Backbone Networks 1 of 2 Wired

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Backbone Networks 1 of 2 Wired
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Agenda

• BPL discussion
• Cable versus Fiber article
• Sad state article
• Backbones
• Architectures
• FDDI (Fiber Distributed Data Interface)
• ATM (Asynchronous Transfer Mode)
• Best Practices
• Next Wireless, WAC questions online
• Be prepared to discuss the case

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Wired Backbones - Overview
Wireless Next session
Source BusinessWeek
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One Key Shift

• Backbone architectures assume business users
• Is this a fair assumption?
• Do your readings convey this message?

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Backbone Networks

• 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

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The Big Picture 93 submarine cable systems
http//www.newscientist.com/gallery/mg20227061900-
exploring-the-exploding-internet/
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BPL Old Wine in a New Bottle?

• 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

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TopologiesBus, Ring, Star
Downsides?
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3 backbone layers
connects different backbone networks together
connects the LANs together
the technology used in LANs
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Backbone Network Architecture

• Fundamental organizing logic?key performance
  driver
• How it interconnects nwks attached to it
• How it moves packets across networks

4 types
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Hierarchical backbone architectureMove packets
based on nwk address layer
Each LAN is a separate and isolated network
connected by a TCP/IP gateway (usually a router)
MSG
shared backbone network
MSG
Based on NWK address
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Flat backbone architectureObsolete design
(routers cheap now)
Typically bus topology
LANs connected using bridges
MSG
MSG
Packets are forwarded based on their data link
layer addresses
MSG
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Collapsed backbone architecture
uses a star topology
Considerations (why?) higher performance simpler
-single failure point why?
Where are these tradeoffs acceptable?
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Collapsed Backbones - 2 Types

• 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

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Virtual LANs

• 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

Virtual
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(Figure 5-8)

• 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

Multi Switch VLANs
Includes a tag field with VLAN information field
packets between multiple switches
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Are these Architectures Relevant today?

• Meaningful for
• DSL service?
• BPL service?

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Part 2 Cable vs. Optical Fiber
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Cable versus Fiber

• 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?

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Coax Cable
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Two Backbone Protocols
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Fiber Distributed Data Interface

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

• gt1000 devices, 120 miles, repeaters every 1.2mi

Primary (data normally travels here)
devices attached to primary (single AS) or both
(dual AS)
Uses dual rings
Secondary (backup)
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FDDIs Self Healing Rings

• 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

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FDDI Message Delineation

• 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

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Asynchronous Transfer Mode (ATM)or cell relay

• 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

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ATM Topology

• Uses a mesh topology
• Mesh Whatever interconnections that make sense
• Full mesh (NN) 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

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ATM Error Control

• 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

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ATM Message Delineation

• 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

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ATM and LANs Making them talk
Like driving on I-35 to DSM

• 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

Like the Union Pacific railroad
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LAN Encapsulation (LANE)

• Breaking Ethernet frames into 48-byte chunks
• _at_ 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 _at_ destination edge
  switch
• LANEs high overhead creates significant delays

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Best Practices

• 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

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Summary

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