大家耐心看看这个，有意思，很久没有看过这么热闹的了

DreamCat

可能看着比较累，这里是原文URL:http://www.mynetlife.com/linux/articles/HubVSSwitch.htm

QUOTE
Hub 和 Switch 之?????路的朋友而言?扎?基本功夫是非常重要的。例如?能?正?了解 Hub 和 Swtich 的分?到底有哪些?就需要您? CSMA/CD 技?有相?的???同??要知道在 switch 上所?#092;用的新技?究竟有哪些... 由 ?中人 所建立。 最後修改??? 2003-03-29 00:32:08 ，已有 1 人?看?本文。Just do it!  wrote in messagenews:3gkAdc$Kn4@bbs.cynix.com.tw...> ※ 引述《YBO.bbs@bbs.yzu.edu.tw (上班啦)》之?言：> > ※ 引述《Mjolnyr.bbs@BirdNest.infoX.Net (Francis Jan)》之?言：> > > 鬼扯蛋.> > hub在多人???上???是平均分配的> > 但switch hub是看?有需要才?他??> > 也就是hub很像是??方式???息> > 而switch hub是直接?到想要的那台主?>> 一般 HUB ? Switch HUB，都是?播的呀，要不然..> ?路芳?怎?看得到，DHCP如何使用呢？>> ?然，supported VLAN ?品例外?..>> 一般 HUB ? Switch HUB 差?，?明一下，如有??，> ?望高人指?指?.. >> Hub ??於 Layer 1 product.> Switch Hub ??於 Layer 2 product.>> Switch Hub 比一般 Hub 多的功能，最少它要?明地??> 每? Port ??的 Mac address。>> 假? Switch Hub port 1 ?到的 Mac address ? 00:10:B5:30:30:A9> port 2 ?到的 Mac address ? 00:10:C1:D3:E2:A2> port 3 ?到的 Mac address ? 00:10:B3:E3:A1:07>> Port 1 底下接的是 Linux，> Port 2 底下接的是 Win98，> Port 3 底下接的是 Router。>> 今天，假?您要? Linux 透? Router ?接上 Internet，那N首先送出> ARP packages ?到 Router IP 所??的 Mac address，然後 Linux 就> ?接到 Router 所??的 Mac address (00:10:B3:E3:A1:07) 做?通。>> 其中，Switch HUB 已?得知 Linux ? Router 的 Mac address，? Linux> ? Router 做?料???，?不???料?到 port 2 ? win98。假如您> 想要在 Win98 上? sniffer 之?的???取封包，那?您??不到 Linux> ? Router 之??送的封包。>> ?就是 Switch HUB ?明的地方。> 但是如果是 HUB，??是???段?路上的任何?料，每? Port 都收得到。>> ??，Switch HUB，比 HUB 更有安全性，?少封包碰撞，??更有效率。>> ?迎大家不吝指教。>我喜?看到??的答案?也喜?和??的朋友??。我????到的 switch 相信都是指 level 2 上面的吧?那?我?要知道 OSI level2 layer 上面有什???才好理解。其中的 IEEE802.x 是?用最?的???而我?最常?的 ethernet ?是使用 IEEE802.3 ?? MAC sublayer ???其上的 DLCsublayer 802.2 就交?? programing 的朋友?忙解?一下 吧。我???看看 IEEE802.3 是怎??#092;作的?其特性有哪些?IEEE802.3 在 ethernet 上使用的??技??最普遍被?用的是 CSMA/CD?其?可以拆?三?部份?了解?1) CS (Carrier Sense)?送??要?信?送至??媒?之前?首先要探?媒?是否已?存在 carrier?如果有??表示有其它??在使用??媒??行其它的?送。然???送??就不能向??媒?送出信??而必?等到下次探??有 carrier 的?候才能?送。?比?好理解?也就是先?先?嘛?好比在?堂上?言??先?手??先??如果已?有人在?了?那就等。2) MA (Mutiple Access)在同一????允?多???使用共享媒?(?然不能?? CS 和 CD 的制?)。在CSMA/CD 技?中???送???利通? CS ??之後向媒?送出信?而?有?生Collision 的??所有分享著同一媒?的???都能收到??信?。每一???都有一?唯一的位址???我?通常?之? MAC 位址?而信?在?送媒?中?是以 frame的形式?送?每? frame 都有一? source 和一? destination 位址?。?送??? frame 送至媒?上之後?只有被??? destination 的的???才??信? copy下??再往上?程式?送 (decapsulate)?而那些???? destination 不是自己的??就??的不?理?? frame (除非在 promiscuous 模式之下)。不同的?定?? MA 使用的不同?也?影?整?效率的?#092;作?例如?播封包?那些以FF:FF:FF:FF:FF:FF ? MAC 位址的封包?switch ?是?送到所有?器上面的?因?使用???播位址的 frame?每?接收??都??之 copy 下??行 decapsulate ?理。例如 Microsoft Network 的?定家族?其使用?播封包的比率是非常高的?就算使用 L2 switch ???的?播也束手?策。只有利用 subnet 和 router 或更高level 的 switch 才有效?但?定的??性和?外增加的交通?也是要另行?估的?恐怕就超出目前的????了。3) CD (Collision Detection)前面的 CS ?程中?在理想的情?之下?所有分享著共同媒?的???都??有??取得?送的??。只是??子??的?#092;作速度??非我?人?所能感?的??些?#092;作?每一秒?可能有上?甚至百?次之多?例如 CAT 5 ??的???就能?理350Mhz 或更高的?送?率。假如???????好在?百?分之一秒之??同?做CS 的?作?而又同?探?到媒?上?有 carrier?那??情形之下??????可能?同???媒??送信???就是我?常?的 Collision (碰撞)了。如果?一?碰撞?生了?就?在媒?上?生frequecy ripple ?象。?一?在?的????到ripple ?它就??出一?高?信?去清除所有其它信?。?句?????信?同?告?所有???碰撞已??生。??候?每一???都???的等待一段??再重新?行 CS?如果??的(非??的)?是遇到 collision?那就按一定比例延???等待?候??共可以?行16次??大家才?最?放?。所以不?看出?如果在同一?segment 上面?在?的??越多?其?生 collision 的??也越大。事?上?除了 CSMA/CD 外??有一? CSMA/CA (CA = Collision Avoidance) 的技?我?可以使用??送端先向接收端送出 RTS(Request To Send) 封包?等收到 CTS(Clear To Send) 回?後?才向媒?送出信?。AppleTalk ?定就是使用??技?。CA 和 CD 的分??可以用??木??比喻?用 CD 的?候?要?就???不了再??用 CA 的?候??先派一?小?探路?如果他通?了?然後您才施然而?。好了??您了解 CSMA/CD ???定之後?那再?看看 HUB 和 Switch 的分?吧?HUB ??的是一? repeater??它?一? port (和 TCP ?定的 port 不一????是指插?路?的接孔)接收信???之後?????信?原原本本的送到所有其它port 上?不管哪些 port 是接到哪一台?器。而 switch 呢?它自己有一份 table???著哪? port 接到哪些 MAC 位址??上。?信??一? port ??之後???查?? frame 的 destination 是哪? MAC?然後按 table 找到?? MAC ??的 port ?而??信?往?? port 送?其它的 port就不送了。??有什?好??先看看 CS 吧??用 hub 的?候?所有 port 所?接到的??都探?到 carrier?然後就要等?而用 switch 呢?那些不是 destination 的?????有探?到carrier?也就?需再等?可以直接向媒?送出信?。?信?到? switch 的?候?switch ?先利用 cache 接收??信??然後?行 table 的比??再向destination 送出。如果 switch 的 cache 越大?CPU ?理能力越??其效率也越高??然??也越?。再看 CD?因?大部份由??送出的信??都?先被 switch cache 起??然後再??table 判?送出?那? collision 的??也大?的?少?由此?因 CD 而中?的?送也就大??少?相?的?所有??的使用效率也大?提高。至於 MA?相信不用多解?了吧?使用 swtich ?有一?好??提高?路的安全性。如果我?用 hub ??接???因? frame ?抵?所有?器?如果某人在其??上?上一?封包抓取???同???路卡的 promiscuous mode 打??那就可以看到所有的封包了?但如果用 switch 呢?只有被送到?台?器上的封包?才能被抓到。通常在?路安全上面?安全性?於效能及便利性是成反比的?要增加安全性?就要?牲效能和便利性?要增加效能和便利性?就要?牲安全性。而 switch?似乎是唯一打破??樊?的?路??了。??我?看到有人? Bridge 和 Switch 混?一?了?我不知道?仁兄? bridge 的理解是怎?的?在下???bridge 的功能只有???filtering 和 forwarding?後者是根?前者判?後才能?生。使用 bridge 的?候?基本上?物理的??切??? segment (或多??? bridge界面而定)?然後?bridge 也?建立起自己的 table?分??不同的 MAC ?分到不同的 segment 去。然後? frame 抵? bridge 的?候?bridge ??查其 source 和destination?如果????? MAC 都在同一? segment 之上?那就不?理??frame (?? filter 的功能)?但如果?? soure 和 destination 不在同一?segment 上呢?就起用 forward 功能?? frame 送到 destination 那? segment上?或是??的向所有‘非 source’到 segment(s) ?送(? bridge 的能力)。??看??bridge ? CS 和 CD 也起到改善的作用?但其? frame 的?理??竟和switch 是不一?的?bridge 以 segment ?依??而 switch ?以??????位?所以在?行效率上?是有分?的。?然?如果您?每一 port 所?接的??看??一的 segment?然後? switch 看? learning bridge?那或?可以?它?看???近似的????吧。至於於 10Base 和 100Base 的???那只是 switch 中一?非常??的功能而已??非是 switch 真正加分的因素。以上???人?知?如有?????指正?以免????。--======= http://www.study-area.org =======?雪迎春到??雨送春?已是寒崖百丈冰?尤有花枝俏俏也不?春?只把春??待得山花?漫??他在?中笑?  回覆本文  Re: ??有?基???的?? 作者: netman (---.seed.net.tw)日期:? 01/06/15 15:26竹??起  wrote in messagenews:3gkYKi$UHC@BirdNest.infoX.Net...>> ?一段你可以把IEEE 802.3?面?於jam的?述再看一看，你的?法???情?有> 出入。多?提????的?程中?真是?不得半??惰?想偷?蒙混??在不容易??。?免??大家??文件查??果?