chp4以太網(wǎng)和交換原理.ppt

以太網(wǎng)和交換原理,教學(xué)目標(biāo)（ Objectives ）,1.Ethernet Fundaments(以太網(wǎng)基礎(chǔ)) 2.Ethernet Operation（以太網(wǎng)操作） 3.10-Mbps and 100-Mbps Ethernet 4.Gigabit and 10-Gigabit Ethernet 5. 交換機學(xué)習(xí)主機地址 （Switche Learn Host Address） 6. 兩種交換方法（Two Switching Methods）,局域網(wǎng)的特點(Character of LAN),1.覆蓋的地理范圍有限; 2.高數(shù)據(jù)傳輸率、低誤碼率、高質(zhì)量的數(shù)據(jù)傳輸環(huán)境； 3.一般屬于一個單位，易建立、維護和擴展 4.決定特性的主要技術(shù)要素：網(wǎng)絡(luò)拓?fù)洹鬏斀橘|(zhì)、介質(zhì)訪問控制方法； 5.從介質(zhì)訪問控制方法的角度可分兩類：共享介質(zhì)局域網(wǎng)和交換式局域網(wǎng)。,局域網(wǎng)的技術(shù)特征,局域網(wǎng)（LAN）的特征是：所有節(jié)點借助于第二層地址（ MAC地址）就能互相直接通信，而不必通過某種第三層或更高層的設(shè)備（例如路由器）進行轉(zhuǎn)發(fā)（高層若存在則設(shè)備另有作用） 。,局域網(wǎng)的分類(class of LAN),決定局域網(wǎng)特性的四個方面：網(wǎng)絡(luò)拓?fù)洹鬏斀橘|(zhì)、信息傳輸方法、介質(zhì)訪問控制方法 按網(wǎng)絡(luò)拓?fù)浞诸悾嚎偩€形、環(huán)形、星形； 按傳輸介質(zhì)分類：雙絞線、同軸電纜、光纖、無線等 按信息傳輸方法分類：基帶、寬帶 按介質(zhì)訪問控制方法分類：載波偵聽多路訪問/沖突檢測(CSMA/CD)、令牌總線(Token Bus)、令牌環(huán)(Token Ring),局域網(wǎng)的發(fā)展歷史(History of LAN),1969 年廣域網(wǎng) ARPAnet 研制成功 (是個廣域網(wǎng)) 當(dāng)時許多大學(xué)和研究機構(gòu)的工作人員都在致力于研究如何在一個比較小的地理范圍之內(nèi)，辟如說一個實驗室、辦公室或一棟樓房，把一些小型機等計算機設(shè)備通過通信設(shè)施連接起來，以便共享資源,發(fā)展過程(Evolution),1969 年，美國貝爾實驗室研究了 Newhall 環(huán)形局域網(wǎng) 1972 年開發(fā)了 Pierce 環(huán)形網(wǎng)絡(luò) 1974 年英國劍橋大學(xué)計算機研究室研究成功了著名的劍橋環(huán)局域網(wǎng)（Cambridge-Ring） 1976年美國 Xerox 公司 Palo Alto 研究中心利用夏威夷大學(xué) ALOHA 無線電網(wǎng)絡(luò)系統(tǒng)原理成功開發(fā)了以太網(wǎng)（Ethernet） 1980 年美國DEC 公司 、Intel 公司和Xerox 公司聯(lián)合公布了以太規(guī)范 DIX 標(biāo)準(zhǔn)（局域網(wǎng)發(fā)展的里程碑） 1985 年 IBM 公司又推出了它的 IBM Token Ring 環(huán)形局域網(wǎng)產(chǎn)品,從產(chǎn)品化到標(biāo)準(zhǔn)(standard),進入80 年代，局域網(wǎng)的研制工作開始由實驗室走向產(chǎn)品化和標(biāo)準(zhǔn)化的階段 1980 年 2 月，IEEE(電子電器工程師協(xié)會) 學(xué)會下屬的 802 局域網(wǎng)標(biāo)準(zhǔn)委員會宣告成立（開始對局域網(wǎng)進行標(biāo)準(zhǔn)化） 從1980年至今，802 委員會已陸續(xù)制定了環(huán)網(wǎng)、總線網(wǎng)、令牌總線網(wǎng)、光纖網(wǎng)、寬帶網(wǎng)、城域網(wǎng)和無線網(wǎng)等多種局域網(wǎng)標(biāo)準(zhǔn),Evolution of Ethernet in 1990s,速度從10Mb/s發(fā)展到100Mb/s 繼之又發(fā)展到1Gb/s即千兆以太網(wǎng) 使得以太網(wǎng)形成了從共享到交換；從半雙工到全雙工；從桌面到骨干；從局域網(wǎng)到城域網(wǎng)的系列技術(shù) 令牌環(huán)網(wǎng)逐漸失去了其應(yīng)有的市場 FDDI環(huán)形網(wǎng)在局域骨干網(wǎng)領(lǐng)域也失去了與以太網(wǎng)的競爭力 寬帶網(wǎng)ATM曾以其信元交換的特性與以太網(wǎng)在局域網(wǎng)領(lǐng)域競爭，最后也被淘汰出局,以太網(wǎng)(Ethernet)1,10Base5的含義： 10-傳輸速率為10Mbps base-基帶傳輸 5-單個網(wǎng)段最長距離是500m,以太網(wǎng)(Ethernet)2,細(xì)纜以太網(wǎng)的連接器為型頭。 10Base2以太網(wǎng)最多30部機器、最長185米。,以太網(wǎng)(Ethernet)3,T:表示雙絞線，單段最常傳輸距離100米 10Base5，10BASE2,10BASET稱為傳統(tǒng)以太網(wǎng)。,以太網(wǎng)(Ethernet)4,傳統(tǒng)以太網(wǎng)比較,Introduction to Ethernet(1),Ethernet and the OSI Model(1),Ethernet and the OSI Model(2),Ethernet operates in two areas of the OSI model, the MAC sublayer and the physical layer. A collision domain is then a shared resource. Stations separated by repeaters are within the same collision domain. Stations separated by bridges or routers are in different collision domains.,MAC and LLC,The MAC sublayer is concerned with the physical components that will be used to communicate the information. The Logical Link Control (LLC) sublayer remains relatively independent of the physical equipment that will be used for the communication process.,MAC Address,Layer 2 Framing,Framing is the Layer 2 encapsulation（封裝） process. A frame is the Layer 2 protocol data unit.,Start frame field Address field Length / type field Data field Frame check sequence field,Ethernet Frame Structures,MAC Rules and Collision Detection/Backoff(2),10BASE5 Architecture (1),5-4-3-2-1,10BASE2 Network Design Limits,There may be up to 30 stations on any individual 10BASE2 segment.,10BASE-T,10BASE-T used UTP copper cable rather than coax cable. a star topology. 