Computer Networks Previous Year Questions (page 2)

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A network operating system, such as Windows Server or Novell NetWare, lets computers on a network share files, printers and other resources.

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In half duplex, data can travel in both directions but only one way at a time, like a walkie-talkie. Full duplex allows both directions at once, and simplex allows only one direction.

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The light is on only when the two inputs differ, which is exactly the XOR truth table: 0,0→0; 1,1→0; 0,1 or 1,0→1.

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A LAN covers a limited area and is faster than a WAN. Communication through satellites and microwave links is a feature of a WAN, so only II and III are true.

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A WAN covers a wide geographical area and often uses satellites and microwave links. It is slower than a LAN, not faster, so statement III is false.

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ICMP stands for Internet Control Message Protocol. It carries error and control messages for IP, and ping and traceroute use it.

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Statement I is true: if the central hub fails, the whole star network goes down. Statement II is false: each node has its own link to the hub, so adding computers does not noticeably increase communication time.

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Manchester encoding has a transition in the middle of every bit, so each bit becomes two half-bit pulses. The pulse width is half that of straight binary, which doubles the baud rate.

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Circuit switching sets up a dedicated path between sender and receiver for the whole session, as in a telephone call. Packet and message switching share links.

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CDMA was first used commercially in cdmaOne (IS-95), a 2G digital cellular standard. Later CDMA-based 3G systems were CDMA2000 and WCDMA.

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RTP (Real-time Transport Protocol) carries real-time audio and video over IP networks.

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FTP is file transfer, TFTP is trivial file transfer, Telnet is remote login, and UDP sends datagrams.

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Infrared waves travel through air with no physical conductor, so they are unguided media. Fiber optic, twisted pair and coaxial cable are guided.

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DHCP assigns IP addresses automatically from a pool and also allows manual (static) assignment, along with other network settings.

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A VPN (Virtual Private Network) creates encrypted tunnels over a public network such as the internet, linking remote users or sites privately.

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In peer-to-peer networks every peer can share and access data on other peers directly. No dedicated server is needed, so II is false.

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As keyed: stateful inspection firewalls track inbound network traffic, packet filters are built into operating systems/routers, proxy servers front services such as mail servers, and application-level gateways handle services like Telnet.

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IRCTC reservations, electronic banking through payment gateways and logistics management applications are all information systems that support management. All three are examples.

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GPRS gives end-to-end packet-switched data transfer for both point-to-point and point-to-multipoint services.

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A URL has a protocol (https://), a hostname (www.example.com) and a path made of the directory and filename. All three are parts.

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Full-duplex (duplex) mode lets both stations transmit at the same time. Half duplex allows both directions but only one at a time, and simplex is one direction only.

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A PERT chart is a network of boxes (or nodes) and arrows. The boxes are activities and the arrows show the dependencies between them, so both statements are true.

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The carrier's frequency changes with the bit value (higher for 1, lower for 0) while the amplitude stays the same, which is frequency modulation (FSK).

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ARQ is an error-control protocol in which the sender waits for a positive acknowledgement (ACK) before sending the next frame and retransmits on timeout or NAK.

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Coaxial cable is guided (wired) media. Radio, microwave and light (infrared) transmission are unguided (wireless).

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WDMA is Wavelength Division Multiple Access, used in optical networks where each station is given its own wavelength.

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A hub works at the physical layer, a switch at the data link layer, a router at the network layer and a gateway up to the application layer.

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A URL (Uniform Resource Locator) gives the address and location of a resource on the internet, e.g. https://example.com/page.html.

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A protocol is a set of rules that governs how two computer systems communicate and exchange data.

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SSL works between the application layer and the transport (TCP) layer, not between the network and transport layers. So D is the incorrect characteristic.

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DHCP (Dynamic Host Configuration Protocol) extends BOOTP. It adds automatic, leased assignment of IP addresses and other settings.

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A transistor is a semiconductor device used as an electronically controlled switch or amplifier, and is the basic element of digital circuits.

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A MAN covers a city by connecting many LANs, and it can carry both data and voice. Both statements are correct.

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A multiplexer combines many low-speed input lines into one high-speed line (shared channel). A demultiplexer does the reverse.

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Star and bus are network topologies (along with ring, mesh, tree). There is no "car topology", so only I and II are correct.

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The transmission modes are simplex, half duplex and full duplex. "Half simplex" does not exist, so I and III are correct.

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The session layer (layer 5) handles dialogue control (who may send, and when) and token management, along with synchronisation.

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The network layer (layer 3) routes packets from source to destination across networks using logical (IP) addresses.

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Layers 1-3 are chained (they work hop-by-hop between adjacent devices), and layers 4-7 are end-to-end. The statements reverse this, so neither is true.

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The OSI layers are 1 Physical, 2 Data Link, 3 Network, 4 Transport, 5 Session, 6 Presentation, 7 Application. Layer five is the session layer.

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ANSI X12 is the standard for electronic data interchange (EDI) of business documents. X.75 links packet networks, and XON is a flow-control character.

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After break the control leaves the switch, and no case label precedes a4 = 10000;, so that statement can never be reached. a1, a2 and a3 run for cases 1 and 2 (case 1 falls through).

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DVMRP is the Distance Vector Multicast Routing Protocol, used for routing multicast traffic.

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The carrier is sent for bit 1 and switched off for bit 0. This is on-off keying, a form of amplitude shift keying, i.e. amplitude modulation of the binary signal.

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Attenuation is the loss of signal energy (strength) as the signal travels through the medium, which is why repeaters or amplifiers are needed.

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Systems where many users share one channel and their transmissions can collide are called contention systems (e.g. ALOHA, CSMA).

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Repeater works at the physical layer (IV), bridge at the data link layer (III), router at the network layer (I) and gateway at the transport layer or above (II).

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GPRS is General Packet Radio Service, a packet-switched data service on 2G/GSM networks.

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TCP sets up a connection with a three-way handshake (SYN, SYN-ACK, ACK). The two sides agree on initial sequence numbers before data is sent.

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The retransmission timer starts when a segment is sent. If its ACK does not arrive before the timeout (RTO), the segment is sent again.