 5 level pulse amplitude modulation on the medium (PAM5) signal sent at the same time, each line to send a. This means that each symbol corresponds to two bits of data. Because the information at the same time by two path transmission, so the circuit must be in the transmission frame and then re segmentation, combined in the receiver. The circuit used for 1000BASE-T Ethernet is shown in the figure diagram.1000BASE-T can also double direction of sending and receiving data on the same line. The communication flow will have a permanent conflict on the line. These conflicts will lead to complex voltage mode. Hybrid circuit signal detection using advanced technology, such as echo cancellation, first layer forward error correction (FEC) level and prudent choice etc. Using these techniques, the system can achieve a throughput of 1000 trillion.In order to help the physical layer synchronization, frame delimiter and frame delimiter package for each frame. Cycle timing by frame gap during each line of successive IDLE symbols transmitted on maintenance flow.Most of the digital signal is usually only a few level is not continuous, but different 1000BASE-T, it uses many level. Even during idle periods, the cable also has nine levels; during data transmission, cable can find 17 level. A large number of state and miscellaneous letter, the signal line looks more like an analog signal, instead of digital signal. As the simulation system, 1000BASE-T is prone to bring clutter to signal cable andterminal problems.The use of optical fiber 1000BASE-SX and 1000BASE-LX EthernetCompared with UTP, 1000BASE-SX and 1000BASE-LX - fiber Gigabit Ethernet has the following advantages: no miscellaneous letters, small volume, and without relay distance, high bandwidth.All the 1000BASE-SX and 1000BASE-LX versions are supported by two cables for full duplex binary transmission at the speed of 1250 Mbps. 8B/10B encoding scheme based on encoding. This encoding overhead, so the data transmission speed is 1000 Mbps.Before sending each frame of data will be encapsulated in the physical layer, link synchronization through continuous flow in the frame gap during sending IDLE code group to maintain.The main difference between the 1000BASE-SX and the 1000BASE-LX version is medium, optical fiber link connector and the wavelength of the optical signal, as shown in figure.IEEE 802.3ae standard has been adapted into the 10 - Gbps, sent by cable for full duplex. The original Ethernet 802.3ae standard and 802.3 standard is very similar. Gigabit Ethernet (10GbE) in the development, not only for LAN, but for WAN and MAN.The other second Ethernet frame format and is compatible with the previous standard specifications, so 10GbE can for those with existing network infrastructure interoperability of individual networks provide higher bandwidth.10Gbps can be compared with other variants of Ethernet proposed in the following aspects:The same frame format, support the interactive operation between the traditional fast and Gigabit and 10 Gigabit Ethernet, without re framing or protocol conversion.The bit time is 0.1 ns, all the other time is proportionally change.Because only the use of full duplex optical fiber connection, so no media competition and CSMA/CD.OSI first and second layers of IEEE 802.3 basic sub layer is preserved, just a little modification to support the 40 km fiber link and optical fiber technology and other interactive operation.End to end Ethernet 10Gbps Ethernet - flexible, efficient, reliable and low cost.The future of Ethernet speedsGigabit Ethernet has been widely used, 10Gigabit products also increased, but IEEE and Gigabit Ethernet Alliance still continue to study the 40, 100 or 160-Gbps standard. Factors of technology adoption depends on many aspects, including speed, mature technology and standard market application speed and the launch of new product cost.In the previous chapter, we have learned how to use the traditional Ethernet shared medium and contention based medium access control. The use of traditional Ethernet hub to connect the nodes in LAN network. The hub does not perform communication filtering of any type, but will be forwarded to all the bits of each device is connected to the. This will make the shared medium bandwidth of all devices in a LAN.In addition, the traditional Ethernet often lead to a conflict in LAN. Because of these performance problems, using the hub Ethernet LAN in the network are very rare, generally only a small LAN or low bandwidth requirements of LAN is still in use.Along with the network equipment sharing medium will expand and cause serious problems. The list of part of the problem, this paper will discuss.ScalabilityIn the hub network, equipment can share the limited bandwidth. With a device of shared media continue to join the ranks of the average bandwidth of each device available in gradually reduced. Therefore, with the increase in the number of media equipment, performance gradually decreased.delayedThe network delay is a medium to all destinations required time for the signal. In order to avoid conflict, each node in the network hub must wait for the chance to send. When the distance between two nodes is extended, the delay will increase. The signal in the medium due to delay and delay through increasing the signal processing hubs and repeaters, will also affect the delay. In addition, medium extension, or network connection hubs and repeaters increased, will increase the delay. The longer the delay, the node does not receive the probability of the initial signal is, the more conflict in the network.Network faultBecause the traditional network shared medium, so any equipment in the network has the potential to cause problems with other equipment. If the formation of harmful flow of any device connected to the hub, it will hinder the communication of all equipment in the medium. This card may be harmful flow on speed or full duplex is not set correctly by.conflictAccording to CSMA/CD, as long as there is a communication network,The node cannot send packets. If two nodes and send data packets, will conflict and lead to packet loss, then the two nodes are sending jam signal, wait for a random time after re send the packet. The package may interfere with each other in the network from two or more nodes in the data, any part of it will be regarded as a collision domain. The same network has more nodes of the network will form a larger conflict domain, there are usually more traffic. With the increase of network traffic will increase the probability of conflict.Therefore, the switch came into being, to replace some of the traditional Ethernet based on competition.In the past few years, switch quickly become a fundamental part of most of the network. Switch LAN can be divided into several separate collision domains, each port represents a separate collision domain, node connections for the port to provide complete medium bandwidth. Because each node collision domain reduces, the average bandwidth of each node available increased, the conflict is also reduced.LAN can use a central switch connected to the hub still node provides connectivity, all nodes can also be directly connected to the switch. The topology shown in figure.The LAN switch is connected to the hub port, will share the bandwidth, which may cause conflicts in a shared environment in a hub. But the switch will be isolated segment, the conflict between the limited communication hub port.Direct connectionWhen all nodes are directly connected to the switch LAN, the throughput of the network greatly increased. This increase mainly due to three reasons:Each port has a dedicated bandwidthThere is no conflict between the environmentFull duplex operationThese physical star topology is essentially a point-to-point link.Click the performance factor.Dedicated bandwidthEach node has medium bandwidth available for use in all connected nodes and switches in. The transmitted signal will copy and hub to all other ports, so the traditional Ethernet hub will form a logical bus. This means that all nodes must share the bus bandwidth. The use of switches, each device can effectively establish a dedicated point-to-point connection in connection with the switch, do not have competition medium.For example, compare each of the two Mbps 100 LAN 10 nodes. In section A, 10 nodes connected to a hub, all nodes share the available bandwidth of 100 Mbps, the average bandwidth of each node is 10 Mbps. In section B, 10 nodes are connected to a switch, all 10 nodes can use all the bandwidth of 100 Mbps.Thus, even in such a small network bandwidth, the increase is also very impressive. When the number of nodes increases, two kinds of available bandwidth in Ethernet gap will form a world of difference.There is no conflict between the environmentSpecial point to point connection between switches and also eliminates the media competition between devices, the nodes with little or no conflict. In the use of traditional network hub, there are about 40% to 50% of the bandwidth for the conflict recovery of a medium-sized network; and in the exchange of Ethernet almost no conflict, no overhead bas