Broadband Access Network Development

Broadband Access Network is a frequently used access method. So I have studied the development and complementarity of broadband access networks. I would like to share with you here, hoping to help you. In recent years, with the rapid development of broadband Internet technology and broadband access network services, broadband access network users have gradually evolved from a single application of high-speed Internet access to comprehensive applications such as VoIP, IPTV, and visual communication, the bandwidth requirements of users are undergoing profound changes. VDSL2 technology developed based on ADSL2 + and VDSL of the first generation can support higher transmission rates and be compatible with traditional ADSL/ADSL2 + technologies, attracting widespread attention in the industry.

Technical Analysis

Band Division is the most critical technical problem in the VDSL2 standard. Its importance lies in that the distribution of band determines the transmission capability of VDSL2. In addition, the distribution of band will affect the system compatibility. To meet the needs of broadband access network business development in different regions and different application scenarios, the maximum bandwidth of VDSL2 can reach 30 MHz. For bandwidth below 12 MHz, the Plan997 and Plan998 bandwidths of VDSL are adopted. Among them, Plan997 is suitable for the application mode of Bidirectional symmetric rate of medium and short distance, while Plan998 is suitable for the application mode of downlink high speed of medium and short distance.

Plan997 and Plan998 have a variety of extended spectrum division modes for the 12 mhz-30mhz frequencies. In addition, VDSL2 also adds the US0 extended band option. In VDSL2, The US0 band can be changed from traditional 25 kHz ~ KHz extended to 25 kHz ~ 276 kHz to improve the uplink transmission performance of VDSL2 at a moderate distance.

Profile configuration of VDSL2

Eight profiles (8a, 8b, 8c, 8d, 12a, 12b, 17aand30a) are defined based on different application scenarios in the VDSL2 standard ), to reduce the complexity of product development and develop products that meet specific business needs. The definitions of various profiles are as follows: the maximum cutoff frequency of 8a, 8b, 8c, and 8d is 8 MHz; the maximum downlink transmit power of 8a is 17.5dBm; 8b is 4505dbm; and 8c is 11.5dBm; 8d is 14.5dBm. The cutoff frequency of 12a and 12b is 12 MHz, while 12a requires US0 and 12b does not. The end frequency of 17a is 17.6 MHz, and the end frequency of 30a is 30 MHz. The transmit power of these profiles is 14.5dBm.

VDSL2 Spectrum Management

Because VDSL2 adopts the OFDM method, it is necessary to use spectrum management technology to reduce the impact of remote crosstalk and optimize VDSL2 transmission performance. Spectrum Management is mainly divided into static spectrum management and dynamic spectrum management. Static Spectrum Management selects the appropriate spectrum and corresponding parameter configurations during device initialization and training, and determines them in the subsequent communication process. Generally, PSDShaping can be used) but cannot adapt to the changes in line conditions, and the efficiency of manual setup is low. Dynamic Spectrum Management focuses on using dynamic spectrum balancing to improve the speed, distance, and stability of the line. The principle is to meet the performance and stability requirements (speed, margin, and error rate) in this case, signals are sent at the minimum power, and a series of methods are used to centrally manage, optimize various parameter configurations, and send PSD, even the Vector or bonding method is used to coordinate the sending and receiving of the same cable bundle (binder) to maximize the performance of the entire cable bundle.

At present, VDSL2 uses static spectrum management technologies such as spectrum slotting, uplink power reduction (UPBO), and MIB-controlled PSD to manage power spectrum, so as to eliminate or reduce the impact of these interference on Transmission Performance. VDSL2 dynamic spectrum management technology is still under discussion and research.

Compatible with ADSL/ADSL2 + Technology

Consider the future transition of VDSL2 and ADSL/ADSL2 + hybrid applications, or VDSL2 gradually replaces ADSL/ADSL2 +, the original DSLAM that supports ADSL/ADSL2 + may be changed to DSLAM that supports VDSL2 due to service needs, but only some users upgrade to VDSL2, some users continue to use the original ADSL/ADSL2 +, which requires that the local device of VDSL2 must support the original ADSL/ADSL2 + client device.

Currently, VDSL2 technology is fully compatible with the ADSL/ADSL2 + technology. It can run in VDSL2 mode in short distance and supports high-bandwidth transmission. After a certain transmission distance is exceeded, it can run in the compatible ADSL/ADSL2 + mode to realize the transmission of COSCO distance, so that the operator can update the device as needed, which not only protects the original investment cost, it also reduces the risks of technical selection.

