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Introduction to Computer Systems
Networking FundamentalsDr. E.C. KulasekereUniversity of Moratuwa
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Network Technology
Connectivity to other computers.Expands the capability of a PC.Satisfies sharing of resources. Expands human communication.Increases security threats.Concurrency effects.
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Modem for Home Connectivity
Most common mode of HAN connection.Some issues related to modems.
Speed: maximum speed 56KNeeds dial up for connection.Telephone line usage while on modem.Price is not to high compared to other services.Needs reconnection when the link dies.
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Other Methods of Connectivity
Cable modem.DSLWirelessSatellite-based services.ISDNLeased LinesAll of these are categorized as broadband. Data rates exceeding 128kbps.
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Home Connection Infrastructure
Modem/NIC/DSLModem interface.ISP/POTS.Switch/Router.Internet/PSTNThen the sequence is inverted. The links maybe digital or analog.
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Cable Modems (Using CATV Services)
This is a piggyback on a cable TV service.Faster than ISDN (128 Kbps).Uses a crossover cable with RJ45 connector.The fiber-coax cable configuration (fig)Not found in Sri Lanka.
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Digital Subscriber Line (DSL)Uses existing POTS to provide a high speed connection. Low cost alternative to ISDN.The connection sharing is more efficient than cable modems. (fig19.2)Common types ADSL and SDSL.Advantageous and disadvantages of DSL/SDSLLow-pass filters are used to isolate the TP signal from DSL signal...\webDocs\DSL.htm
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Wireless Broadband
Used for home users that are out of reach from POTS.Should not be confused with wireless internet services provided for PDAs and mobile phones. Uses microwaves (fig 19.3)Uses routers and modems (fig 19.4)
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Integrated Services Digital network (ISDN)
Uses digital signals on the POTS.Mostly designed for leased lines. Configuration allows for multiple type of terminations (fig 19.7)Uses a terminal adapter (TA) for termination and it is not a modem.Costs more than DSL.
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Leased LinesFor uses with high bandwidth requirements such as businesses.Leased line is 24 hour permanent connection which can only be changed by the TP company (what about DSL?)T1 line 1.5Mbps, T3 line 45Mbps.The BW is split among users by the ISP.Used for connection that has high utilization.
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Sharing Internet Connections
One connection may not be enough for small-office and home (SOHO) systems.Windows 98SE, ME, 2K and XP have built in internet connection sharing (ICS) gateway software (fig 19.12)Routers can also be used for internet sharing (fig 19.13/14)
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Types of NetworksLAN: The smallest office network is referred too as a LANHAN: LAN in a home environment is called a HAN. Used for internet connection sharing.WAN: LANS at different places can be hooked by a WAN.The Internet: A network of LAN/WAN networks.Intranets: One or more LANs in a SOHO environment is called an intranet.Extranets: Intranets that share a part of the network with customers
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Requirements of a NetworkPhysical cable or wireless connection.A common set of communication rules called network protocols.A software to enable transactions called a network operating system.Resources that can be shared.Software that enables computers to access other computers with shared resources: a network client.
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Components of a network
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Network ComponentsLocal area networks contain three basic hardware components
Servers (also called hosts or host computers)ClientsCircuits
Clients and Servers typically work together in client-server networks. Networks without servers are called peer-to-peer networks.Routers are specialized devices responsible for moving information between networks, are also a common network component.Server types: file servers, print servers, Web servers, e-mail and directory servers.
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Network Categorization According to Distance
A common way of thinking about networks is by the scale of the network. 3 common network types are:
Local Area Networks (LANs) which typically occupy a room or building, usually include a group of PCs that share a circuit.Backbone Networks, have a scale of a few hundred meters to a few kilometers. Include a high speed backbone linking the LANs at various locations.Metropolitan Area Networks (MANs) which typically have a scale of a few kilometers to a few tens of kilometers & connects LANs and BNs at different locations, often using leased lines or other commercial services to transmit data.Wide Area Networks (WANs) have a scale of hundreds or thousands of kilometers. Like MANs, leased circuits or other commercially available services are used to transmit data.
