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信息通信网络 知识点

1.Data communication is the transfer of data from one device to another via some form of transmission medium.
2.A data communications system must transmit data to the correct destination in an accurate and timely manner.
3.Data transparency means we should be able to send any combination of bits as data. Or no limitation of user’s data
4.A protocol is a set of rules that governs data communication; the key elements of a protocol are syntax, semantics, and timing.
5.The data link layer is responsible for delivering data units from one station to the next without errors
6.Multiplexing is the simultaneous transmission of multiple signals across a single data link.
7.Inverse multiplexing splits a data stream from one high-speed line onto multiple lower speed lines, with no loss in the collective date rate.
8.Switching is a method in which communication devices are connected to one another efficiently.
9.In synchronousl transmission, we send bits one after another without start/stop bits or gaps. It is the responsibility of the receiver to group the bit.
10.Carrier sense multiple access with collision avoidance (CSMA/CA) is CSMA with procedures that avoid a collision
11.HDLC protocol defines three types of frames: the information frame (I-frame), the supervisory frame (S-frame), and the unnumbered frame (U-frame).
http://www.wendangku.net/doc/d320fa35f111f18583d05a99.htmlwork Control Protocol (NCP) is a set of protocols to allow the encapsulation of data coming from network layer protocols; each set is specific for a network layer protocol that requires the services of PPP.
13.Redundancy is the concept of sending extra bits for use in error detection
14.DTE-DCE interface: Include mechanical, electrical and functional specifications (or standards) between DTE and DCE devices
channel capacity of the medium: is the maximum bit rate a transmission medium can transfer.it depends on type of encoding technique and signal–to–noise ratio of the system
15.CSMA/CD: carrier sense multiple access with collision detection . is an access method of ehternet. (project 802.3)
16.10Base-T 10Mbps Baseband with twisted pair UTP, 100 meters length per segment
17.Data link layer node to node delivery**addressing**access control**floe control**error handling**synchronization
18.What is 4B/5B? 4B/5B ensures that there cannot be a data sequence of more than three 0s transmitted across media in FDDI protocol. This takes care of the bit synchronization problems arising from long strings of 0s in NRZ-I encording.
19.What is synchronization point(major and minor) The session layer provides a mechanism, called synchronization points, for recovering data that have been delivered but mishandled. There are two types of synchronization points may be used:major and minor. Major synchronization point must be acknowledge before the session can continue. Minor synchronization points do not need to be confirmed, there are only security blankets.
1.Data communication: the exchange of data (in form of 0s an

d 1s) between two devices via some of transmission medium.
2.Reliability: frequency of failure 故障间隔时间recovery time after a failure 故障修复时间catastrophe 灾难性事故预防 earthquake; fire
3.Security: unauthorized access 非授权访问virus 病毒
4.a protocol is a set of rules that govern data communication. the key elements of a protocol:syntax(语法),semantics(语义) and timing (时序).
5.There are two possible line configurations:point–to–point and multipoint. In a point-to-point line configuration two and only two devices are connected by a dedicated link.
6.Two ways to share a link: Peer-to-peer (对等方式).The devices share the link equally.Primary-secondary (主从方式).
7.Frequency spectrum: is the combination of all sine wave signals that make that signal.Bandwidth: the width of the frequency spectrum.
8.channel capacity: maximum bit rate a transmission medium can transfer
9.unipolar(单极性编码);polar(极化编码);bipolar
10.B8ZS +000+—0—+ —000—+0+—
11.HDB3 奇+000+ —000— 偶+—00— —+00+
12.PCM is actually made up of 4 separate processes: PAM, quantization, binary encoding, digital-to-digital encoding.
13.In asynchronous transmission, grouping bit stream into bytes we send one start bit (0) at the beginning and one or more stop bits(1s) at the end of each byte. There may be a gap between each byte.
14. In synchronous transmission, we send bits one after another without start/stop bits or gaps. It is the responsibility of the receiver to group the bits.
15.In balanced mode when the complementary (互补的)signals arrive at the receiver, they are put through a subtracter (a differential amplifier) so this circuits is less susceptible to noise.
16.Modem=DEC
17.include twisted-pair cable(双绞线电缆), coaxial cable (同轴电缆), and fiber-optic cable
18.single mode multimode
19.Multiplexing(复用) is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.
20.path(通路): the physical link channel (通道): a portion of a path that carries a transmission between a given pair of device
21.If there are n input lines, the frame contains no more than m slots, with m less than n.
22.Inverse multiplex
23.redundancy, which means adding extra bits for detecting errors at the destination
24.data link: Line Discipline Flow Control Error Control
25.ENQ询问 EOT传输结束
26.A data link protocol is a set of specifications used to implement the data link layer.
27.Asynchronous protocols used primarily in modems, feature start and stop bits and variable length gaps between characters.
28.Synchronous protocols can be divided two classes: character-oriented protocol and bit-oriented protocol.
29.byte stuffing DLE
30.high-level data link control (HDLC), supervisor unnumbered frame
31.Bit stuffing is the process of adding one extra 0 whenever there are five consecutive 1s in the da

ta so that the receiver does not mistake the data for a flag
32.Piggybacking (捎带确认): combining data to be sent and acknowledgement of frame received in one single frame
33.LLC: logical link control 逻辑链路控制MAC: media access control 介质访问控制
34.CSMA/CD: Carrier Sense Multiple Access With Detection
35.MA every workstation had equal access to a link without coordination ACK (NAK)
36.CSMA listen(侦听) for exiting traffic (check the voltage)(no voltage→idle) transmit ; cut down (not eliminate) collision
37.CSMA/CD listen; transmit; listen (extremely high voltage——collision); retransmit
38.Token Ring Each station: check destination address regenerate the data 。Change four bits in the last byte of the frame to indicate the address recognized 。discard the used data frame release token
39.Switching methods: circuit switching ,packet switching(datagram approach virtual circuit approach:SVC,PVC), message switching
40.X.25 (Physical LAPB PLP)is a packet switching protocol used in a wide area network
41.A repeater is a device that operates in the physical layer of the OSI model. purpose is regeneration of the signal
42.simple bridges learning bridges multiport bridges
43.Link state packet 链路状态包 (LSP)
44.Advertiser 45. Network 46. Cost 47. Neighbor
48.Transport layer duties:end-to-end delivery Addressing,Reliable delivery Flow Control Multiplexing
49.Upward: many transport layers use the same network connection.
50.Downward: one transport layer uses many network connections
51.The presentation layer handles translation(翻译), encryption /decryption(加密/解密), authentication(认证) , and compression
52.conventional method and public key method
53.File Transfer, Access and Management (FTAM)