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Comuter Network

2022 Fall, University of Waterloo

The computer networks and Internet

Protocol

Protocol

A protocol defines :

  1. the format and the order of messages exchanged between two or more communicating entities
  2. the actions taken on the transmission and/or receipt of a message or other event.

From edge to center of the Internet

End systems / hosts

  • client(PC, mobile phones)
  • server

Access Network

from home/enterprise access

  • Wireless local area networks, WLAN, (WiFi)

  • wide-area wireless access (3G, 4G, 5G)

Physical Medium

Two types: Guided media & unguided media

Guided media: the waves are guided along a solid medium

  • Twisted Pair Copper Wire
  • Coaxial Cable: can be shared
  • Fiber Optics

Unguided media: waves propagate in the atmosphere and in outer space

  • Terrestrial Radio Channels
  • Satellite Radio Channels

Core

Packet & Packet switches (routers / link-layer switches)

Store & forward Transmission: router

Note

Circuit Switch vs Packet switch

  • Packet Switch more efficient
  • Circuit switch have limited concurrency(10 simultaneous user)

Performance

Loss

happen when arriving rate is higher than processing rate

Delay

\(d_{\text{nodal}} = d_{\text{proc}} + d_{\text{queue}} + d_{\text{prop}}\)

  • \(d_{\text{proc}}\): nodal processing time, < msec

  • \(d_{\text{queue}}\): waiting for output link for transmission [when La/R -> 1, it will become extremely large]

  • \(d_{\text{trans}}\): transmission delay(time to put on the wire), \(=L/R\)
  • \(d_{\text{prop}}\) : propagation delay(time to go through the wire), \(=d/s\)

Throughput

Decided by the bottleneck

Protocol Layers

A layered architecture allows us to discuss a well-defined, specific part of a large and complex system

Modularity makes it easier to update system components.

Drawback:

  • one layer may duplicate lower-layer functionality
  • functionality at one layer may need information that is present only in another layer
    • violates the goal of separation of layers

Encapsulation

Protocol Stack

application: supporting network applications

transport: process-process data transfer

network: routing datagrams from source to destination

link: data transfer between neighboring network elements

physical: bits "on the wire"

Attack

DoS(denial-of-service) attack

Three categories:

  1. Vulnerability attack
  2. Bandwidth flooding
  3. Connection flooding

DDoS: distributed DoS

Summary

Internet: the network of network, ISPs must be connected.

Hierarchy of ISPs: (access ISP,) regional ISP, tier1-ISPs