联通MSTP交流

1、上海贝尔阿尔卡特传输网络部上海贝尔阿尔卡特传输网络部 MSTP产品与技术交流产品与技术交流All rights reserved Jan. 2003, Alcatel Shanghai bell MSTP技术的发展技术的发展新兴的以太网业务新兴的以太网业务 第三代第三代MSTP系统的技术特征系统的技术特征 上海贝尔阿尔卡特的第三代上海贝尔阿尔卡特的第三代MSTP产品产品内容内容All rights reserved Jan. 2003, Alcatel Shanghai bellMSTP技术的发展All rights reserved Jan. 2003, Alcatel Shanghai b

2、ellMSTP的发展的发展MSTP的提出的提出第一代第一代MSTP第二代第二代MSTP第三代第三代MSTPAll rights reserved Jan. 2003, Alcatel Shanghai bellMSTP的提出的提出为在现有的SDH/SONET构架上提供Ethernet/IP/ATM等多业务接入技术上的发展主要体现在对以太网提供的支持上，包括最初的以太网点到点透传MSTP，以及当前提供以太网二层交换能力的MSTP，直到近来的第三代MSTP在近期TDM业务仍为主导的情况下，在步入纯IP宽带城域网之前，选择All rights reserved Jan. 2003, Alcatel

3、Shanghai bell以太网点到点透传以太网点到点透传MSTP(第一代第一代MSTP) MSTP以太网接口的信号直接映射到SDH的虚容器(VC)中，进行点到点传送以太网透传租线业务业务粒度受限于VC，一般最小为2Mbps不能提供不同以太网业务的QoS区分不提供流量控制不提供多个以太网业务流的统计复用和带宽共享保护完全基于SDH物理层，不提供以太网业务层保护All rights reserved Jan. 2003, Alcatel Shanghai bell以太网二层交换以太网二层交换MSTP(第二代第二代MSTP) 一个或多个用户以太网接口与一个或多个独立的基于SDH虚容器的点对点链路之

4、间，实现基于以太网链路层的数据帧交换相比第一代MSTP，第二代MSTP主要在带宽共享方面提供了一定改善提供基于802.3x的流量控制提供多用户隔离和VLAN划分支持提供基于STP/RSTP等的以太网业务层保护倒换一些以太网二层交换MSTP还支持基于802.1p的优先级转发802.1p只是规定了在网络出现阻塞情况下，设备能够按照不同的优先级(07)来转发以太网数据，从而使高优先级的数据丢包较小。业务的QoS支持不仅包括丢包率，还包括带宽、时延、时延抖动等其它指标，因此严格上802.1p并不能提供QoS支持 All rights reserved Jan. 2003, Alcatel Shangh

5、ai bell第三代第三代MSTP(1) 第二代MSTP相对第一代MSTP有相当的技术提高，包括多用户/业务的带宽共享和隔离，但其缺点不提供良好QoS支持，无法很好的取代利润丰厚的租线业务基于STP/RSTP的业务层保护倒换时间太慢和第一代MSTP一样，所能提供的业务带宽粒度也受限于VC，一般最小为2MbpsVLAN的4096地址空间使其在核心节点的扩展能力很受限制，不适合大型城域公网应用节点处在环上不同位置时，其业务的接入是不公平的MAC地址的学习/维护以及MAC地址表影响系统性能基于802.3x的流量控制只是针对点到点链路多用户/业务的带宽共享是对本地接口而言，还不能对整个环业务进行共享A

6、ll rights reserved Jan. 2003, Alcatel Shanghai bell第三代第三代MSTP(2)以太网新业务的QoS要求进一步推动MSTP向第三代发展第三代MSTP主要是在以太网和SDH间引入了一个中间智能适配层，来将以太网的业务要求适配、映射到SDH通道上All rights reserved Jan. 2003, Alcatel Shanghai bellt城域以太网技术和相应服务城域以太网技术和相应服务t以太网技术基础以太网技术基础tVLAN管理t以太网在SDH上的封装方式: VCAT, LCAS, GFPt以太网性能监测计数器t阿尔卡特的城域以太网业务解

7、决方案阿尔卡特的城域以太网业务解决方案 AgendaAll rights reserved Jan. 2003, Alcatel Shanghai bellt 以太网是一种本地网通信技术 (LAN)。通信终端之间可以以 10-100-1000-10000 Mbps 的数率传输。t“共享式以太网共享式以太网” 在此方式下， 连接到同一电缆的通信终端数目无限制。t“交换式以太网交换式以太网” 每个设备有一专用电缆连接到数据交换机上。t 以太网通信中应用的协议称之为 CSMA/CD(only Shared). 即 “ Carrier Sense, Multiple Access, Collision

