Chapter one: Understanding computer networks

Video source: Computer Network Microclassroom

Author: Hu University of Science and Technology teacher

1.2 Overview of the Internet

Network: consists of a number of nodes and links connecting these nodes

Internet: A network of computers connected by an arbitrary protocol

The protocol is TCP and IP. Recursion is a way to split the problem first.

1.3 Three modes of exchange

1.3.1 Circuit Switching (Circut Switching)

Circuit switching is the way a telephone exchange connects to a telephone line

Cons: Data transfer is inefficient, because the call uses communication resources.

1.3.2 Packet Switching

This is how data is transferred over the Internet. Switches on the Internet are routers.

Packet switching is a process in which packets are divided into several small data segments and a header with the destination address and sequence is added to each data segment, so that the packets reach the destination host through different paths of the computer network. After receiving the packets, the host restores the packets to the original packets.

1.3.2 Message Switching (Message Switching)

In short, it was used in the early telegraph communication networks. Now it’s basically replaced by packet switching.

Comparison of the three

1.4 Definition and classification of computer networks

1.4.1 Definition of computer network

A simple definition of a computer network: a collection of interconnected, autonomous computer units.

1.4.2 Classification of computer networks:

According to switching technology: circuit switching network, packet switching network, message switching network

Divided by user: public network, private network

According to transmission media: wired network, wireless network

By coverage: wan, metropolitan area network, LOCAL area network, individual area network

1.5 Performance indicators of computer networks

Rate, bandwidth, throughput, delay, delay bandwidth product, error rate, packet loss rate

1.6 Computer network architecture

1.6.1 Common computer network architecture

1. The OSI system

Open Systen Interconnection Reference. It is supposed to be an international standard in law, but the protocol system has overlapping parts at different levels and is too academic to be widely adopted.

TCP/IP architecture

Strong market background and commercialization.

3. Principle architecture

The relationship between these three architectures:

In terms of status: OSI protocol is an international standard in law; TCP/IP is the de facto international standard; The principle architecture is the standard in teaching. The principle architecture can be understood as a compromise between the OSI and TCP/IP standards.

In terms of merging, the OSI application layer, presentation layer, and session layer are merged into the TCP/IP application layer. The TCP/IP protocol can be split into the physical layer and the data link layer.

1.6.2 Necessity of stratification of computer network system

1.6.3 Examples of layering ideas in computer networks

Simply put, this lecture is “Enter the URL in the address bar, come to this page, what happens?” Detailed answers to the interview questions. It’s the best thing on earth.

1.6.4 Terminology for computer network layering

Three terms: entity, agreement, service

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

Protocol: A set of rules that control logical communication between two peer entities

The three elements of the protocol are syntactic and semantic synchronization

Syntax: Defines the format for exchanging information

Semantics: Defines the operations to be performed by the sender and the receiver

Synchronization: Defines the timing relationship between sender and receiver

Services: Under the control of a protocol, logical communication between two peer entities enables this layer to provide services to the next layer. To use this layer protocol, you also need to use the services provided by the lower layer