WEEK 2 CS2005 Networks and Operating Systems: Application Layer

CS2005 Networks and Operating Systems Application Layer I

J.F Kurose and K.W. Ross ©1996-2016

Page 2: Session Objectives

• Overview of the Internet and its components and services

• Understanding of:

  • Main principles of network applications

  • Application architectures

  • Process communication

  • Transport services

Page 3: Internet Components View

• Connected Devices:

  • Billions of computing devices (hosts = end systems)

  • Running network applications

• Communication Links:

  • Types: fiber, copper, radio, satellite

  • Transmission rate: bandwidth

• Packet Switches:

  • Forward packets (chunks of data)

  • Types: routers and switches (wired and wireless)

Page 4: Internet Components View (Continued)

• Internet Structure:

  • "Network of networks" (interconnected ISPs)

• Protocols:

  • Control sending and receiving of messages (e.g., TCP, IP, HTTP, SMTP, 802.11)

• Internet Standards:

  • RFC: Request for Comments

  • IETF: Internet Engineering Task Force

Page 5: Internet Service View

• Infrastructure Services:

  • Provides services to applications (Web, VoIP, email, etc.)

• Programming Interface:

  • Hooks for sending and receiving app programs to connect to the Internet

• Service Options:

  • Analogous to postal service

Page 6: What is a Protocol?

• Human Protocols:

  • Examples: asking for time, introductions

• Network Protocols:

  • Govern all communication activity in the Internet

  • Define format, order of messages, and actions taken on message transmission

Page 10: Protocol Stack

• Internet Protocol Stack:

  • Application: supports network applications (FTP, SMTP, HTTP)

  • Transport: process-to-process data transfer (TCP, UDP)

  • Network: routing of datagrams (IP, routing protocols)

  • Link: data transfer between neighboring network elements (Ethernet, WiFi)

  • Physical: bits "on the wire"

• ISO/OSI Reference Model:

  • Presentation: data interpretation (encryption, compression)

  • Session: synchronization, checkpointing, recovery

Page 12: Some Network Applications

• Examples include:

  • E-mail

  • Web browsing

  • P2P file sharing

  • Text messaging

  • VoIP

  • Video conferencing

  • Multi-player games

  • Streaming video

  • Social networking

  • Search engines

Page 14: Application Architectures

• Main Structures:

  • Client-server

  • Peer-to-peer (P2P)

Page 15: Client-Server Architecture

• Server:

  • Always-on host with a permanent IP address

  • Data centers for scaling

• Clients:

  • Communicate with the server

  • May be intermittently connected with dynamic IP addresses

  • Do not communicate directly with each other

Page 16: P2P Architecture

• Peer-to-Peer:

  • No always-on server

  • Arbitrary end systems communicate directly

  • Self-scalability: new peers add service capacity and demand

  • Peers are intermittently connected and change IP addresses

Page 18: Sockets

• Functionality:

  • Process sends/receives messages to/from its socket

  • Socket is analogous to a door for message transmission

Page 19: Addressing Processes

• Message Reception:

  • Process must have an identifier (IP address + port number)

  • Example port numbers: HTTP server (80), mail server (25)

Page 20: Application-Layer Protocol Defines

• Message Exchange:

  • Types of messages (request, response)

  • Message syntax and semantics

  • Rules for sending and responding to messages

• Protocol Types:

  • Open protocols (e.g., HTTP, SMTP)

  • Proprietary protocols (e.g., Skype)

Page 21: Transport Service Needs

• Data Integrity:

  • Some apps require reliable data transfer

• Timing:

  • Low delay needed for effective applications (e.g., telephony)

• Throughput:

  • Minimum throughput required for multimedia applications

• Security:

  • Encryption and data integrity

Page 22: Internet Transport Protocols

• TCP Service:

  • Reliable transport, flow control, congestion control

  • Connection-oriented

• UDP Service:

  • Unreliable data transfer, no flow control or connection setup

  • Useful for applications that can tolerate some data loss

Page 23: Securing TCP

• Encryption:

  • TLS/SSL provides encrypted TCP connections

  • Ensures data integrity and end-point authentication

Page 25: Reading Recommendations

• Suggested Readings:

  • "What Is the Internet?"

  • "Protocol Layers and Their Service Models"

  • "Principles of Network Applications"

Page 26: Interesting Videos

• Links to videos on:

  • Data transmission

  • Connecting hosts and networks

  • Understanding the Internet

  • Cybersecurity

This note summarizes the key concepts and details from the provided transcript on networks and