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CS335 Networking & Network Administration

CS335 Networking & Network Administration. Tuesday, April 20, 2010. WAN’s and Routing. LAN’s Local Area Network span a building or campus MAN’s Metropolitan Area Network spans a city WAN’s Wide Area Network can span sites in multiple cities, countries, or continents Large corporations.

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CS335 Networking & Network Administration

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  1. CS335 Networking &Network Administration Tuesday, April 20, 2010

  2. WAN’s and Routing • LAN’s • Local Area Network span a building or campus • MAN’s • Metropolitan Area Network spans a city • WAN’s • Wide Area Network can span sites in multiple cities, countries, or continents • Large corporations

  3. Scalability • A WAN must be able to grow as needed to connect many sites across large distances • Support many simultaneous connections

  4. Packet Switches • Allows many switches to interconnect for expansion

  5. Packet Switched WAN

  6. Physical addressing in a WAN • Hierarchical addressing

  7. Next-Hop forwarding • Packet switch does not keep complete information on how to reach all possible destinations, just its next hop

  8. Source independence • Doesn’t matter where a packet comes from • Next hop depends only on the destination • This allows the forwarding mechanism to be compact and efficient • Because all packets follow the same path, only one table is required • Only the destination address needs to be extracted from the packet • A single mechanism handles forwarding uniformly

  9. Routing table • Forwarding a packet to its next hop is routing • Two-part hierarchical address has practical consequences

  10. Next hop routing table

  11. Default route • Eliminates duplicate entries • Uses default if doesn’t find an explicit entry • Only one default route in a table, and has lower priority than other entries

  12. Routing table computation • Static routing • A program computes and installs routes when the packet switch boots; the routs do not change • Dynamic routing • A program builds an initial routing table when booted; the program alters the table as condition in the network change

  13. Shortest Path Computation • Dijkstra’s algorithm used to find the shortest path from a source to other nodes • Uses weights on edges* as a measure of distance • Path with fewest number of edges may not be the path with the least weight • * edges are connections between nodes • * weights are assigned non-negative values

  14. Shortest Path Computation • Least weight path

  15. Distributed route computation • Packet switches send each other routing info • Distance vector routing – packet switch sends routing info across network and updates routes based on distance vector algorithm (13.2 in book) • Link state routing (known as SPF - Shortest path first)

  16. Routed vs. routing protocols • Routed protocols • Any network protocol that provides enough information in its network layer address to allow a packet to be forwarded. Routed protocols define the field formats within a packet. Uses the routing table to forward packets. IP is an example of a routed protocol. • Routing protocols • Support a routed protocol by providing mechanisms for sharing routing information. Routing protocol messages move between routers to update and maintain tables. TCP/IP examples are: • RIP – Routing information protocol • IGRP – interior gateway routing protocol • EIGRP – enhanced interior gateway routing protocol • OSPF – open shortest path first

  17. Network performance • Delay – the time required to send a bit from one device to another • Throughput – the number of bits per second that can be transmitted across the network • Throughput and delay are not independent. As traffic (congestion) increases, delay increases. A network that operates at close to 100% of its throughput capacity has sever delay. • Jitter – a measure of the variance in delay

  18. Protocols and layering • Protocols – a design that specifies the details of how computers interact, including the format of the messages they exchange and how errors are handled • Protocol suite – a set of protocols that work together to provide a seamless communication system. Each protocol handles a subset of all possible details – also called the protocol stack • OSI layer Model

  19. OSI Model

  20. Multiple nested headers

  21. Data Encapsulation in a layered architecture User data A User data A User data P A User data P A User data S P A User data S P A User data T S P A User data T S P A User data N T S P A User data N T S P A User data D N T S P A User data D N T S P A User data

  22. Retransmitting lost packets • Reliable transfer requires protocols to use positive acknowledgement with retransmission • Can introduce duplicate packets when there is long delay • Flow control mechanisms to handle data overrun – stop and go sender waits for receiver to send an ACK • Inefficient use of network capacity

  23. Sliding Window algorithm

  24. Sliding Window algorithm • Technique a protocol can use to improve throughput by allowing a sender to transmit additional packets before receiving an acknowledgement. A receiver tells a sender how many packets can be sent at a time (called a window size).

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