Data Communication and Computer Networks

A comprehensive set of practice flashcards covering data communication basics, transmission modes, media, devices, network topologies, LAN/WAN concepts, and VPNs.

What is data communication and what are its three essential elements?

Data communication is the process of transferring messages from a sender to a receiver through a medium; the three elements are a sender (source), a medium, and a receiver (sink).

What are the three data transmission modes and how do they differ?

Simplex (unidirectional only), Half-Duplex (two-way but not at the same time), and Full-Duplex (simultaneous two-way transmission).

In Simplex mode, can both devices transmit?

No. Simplex is unidirectional; only one device transmits while the other receives.

Give an example of Simplex communication.

Keyboard input to a monitor (keyboard -> monitor).

Describe Half-Duplex mode.

Stations can transmit and receive, but not at the same time; one direction at a time.

When is Half-Duplex mode typically used?

In situations where simultaneous two-way communication is not required.

Describe Full-Duplex mode.

Both stations can transmit and receive simultaneously; bidirectional communication occurs.

How is bandwidth shared in Full-Duplex communication?

Signals in one direction share the link capacity with signals in the opposite direction.

What is an example of Full-Duplex communication?

Telephone network where two people can talk and listen at the same time.

What are the main transmission media discussed?

Twisted-pair cables, coaxial cables, optical fibers, microwave systems, and satellite communication.

What are twisted-pair cables and their main characteristics?

One or more twisted-pair wires twisted to reduce noise; cheap; low immunity to noise; low data transfer rate; short distance; thin insulation.

What are coaxial cables and their advantages over twisted pair?

Single copper wire with insulating material, braided shield, and outer coating; higher immunity to noise; higher data rate; longer distance; more costly than twisted pair.

What are optical fibers made of and their key advantages?

Made of glass or plastic; transmit data as light; very high speed; not affected by electromagnetic interference; high immunity to noise; large bandwidth; low losses (~0.1 dB/km); flexible; secure.

What is the approximate transmission loss in optical fiber per kilometer?

About 0.1 dB per km.

What is a characteristic of optical fibers regarding electrical voltage and safety?

Fibre optics do not carry high voltages or current, making them safer than electrical cables.

What is microwave communication and its key benefit?

Microwave is line-of-sight wireless communication; high-speed wireless connections for voice, video, and data; suitable for point-to-point links.

What is satellite communication in brief?

A communication satellite acts as a microwave repeater in space, facilitating telecom, radio, TV, and internet; involves uplink and downlink frequencies and transponder frequency changes.

What is uplink versus downlink frequency in satellites?

Uplink frequency is used to send signals to the satellite; downlink frequency is used by the transponder to send signals back to Earth.

What is the role of a repeater and a transponder in satellites?

A repeater strengthens the received signal; a transponder changes the frequency band of the transmitted signal.

What factors influence the choice of transmission media?

Cost, transmission rate, distance, interference, durability, low error rate, land topography, and ease of installation.

What does a modem do in digital communications?

Converts digital signals to analog for transmission (modulation) and converts received analog signals back to digital (demodulation).

What are the claimed advantages of digital transmission over analog?

Lower costs, no modem required, higher transmission speed, and lower error rate.

What is a multiplexer and its purpose?

A device that combines several data signals into one transmission path; at the receiver, the signals are separated back into original streams.

What is a concentrator in networking?

An intelligent multiplexer that stores and forwards information at maximum line speed, reducing idle time.

What is a Front End Processor (FEP)?

A separate processor that handles network processing tasks, usually located with the host computer, offloading work from the host.

What is a router and its primary function?

A device that connects multiple computers and forwards data packets to their destination along the fastest available path, suitable for networks of any size.

What is a bridge in a network?

A device that connects two networks using the same transmission protocol; a 2-port device.

What is a Brouter?

A bridging router that combines features of a bridge and a router, routing across networks and filtering LAN traffic.

What is a switch and its advantage?

A multiport bridge that performs error checking before forwarding, reducing congestion and forwarding only good packets.

What is a gateway in networking?

A device used to connect two networks that use different transmission protocols.

What is a repeater and its key property?

Regenerates the signal on the same network to extend transmission distance; does not amplify the signal.

What is a hub in a network?

