NW203 Ch5_PP Topologies

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  1. What is the most popular network topology?
    star
  2. What the the common network topologies?
    • Bus
    • Ring
    • Star (most popular)
    • Mesh
    • Hybrid topology(Employs more than one topology)
  3. Factors in choosing topology
    • Cost
    • Scalability
    • Bandwidth capacity
    • Ease of installation
    • Ease of troubleshooting
    • Industry standard and Future direction
  4. Describe a Bus Topology
    • A physical bus topology
    • -Utilizes a single main cable that runs throughout the network And to which devices are attached
    • Main cable segment must end with terminator to absorb signals (prevents signal bounce)
    • Bus topology uses Thinnet (10Base2) that connects to the NIC using a BNC connector
  5. 10Base2
    • Thinnet network (10Base2)
    • Max. segment length 185 m. (600 ft.)
    • Max. 30 devices per segment
    • Four repeaters to join maximum of 5 segments, three with attached devices
    • thin coaxial cable
  6. 10Base5
    • Thicknet (10Base5 or Thick Ethernet)
    • Uses heavier gauge coaxial cable
    • Sometimes used as backbone network
    • Max. segment length 500 m. (1625 ft)
    • Up to four repeaters and 5 segments
  7. Ethernet bus topology
    • In Ethernet network
    • Packets received by all devices (broadcast)
    • All devices given equal access
  8. 10BASE2 means
    • 10Mb/s
    • Baseband transmission-carries one signal
    • 2: ~200m limit(185m)
  9. Bus topology Advantages
    • Thinnet networks are relatively inexpensive to install
    • Easy to add more workstations
    • Use less cable than other topologies
    • Works well with smaller networks
  10. Bus topology Disadvantages:
    • Cable failure means network is down
    • Access time and performance degrades as devices added to network
    • Maximum bandwidth for Thinnet is no more than 10 megabits/sec (Mbps)
    • During adding of devices, all devices temporarily prevented from using network
    • Difficult to locate problems such as cable breaks, shorts, bad terminators
  11. Describe A ring topology is a topology
    • stations are connected in a ring
    • Uses a MSAU (Ring In, Ring Out)
    • Data flows in a circle from station to station
    • Two types: Single ring and dual ring
    • Token Ring network (IEEE 802.5)
    • Most common single ring topology
    • Data travels in one direction
    • Devices take turns to transmit
  12. Ring Topology Advantages:
    • No collisions
    • Easy to locate and correct problems
    • In most implementations, failing devices can be detected and isolated automatically
    • No terminators needed
  13. Ring Topology Disadvantages:
    • Requires more cable than bus network
    • In some implementations, break in cable brings network down
    • All devices prevented from using network when adding new devices
    • Equipment can be expensive and difficult to locate
  14. Describe Star topology
    • most commonly seen in modern network implementations
    • If a star network is expanded to include one or more additional hubs connected to the main hub then it is called an extended star
    • Most star configurations use copper wire twisted pair cable, but some high-speed versions use fiber-optic cable
  15. Star Topology Advantages:
    • Easy to add more devices
    • Hardware relatively inexpensive and easy to install
    • Failure of one cable does not bring down the network
    • Hub provides centralized management
    • Easy to find and fix device and cable problems
    • Can be upgraded for faster transmission speeds
    • Most common topology, with many available equipment options
  16. star topology Disadvantages:
    • Requires more media than ring or bus network
    • Failure of single central hub can bring down network
    • Failure of hub of extended star brings down devices connected to that hub
  17. Describe Mesh Topology
    • sometimes called a net topology
    • each device is connected to every other device
    • Allows all the devices to continue to communicate if one connection goes down
    • Most reliable network interconnection
    • rarely used as a LAN topology but is often used to create a WAN topology
    • The one common factor in all mesh topologies is the fact that each node supports multiple connections and multiple paths
    • A well-known mesh technology is the PSTN (public switched telephone network)
  18. Mesh Topology Advantages:
    • Flexible variations can meet most network communication needs
    • Provide fault tolerance and the ability to recover from failures
    • Can choose routes based on factors such as traffic and congestion
    • Uses leased lines, so maintenance and upkeep is handled
  19. Mesh Topology Disadvantages:
    • Complex designs may require the assistance of a consultant
    • Network hardware can be expensive and difficult to install
    • A mesh network is difficult to manage and maintain internally
    • Billing methods are based on traffic volume and can be expensive
    • Can be difficult to troubleshoot
  20. Wireless topologies
    • Based on radio frequency communication topologies
    • IEEE standards:
    • 802.11b, 802.11g
    • 802.11a: Lesser used
    • 802.11n: Most Common
    • 802.11ac, ad newest
    • Two primary topologies:
    • Ad hoc
    • Infrastructure (Access Points)
  21. CSMA/CA
    • Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) media access control approaches:
    • Distributed coordination function (DCF) or physical carrier sense method
    • Relies on the ability of computers to physically listen before they transmit
    • Point coordination function (PCF) or virtual carrier sense method
    • Computers wishing to transmit send a request to transmit (RTS) to the access point
    • The access point responds with a clear to transmit (CTS) with the amount of time for which the circuit is reserved
    • All computers hear the CTS and remain silent for the time period
  22. DCF
    Distributed coordination function (DCF) or physical carrier sense methodRelies on the ability of computers to physically listen before they transmit
  23. PCF
    • Point coordination function (PCF) or virtual carrier sense method
    • Computers wishing to transmit send a request to transmit (RTS) to the access point
    • The access point responds with a clear to transmit (CTS) with the amount of time for which the circuit is reserved
    • All computers hear the CTS and remain silent for the time period
  24. Ad Hoc Mode
    • Also known as peer-to-peer mode
    • Devices communicate directly with each other; no central access point
    • Devices can relay messages between each other, extending range of network
    • Typically used in home networks
  25. Ad Hoc Mode Advantages:
    • It is inexpensive with the hardware often preinstalled in the computer
    • It is easy to configure
    • It is easy to manage and maintain
  26. Ad Hoc Mode Disadvantages:
    • It has little security and is easily accessed by unauthorized computers
    • It is suitable to only very small networks
  27. Infrastructure Mode
    • Devices communicate through use of a wireless access point (WAP)
    • Allows combining of wired and wireless networks
    • WAP handles moving data on and off wired network.
