414Lecture19

414Lecture19 - Lecture 19 Link Layer Ethernet, Hubs,...

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Lecture 19 Link Layer Ethernet, Hubs, Switches, VLANs ECSE 414 – Fall 2010
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ECSE 414, Lecture 19 2 Announcements Homework Assignment #4 Due Thursday Project Presentations During usual class time Starting Thursday, November 25 Final Exam December 21, 9am-noon 2010 Michael Rabbat
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ECSE 414, Lecture 19 3 Addressing: routing to another LAN R 1A-23-F9-CD-06-9B 222.222.222.220 111.111.111.110 E6-E9-00-17-BB-4B CC-49-DE-D0-AB-7D 111.111.111.112 111.111.111.111 A 74-29-9C-E8-FF-55 222.222.222.221 88-B2-2F-54-1A-0F B 222.222.222.222 49-BD-D2-C7-56-2A Walkthrough: send datagram from A to B via R assume A knows B’s IP address Separate ARP tables in router R for each IP network (LAN, interface) Also need to use R’s forwarding table 2010 Michael Rabbat
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ECSE 414, Lecture 19 4 Ethernet “dominant” wired LAN technology: cheap $20 for NIC first widely used LAN technology simpler, cheaper than token LANs and ATM kept up with speed race: 10 Mbps – 10 Gbps Metcalfe’s Ethernet sketch 2010 Michael Rabbat
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ECSE 414, Lecture 19 5 Star topology bus topology popular through mid 90s all nodes in same collision domain (can collide with each other) today: star topology prevails active switch in center each “spoke” runs a (separate) Ethernet protocol (nodes do not collide with each other) switch bus: coaxial cable star 2010 Michael Rabbat
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ECSE 414, Lecture 19 6 Ethernet Frame Structure Sending adapter encapsulates IP datagram (or other network layer protocol packet) in Ethernet frame Preamble: 7 bytes with pattern 10101010 followed by one byte with pattern 10101011 used to synchronize receiver, sender clock rates 2010 Michael Rabbat
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ECSE 414, Lecture 19 7 Ethernet Frame Structure (more) Addresses: 6 bytes if adapter receives frame with matching destination address, or with broadcast address (eg ARP packet), it passes data in frame to network layer protocol otherwise, adapter discards frame Type: indicates higher layer protocol (mostly IP but others possible, e.g., Novell IPX, AppleTalk) CRC: checked at receiver, if error is detected, frame is dropped (4Bytes, predefined generator) 2010 Michael Rabbat
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ECSE 414, Lecture 19 8 Ethernet: Unreliable, connectionless connectionless: No handshaking between sending and receiving NICs unreliable: receiving NIC doesn’t send acks or nacks to sending NIC stream of datagrams passed to network layer can have gaps (missing datagrams) gaps will be filled if app is using TCP otherwise, app will see gaps Ethernet’s MAC protocol: unslotted CSMA/CD 2010 Michael Rabbat
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ECSE 414, Lecture 19 9 Ethernet CSMA/CD algorithm 1. NIC receives datagram from network layer, creates frame 2. If NIC senses channel idle,
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This note was uploaded on 05/09/2011 for the course ECSE 414 taught by Professor Rabbat during the Fall '10 term at McGill.

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414Lecture19 - Lecture 19 Link Layer Ethernet, Hubs,...

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