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Network Topology


Topics Network Topology Cables and connectors Network Devices * * Ethernet is by far the most widely implemented form of local area networking. * When a computer has ... – PowerPoint PPT presentation

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Title: Network Topology

  • Network Topology
  • Cables and connectors
  • Network Devices

Network Topologies
  • LANs and WANs - Geographical coverage
  • LANs
  • A single geographical location, such as office
    building, school, etc
  • Typically High speed and cheaper.
  • WANs
  • Spans more than one geographical location often
    connecting separated LANs
  • Slower
  • Costly hardware, routers, dedicated leased lines
    and complicated implementation procedures.

Network Topologies
  • Topology - Physical and logical network layout
  • Physical actual layout of the computer cables
    and other network devices
  • Logical the way in which the network appears to
    the devices that use it.
  • Common topologies
  • Bus, ring, star, mesh and wireless

Bus topology
  • Uses a trunk or backbone to which all of the
    computers on the network connect.
  • Systems connect to this backbone using T
    connectors or taps.
  • Coaxial cablings ( 10Base-2, 10Base5) were
    popular options years ago.

Bus Topology
Advantages Disadvantages
Cheap and easy to implement Network disruption when computers are added or removed
Require less cable A break in the cable will prevent all systems from accessing the network.
Does not use any specialized network equipment. Difficult to troubleshoot.
Ring Topology
  • Logical ring
  • Meaning that data travels in circular fashion
    from one computer to another on the network.
  • Typically FDDI, SONET or Token Ring technology
    are used to implement a ring network
  • Ring networks are most commonly wired in a star
  • Token Ring has multi-station access unit
    (MSAU),equivalent to hub or switch. MSAU performs
    the token circulation internally.

Ring Topology
Advantages Disadvantages
Cable faults are easily located, making troubleshooting easier Expansion to the network can cause network disruption
Ring networks are moderately easy to install A single break in the cable can disrupt the entire network.
Star Topology
  • All computers/devices connect to a central device
    called hub or switch.
  • Each device requires a single cable
  • point-to-point connection between the device and
  • Most widely implemented
  • Hub is the single point of failure

Star Topology
Advantages Disadvantages
Easily expanded without disruption to the network Requires more cable
Cable failure affects only a single user A central connecting device allows for a single point of failure
Easy to troubleshoot and isolate problems More difficult to implement
Mesh Topology
  • Each computer connects to every other.
  • High level of redundancy.
  • Rarely used.
  • Wiring is very complicated
  • Cabling cost is high
  • Troubleshooting a failed cable is tricky
  • A variation hybrid mesh create point to point
    connection between specific network devices,
    often seen in WAN implementation.

Mesh Topology
Advantages Disadvantages
Provides redundant paths between devices Requires more cable than the other LAN topologies
The network can be expanded without disruption to current uses Complicated implementation
Wireless networking
  • Do not require physical cabling
  • Particularly useful for remote access for laptop
  • Eliminate cable faults and cable breaks.
  • Signal interference and security issue.

Wireless networking
Advantages Disadvantages
Allows for wireless remote access Potential security issues associated with wireless transmissions
Network can be expanded without disruption to current users Limited speed in comparison to other network topologies
Cabling and Connectors
  • General media considerations
  • Broadband versus baseband
  • Baseband transmissions use digital signaling and
    Time Division Multiplexing (TDM)
  • Broadband transmissions use analog and Frequency
    Division Multiplexing(FDM)
  • Dialog modes Simplex, half duplex and full duplex

Cabling and Connectors
  • Media interference
  • Electromagnetic interference (EMI) and cross talk
  • Network media vary in their resistance to the
    effect of EMC.
  • UTP is susceptible and fiber is resistant
  • Attenuation
  • Resistance Coaxial cable gt UTP, STP gt UTP, Fiber
    gt all
  • Maximum distance
  • Repeaters
  • Attenuation-related problems require a network
    analyzer to detect
  • Bandwidth
  • Transmission capacity of a media
  • Data throughput is measured in bits per
    second(bps), Mbps, and Gbps
  • For todays application-intensive networks, Old
    10Mbps is not enough, 100Mbps is very common and
    1000Mbps is used too.