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Dr. E.C. KulasekereLAN Topologies
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Bus Topology
These are the earliest networks.Single cable (coaxial) is used with terminations at end.If some part of the cable malfunctioned, since the termination is lost the connections are lost. Adding a new computer was troublesome.
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Ring TopologyThis is a bus with the two ends connected. No termination necessary.Examples are fiber distributed data interface (FDDI) used for large high speed networks.Token ring (IBM) is another example.Is SeaMeWe an example?Signals go in a ring and get absorbed at the sender terminal.Malfunction of ring results in failure (solution: Fig 20.11)
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Star TopologyMost popular type used today.Uses UTP cables to patch panel.Example implementation is a hub.Failure in one link is not catastrophic.For fast Ethernet this is the most commonly used type of configuration.CAT3 (10MB) or CAT5 (100MB) cables are used.
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High Speed Networking
Switched EthernetFast Ethernet100Base-TGigabit Ethernet: Used with fiber optic cables. Can use CAT5 cable. Also referred to as 1000Base-T.ATM
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Switched EthernetSwitched Ethernet relies on centralized multiport switches to provide a physical link between multiple LAN segmentsThe switch is intelligent and switches between segments with maximum BW allocation.It’s a cost-effective technique for increasing the overall network throughput and reducing congestion on a 10-Mbps network.The infrastructure is the same as usual.
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100Base-T100BASE-T retains the familiar CSMA/CD media access technique used in 10-Mbps Ethernet networks. Hence network management system need not be rewritten.Supports a broad range of cabling options. CAT5 UTP, Type 1 STP or duplex multimode fiber cable.It can easily be integrated into existing 10-Mbps Ethernet LANs, so your previous investment is saved
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ATMcell-based fast-packet communication technique that supports data-transfer rates ranging from sub-T1 speeds (less than 1.544 Mbps) up to 10 GbpsAn ATM network can be treated as a single network, whether it connects points in a building or across the countryThe fixed cell length signaling method offers predictable performance.Can be integrated into the existing network.
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Gigabit EthernetThe Gigabit Ethernet standard was approved in June 1998, and its speed of 1 Gbps is a tenfold increase over Fast Ethernet. two basic types: shared and switched.Shared Gigabit Ethernet is a higher-speed version of 10/100BASE-T using CSMA/CD Medium Access ControlSwitched Gigabit Ethernet uses Logical Link Control (LLC)Its primary use is for backbones. The medium is fiber or Category 5e 100-ohm cable.
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More on Wireless Networking
AdvantagesFlexibility in installingFlexibility in usage (movement of PCs)
DisadvantagesSecurity is not so good.Interference from other devices.
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Adhoc Wireless Networks
Inexpensive and flexible.Each workstation relates on a peer-to-peer basis with the other PCs.You can add a wireless router to gain access to the internet if required. Only suitable for small networks where security is not an issue.
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Adhoc Wireless network
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Infrastructure Mode Wireless Network
Larger installations in larger buildings.Depends on access points connected together.Each workstation communicates with the access point rather than directly with another workstation.May not offer BW for networks with heavy traffic. Security is still a concern.
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Infrastructure mode wireless network
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Completely wired network
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Integrated Network
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Fiber Optic Networks
Fiber optic cable is used in applications that require high BW, long distances, and complete immunity to electrical interference.A common application for fiber optic cable is as a network backbone
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Fiber Optic Networks (Cont …)Greater BW. Eg. two million telephone conversations have been simultaneously transmitted over a single fiber using Wavelength-Division Multiplexing (WDM).Low attenuation, longer distances: less repeaters are used so cost effective.Security:It’s very easy to monitor taps. If tapped, the cable leaks light, causing the entire system to fail.Immunity to interference.
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Cables
Most commonly used are the (unshielded twisted pair) UTP cables.The need for better cabling is tied down to the increase in speeds and BW that is required for todays' applications.
