1-intro

Network Structure and Protocols

• Network Edge: consists of end systems, access networks, and links.
• Network Core: consists of packet switching, circuit switching, and network structure.

Access Networks

• Digital Subscriber Line (DSL):
  • Uses existing telephone line to connect to central office.
  • Data transmission rate: upstream (typically < 1 Mbps), downstream (typically < 10 Mbps).
• Cable Network:
  • Uses hybrid fiber coax (HFC) to connect homes to ISP router.
  • Data transmission rate: up to 30 Mbps downstream, 2 Mbps upstream.

Network Core Functions

• Routing: determines the source-destination route taken by packets.
• Forwarding: moves packets from router's input to appropriate router output.

Packet Switching vs. Circuit Switching

• Packet Switching:
  • Allows multiple users to share network resources.
  • More efficient for bursty data.
  • Requires protocols for reliable data transfer and congestion control.
• Circuit Switching:
  • Provides dedicated resources for a single connection.
  • Requires call setup and teardown.

Internet Structure

• Network of Networks: interconnected access ISPs, regional ISPs, and network core.
• Complexity: driven by economics and national policies.

Protocol Layers

• 5-Layer Internet Protocol Stack:
  • Application layer: supports network applications.
  • Transport layer: process-process data transfer.
  • Network layer: routing of datagrams.
  • Link layer: data transfer between neighboring network elements.
  • Physical layer: bits "on the wire".
• ISO/OSI Reference Model:
  • 7-layered model with additional presentation and session layers.

Network Security

• Field of Network Security: focuses on network attacks, defense, and design of secure architectures.
• Security Considerations: in all protocol layers.
• Threats:
  • Malware: viruses, worms, spyware.
  • Botnets: infected hosts used for spam and DDoS attacks.### Internet Basics
• The Internet consists of end systems, access networks, and links at its edge, and packet switching, circuit switching, and network structure at its core.

Internet History (1961-1972)

• 1961: Leonard Kleinrock's queueing theory demonstrates the effectiveness of packet switching.
• 1964: Paul Baran introduces packet switching in military networks.
• 1967: ARPAnet is conceived by the Advanced Research Projects Agency.
• 1969: The first ARPAnet node becomes operational.
• 1972: The public demonstration of ARPAnet takes place, with NCP (Network Control Protocol) as the first host-host protocol, and the first email program is developed.

Internet History (1972-1980)

• 1970: ALOHAnet, a satellite network, is established in Hawaii.
• 1974: Vint Cerf and Bob Kahn develop an architecture for interconnecting networks.
• 1976: Ethernet is developed at Xerox PARC.
• Late 1970s: Proprietary architectures such as DECnet, SNA, and XNA emerge.
• Late 1970s: Switching fixed-length packets (an ATM precursor) begins.
• 1979: ARPAnet has 200 nodes.
• Cerf and Kahn's internetworking principles include:
  • Minimalism and autonomy: no internal changes are required to interconnect networks.
  • Best-effort service model.
  • Stateless routers.
  • Decentralized control, defining today's Internet architecture.

Network Concepts

• Access technologies.
• Types of physical media.
• Packet switching vs. circuit switching.
• Concept of a network of networks.
• Sources of packet delay.
• Throughput and bottleneck.
• TCP/IP layers.
• Encapsulation.