千兆位以太网PPT课件

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以太网基本知识ppt课件

绞线放在一个绝缘套管中便成了双绞线电缆，在局域网中常用双绞两根绝缘的铜导线按一定密度互相绞在一起，可降低信号干扰的程度，每一根导线在传输中辐射的电波也会被另一根线上发出的电波抵消。把一对或
多对双绞线放在一个绝缘套管中便成了双绞线电缆，在局域网中常用双绞线4对双绞线组成的。管中便成了双绞线电缆，在局域网中常用
n2比纤芯材料折射率n1小，即光纤导光的条件是n1＞n2。一次涂敷层是为了保护裸纤而在其表面涂上的聚氨基甲酸乙脂或硅酮树
脂层，厚度一般为 30～150μm。套层又称二次涂覆或被覆层，多采用聚乙烯塑料或聚丙烯塑料、尼龙等
材料。经过二次涂敷的裸光纤称为光纤芯G.651光纤:渐变多模光纤，工作波长为1.31μm和1.55μm，在1.31μm 处光纤有最小色散，而在1.55μm处光纤有最小损耗，主要用于计算机局域网或接入网。
以太网基本知识
1
以太网分类
按传输介质分
2
双绞线
双绞线双绞线由两根绝缘铜导线相互缠绕而成。两根绝缘的铜导线按一定密度互相绞在一起，可降低信号干扰的程度，每一根导线在传输中辐射的电波也会被另一根线上发出的电波抵消。把一对或多对双绞线放在一个绝缘套
管中便成了双绞线双电绞缆，线在由局域两网根中常绝用缘双绞铜线导4对线双相绞线互组缠成的绕。而由两成根绝。缘铜两导线根相绝互缠缘绕而的成。铜两根导绝线缘的按铜导一线定密度互相绞在一起，可降低信号干扰的程度，每一根导线在传输按一定密度互相绞在一起，可降低信号干扰的程度，每一根导线在传输中辐射的电波也会被另一根线上发出的电波抵消。把一对或多对
Auto MDI/MDIX--网线的交叉线和直连线自动转换，一般用途都不用管这个的;没有这个功能的时候，在使用的时候，就需要注意你所用的网线是交叉线，还是直线。

多媒体通信与网络PPT课件

基于策略的网络管理是指在一个管理策略集的控制下所实施的管理操作，为实现特性化、动态化管理提供了有效的手段。通常，作为一个策略管理系统应具有如下3种能力：
❖允许一个用户定义和修改策略规则的能力 ❖存储和检索策略规则的能力 ❖解释和执行策略规则的能力
3 多媒体通信网络环境
10.3 多媒体通信网络环境
IETF提出了两种QoS保证机制，一是由RSVP提供的保证型服务；二是在区分服务（DiffServ，DS）中定义的区分型服务。由于保证型服务具有面向连接的特性，并通过QoS 协商、接纳控制、保留带宽和实时调度等机制来实现。区分型服务具有无连接的特性，主要通过缓冲管理和优先级调度机制来实现，而无需进行QoS协商和保留带宽等控制。
IEEE 802.3ab定义的传输介质为5类UTP电缆，传输距离为100m，链路操作模式为半双工。
10.3.1 局域网络
3. 100VG-AnyLAN网络
100VG-AnyLAN是由100VG-AnyLAN论坛开发的一种 1 0 0 Mb/s 高速网络。 IEEE 已将 1 0 0 VGAnyLAN 确定为 IEEE 802.12 标准。 1 0 0 VGAnyLAN 的涵义是指在语音级的 UTP 电缆上进行 100Mb/s速率传输且支持IEEE 802.3和802.5两种帧格式（不是同时支持）。
现在主要有3种面向目标的管理手段：一是由 IETF 开发的，主要用于管理 TCP/IP；二是 OMG （Object Management Group）开发的，支持分布式的客户/服务器应用；三是ISO/原CCITT开发的，称为OSI系统管理，适用于广泛的资源管理。

以太网 ppt课件

t=
B B 检测到发生碰撞
IP 数据报 46 ~ 1500
数据
IP 层
4 FCS MAC 层
MAC 帧
物理层
以太网 V2 的 MAC 帧格式
当传输媒体的误码率为 1108 时， MAC 子层可使未检测到的差错小于 11014。
FCS 字段 4 字节
字节 6
6
目的地址源地址
2 类型
IP 数据报 46 ~ 1500
数据
IP 层
A 不接受
只有 D 接受 B 发送的数据
B
B向 D 发送数据
C 不接受
D 接受
E 不接受
以太网的广播方式发送
总线上的每一个工作的计算机都能检测到 B 发送的数据信号。
由于只有计算机 D 的地址与数据帧首部写入的地址一致，因此只有 D 才接收这个数据帧。
其他所有的计算机（A, C 和 E）都检测到不是发送给它们的数据帧，因此就丢弃这个数据帧而不能够收下来。
具有广播特性的总线上实现了一对一的通信。
为了通信的简便以太网采取了两种重要的措施
采用较为灵活的无连接的工作方式，即不必先建立连接就可以直接发送数据。
以太网对发送的数据帧不进行编号，也不要求对方发回确认。
这样做的理由是局域网信道的质量很好，因信道质量产生差错的概率是很小的。
以太网提供的服务
无连接: 在发送和接收适配器之间没有握手不可靠: 接收适配器不向发送适配器发送应答
或否定应答
传送给网络层的数据报流可能有丢包如果应用程序使用TCP，将能弥补丢包否则，应用程序将发现丢包
以太网的MAC协议：CSMA/CD
从总线拓扑到星型拓扑
直到20世纪90年代，总线拓扑流行后来，星型的集线器目前星型的交换机