列如下?4.1.2.2 Access interference and recoveryIn half duplex mode,if multiple stations attempt to transmit at the sametime,it is possible for them to interfere with each other ’stransmissions,in spite of their attempts to a oid this by deferring.Whentransmissionsfrom two stations o erlap,the resulting contention is called acollision.Collisions occur only in half duplexmode,where a collision indicates that there is more than one stationattempting to use the shared physicalmedium.In full duplex mode,two stations may transmit to each othersimultaneously without causing interference.The Physical Layer may generatea collision indication,but this is ignored by the full duplex MAC.A gi en station can experience a collision during the initial part of itstransmission (the collision window)before its transmitted signal has had time to propagate to all stations onthe CSMA/CD medium.Once thecollision window has passed,a transmitting station is said to ha e acquiredthe medium;subsequent collisions are a oided since all other (properlyfunctioning)stations can be assumed to ha e noticed the signaland to be deferring to it.The time to acquire the medium is thus based onthe round-trip propagation time ofthe Physical Layer whose elements include the PLS,PMA,and physical medium.In the e ent of a collision,the transmitting station ’s Physical Layerinitially notices the interference on themedium and then turns on the collision detect signal.In half duplexmode,this is noticed in turn by theTransmit Media Access Management component of the MAC sublayer,andcollision handling begins.First,Transmit Media Access Management enforces the collision by transmitting abit sequence called jam.In 4.4,implementations that use this enforcement procedure are provided.Thisensures that the duration of the collision is suf ?cient to be noticed bythe other transmitting station(s)in olved in the collision.After the jam issent,Transmit Media Access Management terminates the transmission andschedules another transmissionattempt after a randomly selected time interval.Retransmission is attemptedagain in the face of repeatedcollisions.Since repeated collisions indicate a busy medium,howeer,Transmit Media Access Managementattempts to adjust to the medium load by backing off (voluntarily delayingits own retransmissions to reduceits load on the medium).This is accomplished by expanding the interval fromwhich the random retransmission time is selected on each successi etransmit attempt.Eventually,either the transmission succeeds,or theattempt is abandoned on the assumption that the medium has failed or hasbecome o erloaded.In full duplex mode,a station ignores any collision detect signal generatedby the Physical Layer.TransmitMedia Access Management in a full duplex station will always be able totransmit its frames without contention,so there is ne er any need to jam orreschedule transmissions.At the receiving end,the bits resulting from a collision are recei ed anddecoded by the PLS just as are thebits of a alid frame.Fragmentary frames recei ed during collisions aredistinguished from alid transmissions by the MAC sublayer ’s Recei e MediaAccess Management component.4.2.3.2.3 Collision handling (half duplex mode only)Once a CSMA/CD sublayer has ?nished deferring and has startedtransmission,it is still possible for it toexperience contention for the medium.Collisions can occur until acquisitionof the network has been accomplished through the deference of all otherstations ’ CSMA/CD sublayers.The dynamics of collision handling are largely determined by a singleparameter called the slot time.Thissingle parameter describes three important aspects of collision handling:a)It is an upper bound on the acquisition time of the medium.b)It is an upper bound on the length of a frame fragment generated by acollision.c)It is the scheduling quantum for retransmission.To ful ?ll all three functions,the slot time shall be larger than the sumof the Physical Layer roundtrip propagation time and the Media Access Layermaximum jam time.The slot time is determined by the parametersof the implementation,see 4.4.4.2.3.2.4 Collision detection and enforcement (half duplex mode only)Collisions are detected by monitoring the collisionDetect signal providedby the Physical Layer.When a collision is detected during a frametransmission,the transmission is not terminated immediately.Instead,thetransmission continues until additional bits speci ?ed by jamSize ha e beentransmitted (counting from thetime collisionDetect went on).This collision enforcement or jam guaranteesthat the duration of the collisionis suf ?cient to ensure its detection by all transmitting stations on thenetwork.The content of the jam isunspeci ?ed;it may be any ?xed or ariable pattern con enient to the MediaAccess implementation,however,the implementation shall not be intentionallydesigned to be the 32-bit CRC alue corresponding to the(partial)frame transmitted prior to the jam.4.2.3.2.5 Collision backoff and retransmission (half duplex mode only)When a transmission attempt has terminated due to a collision,it is retriedby the transmitting CSMA/CDsublayer until either it is successful or a maximum number of attempts(attemptLimit)ha e been made andall ha e terminated due to collisions.Note that all attempts to transmit agi en frame are completed beforeany subsequent outgoing frames are transmitted.The scheduling of theretransmissions is determined by acontrolled randomization process called “truncated binary exponentialbackoff.”At the end of enforcing acollision (jamming),the CSMA/CD sublayer delays before attempting toretransmit the frame.The delay isan integer multiple of slotTime.The number of slot times to delay beforethe nth retransmission attempt ischosen as a uniformly distributed random integer r in the range:0 r  ??的?> ?把IEEE 802.3??中?switch和bridge的定?拿?看看吧。> 另外，IEEE 802.1D的??正是 MAC bridge。>??查了一下 IEEE 的文件?的???他?? switch 和 bridge 定?在一起了。那就不能怪?初在校?的???而??怪自己?仔?看文件?~~~不??? IEEE 或 RFC 之?的文件?的?是非常乏味的?如果不想??看起?下面是我‘?章取?’下?的引文?希望?那些有?趣看看的朋友有些?助吧。