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
- Decoding
- FDM
- Multiplexing
- 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
- 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)