计算机网络课件-04c.快速以太网和千兆以太网

802.3μ Fast Ethernet 802.3x 802.3z Full Duplex Gigabit Ethernet
帧间空隙前导字符
以太网帧
载波延伸填充字符 collision window
8B1Q4(8-bit 1-Quinary Quarter)和4D-PAM5(4-dimensional 5-level Pulse Amplitude Modulation)。
9/16
10/16
（２）帧突发(frame bursting) 一次传送多个短帧。第一帧具有载波延伸，后面的帧直接发出，不用加载波延伸。每一帧之间有一个小的间隔，并加入延伸位(extension bits)。其它站点识别帧间间隔中的延伸位后不会发送数据而引发冲突。
和快速以太网一样，802.3ab除了把传输速率提高1000Mbps，其它不变。由于1000Base-T的速度提高了100倍，故半双工的冲突域也要减少为1/100，即 25m。这个距离很难接受，怎么办？采用载波延伸技术。（１）载波延伸（carrier extension）如果帧长小于512B，通过附加填充字节，将其延长至512B，使得网络半径可以延长到200m。填充字节称为(extension bits) 。但是发送很多短帧浪费很大，也延长了发送时间，能否加速？采用帧突发。
2/16
快速以太网概述快速以太网
100Mbps 1995年，802.3u
1992年，IEEE召集802.3委员会希望加速802.3，当时提出两种方案：（1）重新设计，并加入新功能（如实时性）；（2）保持802.3，并加快它。第一种方案导致了标准802.12(100VG-AnyLAN)的出现，而第二种方案导致了802.3u (Fast Ethernet)的出现。 802.3u只是802.3的扩展，速度为100Mbps，称为快速以太网，1995年成为标准。 802.12加入了令牌机制，可以支持以太网和令牌环，但是没有取得商业上的成功。与802.3相比，快速以太网只是简单地把传输速率提高了100Mbps, 其它均保持不变：（1）格式保持不变，CSMA/CD协议不变，最短帧和最长帧的长度保持不变（2）段的最大距离仍然为100m，比2500m/10要短(2500m为10base5的最大距离)。（3）帧间空隙隔依然为96b，但是时间长度也变为原来的1/10，即0.96μs。

5千兆以太网组网课件

• IEEE draft Std. 802.3 ab 1000 BASE - T UTP #5 • IEEE Std. 802.3ac - 1998 Virtual Bridged LAN tagging
on 802.3 Networks • IEEE Std. 802.3ad : Link aggregation
D0 D1 D2 D3 D4 D5 D6 D7
Data Bit Current RD(-) Current RD(+)
EDCBA abcdei
abcdei
00000 00001 00010 00011 00100 00101 00110 00111
100111 011101 101101 110001 110101 101001 011001 111000
01000 01001 01010 01011 01100 01101 01110 01111
111001 100101 010101 110100 001101 101100 011100 010111
• 数据码组 ( 标为 D )：用于数据传输；
• 特定控制码组 ( 标为K )：控制序列传输 ( comma, ordered-sets, and so forth )；
码组名 Octet 值 HGF EDCBA abcdei fghj RD(-) abcdei fghj RD(+)
D0.0 00 000 00000 100111 0100
42 - 1496 Octets
VLAN - Tagged MAC 控制信息字段 ( 802.1Q ) Pre SFD DA SA L / T Data PAD FCS Ext
2 Byte 2 Byte

