Introduction and Comparison of four network access methods

Nowadays, with the rapid development of computer communication technology and the national economy, enterprises' demands for databases and retrieval services are becoming more and more complex, and the general network environment is hard to be competent. For enterprises, having a good network environment is very effective for improving office efficiency. Therefore, group users such as finance, securities, customs, and foreign trade have adopted leased lines, in comparison, leased line access has the following advantages:

1. Dedicated leased line, 24-hour online: Two-Way Data Synchronization transmission, fast Internet access, stable quality, low packet loss rate, and more secure.

2. Local self-maintenance Website: publish more information on the website to provide better prerequisites for E-buainess.

3. controllable operation costs: Internet access fees are charged on a monthly basis, which can minimize network operation costs.

IT looks good, but in the face of various leased line access methods on the market, enterprise IT supervisors and O & M personnel have made difficulties, let's take a look at some of the common centralized leased line access methods and their features so that users can easily choose from them.

I. PCM leased line access

In the optical fiber communication system, the binary optical pulse "0" and "1" are transmitted in the optical fiber. It is produced by the binary digital signal for the out-of-band modulation of the light source. The digital signal is produced by sampling, quantization, and coding the connected analog signal. It is called PCM, that is, pulse encoding modulation. This digital signal of electricity is called a baseband signal, it is generated by PCM electrical end machines.

PCM can provide users with a variety of services, not only can provide digital data leased line services at a rate of 2 m to 155M, but also can provide voice, image transmission, remote teaching and other enterprise services. Its initial bandwidth is 2 MB.

Features:

1. high transmission quality, low network latency, and fixed channel allocation fully ensure the communication reliability and ensure that the user's bandwidth is not affected by other users;

2. Users can build their own Internet, E-mail and other application systems through this high-speed international interconnection channel;

3. the user's network is connected to the third party so that the PCs in the LAN can share interconnected resources;

4. You can obtain multiple free Internet valid IP addresses;

5. Users can publish information around the clock, that is, users can build their own Web sites. Publish your own information services to the Internet.

In summary, PCM leased line access costs are relatively low and interfaces are rich, especially for users with high data transmission rate requirements and requiring higher bandwidth.

Ii. ddnleased line access

DDN is a digital transmission network that uses digital channels to provide semi-permanent connection circuits and transmits data signals. Through the cross-connection of DDN nodes, a fixed physical channel of digital circuits is provided for users in the network. Whether or not the user is transmitting data, this channel is always exclusive to the user, unless the network administrator deletes this user circuit.

DDN can provide users with 2.4 k, 4.8 k, 9.6 k, 19.2 k, N * 64 (N = 1 ~ 31) and 2048kbps speed of the fully transparent dedicated circuit DDN user terminal can be asynchronous terminal (DTE), computer (PC) or local area network.

Features:

1. Digital Circuits are used, with high transmission quality and low latency. The communication rate can be set between 2.4kbps2048kbps as needed.

2. The circuit adopts transparent transmission and can be automatically rolled back to ensure high reliability.

3. Multiple frontend services can be used to perform fax, Internet access, conference and television, and other multimedia services.

4. You can easily set up a virtual private network (VPN), establish your own network management center, and manage your own network. The main disadvantage is that ddnleased line is used to access the Internet, and rent is not what ordinary individual users can afford.

To sum up, the DDN-based access to the Internet is dedicated, fast, stable, secure, and reliable, it is applicable to data services that require high data transmission speed, transmission quality, real-time performance, and confidentiality, such as commercial, financial, and e-commerce industries. However, a dedicated communication line is required to be rented to access the Internet through ddnleased lines, high cost, suitable for users with high budgets.