8、 Detect”.tMultiple access means that every station is connected to a single copper wiretCarrier Sense says that before transmitting data, a station checks the wire (power sensing) to see if any other station is already sending somethingtCollision Detection means that if a collision occurs, it is det

9、ected by each interferring station (by different power lavel on the cable). Both station back-off, and try a retransmission at randomly selected later timeOverviewAll rights reserved Jan. 2003, Alcatel Shanghai bellEthernet 802.3BehaviourBus shared by all stationsStations listen to the bus activity

10、before sending a frameDuring first phase of tx, the station checks for collisionIf a collision occurs, then Random delay before retransmissionEfficiency of the CSMA/CD method : 25 % - 60 % according to the frame sizeAll rights reserved Jan. 2003, Alcatel Shanghai bellIEEE 802.3MAC frame structurePRE

11、AMBULEDESTADDRSRCADDRDATAPADSTART OFFRAME DELIMITER10101011Length or TypeCHECKSUM176620-15000-464LLC+dataAll rights reserved Jan. 2003, Alcatel Shanghai bellETH Frame (IEEE 802.3 IETF RFC 894)ETH LAN (frames)HeaderPayload6 6 2 46 - 1500 bytesDASALength/Type4FCSETH V. 2DA: Destination MACSA: Source M

12、ACLength:Lenght up to the CRCLLC/SNAP:802.2 FCS:Frame Check SumAll rights reserved Jan. 2003, Alcatel Shanghai bellEthernet II versus IEEE 802.3DESTADDR6620-15000-464SRCADDRDATAPADCHECKSUMETHERNET II(include LLC)IEEE 802.3 1500DESTADDR6620-15000-464SRCADDRDATAPADCHECKSUM0. 1500The ETH interface supp

13、ort two type of frame .All rights reserved Jan. 2003, Alcatel Shanghai bellLength/Type field of 802.3 Frames如果此字段的值小于或等于maxValidFrame (详见 4.2.7.1)的数值,则 Length/Type字段显示了包括后续业务数据的的以太网数据帧的帧长度。 (Length interpretation).如果此字段的值大于或等于1536 decimal (0 x0600), 则 Length/Type 字段显示的是 MAC client protocol的种类 (Type

14、interpretation). 当此字段是作为 Type 字段使用时, 必须有相应的机制来确保MAC客户端能正确的处理以太网数据帧的业务数据。All rights reserved Jan. 2003, Alcatel Shanghai bell802.2 sub-layer802.2 services802.2 Logical Link control sub-layer provides the following types of service :Connectionless (LLC type 1) : this service is used in QB3 profileConn

15、ection oriented (LLC type 2)The format of the data link frame is the following :In QB3 protocol suite, DSAP = SSAP = 0 xFE, and the control field can get only UI and TEST valuesDSAPSSAPCONTROLDATA1 byte1 byte1 or 2 bytesAll rights reserved Jan. 2003, Alcatel Shanghai bellEthernet 802.3Address format

16、I/G U/L46 bit AddressI/G = 0 individual = 1 groupU/L = 0 globally administrated = 1 locallyXX XX XX YY YY YY24 bits24 bitsE.g.00:20:60:00:00:01Alcatel Telettra01:80:C2:00:00:14AIIL 1ISsFF:FF:FF:FF:FF:FFBroadcastAll rights reserved Jan. 2003, Alcatel Shanghai bellEthernet 802.3优点和缺点优点和缺点缺点以太网通信协议是一不严

17、密的通信协议 (偶然的 CSMA/CD)初始化时, 无法为数据帧分配优先级以太网最大通信线缆长度为2.5 km (with repeaters)在过载网络里，会有大量的冲突存在优点以太网协议算法简单且有效网络安装快速便捷以太网物理连接使用无源电缆，维护简单在无过载的以太网网络上可达到0延迟All rights reserved Jan. 2003, Alcatel Shanghai bellt共享以太网t Bust Star (Hub)t交换以太网t Ethernet Bridging(桥)t Ethernet SwitchingEthernet 拓扑和建网设备All rights reser

