信息通信与网络技术基础总结解析_信息通信工作总结

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1.Data communication is the exchange of data between devices via some form of transmiion medium.2.Data communication system components are meage, sender, receiver, medium and protocol.Protocol is a set of rules that govern data communication Meage is the information(data to be communicated.Sender is the device that sends the data meage.Receiver is the device that receives the meage Medium is the physical path by which a meage travels from sender to receiver 3.A network is a set of devices(often referred to as nodes connected by media links 4.Reliability: frequency of failure recovery time after a failure catastrophe 5.A protocol is a set of rules that govern data communication.the key elements of a protocol are : syntax semantics timing

6.Standards: De facto/by fact De jure/by law 7.ISO: The International Standards Organization ITU-T: The International Telecommunication Union-Telecommunication Standards Sector ANSI: The American National Standards Institute IEEE: The Institute of Electrical and Electronics Engineers EIA: The Electronics Industries Aociation 8.Line configuration: Point-to-point: wired or wirele Multipoint 9.Topology: Mesh Star Bus Tree Ring Peer-to-peer: The devices share the link equally Primary-Secondary: Where one device controls traffic and the other must transmit through it Peer-to-peer: Mesh Ring Bus Primary-Secondary: Star Tree Bus

10.Transmiion Mode: Simplex Half-duplex Full-duplex Simplex mode: one station can transmit, the other can only receive Half-duplex mode: Each station can both transmit and receive, but not at the same time.Full-duplex mode: Both stations can transmit and receive simultaneously 11.The Open System Interconnection(OSI model is a layered framework for the design of network system that allows for communication acro all types of computer systems.OSI model has 7 layers: Physical Data link Network Transportation Seion Presentation Application 12.Peer to peer procees: The procees on each machine that communicate at a given layer are called peer-to-peer procees.This communication is governed by an agree-upon series of rules and conventions call protocols The 7 layers are divided into 3 groups: the network support layers(1,2,3 user support layers(5,6,7 link the above subgroups(4 13.fig.3.3

The proce starts from layer 7, then move from layer to layer in descending sequential order, at each layer(except 7 and 1 a header is added.At layer 2 a trailer is added as well.14.Physical layers: Line configuration Data transmiion mode Topology Signals Encoding Interface Medium 15.The Physical layer coordinates the hardware and software functions required to transmit a bit stream over a Physical medium.It deals with a mechanical and electrical specifications of the primary connections The data link layer is responsible for delivering frames from one station to the next with out errors.It provides error handling and flow control between one station and the next.The network layer is responsible for the source-to-destination delivery of a data packet.It handles switching and routing The transport layer is responsible for the source-to-destination(end-to-end delivery of the entire meage from one application to another.The seion layer is the network dialog controller.It establishes, maintains, and synchronizes the interaction between communicating devices.The presentation layer ensures interoperability among communicating devices.To transact, encrypt, and compre data The application layer enables the user, whether human or software, to acce the network.16.Hz kHz(10^3Hz MHz(10^6Hz GHz(10^9Hz THz(10^12Hz s ms(10^-3s us(10^-6s ns(10^-9s ps(10^-12s 17.The frequency Spectrum of a signal is the combination of all sine wave signals that make that signal.Bandwidth of a signal is the width of the frequency spectrum.18.If we send only those components whose amplitudes are significant(above an acceptable

threshold,we can still recreate the digital signal with reasonable accuracy at the receiver(minimum distortion.We call this part of the infinite spectrum the significant spectrum, and its bandwidth the significant bandwidth.19.Channel capacity is the maximum bit rate a transmiion medium can transfer.It depends on : the type of encoding technique, and the signal-to-noise ratio of the system.20.Encode: Analog/Digital D/D D/A A/A 4 kinds D/D encoding : Unipolar Bipolar Polar Polar: Non-Return to Zero, level NRZ-L: 0 “-” 1 “+” Non-Return to Zero, Inverse NRZ-I: 0 “not changed” 1 “convert” Return to Zero RZ: 0 “-to 0” 1 “+ to 0” Manchester 0 “+ to-” 1 “-to +” Different Manchester 0 “transmiion” 1 “no transmiion” Bipolar: AMI B8ZS HDB3

