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Computer Networks and Network Programming in Java

• Lectures by Dr. inż. Kazimierz Zieliński
• Email: [email protected]

Chapter 1: Introduction

• Goal: Get a feel for the "big picture" of computer networking, introducing terminology, with more depth explored later.
• Approach: Use the Internet as an example.
• Roadmap:
  • What is the Internet?
  • What is a protocol?
  • Network edge: hosts, access networks, physical media
  • Network core: packet/circuit switching, Internet structure
  • Performance: loss, delay, throughput
  • Security
  • Protocol layers, service models
  • History

The Internet: "Nuts and Bolts" View

• Billions of connected computing devices (hosts) running network applications at the Internet's edge.
• Packet switches (routers, switches) forward packets (chunks of data).
• Communication links (fiber, copper, radio, satellite) with transmission rate (bandwidth).
• Collection of devices, routers, and links managed by an organization.

"Fun" Internet-Connected Devices

• Examples: Amazon Echo, Internet refrigerator, security camera, Internet phones, IP picture frame, Slingbox (remote cable TV control), Pacemaker & Monitor, Tweet-a-watt (energy monitor), Web-enabled toaster, AR devices, Fitbit, and others.

The Internet: "Network of Networks"

• Interconnected Internet Service Providers (ISPs).
• Protocols are everywhere, controlling sending/receiving of messages. Examples include HTTP (Web), streaming video, Skype, TCP/IP, WiFi, 4G, and Ethernet.
• Internet standards: RFCs (Request for Comments) and IETF (Internet Engineering Task Force).

The Internet: "Service" View

• Infrastructure that provides services to applications (web, streaming video, teleconferencing, email, games, e-commerce, social media, and interconnected appliances).
• Provides a programming interface to distributed applications with "hooks" allowing sending/receiving of applications to connect to and use Internet transport services.
• Similar in function to postal service, providing service to applications.

What's a Protocol?

• Human protocols (e.g., "what's the time?", "I have a question").
• Network protocols govern communication activity in the Internet.
• Protocols define the format, order of messages, and actions taken during message transmission and receipt.

Chapter 1: Roadmap

• What is the Internet?
• What is a protocol?
• Network edge: hosts, access network, physical media
• Network core: packet/circuit switching, Internet structure
• Performance: loss, delay, throughput
• Security
• Protocol layers, service models
• History

A Closer Look at Internet Structure

• Network edge: Hosts (clients and servers), servers often in data centers.
• Access networks, physical media: Wired and wireless communication links.
• Network core: Interconnected routers, network of networks.

Internet Topology Map

• Source is the Center for Applied Internet Data Analysis (CAIDA).

Access Networks and Physical Media

• How to connect end systems to edge routers: - residential, institutional, mobile networks (WiFi, 4G/5G).
• Specific properties to look for: transmission rate (bits per second), shared or dedicated access among users.
• Examples:
  • Cable-based access (frequency division multiplexing (FDM))
  • Digital Subscriber Line (DSL)
  • Home networks (WiFi, wired Ethernet)
  • Wireless access networks (WLANs, cellular networks)
  • Enterprise networks (Ethernet, WiFi)

Links: Physical Media

• Bit: Propagates between transmitter/receiver pairs.
• Physical link: Connects transmitter and receiver.
• Guided media: Signals propagate in solid media (copper, fiber, coax).
• Unguided media: Signals propagate freely (radio). Specific example types include twisted pair (TP), coaxial cable, fiber optic cable, wireless radio.

Packet Switching: Store-and-Forward

• Hosts break application messages into packets.
• Packets are forwarded from one router to the next across links.
• Each packet is transmitted at full link capacity.

Packet Switching: Queueing Delay, Loss

• Packets queue in router buffers.
• If arrival rate exceeds link transmission rate, packets queue and can be dropped if memory fills up.

Two Key Network-Core Functions

• Forwarding: Local action; move arriving packets from router input links to appropriate output links.
• Routing: Global action; determine source-destination paths.

Alternative to Packet Switching: Circuit Switching

• End-end resources are allocated and reserved for a call between source and destination, similar to dedicated circuits.

Circuit Switching: FDM and TDM

• FDM (Frequency Division Multiplexing): Calls allocated their own frequency band.
• TDM (Time Division Multiplexing): Calls allocated time slots to transmit.

Packet Switching Versus Circuit Switching

• Packet switching allows more users to share a network.
• Circuit switching dedicates resources to single calls.

Internet Structure: A "Network of Networks"

• Hosts connect to the Internet via access ISPs.
• Access ISPs are interconnected.
• ISPs have economic agreements.

Chapter 1: Roadmap

• What is the Internet?
• What is a protocol?
• Network edge: hosts, access network, physical media
• Network core: packet/circuit switching, Internet structure
• Performance: loss, delay, throughput
• Security
• Protocol layers, service models
• History

Performance: Loss, Delay, Throughput

• Loss: Packets can be dropped due to buffer overflow.
• Delay: Transmission, propagation, queuing delays.
• Throughput: Rate at which bits can be sent from sender to receiver.

Security

• Field of network security includes understanding how bad guys can attack networks, how to defend against attacks, and how to build secure network architecture.

Protocol Layers, Service Models

• Networking is a complex system requiring an organizational model for discussion.
• Layered reference models define services via layer-to-layer interactions.

Internet Protocol Stack

• application: Supporting network applications (IMAP, SMTP, HTTP)
• transport: Process-process data transfer (TCP, UDP)
• network: Routing datagrams (IP)
• link: Data transfer between neighboring network elements (Ethernet, 802.11, PPP)
• physical: Bits/on the wire

Additional Chapter 1 Slides

• ISO/OSI reference model; comparison with Internet protocol stack's application, transport, network, link, and physical layers.
• Wireshark (packet analyzer).

Internet History

• Timeline of early packet-switching principles (1961-1972)
• Timeline of internetworking, new and proprietary network development (1972-1980)
• Timeline of new protocols, and proliferation of networks, (1980-1990)
• Timeline of commercialization, the Web, new applications (1990-2000s)
• Timeline showing further development and expanding use of the Internet (2005-present)

Chapter 1 Summary

• Broad overview of internet history and key aspects.