2Motivation Local Area Networks (LAN) were motivated by: Decreasing computer sizeDecreasing computer costRealizing computers could help with many tasks
3Interchangeable Media The first data transfers:Used:Magnetic tapesDisksData transferred between computers in a method similar to using floppy disks.
4LAN Generations First Second Third CSMA/CD and token ring Terminal to host and client serverModerate data ratesSecondFDDIBackboneHigh performance workstationsThirdATMAggregate throughput and real time support for multimedia applications
5Third Generation LANsSupport for multiple guaranteed classes of serviceLive video may need 2MbpsFile transfer can use background classScalable throughputBoth aggregate and per hostFacilitate LAN/WAN internetworking
6LAN technologiesMAC protocols used in LANs, to control access to the channelToken Rings: IEEE (IBM token ring), for computer room, or Department connectivity, up to 16Mbps; FDDI (Fiber Distributed Data Interface), for Campus and Metro connectivity, up to 200 stations, at 100Mbps.Ethernets: employ the CSMA/CD protocol; 10Mbps (IEEE 802.3), Fast E-net (100Mbps), Giga E-net (1,000 Mbps); by far the most popular LAN technology
7A Computer Consists Of Circuit Boards Inside a computer are electronic components on circuit boards.Containing electronic componentsContaining wiresComputers having different circuit boards for external devices.
8Circuit Boards Plug Into A Computer Computers are built so it contains a set of sockets.Using wires to connect sockets togetherUsing wires to carry power and dataPlugging circuit boards into sockets to control external devices
9Illustrations of the components visible in a computer when the cover has been removed. A circuit board can plug into each socket; wires connect the sockets to other components.
10Connecting Computers In Early Systems Transferring data between two computers consisted of two circuit boards connected by a cable.Figure 7.2 Illustration of an early computer communication system formed using two circuit boards plugged into sockets in two computers.
11Early SystemsThe computers use cables to transfer data electronically.Operating like an I/O deviceWriting data to circuit boardFigure 7.3 Two pairs of interface boards connecting three computers. Each new computer added to the set requires a new pair of interface boards and an additional cable.
12Early Systems Advantage of early LANs were speed. Disadvantages of early LANs were inconvenience and cost. Requiring effort to:Add a new computerConnect incompatible hardware
13Connecting A Computer to A LAN A computer needs additional hardware to connect it to a LAN.The speed of the LAN does not depend on the speed of the computer attached to it.Communication by heterogeneous computers
14In many LAN systems, a cable connects each computer to a hub. Computers connected to a LAN. Each computer attaches to the hub with a cable; the computers can then communicate directly.
15NICA computer needs network interface hardware and a cable that connects to the LAN.A computer uses the network interface to send and receive data.
16The Importance Of LAN Technology LANs changed the way people used computer networks.Sharing resourcesConnecting machines within a building
17Relationship To The Internet Xerox gave universities a prototype of a new LAN technology.Beginning of EthernetDeveloping the idea of inexpensive and widely available LANs
18Many Independent Networks By late 1970s, many organizations began installing Local Area Networks because they:Were inexpensive.Were easy to installCould operate them independently of a central administration.
19The Proliferation of LANs AdvantagesAn organization can:budget fundsdecide who has accessdevise policies for useDisadvantagesIndependent groups can:Encourage proliferation of different LAN technologies
20Facts About LANs Engineers have devised many LAN technologies LAN performance determines cost.LAN technology may only work with specific computers.
21LANs Are IncompatibleVarious LAN technologies are completely incompatible.Connecting multiple LANs is not possibleEngineered to operate over limited distanceMay be electrically incompatibleEncoding information may not make sense to another LAN
22IEEE802.3 Medium Access Control Random AccessStations access medium randomlyContentionStations content for time on medium
27Gigabit Ethernet - Differences Carrier extensionAt least 4096 bit-times long (512 for 10/100)Frame bursting
28Gigabit Ethernet - Physical 1000Base-SXShort wavelength, multimode fiber1000Base-LXLong wavelength, Multi or single mode fiber1000Base-CXCopper jumpers <25m, shielded twisted pair1000Base-T4 pairs, cat 5 UTPSignaling - 8B/10B
29Wide Area Technologies Exist WAN technology includes an additional special-purpose computer at each site that:Connects to the transmission linesKeeps communication independent of the computer
30Few WANs, Many WANs WANs cost much more than LANs. Require more planningRequire more hardwareOnly a few companies build their own WAN.
