Common Access Network technical Practical Manual

Currently, there are many access network technologies, which have their own characteristics and are also widely used in various fields. I believe that with the emergence of emerging access network technologies, their market demand will increase significantly.

With the large-scale investment by telecom companies in network infrastructure, it can be said that the backbone of the network is ready to carry various broadband services. However, the connection bandwidth from the backbone network to the client is relatively low, and most users still access the technical backbone network through narrowband circuit switching.

The traditional narrowband dialing method uses MODEM dialing to achieve user access. Currently, the highest speed is 56 kbps, which is far from meeting the transmission needs of broadband multimedia information. Copper wire access network technology is the most widely used technology. There are two methods. One is to deploy cat5e twisted pair wires and form a new Switched Ethernet; the other is to make full use of the original copper wire hotline user line), this Part of valuable resources, using a variety of High-Speed Modulation and coding technology, to achieve broadband access. To sum up, there are several popular copper access networks:

LAN Access Technology

Ethernet/high-speed Ethernet transmission media are twisted pair wires, copper shafts, and optical fibers. Currently, the most widely used and cost-effective twisted pair wires are deployed. Ethernet technology transmits baseband digital signals directly on the transmission media, and the transmission distance on five category lines is 100 meters. Ethernet access network technology is an access network technology with Chinese characteristics. Most houses with Chinese characteristics are concentrated, which meets the application characteristics of Ethernet. The advantages of the Ethernet Access Network technology are that the technology is very mature, standardized, the average port cost is low, the bandwidth is high, and the client device cost is low. The disadvantages are short transmission distance, scattered equipment, high initial investment costs, inconvenient management, and re-wiring.

High-speed digital user line HDSL) Technology

HDSL uses 2B1Q or CAP codes. Two pairs of existing telephone cables can be used to provide full-duplex T1/E1 signal transmission, for a user line with a 0.4-6mm wire diameter, the transmission distance can reach 3-6 km. If the wire diameter is thicker, the transmission distance can be close to 10 km. In addition, there is also an HDSL product that transmits T1/E1 signals on a pair of twisted pair wires, often called SDSL, a single-line digital user loop. HDSL/SDSL technology is widely used in the access of TDM telecom networks and also used in broadband Internet access applications of enterprises. The advantage is bidirectional symmetry with a high speed. The disadvantage is that there is no standard and the cost is high.

Asymmetric Digital user line (ADSL) Technology

ADSL is an asymmetric broadband access network technology, that is, the uplink rate and downlink rate of the user line are different. According to the characteristics of the user's various multimedia services, the uplink rate is low and the downlink rate is relatively high, it is particularly suitable for search-type network services. The typical upstream speed of ADSL is 1.544-8.192 kbps, the downstream speed is 6 km-Mbps, and the transmission distance is 3-. ADSL is a standard transmission service. The ADSL Broadband Access Network Technology can share the same user line with the phone service. In actual application, there is a problem with the line selection rate of ADSL. Generally, the line selection rate is about 10%. In addition, the rate of ADSL decreases with the increase of the line length. Due to various restrictions, the actual service rate of ADSL is reduced to kbps ~ 1 Mbps, up to 64 Kbps. Therefore, the advantage of ADSL is that it can make full use of existing copper resources and share copper with common telephone services. The disadvantage is that there is a problem of line selection rate and low bandwidth rate.

New broadband copper Access Network Technology: VDSL, a high-speed digital user line

To sum up, the popular access network technology has many advantages and disadvantages. From the perspective of practical networking experience, the disadvantages of these technologies always affect the implementation of the broadband access network technology. For example, although the unit cost of Ethernet technology is low, the cost of Ethernet technology is quite high and the initial investment is too large when there are few users, other problems, such as network management and IDC environment, are also very serious restrictions.

According to the characteristics of China, at present, Heli Jinqiao Company in China launched a new access network technology-Ethernet VDSL hereinafter referred to as VDSL), different from the previous ATM-VDSL technology, this technology is completely based on Ethernet. VDSL access network technology uses the QAM modulation method to achieve bidirectional symmetric Transmission of 10 Mbps within a range of 1.5 kilometers, reaching the Ethernet speed. VDSL can also share user lines with common telephone services like ADSL. Due to the proximity, the VDSL technology overcomes problems such as low line selection rate and unstable rate of ADSL technology.

Because the average residential area in China is less than 1km, if VDSL technology is used, the common residential area can centrally manage all the access network technical equipment in one or two centers, it is of great significance for network management and equipment maintenance. In addition, because VDSL covers a wide range of fields, it can cover enough Initial users, with a small initial investment. It also facilitates centralized device management and system expansion. Therefore, the solution using VDSL technology is an access network technology solution suitable for the actual situation in China.

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