Topologies and Access Methods

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Topologies and Access Methods

• Dean (3rd), Chp. 6

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Overview

• Physical and logical topologies
• Simple physical topologies
• Hybrid physical toplogies
• Backbone networks
• Backbone topologies

• Logical topologies
• Ethernet
• CSMA/CD
• Ethernet frams
• Other logical topologies
• FDDI
• ATM
• Wireless networks

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Physical and Logical Topologies

• Physical topologies
• Depict layout of media and devices
• Emphasis on physical paths that carry messages
• Logical topologies
• Model way in which data are transmitted
• Access and transmission protocols
• Emphasis on way transmission protocol views
  connection of nodes

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Simple Physical Topologies

• Bus
• Ring
• Star

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Hybrid Physical Topologies

• Star-wired ring
• Star-wired bus

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Backbone Networks

• Media that connects network devices
• Hubs
• Switches
• Routers
• Gateways
• Carry more traffic than horizontal wiring
• Significant building block of medium and large
  networks

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Backbone Topologies

• Serial backbone
• Daisy chaining
• Distributed backbone
• Collapsed backbone
• Parallel backbone

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Summary Physical Topologies

• Physical topologies concern layout of devices and
  media
• Simple topologies bus, ring, star
• Hybrid topologies use star to emulate bus or ring
• Backbones
• Connect connection devices
• Building block of medium and large networks

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Logical Topologies

• Refers to way data transmitted between nodes
  rather than physical paths
• Each LAN protocol has view of connection of nodes
• Two LAN protocol have logical view of node
  connections, as
• Ring Token Ring (IEEE 802.5)
• Bus Ethernet (IEEE 802.3)

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Switching

• Does not refer to hardware switches
• Types of connection used to send messages or
  frames of message
• Types
• Circuit switching channel dedicated to sending
  all data during a session telephone circuit
• Message switching store and forward all frames
  of message, so entire message travels together
  mailbag traveling through postal system
• Packet switching each frame may take different
  path transport utility gathers frames and
  reassembles them in correct order

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Ethernet

• Developed 1970's by Digital, Intel, and Xerox
  (DIX)
• Most popular modern LAN technology
• Physical layer
• 10/100/1000baseT twisted-pair cable
• 10base5 or 10base2 coaxial cable
• Data Link layer IEEE 802.2
• Modern Ethernet IEEE 802.3

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CSMA/CD

• Carrier Sensed Multiple Access with Collision
  Detection
• Underlying access method for Ethernet

Transmitcomplete
Listen foractivity
Detectactivity?
Detectcollision?
Transmit
Wait
Stop sendingand jam
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Ethernet Frames

• Data frames
• Ethernet 802.2 -- "raw"
• Ethernet 802.3 -- "Novell"
• Ethernet II -- "DIX"
• Ethernet Snap -- various organizations
• Auto detection automatically sets frame used
• Fields in Ethernet II framePreamble Dest
  Source Type data FCS

FCSframe check sequence
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Other Logical Topologies

• LocalTalk--bus
• Developed by Apple for Macintosh devices
• Uses Carrier Sense Multiple Access with Collision
  Avoidance
• Token Ring--ring
• Developed by IBM
• Uses token passing for media access

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FDDI
Secondary ring

• Fiber Distributed Data Interface
• Double ring topology
• Redundancy
• More reliable
• Fiber-optic cable
• Used in WANs and MAN to connect buildings

Primary ring
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ATM

• Asynchronous Transfer Mode
• Fixed size packets
• 48 data bytes
• 5 header bytes
• 53 bytes total
• Predictable performance
• Allows timed transmission of packets
• Virtual circuits
• Quality of Service (QoS)

Source http//www.cellstream.com/Free_Downloads/f
inal_qos.pdf
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Wireless Networks
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Summary

• Physical topologypath data follows
• Bus, ring, star
• Star-wired bus, star-wired ring
• Backbone serial, distributed, collapsed,
  parallel
• Logical topologyLAN protocol view of node
  connection
• Ethernet broadcast on bus
• Token ring token passing on ring
• WANs and MANs FDDI or ATM
• Wireless

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Questions?