********************************************IEEE Std 802.3, 2000 EditionPart 3:Carrier sense multiple access with collision detection (CSMA/CD)access method and physical layer specifications1.4 Definitions1.4.53 bridge:A layer 2 interconnection device that does not form part of aCSMA/CD collision domain butconforms to the ISO/IEC 15802-3:1998 [ANSI/IEEE 802.1D,1998Edition ]International Standard.Abridge does not form part of a CSMA/CD collision domain but,rather appearsas a Media Access Control(MAC)to the collision domain.(See also IEEE Std 100-1996.)1.4.264 switch:A layer 2 interconnection device that conforms to theISO/IEC 10038 [ANSI/IEEE 802.1D-1990 ] International Standard..Syn:bridge.4.1.1 OverviewThe most common configuration envisioned for full duplex operation consistsof a central bridge (alsoknown as a switch)with a dedicated LAN connecting each bridge port to asingle device.12.4.3.2.7 Collision presence startupWhen a hub starts generating CP (as speci ?ed in 12.4.3.2.2 through12.4.3.2.5)it shall synchronize the startup to a half or whole bit-cellboundary of any immediately preceding signal.If it was sending IDLimmediately before the CP,no synchronization or preamble is required.A hub may start transmission of CP at any point in the sequence that doesnot result in periods of more thanone bit time without a transition during the switch from passing on data tosending CP.Depending on thepreceding signal,it may start with L010H,010HL,10HL0,0HL01,or HL010.Becausestartup may be synchronized to any half-bit-cell boundary,a hub may alsotransmit the shifted ersion of CP starting with1LH10,LH101,H101L,101LH,or 01LH1.********************************************ANSI/IEEE Std 802.1D, 1998 EditionPart 3: Media Access Control (MAC) Bridges6. Support of the MAC ServiceMAC Bridges interconnect the separate IEEE 802 LANs that comprise a BridgedLAN by relaying and filteringframes between the separate MACs of the Bridged LAN.The position of thebridging function withinthe MAC Sublayer is shown in Figure 6-1.Figure 6-1-Internal organization of the MAC SublayerThis clause discusses the following aspects of service provision in BridgedLANs:a) Provision of the MAC Service to end stations; Preservation of the MAC Service;c) Maintenance of Quality of Service;d) Provision of the internal sublayer service within the MAC Bridge;e) Support of the Internal Sublayer Service by specific MAC procedures;f) Filtering services.6.5.1 Support by IEEE Std 802.3 (CSMA/CD)The CSMA/CD access method is specified in IEEE Std 802.3. Clause 3 of thatstandard specifies the MACframe structure, and Clause 4 specifies the MAC method.On receipt of an M_UNITDATA.request primitive, the local MAC Entityperforms Transmit Data Encapsulation,assembling a frame using the parameters supplied as specified below. Itprepends a preamble and aStart Frame Delimiter before handing the frame to the Transmit Media AccessManagement Component inthe MAC Sublayer for transmission (IEEE Std 802.3, 4.2.3).On receipt of a MAC frame by Receive Media Access Management, the MAC frameis passed to ReceiveData Decapsulation, which validates the FCS and disassembles the frame, asspecified below, into theparameters that are supplied with an M_UNITDATA.indication primitive (IEEEStd 802.3, 4.2.4).The frame_type parameter takes only the value user_data_frame and is notexplicitly encoded in MACframes.The mac_action parameter takes only the value request_with_no_response andis not explicitly encoded inMAC frames.The destination_address parameter is encoded in the destination addressfield of the MAC frame (IEEE Std802.3, 3.2.3).The source_address parameter is encoded in the source address field of theMAC frame (IEEE Std802.3, 3.2.3).The number of octets in the mac_service_data_unit parameter is encoded inthe length field of the MACframe (IEEE Std 802.3, 3.2.6), and the octets of data are encoded in thedata field (IEEE Std 802.3, 3.2.7).The user_priority parameter provided in a data request primitive is notencoded in MAC frames. Theuser_priority parameter provided in a data indication primitive takes thevalue of the Default User Priorityparameter for the Port through which the MAC frame was received (see 6.4).The frame_check_sequence parameter is encoded in the FCS field of the MACframe (IEEE Std 802.3,3.2.8). The FCS is computed as a function of the destination address,source address, length, data, and PADfields. If an M_UNITDATA.request primitive is not accompanied by thisparameter, it is calculated in accordancewith IEEE Std 802.3, 3.2.8.NOTE 1-Since the PAD field, if present, contributes to the FCS, thisparameter needs to include at least the contributionof the PAD field to the FCS in order for the original FCS to be preserved(See Annex G).No special action, above that specified for the support of use of the MACService by LLC, is required for thesupport of the MAC Internal Sublayer Service by the CSMA/CD access method.NOTE 2-The support by IEEE Std 802.3 is described only in terms of theoperation of a Bridge when relaying framesthat result from the use of LLC services over an 802.3 MAC. ISO/IEC 11802-5defines the recommended practice forbridging Ethernet V2.0 frames.NOTE 3-IEEE Std 802.3, 1998 Edition, describes the use of either a Lengthor an Ethernet protocol type in its frameformat; however, the text of this subclause has yet to be revised todescribe the use of Ethernet protocol types.6.6 Filtering services in Bridged LANsMAC Bridges provide filtering services in Bridged LANs that support someaspects of the maintenance ofQuality of Service; in particular, transit delay, priority, and throughput.In addition, these services providefor a degree of administrative control over the propagation of particularMAC Addresses in the BridgedLAN.The services described are services in the most general sense; i.e., theyare