EPON-based access network technology for triple play integration

With the State Council's approval of the three-network integration policy, the trend of cable television networks evolving into the next-generation broadcasting network (NGB) has become unstoppable. NGB's backbone network and content platform already have relatively mature solutions. The construction of access networks has become the focus and difficulty of current NGB construction due to the complexity of the solution and its importance in the overall investment ratio.

2 Access Network Technology Solution

EPON technology has become the mainstream bearer technology of FTTx due to its high bandwidth, easy maintenance and long-distance coverage. At present, the industry chain is well developed and it is the preferred technology for telecom operators to build access networks. However, due to the high cost of using fiber directly to the home at the resident network level, traditional telecom operators basically adopt FTTB+LAN or FTTB+DSL solutions, which achieve the best network performance while saving the investment in the resident network as much as possible.

Broadcasting and television operators have long focused on the construction of HFC networks and have a huge HFC access network. Using HFC as a home access medium can achieve maximum practicality and economy. The coaxial cable network in the broadcasting and television HFC network is an ideal data transmission medium, especially in the last 100m, the bandwidth support capacity is much higher than the five-category line or telephone line resources. Therefore, how to integrate the two media of optical fiber and HFC in the two-way transformation of the broadcasting and television network and deeply tap the value of the existing network has attracted the attention of broadcasting and television operators. At present, there are three relatively economical and feasible two-way transformation technical solutions: CMTS, EPON+LAN and EPON+EoC.

(1) CMTS is suitable for sparse mode network coverage areas

CMTS uses the existing cable TV network to perform two-way transmission at the low-frequency end of HFC by QPSK/QAM modulation of the signal. The advantages of CMTS are mature technology, strong network management capabilities, and large-scale two-way coverage. The disadvantage is that the noise convergence effect of CMTS affects the bandwidth and performance of the system, the quality requirements of coaxial cables and connectors are high, and the subsequent maintenance workload is large; for most cable TV operators, upstream noise is a common problem, especially in low-frequency bands. The packet forwarding capability of CMTS equipment is weak and cannot meet the growing demand for high-bandwidth services. The services it can carry are limited and it cannot provide full-service carrying. The subsequent system expansion cost is huge. CMTS's Cable access belongs to the shared line mode. If it is only used for broadband access and Internet access, it is more suitable for radio and television to carry out data services when the number of users is not too large. For the current domestic users who live in concentrated areas, users need to occupy the network for a long time and have a large flow of data throughput. The unit bandwidth has dropped significantly, which is not conducive to the development of high-bandwidth services. It is not economical to use CMTS to achieve broadband access for a large range of users.

(2) EPON+LAN is suitable for new residential areas with high user density

The EPON+LAN solution is to access the building through the EPON network, provide Ethernet interface through ONU, and realize user access through Ethernet Category 5 cable. This solution is used to realize user voice and Internet access, and cable TV signals are still realized through HFC lines. Its advantages are mature technology, many equipment vendors, and interface and standard specifications. This solution is suitable for the first integrated wiring of newly built communities with high-density users and large bandwidth business needs. For old users who have already opened cable TV, they need to re-wire. The construction of community corridors and home wiring is difficult, and users are generally unwilling to accept it.

(3) EPON+EoC is the preferred technology for existing CATV users

EPON+EoC technology is to construct a digital bandwidth user access network suitable for radio and television network system based on the existing HFC network. It uses advanced modulation and demodulation technology to synthesize Ethernet signals in coaxial cables and transmit them together with the original CATV signals without affecting the normal operation of the existing CATV, and is used to carry IP-based data, voice, video and other services. It transforms the original unidirectional cable TV network into a bidirectional broadband network capable of carrying multiple services with less transformation cost and engineering workload. The use of EoC technology has good adaptability and flexible networking solutions, making full use of the original coaxial access network resources of radio and television, and saving the line investment of the home part.

