Definitions Computer Networks

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    Computer Network Questions

    Q1. What is a computer network?

    Computer network is an interconnection of computers connected together to share information.

    Q2. Differentiate between a computer network and distributed network.

    Computer network follows a client server model while in a distributed system all computer systems are

    independent.

    Q3. What criteria differentiate LAN, MAN and a WAN?Topology, Geographical area and connecting medium.

    Q4. Name the layers of OSI model.

    Open system Interconnection reference model consists of seven layers namely-> Physical layer, data link

    layer, network layer,tranbsport layer, session layer, presentation layer, application layer.

    Q5. Name the layers of TCP/IP reference model.

    The TCP/IP model consists of four layers namely->Physical layer, transport layer, internet layer and

    application layer.

    Q6. What are protocols and services?

    A protocol is an agreement on how the communication is to proceed. A service is the functionality offered

    by a lower level layer to a higher level layer.

    Q7. Name some connection-oriented networks.

    X.25 was the first public data network consists of a 3 byte header and operates at 28 cobs speed.Frame relay network transmitted data in the form of frames.

    ATM network was capable of transmitting data, audio and video signals. It was designed using fiber optic

    network and transmitted data in the form of cells. ATM network has three layers namely Physical, AAL

    (ATM adaptation layer) and ATM layer.Q8. What is Ethernet?

    Ethernet is a coaxial cable network consisting of 500 m long wiring segments with repeaters and operates

    at the speed of 3 mbps.

    Q9.What is 802.11 specifications?

    802.11 specifications are for wireless LANs like Wi-Fi which can be operated with base station or ad-hoc

    form i.e. direct connectivity.

    Q10. What are the features of an analog signal?

    Features of an analog signal include frequencyNo of cycles completed in one second, wavelength->distance covered in one cycle and amplitude-> maximum strength of a signal. Bandwidth refers to the

    range of frequencies covered by a signal.

    Q11. Name some of the communication tasks performed by a communication model

    A communication model consists of a source, medium and destination. The task of a communication

    model include transmission system utilization,interfacing,signal generation,synchronization,exchangfe

    management, error detection and correction, flow control,addressing,routing,recovery,message

    formatting,security,network management.

    Q12. Name some of the well known protocols.

    Some of the well known protocols areBGP->border gateway protocol

    FTP->file transfer protocol

    HTTP->hypertext transfer protocolICMP->internet control message protocol

    IGMP->internet group management protocol

    IP->internet protocol

    MIME->multipurpose internet mail extension

    OSPF->open shortest path first

    RSVP->resource reservation protocol

    SMTP->simple mail transfer protocol

    SNMP->simple network management protocol

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    TCP->transmission control protocol

    UDP->user datagram protocol

    Q13. Differentiate between guided and unguided transmission.

    A guided transmission is along a physical path like in coaxial or fiber optic cable.

    An un-guided transmission is not along a fixed path e.g. wireless transmission.

    Q14. Differentiate between simplex, half duplex and full duplex transmission.

    Simplex transmission is along a single direction and along a single path.Half duplex transmission is along both direction but on a single path in one direction at a time

    Full duplex transmission is along both directions each on two separate paths.

    Q15. Explain different analog and digital transmission methods.

    Cases of digital and analog transmission areAnalog signal and analog medium

    Analog signal and digital medium

    Digital signal and digital medium

    Digital signal and analog medium

    Q16. What are transmission impairments?

    Transmission impairments are hindrances in transmission due to

    Attenuation and attenuation distortion

    Delay distortionNoise

    Q17. What is thermal noise density at room temperature?

    No = kT(W/HZ) = 1.38 X 10^-23 X 290 = 4 X 10^-21 W/HZ = -204dBW/HZ

    Q18. A voice channel with modem transmits at frequency 3100HZ. What is the data rate?Using nyquist formula data rate = 2VLog2 V = 2 X 3100 X8 = 18,600bps

    Q19. Calculate data rate of a channel with spectrum between 3 MHz and 4MHz and SNR = 24dB

    B= 3- 4 = 1 MHz

    Surd = 10log10 (SNR)

    SNR=251

    Data rate = 2B Log (1 + S/N) = 2 X 1 X 8 = 16Mb

    Q20. Explain different twisted pair categories.Category 3 or class C16 MHz (3 twists/mm)Category 5 or class D - 100 MHZ

    Category 5E (Ethylene propylene jacket) - 100 MHz

    Category 6 Class E200 MHzCategory 7 or class F600 MHz

    Q21. What are different types of twisted pairs?

    UTP- Unshielded twisted pair

    STP- Shielded twisted pair

    SSTPScreen shielded twisted pairQ22. What are types of switching?

    Switching is the process of connecting one out of a number of input lines to one out of a number of output

    lines.Circuit switching is the process of establishing a physical connection between the sender and the receiver.