descriptions of the functionalitythat are made available to the MAC Service user or an administrator inorder to control and access filteringcapabilities in Bridged LANs. The description of each service makes noassumptions in terms of how theservice might be realized. There are at least the following possibilities:a) Use of existing protocols and mechanisms, defined in IEEE 802 standardsand elsewhere; Use of management functionality, either locally defined or implementedvia remote managementprotocols;c) Other means, standardized or otherwise.6.6.1 Purpose(s) of filtering service provisionFiltering services are provided in Bridged LANs for the purposes describedin the following subclauses.6.6.7.1 Dynamic registration and de-registration servicesThese services allow MAC Service users dynamic control over the set ofdestination Group MAC Addressesthat they will receive from the MAC Service provider, bya) Registering/de-registering membership of specific Groups associated withthose addresses; Registering/de-registering their service requirements with regard to theoverall forwarding/filteringbehavior for Groups.Provision of these services is achieved by means of GMRP and its associatedprocedures, as described inClause 10.NOTE-The intent of these services is to provide the MAC Service user withdynamic control over access to multicastdata streams, for example, multiple video channels made available by aserver using a different group MAC Address foreach channel. The ability to both register and de-register Groupmembership, coupled with the filtering action associatedwith the Group membership, limits the impact of such services on thebandwidth available in the Bridged LAN. Theseservices can be used to control the reception of other categories ofmulticast traffic, for similar reasons.REGISTER_GROUP_MEMBER (MAC_ADDRESS)Indicates to the MAC Service provider that the MAC Service user wishes toreceive frames containing thegroup MAC Address indicated in the MAC_ADDRESS parameter as the destinationaddress. The MACAddresses that can be carried by this parameter do not includea) Any individual address; Any of the Reserved Addresses identified in Table 7-9;c) Any of the GARP Application addresses, as defined in Table 12-1.DEREGISTER_GROUP_MEMBER (MAC_ADDRESS)Indicates to the MAC Service provider that the end station no longer wishesto receive frames containing thegroup MAC Address indicated in the MAC_ADDRESS parameter as the destinationaddress.REGISTER_SERVICE_REQUIREMENT (REQUIREMENT_SPECIFICATION)Indicates to the MAC Service provider that the MAC Service user has arequirement for any devices thatsupport Extended Filtering Services to forward frames in the direction ofthe Mac Service User in accordancewith the definition of the service requirement defined by theREQUIREMENT_SPECIFICATIONparameter. The values that can be carried by this parameter area) Forward All Groups; Forward Unregistered Groups.DEREGISTER_SERVICE_REQUIREMENT (REQUIREMENT_SPECIFICATION)Indicates to the MAC Service provider that the MAC Service user no longerhas a requirement for anydevices that support Extended Filtering Services to forward frames in thedirection of the Mac Service Userin accordance with the definition of the service requirement defined by theREQUIREMENT_SPECIFICATION parameter. The values that can be carried by thisparameter area) Forward All Groups; Forward Unregistered Groups.The use of these services can result in the propagation of group MACAddress and service requirementinformation acROSs the Spanning Tree, affecting the contents of GroupRegistration Entries (7.9.3) in Bridgesand end stations in the Bridged LAN, and thereby affecting the frameforwarding behavior of the Bridgesand end stations with regard to multicast frames.7.1 Bridge operationThe principal elements of Bridge operation area) Relay and filtering of frames. Maintenance of the information required to make frame filtering andrelaying decisions.c) Management of the above.7.1.1 RelayA MAC Bridge relays individual MAC user data frames between the separateMACs of the Bridged LANsconnected to its Ports. The order of frames shall be preserved as definedin 7.7.3.The functions that support the relaying of frames and maintain the Qualityof Service supported by theBridge area) Frame reception. Discard on received frame in error (6.3.2).c) Frame discard if the frame_type is not user_data_frame, or if itsmac_action parameter is notrequest_with_no_response (6.4).d) Regeneration of user priority, if required (6.4).e) Frame discard following the application of filtering information.f) Frame discard on transmittable service data unit size exceeded (6.3.8).g) Forwarding of received frames to other Bridge Ports.h) Selection of traffic class, following the application of filteringinformation.i) Queuing of frames by traffic class.j) Frame discard to ensure that a maximum bridge transit delay is notexceeded (6.3.6).k) Selection of queued frames for transmission.l) Selection of outbound access priority (6.3.9).m) Mapping of service data units and recalculation of Frame Check Sequence,if required (6.3.7, 7.7.6).n) Frame transmission.7.1.2 Filtering and relaying informationA Bridge filters frames, i.e., does not relay frames received by a BridgePort to other Ports on that Bridge, inorder to prevent the duplication of frames (6.3.4). The function thatsupports the use and maintenance ofinformation for this purpose isa) Calculation and configuration of Bridged LAN topology.A Bridge also filters frames in order to reduce traffic in parts of theBridged LAN that do not lie in the pathbetween the source and destination of that traffic. The functions thatsupport the use and maintenance ofinformation for this purpose are: Permanent configuration of reserved addresses.c) Explicit