Gigabit Ethernet--千兆以太网技术

Gigabit EthernetVijay Moorthy,(moorthy@)Ethernet is the world's most pervasive networking technology. Gigabit Ethernet is the latest version of Ethernet. It offers 1000 Mbps ( 1 Gbps ) raw bandwidth, that is 100 times faster than the original Ethernet, yet is compatible with existing Ethernets, as it uses the same CSMA/CD and MAC protocols. When Gigabit Ethernet enters the market it will compete directly with ATM. This paper presents a survey of Gigabit Ethernet technology.Other Reports on Recent Advances in NetworkingBack to Raj Jain's Home PageTable of Contents1.Introduction1.1 History of Ethernet1.2 Gigabit Ethernet Alliance2.Physical Layer2.1 1000Base-X2.2 1000Base-TMAC Layer3.3.1 Carrier Extension3.2 Packet BurstingGMII ( Gigabit Media Independent Interface )4.4.1 PCS (Physical Coding Sublayer)4.2 PMA (Physical Medium Attachment)4.3 PMD (Physical Medium Dependent)Buffered Distributor5.6.Topologies6.1 Upgrading server-switch connections6.2 Upgrading switch-switch connections6.3 Upgrading a Fast Ethernet backbone6.4 Upgrading a Shared FDDI Backbone6.5 Upgrading High Performance Workstations7.ATM vs. Gigabit EthernetSummary8.9.Bibliography and Links1. IntroductionEthernet is the world's most pervasive networking technology , since the 1970's. It is estimated that in 1996, 82% of all networking equipment shipped was Ethernet. In 1995 ,the Fast Ethernet Standard was approved by the IEEE. Fast Ethernet provided 10 times higher bandwidth, and other new features such as full-duplex operation, and auto-negotiation. This established Ethernet as a scalable technology. Now, with the emerging Gigabit Ethernet standard, it is expected to scale even further.The Fast Ethernet standard was pushed by an industry consortium called the Fast Ethernet Alliance. A similar alliance, called the Gigabit Ethernet Alliance was formed by 11 companies in May 1996 , soon after IEEE announced the formation of the 802.3z Gigabit Ethernet Standards project. At last count, there were over 95 companies in the alliance from the networking, computer and integrated circuit industries.A draft 802.3z standard was issued by IEEE in July 1997. The last technical changes are expected to be resolved by September. The standard is expected to be adopted by March 1998.The new Gigabit Ethernet standards will be fully compatible with existing Ethernet installations. It will retain Carrier Sense Multiple Access/ Collision Detection (CSMA/CD) as the access method. It will support full-duplex as well as half duplex modes of operation. Initially, single-mode and multi mode fiber and short-haul coaxial cable will be supported. Standards for twisted pair cables are expected by 1999. The standard uses physical signalling technology used in Fiber Channel to support Gigabit rates over optical fibers.Initially, Gigabit Ethernet is expected to be deployed as a backbone in existing networks. It can be used to aggregate traffic between clients and "server farms", and for connecting Fast Ethernet switches. It can also be used for connecting workstations and servers for high - bandwidth applications such as medical imaging or CAD.1.1 History of EthernetToday, Ethernet is synonymous with the IEEE 802.3 standard for a "1-persistent CSMA/CD LAN". The 802.3 standard has an interesting history. The beginning, is generally considered to be the University of Hawaii ALOHA network. This system is the ancestor of all shared media networks. The original Ethernet, developed by Xerox was based on the ALOHA system. It was a 2.94 Mbps CSMA/CD system and was used to connect over 100 personal workstations on a 1 Km cable. It was so successful, that Xerox, DEC and Intel came up with a 10 Mbps standard. The IEEE 802.3 standard was based on the 10 Mbps Ethernet.CSMA/CD refers to the protocol used by stations sharing the medium, to arbitrate use of the medium. A sender has to "listen" to the medium. If no one else is transmitting, then the sender may transmit. If two senders start transmitting at the same time, then a collision is said to have occurred. Transmitting stations, therefore, have to listen to the medium for collisions while transmitting, and retransmit a packet after some time, if a collision occurs.The original 802.3 standard was published in 1985. Originally two types of coaxial cables were used called Thick Ethernet and Thin Ethernet. Later unshielded copper twisted pair (UTP) , used for telephones, was added.In 1980, when Xerox, DEC and Intel published the DIX Ethernet standard, 10 Mbps was a lot of bandwidth. Since then, as computing technology improved, network bandwidth requirements also increased. In 1995, IEEE adopted the 802.3u Fast Ethernet standard. Fast Ethernet is a 100 Mbps Ethernet standard. Fast Ethernet established Ethernet scalability. With Fast Ethernet came full-duplex Ethernet. Until, now, all Ethernets worked in half-duplex mode, that is, if there were only two station on a segment, both could not transmit simultaneously. With full-duplex operation, this was now possible.The next step in the evolution of Ethernet is Gigabit Ethernet. The standard is being developed by the IEEE 802.3z committee. 1.2 The Gigabit Ethernet Alliance (GEA)In March 1996, the IEEE 802.3 committee approved the 802.3z Gigabit Ethernet Standardization project. At that time as many as 54 companies expressed there intent to participate in the standardization project. The Gigabit Ethernet Alliance was formed in May 1996 by 11 companies : 3Com Corp., Bay Networks Inc., Cisco Systems Inc., Compaq Computer Corp., Granite Systems Inc., Intel Corporation, LSI Logic, Packet Engines Inc., Sun Microsystems Computer Company, UB Networks and VLSI Technology. The Alliance represents a multi-vendor effort to provide open and inter-operable Gigabit Ethernet products. The objectives of the alliance are :supporting extension of existing Ethernet and Fast Ethernet technology in response to demand for higher network qbandwidth.developing technical proposals for the inclusion in the standardqestablishment of inter-operability test procedures and processesqCurrently membership of the alliance is over 95 companies. This indicates that the emerging standard will be backed by the industry. The alliance is pushing for speedy approval of the standard. So far, the standardization is proceeding without any delays, and is expected to be approved by March 1998.Contents,2. Physical LayerThe Physical Layer of Gigabit Ethernet uses a mixture of proven technologies from the original Ethernet and the ANSI X3T11 Fibre Channel Specification. Gigabit Ethernet is finally expected to support 4 physical media types . These will be defined in 802.3z (1000Base-X) and 802.3ab (1000Base-T).2.1 1000Base-XThe 1000Base-X standard is based on the Fibre Channel Physical Layer. Fibre Channel is an interconnection technology for connecting workstations, supercomputers, storage devices and peripherals. Fibre Channel has a 4 layer architecture. The lowest two layers FC-0 (Interface and media) and FC-1 (Encode/Decode) are used in Gigabit Ethernet. Since Fibre Channel is a proven technology, re-using it will greatly reduce the Gigabit Ethernet standard development time.Three types of media are include in the 1000Base-X standard :1000Base-SX 850 nm laser on multi mode fiber.q1000Base-LX 1300 nm laser on single mode and multi mode fiber.q1000Base-CX Short haul copper "twinax" STP (Shielded Twisted Pair) cableqThe cabling distances to be supported are given in Table 1 :Table 1. Cabling Types and DistancesCable Type DistanceSingle-mode Fiber (9 micron)3000 m using 1300 nm laser (LX)Multi mode Fiber (62.5 micron)300 m using 850 nm laser (SX) 550 m using 1300 nm laser (LX)Multi mode Fiber (50 micron)550 m using 850nm laser (SX) 550 m using 1300 nm laser (LX)Short-haul Copper25 mSource : Sun Microsystems (Sun and Gigabit Ethernet White Paper)2.2 1000Base-T1000Base-T is a standard