Common network lines

This section mainly introduces some common network lines in daily life, such as analog telephone lines, mobile communications, ADSL, FTTH, cable TV, private lines, VPN and public wireless LAN.

Analog telephone line

Analog telephone lines, also known as telephone LAN, take advantage of the already popular telephone network and connect it to an ADSL MODEM, also known as a cat. The purpose of the Modem is to convert the analog signal of the telephone network into the digital signal needed by the computer, so that communication can be transmitted. But because the transmission rate of the cat is too slow, it is gradually replaced by optical fiber and optical fiber cat.

The Protocol used to connect isPs directly over telephone lines is called POINT-to-point Protocol (PPP). Point-to-point Protocol (PPP) is a link-layer Protocol designed for simple links such as transmitting packets between equivalent units. This link provides full duplex operation and transmits packets sequentially. It is designed to send data through dial-up or dedicated point-to-point connections, making it a common solution for simple connections between hosts, Bridges and routers.

PPP has the following features:

  • PPP has the ability to dynamically assign IP addresses, allowing IP addresses to be negotiated at connection time
  • PPP supports multiple network protocols, such as TCP/IP, NetBEUI, and NWLINK
  • PPP has error detection capability, but does not have error correction capability, so PPP is an unreliable transport protocol
  • No retransmission mechanism, low network overhead, high speed
  • PPP has authentication function (PAP dial-up authentication)

Mobile communication service

There are mainly the following kinds of mobile services:

  • Global System for Mobile Communications (GSM) is a digital Mobile phone network standard developed in Europe.
  • CDMA (China Telecom 3G network mode)
  • Td-scdma (China Mobile 3G Network Mode)
  • WCDMA (China Unicom 3G network mode)
  • Td-lte (China Mobile 4G network mode)
  • Fdd-lte (4G network mode of China Unicom and China Telecom)

FTTH

FTTH (Fiber To The Home) is an optical Fiber that converts optical signals into electronic signals through ONU (optical network unit).

Optical cables usually consist of one line that sends data and another line that receives data. Whereas FTTH sends and transmits on the same cable, users accessing this cable are separated by an optical isolator between the ONU and the OLT (optical transmission terminal).

Cable TV

Television was converted from radio waves to signals transmitted by cable. To access the Internet in this way, a MODEM must also be used for the signal conversion, and the cable port takes care of the digital or analog transmission conversion and digital signal transmission over a cable.

VPN

A virtual private network (VPN) is used to establish a private network on a public network for encrypted communication. There are IP-VPN and enterprise-class VPN:

Ip-vpn: The network provider adds an MPLS label to an IP packet. Through this label, the target address can be easily identified and user-level bandwidth can be controlled.

Enterprise VPN: A VPN server is set up on the Intranet. When non-local employees access the server, the VPN server is used to access the Intranet. To ensure data security, the communication data between the VPN server and clients is encrypted. With data encryption, can think the data is in a special secure transmission of data link, like specially set up a private network, but is actually a public link VPN are using the Internet, so called VPN virtual private network, its essence is to use encryption technology in public encapsulation out a data communications channel.

Public wireless LAN

A public wireless LAN enables users to access the Internet by connecting to their own Intranet through the VPN technology.

Write in the last

Data link this layer about so much practical, if you want to understand the details can see the following books

Diagram to TCP/IP

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