configuration of static filtering information.d) Automatic learning of dynamic filtering information for unicastdestination addresses through observationof source addresses of Bridged LAN traffic.e) Ageing out of dynamic filtering information that has been learned.f) Automatic addition and removal of dynamic filtering information as aresult of GMRP protocolexchanges.A Bridge classifies frames into traffic classes in order to expeditetransmission of frames generated by criticalor time-sensitive services. The function that supports the use andmaintenance of information for thispurpose isg) Explicit configuration of traffic class information associated with thePorts of the Bridge.7.1.3 Bridge ManagementThe functions that support Bridge Management control and monitor theprovision of the above functions.They are specified in Clause 14.7.2 Bridge architecture7.2.1 Architectural model of a BridgeFigure 7-1 gives an example of the physical topology of a Bridged LAN. Thecomponent LANs are interconnectedby means of MAC Bridges; each Port of a MAC Bridge connects to a singleLAN. Figure 7-2 illustratesa Bridge with two Ports, and Figure 7-3 illustrates the architecture ofsuch a Bridge.A Bridge is modeled as consisting ofa) A MAC Relay Entity that interconnects the Bridge’s Ports; At least two Ports;c) Higher layer entities, including at least a Bridge Protocol Entity.7.2.2 MAC Relay EntityThe MAC Relay Entity handles the MAC method independent functions ofrelaying frames between BridgePorts, filtering frames, and learning filtering information. It uses theInternal Sublayer Service provided bythe separate MAC Entities for each Port. (The Internal Sublayer Service andits support are described in 6.4and 6.5.) Frames are relayed between Ports attached to different LANs.7.2.3 PortsEach Bridge Port transmits and receives frames to and from the LAN to whichit is attached. An individualMAC Entity permanently associated with the Port provides the InternalSublayer Service used for frametransmission and reception. The MAC Entity handles all the MAC methoddependent functions (MAC protocoland procedures) as specified in the relevant standard for that IEEE 802 LANMAC technology.7.5 Frame receptionThe individual MAC Entity associated with each Bridge Port examines allframes transmitted on the LAN towhich it is attached.All error-free received frames give rise to M_UNITDATA indicationprimitives, which shall be handled asfollows.NOTE-A frame that is in error, as defined by the relevant MACspecification, is discarded by the MAC Entity withoutgiving rise to any M_UNITDATA indication; see 6.4.Frames with M_UNITDATA.indication primitive frame_type and mac_actionparameter values ofuser_data_frame and request_with_no_response, respectively (6.4), shall besubmitted to the Learning andForwarding Processes.Frames with other values of frame_type and mac_action parameters (e.g.,request_with_response and responseframes), shall not be submitted to the Forwarding Process. They may besubmitted to the Learning Process.Frames with a frame_type of user_data_frame and addressed to the BridgePort as an end station shall besubmitted to LLC. Such frames carry either the individual MAC Address ofthe Port or a group address associatedwith the Port (7.12) in the destination address field. Frames submitted toLLC can also be submitted tothe Learning and Forwarding Processes, as specified above.Frames addressed to a Bridge Port as an end station, and relayed to thatBridge Port from other Bridge Portsin the same Bridge by the Forwarding Process, shall also be submitted toLLC.No other frames shall be submitted to LLC.7.6 Frame transmissionThe individual MAC Entity associated with each Bridge Port transmits framessubmitted to it by the MACRelay Entity.Relayed frames are submitted for transmission by the Forwarding Process.The M_UNITDATA.requestprimitive associated with such frames conveys the values of the source anddestination address fieldsreceived in the corresponding M_UNITDATA.indication primitive.LLC Protocol Data Units are submitted by LLC as a user of the MAC Serviceprovided by the Bridge Port.Frames transmitted to convey such Protocol Data Units carry the individualMAC Address of the Port in thesource address field.Each frame is transmitted subject to the MAC procedures to be observed forthat specific IEEE 802 LANtechnology. The values of the frame_type and mac_action parameters of thecorresponding M_UNITDATA.request primitive shall be user_data_frame and request_with_no_response,respectively (6.5).Frames transmitted following a request by the LLC user of the MAC Serviceprovided by the Bridge Portshall also be submitted to the MAC Relay Entity.7.7 The Forwarding ProcessFrames submitted to the Forwarding Process after being received at anygiven Bridge Port (7.5) shall be forwardedthrough the other Bridge Ports subject to the constituent functions of theForwarding Process. Thesefunctions enforce topology restrictions (7.7.1), use filtering databaseinformation to filter frames (7.7.2),queue frames (7.7.3), select queued frames for transmission (7.7.4), mappriorities (7.7.5), and recalculateFCS if required (7.7.6).The Forwarding Process functions are described in 7.7.1-7.7.6 in terms ofthe action taken for a given framereceived on a given Port (termed “the reception Port”). The frame can beforwarded for transmission onsome Ports (termed “transmission Ports”), and is discarded without beingtransmitted at the other Ports.NOTE-The model of operation of the Forwarding Process described in thisstandard is limited to the operation of therelay function of the MAC Bridge, and does not take into consideration whatmay occur in real implementations onceframes are passed to the MAC for transmission. In some MAC implementations,and