for Gigabit Ethernet over long haul copper UTP. The standards committee's goals are to allow up to 25-100 m over 4 pairs of Category 5 UTP. This standard is being developed by the 802.3ab task force and is expected to be completed by early 1999.Back to Table of Contents3. MAC LayerThe MAC Layer of Gigabit Ethernet uses the same CSMA/CD protocol as Ethernet. The maximum length of a cable segment used to connect stations is limited by the CSMA/CD protocol. If two stations simultaneously detect an idle medium and start transmitting, a collision occurs.Ethernet has a minimum frame size of 64 bytes. The reason for having a minimum size frame is to prevent a station from completing the transmission of a frame before the first bit has reached the far end of the cable, where it may collide with another frame. Therefore, the minimum time to detect a collision is the time it takes for the signal to propagate from one end of the cable to the other. This minimum time is called the Slot Time. ( A more useful metric is Slot Size, the number of bytes that can be transmitted in one Slot Time. In Ethernet, the slot size is 64 bytes, the minimum frame length.)The maximum cable length permitted in Ethernet is 2.5 km (with a maximum of four repeaters on any path). As the bit rate increases, the sender transmits the frame faster. As a result, if the same frames sizes and cable lengths are maintained, then a station may transmit a frame too fast and not detect a collision at the other end of the cable. So, one of two things has to be done : (i) Keep the maximum cable length and increase the slot time ( and therefore, minimum frame size) OR (ii) keep the slot time same and decrease the maximum cable length OR both. In Fast Ethernet, the maximum cable length is reduced to only 100 meters, leaving the minimum frame size and slot time intact.Gigabit Ethernet maintains the minimum and maximum frame sizes of Ethernet. Since, Gigabit Ethernet is 10 times faster than Fast Ethernet, to maintain the same slot size, maximum cable length would have to be reduced to about 10 meters, which is not very useful. Instead, Gigabit Ethernet uses a bigger slot size of 512 bytes. To maintain compatibility with Ethernet, the minimum frame size is not increased, but the "carrier event" is extended. If the frame is shorter than 512 bytes, then it is padded with extension symbols. These are special symbols, which cannot occur in the payload. This process is called Carrier Extension.3.1 Carrier ExtensionGigabit Ethernet should be inter-operable with existing 802.3 networks. Carrier Extension is a way of maintaining 802.3 minimum and maximum frame sizes with meaningful cabling distances.For carrier extended frames, the non-data extension symbols are included in the "collision window", that is, the entire extended frame is considered for collision and dropped. However, the Frame Check Sequence (FCS) is calculated only on the original (without extension symbols) frame. The extension symbols are removed before the FCS is checked by the receiver. So the LLC (Logical Link Control) layer is not even aware of the carrier extension. Fig. 1 shows the ethernet frame format when Carrier Extension is used.3.2 Packet BurstingCarrier Extension is a simple solution, but it wastes bandwidth. Up to 448 padding bytes may be sent for small packets. This results in low throughput. In fact, for a large number of small packets, the throughput is only marginally better than Fast Ethernet. Packet Bursting is an extension of Carrier Extension. Packet Bursting is "Carrier Extension plus a burst of packets". When a station has a number of packets to transmit, the first packet is padded to the slot time if necessary using carrier extension. Subsequent packets are transmitted back to back, with the minimum Inter-packet gap (IPG) until a burst timer (of 1500 bytes) expires. Packet Bursting substantially increases the throughput. Fig. 2. shows how Packet Bursting works.Back to Table of Contents4. GMII ( Gigabit Media Independent Interface )The various layers of the Gigabit Ethernet protocol architecture are shown in Fig. 3. The GMII is the interface between the MAC layer and the Physical layer. It allows any physical layer to be used with the MAC layer. It is an extension of the MII ( Media Independent Interface ) used in Fast Ethernet. It uses the same management interface as MII. It supports 10, 100 and 1000 Mbps data rates. It provides separate 8-bit wide receive and transmit data paths, so it can support both full-duplex as well as half-duplex operation.The GMII provides 2 media status signals : one indicates presence of the carrier, and the other indicates absence of collision. The Reconciliation Sublayer (RS) maps these signals to Physical Signalling (PLS) primitives understood by the existing MAC sublayer. With the GMII, it is possible to connect various media types such as shielded and unshielded twisted pair, andsingle-mode and multi mode optical fibre, while using the same MAC controller.The GMII is divided into three sublayers : PCS, PMA and PMD.4.1 PCS (Physical Coding Sublayer)This is the GMII sublayer which provides a uniform interface to the Reconciliation layer for all physical media. It uses 8B/10B coding like Fibre Channel. In this type of coding, groups of 8 bits are represented by 10 bit "code groups". Some code groups represent 8 bit data symbols. Others are control symbols. The extension symbols used in Carrier Extension are an example of control symbols.Carrier Sense and Collision Detect indications are generated by this sublayer. It also manages the auto-negotiation process by which the NIC (Network Interface) communicates with the network to determine the network speed (10,100 or 1000 Mbps) and mode of operation (half-duplex or full-duplex).4.2 PMA (Physical Medium Attachment)This sublayer provides a medium-independent means for the PCS to support various serial bit-oriented physical media. This layer serializes code groups for transmission and deserializes bits received from the medium into code groups.4.3 PMD (Physical Medium Dependent)This sublayer maps the physical medium to the PCS. This layer defines the physical layer signalling used for various media. The MDI ( Medium Dependent Interface), which is a part of PMD is the actual physical layer interface. This layer defines the actual physical attachment, such as connectors, for different media types.Back to Table of Contents5. Buffered DistributorEthernet today supports full-duplex media, physical layer as well MAC layer. However it still supports half-duplex operation to maintain compatibility. A new device has been proposed which provides hub functionality with full duplex mode of operation. It is called various names such as Buffered Distributor, Full Duplex Repeater and Buffered Repeater.The term "Buffered Distributor" is used for all these devices in the following discussion.The basic principle is that CSMA/CD is used as the access method to the network and not to the link. A Buffered Distributor is a multi-port repeater with full-duplex links.Each port has an input FIFO queue and an output FIFO queue. A frame arriving to an input queue is forwarded to all output queues, except the one on the incoming port. Within the distributor, CSMA/CD arbitration is done to forward the frames to output queues.Since collisions can no longer occur on links, the distance restrictions no longer apply. The only restriction on cabling distances is the characteristics of the physical medium, and not the CSMA/CD protocol.Since the sender can flood the FIFO, frame based flow control is used between the port and the sending station. This is defined in the 802.3x standard and already used in Ethernet switches.The motivation behind development of the Buffered Distributor is it's cost compared to a Gigabit switch and not a need to accommodate half duplex media. The Buffered Distributor