network2 - Network Layer 4-1 Chapter 4: Network Layer r 4....

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Unformatted text preview: Network Layer 4-1 Chapter 4: Network Layer r 4. 1 Introduction r 4.2 Virtual circuit and datagram networks r 4.3 Whats inside a router r 4.4 IP: Internet Protocol m Datagram format m IPv4 addressing m ICMP m IPv6 r 4.5 Routing algorithms m Link state m Distance Vector m Hierarchical routing r 4.6 Routing in the Internet m RIP m OSPF m BGP r 4.7 Broadcast and multicast routing Network Layer 4-2 Router Architecture Overview Two key router functions: r run routing algorithms/protocol (RIP, OSPF, BGP) r forwarding datagrams from incoming to outgoing link Network Layer 4-3 Input Port Functions Decentralized switching : r given datagram dest., lookup output port using forwarding table in input port memory r goal: complete input port processing at line speed r queuing: if datagrams arrive faster than forwarding rate into switch fabric Physical layer: bit-level reception Data link layer: e.g., Ethernet see chapter 5 Network Layer 4-4 Three types of switching fabrics Network Layer 4-5 Switching Via Memory First generation routers: r traditional computers with switching under direct control of CPU r packet copied to systems memory r speed limited by memory bandwidth (2 bus crossings per datagram) Input Port Output Port Memory System Bus Network Layer 4-6 Switching Via a Bus r datagram from input port memory to output port memory via a shared bus r bus contention: switching speed limited by bus bandwidth r 32 Gbps bus, Cisco 5600: sufficient speed for access and enterprise routers Network Layer 4-7 Switching Via An Interconnection Network r overcome bus bandwidth limitations r Banyan networks, other interconnection nets initially developed to connect processors in multiprocessor r advanced design: fragmenting datagram into fixed length cells, switch cells through the fabric. r Cisco 12000: switches 60 Gbps through the interconnection network Network Layer 4-8 Output Ports r Buffering required when datagrams arrive from fabric faster than the transmission rate r Scheduling discipline chooses among queued datagrams for transmission Network Layer 4-9 Output port queueing r buffering when arrival rate via switch exceeds output line speed r queueing (delay) and loss due to output port buffer overflow! Network Layer 4-10 How much buffering? r RFC 3439 rule of thumb: average buffering equal to typical RTT (say 250 msec) times link capacity C m e.g., C = 10 Gbps link: 2.5 Gbit buffer r Recent recommendation: with N flows, buffering equal to RTT C . N Network Layer 4-11 Input Port Queuing r Fabric slower than input ports combined -> queueing may occur at input queues r Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward r queueing delay and loss due to input buffer overflow! Network Layer 4-12 Chapter 4: Network Layer r 4. 1 Introduction r 4.2 Virtual circuit and datagram networks r 4.3 Whats inside a router r 4.4 IP: Internet Protocol m Datagram format m IPv4 addressing m ICMP m IPv6 r...
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This note was uploaded on 09/07/2010 for the course ECE 407 taught by Professor Eun during the Spring '08 term at N.C. State.

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network2 - Network Layer 4-1 Chapter 4: Network Layer r 4....

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