Combining EPON technology and EoC technology, unifying network management, and forming an overall solution can provide the best access network technology for the development of NGB, the integration of radio, television and three networks. EPON+EoC can provide integrated bearer of three types of playback, namely data, video and voice, and provide the functions of multiple networks in the past through one access network. During the development process, this solution fully considered China's national conditions and the actual situation of the current radio and television network. At the resident network level, the existing Cable network of the radio and television network is used as the transmission medium, saving a lot of integrated wiring costs and operation and maintenance investment, and having both high performance and low cost. EPON+EoC technology meets the needs of the two-way transformation of radio and television digital television and the integration of the national three networks. It will promote the in-depth development of the NGB industry in China and is the preferred technology for the NGB network access layer for radio and television operators.

3 EPON and EoC Networking Technologies

(1) EPON technology

As the best medium for transmitting high-speed, large-capacity, and multi-service, optical fiber has long been widely used in backbone networks and metropolitan area networks. It has also been popularized and applied at the access network level. Optical fiber has the advantages of long life, high reliability, and strong anti-interference. Optical transmission has strong bandwidth expansion capabilities and can easily realize the integration of various business platforms.

EPON technology is a technology that combines Ethernet with passive optical networks. According to the IEEE802.3ah international standard, it can support a symmetrical rate of 1.25Gbit/s. As an important solution for fiber-optic access networks, EPON technology has unparalleled characteristics of ADSL, LAN, etc., and it also meets the multi-service access requirements of "Everything over IP" more efficiently than APON, BPON, GPON and other technologies. EPON access network has the advantages of low investment cost, simple operation and maintenance, and provides a very economical and effective broadband access solution for operators to solve the "last mile" problem. At present, EPON technology has been widely used at home and abroad, and has been supported and recognized by domestic and foreign operators and manufacturers.

Through EPON system equipment, FTTH/FTTB optical fiber network can provide a maximum bandwidth of 1Gbit/s transmission rate to households and corporate users. Operators can easily realize the transmission of high-bandwidth IP data services such as high-speed Internet access and IPTV multicast/on-demand with economical cost and minimal investment in optical cable lines.

The EPON system is mainly composed of OLT (Optical Line Terminal), ONU (Optical Network Unit) and splitter. OLT provides uplink interfaces to IP metropolitan area network, IPTV bearer network and NGN soft switching network. In response to the different business needs of end users, operators can flexibly select terminal ONU equipment to meet various application scenarios such as FTTH/FTTB/FTTC/FTTC+EoC. A typical EPON networking solution is shown in Figure 1.

Figure 1 EPON networking solution

(2) EoC technology

EoC refers to the technology of transmitting Ethernet data on coaxial cable. The EoC system consists of headend, terminal, coaxial distribution network and other parts. The headend is usually placed at the optical node position, which plays the role of distributing upper-layer Ethernet data and converging terminal equipment; the terminal is placed at the user's home to access the user's computer or interactive set-top box; the coaxial distribution network is the network from the cable TV network optical node position to the user's home. In addition to coaxial cables, it also includes active amplifiers, EoC jumpers, branch/distributors and other equipment.

The commonly used EoC head-end equipment is an access aggregation device based on HomePlugAV technology with active modulation. Its main function is to modulate the data baseband signal to the 7-30MHz frequency band in OFDM mode, and then mix it with the cable TV network signal and transmit it on the coaxial cable of the cable TV HFC network. The commonly used EoC user-end equipment is a user-end modem device based on HomePlug AV technology. Its main function is to connect various user terminal devices such as computers, set-top boxes, IP phones, etc. to the EoC system to achieve two-way broadband access using coaxial cable as the medium.

For the EPON and EoC technologies of broadcasting and television operators, OLT is placed at the front end of the network system, ONU is placed on the floor, connected to the EoC (Ethernet over Cable) local end equipment, and enters the home through HFC. Users transmit and receive data signals through the cable TV coaxial cable line without affecting the transmission and reception of cable TV signals. The maximum bandwidth of the EoC host can reach more than 80M, and can carry up to 64 slaves, and multiple slaves share the host bandwidth. When the host is connected to a certain number of slaves, the bandwidth of the slaves can be automatically adjusted, and the bandwidth of the slaves can be set with QoS. The host can perform SNMP network management. The bridge can extend the transmission distance of cable TV signals, cross various cable TV signal amplifiers, realize two-way data transmission, and truly realize the one-line transmission of data signals and TV signals.

