Views: 127 Author: Site Editor Publish Time: 2020-09-02 Origin: Site
There are two main ways to connect ONU with optical fibers. One is a point-to-point topology, which uses one fiber from the central office to each user. The other is a passive optical network that uses a point-to-multipoint topology. For an unprotected FTTx system with N end users at a distance of M km, if a point-to-point solution is adopted, 2N optical transceivers and NM km fiber are required. However, if a point-to-multipoint solution is adopted, N + 1 optical transceivers, one or more (depending on the size of N) optical splitters and approximately M km of optical fiber are required. At this point, the use of point-to-multipoint solutions greatly reduces the number of optical transceivers and fiber usage, and reduces the rack space required by the central office, which has obvious cost advantages.
1. Point-to-point FTTx solution
Point-to-point direct fiber connection has the advantages of easy management, no complicated uplink synchronization technology and automatic terminal identification. In addition, the entire upstream bandwidth can be used by a terminal, which is very conducive to the expansion of bandwidth. But these advantages do not offset its disadvantages in terms of device and fiber costs.
Ethernet + Media Converter is a transitional point-to-point FTTH scheme. This scheme uses Media Converter (MC) to convert electrical signals into optical signals for long-distance transmission. MC is a simple photoelectric / electro-optical converter, it does not process the signal package, so the cost is low. The advantage of this solution is that you only need to add MC to the existing electrical Ethernet equipment. There is no need to replace the network card that supports fiber transmission, only need to add MC, so that users can reduce the cost of upgrades, which is the network solution during the transition of point-to-point FTTH scheme. Because its technical architecture is quite simple, cheap and directly integrated with the Ethernet, it once became the mainstream of Japanese FTTH.
2. Point-to-multipoint FTTx solution
In the optical access network, if the optical distribution network (ODN) is composed entirely of passive devices and does not include any active nodes, then this optical access network is PON. The architecture of PON is mainly to transmit the optical signal from the optical fiber line terminal equipment OLT through a single fiber through the passive device splitter (optical splitter) to broadcast the optical signal to each user’s terminal equipment ONU / T. This greatly reduces the cost of network equipment room and equipment maintenance, and saves a lot of optical fiber resources and other construction costs, so PON has become the latest hot technology of FTTH.
3. PON access network technology
As an access network technology, PON is positioned at the "last mile" that is often said, a solution between service providers, telecommunications bureaus, and commercial or home users.
With more and more broadband applications, especially the rise of video and end-to-end applications, people's demand for bandwidth is becoming stronger. In North America, the bandwidth requirements of each user will reach 20-50Mb / s within 5 years, and 70Mb / s within 10 years. Under such high bandwidth requirements, traditional technologies will not be competent, but PON technology can show its talents.
In 1987, the researchers of British Telecom first proposed the concept of PON. Introduce the following separately.
APON was proposed in 1995, at that time, ATM was expected to occupy the main position in the local area network (LAN), metropolitan area network (MAN) and backbone network. Major telecom equipment manufacturers have also developed APON products. Since APON can only provide ATM services to users, FSAN updated the web page at the end of 2001 to rename APON as BPON, or "Broadband PON". The APON standard has evolved into a BPON standard that can provide other broadband services (such as Ethernet access, video broadcasting, and high-speed dedicated lines, etc.).
In the field of local area networks, the rapid development of Ethernet technology has developed into a widely accepted standard. There are more than 4 million Ethernet ports worldwide, and 95% of LANs use Ethernet technology. Ethernet technology has developed rapidly, with transmission rates ranging from 10 Mbit / s, 100 Mbit / s to 1000 Mbit / s, 10 Gbit / s or even 40 Gbit / s, and its transmission rate has increased by orders of magnitude; the application environment has also evolved from LAN to MAN and core networks .
EPON was proposed by the EFM (Ethernet in the First Mile) research group established by the IEEE 802.3 Working Group in November 2000. EPON is a combination of several best technologies and network structures. EPON uses Ethernet as a carrier and adopts a point-to-multipoint structure and a passive optical fiber transmission method. EPON also provides certain operation maintenance and management (OAM) functions.
EPON technology has good compatibility with existing equipment. And EPON can also easily achieve a smooth upgrade of bandwidth to 10 Gbit / s. The newly developed quality of service (QoS) technology makes it possible for Ethernet to support voice, data and image services. These technologies include full-duplex support, priority (p802.1p) and virtual local area network (VLAN). In addition, its transmission efficiency is lower than that of GPON.
In 2001, the FSAN group launched another standard work aimed at regulating PON networks with operating rates higher than 1 Gbit / s. This work is called Gigabit PON (GPON). In addition to supporting higher rates, GPON also supports multiple services with high efficiency, providing rich OAM & P functions and good scalability. Representatives of operators in most advanced countries have proposed a set of "Gigabit Service Requirements" (GSR) documents as one of the standards submitted to ITU-T. This in turn becomes the basis for proposing and developing GPON solutions. This shows that GPON is a solution that is designed according to the exact needs of consumers and driven by operators, and is worthy of the trust of product users.