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
