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Ethernet(2) - IK2211 Data Links and Local Area Networks...

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Ethernet IK2211 Data Links and Local Area Networks Peter Sjödin KTH School of ICT
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Overview Background and recapitulation High speed Ethernet Spanning Tree Protocol Virtual LANs and large scale Ethernet
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MAC Frame Format Two formats IEEE 802.3 Length field less that 1518 DIX (DEC, Intel, Xerox) Length field really is ”PDU” Type field Always greater than 1518 Still most common, and often the default format 3 Data link layer frame Media-specific preamble
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4 Packet Size Versus Bus Length CSMA/CD is half-duplex mode Collisions of two (or more) stations send at the same time Must be detected by all stations Minimum packet size and maximum bus length 72 bytes (64 bytes at data link layer) and 500 meters for 10Base5 (“Thick Ethernet”) Station 1 Station 2 T tr T pr T pr S : frame size [bit] C : link capacity [bit/s] L : bus length [m] v : signal propagation speed [m/s] So what if we want to increase link speed, say from 10 Mb/s to 10 Gb/s?
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100 Mbit/s Ethernet Type Media Type Distance (m) Coding 100Base-TX Cat 5 UTP/STP 100 4B/5B MLT-3 100Base-FX Fiber 2000 4B/5B NRZ-I 100Base-SX Fiber 300 4B/5B NRZ-I
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100 Gbit/s Ethernet Being standardized IEEE 802.3 Higher Speed Study Group (HSSG) 40 Gb/s and 100 Gb/s standards Support at least 10 m over copper cable Support at least 40 km on Single Mode Fiber Full-duplex only Preserve the 802.3 / Ethernet frame format at the MAC Client service interface Preserve minimum and maximum frame size of current 802.3
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Ethernet Routing—Spanning Tree Loop elimination No optimal routing as in IP Shortest path, least cost, etc. Ethernet bridges automatically “learn” the location of stations Check the source MAC address in each received frame Remember the port where the frame arrived MAC address table (or learning table) 7
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Learning Bridges Example
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Learning Bridges—Loop Problem From B. A. Forouzan: Data Communications and Networking, 3rd ed, McGraw-Hill
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Spanning Tree—Basic Idea Discover a subset of the topology that is loop-free (a tree) Just enough connectivity so that: there is a path between every pair of segments where physically possible the tree is spanning Disable (block) all other ports
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Spanning Tree Starting Point Each bridge has a unique ID Each port has a unique ID within the bridge A cost can be calculated for each path between two bridges 11 From B. A. Forouzan: Data Communications and Networking, 3rd ed, McGraw-Hill
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