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Chi-Cheng Lin, Winona State University CS 313 Introduction to Computer Networking & Telecommunication Local Area Networks
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2 Topics l Ethernet l Data Link Layer Switching
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3 802.3 and Ethernet l 802.3 1-Persistent CSMA/CD LAN, 1 - 10 Mbps l Ethernet A specific product that almost implements 802.3
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Classic Ethernet Physical Layer Architecture of classic Ethernet
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Classic MAC Sublayer Protocol l Frame formats. (a) DIX Ethernet, (b) IEEE 802.3 l Preamble: 10101010 for synchronization l Start of frame: 10101011
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6 Ethernet MAC Sublayer Protocol l Addresses Ethernet uses 6 bytes Support Unicast: address begins with 0 Multicasting: 1 + group number Broadcasting: all 1’s
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Classic MAC Sublayer Protocol Collision detection can take as long as 2 .
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8 Ethernet MAC Sublayer Protocol l Minimum frame size: 64 bytes Why? frame_size bits/channel_capacity bps > 2 s In 10-Mbps Ethernet, 2 = 50 s, therefore frame_size > 50 s x 10 Mbps = 500 bits, rounded up to 512 bits = 64 bytes
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9 Binary Exponential Backoff Algorithm l Wait time t time slots after a collision t = a random number between 0 and 2 i - 1 after i collisions t = 1023, for i = 10,...,16 when i > 16, reset i = 0 l Low delay for light load l Reasonable delay for high load
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Switched Ethernet (a) Hub. (b) Switch. Collision Domain?
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Switched Ethernet An Ethernet switch. Switch Twisted pair Switch ports Hub
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Fast Ethernet The original fast Ethernet cabling. Xbase-Y Channel capacity Cable type
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Gigabit Ethernet A two-station Ethernet
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Gigabit Ethernet A multistation Ethernet
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Gigabit Ethernet Gigabit Ethernet cabling.
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10 Gigabit Ethernet 10-Gigabit Ethernet cabling
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17 Retrospective on Ethernet l Has been 20+ years l Simple and flexible Reliable Cheap Easy to maintain l Works easily with TCP/IP Both IP and Ethernet are connectionless l Evolution – no software change required Speed: higher and higher Hubs, switches
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Data Link Layer Switching Uses of bridges Learning bridges Spanning tree bridges Repeaters, hubs, bridges, switches, routers, and gateways
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Learning Bridges Bridge connecting two multidrop LANs
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Learning Bridges Bridges (and a hub) connecting seven point-to- point stations.
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21 Learning Bridges l Transparency Plug and play l Operates in Promiscuous Mode Accepting every frame transmitted on all LANs to which it is attached l Decides Discard or forward If forward, to which LAN? Look up a huge destination address hash table
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22 Learning Bridges l Hash Table Initially empty Flooding algorithm Backward learning algorithm Arrival time noted for dynamic topology Scanned periodically to remove old entries l Routing procedure for an incoming frame If dest LAN = src LAN then discard If dest LAN != src LAN then forward If dest LAN unknown then use flooding
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Learning Bridges Protocol processing at a bridge.
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Spanning Tree Bridges l To increase reliability Two or more bridges between 2 LANs l Problem: looping Bridges with two parallel links
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Spanning Tree Bridges (2) A spanning tree connecting five bridges. The dotted lines are links that are not part of the spanning tree.
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Repeaters, Hubs, Bridges, Switches, Routers, and Gateways (a) Which device is in which layer. (b) Frames, packets, and headers. Discussions: Collision domain? Plug-and-play?
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