Computer Network and Security

Vocabulary-style flashcards covering key networking concepts from the lecture notes.

Data communication

The exchange of data between devices via a transmission medium. It involves five key components: sender, receiver, message, medium, and protocol.

Sender

The device that initiates and transmits the message in a data communication system.

Receiver

The device that receives the message transmitted by the sender.

Medium

The physical path over which the message travels from sender to receiver. Examples include twisted-pair cable, fiber-optic cable, and wireless (air).

Protocol

A set of rules that governs data communication, ensuring proper understanding and interaction between devices.

Network

A group of interconnected devices, such as computers, printers, and servers, that can share data, applications, and resources.

Local Area Network (LAN)

A network that spans a small geographic area, typically within a building or campus, used for sharing data, printers, and Internet access among a limited number of users.

Wide Area Network (WAN)

A network that spans a large geographic area, connecting multiple LANs across cities, states, or even countries.

Metropolitan Area Network (MAN)

A network that covers a geographic area larger than a LAN but smaller than a WAN, typically spanning a city or a large campus.

Personal Area Network (PAN)

A small, personal network typically used for connecting personal devices like smartphones, laptops, and wearables over a very short range (e.g., Bluetooth connection).

Mesh topology

A network topology where every device is connected to every other device via a dedicated point-to-point link. This offers high redundancy but is expensive to implement.

Star topology

A network topology where each device connects to a central hub or switch. All communication passes through the central device.

Bus topology

A network topology where all devices are connected to a single backbone cable through drop lines and taps. Data travels in both directions along the backbone.

Ring topology

A network topology where each device connects to exactly two neighbors, forming a closed loop. Data typically travels in one direction around the ring.

Point-to-Point

A type of connection where a dedicated link is established between two devices, providing the entire capacity of the link for their communication.

Multipoint

A type of connection where a single link is shared by multiple devices. Sharing can be done spatially (multiple devices access different parts of the link) or by time-sharing (devices take turns using the link).

Throughput

The actual rate at which data is successfully transferred over a communication channel or network per unit of time.

Collision domain

A network segment where data packets sent by different devices can collide if they transmit simultaneously. Switches divide a network into smaller collision domains, typically one per port.

Broadcast domain

A network segment in which all connected devices receive broadcast frames originating from any device within that segment. Routers separate broadcast domains.

MAC address

A 48-bit (6-byte) hardware address uniquely assigned to a Network Interface Card (NIC). It operates at the Data Link Layer (Layer 2) and is used to identify devices within a local network segment.

Organizationally Unique Identifier (OUI)

The first 24 bits (3 bytes) of a MAC address that identifies the manufacturer of the network adapter.

IP address

A logical address used for identifying a device on a network and for routing data across different networks (inter-network communication). It can be IPv4 (32-bit) or IPv6 (128-bit) and operates at the Network Layer (Layer 3).

Domain Name System (DNS)

A hierarchical distributed naming system that translates human-readable domain names (e.g., example.com) into numerical IP addresses. This translation (resolution) typically occurs before network communication with that domain begins.

Address Resolution Protocol (ARP)

A protocol used to resolve an IP address to a corresponding MAC address within a local network segment. It typically uses broadcast requests to find the MAC address and then caches the result for future use.

Ethernet

IEEE 802.3 LAN technology that defines the physical and Data Link Layer specifications for wired networks. Classic Ethernet used CSMA/CD, but modern Ethernet primarily uses switches in a star topology without collision detection due to dedicated per-port bandwidth.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

A media access control method used in classic Ethernet where devices 'listen' before transmitting (carrier sense) and, if a collision occurs, stop transmitting, wait a random amount of time, and retry (collision detection).

Ethernet frame

A data unit at the Data Link Layer (Layer 2) for Ethernet. It includes fields such as preamble, Start Frame Delimiter (SFD), destination MAC address, source MAC address, EtherType/Length, payload (data), and Frame Check Sequence (FCS) for error detection.

802.3 frame format

The specific frame format defined by IEEE 802.3 for Ethernet, which includes preamble, Start Frame Delimiter (SFD), Destination Address (DA), Source Address (SA), Length field (followed by LLC for 802.2), payload, and Frame Check Sequence (FCS).

PPP

Point-to-Point Protocol (PPP): A Data Link Layer protocol used to encapsulate various network-layer protocols (like IP) over a serial point-to-point link. It uses Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection, and Network Control Protocols (NCPs) for configuring network-layer protocols.

Serial Line IP (SLIP)

A simpler Data Link Layer protocol for encapsulating IP packets over serial lines. It lacks error detection, compression, and authentication mechanisms, making it less robust and largely replaced by PPP.

What are the fundamental components required for data communication?

Sender, receiver, message, medium, and protocol.

Can a device act as both a sender and a receiver?

Yes, in most full-duplex communication systems, a device can both send and receive data simultaneously or alternately.

What forms can a message take in data communication?

Text, numbers, images, audio, and video.

Differentiate between guided and unguided media.

Guided media (e.g., cables) provide a physical conduit for signals, while unguided media (e.g., air) transmit signals wirelessly.

Why are protocols essential in network communication?