31WANs And LANs Are Incompatible Many Wide Area Networks and Local Area Networks exist.Cannot connect a WAN to a LANCannot interconnect the wires from two different networks
32WANs for VoiceRequires very small and nonvariable delays for natural conversation--difficult to provide this with packet-switchingAs a result, the preferred method for voice transmission is circuit-switchingMost businesses use public telephone networks, but a few organizations have implemented private voice networks
33WANs for Data Public packet-switched networks (X.25) Private packet-switched networksLeased lines between sites (non-switched)Public circuit-switched networksPrivate circuit-switched networks (interconnected digital PBXs)ISDN (integrated X.25 and traditional circuit-switching)
34WAN Considerations Nature of traffic stream generally works best with dedicated circuitsbursty better suited to packet-switchingStrategic and growth control--limited with public networksReliability--greater with packet-switchingSecurity--greater with private networks
35Wireless LANs IEEE 802.11 Basic service set (cell) Set of stations using same MAC protocolCompeting to access shared mediumMay be isolatedMay connect to backbone via access point (bridge)Extended service setTwo or more BSS connected by distributed systemAppears as single logic LAN to LLC level
36Wireless LAN—links clients within the vicinity of each other. A network adapter card that is connected to a transmitter, called an access point, via a cable.The transmitter located on a wall gives the signal an uninterrupted path to a wall-mounted receiver on the far side of the room.Data packets are transmitted over the airwaves to the receiver, which is also connected to network clients by a cable.Wireless Extended LAN—connections to clients a couple of miles away.Similar connectivity is an Extended LAN.Transmitter and receiver are typically located outside the buildings.Forms an electronic data communication bridge called a wireless bridge.Data packets up to 25 miles away from the transmitter use spread spectrum radio technology.
37Wireless LAN - Physical Infrared1Mbps and 2MbpsWavelength nmDirect sequence spread spectrum2.4GHz ISM bandUp to 7 channelsEach 1Mbps or 2MbpsFrequency hopping spread spectrum1Mbps or 2MbpsOthers under development
38Wireless LANs Mobility Flexibility Hard to wire areas Reduced cost of wireless systemsImproved performance of wireless systems
39LAN Extension Buildings with large open areas Historical buildings Manufacturing plantsWarehousesHistorical buildingsSmall officesMay be mixed with fixed wiring system
42Client/Server Architecture Combines advantages of distributed and centralized computingCost-effective, achieves economies of scaleFlexible, scalable approach
43Intranets Uses Internet-based standards & TCP/IP Content is accessible only to internal usersA specialized form of client/server architecture
44ExtranetsSimilar to intranet, but provides access to controlled number of outside usersVendors/suppliersCustomers
45Topology: The way in which components are assembled. Every computer network has the same basic components:Cables or wireless connectionNetwork adapter cards that transmit and receive informationClient software that makes all these components work togetherTopology: The way in which components are assembled.There are six topologies used in the design of a computer network:BusStarRingToken PassingHubsHybrid
46Topologies Tree Bus Ring Star Special case of tree One trunk, no branchesRingStar
48A bus topology requires: Clients are connected to the same cable known as a trunk, segment, or backbone.All data packets are received by every client regardless of whether the data packet is addressed.Data packets not addressed to the client are ignored.Data packets addressed to the client are accepted and processed by the client.Data packets travel the complete length of the cable, then bounce back.This is called signal bounce and continues until the signal loses energy and dissipates.The network operating system has the responsibility to keep the transmission moving along the cable.A client can malfunction and the network continues to operate, which is called a passive topology.A passive topology is easy to construct, highly reliable, and susceptible to slow performance during heavy network traffic.A break in the cable is commonly caused by an improper network connection.Breaks are hard to track down because every client and device on the network could be suspect.A network outage does not shut down a client's operation. Clients work as a stand-alone.
