INTRODUCTION
• Technologytrendsaffectingnetworks • Communicationmodelandtasks
• Networkcriteria
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• NetworkTopology
Technological Driving Forces
Notable Technology Trends
• Trendtowardfasterandcheaper,inbothcomputing and communication
– More powerful Processors supporting more demanding applications
– The increasing use of optical fiber and high-speed wireless has brought transmission prices down and greatly increased capacity
Notable Technology Trends
• TheInternet,WebServices,andassociated applications have emerged as dominant features for both business and personal network landscapes
– “Everything over IP”
– Intranets and extranets are being used to isolate proprietary information
Notable Technology Trends
• Today’snetworksaremoreintelligent
– Differing levels of quality of service (QoS)
– Variety of customizable services in the areas of network management and security
Notable Technology Trends • Mobility
– Smart phones and Pads have become drivers of the evolution of business networks and their use
Enterprise applications are now routinely delivered on mobile devices
– Cloud computing is being embraced
A Communications Model
A Communications Model
Communications Tasks
Back to Basics
The term telecommunication means communication at a
The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data.
Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.
Five components of data communication
1. Message:Themessageistheinformation(data)tobe communicated. Popular forms of information include text, numbers, pictures, audio, and video.
Five components of data communication
2. Sender:Thesenderisthedevicethatsendsthedata message. It can be a computer, workstation, telephone handset, video camera, and so on.
Five components of data communication
3. Receiver:Thereceiveristhedevicethatreceivesthe message. It can be a computer, workstation, telephone handset, television, and so on.
Five components of data communication
4. Transmissionmedium:Thetransmissionmediumisthe physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
Five components of data communication
5. Protocol:Aprotocolisasetofrulesthatgoverndata communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.
Data Flow Types
Data Flow Types – Simplex
• Insimplexmode,thecommunicationisunidirectional.
– Only one of the two devices on a link can transmit; the other can only receive
– Keyboards and traditional monitors are examples of simplex devices
Data Flow Types – Half-Duplex
• Inhalf-duplexmode,eachstationcanbothtransmitand receive, but not at the same time.
– When one device is sending, the other can only receive, and vice versa
– is like a one-lane road with traffic allowed in both directions
– Walkie-talkies are example of half-duplex systems.
Data Flow Types – Full-Duplex
• Infull-duplexmode(alsocalledduplex),bothstations can transmit and receive simultaneously
– is like a two-way street with traffic flowing in both directions at the same time
– signals going in one direction share the capacity of the link with signals going in the other direction
– used when communication in both directions is required all the time
Data Flow Types – Full-Duplex
• Infull-duplexmode(alsocalledduplex),bothstations can transmit and receive simultaneously
1. Eitherthelinkmustcontaintwophysically separate transmission paths, one for sending and the other for receiving; or
2. thecapacityofthechannelisdividedbetween signals traveling in both directions.
Data Flow Types – Full-Duplex
• Infull-duplexmode(alsocalledduplex),bothstations can transmit and receive simultaneously
– One common example of full-duplex communication is the telephone network
When two people are communicating by a telephone line, both can talk and listen at the same time.
Type of Connection
• Apoint-to-pointconnectionprovidesadedicatedlink between two devices.
– The entire capacity of the link is reserved for transmission between those two devices.
– Most point-to-point connections use an actual length of wire or cable to connect the two ends
– other options, such as microwave or satellite links, are also possible
Type of Connection
• Amultipointconnectionisoneinwhichmorethantwo specific devices share a single link
– In a multipoint environment, the capacity of the channel is shared, either spatially or temporally.
– If several devices can use the link simultaneously, it is a spatially shared connection.
– If users must take turns, it is a timeshared connection.
Categories of Topology
• Inameshtopology,everydevicehasadedicatedpoint-
to-point link to every other device
– need n(n–1) physical links
– need n(n–1) / 2 duplex-mode links
– Advantages: Robust, secure, fast, maintainable
– Disadvantages: the amount of cabling and the number of I/O ports required is very large
• Inastartopology,eachdevicehasadedicatedpoint- to-point link only to a central controller, usually called a hub
– The devices are not directly linked to one another
– Ifonedevicewantstosenddatatoanother,it sends the data to the controller, which then relays the data to the other connected device
– Advantages: Less expensive, robust, fault isolation
– Disadvantages: If hub fails the network fails
• Abustopologyismultipoint,onelongcableactsasa
backbone to link all the devices in a network
• Nodesareconnectedtothebuscablebydroplinesand taps. A drop line is a connection running between the device and the main cable
• Advantages:easeofinstallation
• Disadvantages:difficultreconnectionandfaultisolation
• Inaringtopology,eachdevicehasadedicatedpoint- to-point connection with only the two devices on either side of it.
• Asignalispassedalongtheringinonedirection,from device to device, until it reaches its destination.
• Eachdeviceintheringincorporatesarepeater.Whena device receives a signal intended for another device, its repeater regenerates the bits and passes them along
• Advantages:easytoinstallandreconfigure,fault isolation is simplified
• Disadvantages:unidirectionaltraffic(canbesolvedby using a dual ring), A fault in any node will affect the whole network
Network Types
• LocalAreaNetwork
• WideAreaNetwork:Point-to-Point/Switched • Internetwork
• Circuit-SwitchedNetwork
• Packet-SwitchedNetwork
Local Area Network (LAN)
• Alocalareanetwork(LAN)isusuallyprivatelyowned and connects some hosts in a single office, building, or campus
Wide Area Network: Point-to-Point
• Apoint-to-pointWANisanetworkthatconnectstwo communicating devices through a transmission media (cable or air).
Wide Area Network: Switched
• AswitchedWANisanetworkwithmorethantwoends.
• AswitchedWANisusedinthebackboneofglobal communication today.
• AswitchedWANisacombinationofseveralpoint-to- point WANs that are connected by switches.
Internetwork
• Whentwoormorenetworks(LAN/WAN)areconnected, they make an internetwork, or internet.
Internetwork
• HeterogeneousinternetworkofWANS&LANS
Circuit-Switched Network
• Inacircuit-switchednetwork,adedicatedconnection, called a circuit, is always available between the two end systems; the switch can only make it active or inactive.
– The high capacity line can serve multiple low capacity lines (4 in this case)
– Fully utilized when all devices are busy – Might not be fully utilized all the time
Packet-Switched Network
• Inacomputernetwork,thecommunicationbetweenthe two ends is done in blocks of data called packets.
• Exchangeofindividualdatapacketsbetweenthetwo computers, allows many to many connections
• Arouterinapacket-switchednetworkhasaqueuethat can store and forward the packet
– if packets arrive at one router when the thick line is already working at its full capacity, the packets should be stored and forwarded in the order they arrived
References
• DataCommunicationsandNetworking5thedition– 2013, Behrouz A. Forouzan; Chapter 1
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