Network Media
  • Cable-based media
  • Coaxial
  • Copper wire to conduct the signals electronically
  • Was the choice for LAN for many years.
  • Retiring
  • Twisted pair
  • Copper wire to conduct too
  • Most widely used
  • Fiber-optic
  • transmits the signals as light
  • Uses glass or plastic conductor and
  • High Cost. Restricted to where segment length and
    higher speeds are needed.
  • Server room, backbone

Twisted-pair cabling
  • Has been around for a long time
  • Created for voice transmissions
  • Most widely used media for networking
  • Lighter
  • More flexible
  • Easier to install
  • Cheaper
  • Greater speeds
  • Two types
  • Unshielded twisted pair (UTP)
  • Shielded twisted pair (STP)

Twisted-pair cabling
  • UTP is more commonplace
  • STP
  • provides the extra shielding by using an
    insulating material wrapped around the wire
  • Greater resistance to EMI and attenuation
  • More cost

Five main categories
Category Cable Types Application
1 UTP Analog voice
2 UTP Digital voice, 1Mbps data
3 UTP, STP 16Mbps data
4 UTP, STP 20Mbps data
5, 5e UTP, STP Data, 100Mbps, 1G
6, 6e UTP, STP Data, 1G, 10G
RJ-45 connectors
  • RJ-45 are used with twisted-pair cabling.
  • Resemble ordinary phone jacks (RJ-11)
  • Eight wires instead of four
  • Larger.
  • Check out this page for how to make cat5 cable.

Fiber-optic cable
  • Use light transmissions
  • EMI, crosstalk and attenuation become no issue.
  • Well suited for data, video and voice
  • Most secure of all cable media
  • Installation and maintenance procedures require
  • Cost of cable
  • Cost of retrofitting of existing network
    equipment because incompatible with most
    electronic network equipment

Fiber-optic cable
  • Single mode fiber
  • A single direct bean of light, allowing for
    greater distances and increased transfer speeds.
  • Multimode fiber
  • Many beams of light travel through the cable
  • This strategy weakens the signal, reducing the
    length and speed the data signal can travel.

Fiber-optic connectors
There are a variety of connectors and several
ways of Connecting these connectors, such
bayonet, snap-lock, and push-pull connectors. A
couple here
MIC, Standard FDDI connector
SC duplex
Wireless media
  • Three types
  • Radio wave
  • Infrared
  • Microwave
  • Speeds of wireless solutions dont keep pace with
    cable solutions
  • Installation and maintenance are far more
    complicated and costly.
  • Some solutions require line-of-sight, such as
    infrared and microwave.

IEEE 802.3 standards
  • IEEE 802.3 standards defines a range of
    networking systems that are bases on the original
    Ethernet standard.

Standard Cable type Segment Length Connector Topology
10Base2 Thin Coaxial 185 meters BNC Physical bus
10Base5 Thick Coaxial 500 meters Vampire Taps Physical bus
10BaseT Category 3,4,5 twisted pair 100 meters RJ-45 Physical star
Fast Ethernet IEEE 802.3u
Standard Cable Type Segment Length Connector Topology
100BaseTx Category 5 UTP 100 meters RJ-45 Physical star
100BaseT4 Category 3,4,5 UTP 100 meters RJ-45 Physical star
100BaseFX Multimode/Single-mode fiber-optic cable 412/Multimode fiber-optic 10,000/single-mode fiber-optic SC,ST,MIC Physical star
Gigabit Ethernet 802.3z and 802.3ab
Standard Cable Type Segment length Connector
1000BaseLX Multimode/ single-mode fiber 550/multimode 5000/single-mode Fiber connectors
1000BaseSX Multimode fiber 550 meters using 50 Micron multimode fiber Fiber connectors
1000BaseCX STP twisted pair 25 meters 9-pin shielded connector, 8-pin fiber channel type 2 connector
1000BaseT Category 5 UTP 100 meters RJ-45
  • Check out this page for how to make cat5 cable.
  • Color codes

  • Pin Number Designations
  • There are pin number designations for each
    color in T568B
  • The pin designations are as follows
  • Color Codes for T568B
  • Pin    color  pair  name
  • ---     -----  ---- ---------
  • 1       wh/or   2   TxData
  • 2       or      2   TxData
  • 3       wh/grn  3   RecvData
  • 4       blu     1
  • 5       wh/blu  1
  • 6       grn     3   RecvData-
  • 7       wh/brn  4
  • 8       brn     4

  • The pinouts for a crossover cable

Crossover cable

Networking Devices
  • repeaters
  • Hubs
  • Switches
  • Bridges
  • Routes
  • Gateways
  • Network Interface Cards (NICs)
  • Wireless access points
  • Modems
  • Punch_down panels

  • The bottom of the networking food chain
  • Connect device and create larger networks
  • Small hubs 5-8 ports (workgroup hubs)
  • Some hubs have more ports, up to 32 normally
  • Direct data packets to all devices connected to
    the hub - shared bandwidth
  • animation
  • Scalability, Collision, inefficient

  • Divide larger networks into smaller sections
  • Check MAC address, forward or block the data
  • Learning bridge builds list of MAC address by
    watching the traffic on the network.
  • Two issues to consider
  • Placement 80/20 rule
  • Bridging loops
  • IEEE 802.1d Spanning tree protocol
  • Types of bridges
  • Transparent bridge
  • Source route bridge
  • Translational bridge

  • Source Route Bridge
  • Used in Token Ring networks.
  • The entire path (ring number and bridge number)
    is embedded within Packet
  • Search frame
  • Route discovery frame
  • Translational bridge
  • Used to convert one networking data format to
  • For example, from Token Ring to Ethernet and vice

  • Like hub, connectivity points of Ethernet network
  • Forward only to the port that connects to the
    destination device
  • knows MAC address
  • Match the MAC address in the data it receives.
  • Fully switched network, a dedicated segment for
    each device is connected to switch. Expensive.

