Internet Technologe

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