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    1. Backbone Networks 1 of 2 Wired 1

    2. 2

    3. Wired Backbones - Overview

    4. One Key Shift 4 Backbone architectures assume business users Is this a fair assumption? Do your readings convey this message?

    5. Backbone Networks 5 What purpose do backbones serve? A network that connects many networks High speed networks that link an organizations LANs provide connections to other backbones, WANs, Internet Enterprise network?backbone connects all networks in a company Concepts Routers: Across nwks with same network protocol Bridges: Across nwks with different network protocols Switches: Hardware-only routers Backbone architecture

    6. The Big Picture = 93 submarine cable systems

    7. BPL: Old Wine in a New Bottle? 7 How does BPL work? Core idea? How old is the BPL idea? What is the business significance of BPL? For consumers? For firms? Is remote power management really a selling point? Why now? The curb problem? Wifi feasible? Bottlenecks (Economist article) RF interference Step down transformer problems ? data problems

    8. Topologies Bus, Ring, Star 8

    9. 3 backbone layers 9

    10. Backbone Network Architecture 10 Fundamental organizing logic?key performance driver How it interconnects nwks attached to it How it moves packets across networks

    11. Hierarchical backbone architecture Move packets based on nwk address layer 11

    12. Flat backbone architecture Obsolete design (routers cheap now) 12

    13. Collapsed backbone architecture 13

    14. Collapsed Backbones - 2 Types 14 Rack-Mounted (equipment racks) Backbones collapse into main distribution facility (MDF) Devices are connected using short patch cables + Moving devices b/w LANs is relatively simple Chassis-switch based Chassisopen slots for modules + Modularflexibility in network configuration + Very high performance/speeds Why? Because backbone is an internal bus

    15. Virtual LANs 15 What does virtual imply here? Architecture using intelligent, high-speed switches VLANs assign computers to LAN segments via software All others physically hardwire them The two basic designs are: Single-switch VLANs Multiswitch VLANs

    16. (Figure 5-8) 16 Single Switch VLANs Device?VLAN assignment via software Physically connected to single switch 4 ways to assign to VLANs Explain logic Port-based MAC-based data link layer address IP-address based Application-based

    17. Are these Architectures Relevant today? 17 Meaningful for DSL service? BPL service?

    18. Part 2: Cable vs. Optical Fiber 18

    19. Cable versus Fiber 19 Difference between fiber and cable? Whats happening? Significance? $135 bn home market Is it really cable versus fiber (as BW implies)? Whos got a leg up? Why? (cost/home, reach) Which one will scale better? Architectural reasons? Who will get the dominant market-share? Why? Content challenges for the Bells? How do the utility BPL providers fit in? Whos the arch nemesis of Qwest and Mediacom?

    20. Coax Cable

    21. Two Backbone Protocols 21

    22. Fiber Distributed Data Interface 22 Obsolete: Replaced by Gigabit Ethernet and ATM Operates at 100 Mbps over a fiber optic cable Also: Cat5 Copper Distributed Data Interface (CDDI)

    23. FDDIs Self Healing Rings 23 Can handle breaks in network by forming a single temporary ring out of the pieces of the primary and secondary rings traffic rerouted through a new ring until the break can be repaired

    24. FDDI Message Delineation 24 3 parts Frame Start: like Ethernet, the frame begins with a preamble and a 1-byte start delimiter Frame Body: the main body of the frame includes: 1-byte frame control field (used for the token) 2 or 6 byte fields for the destination and source addresses data field contains 0-4500 bytes of data the frame check sequence (FCS)error control Frame End: the frame ends with a 1-byte end delimiter and a 2-byte frame status field

    25. Asynchronous Transfer Mode (ATM) or cell relay 25 Data packets = ATM cells Designed to carry both voice and data traffic over WANs Cannot directly connect to TCP/IP networks Needs ATM gateways for TCP/IP frame ? ATM cell conversion

    26. ATM Topology 26 Uses a mesh topology Mesh: Whatever interconnections that make sense Full mesh (N:N) versus partial mesh connections Operates at 155 Mbps in each direction (full duplex) Connection-oriented (virtual channels)2 ways Permanent Virtual Circuits (PVCs) Switched Virtual Circuits (SVCs) temporary/session only

    27. ATM Error Control 27 Throw-it-on-the-floor technique Error checking is only done on the ATM header If an error is detected, the cell is discarded Full error control including requests for retransmission are handled at the source and destination computers ~LANs use TCP for this

    28. ATM Message Delineation 28 ATM has a 53-byte frame (~ cell) Protocol efficiency? High/low? ATM header fields Generic Flow Control: controls the flow of data across the circuit Virtual Path Identifier: identifies the group of channels the data is moving with Virtual Circuit Identifier: identifies the specific channel Payload Type: indicates type of data in data field Cell Loss Priority: whether or not the cell is discarded if the circuit gets busy Header Error Control: for error control

    29. ATM and LANs: Making them talk 29 Ethernet & TCP/IP must first be translated before being sent over ATM networks Ethernet & TCP/IP use large variable length frames/packets with fixed addresses But ATM uses small fixed length cells addressed using virtual channels Two approaches LAN Encapsulation (LANE), which splits frames into 48 byte pieces, reassembling them when they reach their destination LAN Multiprotocol Over ATM (MPOA) extension of LANE that uses both IP and Ethernet addresses

    30. LAN Encapsulation (LANE) 30 Breaking Ethernet frames into 48-byte chunks @ LANs gateway ATM edge switch The edge switch also creates a virtual channel identifier for the cells to use cells then sent over ATM backbone using this identifier The frame is reassembled @ destination edge switch LANEs high overhead creates significant delays

    31. 31

    32. Best Practices 32 3 Trends Gigabit Ethernet replacing ATM as a backbone technology Upto 30 times faster than ATM Shift to collapsed backbones or VLANs Emergence of alternative backbone architectures Key emerging practices 1. Architecture: collapsed backbone or VLAN 2. Technology: Gigabit Ethernet 3. Reliability: Redundant switches

    33. Summary 33 Role of backbone networks Key industry changes Backbone architectures (types) Backbone protocols FDDI and ATM Cable versus fiber versus BPL Up next: Wireless backbones