18、ved Jan. 2003, Alcatel Shanghai bellEthernet Devices - RepeatersRepeaters (shared Ethernet) :用来将码流从一个网络转发到另一个网络上, 使两个网络在逻辑上表现为一个网络提供信号放大和必要的信号同步，使之信号能够传送更远的距离Repeater 有一个输入和一个输出 Repeaters 必须符合 IEEE 802.3c repeater 标准并使用在半双工模式的网络结构下All rights reserved Jan. 2003, Alcatel Shanghai bellEthernet Devices

19、- HubHub (shared Ethernet) IEEE802.3 Clause 12:用来将两个或多个单独的网段连接在一起。所有收发以太网数据帧的终端设备均处在同一个冲突域里。提供两个DTE的连接性，并且执行恢复信号振幅，时钟同步和冲突检测的基本功能。All rights reserved Jan. 2003, Alcatel Shanghai bellEthernet Devices - BridgesBridges:网桥的主要功能是将两个单独的网络连接在一起. 特别是网桥可将两种不同类型的以太网连接在一起，如以太网（Ethernet）和快速以太网（Fast ethernet）网桥侦

20、听网络上所传输的所有数据包，并且根据每个网段来映射相应通信结点的以太网地址，网桥通过这种方式还实现只允许必要的数据流通过网桥。大多数网桥将侦听到的以太网地址记录下来，并通过建立一张表来维护学习到的以太网地址。此过程是网桥自动实现的. 如果在一个稳定的网络中，如果每个网桥的地址表均在急速增长，那么极有可能是因为网络中存在拓扑环.使用生成树协议（The Spanning Tree Protocol）通过协议信令通信可以避免网络拓扑成环，从而避免广播风暴的产生。生成树协议是一个软件通信标准，在IEEE802.1d中有详细描述。All rights reserved Jan. 2003, Alcate

21、l Shanghai bellEthernet Devices - Switches交换机:交换机实际上是以太网网桥的扩展. 多端口网桥则成为交换机. 每个通信终端有自己的连接直接连接到交换机上，以至于可以以全双工，全速率方式与交换机通信. 虽然物理连接依然使用共享式传输介质，但实际通信中物理连接并不互相共享.All rights reserved Jan. 2003, Alcatel Shanghai bellEthernet DevicesSwitched vs. Shared:Reduces TrafficIncreases performanceIn a single collisio

22、n domainIn a single bordcast domainAll rights reserved Jan. 2003, Alcatel Shanghai bellExamples of Ethernet SwitchesGigabit EthernetSwitched EthernetAll rights reserved Jan. 2003, Alcatel Shanghai belltTransparent Bridging: How Ethernet bridging/switching works ?t Auto_Learning(网桥自动记录它所看到的所有帧的源地址和端口

23、信息)(自学)t Flooding向所有端口转发(除源端口外)一个目标地址不确定(FFFF)的帧信号,(泛洪)t Filtering(网桥将帧信号只向符合目标地址的端口转播出去,如果源和目标地址相同,则丢弃该帧)t Forwarding(网桥转发具有明确目标地址的帧信号)t Aging(MAC地址标中每一条转接地址存活的时间)(老化)Ethernet Transparent Bridging (IEEE 802.1D)All rights reserved Jan. 2003, Alcatel Shanghai bellt A Layer 3 packet retrieve the MAC a

24、ddress of the destination node he wants to send a packet through ARP protocoltwhen a destination MAC address is unknown, the layer 3 packet is broadcasted (L2 broadcast ?) over the network. The destination station answers with a packet containing the destination MAC address which is now known by the

25、 emitting station t Layer 2 switches manage lookup tables for frames forwarding purpose (see illustration in next slides)tPacket are flooded all aver the network =each time an incoming frame with a unicast (or unknown) MAC address has no entry in the lookup table, it is broadcasted to all the other

26、ports tMAC addresses are progressively learned by the switches = the acknoledgment packet allows each switch on the packet route to understand locally the ports it has to “link” together for an incoming MAC addressEthernet Transparent Bridging (IEEE 802.1D)All rights reserved Jan. 2003, Alcatel Shan

27、ghai bellt如果接收帧的目的MAC地址能在MAC地址表里能查询到的话，数据帧可以从某个特定端口转发出去，否则，数据帧将会以广播到所有端口的方式传送。tLayer 2 交换机会根据目的MAC地址来过滤数据帧，使之数据帧能从正确的端口转发。t交换机会略过同一网络段里通信结点的数据包转发tLayer 2 交换机通过超时机制来避免MAC地址表里的地址永久存在tMAC地址表的表项在经过没有更新的一定时间后，会从MAC地址表中将此表项删除掉Ethernet Transparent Bridging (IEEE 802.1D)IEEE802.1D;IN SWITCH BASE ON MAC ADDR