Application Analysis

New developments in VDSL2 Devices
With the joint efforts and promotion of chips, devices and operators, VDSL2 Technology Based on G.993.2 has made great progress over the past two years, currently, most equipment vendors have launched commercially available VDSL2DSLAM devices and VDSL2 client devices.

From the perspective of understanding, VDSL2 technology has mature products from chips to devices for commercial use. Because the DSLAM device can implement mixed insertion between VDSL2 and ADSL2 + in the same frame, DSLAM Based on VDSL2 provides complete functions and forwarding performance in VLAN, multicast, QoS, and security. It supports most of the features of VDSL2 technology, in particular, multi-profile configuration, multi-spectrum division Solution Support, and spectrum management features provide powerful technical support for operators to carry out flexible and diverse broadband services. In addition, because VDSL2 features high bandwidth and is especially suitable for multi-service operations, VDSL2 client devices are basically in the form of home gateways, and not only have four Ethernet ports and WLANAP functions, it also supports layer-3 routing.

Factors to consider when using VDSL2 Technology

1. VDSL2 technical troubleshooting
For fixed network operators, how to locate VDSL2 technology is a key issue while vigorously developing broadband services. Because VDSL2 is not widely used in China, it has no commercial advantage over ADSL/ADSL2 +.

I personally think that VDSL2 and ADSL2 + are complementary in the near future. VDSL2 is mainly oriented to high-bandwidth applications. In the future, with the development of broadband access network services, the scale of VDSL2 technology, and the decline in VDSL2 prices, VDSL2 local equipment will completely replace ADSL2 + technology and become the mainstream broadband access technology based on telephone lines. For user-end devices, VDSL2 and ADSL2 + will coexist and complement each other for a long time. carriers can choose ADSL2 + or VDSL2 technologies based on their broadband access network business needs.

2. Selection of VDSL2 spectrum and profile solutions
At present, the VDSL2 international standard spectrum division solutions mainly include BandPlan998 and BandPlan997 and their extensions. Bandplan998 is mainly intended for Asymmetric High-Speed Downlink broadband access networks with medium and short distance conditions, while at the same time taking into account a certain amount of uplink bandwidth capabilities. Bandplan997 is mainly intended for upstream and downstream symmetric broadband access networks with medium and short distance conditions. Operators can flexibly select the two spectrum division schemes based on their own broadband access network business needs. However, to avoid spectrum incompatibility problems, VDSL2 in the same region should select the same spectrum division scheme.

In addition, when deploying VDSL2 technology, the carrier must carefully consider how to select the profile configuration file of VDSL2 technology. According to the current situation of broadband access network in China, VDSL2 local devices should support at least 8b, 12a, and 17a pro-files, so that carriers can flexibly select different profile configurations based on different application scenarios. Among them, 8b is mainly used for the CO-end deployment mode, and there are ADSL/ADSL2 + applications in the same basic unit cable; 12a is mainly used for medium distance applications; the apaas is mainly used for short-distance high-bandwidth applications in the remote module mode.

3. Integration of VDSL2 and PON
From the technical characteristics and development of VDSL2 and PON, we can see that the application of the PON system and VDSL2 can complement each other to extend the coverage of optical fiber cables, at the same time, flexible and economical use of optical fiber and port resources based on business needs can protect Telecom's existing advantages in copper cable resources, shorten engineering construction periods and reduce costs, and quickly meet business needs. From the perspective of application scenarios, the copper cable is gradually shortened as the fixed network operator moves forward to copper withdrawal, and local equipment is closer to users, however, when the number of nodes increases and the number of nodes is scattered, and the user capacity of most nodes decreases, there will also be many micro POP points. At this time, DSLAM devices with VDSL2 access capabilities can better meet the bandwidth requirements of current and future businesses, and use PON for aggregation and reasonable planning of interface capacity, this greatly saves optical fiber and pipeline resources.

In response to the above situation, we recommend that you add the application and deployment of a small integrated VDSL2DSLAM device connecting the PON interface during the DSL network transformation of the POP point move down, and implement FTTN access with the OLT, it also supports multiple networking modes to meet the networking requirements of users in different environments and businesses and achieve small-capacity user access. The OLT device can also manage the ONUDSLAM device using a graphical interface.