NW203 Ch5_PP Topologies

star

• Bus
• Ring
• Star (most popular)
• Mesh
• Hybrid topology(Employs more than one topology)

• Cost
• Scalability
• Bandwidth capacity
• Ease of installation
• Ease of troubleshooting
• Industry standard and Future direction

• 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

• 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

• 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

• In Ethernet network
• Packets received by all devices (broadcast)
• All devices given equal access

• 10Mb/s
• Baseband transmission-carries one signal
• 2: ~200m limit(185m)

• Thinnet networks are relatively inexpensive to install
• Easy to add more workstations
• Use less cable than other topologies
• Works well with smaller networks

• 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

• 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

• No collisions
• Easy to locate and correct problems
• In most implementations, failing devices can be detected and isolated automatically
• No terminators needed

• 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

• 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

• 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

• 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

• 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)

• 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

• 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

• 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)

• 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

• 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

Distributed coordination function (DCF) or physical carrier sense methodRelies 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

• It is inexpensive with the hardware often preinstalled in the computer
• It is easy to configure
• It is easy to manage and maintain

• It has little security and is easily accessed by unauthorized computers
• It is suitable to only very small networks

• 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

• Inexpensive, easy to configure
• Provides easy access between wired and wireless networks
• Scalable to meet requirements of large networks
• Easy to manage and maintain

• Not secured by default
• Limited security options
• Difficult to configure secured network

• 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.)

• 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

• 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)

• 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

• Collisions occur easily
• Only one device at time can access media
• Performance degrades as more devices added

• Implements logical ring topology using physical star topology.
• Uses multistation access unit (MAU) as central hub.

• 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.

• Broken ring can stop all transmissions.
• Device must wait for empty token to transmit.
• Hardware is more expensive than logical bus.

• 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.

• Can use legacy networks and hardware
• Allows scaling out of network without the expense of changing existing network segments
• Greater flexibility in design

• Network is more complex and difficult to maintain
• Difficult to isolate communication problems
• Specialized equipment needed to connect different topologies: Bridges and Brouters

• Most common hybrids
• WAP is physically connected to wired network

• Allows effective cost-scaling to meet growth requirements
• Wireless NICs come preinstalled in laptops
• Can extend network into areas difficult to wire

• Network is more complex and difficult to troubleshoot
• Default WAP security settings may be a security risk
• Losing sight of careful network planning