28、ESS, THE STP ACCORDING WITH IEEE802.1D)All rights reserved Jan. 2003, Alcatel Shanghai bellEthernet bridging: Flooding And LearningABCDEFA-EA-EA-EMAC addr “A” is learned by S1 (port 1)123123132MAC addr “A” is learned by S2 (port 1)MAC addr “A” is learned by S3 (port 1)A-EA-EA-EA-EA-E123A-EMAC addr “

29、A” is learned by S4 (port 3)Until E replies, all the frames sent to E are flooded toward all the Ethernet networkS1S2S3S4All rights reserved Jan. 2003, Alcatel Shanghai bellEthernet Bridging: Learning And ForwardingABCDEFE-AE-AE-AMAC addr “E” is learned by S1 (port 3)123123132MAC addr “E” is learned

30、 by S2 (port 2)E-A123MAC addr “E” is learned by S4 (port 1)From now on, all the frames to A and E will be forwarded to the right path onlyS1S2S3S4All rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree Protocol (STP)The flooding mechanism works if the Ethernet bridges are connected in a tr

31、ee topologyAny loopback will result in a broadcast storm(在具有路由回路的情况下,广播信息可能在次回到源点而今使其在网络中无休止的传播)Networks with a tree topology are not reliableA single failure affects communication (the network is partitioned)The STP protocol is used to “open the loops”(STP 用以在存在回路的网状网络中,阻塞断开某个端口以消除回路,在树状网络中其它端口出现故障

32、时,激活某个段口以保持网络成树状结构,用以消除冗余的回路).Some ports are auto- blocked by the Spanning Tree Protocol in order to build a tree active topology over a meshed physical topologyIn case of failures, some ports are unblocked to restore communicationThe STP protocol (defined in IEEE 802.1D-1998) requires long reconfig

33、uration times (minutes) in case of topology changesThe Rapid STP protocol has been defined in IEEE 802.1w and included into IEEE 802.1D-2003 to support fast reconfiguration times (few seconds)802.1D-2003 的协议中也包含的协议中也包含R-STPAll rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree ProtocolABC

34、DEFA-*A-*A-*123123132A-*A-*A-*A-*A-*123A-*Blocked portsBlocked ports由由STP自动计算确定自动计算确定BLOCK的端口的端口,两个两个BLOCK端口之间的通信中断端口之间的通信中断All rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree Protocol Link FailureABCDEFA-*A-*A-*123123132A-*A-*A-*A-*A-*123A-*Blocked ports当原来的线路中断后当原来的线路中断后,被阻塞的端口由被阻塞的端

35、口由STP自动激活形成通路自动激活形成通路All rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree Protocol STP;有不同的STP版本; IEEE802.1D是一种常用的STP版本.STP;在网络中选则一个网桥为根网桥作为参考,然后确定到该参考点的可用路径,STP选择一个最佳路径来转发数据,冗余路径回路被阻断.BPDU(bridge protocol data unit) ;STP会使用到BPDU信息(由各网桥向其它网桥发出,由各网桥比较接收到的各个BPDU,只转发最小的BPDU,),BPDU涉及到三个重要信息

36、; - 网桥ID; (= BID)=网桥优先级X网桥MAC地址;BID确定具有最小优先级的网桥可能选作根网桥,优先级的范围是0-65535, 默认情况下,网桥的优先级被设置为32768或0X8000.(一个桥接收到从各端口来的多个BPDU后,比较将最小BPDU在各端口中发出) 当两个网桥优先级一样,则MAC地址小的可能选为根网桥. 交换机只使用内存的MAC中的某一个MAC作为BID中的MAC地址. - 路径开销(COST); 为每两个交换机端口之间的为一段路径,设置一个开销值,(路径数据速率越高,开销越小),A交换机到根交换机之间要经过多少段路径,总的路径开销值为各段开销值之和(. - 端口I

37、D; 端口ID与BID相似,端口BID=端口优先级X端口号组成,STP的构成中,端ID号低的比ID号高的更具有优势,先比教优先级,如优先级相同,再比较端口号.当两个端口收到的网桥ID和COST一样,所明两个端口到根网桥的路径相同,就要自动阻塞掉一个端口,就比较接收到的两个端口的ID,接收到的端口ID号大的端口阻塞关闭. All rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree Protocol一个交换机发出的BPDU内容; - 根网桥的ID(该交换机所知道的根网桥ID). - 到根网桥的路径开销(发送BPDU信号的桥到根