    • Wireless clients must be configured for either ad hoc or infrastructure mode; they can’t operate in both at the same time
    • In a home network, the WAP is often a wireless router used to connect computers and share the Internet connection
  28. Infrastructure Mode Advantages:
    • Inexpensive, easy to configure
    • Provides easy access between wired and wireless networks
    • Scalable to meet requirements of large networks
    • Easy to manage and maintain
  29. Infrastructure Mode Disadvantages:
    • Not secured by default
    • Limited security options
    • Difficult to configure secured network
  30. wireless mesh
    • Set of WAPs or other transmission towers with overlapping ranges(E.g.: Cell phone tower network)
    • LAN may become a wireless mesh as more WAPs are added
    • WAP range: Typically 30 -100 m (100-300 ft.)
  31. Logical Topology
    • Describes how devices on a LAN communicate and transmit data
    • Two logical topologies for current PC networks:
    • Logical Bus: Data travels in a linear fashion from the source to all destinations
    • Logical Ring: Data travels in ring from one device to next and back to beginning of the circle
  32. Logical Bus
    • Modern Ethernet networks use a physical star topology with central hub that transmits using a logical bus topology
    • Original standard was 10BaseT (10Mbps star topology)
    • Most common configuration is 100BaseT (100Mbps star topology)
  33. Logical Bus Advantages:
    • One node down does not bring down the entire network
    • The most widely implemented of the logical topologies
    • Hardware readily available and inexpensive
    • Easy to troubleshoot, maintain
    • Additions and changes don’t affect other workstations
  34. Logical Bus Disadvantages include:
    • Collisions occur easily
    • Only one device at time can access media
    • Performance degrades as more devices added
  35. Logical Token Ring
    • Implements logical ring topology using physical star topology.
    • Uses multistation access unit (MAU) as central hub.
  36. Logical Token Ring Advantages:
    • No collisions; uses token-passing access method.
    • Easy to locate and correct problems.
    • Devices may be added without interrupting network.
    • In most implementations, failing devices can be detected and isolated automatically.
  37. Logical Token Ring Disadvantages:
    • Broken ring can stop all transmissions.
    • Device must wait for empty token to transmit.
    • Hardware is more expensive than logical bus.
  38. Wired Hybrid topologies
    • One or more different physical topologies in a single network.
    • Star-ring topology
    • Token Ring network using multiple MAUs
    • Vertical bus connecting LANs on separate floors.
    • WAN mesh connecting LANs
  39. Wired Hybrid Topologies Advantages:
    • Can use legacy networks and hardware
    • Allows scaling out of network without the expense of changing existing network segments
    • Greater flexibility in design
  40. Wired Hybrid Topologies Disadvantages:
    • Network is more complex and difficult to maintain
    • Difficult to isolate communication problems
    • Specialized equipment needed to connect different topologies (Bridges, Brouters)
  41. Wired/wireless Ethernet hybrids
    • Most common hybrids
    • WAP is physically connected to wired network
  42. Wired and Wireless Topologies Advantages:
    • Allows effective cost-scaling to meet growth requirements
    • Wireless NICs come preinstalled in laptops
    • Can extend network into areas difficult to wire
  43. Wired and Wireless Topologies Disadvantages:
    • Network is more complex and difficult to troubleshoot
    • Default WAP security settings may be a security risk
    • Losing sight of careful network planning
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NW203 Ch5_PP Topologies
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NW203 Ch5_PP Topologies
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