Iii. optical fiber access

Optical fiber access refers to the use of optical fiber as the transmission media between the local terminal and the user. Optical fiber access can be divided into active and passive optical access. The main technology of the optical fiber user network is the optical fiber transmission technology. At present, the multiplexing technology of optical fiber transmission has developed rapidly, and most of them are in practical use. Because the optical fiber access network uses optical fiber as the transmission medium, the optical fiber access network can be divided into FTTC (optical fiber to the roadside) and FTTZ (optical fiber to the residential area) based on the depth of the user base) FTTB (fiber-to-building), FTTO (fiber-to-Office), and FTTH (fiber-to-house) are collectively referred to as FTTx.

Features:

1. long transmission distance, fast transmission speed, and low loss;

2. In the communication line, you can reduce the number of relay stations, improve the communication quality, and provide strong anti-interference capabilities.

3. high-speed Internet access or enterprise LAN interconnection can be achieved based on the needs of different user groups for different rates.

4. At the same time, because the optical fiber access method has a high bandwidth for uploading and downloading data, it is particularly suitable for online applications with a large volume of external information such as remote teaching, remote medical care, and.

The optical fiber access method is suitable for users who live in a concentrated area of residential buildings, residential areas, and office buildings that have or facilitate integrated cabling. Large enterprises or enterprises with exclusive optical fiber access needs or group users.

Iv. SDH point-to-point access

The English name is SDH (Synchronous Digital Hierarchy, that is, Synchronous Digital System) leased line. The Chinese name is Digital leased line. It is a data transmission service opened through optical fiber, digital microwave, and * circuits. It uses a digital transmission channel to transmit data signals. It provides a leased line rental circuit for point-to-point and point-to-point transparent transmission of data to transmit data, images, sounds, and other information for users.

Features:

1. The SDH Transmission System has a unified frame structure digital transmission standard rate and standard optical path interface in the world, so that the network management system can communicate well.

It is fully compatible with the existing PDH and can accommodate a variety of new business signals, forming a globally unified digital transmission system standard, improving the reliability of the network;

2. different levels of code streams of the SDH access system are arranged in the frame structure Net Load area, while the net load is synchronized with the network, it uses software to directly split high-speed signals into low-speed branch signals at a time, achieving a unique reuse feature, the PDH quasi-synchronous multiplexing method is used to decompose all high-speed signals step by step and then regenerate the multiplexing process. Because DXC is greatly simplified, the back-to-back interface multiplexing equipment is reduced, improves the transparency of network service transmission;

3. The advanced plug-in Multiplexing (ADM), Digital cross-connection (DXC), network self-healing and reorganization functions are very powerful, with a strong survival rate. Because 5% overhead bits of signals are arranged in the SDH frame structure, the network management function is extremely powerful and can form a unified network management system, it plays a positive role in the automation, intelligence, channel utilization, and reduction of network maintenance fees and viability;

4. due to the various network topologies of SDH, the network composed of SDH is very flexible. It can enhance network monitoring, operation management, and automatic configuration functions, and optimize network performance, at the same time, the network is flexible, secure, and reliable, and the functions of the network are very complete and diversified;

5. SDH has transmission and exchange performance. the composition of its series of devices can be freely combined with function blocks to realize the network at different levels and various topologies, which is very flexible;

6. SDH is not a transmission medium. It can be used for twisted pair wires and coaxial cables. However, SDH is used to transmit high data rates and requires optical fiber cables.

7. from the perspective of the OSI model, SDH belongs to its bottom-Layer Physical Layer and does not have strict restrictions on its senior management. It facilitates the adoption of various network technologies on SDH and supports the transmission of ATM or IP addresses;

8. SDH is strictly synchronized, which ensures the stability and reliability of the entire network, with fewer error codes, and is easy to reuse and adjust;

9. The standard open optical interface can achieve horizontal compatibility on the basic optical cable segment, reducing the cost of network connection.

SDH access methods have been greatly developed in the WAN field and the dedicated network field. Operators have already constructed SDH-based backbone optical transmission networks on a large scale. Using a large SDH loop to carry IP services, ATM services, or leasing a circuit directly to enterprises and institutions.