10BASE-T also uses Manchester encoding.,100-Mbps Ethernet,100-Mbps Ethernet is also known as Fast Ethernet(快速以太網(wǎng)). 100BASE-TX and 100BASE-FX The 100-Mbps frame format is the same as the 10-Mbps frame . Encoding :4B/5B Bits per second,1000-Mbps Ethernet,The 1000BASE-X standard, IEEE 802.3z, 1000BASE-TX, 1000BASE-SX, and 1000BASE-LX The Gigabit Ethernet frame has the same format as is used for 10 and 100-Mbps Ethernet. 8B/10B encoding,10GbE,Frame format is the same, allowing interoperability between all varieties of legacy, fast, gigabit, and 10 Gigabit, with no reframing or protocol conversions. Since only full-duplex fiber connections are used, CSMA/CD is not necessary Flexible(靈活的), efficient（高效的）, reliable（可靠的）, relatively low cost（低廉的） end-to-end（端到端） Ethernet networks become possible.,10-Gbps Ethernet,10-Gbps Ethernet (IEEE 802.3ae) was standardized in June 2002. It is a full-duplex protocol that uses only optic fiber as a transmission medium. The maximum transmission distances depend on the type of fiber being used.,The future of networking media,Copper (up to 1000 Mbps, perhaps more) Wireless (approaching 100 Mbps, perhaps more) Optical fiber (currently at 10,000 Mbps and soon to be more),地址學(xué)習(xí)（Address learning） 決定轉(zhuǎn)發(fā)或過濾（Forward/filter decision） 避免環(huán)路（Loop avoidance）,交換機三種功能 （Three Switch Functions ）,交換機學(xué)習(xí)主機地址 （Switche Learn Host Address）,初始MAC地址表是空的 Initial MAC address table is empty,MAC address table,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,F0/1,F0/3,F0/2,F0/4,A,B,C,D,交換機學(xué)習(xí)主機地址 （Switche Learn Host Address）,A向C發(fā)送幀（Station A sends a frame to Station C） 交換機將A的MAC地址和其對應(yīng)的接口f0/1放入MAC地址表 Switch caches station A MAC address to port E0 by learning the source address of data frames 該幀向除了F0/1接口的所有接口泛洪 The frame from station A to station C is flooded out to all ports except port F0/1,MAC address table,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,F0/1 : 0260.8c01.1111,F0/1,F0/3,F0/2,F0/4,D,C,B,A,交換機學(xué)習(xí)主機地址 （Switche Learn Host Address）,D向C發(fā)送幀(Station D sends a frame to station C) 交換機將D的MAC地址和其對應(yīng)的接口f0/3放入MAC地址表 Switch caches station D MAC address to port f0/3 3 by learning the source Address of data frames 該幀向除了f0/3接口的所有接口泛洪 The frame from station D to station C is flooded out to all ports except port f0/3 (unknown unicasts are flooded),MAC address table,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,F0/1 : 0260.8c01.1111,F0/2 : 0260.8c01.2222,F0/1,F0/3,F0/2,F0/4,D,C,A,B,交換機過濾幀（ Switches Filter Frames）,A向C發(fā)送幀 Station A sends a frame to station C 目的地址已知，幀不被泛洪 Destination is known, frame is not flooded 交換機的MAC地址表是基于源地址構(gòu)建的,F0/1: 0260.8c01.1111,F0/2: 0260.8c01.2222,F0/3: 0260.8c01.3333,F0/4: 0260.8c01.4444,0260.8c01.1111,0260.8c01.2222,0260.8c01.3333,0260.8c01.4444,F0/1,F0/3,F0/2,F0/4,X,X,D,C,A,B,MAC address table,兩種交換方法（Two Switching Methods）,存儲轉(zhuǎn)發(fā)特征（Store-and-forward Feature）,1. 在轉(zhuǎn)發(fā)之前整個幀被接收 The entire frame is received before any forwarding takes place. 2.由于交換開始之前要接收完整幀，較大的數(shù)據(jù)幀延遲較大 Latency is greater with larger frames because the entire frame must be received before the switching process begins.,直通特征（Cut-through Feature）,1.在接收完整幀之前，幀就被轉(zhuǎn)發(fā)。 The frame is forwarded through the switch before the entire frame is received. 2.最快的是只要讀到目的地址就轉(zhuǎn)發(fā)。 At a minimum the frame destination address