(A) Layer 1: Link (a first layer: the link layer)
1.Introduction (description)
- Network of the sixties to the eighties of the 20th century:
① how to avoid a direct connection between all the computers it?
② how to effectively transmit messages?
③ how dynamic processing downtime?
- Effective information transmission: the packet switched
Cause: In a simple way, such as store and forward, the big news will clog small news
Packet switching features:
① each message into packets
② allows packets from the same message is transmitted on a different path, and dynamically adjusted based on the use of
③ using special purpose computer - a router, to control the flow
- network sharing:
① In order to keep costs low and short distance connections, data transfer through a plurality of routers
② data across the entire country usually takes 10 hops
③ network designers to "tune" the network by adding and removing links
- Network hierarchical model
① hierarchical network design model allows to decompose the problem into more manageable sub-problems
② most famous models: TCP / IP - "Internet Protocol Suite"
③7 layer OSI: Open Systems Interconnection Model
- Internet standards
① all standard Internet Protocol (internal work) is developed by an organization - the Internet Engineering Task Force (IETF)
② standard called "RFC" - "comments"
2.Link Layer (link layer)
- A link layer (also called the physical layer)
① When the data spread across the country, each node may use different physical media - as wire, wireless point, optical fiber
② attention to the range of each node is very small, only concerned with its adjacent node
- What link layer to solve the problem?
① how the data is pushed onto the link?
How ② shared link?
- Common connection technology
Ethernet, a wireless network, a cable modem, DSL, satellite, light
- Link-layer address
When the physical layer device has a number of manufacturers to produce address configuration
- Link layer
① physical addresses allows the system to identify themselves at the end of a single link
② Sometimes, such as Wifi and wired Ethernet link is shared with multiple computers
(B) Layer 2: Internet Protocol (Internet Protocol)
- To avoid confusion
①CSMA / CD (Carrier Sense Multiple Access / Collision Detection)
② In order to avoid confusion of the message, the system must comply with the "rules" (agreement)
③ Ethernet rules:
Wait - start transmitting data - monitor their own data - if not receive their own data, assumptions clashed, stop and wait for retransmission - different for each system wait time to avoid a collision again
- Ethernet
① invention in PARC (Xerox)
② is the first local area network to connect the PC to a laser printer, a wireless network inspired by the early University of Hawaii Aloha