Grasp the key points:

  • Network architecture
  • Classic Network (Ethernet)
  • agreement
  • Network equipment

– The concept of computer networks

Computer network: it is a decentralized (cross-region), with independent function of the computer system, through communication equipment and lines connected, by the functional software to achieve resource sharing and information transfer system.

Computer system :IOS Androd Windows macOS

A computing network is an interconnected, autonomous collection of computers.

Interconnect – Interconnect communication links

All computers are connected directly via a communication link (optical fiber)

Autonomy – No master/slave relationship. Computers are independent of each other and cannot directly control each other

1. Data communication (connectivity)

Data can be transferred between channels

2. Resource sharing

  • Hardware resource sharing (printer, fax machine)
  • Software resource sharing (App Store downloads)
  • Data Resource Sharing (Baidu Library)

3. Distributed processing

Multiple computers performing different parts of the same task (Hadoop platform: Data processing and storage)

4. Improve reliability

If a circuit swing machine, the link can not go, another computer can become a replacement machine

5. Load balancing

Distributed to achieve the effect

– The composition of the computer network

1. Components

It is divided into hardware, software and protocol

2. Working mode

1. Edges

Users can directly use it in C/S mode or P2P mode

2. The core

Serve the edge

3. Function composition

It is divided into two functions: data communication and resource sharing, and implements communication subnet and resource subnet according to function classification

1. Communication subnet

Data communication, and is composed of a variety of transmission media, communication equipment, the corresponding network protocol

Category layer:

  • Physical layer (integrator, repeater)
  • Data link layer (switch, bridge)
  • Network layer (router)
2. Resource subnet

Realizing resource sharing/data processing is a collection of equipment and software to realize resource sharing

Category layer:

  • The application layer
  • The presentation layer
  • The session layer

The transmission layer is the communication interface between resource subnet and communication subnet

For example:

If be in treasure out buys lipstick to oneself or give oneself girl friend to call treasure out inn home to pack according to your requirement add a piece of small card, in the process that pack, corresponding our resource is shared and data process, and it is the process that data communicates when post

– Classification of computer networks

  1. According to the range of distributionWAN WAN(Switching technology),MAN MAN(Broadcasting Technology),Local area network (LAN).Personal regional network PAN
  2. By user:Public network(China Telecom),Private networks (VPNS)(Military Network)
  3. By exchange technology:Circuit switching,Message switching,Packet switching
  4. By topology structure (Network shelf) :Main line,The star,ring,Mesh type

Note that the mesh type is used for a wide area network (Internet), and the star type has six nodes and of course five links

  1. By transmission technology:Broadcast network(Shared common communication channel),Peer-to-peer networks(Using packet store-and-forward and routing mechanisms)

The difference between the two networks: whether to use packet store-and-forward and routing mechanisms

– Standardization work

Classification of standards: statutory standards and implementation standards

Statutory standard: The OSI, a formal, legal standard established by an authoritative body

De facto standards: Some companies have products that dominate the competition, and TCP/IP has been around for a long time, so their protocols and technologies have become the standard

Request For Comments (RFC) – Internet standard form

There are four stages in the RFC’s rise to become an official Internet standard:

1) Internet Draft This is the stage that starts to become an RFC document

2) The Proposed Standard becomes an RFC document from this stage.

3) Draft Standard (cancelled in 2013)

4) Internet Standard

– Standardization related organizations *

ISO:OSI reference model, HDLC protocol

ITU: Sets rules for communication

IEEE: Academic institution, IEEE802 series standards, 5G

Internet Engineering Task Force IETF: responsible for the development of Internet-related standards RFC XXXX

– Performance indicators

Rate of 1.

Rate is data rate or data transfer rate or bit rate

Bit: A signal sent by a computer is sent in the form of data, and a bit is a unit of the amount of data sent: 1/0 bit

The rate at which a host channel connected to a computer network uploads bits of data

The unit is B /s KB /s Mb/s Gb/s Tb/s

Thousands of 1 KB/s = 10 ^ 3 b/s

MB /s = 10^ 3KB /s = 10^ 6B /s

Gigabit 1Gb/s = 10^3Mb/s = 10^ 6KB /s = 10^ 9B /s

Too 1Tb/s = 10^3Gb/s = 10^6Mb/s = 10^9kb/s = 10^12b/s

2. The bandwidth

(1) “bandwidth” originally referred to the width of a given frequency band, the difference between the highest and lowest frequency, in Hertz

(2) In computer networks, bandwidth is used to indicate the ability of the communication lines of the network to transmit data. It usually refers to the “highest data rate” that can pass from one point of the network to another in a unit of time. The units are “bits per second”, b/s, KB /s, Mb/s, Gb/s. Maximum speed supported by the network device

The propagation rate of electromagnetic waves in the medium is 2 X 10^8 m/s

3. The throughput

Indicates the amount of data passing through a network (channel, interface) in a unit time, that is, the total amount of data in a link. Unit: B /s, KB /s, Mb/s, etc. Throughput is limited by the bandwidth of the network or the rated rate of the network.