  • Allow full duplex Ethernet
  • Nodes only communicate with switch, never
    directly to each other
  • Use twisted pair or fiber optic cabling, using
    separate conductors for sending and receiving
  • collision pair is used to transmit data
  • It was half duplex before one device can
    transmit at one given time,
  • double the capacity, 100Mbps become 200Mbps
  • Most LAN are mixed with hubs and switches.

Switch routing method
  • Packet-based switches use one of the following
    method to route packet.
  • Cut-through
  • Forward as soon as it received the destination
    MAC first 14 bytes
  • Can cause propagation of error
  • Store-and-forward
  • Error checked before being forwarded
  • Errors are not propagated through network
  • Bad frames are discarded
  • Error checking takes time.
  • Considerably slower

Switch Routing Method
  • FragmentFree
  • Take the advantage of both.
  • Check errors by reading the first 64byte of
    packets where collision most likely happens
  • Offer near cut-through switching performance

Switch physical design
  • LAN switches vary in their physical design
  • Shared-memory
  • Common buffer for all ports
  • Matrix
  • Internal grid with input port and output crossing
    each other
  • First check MAC, then switch makes a connection
    where two ports (input/output) intersect
  • Bus-architecture
  • Common-bus
  • Dedicated buffer for each port and a circuit to
    control the bus access

Switch and Transparent Bridging
  • Most LAN switches use transparent bridging to
    create address lookup tables
  • Transparent bridging is a technology that allows
    a switch to learn everything it needs to know
    about the location of nodes on the network within
    the network administrator having to do anything.
    Has five parts
  • Learning
  • Flooding
  • Filtering
  • Forwarding
  • Aging

Hub and switch cabling
  • To create larger networks, connect hubs and
    switches using
  • Standard port with special cable
  • Special ports with a standard cable
  • Standard port - Medium Dependent
    Interface-Crossed (MDI-X)
  • Two wires are crossed internally
  • Medium Dependent Interface (MDI)
  • To see each other as an extension, no signal to
    be crossed
  • Using crossover cable between two MDI-X ports
  • To uncross the internal crossing

Punch_down panels
  • Wiring closets
  • http//
  • Labeling schemes

  • Create larger networks by joining two networks
  • Dedicated hardware device or computer systems
    with more than one network interface and routing
  • Routing table
  • Static routing
  • Dynamic routing
  • Use special routing protocols to pass info to
    other routers.
  • Distance Vector Routing (RIP)
  • Link state routing (OSPF)

Switch and Router
  • Different with router
  • Typically switch works on lower level (Data link
    Layer) while Router works in higher level
    (Network Layer)
  • Algorithms for router and switch about how to
    forward packers are different
  • For example, switch will forward broadcast, so
    does hub, not router- the address has to be

Routers and Layer 3 Switch
  • While most switches operate at the Data link
    layer(layer2), some incorporate features of a
    router and operate at the network layer (layer3).
  • Layer 3 switches are faster because they are
    build on switching hardware
  • a router is needed for VLANS communication
  • Why not build a router in the switch itself and
    do the forwarding in hardware
  • EX IP forwarding all in hardware
  • Route lookup
  • Decrement the Time to Live (TTL)
  • Recalculation the checksum
  • Forward the frame the frame to correct output

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  • Any device that translate one data format to
    another is called a gateway.
  • Router
  • Bridge
  • Software
  • Gateway and default gateway

  • Channel Server Unit/Digital Service Unit (
    CSU/DSU) or Data Service Unit
  • Convert digital format on LAN into signal used on
  • Sit between LAN and access point provided by
    telecom company
  • Many routers have CSU/DSU functionality

Wireless access points
  • Devices that provide connectivity between
    wireless LAN devices and in most cases a wired
  • Antennae
  • Convert signal from radio wave or other to that
    used on the LANs.

