The network architecture of the first chapter of computer network examination in 2016.6.6

1. Agreements and levels of demarcation

The rules, standards, or conventions established for the exchange of data in a network are called network protocols.

The network protocol is also referred to as the agreement, mainly consists of the following three elements:

(1) syntax, i.e. the structure or format of data and control information;

(2) Semantics, that is, what kind of control information needs to be emitted, what action to complete and what response to make;

(3) synchronization, that is, the details of the sequence of event implementation;

2. Layering can bring many benefits:

(1) Each layer is independent.

(2) Good flexibility

(3) The structure can be split open

(4) Easy to implement and maintain

(5) Can promote standardization work

3. The main functions to be performed by each layer are as follows:

(1) Error control, so that the corresponding level of network peer communication more reliable.

(2) Flow control, so that the sending end of the sending rate is not too fast, to make the receiving end time to receive.

(3) segment and reload, the sending side divides the data block to be sent into smaller units and restores it at the receiving end.

(4) Multiplexing and separation, the sending end of several high-level sessions to reuse an underlying connection, at the receiving end of the division.

(5) Connection establishment and release, the exchange of data before the establishment of a logical connection, the end of data transfer to release the connection.

4. Architecture

* * Each layer of the computer network and the set of protocols, called the network architecture.

* * The architecture of computer network is the precise definition of the function that the computer network and its components should accomplish.

* * In short, the architecture is abstract, and the implementation is specific and is really running on the computer hardware and software.

5. Architecture with five tiers of protocol

(1) OSI seven-layer protocol architecture

Physical layer, Data link layer, network layer, transport layer, Session layer, presentation layer, application layer

(2) Architecture of TCP/IP

Network interface layer, internetwork IP, Transport layer (TCP or UDP), application layer

(3) Architecture of the five layer protocol

Physical layer, Data link layer, network layer, Transport layer, application layer

① Application layer: Complete specific network applications by applying inter-process interactions. Different Web applications require different application-layer protocols. The HTTP protocol that supports the Web application, the SMTP protocol that supports email, and the FTP protocol that supports file transfer.

② Transport Layer: responsible for providing a common data transfer service to the communication between processes in two hosts. The so-called universal, is not for a particular network application, but a variety of applications can use the same transport services, so the transport layer has the function of reuse and separation.

Transmission Control Protocol TCP: Provides a connection-oriented, reliable data transmission service, the unit of data transmission is the message segment.

User Datagram Protocol UDP: Provides non-connected, do the best efforts of data transmission services, the unit of data transmission is the user datagram.

③ Network layer: When the data is sent, the network layer transmits the packets or packets that are generated by the transport layer or the User datagram encapsulated component groups or packages.

This book uses "grouping" and "datagram" as synonyms. In addition, no matter which data unit is transmitted, it can be represented in a general way by "grouping".

The main network layer protocol of the Internet is the non-connected Internet Protocol IP and many kinds of router selection protocols.

④ Data Link layer: When data is transferred between two adjacent nodes, the data link layer assembles the IP datagram that is delivered by the network layer into frames and transmits the frames across the links between the two adjacent nodes. Each frame includes data and necessary control information.

Control information includes: synchronization information, address information, error control information

⑤ Physical layer: The unit of data transmitted on the physical layer is bit. Therefore, the physical layer should consider how much voltage is used to represent "1" or "0", and how the receiver recognizes the bits sent by the sender.

Note that some of the physical media used to deliver the information, such as twisted pair, coaxial cable, optical cable, wireless channel, etc., are not within the physical layer protocol but under the physical layer protocol.

(4) The OSI Reference Model refers to the data units transmitted between peers as protocol data unit PDUs for that layer.

(5) Entities, agreements, services and service access points.

Entity: Any hardware or software process that can send or receive information.

Protocol: is a collection of rules that control the communication of two peer entities.

* * Under the control of the Protocol, the communication between the two peers enables this layer to provide services up to one level. To implement this layer of protocol, you also need to use the services provided in the following layer.

* * Entities using this layer service can only see the service and cannot see the following protocol, that is, the following protocol is transparent to the entity above.

* * The protocol is "horizontal", that is, the protocol controls the communication rules between peer entities. But the service is "vertical", that is, the service is provided from the lower level to the upper layer through the inter-tier interface.

* * Services provided by the upper layer using the lower layer must exchange some commands in the OSI called Service Primitives.

Service access point SAP: where two-tier entities in the same system interact (that is, exchanging information), often referred to as service access points.

* * Service access point SAP is an abstract concept, which is actually a logical interface, a bit like a P.O. box.

**osi the unit of data exchanged between layers and layers is called the service data unit SDU, which can be different from the Protocol data unit PDU.

Architecture of the 5.TCP/IP

Application layer, Transport layer, internetwork layer, network interface layer

TCP/IP protocol family, upper and lower two big middle small: the application layer and the network interface layer have many kinds of protocols, and the middle IP layer is very small

The ①everything over IP:TCP/IP protocol provides services for a wide range of applications.

②ip over everything: Allows the IP protocol to run on a wide variety of network-composed internet.

The network architecture of the first chapter of computer network examination in 2016.6.6