    Message switching is the process of transmitting data messages of variable lengths from sender to

    receiver without setting up a physical path.

    Packet switching involves transmitting fixed sized packets from the sender to the receiver.

    Q23. What is multiplexing?

    Multiplexing is the method of selecting inputs to be transmitted on a single channel.

    Q24. Explain different generations of mobile phone?

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    First generation used analog voice signals, used AMPS (Advanced mobile phone system) in which each

    region was divided into number of cells with a tower at the center of each. While moving from one cell to

    another there was soft handoff (the phone is acquired by new station before leaving the old one) or hard

    handoff (old base station drops before phone shifts to new one). Call management occurs using control,

    paging, access and data signals.

    Second generation used digital voice signals or d_AMPS using TDM (Time division multiplexing)

    Supports GSM (Global system for mobile comm.) which uses tdm or Code division multiple accesses(CDMA) which uses chip sequences to encode signals for each device.

    Third generation uses W_CDMA or UMTS.

    Q25. Name a few error detection methods used in data link layer

    Character count

    Flag bytes with byte stuffing

    Starting and ending flags with bit stuffing

    Physical layer coding violations

    Q26. How is flow control achieved?

    Flow control is achieved using feedback method from the receiver or controlling the rate of flow of the

    transmission

    Q27.Explain error correcting-codes.

    Parity bit (no of 1s in the sending and receiving signal)Hamming distance (difference in numbers of bit at the sending and receiving station)

    CRC(Cyclic redundancy codes in which after division of sending bits by a generator bit set remainder is

    subtracted so that at the receiving station the transmitted bits are fully divisible by the generating bits , if

    not it is considered as error)Q28. Explain elementary data link protocols.

    Simplex protocol (consists of sending and receiving function. the sending functions consists of

    form_networl_layer () and to_ physical_layer () functions. the receiving program consists of

    from_physical_layer () and to_network_layer () functions)

    Stop and wait protocol uses wait_for_event () function, is considered error free, and sender has to wait for

    the receiver acknowledgement before retransmitting.

    Simplex protocol for noisy channel uses positive and negative ack along with a timer.

    Sliding window protocol uses a sliding window or a queue which maintains a list sent frames and ackframes both at the sender and the receiver.

    Go back N is a sliding window protocol which requires all n-I packets to be resent if nth packet is not

    acknowledged.

    Selective repeat requires repletion of only unacknowledged frames and not all the frames. It uses between

    function, case structure with frame_sent, frame_arrival, time_out cases. Sequence numbers and ack

    numbers are also required.

    Q29. Write a few example data link protocols

    HDLC-high level data link control protocol uses a frame format consisting of starting flags, addrss,

    control, data and checksum fields.

    PPP-point to point protocol used in data link layer of internet used for sending ip packets uses frame

    format consisting of address, control, checksum, and payload and starting and ending flags.

    Q30. What are digital signal encoding formats?NRZ-L on return to zero level (high=0 low=1)

    NRZI (non return to zero inverted 0=no transition 1=transition)

    Bipolar (0=no signal 1 = positive or negative level)

    Manchester (0=high to low 1=low to high)

    Differential Manchester (0=transition 1=no transition)

    B8ZS (bipolar zero string 8 zeros replaced by 2 code violations)

    Q31. What is PSK?

    Phase shift keying shifts the phase of carrier signal to represent data

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    Q32. What is deterministic method of error detection?

    It allows associating a probability with successful data transmission

    Q33 Explain characterizes of HDLC.

    HDLC uses three types of base stations (primary station for control, secondary station under primary

    station and combined station having features of both)

    It also uses two link configurations (unbalanced configuration with one primary and one or more

    secondary stations and balanced configuration consisting of two combined stations).It supports three transfer modes (normal response mode, asynchronous balanced mode and asynchronous

    response mode where secondary station initiates transmission without permission of primary station)

    Q34. Differentiate between static and dynamic channel allocation.

    Static channel allocation requires assigning a single channel for communication e.g telephone line

    Dynamic channel allocation assigns the channel based on traffic conditions, collision chances.

    Q35. What is ALOHA?

    ALOHA is a mac layer protocol example in which multiple users share a single channel using contention

    method and there is probability of successful transmission associated with each frame.

    Q35. What is CSMA?

    Carrier sense multiple protocol involves sensing of channel by multiple users before transmitting.

    CSMA can be persistent or non-persistent depending on whether there is persistent sensing for thechannel to be free.

    P-persistent CSMA involves transmitting on the channel with a probability p and q of unsuccessful

    transmission.

    Q36. Explain CSMA/CD?Carrier sense multiple access and collision detect senses the channel before transmitting and if a collision

    occurs it is detected and data is retransmitted.

    Q37. Name a few collision free-protocols.