  • Modulator/Demodulator, convert digital signal
    generated by computer into analog signals that
    can travel over conventional phone line.
  • Connect to ISP
  • Dialing up to a LAN
  • Internal add-in expansion cards or external
    devices connect to serial or USB port
  • PCMCIA cards for laptop
  • Speed
  • Modem itself
  • Speed of the Universal Asynchronous
    Receiver/Transmitter (UART) chip,
  • UART 16950 has the speed of 921,600kbp

Network cards
  • Called Network Interface Cards (NIC)
  • Attached to external port
  • PC card
  • Internal Network card
  • System bus compatibility
  • Peripheral Component Interconnect (PCI)
  • Industry Standard Architecture (ISA)
  • System Resources device conflict
  • Media compatibility
  • Twisted pair, coaxial or fiber-optic connection?
  • Driver

ISDN adapters
  • Integrated Services Digital Networking (ISDN) is
    a remote access and WAN technology that can be
    used in place of a Plain old telephone systems
    dial-up link
  • Greater speeds than modem, pick up and drop the
    line considerable faster.
  • Require ISDN terminal adapter
  • Although digital signal, different format with
    the those used on LAN.
  • Create multiple communication channels on a
    single line.

System area network cards
  • Connecting computer systems in a cluster
  • High-performance unit.

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MAC addresses
  • Unique 6-byte address burned info network
    interface, expressed in hexadecimal
  • No matter which protocol is used, MAC address is
    the means by which the network interface is
    identified on the network.
  • IEEE managing MAC address assignment
  • IEEE has a system Identifying the manufacturer by
    looking at the MAC address
  • Discover MAC address, depend on the OS
  • Ifconfig /all on WINDOWs NT/2000
  • Ifconfig a on Linux/UNIX

  • Watch the Intel Gigabit demo.
  • http//

IEEE and Networking standards
  • Institute of Electrical and Electronic Engineers
    (IEEE) developed a series of networking standards
  • Networking technologies developed by
    manufacturers are Compatible
  • Cabling, networking devices and protocols are all
    interchangeable under the banner of a specific

Specification Name
802.1 Internetworking
802.2 The LLC(Logincal Link Control) sublayer
802.3 CSMA/CD ( Carrier Sense Multiple Access with Collision Detection) for Ethernet networks
802.4 A token passing bus
802.5 Token Ring networks
802.6 Metropolitan Area Network (MAN)
802.7 Broadband Technical Advisory Group
802.8 Fiber-Optic Technical Advisory Group
802.9 Integrated Voice and Data Networks
802.10 Standards for Interoperable LAN/MAN Security (SILS) (Network Security)
802.11 Wireless networks
802.12 100Mbps technologies, including 100BASEVG-AnyLAN
802.3 IEEE standard
  • Defines characteristics for Ethernet networks.
  • New additions, 802.3u for Fast Ethernet, 802.3z
    for Gigabit Ethernet, referred to as 802.3x.
  • Speed Original 10Mbps, Fast Ethernet 100Mbps,
    Gigabit Ethernet 1000Mbps
  • Topology bus or star.
  • Media Coaxial and twisted pair cabling, also
    fiber optic cable.
  • Access method CSMA/CD

802.5 IEEE standard
  • Specifies the characteristics for Token Ring
  • Introduced by IBM in the mid 80s, network
    topology of choice until the rise of the
    popularity of Ethernet.
  • Speed 4 to 16Mbps
  • Topology logical ring and most often a physical
    star. Logical ring is often created in the
    Multistation Access Unit (MSAU)
  • Media twisted pair cabling.
  • Access method token passing.

802.11b IEEE Standard
  • Specifies the characteristics of wireless LAN
    Ethernet networks.
  • Special devices called wireless access points to
    allow communicate.
  • Also connect to wired networks to create wireless
    portions of entire networks.
  • Speed 802.11b specifies 11M. Today 802.11g can
    be 108Mbps
  • Media 802.11b standard is 2.4G radio waves.
  • Topology physical wireless, logical bus
  • Access method Carrier Sense Multiple
    Access/Collision Avoidance (CSMA/CA ), a
    variation of CSMA/CD.

  • Fiber Distributed Data Interface (FDDI) standard
    was developed by American National Standards
    Institute (ANSI)
  • Dual ring technology for fault tolerance
  • Speed 100Mbps or higher
  • Topology dual ring topology
  • Media fiber optic cable, gt 2 kilometers. Also
    possible use copper wire as Copper Distributed
    Data Interface (CDDI).
  • Access method token-passing access method

Standard Speed Physical Topology Logical Topology Media Access Method
802.3 10Mbps Bus and Star Coaxial and Twisted pair CSMA/CD
(802.3u) 100Mbps( Fast Ethernet) Star Bus Twisted pair CSMA/CD
(802.3z) 1000Mbps Star Bus Twisted pair CSMA/CD
802.5 4Mbps and 16Mbps Star Ring Twisted pair Token passing
802.11b 11Mbps Wireless Bus Radio waves CSMA/CA
FDDI 100Mbps Dual Ring Ring Fiber-optic Twisted pair/CDDI Token passing
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