4. The time delay

The time it takes for data (packets/packets/bitstreams) to travel from one end of a network (or link) to the other. Also called delay or delay. The unit is s

Delay classification: transmission delay (transmission delay), transmission delay, queuing delay, processing delay

Transmission delay: The time from the first bit of the packet to the last bit of the packet.

Formula: Transmission delay = data length/channel bandwidth (transmission rate)

Propagation delay: depends on electromagnetic wave propagation speed and link length

Formula: propagation delay = channel length/electromagnetic wave propagation rate in the channel

Queuing delay: waiting for the output/incoming link to be available

Processing delay: error detection exit

Addendum: High speed link refers to the increase in transmission rate

5. Latency bandwidth product

Delay bandwidth product (bit) = Propagation delay (s) X bandwidth (B /s)

The latency bandwidth product is also called the link length in bits.

“How many bits does a link have now” (capacity)

6. Round-trip delay RTT

The total delay from the time the sender sends data to the time the sender receives the acknowledgement from the receiver (the receiver sends the acknowledgement immediately after receiving the data).

ping www.baidu.com
Copy the code

The larger the RTT, the more numbers you can send before receiving an acknowledgement

RTT includes: round-trip propagation delay = propagation delay * 2 and end processing time

Utilization rate of 7.

Usage: channel usage and network usage

Channel utilization: data passing time/(data passing time + none)

Network utilization: weighted average of channel utilization

Relationship:

Summary:

– Computer network hierarchical structure

1. Why layer?

Work to be done before sending the file: (1) The computer initiating the communication must activate the data communication channel. (2) to tell the network how to identify the destination host. (3) The computer that initiates communication should check whether the target host is powered on and connected to the network normally. (4) initiate communication computer to make clear, the other computer in the file management program is ready to work. (5) Ensure that errors and accidents can be resolved.

2. How to layer?

It is divided into entities, and the entities at the same layer are peer entities, followed by protocols, and only peer entities have protocols, followed by joints as interfaces, and finally services, which are top-down

Basic principles of layering

  1. The layers are independent of each other, and each layer implements only one relatively independent function.

  2. The interface between each layer is natural and clear, easy to understand, with as little interaction as possible,

  3. Structurally separable. Each layer is implemented using the most appropriate technology.

  4. Maintain the independence of the lower layer from the upper layer, and the upper layer one-way access to the services provided by the lower layer.

  5. The entire hierarchy should facilitate standardization efforts.

3. Formally recognize hierarchical structures

  1. Entities: The active elements in the NTH layer are called n-layer entities. Entities at the same – level are called peer entities.

  2. ** Protocol :** The rules, standards, or conventions established for the exchange of data between peer entities in a network are called network protocols. [level]

The three elements of the protocol: syntax (specifying the format of the transmission), semantics (specifying the function to be performed), and synchronization (specifying the order of various operations)Copy the code

  1. Interface (access service point SAP) : Entry point for upper layer to use lower layer services.

  2. Service: A function call provided by a lower layer to an adjacent upper layer. “Vertical”

Service transfer process:

4. To summarize

  • Network architecture is a functional description of computer network architecture.

  • Computer network architecture is a hierarchical structure.

  • Each layer follows certain network protocols to fulfill its functions.

  • Computer network architecture is a collection of computer network layers and their functions and protocols.

  • When layer N provides a service to layer N +1, the service contains not only the functionality of layer N itself, but also the functionality provided by the services below it.

  • Interfaces exist only between adjacent layers, and the implementation details of the services provided are completely shielded from the previous layer.

  • Architecture is abstract, while implementation refers to the software and hardware that can be run.

– Brief talk about the OSI reference model

1. ISO/OSI reference model — where did it come from?

To solve the big problem of computer networks hierarchical structure (by function)

Objective: To support the interconnection of heterogeneous network systems. The International Organization for Standardization (ISO) proposed the Open Systems Interconnection (OSI) reference model in 1984.

