- Physical Layer
Data Link layer: Research on how to transfer from one host to another (within a LAN)
- using a point-to-point channel
- Frame--point-to-point channel Data Link Layer Protocol data unit
- IP datagram (PDU)-Protocol Data Unit Network layer
- transfer mode: see
- three basic questions
- package Cheng: Add headers and tails before and after a piece of data 7
The
- header and tail function is: Frame delimitation
The data portion of the
- Maximum Transfer unit mtu--frame is less than this value
- frame delimiters: Soh and EOT (they are binary code: 1 and 4, respectively). (this thing in the transmission error when the function is obvious, when the transmission is incomplete, we can determine whether the frame is complete by the frame delimiter.)
- Transparent transport
- transmitted frames-text files;
- This time the transmission will not be wrong, just enter anything can be transmitted Go: This is called Transparent transport
- transferred frames: binary file
- binary file may conflict with frame delimiter, resulting in missing frame header trailing output Error: Opaque transport
- Workaround:
- error detection
- cyclic redundancy test: Add redundant code, redundant code called frame Detection sequence FCS
- Reliable transmission: transmission without transmission error. Transmission Error Classification: ①: Basic bit error. ②: The received frame is missing frame, frame is duplicated, frame is out of sequence. The
in the data link layer uses the CRC loop test method can realize the transmission without bit error, but is not the transmission error, is not reliable transmission.
- Point-to-Point Protocol PPP
- Characteristics
- Demand:
① Simple: CRC is checked for each frame received. Check correctly, accept this frame, and vice versa, discard.
The ② is encapsulated into frames. ③ transparency: Ensure the transparency of data transmission. ④ multiple Internet protocols: supports multiple Internet protocols (IP,IPX)
- Composition
① a method that encapsulates an IP datagram to a serial link. ② Link Control Protocol Lcp.③ Network Control protocol.
- Data link layer using broadcast channel
- Lan
- In order to better adapt the data link layer to a variety of LAN standards, split it into two parts:
① Logical Link Control LLC: It is independent of the transport media
② Media access Control Mac: Everything that's connected to the media is on the inside.
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- Csma/cd
- Broadcast communication mode: When a computer signals, this data can be detected by all computers on the bus.
- Ethernet in order to make communication convenient, two measures were taken:
- Network layer
- Transport Layer
- Application Layer
Computer network--Data link layer