38、桥的路径开销(COST),每经过一端路径,累加上该段的COST. - 发送BPDU信号的网桥的ID - 发送BPDU信号端口的IDAll rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree ProtocolSTP的收敛过程;-选举根网桥;刚开机时,都视自身为根网桥,把自声的BID放到根网桥中,2S后,接收到其它端口发来的BPDU信号,进行比较,若接收到的BPDU中的根BPDU和端口ID比自已的大,则不理睬,若接收到的BPDU中的根BPDU和端口ID比自已的小,则用接收到的BID和端口ID替换自己发送的BPDU信号内容.-选

39、举根端口; 根端口到根网桥的开销为0;-其它交换机上各端口收到BPDU后,通过比较根路经的开销值,距根桥路径开销最小的端口及为根端口.-在网络上的每一个物理段上, 选择标志端口; 两个标志端口之间处于可转发的状态,每个物理段上的两个端口互向对方发的BPDU信息中,比较到根桥的路径开销,路径开销小的为端口为标志端口,当两个端口到根桥的路径一样,则比较端口ID,小的为标志端口,大的处于阻塞状态.All rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree Protocol端口的几种状态;-禁用状态;(SHUTDOWN),由管理员

40、人工关闭某个端口-阻塞状态(DISABLE);所有桥的端口都以阻塞作为启动状态,这是为了防止形成回路,处于阻塞状态的端口不能转发数据,不能发BPDU,但可接收BPDU信号.-监听状态; 阻塞状态后转变为监听状态,处于监听状态的端口不能转发数据,可以收发BPDU信号,并选择根桥,根端口,和标志端口,如果某个端口选举为非标志端口,则从新返回阻塞状态.-学习状态; 建立MAC交换表-转发状态; 开始转发数据.All rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree ProtocolSTP所需的时间参数;-HELLO ; 活动端

41、口发送BPDU所需的时间.-转发延迟; 监听或学习状态的持续时间-最长寿命; BPDU的存储过期时间.All rights reserved Jan. 2003, Alcatel Shanghai bellSpanning Tree Protocol Port StatesPower onInitializationBlockingStateListeningStateLearningStateForwarding StateDisabledStateEach switch at the initialization time enters the blocking state Discard

42、 frames received from the attached segment Discard frames switched from another port for forwarding No learn station location Reception of BPDU No transmission of BPDU Discard frames received from the attached segment Discard frames switched from another port for forwarding No learn station location

43、 Reception and Process of BPDU Discard frames received from the attached segment Discard frames switched from another port for forwarding Learn station location Reception, Process and Forwarding of BPDU Forward frames received from the attached segment Forward frames switched from another port for f

44、orwarding Learn station location Reception, Process and Forwarding of BPDUActions performed at each STP stateIt waits for the input to go in blocking state until the expiration time, then it moves to Learning StateIt waits for the input to go in blocking state until the expiration time, then it move

45、s to Forwarding StateIt waits for the input to go in blocking state until the expiration time, then it moves to Listening StateA port in Disabled State doesnt participate to the STPProcessing from a STP state to the otherAll rights reserved Jan. 2003, Alcatel Shanghai belltMedia Type: 10/100 Mb/s, 1

46、Gbs, 10Gbs (TBC)t自协商 Auto negotiationt流量控制 Flow controlEthernet Physical InterfacesAll rights reserved Jan. 2003, Alcatel Shanghai bellAuto negotiationIEEE 802.3:2002 Clause 28 of the ANSI/IEEE Std 802.3Auto negotiation is a flexible mechanism for providing connection interoperability between IEEE 8

47、02.3 device at the highest performance technology available without intervention from a user, manager,Auto negotiation detects the various modes that exist in the device on the other end of the wire and advertises its own abilities to automatically configure the highest performance mode of interoper

48、ationParallel detection function is for the case where only one end of the link supports the auto negotiationAll rights reserved Jan. 2003, Alcatel Shanghai bellAuto negotiation IEEE 802.3:2002 Clause 28 of the ANSI/IEEE Std 802.3Half duplex : Alternat bidirectionnalFull duplex :Point to point commu

