Computer Network - Mu class notes

basic concepts

Computer Communications Technology & Technology

A computer network is a collection of autonomous computers interconnected in a
network: via a communication link
autonomy: no master-slave relationship

Network size growth problem

Introducing switched network
to each host connected through the switching network hosts need to exchange node (router | switches)

Internet

ISP Internet provider's network
Global - Regional - college - mobile network - home network
one million computing devices
unit: host = end systems

Internet service standpoint
to provide communications infrastructure for distributed network applications, providing application programming API for the web application

Network Protocols Network data exchange standard, predetermined, stipulated

Data exchange rules, any communication and information needs to talk to the rules of
interrogation time
to ask questions
staff recommendation
to send a specific message to take to respond to a particular message
format, meaning, order, action feedback

Three elements

• Syntax Syntax
  data structure and format control information
  signal level
• Semantics Semantics
  what information
  what response
  error control
• Timing The timing
  chronologically
  speed matching
• For example
  tcp
  ip
  HTTP
  802.11
  • RFC documents

Network architecture

• Network edge
  • Host computer
  • Internet application
• Access Network
  • Limited or wireless communication link
• Network core
  • Internet router (packet forwarding device

Network edge use of network resources, shared

• Host (end system)
  - run network applications Web, email
• Client-server application model
  • The requesting client, server response
• P2P application model
  • No or only rely on dedicated server
  • Directly between peer entities

Access Network

• Residential access
• Agency access
• Mobile Access

Bandwidth: data bandwidth, the amount of information per unit of time

Examples: digital subscriber line DSL

Using different carrier frequencies to transmit data and voice, DSL access multiplexer, demodulates the modulated
voice to the telephone network
data to the Internet
using the FDM
0-4 kHz for the conventional telephone
4k - 50k uplink
50k - 1MHz downstream
ADSL upstream and downstream number of different

Example: cable network

Data, the television transmission in different frequencies, HFC on a shared cable
asymmetric uplink and downlink data rate is inconsistent, the FDM
shared channel, the more users, the low bandwidth

Enterprise Access Network

Ethernet switch connected to end systems, speed
1000M bps

Wireless network access

Via a base station (access point)

• LANs Wireless LAN
  54 Mbps, the home router
• Wide-area wireless access
  operator
  mobile Internet

Network core

Features: + routing forward, how a packet to the correct interface

routing

路由算法->路由表

Forwarded

从输入端口转到正确的输出端口

Internet structure

端系统接入ISP，网络互连的复杂网络，随时有接入、随时有离开
多级ISP  
ISP之间对等链路，区域网络，
IXP（互联网交换节点 高速），内容提供商

Data Exchange

Solution transferred from the information from the source host to the destination host

N ^ 2 problem link, between two interconnected feasible, large-scale network when feasible
solution : switch, switching network
to exchange : dynamic adapter, physically, logically, many devices in parallel, dynamic allocation of transmission resources

The type of data exchange

• Circuit switched
  telephone network, dial-up connection is established, communications, hook removal (release the connection)
  exclusive resources
  and a lot of common link, shared trunks
  • Multiplexing
    communication resource partitioning, and give many communication paths, each call exclusive channel resources, resource sheet possible idle
    • FDM
      by frequency division, with a guard band between the respective frequencies, each user account different bandwidth frequencies
      examples: Television
    • TDM
      time, is divided into equally long time division multiplexed frame of
      the frame number of each user occupies a fixed, periodically occurring frames, each period occupied by all network resources
    • WDM
      optical frequency division multiplexing, the wavelength of light is often used to distinguish between data to transmit light of different wavelengths of
      light modulator using
    • CDMA
      code division multiplexing, a wireless link, a cellular network, a satellite communication network,
      each user is assigned a chip sequence of m bit (0: 1,1: 1), sending a user chip sequence is transmitted, transmission 0 transmitted chip sequence is inverted
      for each user using the same carrier frequency, the transmission information data encoded with the code chip sequence, a plurality of user information may be superimposed
      encoded signal = (original signal) * (chip sequence)
      chip sequence orthogonal to each other, only themselves and their multiplying only 1, and other people's code is multiplied by zero, and want to take their anti-code -1
      • Decoding
        wants information about a coded information on the chip and the encoded signal encoded by the product of
        
• Packet switching
  transmits information as a whole (a file), and then forwarded over after receiving a message out to
  the store and forward
  • Example: Telegraph
    
• Packet switched
  to packet split, split into a series of relatively small data packets
  division and recombination, the switch while the reception side transmits a small packet
  store and forward
  • Statistical multiplexing, no allocation in advance, according to the packet packet of hair

  Composition: head + data packet (there are overhead, but not serious)