provides full duplex connectivity, just like a switch, yet it is not so expensive, because it is just an extension of a repeater.Back to Table of Contents6. TopologiesThis section discusses the various topologies in which Gigabit Ethernet may be used. Gigabit Ethernet is essentially a "campus technology", that is , for use as a backbone in a campus-wide network. It will be used between routers, switches and hubs. It can also be used to connect servers, server farms ( a number of server machines bundled together), and powerful workstations. Essentially, four types of hardware are needed to upgrade an exiting Ethernet/Fast Ethernet network to Gigabit Ethernet : Gigabit Ethernet Network Interface Cards (NICs)qAggregating switches that connect a number of Fast Ethernet segments to Gigabit EthernetqGigabit Ethernet switchesqGigabit Ethernet repeaters ( or Buffered Distributors)qThe five most likely upgrade scenarios are given below :6.1 Upgrading server-switch connectionsMost networks have centralized file servers and compute servers A server gets requests from a large number of clients. Therefore, it needs more bandwidth. Connecting servers to switches with Gigabit Ethernet will help achieve high speed access to servers. . This is perhaps the simplest way of taking advantage of Gigabit Ethernet.6.2 Upgrading switch-switch connectionsAnother simple upgrade involves upgrading links between Fast Ethernet switches to Gigabit Ethernet links between 100/1000 Mbps switches.6.3 Upgrading a Fast Ethernet backboneA Fast Ethernet backbone switch aggregates multiple 10/100 Mbps switches. It can be upgraded to a Gigabit Ethernet switch which supports multiple 100/1000 Mbps switches as well as routers and hubs which have Gigabit Ethernet interfaces. Once the backbone has been upgraded, high performance servers can be connected directly to the backbone. This will substantially increase throughput for applications which require high bandwidth.6.4 Upgrading a Shared FDDI BackboneFiber Distributed Data Interface (FDDI) is a common campus or building backbone technology. An FDDI backbone can be upgraded by replacing FDDI concentrators or Ethernet-to-FDDI routers by a Gigabit Ethernet switch or repeater.6.5 Upgrading High Performance WorkstationsAs workstations get more and more powerful, higher bandwidth network connections are required for the workstations. Current high-end PCs have buses which can pump out more than 1000 Mbps. Gigabit Ethernet can be used to connect such high speed machines.Back to Table of Contents7. ATM vs. Gigabit EthernetWhen ATM (Asynchronous Transfer Mode) was introduced, it offered 155 Mbps bandwidth, which was 1.5 times faster than Fast Ethernet. ATM was ideal for new applications demanding a lot of bandwidth, especially multimedia. Demand for ATM continues to grow for LAN's as well as WAN's.On the one hand , proponents of ATM try to emulate Ethernet networks via LANE ( LAN Emulation) and IPOA ( IP over ATM). On the other, proponents of Ethernet/IP try to provide ATM functionality with RSVP( Resource Reservation Protocol ) and RTSP ( Real-time Streaming Transport Protocol ). Evidently, both technologies have their desirable features, and advantages over the other. It appears that these seemingly divergent technologies are actually converging.ATM was touted to be the seamless and scaleable networking solution - to be used in LANs, backbones and WANs alike. However, that did not happen. And Ethernet, which was for a long time restricted to LANs alone, evolved into a scalable technology.As Gigabit Ethernet products enter the market, both sides are gearing up for the battle. Currently, most installed workstations and personal computers do not have the capacity to use these high bandwidth networks. So, the imminent battle is for the backbones, the network connections between switches and servers in a large network.Gigabit Ethernet seems to be ready to succeed. It is backed by the industry in the form of the Gigabit Ethernet Alliance. The standardization is currently on schedule. Pre-standard products with claims of inter-operability with standardized products have already hit the market. Many Fast Ethernet pre-standard products were inter-operable with the standard. So it is expected that most pre-standard Gigabit Ethernet products will also be compatible with the standard. This is possible because many of the companies that have come out with products are also actively participating in the standardization process.ATM still has some advantages over Gigabit Ethernet :ATM is already there. So it has a head start over Gigabit Ethernet. Current products may not support gigabit speeds,but qfaster versions are in the pipeline.ATM is better suited than Ethernet for applications such as video, because ATM has QOS ( Quality of Service) and different qservices available such as CBR (constant bit rate) which are better for such applications. Though the IETF (InternetEngineering Task Force, the standards body for internet protocols) is working on RSVP which aims to provide QOS on Ethernet, RSVP has it's limitations. It is a "best effort" protocol, that is , the network may acknowledge a QOS request but not deliver it. In ATM it is possible to guarantee QOS parameters such as maximum delay in delivery.Gigabit Ethernet has its own strengths :The greatest strength is that it is Ethernet. Upgrading to Gigabit Ethernet is expected to be painless. All applications that qwork on Ethernet will work on Gigabit Ethernet. This is not the case with ATM. Running current applications on ATM requires some amount of translation between the application and the ATM layer, which means more overhead.Currently, the fastest ATM products available run at 622 Mbps. At 1000 Mbps, Gigabit Ethernet is almost twice as fast.qIt is not clear whether any one technology will succeed over the other. It appears that sooner or later, ATM and Ethernet will complement each other and not compete.Back to Table of Contents8. SummaryGigabit Ethernet is the third generation Ethernet technology offering a speed of 1000 Mbps. It is fully compatible with existing Ethernets, and promises to offer seamless migration to higher speeds. Existing networks will be able to upgrade their performance without having to change existing wiring, protocols or applications. Gigabit Ethernet is expected to give existing high speed technologies such as ATM and FDDI a run for their money. The IEEE is working on a standard for Gigabit Ethernet, which is expected to be out by the beginning of 1998. A standard for using Gigabit Ethernet on twisted pair cable is expected by 1999. Back to Table of Contents9. Bibliography and LinksAnnotated BibliographyIEEE Draft P802.3z/D3 "Media Access Control (MAC) Parameters, Physical Layer, Repeater and Management Parameters1.for 1000 Mb/s operation", June 1997This is the draft document of the 802.3z standard. It is available from IEEE on request. The IEEE standards site hasinformation on ordering IEEE standards and draft documents at /faqs/order.html2.Gigabit Ethernet Alliance "Gigabit Ethernet : White Paper", Aug 1996,/technology/whitepapers/gige/A whitepaper from the GEA. Gives comparison of technologies like FDDI and ATM with Gigabit Ethernet.Joe Skorupa, George Prodan, "Battle of the Backbones: ATM vs. Gigabit Ethernet", Data Communications, April 1997,3./tutorials/backbones.htmlThis article features arguments for and against Gigabit Ethernet vs. ATM.4.Michelle Rae McLean, "Gigabit Speeds Mandate Fix", LAN Times, Sep 1996,/96sep/609c029a.htmlThis article discusses problems in migrating to Gigabit Ethernet.Gigabit Ethernet Related WWW Links/1.Gigabit Ethernet Alliance Home Page.2./Gigabit_Ethernet.htmGigabit Ethernet page at PC Webopaedia. Contains Definitions and Links:8080/ethernet/gigabit.html3.This page contains some Gigabit Ethernet information and links.Back to Table of ContentsVijay Moorthy, Aug 14, 1997。