21.PCM four procees: PAM quantization binary encoding digital encoding 22.A/D PAM: Pulse Amplitude Modulation PCM: Pulse code Modulatio 23.Nyquist 采样定理: f >= 2 f_max

24.D/A encoding: ASK FSK PSK QAM 25.Bit rate(比特率 is the number of bits per second(bps Baud rate(波特率 is the number of signal units per second.ASK baud rate = bit rate = bandwidth(带宽 FSK bandwidth = fc1-fc0 + Nbaud(波特率

26.A diagram called constellation or phase-state diagram is used to show the relationship between phase in PSK 27.Data transmiion: Parallel Serial(Asynchronous Synchronous 28.Parallel transmiion: use n wires to send n bits at one time.In Serial transmiion: one bit follows another, so we need only one communication channel rather than n In Asynchronous transmiion mode: start bit(0 stop bit(1 gaps In Synchronous transmiion mode: we send bits one after another without start/stop bit or gaps.It is responsibility of the receiver to group the bits into meaningful frames.29.A DTE is any device that is a source of or destination for binary digital data.A DCE is any device that transmits or receives data in the form of an analog or digital through a network.DTE-DCE standards try to define the mechanical, electrical and functional characteristics of connection between the DTE and DCE.30.EIA-530 standard is a version of EIA-449 that uses DB-25 Pins.31.Modem is the most familiar type of DCE.Modem stands for modulator/ demodulator.A modulator converts a digital signal to an analog signal.A demodulator converts an analog signal to a digital signal.32.Intelligent modem contain software to support a number of additional functions, such as automatic answering and dialing.33.Transmiion media : Guided media Unguided media Guided media: twisted-pair cable, coaxial cable fiber-optic cable UTP: Unshielded Twisted-pair STP: Shielded Twisted-pair 34.Propagation mode: Multimode Single mode Multimode: Step-index Graded-index 35.光纤优点:noise resistance, le signal attenuation, higher bandwidth

缺点:cost much, hard to installate/maintain, fragility easy broken than wire 36.Multiplexing is the set of techniques that allows the simultaneous transmiion of multiple signals acro a single data link A Path refers to a physical link.Channel refers to a portion of a path that carries a transmiion between a given pair of devices.Multiplexing: Frequency-division multiplexing(FDM Time-division multiplexing(TDM TDM: overlapping.Definition: Synchronous Asynchronous 37.In FDM, channels must be separated by trips of unused bandwidth to prevent signals from FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidth of the signal.TDM is a digital proce that can be applied when the data rate capacity of the transmiion medium is greater than the data rate required by the sending and receiving devices.38.Errors: Single-bit-error, Multiple-bit error, burst-error Error detection and correction is done by the data link layer or transport layer.Single-bit errors is when only one bit in the data unit has changed.Multiple-bit error is when two or more nonconsecutive bits in the data unit have changed.Burst error means that two or more consecutive bits in the data unit have changed.39.Redundancy means adding extra bits for detecting errors at the destination.Redundancy check(冗余校验: VRC, VRC: LRC: CRC: LRC, CRC, checksum Vertical Redundancy Check(垂直冗余校验 Longitudinal Redundancy Check(纵向冗余校验 Cyclical Redundancy Check(循环冗余校验 used in data link layer VRC, LRC, CRC is implemented in physical layer, transport layer.1.Checksum is primarily used by networks, including the internet, and is implemented in the In VRC a parity bit is added to every data unit so that the total

