A Summary of Computer Network Learning
abstract:
This course mainly talks about the formation and development of computer networks, the hierarchical structure of computer networks, and focuses on all levels of computers.
The architecture and related protocols of.
Through this course, we have made a systematic study.
transmission control protocol (TCP)
Five levels: physical layer, data link layer, network interconnection layer, transport layer,
Application layer. In addition, we have deeply studied the related protocols of each layer and their applications.
By studying this course,
We are interested in the formation and development of computer networks.
Have a general and basic understanding of the network hierarchy and related protocols.
And a preliminary understanding of the basic principles and working methods of computer networks.
main body
1
.
Network overview
1. 1
Four stages of the formation and development of computer network;
The first stage:
20
hundred years
50
age
-
Research and Development of Data Communication Technology
The second stage:
20
hundred years
60
age
-ARPANET
Research and Development of Packet Switching Technology
The third stage:
20
hundred years
70
age
-
Research on Network Architecture and Protocol Standardization
Wide area network,
Research and Application of Local Area Network and Public Packet Switching Network
The fourth stage:
20
hundred years
90
age
-Internet
Wide application of technology
1.2
packet switching technology
Packet switching adopts store-and-forward technology.
The characteristics of packet switching are label-based.
Packet switching network
It consists of several node switches and links connecting these switches.
When the traffic of the link is too large or
When interrupted,
Routing protocols running in node switches can automatically find other paths to forward packets.
adopt
The essence of store-and-forward packet switching is to dynamically allocate transmission bandwidth during data communication.
Strategy.
1.3
Network architecture
ISO/OIS
Reference model:
Application layer, presentation layer, session layer, transport layer, network layer, data link layer and physical layer.
transmission control protocol (TCP)
reference model
Application layer, transport layer, network interconnection layer, data link layer and physical layer.
1.4
Local area network related technology
2
Reference model:
IEEE 802
reference model
2
.
physical layer
Physical layer is located
Open system interconnection reference model.
Participate in the bottom layer of the model and directly face the physics of data transmission.
medium
(
I.e. channel
)
The transmission unit of the physical layer is bits.
The physical layer refers to the data link above the physical medium.
The road layer provides the physical connection of the original bit stream.
The physical layer protocol specifies the connection to the facility,
Mechanical, maintenance and disconnection of physical channels,
Electrical,
success
Characteristics, rules and procedures of energy. Its function is to ensure that the bit stream can be transmitted on the physical channel.
Examples of related protocols:
EIA RS-232C
interface standard
EIA RS-449
and
RS-422
and
RS-423
interface standard
EIA RS-449
and
RS-422
and
RS-423
interface standard
Examples of transmission media:
Twisted pair, coaxial cable, optical fiber, wireless transmission media, etc.
three
.
data link layer
The most basic service of data link layer is to transmit data reliably from source network layer to neighboring nodes.
Target machine network layer.
In order to achieve this goal,
The data link layer must have a series of corresponding functions,
it
The main ones are:
How to combine data into data blocks,
Such data blocks are called frames in the data link layer,
Of painting or calligraphy
Is the transmission unit of the data link layer;
How to control the frame transmission on the physical channel,
Including how to handle the transmission.
Mistakes,
How to adjust the sending rate to match the receiver;
Providing data between two network entities
Establishment, maintenance and release management of link paths.
Link management function:
Link management function is mainly used for connection-oriented services.
Before the nodes at both ends of the link want to communicate,
must
First, confirm that the other party is in a ready state.
And exchange some necessary information to initialize the frame number,
then
Establish contact.
The connection should be maintained during transmission.
If something goes wrong,
Need to reinitialize,
Automatically re-establish the connection.
Release the connection after the transmission is completed.
The establishment of data link layer connection,
preserve peace
Publishing is called link management.
In the case that multiple sites * * * share the same physical channel.
(e.g. in a local area network)
How to communicate in the request
Inter-site allocation and management channels also belong to the category of data layer link management.
Frame synchronization function:
three
( 1)
Byte counting method;
(2)
Leading and trailing separator methods using character padding;
(3)
Head and tail delimiter method using bit filling;
(4)
Illegal coding method;
Examples of data link control protocols:
Asynchronous protocols regard characters as independent information transmission units,
At the beginning of each character, start checking the character.
But the spacing between characters is not fixed.
(
In other words, characters are asynchronous.
about
)
. Because the two agreed clock frequencies in the transmitter and receiver are similar, they can be used in a short time.
The time is synchronized, so you can sample the ratios in the character with the synchronous clock at the beginning of the character.