以太网技术原理课件(PPT 56张)

1000BaseT是一种使用5类UTP作为网络传输介质的千兆以太网技
术，最长有效距离与100BASETX一样可以达到100米。用户可以采用这种技术在原有的快速以太网系统中实现从100Mbps到 1000Mbps的平滑升级。
万兆以太网
已经开始部署，预计未来将有大规模的应用标准为IEEE802.3ae
HUB设备工作原理：
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2
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OUT IN
OUT
OUT
OUT
HUB仅仅改变了以太网的物理拓扑
冲突域
LAN
LAN
HUB
LAN
LAN
LAN
HUB对所连接的LAN只做信号的中继，所有的物理设备构成了一个冲突域。
由HUB组建以太网的实质
实际上网络中由HUB组建以太网，仍然存在以下缺陷：
冲突严重；
向所有端口转发广播帧和多播帧。
上述原则中存在三处严重的错误，你知道是什么吗？
正确答案
1.接收网段上的所有数据帧； 2.利用接收数据帧中的源MAC地址来建立MAC地址表（源地址自学习），使用地址老化机制进行地址表维护； 3.在MAC地址表中查找数据帧中的目的MAC地址，如果找到就将该数据帧发送到相应的端口（不包括源端口）；如果找不到，就向所有的端口发送（不包括源端口）； 4.向所有端口转发广播帧和多播帧（不包括源端口）。
目标
学习完此课程，您将会：
了解以太网相关标准掌握以太网技术原理和发展过程
内容介绍
第1章以太网相关标准
第2章以太网技术原理
以太网的诞生
以太网最初是由Xerox公司开发的一种基带局域网技术，使用同轴
电缆作为网络媒体，采用载波多路访问和碰撞检测（CSMA/CD）机制,数据传输速率达到10Mbps。