But! Theory succeeds, market fails.

2. ISO/OSI reference model

Rhymes: Internet of Things shuhui trial

3. The ISO/OSI reference model explains the communication process

The intermediate system has only three layers of communication subnet, the upper four layers end to end, the lower three layers point to point

Transmission process:

– OSI reference model structure

1. The application layer

Definition: any program that generates network traffic with the user

Classic application layer services:

File Transfer (FTP)

Email (SMTP)

World Wide Web (HTTP)

.

2. The presentation layer

Definition: Used to deal with the expression (syntactic and semantic) of information exchanged between two communication systems

Function 1: Data format Transformation (Translator)

Function 2: Encrypt and decrypt data

Function 3: Data compression and recovery

3. The session layer

Definition: provides the presentation layer entity/user process with the ability to establish a connection and order the transfer of data over the connection. This is called a session, and it is also called establishing a synchronization (SYN)

Function 1: Establish, manage, and terminate a session

Function 2: The effect point can be used to restore the communication between the effect point and synchronization point when the communication fails to achieve data synchronization.

Suitable for transferring large files. Main protocols: ADSP, ASP

4. The transport layer

Definition: Mainly responsible for communication between two processes, that is, end-to-end communication. The transmission unit is a packet segment or a user datagram.

Function 1: Reliable transmission, unreliable transmission

Function 2: Error control

Function 3: Flow control (control the speed of the sender)

Function four: reuse and reuse

Reuse: Multiple application layer processes can simultaneously use the services of the transport layer below. Reuse: The transport layer delivers the received information separately to the corresponding processes in the upper application layer.

If you are more vague about the use of points, here is an example

When sending QQ messages to your friends, your mobile phone occupies port 4000, and the phone that sends messages to your friends is allocated to port 4000, and your friends also get messages from port 4000, which is the process of reuse and reuse

Main protocols: TCP and UDP

5. The network layer

The main task is to transfer packets from the source to the destination and provide communication services for different hosts on the packet switching network. The unit of transmission at the network layer is the datagram

Function 1: Routing (Optimal Path)

Function 2: Flow control

Function three: Error control

Function 4: Congestion control

If there is too little time for all nodes to accept groups and too many groups to discard, the network becomes congested. Therefore, some measures should be taken to relieve the congestion.Copy the code

6. Data link layer

Definition: The main task is to assemble the datagrams from the network into frames.

Data link layer/link layer transmission unit is frame

Function 1: Frame (define the start and end of a frame)

Function two: error control frame error + bit error

Function 3: Flow control

Function 4: Access control Controls channel access

Main protocols: SDLC, HDLC, PPP, STP

7. The physical

The main task is to achieve transparent transmission of bitstream on physical media.

The unit of physical layer transmission is bit

Transparent transmission: The ability to transmit data over a link regardless of the combination of bits.

Function 1: Define interface features

Function 2: Define transmission mode simplex, half duplex, duplex

Function 3: Define the transmission rate

Function four: Bit synchronization

Function five: bit coding

Conclusion:

– OSI and TCP/IP reference models

1. The OSI reference model is similar to the TCP/IP reference model

  • All layers
  • Based on the concept of an independent protocol stack
  • Heterogeneous network interconnection can be implemented

2. Differences between OSI reference model and TCP/IP reference model

  • OSI defines three points: services, protocols, and interfaces

  • OSI came first, the reference model was invented before the protocol, not biased towards a particular protocol

  • At the beginning of TCP/IP design, heterogeneous network interconnection was considered, and IP was regarded as an important level

  • Differences in the hierarchical structure of computer networks

Connection-oriented is divided into three phases. The first is the establishment of a connection, in which a request is made to establish a connection. Only after the connection is successfully established can the data transfer begin, which is the second stage. Then, when the data transfer is complete, the connection must be released. Connectionless doesn’t have so many phases, it transfers data directly.

3. Layer 5 reference model

It combines the advantages of OSI and TCP/IP

Support various network applications: FTP, SMTP, HTTP

Process-process data transmission: TCP and UDP

Packet routing and forwarding from the original host to the destination host: IP, ICMP, OSPF

The network layer passed down the datagram assembly into frame Ethernet, PPP

Bit transmission

4. Data encapsulation and unencapsulation of layer 5 reference model

workflow

Conclusion as a whole