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Questions and Answers
What is a characteristic of the application layer in networking?
What is a characteristic of the application layer in networking?
Which statement regarding TCP and UDP is true?
Which statement regarding TCP and UDP is true?
What does the transport layer primarily do?
What does the transport layer primarily do?
In protocol layering, which layer is responsible for defining the fields in a datagram?
In protocol layering, which layer is responsible for defining the fields in a datagram?
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What are the packets called that are processed by the link layer?
What are the packets called that are processed by the link layer?
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When using TCP, what services are typically provided?
When using TCP, what services are typically provided?
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Which of the following statements correctly describes the physical layer?
Which of the following statements correctly describes the physical layer?
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Which layer is primarily responsible for determining the routes that datagrams take across networks?
Which layer is primarily responsible for determining the routes that datagrams take across networks?
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What is the primary function of a socket in computer networking?
What is the primary function of a socket in computer networking?
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Which characteristics are NOT guaranteed by TCP and UDP in the Internet transport protocols?
Which characteristics are NOT guaranteed by TCP and UDP in the Internet transport protocols?
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Which component of a URL specifies the server that houses a web object?
Which component of a URL specifies the server that houses a web object?
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How do web browsers interact with web servers following the HTTP protocol?
How do web browsers interact with web servers following the HTTP protocol?
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Which HTTP version introduced significant improvements over its predecessor by allowing multiplexing of requests?
Which HTTP version introduced significant improvements over its predecessor by allowing multiplexing of requests?
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What distinguishes TCP from UDP in terms of transport layer services?
What distinguishes TCP from UDP in terms of transport layer services?
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In the context of services provided by transport-layer protocols, which feature is primarily associated with reliable data transfer?
In the context of services provided by transport-layer protocols, which feature is primarily associated with reliable data transfer?
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Which of the following best describes the relationship between a client and a server in P2P file sharing?
Which of the following best describes the relationship between a client and a server in P2P file sharing?
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What is the primary function of the transport layer in network communication?
What is the primary function of the transport layer in network communication?
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Which protocol primarily governs the operation of the World Wide Web?
Which protocol primarily governs the operation of the World Wide Web?
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Which of the following accurately describes the functions performed by a web server?
Which of the following accurately describes the functions performed by a web server?
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What distinguishes TCP from UDP in terms of transport layer services?
What distinguishes TCP from UDP in terms of transport layer services?
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Which component adds network-layer header information to the transport-layer segment?
Which component adds network-layer header information to the transport-layer segment?
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Which network application emerged in the mid-1990s and significantly impacted online interactions?
Which network application emerged in the mid-1990s and significantly impacted online interactions?
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What is a fundamental characteristic of peer-to-peer file distribution?
What is a fundamental characteristic of peer-to-peer file distribution?
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Which layer of the Internet protocol architecture is responsible for creating a link-layer frame after adding its own header?
Which layer of the Internet protocol architecture is responsible for creating a link-layer frame after adding its own header?
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Study Notes
Computer Networks Lecture 01: Introduction
- Course title: Computer Networks
- Instructor: Dr. Sahar M. Ghanem, Associate Professor
- Department: Computer and Systems Engineering
- University: Alexandria University
- Textbook: Computer Networking: A Top-Down Approach, 8th ed., Kurose & Ross
- Course materials and discussions on MS Teams
- TA: Eng. Mohamed Essam
Course Outline
- Grading:
- Attendance & participation: 5-7%
- Assignments & quizzes: 40%
- Midterm: 15%
- Final: 40%
- Join code: 142tcab
- Course outline:
- What is the Internet?
- The Network Edge
- The Network Core
- Delay, Loss, and Throughput in Packet-Switched Networks
- Protocol Layers and Their Service Models
Chapter 1: Computer Networks and the Internet
- The Internet is a computer network connecting billions of devices.
- These devices are called hosts or end systems.
- In 2017, approximately 18 billion devices were connected to the Internet.
- By 2022, the estimated number of connected devices is expected to reach 28.5 billion.
- End systems are connected by communication links and packet switches.
- A packet switch takes a packet, forwards it to an outgoing communication link.
- Transmission rate of a link is measured in bits per second (bps).
- Two prominent types of packet switches are routers and link-layer switches.
- The sequence of communication links and packet switches a packet traverses is termed route or path.
- End systems access the Internet through Internet Service Providers (ISPs).
- Each ISP is a network of packet switches and communication links.
- The Internet runs on protocols, with TCP and IP being important ones.
- TCP/IP protocols collectively are used.
- Internet standards are documented as requests for comments (RFCs).
- There are nearly 9000 RFCs.
- Other bodies also specify network component standards (e.g., IEEE 802 LAN Standards Committee).
A Nuts-and-Bolts Description
- The Internet is a computer network connecting billions of devices.
- All these devices are referred to as hosts or end systems.
- The number of Internet-connected devices is growing rapidly.
- End systems are connected through communication links and packet switches.
- These devices use protocols to communicate.
- The sequence of communication links and packet switches a packet traverses is its route or path.
- Users access the Internet through ISPs.
- ISPs are networks of packet switches and communication links.
