计算机网络复习笔记

computer network note
ISP:Internet Service Provider
TDM：Time Division Multiplexing
FDM：Frequency Division Multiplexing
DHCP:自动获取ip
ADSL: Asymmetric Digital Subscriber Line --not share bandwidth
协议：

A protocol defines the format and the order of messages exchanged between two or more communicating entities ,as well as the actions taken on the transmission and/or receipt of a message or other event.

two most important protocols
TCP:Transmission Control Protocol
IP: Internet Protocol
标准：
Internet standards are developed by
IETF:the Internet Engineering Task Force,also called
RFCs:request for comments
whitch defined protocols such as
TCP,IP,HTTP,SMTP(for e-mail)

specify standards:
IEEE 802 LAN/MAN Standards Committee specifies the Ethernet and wireless WIFI standards

distributed application:
Voice-nover-IP(VoIP)
P2P:peer to peer

API:Application Programming Interface

R:rate   S:speed   m:the length of the link
R*d(prop)<1
该链路上一个bit宽度=d/(R*d(prop))=d/(R*d/s)=s/R=速度/速率

share a 2 Mbps link,each user 1Mbps when transmitting,each user tansmits only 20percent of the time

circuit switching:2Mbps/1Mbps=2 users can be supported--telephone
packet switchig:there be a queuing delay if three users transmmiting at                 the same time--tatistical multiplexing enables

OSI 7 layers seven:A Presentation session T
4000
N 'Data link'
host:application transport network link physical 5
Router:network link physical                     3
Link-layer switch:link physical                  2

full text in English of RFC is request for comments

all communication activity in Internet by protocols

circuit switching is commonly used in traditional telephone networks

there is no difference between a host and an end system

end system not include router

in addition to delay and packet loss ,another critical performance measure in computer net works is end-to-end throughput