Introduction to Computer Networks - Key Concepts

100 question-and-answer flashcards covering fundamental terms, devices, protocols, models, addressing, cabling, topologies, and standards from the lecture notes on Introduction to Computer Networks.

What is a computer network?

A group of computers and other devices connected by transmission media to share resources and information.

Name two major advantages of using a network over stand-alone computing.

Resource sharing (devices & data) and centralised management/administration.

Which two fundamental network models define how computers share resources?

Peer-to-Peer and Client/Server models.

In a peer-to-peer network, how is authority distributed?

No computer has more authority than another; each controls its own resources.

Give one disadvantage of scaling a large peer-to-peer network.

Difficult to locate and manage resources as the number of computers grows.

What device in a client/server network stores shared data and services?

A server.

List three advantages that client/server networks have over peer-to-peer networks.

Centralised user accounts, easier management/security, and higher scalability/performance.

Define an ‘end device’ and give two examples.

A host that sends or receives data on a network, e.g., laptop, VoIP phone.

What is an ‘intermediary device’?

A device that connects end devices or networks, e.g., switch, router, firewall.

What is meant by ‘network service’?

Software that responds to requests for information (e.g., email hosting, web hosting).

Give four common network service categories.

File/Print, Communications, Mail, Internet, and Management services.

What does LAN stand for, and what is its typical scope?

Local Area Network; confined to a room, building, or campus.

Define WAN.

Wide Area Network; connects geographically distant LANs, often across cities or countries.

What is a MAN (or CAN)?

Metropolitan (or Campus) Area Network; links multiple LANs within the same city or campus.

What IEEE standard family defines Wi-Fi networks?

IEEE 802.11.

Which IEEE standard covers Ethernet?

IEEE 802.3.

What is the smallest network category and what does it connect?

PAN (Personal Area Network); connects personal devices around one person.

Which OSI layer is responsible for physical signal transmission?

Layer 1 – Physical layer.

At which OSI layer are MAC addresses used?

Layer 2 – Data Link layer.

Which OSI layer chooses the best path for packets?

Layer 3 – Network layer.

Name the two main Transport-layer protocols and state whether each is connection-oriented or connectionless.

TCP – connection-oriented and reliable; UDP – connectionless and best-effort.

Which OSI layer handles encryption and translation of data formats?

Layer 6 – Presentation layer.

What is encapsulation in networking?

Adding headers/trailers to data as it moves down the OSI layers to form a PDU.

What organisation developed the OSI model?

ISO – International Organization for Standardization.

Which body assigns global IP address blocks?

IANA – Internet Assigned Numbers Authority (under ICANN).

What is the purpose of ANSI?

Coordinates and publishes U.S. technology standards and represents the U.S. at ISO.

Which professional society maintains the IEEE 802 standards?

IEEE – Institute of Electrical and Electronics Engineers.

What wiring standard defines commercial cabling categories such as Cat5e and Cat6?

TIA/EIA-568.

Give two differences between Cat5e and Cat6 cables.

Cat6 supports up to 10 Gbps and has tighter twists/insulation; Cat5e supports up to 1 Gbps.

What is attenuation?

Loss of signal strength as it travels through a medium.

Define crosstalk.

Interference caused when a signal on one wire induces signal on an adjacent wire.

What device regenerates digital signals to combat attenuation?

Repeater.

Which duplex mode allows simultaneous two-way data flow?

Full-duplex.

What is the maximum cable length for a 100 m Cat5e Ethernet segment before a repeater is required?

100 metres (approx. 328 ft).

Name two advantages of fibre-optic cabling over copper.

Higher bandwidth and immunity to electromagnetic interference.

What does MAC in MAC address stand for?

Media Access Control.

How many bits are there in an IPv4 address?

32 bits.

What private IPv4 address range is reserved for Class A?

10.0.0.0 – 10.255.255.255 (/8).

What protocol automatically leases IP addresses to hosts?

DHCP – Dynamic Host Configuration Protocol.

Which four messages complete a typical DHCPv4 lease process?

DISCOVER, OFFER, REQUEST, ACKNOWLEDGE.

What record type in DNS maps a host name to an IPv4 address?

A record.

What is the hierarchical top-level DNS domain used for U.S. government sites?

.gov

Which TCP/IP port number is used by HTTPS?

443.

Which utility sends ICMP Echo Request messages to test reachability?

PING.

What is CSMA/CD and where is it used?

Carrier Sense Multiple Access with Collision Detection; legacy Ethernet access method on half-duplex shared media.

Define MTU.

Maximum Transmission Unit – largest packet size a network layer can transmit without fragmentation.

How many bytes are in the data field of a standard Ethernet frame (minimum and maximum)?

Minimum 46 bytes, maximum 1500 bytes.

What field in an Ethernet II frame stores error-checking information?

FCS – Frame Check Sequence.

Name the internal database a switch uses to map MAC addresses to port numbers.

MAC Address Table (MAT) or CAM table.

What is the primary difference between a hub and a switch?

Hub repeats bits to all ports; switch forwards frames only to the destination port based on MAC address.

Which device operates at OSI Layer 3 and makes forwarding decisions using IP addresses?