under some traffic conditions, adegree of indeterminacy may be introduced between the modeled descriptionof the process of passing selected frames tothe MAC for transmission and the actual sequence of frames as visible onthe LAN medium itself. Examples can befound in the handling of access_priority in Token-Passing Bus MACs, or inthe effect of different values for Token HoldingTime in FDDI LANs. Such indeterminacy could result in apparent violation ofthe queuing/de-queueing and prioritiationrules described for the Forwarding Process, when observing traffic on themedium. As a consequence, in someimplementations of this standard, it may prove to be impossible to testconformance to the standard simply by relatingobserved LAN traffic to the described model of the Forwarding Process;conformance tests would have to allow for the(permissible) behavior of the MAC implementations as well.Figure 7-4 illustrates the operation of the Forwarding Process in a singleinstance of frame relay between thePorts of a Bridge with two Ports. Figure 7-8 illustrates the detailedoperation of the Forwarding Process.7.8 The Learning ProcessThe Learning Process observes the source addresses of frames received oneach Port and updates the FilteringDatabase conditionally on the state of the receiving Port.Frames are submitted to the Learning Process by the individual MAC Entitiesassociated with each BridgePort as specified in 7.5.The Learning Process may deduce the path through the Bridged LAN toparticular end stations by inspectionof the source address field of received frames. It shall create or update aDynamic Filtering Entry (7.9, 7.9.2)in the Filtering Database, associating the Port on which the frame wasreceived with the MAC Address in thesource address field of the frame, if and only ifa) The Port on which the frame was received is in a state that allowslearning (8.4), and The source address field of the frame denotes a specific end station,i.e., is not a group address, andc) No Static Filtering Entry (7.9, 7.9.1) for the associated MAC Addressexists in which the Port Mapspecifies Forwarding or Filtering for that Port, andd) The resulting number of entries would not exceed the capacity of theFiltering Database.If the Filtering Database is already filled up to its capacity, but a newentry would otherwise be made, then anexisting entry may be removed to make room for the new entry.Figure 7-5 illustrates the operation of the Learning Process in theinclusion of station location informationcarried by a single frame, received on one of the Ports of a Bridge, in theFiltering Database.7.9 The Filtering DatabaseThe Filtering Database supports queries by the Forwarding Process as towhether frames received by theForwarding Process from a given reception Port, and with given values ofdestination MAC Address parameter,are to be forwarded through a given potential transmission Port (7.7.1,7.7.2). It contains filtering informationin the form of filtering entries that are eithera) Static, and explicitly configured by management action; or Dynamic, and automatically entered into the Filtering Database by thenormal operation of thebridge and the protocols it supports.A single entry type, the Static Filtering Entry, represents all staticinformation in the Filtering Database, forindividual and for group MAC Addresses. It allows administrative control ofc) Forwarding of frames with particular destination addresses; andd) The inclusion in the Filtering Database of dynamic filtering informationassociated with ExtendedFiltering Services, and use of this information.The Filtering Database shall contain entries of the Static Filtering Entrytype.Static filtering information is added to, modified, and removed from theFiltering Database only underexplicit management control. It shall not be automatically removed by anyageing mechanism. Managementof static filtering information may be carried out by use of the remotemanagement capability provided byBridge Management (7.11) using the operations specified in Clause 14.Two entry types are used to represent dynamic filtering information.Dynamic Filtering Entries are used tospecify the ports on which individual addresses have been learned. They arecreated and updated by theLearning Process (7.8), and are subject to ageing and removal by theFiltering Database. Group RegistrationEntries support the registration of group MAC Addresses. They are created,updated, and removed by theGMRP protocol in support of Extended Filtering Services (6.6.5, 7.9.3, andClause 10). Dynamic filteringinformation may be read by use of the remote management capability providedby Bridge Management(7.11) using the operations specified in Clause 14.Both static and dynamic entries comprisee) A MAC Address specification;f) A Port Map, with a control element for each outbound Port to specifyfiltering for the MAC Addressspecification.The Filtering Services supported by a Bridge (Basic and Extended FilteringServices) determine the defaultbehavior of the Bridge with respect to the forwarding of frames destinedfor group MAC Addresses. InBridges that support Extended Filtering Services, the default forwardingbehavior of each Port for groupMAC Addresses can be configured both statically and dynamically by means ofStatic Filtering Entries and/or Group Registration Entries that can carry the following MAC Addressspecifications:g) All Group Addresses, for which no more specific Static Filtering Entryexists;h) All Unregistered Group Addresses (i.e., all group MAC Addresses forwhich no Group RegistrationEntry exists), for which no more specific Static Filtering Entry exists.NOTE-The All Group Addresses specification (item g above), when used in aStatic Filtering Entry with an appropriatecontrol specification, provides the