    Bit-map protocol assigns to each slot a bit depending whether a station needs to transmit and depending

    on the bits stations are allowed to transmit.

    Binary countdown protocol assigns a bit pattern to each station which are ordered and all stations with a

    particular bit set in a positon are allowed to transmit.

    Adaptive tree walk protocol (limited contention protocol) creates stations tree with stations at leaf leveland then tree traversal allows station to transmit.

    Q38. What is WDMA?

    Wavelength division multiple access makes each station transmit at a particular wavelength using fixed-

    length receiver, tunable transmitter, fixed wavelength transmitter and a tunable receiver.

    Q39. Explain wireless-lan protocol.

    MACAmultiple accesses with collision avoidance makes receiver output a short frame so that nearbysending stations can sense it and other stations can avoids to transmit at the same time. for this purpose

    request to send(RTS) and confirm to send (CTS) are used.

    MACAW-MACA for wireless overcomes hidden station and exposed station and other problems using

    acknowledgements so that lost frames can be re-transmitted.

    Q40. Explain features of Ethernet?

    Ethernet uses 10base5 (max segment size of 500 m) thick coax, 10base2 thin coax,10base-T twisted pairand 10Base-F fiber optics.

    Ethernet uses Manchester and differential encoding.

    Ethernet uses multicasting and broadcasting at MAC layer with frame consisting of source, destination,

    preamble, checksum and data fields.

    Ethernet uses binary exponential back off algorithm in which in the event of collisions the sender waits

    for a random no of slots before transmitting again.

    IN switched an intermediate switch is used for transmission.

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    Fast Ethernet uses fiber optic cables 802.3u standard to transmit using 100bast-t4, 100baseTX, and

    100baseFX

    Gigabit Ethernet transmits at more than 1 gbps using fiber optic standards 1000baseSX, 1000baseLX,

    1000baseCX, 1000baseT (UTP),

    Q41. What is IEEE 802.3?

    IEEE 802.3 is logic link control which runs above mac and maps various networks by adding and

    removing its own headers.Q42. What is 802.11?

    IEEE 802.11 standard refers to wireless LANs and consists of protocol stack which has physical layer,

    data link layer and higher layers.

    Physical different 802.11 standards like 802.11(infra-red at 2mbps and speed gray code),802.11(FHSS

    frequency hopping spread spectrum uses 79 channels spending a dwell time at each frequency 2.4

    GHz),802.11(DSSS direct sequence spread spectrum transmits a chip sequence called barker sequence at

    2mbps),802.11a(OFDM orthogonal frequency division multiplexing at 54mbps),802.11b(HR-DSSS high

    rate dsss using walsh/hadamard codes at 11mbps at 4 and 8 bits per baud),802.11g(OFDM ).

    At MAC layer IEEE 802.11 uses csma/ca and macaw protocols using a NAV (network allocation vector)

    storing routing info aboutneighbouring node. A beacon frame is transmitted with dwell time and hopping

    sequence parameters in DCF(distributed coordination function) and PCF(point coordination function)

    mode.Interframe spacing is obtained using SIFS(short interface spacing),PIFS(PCF interfacespacing),DIFS(DCF inter-frame spacing), EIFS(Extended inter frame spacing)

    Q43. What is 802.16?

    IEEE 802.16 is a broadband wireless standard which has layers physical layer (QPSK, QAM-16, QAM-

    64), transmission convergence sub layer, MAC layer, frame structure (type, length, connection ID

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    Q48. What is SONET?

    SONET or synchronous optical network is an optical transmission network with data rate from 50 mbps

    to 150 gbps with each frame consisting os 90 X 9 octets with field like line overhead, path overhead and

    section overhead.

    Q49. What is statistical-TDM?

    This TDM method uses a statistical multiplexer to allocate slots dynamically based on the data rate of the

    devices attached to it.Q50.what is ADSL?

    Asymmetric digital subscriber line is used to transmit more downstream as compared to upstream data

    using fdm.it supports both voice and data channels each at a different frequency.

    HDSL or xDSL transmits at 1.544 mbps

    Q51. What is store and forward packet switching?

    A packet being sent over the network is stored on a router until its checksum has been verified after which

    it is forwarded on to a LAN.

    Q52. What is a virtual circuit?

    A virtual circuit is a physical path established between the source and the destination in a connection

    oriented network.

    Q53. What is a datagram subnet?

    A data gram subnet is used to send independent packets from the source to destination in a connectionlessservice.

    Q54. Differentiate between adaptive and non-adaptive routing.

    Non adaptive routing algorithms do not base their decisions on current traffic conditions and routing

    information is computed offline or in-advance.Adaptive routing algorithms change their routing algorithms to reflect changes in traffic and topology.

    Q55. Enumerate various routing algorithms.

    Optimality principal creates a sink tree which defines optimal route between source and destinations.