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CAT5 CablingCategory 5 (CAT5) cabling is good, solid cable for 100-Mbps LANsCategory 5 standard has been around since 1991If you still have a lot of 10-Mbps equipment, CAT5 cabling will serve your needs. Also handles 100Mbps fast ethernet as well.If you are hitting the limit at 100Mpbs upgrade to CAT5e.
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CAT5e CablingEnhanced Cat 5, was ratified in 1999.It’s an incremental improvement designed to enable cabling to support full-duplex Fast Ethernet operation and Gigabit Ethernet. CAT5e has stricter specifications for PS-ELFEXT (Power Sum Equal-Level Far-End Crosstalk), NEXT (Near-End Crosstalk), Attenuation, and Return Loss (RL) than those for Category 5This is also a 100MHz standard.
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CAT6 CablingFeatures more stringent specifications for crosstalk and system noise. Ratified in 2002.to transmit according to CAT6 specs, jacks, patch cables, patch panels, cross-connects, and cabling must all meet CAT6 standardsall CAT6 components must be backward compatible with CAT5e, CAT5, and Category 3.if CAT6 cable is used with CAT5e jacks, the channel will perform at a CAT5e level.
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Cable Standards
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Cabinets and RacksA cabinet is an enclosure with a door (or doors); a rack is an open frameAn enclosed cabinet can be locked with a simple lock and keyFans are installed to cool.Built in power cabling.Cabling infrastructure provided.
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Connectors/Data Interfaces
..\webDocs\Connector Guide.htmConnectors are important for the cabling infrastructure.If two types of connectors are mixed. The lower speed one will set the limit of operation. ..\webDocs\Data Interfaces.htm
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LAN HardwareIn traditional LANs, only one network node transmits data at a time while all other stations listen. This can lead to timing requirements not satisfied for video tx etc. bridges and routers process data packets on an individual basis, switches maintain multiple, simultaneous data conversions among attached LANsSwitched circuits are better since they are dedicated connections.
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Switch Technologies
The switch you have to buy for the LAN depends on the type of switching that have to be carried out. ..\webDocs\Layer 2, 3, and 4 Switching Overview.htmIn depth analysis of such switches will be done next year.
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Routers and BridgesRouters and bridges link two or more individual Local Area Networks (LANs) to create an extended-network LAN or Wide Area Network (WAN).
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RoutersLink networks using different network identities.Transmit only the data needed by the final destination across the LAN.Examine and rebuild packets without passing errors on to the next LAN. Routers are "smarter" than bridges, because they find the best route for all the data sent to them by the previous router or the end station of the LAN.
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BridgesConnect two parts of the same LAN network to make it larger.Unlike routers, every bridge builds an internal list of addresses of the attached network devices on both sides of it.If the destination address is on the opposite segment or if the bridge doesn't have the address logged, it forwards the information.Bridges operate on MAC-Layer addresses. They're protocol independent, so they transfer data between workstations without having to understand the protocol.
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Media Converters
interconnects different cable types—twisted pair, fiber, and Thin or thick coax—within an existing network
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Media Converters (Cont …)
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Wiring
Cable is cable, so buy the cheapest! – Follow this advice to fall in trouble.experts estimate that 70% of network failures are primarily caused by cable-related problems.So what’s a LAN manager to do?
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Backbone Wiring
Main wiring between closet and floors.Star topology is used for backbone wiring.Starting point for horizonal wiring.
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Horizontal Wiring
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Horizontal Wiring (Cont…)encompasses all cable from a work-area wallplate or network connection to the telecommunications closet.The outlets, cable, and cross-connects in the closet are all part of the horizontal wiring, which gets its name because the cable typically runs horizontally above ceilings or along the floor. ..\webDocs\Premise Wiring.htm
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Other Devices
..\webDocs\Routers & Bridges.htm
..\webDocs\USB & FireWire.htm
..\webDocs\Video Connectors.htm