Connects multiple wires from different nodes, such as in a star topology.

What is synchronous transmission?

Data is sent in blocks or frames with constant time intervals and no gaps between characters; faster but more costly.

What is asynchronous transmission?

Data is sent character by character with irregular time intervals and gaps between characters; cheaper but slower with idle time.

What is a network topology?

The arrangement of end points or stations in a network; examples include Star, Ring, Bus, and Mesh.

Describe Star Topology and its advantages.

A host computer connects to local computers via separate channels; devices communicate through the host; adding/removing nodes is easy; centralized and simple to operate; easy fault isolation.

What is Token Ring topology and how does it operate?

Nodes communicate in a ring without a central host; data passes from one node to the next; only one node transmits at a time using token passing.

List advantages of Ring topology.

Easy to add/remove nodes; no central server required; faults easier to identify; equal opportunity to transmit; high-speed, single-direction traffic with token control.

List disadvantages of Ring topology.

Data must pass through all intermediate nodes; a single node failure can affect the whole ring; changes affect performance; dependence on the ring wiring.

Describe Bus topology.

A single shared transmission medium; every node monitors the line; messages are broadcast and read by addressed nodes; simple but has scalability and fault isolation issues.

Advantages of Bus topology.

Reduces the amount of physical cabling required.

Disadvantages of Bus topology.

Difficult to troubleshoot, performance degrades with more traffic, cable length is limited, central bus dependence, potential security risk, signals degrade without boosters.

What is Mesh topology?

Each computer has a direct, dedicated link to every other computer; control is distributed.

Advantages of Mesh topology.

Handles heavy traffic due to dedicated paths; data can be sent to multiple nodes simultaneously; failure of one node does not disrupt the whole network; easy fault identification.

Disadvantages of Mesh topology.

Extremely high cabling costs and complexity; many redundant connections and difficult administration.

What is a Local Area Network (LAN)?

A private network interconnecting computers and peripherals within a limited geographical area.

What is a Wide Area Network (WAN)?

A network that interconnects computers across different sites and geographical locations, often relying on ISPs.

How do LAN and WAN differ in reliability and control?

LANs are private and typically more reliable and secure; WANs depend on third-party service providers and are less reliable and secure.

Compared to WAN, how do LANs typically differ in bandwidth and setup costs?

LANs generally have higher bandwidth and lower initial setup costs than WANs.

What are some typical advantages of LANs?

Shared printers and software, centralized backups, easier software updates, files shared across users, improved communication and collaboration.

What are common disadvantages of LANs?

Email overuse causing time waste, printer queues, security concerns, need for network administration and maintenance.

What are common security concerns in LANs?

Viruses spreading via central backups, user credential security, reliance on file servers, risk of unauthorized access.

What is the difference between Wireless and Wired networks?

Wireless offers mobility and no cabling; Wired provides reliable, fast, and secure connections but less flexibility.

What are advantages of Wireless networks?

Mobility, easy addition of devices, no cabling, potential for guest access, broad user reach.

What are disadvantages of Wireless networks?

Slower and variable speeds, distance and obstacles affect performance, potential security vulnerabilities, neighbor bandwidth usage.

What is Peer-to-Peer (P2P) networking?

All nodes are equal; no central server; each user can share resources directly with others.

What are advantages of P2P networks?

Easy to set up, no central administrator, scalable distribution of traffic, lower hardware cost.

What are disadvantages of P2P networks?

Less secure, harder to administer and backup, data and resources are not centrally organized.

What is Client-Server networking?

A server provides services to clients; clients connect to a centralized server to access resources.

What are advantages of Client-Server networking?

Easy resource location and security, centralized administration and backup, scalable management of data.

What are disadvantages of Client-Server networking?

Servers are a single point of failure, higher hardware cost, potential congestion from many client requests, requires specialized staff.

What is a Virtual Private Network (VPN)?

A network built over public telecommunications lines (usually the internet) to connect remote users or sites to a private network.

What are some advantages of VPNs?

Improved security, remote access from anywhere, potential cost savings, scalability, anonymity in some cases.

What are some disadvantages of VPNs?

Possible slower connection speeds due to added VPN layer, platform compatibility issues, legal considerations in some countries, security depends on proper configuration.