50Bus and Tree Multipoint medium Transmission propagates throughout mediumHeard by all stationsNeed to identify target stationEach station has unique addressFull duplex connection between station and tapAllows for transmission and receptionNeed to regulate transmissionTo avoid collisionsTo avoid hoggingData in small blocks - framesTerminator absorbs frames at end of medium
51Clients connect to a central device called a concentrator or hub. Clients transmit and receive data packets to and from the concentrator.It is the job of the concentrator to redirect data packets to the appropriate client.Clients only receive data packets addressed to them.Star topology reduces the network traffic clients must handle.The concentrator detects if a client is not connected to the network and returns data packets to the sender.Failure of one client does not disable the entire network.Network services become unavailable if the concentrator malfunctions.Clients use 10BaseT network adapter cards that automatically detect trouble with the concentrator.The client then stops any transmission of data packets and operates as a stand-alone computer untilthe concentrator becomes operational.
52Ring Topology Repeaters joined by point to point links in closed loop Receive data on one link and retransmit on anotherLinks unidirectionalStations attach to repeatersData in framesCirculate past all stationsDestination recognizes address and copies frameFrame circulates back to source where it is removedMedia access control determines when station can insert frame
54Each client is connected consecutively to the single cable. There are no ends to the ring network that must be sealed with a terminator.Data packets pass clockwise from one client to the next.If the data packet isn't addressed to the client, the client resends the data packet to the next client.The client strengthens the signal, allowing the data packet to travel a further distance.Clients connect to a hub. Within the hub is the ring.If one client is not working properly, there is a good chance the entire network will fail.This depends on the network operating system.IBM token ring automatically ignores inactive clients.
55A token ring is a ring-like topology. Clients are connected together to form a ring.Each data packet is transmitted to each client on the network.A special packet, called a token, is used to control transmissions on the network.The token packet is delivered to a client clockwise along the network.The client can accept the token and transmit a data packet.Addresses, data, and other necessary information are added to the token packet.The modified token packet becomes the new data packet and is sent to the hub for delivery to the destination.The destination client acknowledges the data packet.The client that sent the data packet creates a new token packet and passes it to the next client.The client can ignore the token packet, which is then passed along to the next client on the ring.This is called token passing.Token packets can travel more than 10,000 times around the network per second.
56Star Topology Each station connected directly to central node Usually via two point to point linksCentral node can broadcastPhysical star, logical busOnly one station can transmit at a timeCentral node can act as frame switch
57Hubs Types of Hubs Passive Hubs Active Hubs A hub is a central processing device on a network.A hub is used with the star and ring topologies as a concentrator for network traffic.Hub topology is used to divide large network requirements into smaller, serviceable LANs called segments.A hub enables a network administrator to monitor and manage network traffic.A hub is used to link segments together; cabling used by various clients can be mixed and matched.Types of HubsNetworks use one of two kinds of hubs:Passive hubsActive hubsPassive HubsA passive hub acts as a connector box known as a wiring panel.A passive hub connects cables from all clients.A passive hub only provides connectivity among network clients. It does not interrupt transmissions on the network.Active HubsAn active hub ID known as a multi-port repeater.An active hub joins together clients.An active hub boosts the signal along the network like a repeater.An active hub can, in some cases, redirect data packets to the appropriate client.
58Hybrid Topology Star Bus Topology The disadvantage of each topology is reduced by combining topologies.The combined topology is called a hybrid network.There are two common hybrid networks: star bus and star ring topology.Star Bus TopologyThe star bus topology combines the star topology and the bus topology.Clients of the smaller networks use the star topology to connect to its network concentrator.Network concentrators are linked together in a bus topology.The star bus topology controls traffic flow on the network.Traffic between concentrators is less demanding than traffic among clients.The bus topology is a more direct and efficient design for connecting concentrators.The star topology avoids transmission conflicts among clients.The star bus topology enables network expansion.If network response time is slow because of an increase in traffic, clients can be transferred to a differentsegment with its own concentrator.
59The star ring topology combines the best of the star and ring topologies. The star ring topology is referred to as the star wired ring topology.The star ring topology divides the network into smaller networks each having a concentrator or hub used to connect clients.Concentrators are joined together using a master concentrator (sometimes called the main hub) in the form of a ring.The advantage is that network traffic is handled by a topology that best suits the volume of traffic.The network is scalable.A hybrid network reduces the chance that a complete network failure will occur.Only clients directly linked to a concentrator will lose access to network services if the concentrator malfunctions.