ability to configure a Bridge thatsupports Extended Filtering Services to behave as aBridge that supports only Basic Filtering Services on some or all of itsPorts. This might be done for the following reasons:- The Ports concerned serve “legacy” devices that wish to receivemulticast traffic, but are unable to register Groupmembership;- The Ports concerned serve devices that need to receive all multicasttraffic, such as routers or diagnostic devices.The Filtering Database shall support the creation, updating, and removal ofDynamic Filtering Entries by theLearning Process (7.8). In Bridges that support Extended FilteringServices, the Filtering Database shallsupport the creation, updating, and removal of Group Registration Entriesby GMRP (Clause 10).Figure 7-4 illustrates the use of the Filtering Database by the ForwardingProcess in a single instance offrame relay between the Ports of a Bridge with two Ports.Figure 7-5 illustrates the creation or update of a dynamic entry in theFiltering Database by the LearningProcess.Figure 7-6 illustrates the operation of the Bridge Protocol Entity (7.10),which operates the Spanning TreeAlgorithm and Protocol, and its notification of the Filtering Database ofchanges in active topology signaledby that protocol.7.12.1 End stationsFrames transmitted between end stations using the MAC Service provided by aBridged LAN carry theMAC Address of the source and destination peer end stations in the sourceand destination address fields ofthe frames, respectively. The address, or other means of identification, ofa Bridge is not carried in framestransmitted between peer users for the purpose of frame relay in theBridged LAN.The broadcast address and other group MAC Addresses apply to the use of theMAC Service provided by aBridged LAN as a whole. In the absence of explicit filters configured viamanagement as Static FilteringEntries, or via GMRP as Group Registration Entries (Clause 14, Clause 10,7.9), frames with such destinationaddresses are relayed throughout the Bridged LAN.7.12.2 Bridge PortsThe individual MAC Entity associated with each Bridge Port shall have aseparate individual MAC Address.This address is used for any MAC procedures required by the particular MACmethod employed.Frames that are received from the LAN to which a Port is attached and thatcarry a MAC Address for thePort in the destination address field are submitted to the MAC Service User(LLC) exactly as for an endstation.******************************************************有?多人?如弟?不是很喜?看文件?但就算看得懂文件?如何整理出??向大家?明白?看?比起看文件更??-----------?源: ?石 ??: 2001年 6月16日 周六 08?23分29秒 CST??: Re: ?能麻?一下，解?switch hub和hub的差?...@@"??: tw.bbs.comp.network==> 在 Toidi@cis_nctu (白?小孩) 的文章中提到:> ==> 在 siklo@cis_nctu (小翅膀) 的文章中提到:> > VLAN 要能通，是 Layer 3 的 Switch, 你用的哪牌子 Layer 2 Switch> > 上切 VLAN 是可以互通的?>???? 之所以切 VLAN 不就是要? VLAN 彼此之?分?...>???? 你互通的定?是什?可以?清楚一???>???? 我手上就有一台 VLAN 正常?#092;作的 switch hubL3 Switch ?有?outing Module，互通??就是指透? L3 Swtich 上的 Routing Module，而不需要?每? VLan 上找一? Port uplink 到上?的 Switch或是直接接到 Router 上，以?到 VLan 互通吧！--------?源: ?石 ??: 2001年 6月16日 周六 18?24分15秒 CST??: Re: ?能麻?一下，解?switch hub和hub的差?...@@"??: tw.bbs.comp.network==> 在 siklo@cis_nctu (小翅膀) 的文章中提到:> ==> 在 Toidi@cis_nctu (白?小孩) 的文章中提到:> >???? 不??在是 Layer 2 的 Switch> >???? 不?有?? Module> >???? 所以 VLAN 本?就不能互通...> >???? ?也是 VLAN ??的目的啊> 小弟不懂..???做 VLAN 用 Layer 3 就可以 route 互通> 小弟在一般企?公司?中，?到的也都是用 Layer 3 Switch> 把各 VLAN 使用 route 方式互通。??VLAN 是在 L2 Switch 上就有了，L3 是後?有　　需要而且?? Router 太?了（想想看那?候　　Cisco 股?有多高！??那?生出?的就知道　　?！）而?展出?的，所以 VLAN 的目的就是　　把某些 Ports 跟其他 Ports “?清界限”！　　分成不同的 collision domain 呀！但是不同　　的 VLAN 之?真的可以“老死不相往?”?？　　抱?！同公司、?校、??………耶！所以要　　通的?候，就在 Layer 3 上做！最“??”的　　做法?然是在 Router 上“?送”，但是因?　　$$ 同?技??步了，所以 Switch 愈?愈?，　　就“?便”把??工作也做?～～～?就是　　Layer 3 Switch 了！> >???? 不??是可以把每? VLAN 的 uplink>???????????? ^^^^^^^^^^^^^^^^^^^^> 不懂??的?法..　　若你的 Switch 只有 Layer 2 的?，不 uplink??你的 VLAN 之?要怎?通？> >???? ?在同一? port 就可以了..> 看起?你?的很像是 port trunking 的方式　　Trunking 是 Trunking，跟 VLAN ???！外行人道???，有??高手指正?！--------?源: 老?少年心 ??: 2001年 6月17日 周日 02?05分50秒 CST??: Re: ?能麻?一下，解?switch hub和hub的差?...@@"??: tw.bbs.comp.network==> 在 hardstone@cis_nctu (?石) 的文章中提到:> ==> 在 siklo@cis_nctu (小翅膀) 的文章中提到:> >???????????? ^^^^^^^^^^^^^^^^^^^^> > 不懂??的?法..> 　　若你的 Switch 只有 Layer 2 的?，不 uplink>?? 你的 VLAN 之?要怎?通？> > 看起?你?的很像是 port trunking 的方式> 　　Trunking 是 Trunking，跟 VLAN ???！> 外行人道???，有??高手指正?！?????siklo?的?????有?trunking??字眼，你?如何去定?？???在Cisco?一派?，Trunking指的就是vlan port trunking???同一台switch?切割了??VLAN，而只有一????????至另一台也切割了?? VLAN的switch，??台switch中????只有一?????，我?就要在??port上?定VLAN Trunk???加上802.1q or ISL 的封?，才能???台的vlan information???可以互相?通，不同switch的同一?VLAN才能通???如VLAN1@SW1  VLAN1@SW2, VLAN2@SW1  VLAN2@SW2???以上是Cisco的"trunking"???而一般我??trunking可能是指Cisco的EtherChannel???也就是介於?switch??????路合???及做redudant的技????跟上面所述是完全不一?的?西，?明清楚可能?比?好----------?源: 死老百姓 ??: 2001年 6月17日 周日 15?20分22秒 CST??: Re: ?能麻?一下，解?switch hub和hub的差?...@@"??: tw.bbs.comp.network※ 引述《hardstone.bbs@bbs.cis.nctu.edu.tw (?石)》之?言：: 嗯～～～受教了！: ??！我所“??”的 trunking 是?合???的那一?！: Cisco 的 VLAN Trunking ?初也有??，不??看?有人: 在用，所以………port trunk(EtherChannel) 和 VLAN trunk 是??子事VLAN trunk 在 MAN 上面用的很多, 有?趣的可以去查查其它?商(eg. Extreme)的 solution, Cisco 在 switch 方?K不是特??.: ?得上那?把多台 Switch△?式圻?_?”，?如一台?: ?的 Switch 是?？基本上要? VLAN 延展到一台以上的??, 就需要 VLAN trunk?有一?可能性就是要?多? VLAN 透? router 互通, 也可以用 VLAN trunk: 我想要??做的原因，??是有一台 L3 Switch 做?是: backbone Switch，其下再接?台 L2 的 Switch，??子: 比?有意?吧！right??在的??是把 L2/L3 整合在一台上面, ??做的? VLAN 之?的互通不?有瓶?, 而且?度不高.---------?源: 羊大便?巧克力 ??: 2001年 6月18日 周一 00?28分32秒 CST??: Re: ?能麻?一下，解?switch hub和hub的差?...@@"??: tw.bbs.comp.network==> wchuang.bbs@bbs.cis.nctu.edu.tw (老?少年心) 提到:> ==> 在 hardstone@cis_nctu (?石) 的文章中提到:> > 　　若你的 Switch 只有 Layer 2 的?，不 uplink> >?? 你的 VLAN 之?要怎?通？> > 　　Trunking 是 Trunking，跟 VLAN ???！Trunking和VLAN有很大的??