Analysis of the characteristics of construction and deployment of FTTH network
With the rapid development of IPTV and multimedia services, users' requirements for access bandwidth are increasing. The current copper access technology is difficult to meet the requirements of high bandwidth, two-way transmission, and security. Before 2010, FTTB was the mainstream FTTx networking model in China, and FTTH had only a small amount of experimental construction. With the strong support of national policies and the rapid development of the industrial chain, and the continuous reduction of equipment and terminal costs, FTTH has the dual advantages of cost and technology. In the next few years, FTTH will be the first choice for broadband access technology of China's fiber-optic broadband network.
GPON FTTH becomes the mainstream choice
At present, the main implementation technology of FTTx is PON. The EPON and GPON in PON technology are compared at multiple angles.
From the perspective of the offered rate, the EPON uplink and downlink rates are both 1.25 Gbit/s; GPON supports multiple rate classes and supports uplink and downlink asymmetric rates (downlink 2.5 Gbit/s, uplink 1.25 Gbit/s or downlink 1.25 Gbit/s, Upstream 625 Mbit/s).
From the perspective of QoS, EPON implements dynamic bandwidth allocation (DBA) through the state machine and timer of the MPCP multipoint control protocol. The MPCP protocol includes ONU transmission time slot allocation, ONU automatic discovery join, report congestion to the upper layer, and DBA. Content, but the protocol does not classify the service priority level, and various services can only compete for bandwidth randomly; while GPON has a more complete DBA function, the bandwidth allocation mode is divided into multiple types, such as fixed bandwidth, guaranteed bandwidth, and non-guaranteed. Bandwidth, best-effort bandwidth allocation, etc.
From the perspective of OAM function, EPON only has simple ONU remote fault indication, loopback and link detection. GPON defines physical layer and high-level OAM management functions respectively, which implements data encryption, state detection error monitoring, and QoS parameters. Request a variety of OAM functions such as configuration information and performance statistics.
In summary, GPON can provide a more high-speed and flexible bandwidth mechanism, richer QoS management functions and OAM management functions, and in the current FTTH deployment phase, GPON technology, chips and products have matured, and the cost is only slightly higher. EPON, so GPON will become the mainstream technology for deployment in FTTH networks.
FTTH should use symmetrical splitting
One of the core components of the FTTH network is the optical splitter, which acts as a passive optical device that splits an optical signal into multiple optical signals and performs the reverse process.
According to the power ratio of the splitting, the optical splitter can be divided into a symmetrical type (such as 1:16 splitting) and an asymmetric type (such as a splitting ratio of 10:90). To reduce power consumption, make full use of port resources, and simplify optical path loss accounting, FTTH networks typically use symmetric splitting.
According to the split-light cascade structure, it can be divided into one-level and multi-stage splitting: the first-level splitting is characterized by single-point maintenance, high port utilization, small insertion loss, and convenient maintenance and management. For general applications such as urban areas, in the FTTH networking, in principle, the first-level spectroscopic method should be adopted to facilitate maintenance and management in the future; for special applications, such as some residential projects or rural users, the second place can be used. The method of splitting the light, the first-level splitting 1:8, the second-level splitting 1:8, the first-level splitting is in the optical junction box, and the second-level splitting is generally concentrated in the user.
In the fiber-to-the-building (FTTB) and fiber-to-the-road (FTTC) access modes, the fiber does not need to enter the user's home or even enter the room, which can benefit the old copper resources laid in the early stage, and generally do not need Construction of existing building structures. For the FTTH mode, the fiber needs to enter the user's home, so that it is necessary to break through the wall and the floor hole.
ODN operation and maintenance problems need to be solved
The Optical Distribution Network (ODN) is an important part of the FTTH network, and ODN investment accounts for more than 50% of the total FTTH investment. With the expansion of the scale of FTTH networks, how to effectively manage the massive optical cables and ports of ODN networks, and timely and accurate detection of possible faults has become a research hotspot.
Based on existing methods, ODM network operation and maintenance management is very difficult.
First, the installation process mainly relies on paper work orders and manual operations, the construction error rate is high, and the feedback of construction results is not timely.
Second, the status of the fiber port cannot be monitored and the port utilization is low. The illegal insertion and removal, illegal jumper and other actions cannot be controlled.
Third, the failure of the fiber (the fiber is damaged, such as road construction and other reasons) can not be quickly and accurately positioned.
Fourth, the way of operation and maintenance personnel to deal with faults is mainly the traditional telephone reporting obstacles, and it is time-consuming and laborious to arrange the troubleshooting of the maintenance personnel. Critical device failures (such as OLT upgrades) cannot be quickly recovered.
The introduction of technologies such as optical time domain reflectometry (OTDR) and intelligent ODN will effectively solve the above problems. OTDR can detect loss and disconnection events of fiber links in real time. Intelligent ODN can realize electronic construction and maintenance of ODN. And the perceived portability of the fiber optic port.
Backward compatible with 10G PON and NG PON2
With the advancement of FTTH network construction, PON technology is also evolving to the next generation. On the basis of EPON, IEEE completed the development of 10G EPON standard in September 2009, and ITU/FSAN completed the standardization of 10G GPON in June 2010 on the basis of GPON. Although this 10G PON technology is not yet mature, optical modules and costs are still high, but with the demand for high-bandwidth services, it is expected that under the dual drive of business and technology, 10G PON technology will gradually become commercial in the next few years. . At the same time, higher transmission rates can be provided, and NG PON2 standards based on technologies such as TWDM-PON and WDM-PON are also being developed.
In order to ensure the smooth evolution of the network and to protect the investment of the existing network as much as possible, in the construction of the FTTH network, it is necessary to consider the coexistence of the existing PON network and the 10G PON network. Since the investment in the ODN network accounts for a large proportion of the overall investment of the FTTH network, in the coexistence strategy, the reuse of resources such as optical splitters and optical fibers in the ODN network should be considered; in addition, the OLT rack and the wavelength division multiplexing device should also be considered. Shared use of devices such as (WDM1r).
Author: China Unicom Research Institute Zhongxiu Fang Guo Lin Shao Yan Zhang Pei Source: Communications World Weekly