NW203 Ch5_PP Topologies

  1. What is the most popular network topology?
  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. 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
  23. DCF
    Distributed coordination function (DCF) or physical carrier sense methodRelies on the ability of computers to physically listen before they transmit
  24. 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
  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. For example: Star-ring topology
    • Token Ring network using multiple MAUs
    • Typically a combination of two or more bus, star, or ring topologies.

    • Two common hybrid topologies:
    • 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 and Brouters
  41. Wired and Wireless 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
Card Set
NW203 Ch5_PP Topologies
NW203 Ch5_PP Topologies