Computer Networks 1: Physical Layer Technologies

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Questions and Answers

What is the primary function of an ISP?

To develop and maintain the HyperText Transfer Protocol

To manage and maintain the Internet of Things

To regulate the Internet Engineering Task Force

To provide access to the Internet for individuals and organizations (correct)

What is the main difference between ADSL and DSL?

ADSL is a type of satellite channel, while DSL is a type of 4G/5G cellular network

ADSL is a type of Wi-Fi, while DSL is a type of twisted pair cable

ADSL is a type of fiber optic cable, while DSL is a type of coaxial cable

ADSL is an asymmetric form of DSL, while DSL is a symmetric form of ADSL (correct)

What is the role of the IETF in the development of the Internet?

To develop and publish standards for the Internet (correct)

To manage and maintain the Internet of Things

To develop and maintain the Internet Protocol

To provide access to the Internet for individuals and organizations

What is the primary function of IP?

To route data packets over the Internet Signup and view all the answers

What is the relationship between Wi-Fi and IEEE 802.11?

Wi-Fi is a marketing term for IEEE 802.11, which is a type of wireless network Signup and view all the answers

What is the primary function of TCP?

To ensure error-free data transfer over the Internet Signup and view all the answers

What is the primary role of an ISP in providing Internet services?

To act as an intermediary between applications and the Internet infrastructure Signup and view all the answers

What type of ISP is typically used by home users?

Local ISP Signup and view all the answers

Which of the following is NOT a type of ISP?

Postal ISP Signup and view all the answers

What is the primary function of a national ISP?

To connect regional ISPs to the global Internet infrastructure Signup and view all the answers

Which type of ISP is typically used by large businesses and organizations?

Enterprise ISP Signup and view all the answers

What is the role of a global ISP in providing Internet services?

To manage and regulate the Internet infrastructure globally Signup and view all the answers

What is the primary difference between a regional ISP and a national ISP?

The scope of their services Signup and view all the answers

Which type of ISP is responsible for connecting mobile devices to the Internet?

Mobile ISP Signup and view all the answers

What type of ISP provides internet connection to homes and small businesses?

Local ISP Signup and view all the answers

What is the main function of a central office in a DSL access network?

To transmit voice and data signals to the ISP Signup and view all the answers

What is the primary function of a DSLAM in a DSL access network?

To multiplex data signals Signup and view all the answers

What is the typical transmission rate of a DSL access network?

24-52 Mbps Signup and view all the answers

What type of network is used to connect end systems to a router?

Wireless access network Signup and view all the answers

What is the typical transmission rate of a wireless local area network (WLAN)?

54-450 Mbps Signup and view all the answers

What type of network is used to connect companies and universities to the internet?

Enterprise network Signup and view all the answers

What is the primary function of a router in an enterprise network?

To connect to the ISP Signup and view all the answers

What type of network is used to connect mobile devices to the internet?

Wide-area cellular access network Signup and view all the answers

What is the typical transmission rate of a 4G/5G cellular network?

10’s Mbps Signup and view all the answers

Study Notes

Physical Layer Technologies

Fiber optic cable has the highest transmission rate and lowest bit error rate in practice.

Jargon and Abbreviations

Nuts and bolts: the basic practical details.
HTTP: HyperText Transfer Protocol.
Wi-Fi: actually IEEE 802.11, but a marketing firm suggested the name Wi-Fi which resembles Hi-Fi.
There are many types of Wi-Fi: b, a, g, n, ac (wave 1,2), ax.
TCP: Transmission Control Protocol.
IP: Internet Protocol.
ISP: Internet Service Provider.
IETF: Internet Engineering Task Force.
RFC: Request for Comments.
IEEE: Institute of Electrical and Electronics Engineers.
IoT: Internet of Things.
DSL: Digital Subscriber Line.
ADSL: Asymmetric DSL.

Access Networks

Residential access networks.
Institutional access networks (school, company).
Mobile access networks (Wi-Fi, 4G/5G).

Digital Subscriber Line (DSL)

Uses existing telephone line to central office DSLAM.
Data over DSL phone line goes to the Internet.
Voice over DSL phone line goes to the telephone network.
24-52 Mbps dedicated downstream transmission rate.
3.5-16 Mbps dedicated upstream transmission rate.

Home Networks

Wireless and wired devices.
Often combined in a single box.
Cable or DSL modem.
WiFi wireless access point (54, 450 Mbps).
Wired Ethernet (1 Gbps).
Router, firewall, NAT.

Wireless Access Networks

Shared wireless access network connects end system to router.
Via base station aka “access point”.
Wireless local area networks (WLANs) typically within or around a building (~30 m).
802.11b/g/n (WiFi): 11, 54, 450 Mbps transmission rate.
Wide-area cellular access networks provided by mobile, cellular network operator (10’s km).
10’s Mbps transmission rate.

Enterprise Networks

Companies, universities, etc.
Enterprise link to ISP (Internet).
Institutional router.
Ethernet switch.
Institutional mail, web servers.
IEEE: Institute of Electrical and Electronics Engineers.
WiFi.

The Internet: A “Services” View

Infrastructure that provides services to applications.
Provides programming interface to distributed applications.
“Hooks” allowing sending/receiving apps to “connect” to, use Internet transport service.
Provides service options, analogous to the postal service.