Ch. 1 - Intro to Computer Networks Flashcards
Internet overview, protocols, networks, performance, layering
What is the Internet?
Millions of connected computing devices.
Network Protocols
Define the format and order of messages sent/received among network entities, and actions taken on message transmission and receipt.
Network structure
Network edge, access networks, physical media, and network core
Network Edge
- hosts, access network, physical media
- Devices connected to the network, such as computers, smartphones, and IoT devices.
Network core
mesh of interconnected routers; network of networks
Performance
loss, delay, throughput
Key Network Core functions (2)
- forwarding (a.k.a. “switching”)
- routing
Store-and-Forward
entire packet must arrive at router before it can be transmitted on the next link
Packet queueing and loss
if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time:
* packets will queue, waiting to be transmitted on output link
* packets can be dropped (lost) if memory (buffer) in router fills up
How are end systems connected to edge routers?
Via access networks/nets
DSL
Digital Subscriber Line. A method of connecting to the Internet via a phone line. Voice goes over the DSL to the telephone net, and Data goes over to the internet.
Frequency Division Multiplexing
different channels transmitted in different frequency bands
Time Division Multiplexing
each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band (only) during its time slot(s)
What is The difference between DSL and HFC
For HFC homes share access network to cable headend, where as DSL (digital subscriber line) has dedicated access
Hybrid Fiber Coax (HFC)
A network architecture that typically uses fiberoptic cables to bring signals to selected areas of the system called nodes, which are usually based on number of subscribers to be served.
Wireless access networks
Connects end system to router via base station (“access point”)
Packet switching
Where the host breaks application-layer messages into packets
Circuit switching
end-end resources allocated to and reserved for “call” between source and destination
What methods are used for resource allocation?
Packet switching and Circuit switching
What can a ‘bad guy’ do in network security?
Eavesdrop, impersonate, hijack, and DoS.
DoS
Denial of service. Attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resources.
What is packet sniffing?
An application/device monitors and reads network packets as they transverse the network. Plaintext/Cleartext can be read.
What is IP spoofing?
Sending information into the network with false “Sender IP” information.
Communication links
fiber, copper, radio, satellite
transmission rate = bandwidth
What are Networks?
Collection of devices, routers, links: managed by an organization
Internet standards (2)
RFC: Request for comments
IETF: Internet Engineering Task Force
ISP
Internet Service Provider
Packet switches
forward packets (chunks of data)
e.g. routers and switches
IXP
Internet Exchange Point
Packet delay formula
d[nodal] = d[proc] + d[queue] + d[trans] + d[prop]
d[proc]
Nodal processing
- check bit errors, determine output link
d[queue]
Queueing delay
- time waiting at output link for transmission
- depends on congestion level of router
d[trans]
Transmission delay
d[prop]
Propagation delay
Transmission delay formula
d[trans] = L / R
L = Length (bits)
R = Link Transmission Rate (bits/sec)
Propagation delay formula
d[prop] = d / s
D = Distance (m)
S = Speed (m/s)
Traffic intensity formula
(L * a) / R
L = packet length (bits)
a = average packet arrival rate
R = link bandwidth
Traceroute program
Provides delay measurement from source to router along end-end internet path towards destination
Throughput
Rate at which bits are sent from sender to receiver (in bits/[time unit])
Bottleneck link
The link on an end-end path that constrains the end-end throughput
Packet “sniffing”
An attack on wireless networks to capture data and register data flows in order to analyze what data is contained in a packet.
IP spoofing
When an intruder uses another site’s IP address to masquerade as that other site. : injection of a packet with a false source address.
Network security lines of defense
Authentication
Confidentiality
Integrity checks
Access restrictions
Firewalls
[Network security] Authentication
Proving you are who you say you are
[Network security] Confidentiality
- Protecting sensitive information from unauthorized access.
- Ensuring data privacy and secrecy.
[Network security] Integrity checks
Verify the authenticity and completeness of data transmitted over a network.
* checking for data corruption, unauthorized modification, ensuring data hasn’t been tampered with during transmission.
* Common methods: checksums, message authentication codes (MACs), and digital signatures.
[Network security] Access restrictions
- Limiting access to authorized users.
- authentication, authorization, and encryption.
- e.g. Password-protected VPNs
[Network security] Firewalls
specialized “middleboxes” in access and core networks:
- off-by-default: filter incoming packets to restrict senders, receivers, applications
- detecting/reacting to DOS attacks
5 Layers of the Internet Protocol Stack
Physical, Data Link, Network, Transport, Application
Physical Layer
Transmits raw bit streams over physical media.
Data Link Layer
Provides reliable data transfer between nodes on a network.
Network Layer
Routes packets between networks.
Transport Layer
Provides end-to-end reliable data delivery.
Application Layer
Provides services to users, such as email, web browsing, and file transfer.
Packet-Switched Networks
Data is divided into packets and routed independently through the network.
Circuit-Switched Networks
Dedicated circuit is established between the sender and receiver.
Radio link types (5)
- Wireless LAN (WiFi)
- Wide-area (e.g. 4G/5G cellular)
- Bluetooth
- Terrestrial microwave
- satellite
Peering link
a process by which two Internet networks connect and exchange traffic
Content provider network
(e.g, Google); private network that connects its data centers to internet, often bypassing tier-1, regional ISPs
Ethernet (speeds)
Wired access at 100Mbps, 1Gbps, 10Gbps
WiFi
Wireless access points at 11, 54, 450Mbps
IP
Internet Protocol - An addressing system that finds paths to distant computers. Specifies how a router handles a request for another IP address.
Network frame
When the network interface card takes the packets and wraps them up and send them out along the cable to the central hub or switch.
Data center
Physical or virtual infrastructures used by enterprises to house computer, server and networking systems and components for the company’s IT needs
OSI Model
Layers: Physical, Data Link, Network, Transport, Session, Presentation, Application
Focus: Conceptual framework for network communication.
Approach: Vertically layered, clear separation of concerns
Protocol Examples: Not tied to specific protocols, but examples include HTTP (Application), SSL/TLS (Presentation), TCP (Transport), IP (Network), Ethernet (Data Link)
Usage: Primarily educational and conceptual
TCP/IP Model
Layers: Application, Transport, Internet, Network Interface
Focus: Practical model based on internet protocols
Approach: Horizontally layered, with some overlap in responsibilities
Protocol Examples: HTTP, FTP, TCP, UDP, IP, Ethernet
Usage: Widely used in real-world network implementations.