计算机网络实用技术知识点之千兆以太网

计算机网络实用技术知识点之千兆以太网千兆以太网随着多媒体技术、网络分布计算、桌面视频会议等应用的不竭发展，用户对局域网的带宽提出了更高的要求；同时，100M快速以太网也要求主干网、办事器一级有更高的带宽。

别的，由于以太网的简单、实用、廉价及应用的广泛性，人们又迫切要求高速网技术与现有的以太网保持最大的兼容性。

千兆以太网技术就是在这种需求背景下开始酝酿的。

1996年3月成立的IEEE1302.3Z工作组，专门负责千兆以太网的研究，并制定相应标准。

千兆以太网使用原有以太网的帧结构、帧长及CSMA/CD合同，只是在低层将数据速率提高到了1Gbps.因此，它与标准以太网（1OMbps）及快速以太网（100Mbps）兼容。

用户能在保留原有操作系统、合同结构、应用程序及网络办理平台与工具的同时，通过简单的修改，使现有的网络工作站廉价地升级到千兆位速率。

1.千兆以太网的物理层合同千兆以太网的物理层合同包罗1000BASE-SX、1000BASE-LX、1000BASE-CX和1000BASE-T等标准。

（1）1000BASE-SX.使用芯径为50及62.51im、工作波长为850m1的多模光纤，采用8BAOB编码方式，传输距离别离为260m和525m，适用于建筑物中同一层的短距离主干网。

来源：（2）1000BASE-LX.使用芯径为50及62.51im的多模、单模光纤，工作波长为1300m1，采用8B/10B编码方式，传输距离别离为525m、550m和3000m，主要用于校园主干网o来源：（3）1000BASE-CX.使用1500平衡屏蔽双绞线（STP），采用8BAOB编码方式，传输速率为1.25Gbps，传输距离为25m，主要用于集群设备的连接，如一个交换机房内的设备互连。

来源：（4）1000BASE-To使用4对5类非平衡屏蔽双绞线（UTP），传输距离为100m，主要用于结构化布线中同一层建筑的通信，从而可以利用以太网或快速以太网已铺设的UTP电缆。

【办公资料】以太网基础知识ppt课件

中继器：又叫转发器，在物理层任务；对网络电缆上传输的数据信号经过放大整形后再发
送到其他电缆段 .留意运用中不能构成环路，并且有个数限制
网桥：又叫桥接器，任务在数据链路层 .有挑选/过滤功能，隔离不需求在网间传输的信息，
寻址和途径选择靠DL层的帧头中的MAC地址，不能广播包抑制和子
网隔离.
路由器：任务在网络层，能广播包抑制和子网隔离，
。经过一段时间，随着站不断地发送帧，网桥就会知道一切活动站的地址-端口对应关系。
• 阐明：
• 〔1〕一个网桥衔接的LAN的数量没有限制； • 〔2〕每个站有一个全局独一的48位单播地址。这是很
•
2.LLC方式的选择取决于高层协议的要求。
1.3 以太网补充知识
• 1.3.1 网桥
• 网桥和中继器非常相像，它与中继器的不同之处就在于它可以解析它收发的数据。网桥任务在OSI模型的数据链路层；数据链路层可以进展流控制、纠错处置以及地址分配。网桥可
网桥原理
• 知目的地址的帧的转发
• 网桥内部有一个网桥端口与一切站相对应的地址映射表，当网桥的一个端口接纳到帧后，网桥检查该帧的目的地址，然后查找地址表，确定与该地址对应的端口。
•
a.假设收到帧的端口正是帧目的地址所在的端口，那么网桥就会丢弃这个帧。由于可以
认定经过正常的LAN传输机制，目的机曾经接纳过这个帧。
•
b 假设收到的帧的端口不是目的地址所在的端口，为了使目的站正确地收到该帧，网
桥必需把这一帧转发到目的地址所在的端口。
• 未知目的地址的帧的转发 • 假设网桥当前还不知道站发送帧的目的地址，网桥在地址表中找不到该目的地址与端口，
1.2.2 Data link layer

