Computer Network Technology and Application

Chapter 14 Internet Network Protocols and Technologies (2)
(2) Based on the fiber-optic coaxial cable hybrid network (HFC) Cable Modem as the high-speed plan of the access line is hindered.Although the use of Cable Modem can provide several Mbps data transmission capabilities for CATV user lines, the users who can use this service are greatly limited due to factors such as multiple users sharing bandwidth and security.Experiments and surveys have shown that:

On the existing infrastructure, only about 15% of users can use Cable Modem. If two-way transformation is carried out on the existing facilities, the investment will be huge.

(3) Using ADSL technology, the voice and data can be sent to the telephone exchange and the Internet respectively through the splitter, thereby restraining the traffic of the Internet from flowing into the telephone network.

Currently, in China's broadband services, most home users use ADSL access.

4.3.2 Wireless LAN access
With the widespread use of mobile phones, notebook computers and PDAs, people's demand for wireless communication is increasing, the user base is increasing, and wireless network technology is becoming more and more mature.

1. Wireless network technical standards

Wireless network technical standards usually include Bluetooth technology, IEEE802.11 standard and HomeRF standard for home network.

(1) IEEE802.11 standard
IEEE802.11 is the first wireless local area network standard introduced by the Institute of Electrical and Electronics Engineers (IEEE). It is mainly used to solve the problem of wireless access between users and user terminals in office LANs and campus networks; it is mainly limited to data access, and the highest rate is only Can reach 2Mbps.

IEEE802.11 mainly includes three standards: 802.11a, 802.11b, and 802.11g.

IEEE802.11a is a wireless local area network protocol standard introduced in order to improve its original wireless standard IEEE802.11, and it is a beneficial supplement to IEEE802.11.

IEEE802.11b is the second-generation wireless local area network protocol standard launched by the Institute of Electrical and Electronics Engineers (IEEE) in order to improve its original wireless standard IEEE802.11.

The advantage of the IEEE802.11a standard is that the transmission speed is fast, up to 54Mbps, which can fully meet the needs of voice, data, image and other services. Unfortunately, it cannot be compatible with IEEE802.11b, resulting in some wireless networks that have already purchased the IEEE802.11b standard The device cannot be used in the new IEEE802.11a network.

IEEE802.11g工作在2.4GHz频段内，比现在通用的IEEE802.11b速度要快5倍，并且与IEEE802.11完全兼容。

(2) Bluetooth technical standard

Bluetooth technology standard (IEEE802.15) is a new standard, which can be said to be a supplement to IEEE802.11.Bluetooth can support longer distances and higher speeds. The transmission distance is from 0.1 to 10m. By increasing the transmission power, it can reach 100m, and the maximum speed is 1Mbps; and Bluetooth is low in cost and small in size, and can be used in more devices.Bluetooth technology is more mobile. If IEEE802.11 is limited to offices and campuses, Bluetooth can connect a device to LAN and WAN, and even support global roaming.

(3) HomeRF standard for home network
Under the leadership of the American Household Radio Frequency Committee, the HomeRF working group was established in 1997. Its main task is to establish an interoperable voice and data communication network for home users.The working group launched the HomeRF standard, which integrates voice and data transmission technologies. The working frequency band is 10 GHz, and the data transmission rate reaches 100 Mbps. In terms of WLAN security, access control and encryption technologies are mainly considered.

HomeRF also uses spread spectrum technology, works in the 2.4GHz frequency band, and can simultaneously support 4 high-quality voice channels.

At present, the transmission rate of HomeRF is only 1Mbps-2Mbps.

HomeRF is a synthesis and improvement of existing wireless communication standards. When performing data communication, it uses the TCP/IP transmission protocol in the IEEE802.11 specification; when performing voice communication, it uses digital enhanced wireless communication standards.This standard is not compatible with IEEE802.11b, so there will be great limitations in the scope of application, and it is more used in home networks.

2. Wireless network access method
Wireless network access is currently mainly used in local area networks. For equipment and access methods, please refer to Section 3 in Chapter 3.5.

4.3.3 Virtual Private Network
Virtual private network (Virtual Private Network, VPN) technology is widely used in network interconnection and data transmission, which can provide a secure and dedicated network channel.Due to the use of encryption technology in the VPN, the shared facilities of the wide area network used become a more secure environment.

Virtual private network can help remote users, company branches, business partners and suppliers establish credible and secure connections with the company's intranet, and ensure the safe transmission of data.At present, VPN is being widely used in the interconnection between organizations and their branch LANs.

1. Working principle of VPN
Virtual private network is a technology that relies on network service providers to establish a private data communication network in a public network.

In the virtual private network, the connection between any two nodes does not have the end-to-end physical link required by the traditional private network, but uses the public network resources to dynamically form a logical link.

The meaning of IP-based VPN understood in the Internet Engineering Task Force (The Internet Engineering Task Force, IETF) draft is "to simulate a private wide area network using the IP mechanism". Point-to-point dedicated line technology.The so-called virtual means that users no longer need to have actual long-distance data lines, but use the long-distance data lines of the Internet public data network.The so-called private network means that users can design a safe channel that best meets their own needs.

2. The main way to establish a tunnel

In a VPN, the data packet flow of the point-to-point protocol PPP is sent by a router on a LAN and transmitted to a router on another LAN through a tunnel on a shared IP network.

Compared with traditional PPP, the key difference between the two is that the tunnel replaces the actual dedicated line.A tunnel is like a serial communication cable in a wide area network.

Client-Initiated and Client-Transparent are the main ways to establish a VPN tunnel.Client initiation requires tunneling software to be installed on both the client and the tunnel server (or gateway).Client Transparency is usually installed on the company's central station.

The tunnel is initialized through the client software, and the tunnel server is responsible for stopping the tunnel. The Internet service provider may not support the tunnel. The client and the tunnel server only need to establish a tunnel, and use user ID and password or digital license to authenticate authority.

Once the tunnel is established, communication can proceed as if the ISP were not involved in the connection.

If tunneling is to be transparent to customers, the ISP must have access servers and routers that allow tunneling.The client first dials into the server, and the server must be able to identify that the connection needs to establish a tunnel with a specific remote node, and then the server establishes a tunnel with the tunnel server.Usually user ID and password are used for authority authentication, so that the client establishes a direct dialogue with the tunnel server through the tunnel.This method does not require the client to install special software, but the client can only dial into a properly configured access server.

In order to better understand and use VPN technology, this chapter arranges VPN experiments.

3. Application of VPN

VPN technology is widely used in the construction of enterprise intranets, especially in enterprise intranets with multiple branches in different places. Using VPN for interconnection is economical and has high security performance.At present, the main technologies used for self-built VPNs within enterprises are "IPSec VPN" and "SSLVPN".

(1) IPSec VPN
It is suitable for enterprises with a certain scale, employees with certain experience in IT construction, management and maintenance, and enterprises with many branches.By connecting sites through VPN tunnels, enterprises can exchange large-capacity data.

Enterprises are sensitive to data and require a higher level of security.Employees of the enterprise cannot access the internal information of the enterprise through any computer at will, and the notebooks or computers of mobile office employees must be equipped with firewalls and anti-virus software.

(End of this chapter)