Morning flowers and evening flowers

Standardization of computer networks

1. Specified standard ：OSI（ Seven layers ）
2. Actual standard ：TCP/IP( The product is so awesome , As a result, almost all products began to use his standards ）（4 layer ）

Performance index of computer network

data rate ： The rate at which data is transmitted

bandwidth ：

The ability to represent the transmission rate of communication lines in the network , That is, in unit time , What can be passed from one point to another in the network The highest data rate
For example, a router , His specifications are 100M, It means in the 1s It can transmit at most 100Mbit The data of
Be careful ： The difference between bandwidth and data rate is that bandwidth does not affect the speed of data transmission , But it affects how much data is being transmitted at the same time

throughput

And bandwidth ：
Throughput is the data size of the actual channel , The bandwidth is the largest transmission data size of the channel

Time delay

1. transmission delay ： Data length / bandwidth
High speed link ： Send links with small delay （ It's not that the propagation delay is small ）
2. Propagation delay ： Channel length / Propagation rate
Influencing factors ： Media （ Optical fiber , Electromagnetic wave, etc ）
3. Queuing delay
4. Processing delay

Delay bandwidth product

Propagation delay * bandwidth
That is, the capacity of a link

Round trip delay RTT

Starting from the sender sending data , Until the confirmation signal sent by the receiver is received
= Propagation delay *2+ The processing time （ Generally ignored ）

utilization

Hierarchical structure

agreement

elements ：

1. grammar ： Specify the format of the transmitted data
2. semantics ： Specify the functions to be realized
3. Sync ： Define the sequence of operations

service

The lower layer is provided to the upper layer （ adjacent ） Function call

Interface

The upper layer uses the entrance of the lower service
Generally, the utilization rate is proportional to the delay （ Similar to traffic jam , High utilization is not necessarily a good thing ）
In the hierarchical structure , Lower to upper “ transparent ” The meaning of : The upper layer only needs the protocol provided by the lower layer , Do not deal with the details of its implementation

OSI Overview of standards

Bottom up 7 layer : Internet of things Shuhui trial
The first three layers realize the data processing function
The latter three layers realize the data communication function
How to realize data transmission

host a First, the data to be transmitted data pack （ Start with the application layer , Each layer ＋ Add the tail or add the head and tail ）, Then send it to the host b,b Then unpack the package layer by layer from the physical layer , Finally, you can get information data

OSI Layer by layer analysis

1. application layer ： seeing the name of a thing one thinks of its function

2. Transport layer ：

function 1： Reuse and reuse （ It's similar to sending mail by mailbox ）
function 2： Reliable transmission and unreliable transmission （ For example, there is no need to use reliable transmission to transmit a small amount of data, because it is troublesome ）
function 3： flow control
function 4： Error control
（ But bad ones can also be retained ？）

3. The network layer

function 1： flow control
function 2： Error control
function 3： Congestion control
And flow control ： Flow control is to limit the prime of the sender , Congestion control is a kind of global control （ If all nodes in the whole world have no time to accept packets and have to discard packets, they will enter a congestion state ）

4. Data link layer

function 1： flow control
function 2： Error control
function 3： Encapsulate the datagrams delivered from the network layer into frames

5. The physical layer

function ： Ensure that no matter what bit combination the transmitted data is , Can be transmitted on the link （ Transparent transmission ）