10 - WAN technologies and routing Packet switches and store...

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WAN technologies and routing Packet switches and store and forward Hierarchical addresses, routing and routing tables Routing table computation Example WAN technologies
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Categories of network technology Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area network (WAN) Key distinguishing feature is scale: geographic distance AND number of connected computers
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Packet Switches In order to grow, WANs use many switches Basic component is the packet switch that can connect to local computers and to other packet switches
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WAN topology Chosen to accommodate expected traffic and to provide redundancy
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Store and forward Each switch receives packets, queues them in its memory and then sends them out when possible (i.e., when the destination is available) Many computers can send packets simultaneously
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Physical addressing in a WAN A WAN defines a frame format and assigns physical addresses to its computers Hierarchical addressing, e.g., first part identifies packet switch second part identifies computer on this switch switch 1 switch 2 A B C D [1,2] [1,5] [2,2] [2,6] address
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Next hop forwarding A packet switch determines the destination for each packet from the destination address local computer or another packet switch Only has information about how to reach the next switch - next hop This is held in a routing table
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Example routing table A B C D E F S1 S2 S3 Routing table for S2 Destination Next Hop [1,2] interface 1 [1,5] interface 1 [3,2] interface 4 [3,5] interface 4 [2,1] computer E [2,6] computer F [1,2] [1,5] [2,1] [2,6] [3,2] [3,5]
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Source independence The next hop depends upon the destination address but not on the source address
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10 - WAN technologies and routing Packet switches and store...

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