A Services Description
- The Internet provides services to applications.
- Applications run on end systems, not packet switches.
- End systems provide a socket interface for applications to interact with the underlying network infrastructure.
- The Internet offers multiple services to applications..
What is a Protocol?
- A protocol defines the format and order of messages exchanged between entities.
- A protocol also defines the actions taken during the transmission or receipt of a message or event.
The Network Edge
- End systems include desktop computers, laptops, smartphones, servers, and other devices connecting to the Internet.
- Non-traditional "things' are also being introduced as end systems..
- End systems are also referred to as hosts as they host applications.
- Hosts can be further categorized as clients and servers.
- Most servers are located in large data centers.
Access Networks
- Home Access: DSL, Cable, FTTH, and 5G Fixed Wireless
- Access in the Enterprise (and the Home): Ethernet and WiFi
- Wide-Area Wireless Access: 3G, LTE 4G, and 5G
Home Access: DSL
- A customer's telco is also its ISP.
- DSL modems use existing telephone lines to exchange data.
- Data and traditional phone signals are encoded on the same line at different frequencies.
- There's a downstream (carrier to user) and upstream (user to carrier) channel.
- DSL is designed for short distances.
- Households can connect to a single DSLAM.
Other Home Access
- Cable Internet uses cable TV infrastructure.
- It's a shared broadcast medium.
- FTTH provides gigabit speeds.
- 5G fixed wireless offers high-speed access without physical cabling.
Access in the Enterprise/Home: Ethernet
- LAN is used to connect end systems to the edge router.
- Ethernet users use twisted-pair copper wire to connect to the Ethernet switch.
- Typical user access is 100 Mbps to tens of Gbps, and servers can have 1 to 10 Gbps access.
Access in the Enterprise/Home: WiFi
- Wireless LAN access based on IEEE 802.11 technology (WiFi).
- A user must be within tens of meters of the access point.
- Shared transmission rates up to 100 Mbps are common.
Wide-Area Wireless Access
- Mobile devices use the same wireless infrastructure as cellular telephony.
- Users need to be within tens of kilometers of the base station.
- 4G wireless offers up to 60 Mbps download speeds.
- 5G will offer higher speeds.
Physical Media
- Bits travel from source to destination by electromagnetic waves or optical pulses.
- Physical media are categorized as guided (fiber optic, twisted-pair, coaxial) or unguided (wireless LAN, digital satellite).
The Network Core
- Packet Switching
- Circuit Switching
- Multiplexing
Packet Switching
- In network applications, end systems exchange messages.
- Sources break messages into smaller chunks called packets.
- Packets travel through communication links and switches (routers, link-layer switches).
- Most switches use store-and-forward transmission —receiving the entire packet before forwarding.
Packet Switching (continued)
- Each packet consists of L bits. Transmission rate R bits/sec.
- For N links, end-to-end delay = NL/R
Packet Switching (continued)
- Each link has an output queue.
- Packets endure queuing delays due to congestion.
- Packet loss occurs when the buffer space is full.
Circuit Switching
- Traditional telephone networks use circuit switching.
- Resources (buffers, link transmission rate) are reserved.
- A dedicated end-to-end connection is established between hosts.
- Data transfer is guaranteed at a constant rate
Multiplexing in Circuit-Switched Networks
- Implementing circuits uses frequency-division multiplexing (FDM) or time-division multiplexing (TDM).
Delay, Loss, and Throughput
-
Physical laws introduce delay and loss, constraining throughput.
-
Throughput is the rate of data transfer between end systems.
-
Packets experience processing delays (microseconds / less), queuing delays (microseconds-milliseconds).
-
Transmission delay = L/R. Propagation delay = d/s.
Nodal Delay
- dnodal = dproc + dqueue + dtrans + dprop
Queuing Delay and Packet Loss
- Queuing delay varies between packets.
- Factors affecting queuing delay are arrival rate of packets, transmission rate of the link, and traffic patterns.
- Trafic Intensity = La/R; if intensity > 1, queue will increase indefinitely, causing infinite queuing delay.
End-to-End Delay
- If there are N-1 routers and no queuing delay: dend-to-end = N(dproc + dtrans + dprop)
Throughput
- Speed test applications measure end-to-end delay and throughput.
- Throughput = F bits/T seconds = F/T bits/sec.
- In a two-link network, throughput is the minimum link rate.
- In a network with N links, throughput is the minimum of the individual link rates.
Example #4
- 10 servers and 10 clients have the same rates (Rs=Rc).
- R (shared link) is very large.Throughput is the minimum of the rates.
Protocol Layers
- The Internet's complexity is managed by a layered architecture.
- Each layer provides a service to the layer above, using the services of the layer below.
- This modularity simplifies design, implementation, and changes.
Encapsulation
- The transport layer encapsulates application layer messages, adding header information.
- The network layer adds more header information for routing, creating a datagram.
- The link layer encapsulates the datagram, creating a frame.
Protocol Layering
- Protocols can be implemented in software, hardware, or a mix.
- The physical layer deals with transmitting bits across the physical medium.
- The application layer provides services for network applications.
- The transport and network layers are responsible for handling communication between end systems (segments).
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