number of 1s(including Parity bit becomes even for even-parity check or odd for odd-parity check.VRC can detect all single-bit errors.It can detect multiple bit or burst errors only if the total number of errors is odd.2.In LRC, a redundant unit is added after a number of data units.3.In CRC a sequence of bits, called the CRC or the CRC remainder is appended to the end of a data unit, so that the resulting data unit becomes exactly divisible by a second, predetermined binary number.40.Application Presentation Seion Transport Network Data link : Physical Line discipline: Who should send now? Flow control: How much data may be sent? Line discipline Flow control Error control Error control: 41.Line discipline: How can errors be corrected? ENQ/ACK Poll/Select Enquiry/acknowledgement: ENQ/ACK.is used in peer to peer communication, where there are dedicated link between two devices Poll/Select line discipline is used in primary-secondary communication if the primary wants to receive data, it asks the secondaries If they have anything to send;this function is called polling.If the primary wants to receive, this function is called selecting.43.Flow control: stop-and-wait ARQ go-back-n Sliding window ARQ selective-reject sliding window ARQ: In go-back-n ARQ, retrains miion begins with the last unacknowledged frame even if subsequent frames have arrived correctly.Duplicate frames are discarded.44.Data link protocol: Asynchronous protocol Character-oriented protocol Synchronous protocol Bit-oriented protocol 45.Synchronous protocols: of bits as data.Data transparency in BSC is achieved by a proce called byte stuffing.It involves two activities: Defining the transparent text region with data link escape(DLE characters and preceding any DLE character within the transparent region by an extra DLE character.47.HDLC defines 3 claes of frames Information frame(I-frame Flag Addre Control Information FCS Flag 46.Data transparency in data communication means we should be able to send any combination Supervisory frames(S-frame Flag Addre Control FCS Flag Unnumbered frame(U-frame Flag Addre Control Information FCS Flag 48.Bit stuffing 作用 Bit stuffing in HDLC is the proce of adding one extra 0 whenever there are five consecutive is in the data so that the receiver does not mistake the data for a flag.49.LANs: Ethernet 50.LLC 定义: MAC 定义: Token bus Token ring FDDI logical link control is the upper sub layer of the data link layer.Media acce control is the lower sub layer of the data link layer.Broadband Analog 51.802.3 defines two categories of LAN : Baseband Digital 52.CSMA/CD : Carrier Sense Multiple Acce with Collision Detection is the result of an evolution from MA to CSMA to CSMA/CD.53.[ 10Base5 ] 10Base-T, cable.10-10Mbps Base-Baseband 5-500meters a star-topology LAN using unshielded twisted pair(UTP cable instead of coaxial 54.Token ring(令牌环网 allows each station to send one frame per turn.Each situation may transmit only during its turn and may send only one frame during each turn.The mechanism that coordinates this rotating is called token paing.55.FDDI: Fiber Distributed Data Interface.（光纤分布式数据接口）FDDI is a local area network protocol standardized by ANSI and the ITU-U.It supports data rates of 100 Mbps.56.4B/5B: FDDI uses a special encoding mechanism called four bits/five bits(4B/5B.Each for-bit segment of data is replaced by five-bit code before being encoded in NRI-I 4B/5B encoding mechanism is designed to avoid long sequence of 0s.57.Switching methods: Circuit switching: circuit Packet Meage switching Time-devising switching Space-division switching 58.TSI(Time-Slot Interchange作用 The main component of time-division switching is a device called a time-slot interchange(TSI.In TSI time slot are sent out in an order based on the decision of a control unit.59.Packet switching: Datagram approach virtual circuit approach 60.X.25 is a packet switching protocol used in a wide area network X.25 is an interface between data terminal equipment and data circuit terminating equipment for terminal operation at the packet mode on public data networks.61.the relationship of X.25 and OSI Network: Data link: Physical: D = 1: D = 0: M = 1: Packet layer protocol(PLP Link acce procedure balanced(LAPB EIA-232 V-Series X-Series others 62.complete packet sequence the packet requires an acknowledgement from final destination no acknowledgement is needed.后面有包 M = 0: 后面没包 63.connecting devices: a.Networking i.ii.i.ii.Repeaters: Bridges: Routers: physical layer1、2 层1、2、3 层 b.Internetworking Gateways: 1~7 层 64.A bridge divide a large

network into smaller segments.They have acce to station addrees and can forward or filter a packet in a network.65.Gateways operate in all seven layers of the OSI model.They covert one protocol to another and can therefore connect two diimilar networks.