Features of 4 access solutions for fiber-to-the-home
At present, the main target market of FTTH is undoubtedly the residents of large, medium and small urban residential quarters. Urban residential quarters are generally garden-style residential quarters, and their outstanding features are:
1. High density of households, a single garden residential area generally has 500-3000 households, and some even have tens of thousands of households;
2. Residential quarters (including commercial buildings) are generally equipped with a communication computer room for the installation of communication access equipment and line handover in the entire community. This configuration is required for telecom operators to compete with each other and comprehensive access to various telecom services. From the computer room to the user The distance is generally less than 1km;
3. Major telecom operators and cable TV operators have generally laid small-core (usually 4 to 12 cores) optical cables to the computer rooms of residential quarters or commercial buildings;
4. Residential communication and CATV access cable resources in the community belong to each operator. Another feature of my country's FTTH target market is that there are industry barriers in the provision of telecom services: telecom operators are not allowed to operate CATV services, and this status quo cannot be changed for a considerable period of time in the future.
There are currently 4 FTTH access technology solutions, including 3 passive optical network (PON) access technology solutions and 1 active optical network (P2P) access technology solution
The first type: ideal passive optical network (PON) network structure and distribution, its main features are: optical line terminal (Optical Line Terminal - OLT) is placed in the central computer room of telecom operators, passive optical splitter is placed (Splitter) As close as possible to the optical network unit (Optical Network Unit - ONU) of the user end.
The distance between the OLT and the ONU is equal to the distance between the telecom operator's central computer room and the user, which is similar to the current access distance of a fixed phone, generally several kilometers, and the distance between the Splitter and the ONU is generally tens to hundreds of meters. This structure and layout of PON highlights the advantages of PON:
1. The entire network from the central computer room to the user is a passive network;
2. Save a lot of optical cable resources from the central computer room to the user;
3. Because it is point-to-multipoint, the number and scale of equipment in the central computer room are simplified, and the number of wiring in the central computer room is reduced.
The second: the ideal layout of passive optical network (PON) in residential areas, OLT is placed in the central computer room of telecom operators, and according to the principle of splitter as close to the user as possible, the splitter is placed in the floor wiring box. Obviously, this ideal layout can highlight the inherent advantages of PON, but it will inevitably bring the following problems:
1. From the central computer room to the community, a high-core fiber cable is required. For example, a 3,000-household community requires nearly 200-core fiber-optic cables according to the branch ratio of 1:16, and currently there are generally only 4-12 cores. It is very difficult to increase the laying of fiber-optic cables;
2. Users cannot freely choose operators, but can only choose the services provided by a single telecom operator. It is inevitable that a single operator monopolizes the business, which is not conducive to the competition of multiple operators, and the interests of users cannot be effectively guaranteed;
3. The placement of the passive optical distributor in the floor wiring box will make the wiring nodes very scattered, resulting in very difficult or even impossible to assign, maintain and manage;
4. It is impossible to improve the utilization rate of network equipment and its access ports, because it is difficult to achieve 100% user access rate within the coverage of a single PON.
The third type: the actual layout of the passive optical network (PON) in the residential area, the OLT and the Splitter are placed in the computer room of the residential area. The advantages of this realistic layout are:
1. Only low-core optical cables are needed from the central computer room to the residential area, and the existing optical cable resources can meet the needs;
2. The access lines of the entire residential community are wired in the community computer room, allowing users to freely choose different telecom operators. For telecom operators, the network is very easy to assign, maintain and manage;
3. Since the access equipment and the patch panel are located in the computer room of the community, the utilization rate of the equipment ports will undoubtedly be significantly improved, and the access equipment can be gradually expanded according to the increase in the number of access users.
But this realistic layout also has its obvious shortcomings: first, discarding the PON network structure is the biggest advantage of passive networks, and the central computer room to the user network is still an active network; second, it does not save optical cable resources because of PON; , PON equipment has high cost and complex network structure.
The fourth: the point-to-point (P2P) access technology of the cell active switched optical network (AON).
Clearly, the advantages of PON are lost in high-density residential areas. In the current situation that PON technology is not very mature and equipment prices remain high, we believe that it is more scientific and feasible to choose AON technology for FTTH access, because: the community generally has a computer room;
AON's P2P technology is mature and low-cost, it can easily provide 100M or 1G bandwidth, and can seamlessly link with existing computer networks;
There is no need to increase the laying of optical cables from the central computer room to the community;
Simple network structure, low construction and operation and maintenance costs;
The wiring is concentrated in the computer room of the community, which is easy to assign, maintain and manage;
Allow users to freely choose operators, which is conducive to the competition of multiple operators, and the interests of users can be effectively guaranteed through competition;
The device port utilization rate is very high, and the capacity can be gradually expanded according to the increase in the number of access users.
The typical AON-based FTTH network structure uses the existing low-core fiber optic cables from the central computer room of the telecom operator to the residential computer room. The switching system is placed in the residential computer room. Into the equipment and the distribution frame are placed in the community computer room uniformly, and the entire network adopts the Ethernet protocol with mature technology and low cost. AON's point-to-point FTTH network is currently the commonly used FTTH access technology in Japan and the United States. Among the current global 5 million FTTH users, more than 95% use active switching P2P technology. Its outstanding advantages are:
High bandwidth: easy to achieve stable two-way 100M broadband access;
It can support Internet broadband access, CATV access and telephone access, and realize the integration of three networks in the access network;
Support foreseeable new services in the future: videophone, VOD, digital cinema, telecommuting, online exhibition, TV education, telemedicine, data storage and backup, etc.;
Simple network structure, mature technology and low access cost;
Only the computer room in the community is an active node, and the wiring of the computer room is centralized, which reduces the maintenance cost and improves the utilization rate of equipment ports;
Allow users to freely choose operators, which is conducive to the mutual competition of telecom operators;
It can effectively save the optical cable resources from the central computer room to the community, and there is no need to increase the laying of the optical cable from the central computer room to the community.
It is more scientific and feasible to choose AON technology for FTTH access, because there are uncertainties in the development of PON standards and technologies:
The standard has just appeared, with multiple versions (EPON & GPON), and the competition of the standard is uncertain for future promotion.
Relevant devices require 3-5 years of standardization and maturation process, and it will be difficult to compete with current Ethernet P2P devices in terms of cost and popularity in the next 3-5 years.
The cost of PON optoelectronic devices is high: high-power, high-speed burst transmission and reception; the current optoelectronic devices are far from meeting the requirements of producing low-cost PON systems.