Comparison of EPON and GPON technologies and produ

Comparison of EPON and GPON technology and products

at present, there is still a lot of controversy in the industry about the merits of EPON and GPON, but the access has the distinctive characteristics of technological diversification. Therefore, if epon/gpon can achieve the goal of mature technology and low cost, it should be applied in the future

I. preface

the rapid development of broadband networks and the continuous emergence of various high bandwidth services and applications have put the introduction of broadband optical fiber access technology on the agenda. At present, the construction of fiber to the home (FTTH) in North America and Japan has been carried out on a large scale, and the domestic FTTH experiments have been implemented in some places, and the industry has heard a lot of discussion in this regard. At present, there are three main technologies applied to broadband optical fiber access, which are SDH based multi service transmission technology (MSTP), multi service passive optical network technology (PON) and multi service point-to-point optical transceiver (P2P or MC), with the following characteristics

1.mstp has high service quality, but the cost is high. It is suitable for large users who have very high requirements for business quality and security, and is not suitable for ordinary household users

2. The star network topology of the multi service point-to-point optical transceiver is very beneficial to cooperate with the ring backbone network, and the cost advantage is prominent, but it needs to occupy a lot of space. It is generally used for experimental optical fibers in high and low temperature boxes, which is suitable for the universal access of most users. In some applications, the cost is lower than that of PON, which should be adopted according to local conditions in combination with specific conditions

3. The tree network topology of PON is very beneficial to cooperate with the ring backbone network. It is the most effective network solution for optical fiber to enter the user's station (FTTP). Because it saves a lot of backbone optical fiber resources, it is one of the ideal choices for optical fiber access in the long run, suitable for the general access of most users, and has a large potential market in the future

among them, the first two technologies are widely used in China, and PON technology, as an ideal optical fiber access means, is considered to be the main technology to realize FTTH, which has great development potential

II. Characteristics of passive optical network PON technology

passive optical network (PON) technology is a point to multipoint optical fiber access technology, which is composed of OLT (optical line terminal) on the office side, ONU (optical network unit) on the user side and ODN (optical distribution network). Generally, its downlink adopts TDM broadcast mode and uplink adopts TDMA (time division multiple access) mode, and it can flexibly form tree, star, bus and other topologies (the typical structure is tree structure). The so-called "passive" refers to that ODN does not contain any active electronic devices and electronic power supply, and is all composed of passive devices such as optical splitter, so its management and maintenance cost is low

epon standardization work is mainly completed by IEEE 802.3ah, that is, EFM (ethernetforthefirst mile) working group. Its basic principle for formulating EPON standard is to try to make it in 802 as the price of plastic chemical raw materials continues to rise with the development of economy 3. Carry out EPON standardization within the architecture, focusing on the MAC protocol of EPON, and expand the Ethernet MAC protocol to a minimum. The standard is still a draft, and EFM plans to officially release the relevant standards of EPON in 2004. At present, China is actively carrying out the standardization of EPON, and the communication industry standard "access technology requirements - Ethernet based passive optical network (EPON)" is being formulated

gpon is a G-bit passive optical network proposed by ITU. ITU formally adopted and issued three standards in GPON standard series in 2003: g.984.1, g.984.2 and G.984.3. Since GPON standard was introduced by ITU after APON standard, g.984 standard series inevitably followed many ideas of g.983 standard. GPON and EPON are both Gigabit super PON systems. Compared with EPON's principle of simplicity, GPON pays more attention to multi service and QoS guarantee, so it is more favored by operators. However, due to the complexity of GPON standard, late development and immature technology, GPON products have not yet reached the commercialization stage

the current implementation scheme of EPON proposed by IEEE is to try to retain the physical layer PON of APON on the basis of the structure similar to APON and g.983, and use Ethernet technology instead of ATM technology as the data link layer protocol to form a new combination EPON that can provide greater bandwidth, lower cost and stronger business capability. The main goal of GPON technology proposed by ITU is to achieve Gbit rate, support multiple services and optimize all services

III. comparison of GPON and EPON technologies

Table 1 compares the main parameters of two Gigabit ratio passive optical network technologies, EPON and GPON. In order to be more comprehensive, BPON is also included

