Ethernet1 - What is Ethernet? Ethernet It is a "standard"...

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Ethernet Metcalfe’s Ethernet sketch What is Ethernet? • It is a "standard" (IEEE 802.3) • “dominant” LAN technology: • cheap – $20 for 100Mbs! • first widely used LAN technology • Simpler, cheaper than token LANs and ATM What is Ethernet? (cont.) • Comes in various speeds: – 10Mbps, – 100Mbps (Fast Ethernet), – 1000Mbps (Gigabit Ethernet) – 10000Mbps (10G Ethernet) • A choice of media – Coaxial Cable (10Base5, 10Base2) –UTP –F ibre Ethernet Addresses • MAC address: Each node has a unique Ethernet address (6 bytes) – e.g. 08:0f:20:a5:e7:77 • Each packet must include the MAC address of the recipient host • Although others receive the packet, they discard it • MAC address ff:ff:ff:ff:ff:ff (all 1s) used for broadcasting to all hosts Ethernet Frame Structure Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame • Addresses: 6 bytes each • Type: indicates the higher layer protocol – IP, Novell IPX, AppleTalk, etc. • CRC: checked at receiver, if error is detected, the frame is simply dropped Unreliable, connectionless service • Connectionless: No handshaking between sending and receiving adapter. • Unreliable: receiving adapter doesn’t send acks or nacks to sending adapter – stream of datagrams passed to network layer can have gaps – gaps will be filled if app is using TCP – otherwise, app will see the gaps
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Ethernet uses CSMA/CD • No slots • adapter doesn’t transmit if it senses that another adapter is transmitting, that is, carrier sense • transmitting adapter aborts when it senses that another adapter is transmitting, that is, collision detection • Before attempting a retransmission, adapter waits a random time, that is, random access Network Topologies Bus Topology : All the hosts are physically connected to the same cable Network Topologies (cont.) Star Topology : Individual connections from each host to the center HUB Ethernet Technologies: 10Base5 and 10Base2 • 10: 10Mbps; 5: 500 meters max cable length • 10: 10Mbps; 2: 200 meters max cable length • coaxial cable in a bus topology • has become a legacy technology 10BaseT and 100BaseTX • 10/100 Mbps rate; latter called “fast ethernet” • T stands for Twisted Pair • Nodes connect to a hub: “star topology”; 100 m max distance between nodes and hub hub nodes Hubs • Hubs are essentially physical-layer repeaters: – bits coming in one link go out all other links
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This note was uploaded on 05/07/2010 for the course DMO electro23 taught by Professor Taflove during the Spring '10 term at Unicamp.

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Ethernet1 - What is Ethernet? Ethernet It is a "standard"...

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