Store and Forward Networking

Efficient Message Transmission:Packet Switching(分组交换)

  • Challenge: in a simple approach, like store-and-forward, large messages block small ones(延迟问题)
  • Break each message into packets(大化小)
  • Can allow the packets from a single message to travel over different paths, dynamically adjusting for use(可不同路径)
  • Use special-purpose computers, called routers, for the traffic control(路由器来控制数据移动)

Shared Network

  • In order to keep cost low and the connections short geographically - data would be forwarded through several routers.
  • Network Connection
    • Host A-->Router-->Router-->Host B
  • Getting across the country usually takes about 10 “hops”

Layered Network Model

  • A layered approach allows the problem of designing a network to be broken into more manageable sub problems(大问题拆分为小问题)
  • Best-known model: TCP/IP—the “Internet Protocol Suite”(TCP/IP模型)
  • There was also a 7 layer OSI: Open System Interconnection Model(7层模型)

Internet Standards

  • The standards for all of the Internet protocols (inner workings) are developed by an organization——Internet Engineering Task Force (IETF)
  • Standards are called “RFCs” - “Request for Comments”(个人可以查看RFC并提出建议,建议-->草案-->审核通过-->新标准)

Layered Architecture

  • The Physical and Internet Layers are like trucks and trains - they haul stuff and get it to the right loading dock - it takes multiple steps
  • The Transport layer checks to see if the trucks made it and send the stuff again if necessary

Link Layer(aka Physical Layer)

  • phisical
  • the lowest layer in the Internet Protocol Suite
  • described in RFC 1122 and RFC 1123
  • Link Layer Addresses
    • Many physical layer devices have addresses built in to them by the manufacturer(制造时就有)
    • Wireless Ethernet (Wifi)

Sharing Nicely - Avoiding Chaos

  • To avoid garbled messages, systems must observe “rules” (Protocols)
  • Ethernet rules are simple
  • steps(步骤 !!!)
    • Wait for silence
    • Begin Transmitting data
    • Listen for your own data
    • If you cannot hear your own data clearly, assume a collision, stop and wait before trying again
    • Each system waits a different amount of time to avoid “too much politeness”

Ethernet(第一个本地计算机网络)

  • Invented at PARC (Xerox)
  • The first Local-Area-Network
  • Connected PC's to laser printers
  • Inspired by an earlier wireless network called Aloha from the University of Hawaii

Internetwork Layer(IP)

Internet Protocol Layer(实际移动)

  • Goal: Gets your data from this computer to the other computer half way across the world
  • Each router knows about nearby routers
  • IP Is best effort - it is OK to drop data if things go bad...(丢弃)

IP Addresses

  • The IP address is the worldwide number which is associated with one particular workstation or server(全球性)
  • network number(6 bit) + computer number within network(6 bit)

Router tables

The best outbound route for each router record to reach another router, dynamic update, an index

DHCP(dynamic host configuraton protocol动态主机配置协议)

  • is given a temporary address (被给了临时地址)
  • it can not run in the Internet network. It only applies to local network,
  • such as 192.168.xxx.xxxx and so on.
  • the non-routable website.(不可路由地址)

TTL(Time-to-live)

  • to control the count of hop
  • Abandoned from 255 to 0(减到0时认为无法到达,便舍弃)

Transport Layer(负责移动的可靠性)

TCP(Transport Protocol)

  • built on the IP Layer.
  • function:to solve some problems that may arise in the IP layer.(弥补Link Layer的不足)
  • steps(过程):
    • Send and receive feedback(先确认一下)
    • acknowledged --> Discard acknowledged packets(确认接受后丢弃)
    • Not confirmed --> again(未确认则再发知道成功确认)

Slow Start Algorithm(慢启动算法)(看不太懂)

  • First send slowly, then slowly increase the speed.

DNS(Domain Name System)(域名系统)

  • A way to remember more easily than an IP address.
  • IP:left to right : DNS:right to left
  • such as:www.si.umich.edu

Application Layer(应用层)

Application Protocol

port

  • Ports are dependent on IP, similar to branch paths of IP addresses. Different ports correspond to different functions and services.
  • such as:80 , 45

HTTP(Hyper Text Transfer Protocol)

  • base on TCP/IP
  • client --> click link--> generate links to server --> look up server --> show
  • "Hacking" HTTP:pretend browers ,ues "get" commond


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