    Shortest path algorithm also called dijkastras algorithm computes the shortest path in a network byfinding the next node with the shortest hop distance from the source to the destination.

    Flooding is a static algorithm in every incoming packet is sent on every possible route to make it reach

    the destination.

    Distance vector routing or bellman-ford or ford-Fulkerson algorithm maintains a table or vector givingbest known distance to each destination and is updated every few milli-seconds.

    Count-to-infinity problem means that if a router goes down the news travels fast so that every router has

    to update its table in which case a packet may take infinitely long to reach its destination.

    Link state routing finds the shortest path to each node by sending a packet, calculating the time delay and

    sending the information further to its neighbors after which new routes can be computed.

    Hierarchical routing divides the routers into regions so that each router knows all information about the

    routers in its regions but knowing nothing about other regions.

    Broadcast routing requires data packets be sent ob all the paths to compute the cost.

    Ad hoc routing is followed in mobile hosts using ad hoc on demand distance vector routing algorithms.

    Q56. How is congestion control accomplished?

    Warning bit is included in packets header to be set by the router.Choke packets are sent by the router back to the source to warn congestion.

    Load shedding means throwing away packets by routers in case of congestion.

    RED or random early detection is done by detecting lost packets by the router from the source.

    Jitter control can be used in av data transfer as a means to control congestion by measuring the amount of

    jitter in data packets.

    Q57. Name the parameters for quality of service.

    Over provisioning is achieved by assigning more network resources than required by a transmission.

    Buffering can be used to avoid jitters

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    Traffic shaping is method of carrying service level agreements to smooth out traffic.

    Leaky bucket algorithm allows data to be transmitted at a fixed rate without considering the inflow of

    data.

    Token bucket algorithm transfers data using token to ease out jitters. Resource reservation allows a fixed

    number of resources to be set for good quality of service avoiding packet loss.

    Admission control, packet scheduling and proportional routing are other algorithms for goss qos.

    Q58. What is RSVP?RSVP is resource reservation protocol for maintaining good qos.

    Q59. Explain IP?

    IP is internet protocol responsible for packet routing. Its variants are ipv4 and ipv6.

    An ip header consists of a stack of 32 bits consisting of version number, header lemgth,type of service,

    total length, time to live ,protocol,header checksum, source and destination address.

    There are 4 classes of ip address class A, class B,class C and class D.

    CIDR classless inter domain routing is to assign some of the class B address to class C addresses.

    NAT network address translation is required to fetch ip address of a machine given its hardware address.

    Q60. Discuss internet control protocols.

    ARP address resolution protocol

    RARP reverse address resolution protocolBootp network boot protocol

    DHCP dynamic host configuration protocol for setting up internetworking in a LAN.

    OSPF open shortest path first is an internet gateway routing protocol.

    Interior gateway protocol is supported within the LAN and exterior gateway protocol supports outsidenetwork.

    BGP border gateway protocol is an exterior gateway routing protocol to control routing with certain

    outside hosts and servers for security.

    Q61. Differentiate between ipv4 and ipv6.

    Ipv6 supports 128 bit address.

    Ipov6 supports extensible headers.

    Ipv6 fixed header consists of version, traffic class, flow label, paylosad length, next header, hop limit,

    source and destination address.Q62. What are primitives for transport service?

    Listen, connect, send, receive, disconnect.

    Q63.what is tpdu.

    Transport packet data unit.

    Q64. What is three way handshake?

    It involves the client sending request to server which ack by server followed by server placing its own

    request followed by data exchange.

    Q65. What is rttp?

    Real time transport protocol uses udp to create real time data streams for internet radio,

    videoconferencing etc.

    Q66. What are differ port numbers assigned to tcp service.

    0-1024well known ports (ftp-21, telnet-23, smtp-25, tftp-69, finger-79, http-80, pop3-110, nntp usenet-119)

    1025-65535-reserved ports for tcp programming.

    >65536-ephermal ports which can be used at random.

    Q67.What is components of a TCP header?

    A tcp header consists of source port, destination port, sequence number,ack number, window

    size,checksum,options,data,flags(URG,ACK,PSH,RST,SYN,FIN)

    Q68. What is nagles theorem?

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    Nagles theorem suggests that in tcp communication when data has to be sent by sender just send the first

    bytes and buffer the rest till the first byte is acknowledged.

    Q 69.at is silly window syndrome?

    Silly window syndrome occurs when sender send sends large amount of data while receiver can receive

    one byte at a time.

    Q70. What is tcp congestion control?

    Tcp congestion control can be achieved by congestion window, threshold values.Q71. What is dns?

    Domain name system to specify domains like .com, .org.

    Q72. What is resource record?

    A resource record is used to provide ip address of a hoist against domain name and consists of fields

    SOA(start of authority),A(IP address),MX(Mail exchange)