Router.

What is a default gateway?

The router interface that a host uses to reach networks outside its local subnet.

What WAN topology connects every site to every other site directly?

Full-mesh topology.

Name two digital subscriber line technologies.

ADSL and VDSL (any DSL accepted).

What does SONET stand for?

Synchronous Optical Network.

Which WAN technology uses short labels instead of long network addresses for faster forwarding?

MPLS – Multiprotocol Label Switching.

What OSI layer is primarily concerned with flow control and segmentation?

Layer 4 – Transport layer.

Give two common Application-layer protocols and their default ports.

HTTP – port 80, SMTP – port 25 (other valid pairs accepted).

What is a socket in TCP/IP terminology?

Combination of an IP address and a port number identifying a specific process on a host.

Explain ‘broadcast’ traffic in IPv4.

Traffic sent from one host to all hosts on the local network (destination 255.255.255.255 or subnet broadcast).

What is the main purpose of NAT on a router?

Translate private internal IP addresses to a public address for Internet access.

Which layer of the TCP/IP model corresponds to the OSI Physical and Data Link layers combined?

Network Access layer (or Link layer).

State one key similarity between the OSI and TCP/IP models.

Both divide network communication into layered functions to promote interoperability and standardisation.

What is the range of ‘well-known’ TCP/UDP ports?

0–1023.

Which command in Windows displays current IP configuration?

ipconfig (or ipconfig /all).

What kind of address does IPv6 link-local use?

FE80::/10 prefix addresses used only on the local segment.

What IPv6 address type delivers packets to the nearest of several possible hosts?

Anycast address.

Describe the main function of the Presentation layer in three words.

Format, Compress, Encrypt.

Which three layers of the OSI model are often grouped together in actual software (e.g., within an OS)?

Application, Presentation, and Session layers.

What does SSL/TLS provide for web traffic?

Encryption and secure session establishment.

Name two common errors detected by the Data Link layer.

Bit errors (via CRC/FCS) and frame collisions.

What is the purpose of the ‘Time to Live’ (TTL) field in an IPv4 header?

Limits the packet’s lifespan by decrementing at each hop to prevent infinite looping.

Which type of cable has a central copper core, dielectric insulator, and braided shield?

Coaxial cable.

Give one historical Ethernet variant that used coaxial cable.

10Base-2 (Thin Ethernet) or 10Base-5 (Thick Ethernet).

What is signal ‘noise’?

Any undesirable interference that distorts or degrades the transmitted signal.

Explain ‘full-duplex’ in the context of Ethernet switches.

Both devices can transmit and receive simultaneously on separate transmit and receive pairs.

What does VPN stand for and what problem does it solve?

Virtual Private Network; provides secure tunnelling over untrusted networks such as the Internet.

List four fields present in an IPv4 packet header.

Version, Source IP, Destination IP, TTL (others valid: Protocol, Header Checksum, etc.).

Which protocol translates hostnames to IP addresses?

DNS – Domain Name System.

What term describes the unique numerical identifier for every node on a network?

Address (network or MAC/IP depending on layer context).

Define ‘segment’ in networking.

A portion of a network where devices share the same physical medium and collision domain (or subdivision by routers).

What network backbone type has all inter-switch links collapse into a single core device?

Collapsed backbone.

In WAN design, what is the ‘local loop’?

The last-mile connection between customer premises and a telecom provider’s central office.

Which DSL variant provides higher downstream than upstream bandwidth?

ADSL – Asymmetric Digital Subscriber Line.

How many host bits are available in a /24 IPv4 subnet?

8 bits (256 addresses minus network/broadcast).

True or False: UDP guarantees packet order.

False – UDP is unordered and unreliable.

What device combines the functions of a switch and router for home networks?

Home gateway or combo router/switch (often called a home router).

Which Ethernet media access method is used in modern switched networks?

None – switches use dedicated collision-free links; CSMA/CD is effectively disabled.

What command-line tool traces the path packets take to a destination?

tracert (Windows) or traceroute (Linux/macOS).

Name two common connectors used with coaxial cable.

BNC and F-type connectors.

Which transport-layer protocol does DNS primarily use for queries?

UDP (port 53); TCP is used for zone transfers.

What is the default subnet mask for a Class B IPv4 network?

255.255.0.0 (/16).

Describe ‘flow control’ in data communication.

Techniques to prevent a faster sender from overwhelming a slower receiver (e.g., TCP windowing).

What is the main purpose of the Session layer?

Establish, manage, and terminate sessions between applications.

Which OSI layer is responsible for physical addressing?

Layer 2 – Data Link layer.

Give one reason fibre installs are more expensive than copper.

Requires specialised tools and expertise for splicing/termination.

What type of Ethernet cable is needed for 10GBASE-SR connections?

Multimode fibre (e.g., OM3/OM4).

What protocol is used to securely transfer files and replaces insecure FTP?

SFTP (SSH File Transfer Protocol) or FTPS.

Define ‘bandwidth’ in networking terms.

The maximum capacity of a medium to carry data, often measured in bits per second.

What IEEE specification covers Bluetooth PANs?

IEEE 802.15.