Computer networks-computer networks and the Internet

I. What is the Internet

1. Specific composition Description

The public Internet is a worldwide network of computers that are connected to millions of computer devices (host or end Systems ) across the world.

End systems are connected to each other through communication links and packet switches .

The sending system segments the data and adds the header bytes to each segment (the resulting packets are called groupings ), which are sent over the network to the destination system.

Two of the most famous packet switches: router link-layer switches .

Two most important protocols : TCP (Transmission Control Protocol) IP (Internet Protocol)

The IP protocol defines the format for sending and receiving packets in routers and end systems.

Intranet : hosts in the network cannot exchange information with hosts outside the private network

2. Service Description

distributed Applications : E-mail, web surfing, instant messaging, VoIP, internet broadcast, streaming video, distributed gaming, peer-file sharing, TV on the Internet, remote registration, and more. (They involve multiple end systems that Exchange data with each other)

A terminal system connected to the Internet provides an application programming interface (application Programming Interface). The API specifies that the software that runs on one end of the system requests the Internet infrastructure to deliver data to the specific destination software running on the other end of the system.

3. What is an agreement

in order to complete a job, two (or more) communication entities are required to run the same protocol.

A protocol defines the format and sequence of messages exchanged between two or more communication entities, as well as the actions taken in connection with message transmission/reception/other events.

Second, the network edge

End Systems (hosts) are sometimes further divided into two categories: client Server (server)

Client informally equates to PC, mobile PC, etc.

Server informality equates to more powerful machines for storing and publishing Web pages, streaming videos, and forwarding e-mails.

1. Client and server programs

Client Programs (client program) programs that run on one end of the system, make requests, and receive services from server programs on the other side of the system.

Client-server Internet applications are distributed applications .

2. Access Network

Edge Router : The first router on the path of the end system to any other remote end system.

The physical link that connects the end system to its edge router.

The new broadband access technology provides a higher bit rate for residential users and provides a means for users to access the Internet while still making calls.

Two common types of access for broadband residential areas: Digital Subscriber lines (digitally subscriber line DSL) hybrid fiber coaxial cable (hybrid fiber-coaxial cable HFC)

One of the attractions of DSL, HFC and satellite access is always online .

3. Physical media

Two types of physical media: boot-based media (guided medium) non-bootable (unguided media).

Double stranded conductors: the cheapest and most popular boot-based transmission media.

Coaxial cable: With higher bit rate.

Optical Cable: A thin, soft medium that guides light pulses, where each pulse represents a bit.

Terrestrial Radio channel: carries the signal in the electromagnetic spectrum.

Satellite Radio channel: Connects two or more microwave emitters/receivers located on the earth.

Third, the core of the network

1. Circuit switching and packet switching

Circuit Switching (circuit switching) and packet switching (packet switching) are two basic ways to move data through network links and switches.

Circuit switching: When two hosts are communicating, the network creates a dedicated end-to-end connection between the two hosts (End-to-end connection). Host A in order to send a message to Host B, the network must reserve a circuit on one of the links.

2. Multiplexing in circuit-switched networks

Two multiplexing implementations: Frequency Division Multiplexing (frequency-division MULTIPLEXING,FDM) Time Division Multiplexing (Time-division MULTIPLEXING,TDM).

FDM: The spectrum of the link is shared by all connections created across the link. The link is dedicated to one band for each connection during the connection.

TDM: Time is divided into frames of fixed intervals, and each frame is divided into a fixed number of slots. When a network creates a connection across a link, the network specifies a time slot for the connection in each frame. These slots are used exclusively by the connection and a single timeslot transmits the data of the connection.

3. Packet switching

4. Packet switching vs. Circuit Exchange: Statistical multiplexing

5. How groups form their pathways through a packet-switched network

6.ISP and Internet backbone

Iv. delay, packet loss and throughput in packet switching networks

V. Level of agreement and their service model

Vi. network under threat of attack

VII. History of computer networks and the Internet

Computer networks-computer networks and the Internet