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WAN Technologies & Topologies

WAN Technologies & Topologies. Lecture 8 October 4, 2000. WAN Background. WAN - Wide Area Network, spans multiple cities/states. MAN - Metropolitan Area Networks exist in a single city. LAN – Single building environment. Multiple MANs can make a WAN, multiple LANs can make a MAN, etc.

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WAN Technologies & Topologies

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  1. WAN Technologies & Topologies Lecture 8 October 4, 2000

  2. WAN Background • WAN - Wide Area Network, spans multiple cities/states. • MAN - Metropolitan Area Networks exist in a single city. • LAN – Single building environment. • Multiple MANs can make a WAN, multiple LANs can make a MAN, etc.

  3. WAN Example

  4. MAN As A Building Block • As I mentioned earlier, multiple MANs usually make up the WAN. • Each MAN has control of its own domain, but it’s uplink to the other MANs is considered the WAN (backbone). • Using Verio Boston’s example…

  5. The Interconnects • MAN & WAN circuits must terminate in some form of a packet switch. • Using the UNet example from the other day, the packet switches were the Cisco Catalyst 6509 switches. • But keep in mind, the telephone company also has some switches in the field that handle even more traffic than what you’re getting!

  6. Switch Interconnects – The “Cloud”

  7. WAN Switch Functionality • WAN switches use store and forward technology. • The store operation occurs when the packet arrives: the I/O hardware copies the packet, sticks it in memory, and signals the processor to forward the packet. • The forward operation is the act of removing the packet from memory, and sends it to the appropriate interface.

  8. WAN Switch Functionality (cont.) • Storing the packets also leads to a form of queuing for each interface. • If the destination interface is busy, the packet is queued until the destination interface is idle, then the forward occurs. • The store and forward paradigm allows to handle the maximum bandwidth of the WAN connection, since all data is buffered!

  9. Physical Addressing in the WAN Environment • A hierarchical scheme is used with WAN addressing. • The simplest form of this scheme: The first part of the address holds the destination switch, the second part holds the specific machine that the packet is destined for on that switch. • This is scheme is used in many WAN environments.

  10. WAN Addressing (cont.)

  11. Next-Hop Forwarding • In order for networking to occur, each device must have some knowledge of the devices which it is connected to. • Next-hop forwarding is a scheme where devices know their neighbors, but don’t know the specifics of what is connected to each neighbor.

  12. The Airline Example • Suppose a passenger is traveling from San Francisco to Miami. Only one flight is listed, with three legs: Dallas, Atlanta, Miami. • From San Francisco, his next destination is Dallas. • From Dallas, his next destination is Atlanta. • From Atlanta, his last destination is Miami. • But all along, the LAST destination was Miami, even though the next hop was changing at each leg.

  13. Next-Hop Diagram

  14. Source Independence • The next hop does not depend on the direction that the packet came from. • This is referred to source independence. • Source independence is a fundamental concept in data networks. It allows for low-overhead, efficient networks.

  15. Hierarchical Addressing & Routing • Heirarchical addressing is almost routing… • The act of forwarding a packet to the next address is dubbed routing. • Routing uses a table format to determine the next hop of the communication, and since it only needs to inspect the first part of the address, it is efficient!

  16. A Simplified Routing Table

  17. Routing (cont.) • The two part addressing scheme provides us with the following: • Switches along the path of the transmission need to inspect the first part of the hierarchical address. • The last switch in the transmission must inspect the last part of the address. • Really efficient network transport! Not much overhead.

  18. Routing in the WAN • There are LOTS of routing algorithms that are commonly used in the WAN environment. • RIP: Router Information Protocol • OSPF: Open Shortest Path First • BGP: Border Gateway Protocol • IGRP: Interior Gateway Routing Protocol • I’m not going to focus on the different algorithms, but please read up and understand the differences between them!

  19. Routing in the WAN (cont.) • The best way to visualize routing is to imagine how all of the networks are connected together. • Each node in the network is a packet switch. • Each connection between switches is a link or an edge.

  20. A Network Diagram

  21. Routing Table for the Example

  22. Default Routes • Default routes allow for the simplification of routing tables. • Since many packets would have the same routes, a default route would reduce the amount of work the router/switch would have to do.

  23. Simplified Routing Table

  24. Default Routing (cont.) • Only one default route per device is allowed. • The default route has lower priority to other entered routes. • If a transmission does not find a valid route, it will send the packet down the default route.

  25. Determination of the Routing Table • Two ways exist for route determination: • Static routing • Dynamic routing • Why have different options?

  26. Static Routing • Static routing is the most straightforward of the two schemes. • Pros: • Simple to visualize • Low overhead on devices which perform routing • Cons: • Static, inflexible

  27. Dynamic Routing • Dynamic routing can be very confusing. • Multiple types of dynamic routing exist: • OSPF • IGRP • BGP • RIP • Main disadvantage of dynamic routing: difficult to understand.

  28. OSPF • OSPF – Open Shortest Path First • Uses a system of metrics to determine route preference. • The entire route preference is the sum of the individual metrics of the links between the computers. • The routers send their routing tables out periodically to their neighbors.

  29. Common WAN Technologies • ATM- Asynchronous Transfer Mode • Frame Relay • SONET

  30. ATM • Data is divided into small, fixed packets called cells. • Each cell is 53 octets: • 5 octets for header info • 48 octets for data transmission • ATM originally designed for simultaneous transmission of data, voice, and video. • Quality of Service (QOS) is adjustable with bandwidth needs: higher for video, lower for data and video.

  31. ATM (cont). • Connections are usually 155Mbps OC-3. • Uses the “cloud” concept.

  32. Frame Relay • Data is divided into small, variable sized cells, up to 16,000 octets! • Up to 1.544Mbps transmission rate. • Uses “cloud” concept – shared bandwidth with other connections.

  33. OSPF Example

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