1千兆位以太网体系结构和功能模块

1千兆位以太网体系结构和功能模块 2以太网端口之间存在多个数据通道网段站PHY 层网段段屏蔽铜缆 MMF SMF 五类UTP100M （2对）站 3net FLOW 交换示意图路由器4以太网功能模块图 5 CSMA/CD 接受流程图EEE802 LLC OSIYYMAC 子层 DL 层NPHY 层 PHY 层媒体NCSMA/CD 全双工，半双工 8b/10b 编/译码专门的编译码 1000BASECX 1000BASELX1000BASESX 1000BASET CHACHE 没命中 CACHE 命中路由表安全过滤规则流量统计路由任务安全任务统计任务处理结果存放在CACHE NETFLOW 任务 Net FLOW CACHE NETFLOW 统计 NETFLOW 输出数据分组物理信令PLS 媒体链接单元MAU 媒体访问控制帧的封装与解封接收完成帧碎片 CRC 正确目的地交符合有另外位长度正确长度否开始接受6A TM 协议参考模型 7NHRP 协议的NBMA 网络源端到目的端8群组交换器典型组网方式连接图（红色字另外为注释！） 9FDDI 组网图（注释说明）主干交换器重要站点共享集线器服务器上端端口服务器客户占集中器端口交换10MBPS100MBPS 客户机10 以太网帧结构7 1 6 6 2 46-------1500 4前导码帧首界定符目的地址源地址类型数据区帧检验序列11 IEEE802.5协议帧格式和令牌格式SFS FCS 作用范围 EFSSD AC FC DA SA INFO FCS ED FS 帧格式SD AC ED 令牌格式 12 IEEE802体系(802.1 802.2 802.3 802.4 802.5)关系分层结构802.1（B ）802.2 LLC 层MAC 层802.1(A) 802.1（B ） PHY 层802.3 802.4 802.5 高层协议 ATM 适配层 ATM 层物理层 IP 逻辑子网 1 IP 逻辑子网2 路由器1 路由器3 路由器2 源端目的端 HUB 群组交换器 S PS13 IEEE802.3CSMA/CD的发送流程图帧准备好Y 媒体忙延迟随机时间TN开始发送帧N NN发送完毕碰撞N>=16 Y停止发送（形成碎片）Y发NELLY 碰撞次数N+1碰撞次数过多发送成功（差错处理）14 IP路由器的工作流程图接受帧，并分解出IP包N IP包头合法性验证IP包选项处理丢弃IP包本地交或转发本地提交转发寻址转发验证转发TTL处理数据包分段VP VC 多个虚通道可以复用链路层寻址传输链路VP VC 一个虚通路，而多个虚15 A TM中虚通道虚通路和传输链路关系图VP VC通路又可以复用一条传输链路。

以太网基本知识PPT课件

Auto MDI/MDIX--网线的交叉线和直连线自动转换，一般用途都不用管这个的;没有这个功能的时候，在使用的时候，就需要注意你所用的网线是交叉线，还是直线。
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光纤的结构示意图
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光纤的结构
纤芯位于光纤中心，直径2a为5～75μm, 作用是传输光波。包层位于纤芯外层，直径2b为100～150μm,作用是将光波限制在纤芯中
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ITU-T建议的光纤分类
G.651光纤:渐变多模光纤，工作波长为1.31μm和1.55μm，在1.31μm 处光纤有最小色散，而在1.55μm处光纤有最小损耗，主要用于计算机局域网或接入网。
G.652光纤：常规单模光纤，也称为非色散位移光纤，其零色散波长为 1.31μm，在1.55μm处有最小损耗，是目前应用最广的光纤。
以太网基本知识
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以太网分类
按传输介质分
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双绞线
双绞线双绞线由两根绝缘铜导线相互缠绕而成。两根绝缘的铜导线按一定密度互相绞在一起，可降低信号干扰的程度，每一根导线在传输中辐射的电波也会被另一根线上发出的电波抵消。把一对或多对双绞线放在一个绝缘套
管中便成了双绞线双电绞缆，线在由局域两网根中常绝用缘双绞铜线导4对线双相绞线互组缠成的绕。而由两成根绝。缘铜两导线根相绝互缠缘绕而的成。铜两根导绝线缘的按铜导一线定密度互相绞在一起，可降低信号干扰的程度，每一根导线在传输按一定密度互相绞在一起，可降低信号干扰的程度，每一根导线在传输中辐射的电波也会被另一根线上发出的电波抵消。把一对或多对
双绞线放在一个绝缘套管中便成了双绞线电缆，在局域网中常用双绞线4对双绞线组成的。由两双绞线由两根绝缘铜导线相互缠绕而成

第十章千兆位以太网

Shared
Low cost Short distance
Half duplex
Multimode fiber Copper
Server farms Desktops
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史忠植高级计算机网络
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10.1 概述
*德国的RERKOM研究环境中铺设了大量光纤，购置了高速网及
高性能工作站。目前主要研究ATM技术。 *AT&T与加利福尼亚大学伯克利分校、Illinois大学和 Wisconsin大学等联合启动了实验大学网络（XUNET），研究基于信元的广域网计划。1990年XUNET扩展为Blanca验证环境。其研究内容十分广泛，主要有呼叫、多路复用、拥塞控制、计算机与网络界面（如超级计算机的整合、网络虚拟存储机制）及Gigabit应用等。该工程已产生了不少有趣的结果，包括对多媒体协议的支持、拥塞控制与回避。在XUNET工程中，也有来自哥伦比亚大学、宾夕法尼亚大学的研究人员。NCSA（National Center for Supercomputing Applications）的Catlell是当今高速应用的专家，AT&T的Fraster是信元网络的专家。
史忠植高级计算机网络
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路由交换机
第三层交换机是基于千兆位以太网的 IP网络迁移的理想选择。当在骨干中从 100Mbps 转向千兆位技术时，它对于以网络性能来衡量路由性能是必不可少的。第三层交换机使得这个努力既实际又经济。这个理想的网络将由网络边缘的高密度交换机构成，他级联到千兆位第三层交换机上。边缘交换机应能够在应用层信息基础上过滤和转发。所谓第三层交换，实际上是实现了第三层（网络层）的功能。 2018/11/23 24 史忠植高级计算机网络