Protocols define how devices communicate, ensuring data is formatted, transmitted, and received correctly, allowing diverse systems to interoperate.

What is the primary purpose of a network?

To enable the sharing of data, applications, and resources among interconnected devices.

What are the typical characteristics of a local area network regarding its scope and ownership?

A LAN covers a small geographic area (e.g., a building or campus) and is typically privately owned and managed.

Provide an example of a common wide area network and describe its function.

The Internet is the most common WAN, connecting billions of devices globally and facilitating worldwide communication and resource sharing.

How does a Metropolitan Area Network differ from a Local Area Network and a Wide Area Network in terms of coverage and typical implementation?

A MAN's coverage is geographically larger than a LAN (city/campus) but smaller than a WAN (countries), often implemented by public entities like city councils or large corporations.

What technology is commonly used to establish a personal area network?

Bluetooth is the most common technology used for establishing a PAN.

What are the advantages and disadvantages of a mesh topology?

Advantages include high fault tolerance and security. Disadvantages are high cost, complex installation, and extensive cabling requirements.

What is the critical point of failure in a star topology?

If the central hub or switch fails, the entire network connected to that device becomes inoperable.

What is a major drawback of the bus topology regarding network traffic and fault isolation?

A single cable break can bring down the entire network, and it's difficult to isolate faults. Also, increased traffic can lead to collisions and degraded performance.

How is data typically transmitted in a ring topology, and what is its vulnerability?

Data usually travels in one direction (unidirectionally) around the ring. Its vulnerability is that a break in the ring or a single device failure can disable the entire network.

When is a direct link between two devices, utilizing its full capacity, most appropriate in network design?

A point-to-point connection is most appropriate when high bandwidth, security, and dedicated communication are required between two specific devices.

Explain the concept of time-sharing in a connection where a single link is shared by multiple devices.

In a multipoint time-sharing connection, multiple devices take turns using the single link during different, allocated time slots to transmit data.

How does network congestion affect the rate of successful data transfer?

Network congestion significantly reduces throughput by increasing delays, packet loss, and retransmissions, leading to overall slower data transfer rates.

What network devices operate at Layer 2 to segment areas where data packets can clash, and what is the benefit of this segmentation?

Switches operate at Layer 2 to segment collision domains, typically assigning one per port. This reduces the likelihood of collisions, improving network performance and efficiency.

What network device is primarily responsible for separating segments where all connected devices receive broadcast frames, and what is the implication of having very large ones?

Routers are primarily responsible for separating broadcast domains. Very large broadcast domains can lead to excessive broadcast traffic, consuming bandwidth and degrading network performance.

How does a hardware address differ from a logical address in terms of function and layer of operation?

A MAC address is a hardware address at Layer 2 for local device identification, while an IP address is a logical address at Layer 3 for routing across networks.

How can the initial 24 bits of a hardware address be used to identify the vendor of a network device?

The Organizationally Unique Identifier (OUI), which comprises the first 24 bits of a MAC address, is assigned to manufacturers and can be used to identify the vendor of a network device.

Explain the difference between IP addresses intended for internal networks versus those used for external internet communication.

Private IP addresses are used within local networks and are not routable on the public internet, whereas public IP addresses are globally unique and used for internet communication.

Describe the process of a domain name resolution when a user types a website address into their browser.

When a user types a website address, the browser queries a DNS resolver, which then performs recursive lookups through root, TLD, and authoritative DNS servers to find the corresponding IP address for the domain name.

When and why would a device use a protocol to find a hardware address based on a logical address?

A device uses ARP when it needs to communicate with another device on the same local network, but only knows its IP address. ARP resolves the IP address to the necessary MAC address for Layer 2 framing.

What are the key characteristics of current wired LAN technology in terms of physical arrangement and how devices access the network?

Modern Ethernet typically uses a star topology with switches, providing dedicated bandwidth per port, and has largely moved away from collision detection methods like CSMA/CD.

Why is a media access control method involving collision detection no longer widely used in contemporary switched networks?

CSMA/CD is largely deprecated in switched Ethernet networks because switches provide dedicated full-duplex connections between devices and the switch port, effectively eliminating collision domains.

What is the purpose of the Frame Check Sequence (FCS) in a data link layer unit for wired networks?

The Frame Check Sequence (FCS) in an Ethernet frame is an error-detecting code (checksum) used to detect errors in the received frame, ensuring data integrity.

How does the IEEE 802.3 frame format differ from the Ethernet II format, regarding a specific field that indicates the type of data or its size?

The 802.3 frame format uses a 'Length' field to indicate the length of the data portion, while the Ethernet II frame uses a 'Type' field which indicates the protocol type present in the payload.

What are the primary functions of Link Control Protocol (LCP) and Network Control Protocols (NCPs) within a serial link data link layer protocol?

LCP is used for establishing, configuring, and testing the data-link connection, while NCPs are responsible for configuring and bringing up different network-layer protocols (like IP) over the PPP link.

Why was a more robust data link layer protocol developed as a replacement for a simpler one for encapsulating IP packets over serial lines?

PPP was developed as a replacement for SLIP because SLIP lacked crucial features such as error detection