Currently, the mainstream EoC products use HomePlug AV/BPL technology. The EoC head-end device is a cable bridge switch. The cable bridge switch is a device that jumpers the cable TV unidirectional amplifier in the coaxial data network. It divides the mixed signal by frequency so that the data signal does not pass through the amplifier. After amplification, the cable TV signal is mixed with the data signal again through the jumper.

The cable bridge switch adopts modular design, and the main modules are CATV module, ONU module, EoC headend module, and master switch module. These modules are configured as optional modules in the corresponding chassis. Among them, the master switch module is only used in multi-port cable bridge switches. The advantage of modular design is that it can more flexibly meet the needs of radio and television operators at different times and flexible expansion in the long term, minimize investment costs, and obtain high returns.

Operators in different regions can choose cable bridge switches with different numbers of interfaces according to economic development, user density, coverage, opening rate and user bandwidth requirements. The installation location can be indoors or outdoors. User terminal equipment is mainly divided into single interface, dual interface and quad network interface according to the number of network interfaces. The number of EoC head-end modules can be configured as needed. Each module provides one TV signal input and one Cable mixer port, which can simultaneously transmit and receive mixed signals of data signals and Cable TV signals. CATV access module supports single CATV access port and provides one Cable TV interface for transmitting Cable TV signals.

The main end can support multiple downlink coaxial channels through a coupler. With high-performance optical devices, the coverage distance reaches 20km when the splitting ratio is 1:32, and the coverage distance reaches 10km when the splitting ratio is 1:64. When the splitting ratio is 1:64, the average bandwidth can reach 15Mbit/s, meeting the bandwidth requirements of users.

(3) EPON+EoC Network Application

The traditional cable TV network is technically transformed by using EPON and EoC technologies. EPON equipment can be used to complete the bidirectional transformation of the optical cable trunk and the bidirectional transformation of the user coaxial cable access network. Active EoC is used for networking. The active EoC head end is connected to the ONU to cover all users under the optical node. For users with bidirectional needs, the EoC user end is used for access. In this way, the unidirectional broadcast transmission network is built into a bidirectional transmission network.

The typical application networking scheme of EPON+EoC is shown in Figure 2. The cable bridge switch is placed in the corridor or outdoors to cover a building or a unit. The existing network has laid optical nodes, and the cable bridge switch does not need to be configured with a CATV module. It is connected to the cable bridge switch through a radio frequency cable. The ONU module is configured in the cable bridge switch to realize the return of data or interactive TV signals.

Figure 2 EPON+EoC application networking solution

If the existing network has moved the optical receiver downward, the cable bridge switch needs to integrate the optical receiving function. At this time, the cable bridge switch needs to be equipped with a CATV module to connect the TV signal to the cable bridge switch through optical fiber. The ONU module is configured in the cable bridge switch to realize the return of data or interactive TV signals. In another case, if the existing network has laid optical nodes, the ONU is placed outside the building and connected to several single-port cable bridge switches. The data signal is connected to the cable bridge switch through cables to realize the return of data or interactive TV signals, and the TV signal is connected to the cable bridge switch through RF cables.

4 Conclusion

The use of EPON and EoC technologies by radio and television operators helps to comprehensively utilize network resources, quickly complete the construction of the NGB access layer, realize digital two-way transformation, reduce a large amount of duplicate construction, and save construction and operation and maintenance costs. With the EPON+EoC solution, users do not need to make any changes to the indoor wiring. They only need to add CNU terminal equipment to achieve two-way, interactive, multi-functional, and multi-service, and enjoy the rich content brought by the integration of three networks. The EPON+EoC solution can comprehensively improve the technical level and business carrying capacity of cable TV networks, give full play to the advantages of cable TV networks with wide bandwidth, low cost, and easy popularization, and make cable digital TV a multimedia information platform that enters thousands of households.

The cable TV network after two-way transformation is the most important network for carrying and providing three-network integration services, and will become the most important information and communication infrastructure in modern social activities. After two-way transformation, the radio and television network adopts the access method of optical fiber plus coaxial cable to provide scalable broadband access for each household user, which can meet the bandwidth requirements of standard-definition and high-definition TV programs. The picture quality enjoyed by users will be sharper and more realistic, and the image will be clearer. Through this "highway", users can quickly and conveniently process daily information and enjoy the convenient services of the information society.