49、nicationBetween 2 equipmentsTwo levels :All rights reserved Jan. 2003, Alcatel Shanghai bellAuto negotiation IEEE 802.3:2002 Clause 28 of the ANSI/IEEE Std 802.3Auto negotiation means :Speed resolutionDuplex resolutionPause mode resolutionFor instance100BaseT full duplex 100BaseT half 10BaseT full10

50、BaseT halfAll rights reserved Jan. 2003, Alcatel Shanghai bellEvolution: 10 Gigabit Ethernet IEEE 802.3aeTimelineIEEE 802.3ae Task force (first step in March 1999)first draft discussed in September 200010 Gb/s Ethernet Task Force complete in June 2002Objective: typical Ethernet “price performance”10

51、 x bandwidth with 34x costObjective: connectivity for MAN/WANinterfaces at 1500 nm on SMF; distances up to 40 kmPMD compatible with framing SONET/SDHObjective: “economic” connectivity for LANInterfaces for MMF, VCSEL, wide WDMFull-duplex onlyAll rights reserved Jan. 2003, Alcatel Shanghai bell802.3z

52、 to 802.3ae ComparisonCSMA/ CD + Full DuplexCarrier ExtensionOptical/ Copper MediaLeverage Fibre Channel PMDsReuse 8B/ 10B CodingSupport LAN/MAN distances to 5 kmFull Duplex OnlyThrottle MAC Speed (rate adapt)Optical Media OnlyLeverage OC- 192 PMDs & Create New Optical PMDs From ScratchNew Codin

53、g Schemes (64B/ 66B)Support LAN/MAN distances to 40 km; Provide Direct Attach to SONET/ SDH Gearsource:All rights reserved Jan. 2003, Alcatel Shanghai bellVLAN Bridging (IEEE 802.1Q)洪泛 (i.e. frames with an unknown unicast MAC DA), 组播和广播帧总是广播到网络里的所有设备端口而因此导致了网络的性能和安全问题同一网络里的不同用户可以被隔离到不同的虚拟局域网里(VLANs)

54、，这样的不同用户组是逻辑地工作在不同网络里若处在不同VLAN的通信设备之间需要互相通信时，只有通过上层数据设备才能实现。(e.g. IP routers)VLAN技术允许不同的物理网络划分为同一个逻辑网段，不同的逻辑网段(Virtual LANs) 属于不同的广播域。All rights reserved Jan. 2003, Alcatel Shanghai bellProvider Bridges (IEEE 802.1ad)The nature of Ethernet bridging is not suitable for carrier networks because it doe

55、s not allow segregating the traffic coming from different customersThe VLAN (IEEE 802.1Q) is not enough because it is not possible to ensure that different customers are not using the same VIDVLANs of different customers with the same VID will be managed as the same VLAN in the carrier network (no c

56、ustomer traffic segregation)The S-VLAN (pre-IEEE 802.1ad) allows the service provider to stack another VLAN tag on the frames coming on the UNI such that traffic from different customers is put on different S-VID and thus segregatedIf the customer is sending untagged Ethernet frames, these are sent

57、toward the carrier network as a single S-VLAN tagged framesIf the customer is sending Q-VLAN tagged Ethernet frames, these are sent toward the carrier network as dual tagged framesAll rights reserved Jan. 2003, Alcatel Shanghai bellObjective of VLAN stackingEnhance the existing Ethernet switching te

58、chnology (based on IEEE 802.1Q VLAN) to provide Metro Ethernet servicesThe existing Ethernet technology is not enough to satisfy carrier-grade requirementsIt is not able to provide the segregation of traffic from different customersThe ranges of VLANs used by different customers can overlap so using

59、 the 802.1Q VLAN tag (Q-VLAN) is not enoughIt is not able to provide carrier-grade QoS capabilitiesThe existing Ethernet technology can be simply enhanced with a new Service Provider VLAN tag (S-VLAN) to become a carrier solutionThe S-VLAN can be stacked over the existing customers 802.1Q-VLAN to pr

60、ovide transparency to customer VLANs (thus the name of VLAN stacking)(在输入的V-LAN客户业务上在加上V-LAN的标号,叫作V-LAN堆栈)All rights reserved Jan. 2003, Alcatel Shanghai bellFrame FormatsDA(6 Byte)Type (8100)(2 Byte)Q-VLAN Tag(2 Byte)Length/Type(2 Byte)Data( 1500 Byte)FCS(4 Byte)Untagged FrameDA(6 Byte)SA(6 Byte)Length