【正文】 Topics 1 ? Network Topology ? Cables and connectors ? Network Devices Network Topologies 2 ? 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 plicated implementation procedures. Network Topologies 3 ? Topology Physical and logical work layout ? Physical – actual layout of the puter cables and other work devices ? Logical – the way in which the work appears to the devices that use it. ? Common topologies: ? Bus, ring, star, mesh and wireless Bus topology 4 ? Uses a trunk or backbone to which all of the puters on the work connect. ? Systems connect to this backbone using T connectors or taps. ? Coaxial cablings ( 10Base2, 10Base5) were popular options years ago. Bus Topology 5 Advantages Disadvantages Cheap and easy to implement Network disruption when puters are added or removed Require less cable A break in the cable will prevent all systems from accessing the work. Does not use any specialized work equipment. Difficult to troubleshoot. Ring Topology 6 ? Logical ring ? Meaning that data travels in circular fashion from one puter to another on the work. ? Typically FDDI, SONET or Token Ring technology are used to implement a ring work ? Ring works are most monly wired in a star configuration ? Token Ring has multistation access unit (MSAU),equivalent to hub or switch. MSAU performs the token circulation internally. Ring Topology 7 Advantages Disadvantages Cable faults are easily located, making troubleshooting easier Expansion to the work can cause work disruption Ring works are moderately easy to install A single break in the cable can disrupt the entire work. Star Topology 8 ? All puters/devices connect to a central device called hub or switch. ? Each device requires a single cable ? pointtopoint connection between the device and hub. ? Most widely implemented ? Hub is the single point of failure Star Topology 9 Advantages Disadvantages Easily expanded without disruption to the work 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 10 ? Each puter connects to every other. ? High level of redundancy. ? Rarely used. ? Wiring is very plicated ? Cabling cost is high ? Troubleshooting a failed cable is tricky ? A variation hybrid mesh – create point to point connection between specific work devices, often seen in WAN implementation. Mesh Topology 11 Advantages Disadvantages Provides redundant paths between devices Requires more cable than the other LAN topologies The work can be expanded without disruption to current uses Complicated implementation Wireless working 12 ? Do not require physical cabling ? Particularly useful for remote access for laptop users ? Eliminate cable faults and cable breaks. ? Signal interference and security issue. Wireless working 13 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 parison to other work 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 15 ? Media interference ? Electromagic 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 UTP, STP UTP, Fiber all ? Maximum distance ? Repeaters ? Attenuationrelated problems require a work analyzer to detect ? Bandwidth ? Transmis