In particular,
And each bit does not need to be synchronized by other methods.
The "start-stop" communication rules introduced earlier.
Is a typical asynchronous protocol, which is based on the slave.
(
logic
0)
And a stop bit.
(
logic
1)
In order to realize the determination of characters
Boundary and synchronization of bits in characters. In the asynchronous protocol, because each transmission character needs to be added, such as the start bit,
Check bits, stop bits and other redundant bits, so the channel utilization rate is very low, and it is generally used in situations with low data rate.
Synchronization protocol is a data block frame organized by many characters or bits as transmission units.
Within the framework
At the beginning of synchronization,
Keep a fixed clock in the frame.
Since the frame is used as a transmission unit,
So the synchronization protocol
The channel can be used more effectively, and the functions such as error control and flow control can be realized conveniently.
four
.
Network interconnection layer
The network layer is
Open system interconnection reference model.
The third layer in the reference model.
,
Between the transport layer and the middle layer of the data link. It came in.
According to the transmission function of data frames between two adjacent endpoints provided by the data path layer,
Further management
Data communication,
Data is managed to be transmitted from a source end to a destination end through a plurality of intermediate nodes,
So as to reach the transport layer
Provide the most basic end-to-end data transmission service.
The network layer involves the operation control of the communication subnet,
include
This paper introduces the way that the resource subnet accesses the communication subnet under the network application environment,
be
Open system interconnection reference model.
Data communication-oriented model
Xiasanlou
(
The communication subnet.
)
The most complex and critical layer in.
The purpose of the network layer is to realize the transparent transmission of data between two terminal systems,
Specific functions include routing.
Selection, blocking control and internet interconnection.
Datagram operation mode
In the datagram operation mode,
Each packet is called a datagram,
Several datagrams constitute a transmission.
A message or data block sent.
Each datagram itself carries enough information,
Its transmission is handled separately.
Yes
After the node receives the datagram,
According to the address information in the datagram and the path stored by the node
From the information, find a suitable way out and send the datagram to the next node as it is.
four
When the terminal system wants to send a message,
The message is divided into several data with serial number and address information.
The report is then sent to the network node. After that, the path taken by each datagram may be different because each datagram
Nodes at any time according to the network traffic,
Fault and so on and so on.
Because of its reputation,
Each datagram does not
It can be ensured that the destination node is reached in sequence,
Some datagrams may even be lost on the way.
In the whole datagram
In the process of transmission, there is no need to establish a virtual circuit, but the network node should route each datagram.
Communication subnet provides the possibility of multiple transmission paths for network source nodes and destination nodes.
network node
After receiving the packet,
In order to determine the transmission path to the next node,
This is a route.
In the data
In the way of reporting,
Network nodes should make a choice for each packet route;
When in virtual circuit mode,
Right here in the company
Determine the route when establishing. The strategy to determine the route is called routing algorithm.
Many technical factors need to be considered when designing routing algorithms.
First of all,
Consider whether to choose the shortest route or choose
Optimal routing; Secondly, it is necessary to consider whether the communication subnet adopts virtual circuit or datagram operation mode;
Third,
Adopt a distributed routing algorithm,
That is, each node selects the next route for the arriving packet,
still
Adopt a centralized route algorithm,
That is, the central node or the originating node decides the whole route;
Fourth,
take an examination
Regarding the network topology,
Sources of network information such as traffic and delay;
Finally,
Determine whether to use static routing.
Select a policy or dynamic routing policy.
five
.
transport layer
Open system interconnection reference model.
The physical layer, data link layer and network layer in the seven-layer model are the next three layers of network communication.
Agreement.
The transport layer is responsible for end-to-end communication,
Not only is it the highest layer responsible for data communication in the seven-layer model,
and
The middle layer between the lower three layers is used for network communication, and the upper three layers are used for information office.
The transport layer is located in the network.
Above the layer and below the session layer, it uses the service area provided by the network layer subsystem to develop the functions of this layer.
And realize the service of this layer to the session layer.
The transport layer is
Open system interconnection reference model.
The most important and critical layer in the seven-layer model is the only layer responsible for the overall data transmission.
Transmission and control layer. The two main purposes of the transport layer are: first, to provide reliable end-to-end communication;
Second, provide network-independent transmission services for the session layer.
According to the purpose and unit of the transport layer in the seven-layer model, its main functions are: executing.
Dialogue or connection provides reliable transportation services,
This connection is replicated on a single physical connection to the network.
Provide end-to-end sequence number and end-to-end error control and flow control recovery on a single connection.
Service.