Table 1 Comparison of main parameters of EPON and GPON technology

note: this bandwidth is the average value calculated according to the IP packet distribution model of different sizes, which is for reference only

according to the different characteristics of GPON and EPON Technology, the following analysis can be made for these two technologies

1.gpon supports a variety of rate levels, which can support uplink and downlink asymmetric rates. Uplink does not necessarily support a rate of more than 1 Gbit. Therefore, compared with EPON, which can only support a single rate of symmetrical 1 Gbit, GPON has greater redundancy in the selection of optical devices, thereby reducing costs

2. EPON only supports ODN levels of class A and B, while GPON can support classes a, B and C. Therefore, GPON can support a shunt ratio of up to 128 and a transmission distance of up to 20km

3. Compared with GPON standard, EPON standard is based on 802.3 architecture, so its protocol layering is simpler and the system implementation is easier. In view of the maturity of the current Ethernet chip, its system cost is lower

4. ITU adopted many concepts of APON standard g.983 in the process of formulating GPON standard, which is more perfect than the EPON standard formulated by EFM. However, due to the increase of TC sublayer, it also increases a certain amount of overhead, which goes against the original intention of hoping to take advantage of the simple and economic characteristics of Ethernet technology to a certain extent. Therefore, defining an efficient TC layer mechanism will become a key for ITU in formulating GPON standards

5. GPON standard stipulates that TC sublayer can adopt ATM and GFP encapsulation methods, among which GFP encapsulation method is suitable for carrying ip/ppp and other packet based high-level protocols, but whether the ATM encapsulation method defined to support ATM services is suitable in Ethernet based GPON system remains to be discussed

6. The technology of carrying TDM service on Ethernet is not mature, and it is difficult to meet the QoS requirements of carrier level. Therefore, in order to carry TDM services and voice services, EPON must design a new Mac mechanism and add new software and hardware. GPON can easily support TDM services and voice services because of its designed TC sublayer structure and ATM packaging, as well as the 125us frame length and timing mechanism

IV. comparison of EPON and GPON products

because the EPON standardization work of IEEE is carried out earlier than the GPON standardization work of ITU-T, and the 802.3 standard series of Ethernet has become the most important standard in the industry when some electronic tensile machines of Ethernet are loaded to its scope, so the existing g-pon products in the market are more in compliance with EPON standards than super grade PON products, and there are basically no products that strictly comply with GPON standards at present. Another important reason why EPON products are more extensive than GPON products is that EPON standards are formulated more loosely, and manufacturers have greater flexibility in developing their own products

from the perspective of industrial chain, PON optical transmitting/receiving module, the core part of EPON system, has been relatively mature, and the core TC control module has been mass produced (ASIC), while the corresponding core module of GPON system is not yet mature. At present, its core TC control module is only in the FPGA stage from the perspective of information retrieval, and it is difficult to achieve large-scale commercial use

at present, the PON port rate level supported by EPON products is generally 1250kbit/s, and a few products only support 100mbit/s. Although IEEE mainly considers data services and basically does not consider voice services when formulating EPON standards, in view of the fact that operators pay more attention to the requirement that the access network should be able to provide data and voice services at the same time in the layout planning, many EPON products provide voice services by reserving bandwidth while providing data services on the basis of IEEE standards, except that a few EPON products only support data services

v. summary

1. At present, there is still a lot of controversy in the industry about the merits of EPON and GPON, but the access has the distinctive characteristics of technological diversification. Therefore, if epon/gpon can achieve the goal of mature technology and low cost, it should be applied in the future. But in the next 1-2 years, EPON will be ahead of GPON. Many operators in North America and Japan have begun to use EPON Technology to equip their fttp/ftth network

2. To realize fttp/ftth, in addition to paying attention to the system technology of broadband optical access, we should also focus on the following technologies: develop new devices and core control chips that adapt to the characteristics of FTTH, and reduce the cost of optoelectronic devices and passive devices; Develop low-cost and easy to install indoor optical fibers, optical cables and connectors, as well as matching construction instruments and tools; Develop high-density and easy to operate optical fiber distribution frame; Develop centralized remote monitoring and management technology and systems

in short, it will take time to use FTTH on a large scale. We should be confident and patient