喔....不同的?路???商?於trunk有不同的??Intel的trunk????port聚集成一?group，如果是4?port做trunk，那??台switch之?的???400MB full-duplex，同?的技?Extreme?之?link aggregation，Cisco?之?Fast EtherChannel。Cisco的trunk是一?link上可以????VLAN的traffic，假?switch1有三?VLAN，switch2也有三?VLAN，vlan1@switch1想和vlan1@switch2?通?，最??的方法，就是三???分??接?台switch相??的三?vlan，但??方法太浪?port，解?方法就是?台switch各?一?port?定?trunk port，然後?起?，?一?trunk link就可以??三?vlan的traffic(set trunk 1 on 1-3)，?上就省下??port。但??止於相同vlan之?的?通。如果vlan1想和vlan2?通的?，就必?要靠router或者是multilayer switch??行routing的功能。如果是Extreme switch的?，一行指令ip forwarding就搞定，如果是cisco switch的?，就必?加?route switching module。?然cisco的switch不是?好，但是如果向市?主流看?的?，那?trunk和vlan之?密不可分的??就不可不知。by the way，CCNP中的BCMSN一科就考了相?多的trunk and vlan的?念。--------?源: 夜班火? ??: 2001年 6月18日 周一 16?19分18秒 CST??: Re: ?能麻?一下，解?switch hub和hub的差?...@@"??: tw.bbs.comp.network《 在 shinlong. 的大作中提到: 》: ??你?~@@"...: 我查?上篇都?有?...>" 提出一?建?，?路的世界何其之大，有?不完的?定，日新月?的硬?技?，> ?奇不有的?路架?，大家在?????彼此?心的交流，不要以??嘲弄的??> ?回?。> ==> siklo.bbs@bbs.cis.nctu.edu.tw (小翅膀) 提到:> > ==> 在 airborne.bbs@bbs.ntu.edu.tw (羊大便?巧克力) 的文章中提到:> > > 基本上??，meeds兄的解???有?。> > > 在???????，除了Ethernet的存取方式外，?需注意switch硬?的function，> > > switch再?理traffic?基本上有??模式，store-and-forward和cut-through，> > ?有????你的乙太?路?? Switch 哪一款式能?? b,c,d,e 同?去存取 a 啊?> > > 不?何?模式，?b,c,d,e同?存取a?，一?始b,c,d,e都可以充分利用10mbps的??，> > ?就是笑?了, ?都知道在乙太?路?面 b,c,d,e 是不可能同?存取 a 的> > 你居然?能充分利用 10Mbps 的??? 你的 Switch 超猛的?@_@> 可能是我表?的不?清楚，所?bcde同?存取a，指的是在initializing的?候，> bcde同??traffic?a，traffic?然是先到switch，再由switch forward?a，> ?然switch不可能把bcde的packet同???a，一定是packet-by-packet> (以process-switching??，先不予考?fast-switching的情?)。> > ?接到下面?段, 居然掰出 b,c,d,e 一共灌了 40Mbps ? a 的笑?~~> ?容?我?明白一?，所?bcde灌了40mbps?a的意思是，bcde?共有40mbps的> traffic?到switch backplane fabric，然而port A的bandwidth只有10mbps，> ?然?法消化switch backplane?的40mbps traffic，所以剩下的traffic就> 存在port A的output queue?面，?output queue的buffer?了(oversubscription)，> packet?始被drop。> > > b,c,d,e一共40mbps的traffic流到a port的buffer?理，但??上a port的??> > > 也只有10mbps，所以a port的buffer?了，data?始被drop，同?因?a port的loading> > > 超出?荷，switch也?在b,c,d,e port?出notification，使得b,c,d,e四台?器> > > ???料送出的速度，因此?b,c,d,e同?存取a?，意味著b,c,d,e共同share a的10mbps> > > 以?期看?，b,c,d,e??只能使用2.5mbps。> > 上面?一段是你掰的吧~~?笑痛我了..> ?一段本人的???不??，在此??抱歉。但我可??掰！！！> 所?的port B,C,D,E??出notification，指的是IEEE 802.3Z flow control on> gigabit ethernet port，cisco catalyst 6000 switch支援，> ??考：> http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000> /sw5_1/cnfigide/ether.htm#xtocid1934811> 就算今天我?的switch?有flow control好了，???，我??有TCP，> TCP?算有error control和flow control了吧，a必??b的packet?理完後，> 回??b一?ack，b才?????料?a，?一?微?的角度?看，第一秒?理b,> 第二秒?理c，第三秒?理d，第四秒?理e，第五秒才能再?理b，?b的角度?看，> 四秒?只有一秒能??料(a?b一?ack，b才????)，相???，??只用了1/4。> TCP/IP的?#092;作????考：> http://www.cisco.com/univercd/cc/td/doc/ci...m#xtocid2236316> > > > 但??不代表剩下的7.5mbps平白?故消失，7.5mbps?是可以?#092;用在> > > 其他的traffic pattern，譬如上internet或是存取另外一?f。> > 哇 @_@?更猛!?以上的笑?已??爆笑了, 居然?可以掰出被 drop 的?料?有其他> > ?#092;用咧~~> > 哪?半路跑???掰?笑?的??大家看看笑笑就好?哈?我笑痛了..> ?容?我?的更明白一?，> ??所?的被drop的?料指的是b??a的?料，> ?port A 的output queue overflow之後被drop的，而B->A的traffic flow> 只用到2.5mbps的utilization，port B的bandwidth有10mbps，但由於port A> 的??，使得B->A只能用2.5mbps，那剩下的7.5mbps?然可以用於其他的> traffic pattern，?的再??一?，就是一秒??料?a，三秒??料到internet> (假??人跟他?internet)，如此便可?port B的utilization?到100%。> 因此，在Design Network?，通常??取hierarchical design，access layer> ?用10或100，distribution lay?用100或1000，如此作?access layer流量> 聚集?的distribution layer方能有效率的?理四面八方?聚?的traffic。> > 如果你?是不能?同我的?法，或?你可以?考?考Cisco出版的> CCNP/CCDP--Building Cisco Multilayer Switched Networks(P.56-59)> 天??局有。---------- wrote in message news:3h2I7G$W1g@bbs.cis.nctu.edu.tw...> ==> 在 siklo@cis_nctu (小翅膀) 的文章中提到:> > ==> 在 airborne.bbs@bbs.ntu.edu.tw (羊大便?巧克力) 的文章中提到:> > > 基本上??，meeds兄的解???有?。> > > 在???????，除了Ethernet的存取方式外，?需注意switch硬?的function，> > > switch再?理traffic?基本上有??模式，store-and-forward和cut-through，> > ?有????你的乙太?路?? Switch 哪一款式能?? b,c,d,e 同?去存取 a 啊?> > > 不?何?模式，?b,c,d,e同?存取a?，一?始b,c,d,e都可以充分利用10mbps的??，> >???????? ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^> > ?就是笑?了, ?都知道在乙太?路?面 b,c,d,e 是不可能同?存取 a 的> > 你居然?能充分利用 10Mbps 的??? 你的 Switch 超猛的?@_@> > ?接到下面?段, 居然掰出 b,c,d,e 一共灌了 40Mbps ? a 的笑?~~> > airbone兄?的??> 你所?的乙太?路是指之前的 coaxial cable (10base2,10base5)> 那?的shared LAN, 所以主?使用?一channel去?行communication.> 所以在MAC?是?取CSMA/CD的方式.?句??,同??只有> ?一主?能使用?路.否??有collision. 可是 自?有了switch 及 UTP 後,?一> shared medium的限制也被移除,(使用UTP有四??,10baseT和100baseTX是使用其中??> TX/RX)也?始有了全?工的名?> full-duplex 是移除三?早期ethernet的特性> 1.carrier sense: full-duplex 下,主?不需要??carrier ??> 2.multiple access: 因?Host跟switch之?可以分?用TX/RX互相??料> 3.collision detection: 同上,因?分?用TX/RX??料也就?有collision的情??生> > ?句??,在ful-duplex之下,已??有CSMA/CD> 所以b,c,d,e如果要??料?a ?,理?上可以到??速(只有在??始那微小的????)> 所以data 都在放在output queue?(假?是使用store-and-forward方式),switch?了防止> buffer overflow,它可以?始drop packets,如果b,c,d,e上?是使用TCP等有flow control> 的protocol, 上?的protocol?因?packet loss而?整packet送到data link的速度.> 或者switch也可以送出 PAUSE Frame(full-duplex?,?於MAC?),?sending host降低?送> 速度.> > > > b,c,d,e一共40mbps的traffic流到a port的buffer?理，但??上a port的??> > > 也只有10mbps，所以a port的buffer?了，data?始被drop，同?因?a port的loading> > > 超出?荷，switch也?在b,c,d,e port?出notification，使得b,c,d,e四台?器> > > ???料送出的速度，因此?b,c,d,e同?存取a?，意味著b,c,d,e共同share a的10mbps> > > 以?期看?，b,c,d,e??只能使用2.5mbps。> > 上面?一段是你掰的吧~~?笑痛我了..> > > 但??不代表剩下的7.5mbps平白?故消失，7.5mbps?是可以?#092;用在> > > 其他的traffic pattern，譬如上internet或是存取另外一?f。> > 哇 @_@?更猛!?以上的笑?已??爆笑了, 居然?可以掰出被 drop 的?料?有其他> > ?#092;用咧~~> > -----------> > 哪?半路跑???掰?笑?的??大家看看笑笑就好?哈?我笑痛了..> airbone?兄?的??> 如果 a 跟 b互?,在100base-TX, full-duplex下???可以?到200Mbps.可是?不是?> a --> b = 200Mbps 或 b --> a = 200Mbps 或 a -> b + b -> a = 200Mbps&g

DreamCat

长了点，不过后面的争吵确实有意思。想必很多朋友还不是很清楚 HUB 和 SWITCH 之间的区别吧？不知道大家看完了有什么感想。。。

貪玩的風箏

????之前我也不了解但前段??苦?“Windows2003大全”?本?（?色封面）??些??已???了很多其?...我?得我的同行之中 很多都是在浪?青春混日子?然?吧的工作比?????但我?得?事?是??多看看? ?修一下

ycfei

不好看。。