Shulou(Shulou.com)06/01 Report--

First, take a look at the OSI seven-tier model:

Physical layer:

[binary] denoted by physical signals 1 and 0

Interface [network cable interface]

Establishment and disconnection of communication between the two parties [software disconnection]

Data transmission can be carried out at the same time [network cable]

Data Link layer:

Data frames, sorting out incoming data 1 and 0

Physical address of the source and destination [MAC address]

Self-monitoring to see if data frames are missing

Network layer:

Packet sorting packaged data frames

Source and destination logical addresses such as IP addresses

Routing according to the logical address of the packet header

Transport layer:

Communicate with the software or program you use [data segment]

form a connecting link between the preceding and the following

Session layer:

The conversational relationship between software and software

Presentation layer:

Define the language in which the message is transmitted

Application layer:

Provides the use of the user

Just a brief introduction to the OSI seven-layer model, about the network only need to pay attention to the five layers of OSI, because the session layer and presentation layer have little to do with us.

First of all, introduce

1 physical layer:

Physical layer transmission medium

1 Wired Media:

Twisted pair optical fiber

2 Wireless Media:

Radio microwave laser infrared

HDMI digital signal

Strong anti-interference

Long-distance transmission to ensure quality

VGA analog signal

Active equipment: network cable, twisted pair [100-150m]

Unshielded twisted pair UTP

Shielded twisted pair STP

Type of twisted pair

Cat5 transfer rate 100Mbps

Cat5e transfer rate 100Mbps

Cat6 transfer rate 1000Mbps

Cat7 transfer rate 10000Mbps

T568A: White green, green, white orange, blue, white blue, orange, white brown, brown

T568B: White orange, orange, white green, blue, white blue, green, white brown, brown

Interface model: RJ-45

Passive equipment: optical fiber [5 km]

High transmission bandwidth

Far transmission

Strong anti-interference

Optical fiber: 1 single mode fiber [10 micron]

Use [laser light source] over long distances

2 multimode fiber [50 microns]

[LED light source] close use

Through line

Crossover line

Reverse line:

Console line [control line]

2 functions of the data link layer

1 establishment, maintenance and dismantling of data links

2-frame packaging, transmission and synchronization

Error recovery of 3 frames

4 flow control

Ethernet

1 conflict problem: CSMA-CD: multi-access with monitoring and monitoring conflict

[avoid signal conflicts, equivalent to traffic lights]

Working principle: 1 listen to whether the channel is idle before sending

Send data if you are idle

2 when sending, send and monitor at the same time

3 if a conflict is detected, stop sending immediately

4 wait for a period of time [avoid]

2 address problem: MAC address [globally unique]

The first 24 bits are the manufacturer's code, and the last 24 bits are the equipment sorting code.

MAC addresses identify individual devices or a group of devices

One hexadecimal = 4 binary

0 = physical address-unicast addr

1 = logical address-Multicast addr

FF-FF-FF-FF-FF-FF-FF [broadcast address, all 1]

(3) uniform format specification

Write according to the PDU format of each layer

Ethernet Typ

Btye byte bit bit

For example, mac address:

6 bytes, 8 times 48 bits

Ip address:

4 bytes, 8 times 32 bits

Ethernet frame format:

[preamble frame start delimiter [destination address source address type / length data check]]

7 bytes 1 byte 6 bytes 6 bytes 2 bytes 46-1500 4 bytes

[data link layer encapsulation minimum 64 bytes-maximum 1518 bytes] [physical layer encapsulation minimum 72 bytes-maximum 1526 bytes]

Ethernet naming method:

N-signal-physical medium

N: data rate in megabytes, such as 100.100

Signal: baseband or broadband

Physical media: represents media typ

For example: 100BASE-TX-FX

100 data rate is 100

BASE: baseband: used separately for the network only [but data transmission]

Broadband: can only be used for multi-purpose such as network, telephone line, etc. [transmit multiple data]

TX: twisted pair UTP STP

FX: optical fiber

Sublayer of the data link layer

Media access control [MAC] sublayer

Unencapsulate the physical layer

Logical link control [LLC] sublayer

Establish a connection to the network layer

3 functions of the network layer

Define the logical address based on IP protocol.

Connect different devices on the same network segment

Choose the best route for packets to pass through the network

Format of IP header

Version header length priority and total service type length

Identifier flag segment offset

The first checksum of TTL protocol number

Source address

Destination address

Optional

data

Split

classification

Order

The maximum TTL life cycle of 255is reduced by one point per router.

4 transport layer

Port number 0Murray 65535

TCP

Transmission Control Protocol:

Reliability, connection-oriented protocol

Low transmission efficiency

TCP encapsulation format

Source port number destination port number

32-bit serial number

32-bit confirmation number

First length

Keep

[1 valid 0 is invalid]

SYN establishes a connection

ACK confirms connection

FIN disconnected

URG emergency pointer [priority]

RST reconnect [reset]

PSH application layer emergency transmission

Window size

16-bit checksum

16-bit emergency pointer

Optional

data

Disconnection and connection of TCP

Three-way handshake

Disconnect four times

Flow Control and differential Control of TCP

Flow Control Mechanism of TCP-flow window

Flow Control Mechanism of TCP-congestion Control

TCP error control 3 mode

1 checksum

2 confirm

3 timeout

Application of TCP

Port number:

21 FTP File transfer Protocol [instruction]

20 data transmission

23 Telnet remote

25 SMTP send email

110POP3 accept email

53 DNS domain name resolution

80 HTTP hypertext transfer

Realization of Hypertext Transmission on the Network through http

443 HTTPS [secure Hypertext transfer Protocol]

Development based on HTTP

Provide encryption to ensure the privacy and integrity of messages

UDP

User Datagram protocol

Unreliable, connectionless service

Fast transmission speed

Flow Control and error Control of UDP

UDP has no flow control mechanism.

UDP only has checksum to provide error control.

Upper layer protocols are required to provide error control: for example, TFTP protocol

Application of UDP

Port number:

69 TFTP simple File transfer Protocol

53 DNS domain name resolution

123NTP Network time Protocol

111RPC remote procedure call

5 the role of the application layer

Work with applications to take advantage of data specific to basic network switch applications

Common application layer protocols

DNS

SMTP and POP3

HTTP and HTTPS

Telnet

FTP and TFTP

This is the OSI five-tier model. I hope it can help the friends who need it.

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