Epongpon: The best technology to achieve FTTH

FTTH Fiber to household this seemingly distant thing began to enter the market in 2004, especially in Japan and North America has begun to scale applications, development is very rapid, thus becoming a weak optical communications market, and even recognized as the biggest driving force for the resurgence of optical communications. Affected by foreign countries, China in some areas (such as Wuhan) also began a small-scale FTTH test, some operators (such as Beijing Communications) even began a FTTH commercial trial.

FTTH involves a lot of technology, including optical devices, optical transmission systems, optical fiber and cable, installation, maintenance monitoring, including transmission technology and equipment is the key, and Epon/gpon technology is recognized as one of the best technology to achieve FTTH.

Passive optical Network (PON) technology is a point-to-point optical fiber access technology, which consists of olt (optical circuit terminal), user side ONU (Optical Network Unit) and ODN (optical distribution network). In general, the downlink adopts TDM broadcasting mode, the Uplink adopts TDMA (time division Multiple Access) mode, and it can compose the topological structure of tree type, star type and bus type flexibly (typical structure is tree-shaped structure). The so-called "passive" refers to the ODN does not contain any active electronic devices and electronic power supply, all by the optical splitter (Splitter) and other passive components, so its management and maintenance costs are lower. The concept of PON technology was proposed in the early 1990s, which can be divided into narrowband pon technology for narrowband TDM service access and ATM based Bpon (APON) for broadband access, Epon technology based on Ethernet packet transmission, and both atm/ethernet/ The Gpon technology of TDM integration. It should be said that after more than 10 years of change, PON technology experienced from narrowband pon to Bpon (Atmpon) to Epon and gpon development process, of which, ITU-T in the standardization of PON Technology has played a leading role, has introduced g.982 (narrowband pon), g.983 Series (Bpon) and g.984 series (GPON) and a series of standard recommendations, and IEEE in recent years in the standardization of PON is also very active, and in 2004 launched the Ieee802.3ahepon standards.

For the different characteristics of gpon and Epon technology, the following analysis can be made on these two technologies.

Gpon supports a variety of rate levels, can support up and down line asymmetric rate, uplink does not necessarily support more than 1Gbit speed, so with Epon can only support the symmetrical 1Gbit single rate compared to the Gpon optical devices to choose more space, which can reduce costs.

Epon only supports Class A and B odn levels, while Gpon supports ClassA, B, and C, so gpon can support up to 128 of the tap ratio and up to 20km of transmission distance.

Compared to the protocol, the Epon standard is based on 802.3 architecture, so it is simpler and easier to implement than the Gpon standard. Even more because of the maturity of Ethernet chips, the system cost is lower.

The ITU has adopted many concepts of apon standard g.983 in the process of developing gpon standards, which is more perfect than the EPON standard established by EFM. However, because of the increased TC sub layer, it also increases the cost, which violates the original intention of hoping to use the Ethernet technology simply and more economically. Therefore, the provision of an efficient TC layer mechanism will be a key to the ITU's GPON standards. The Gpon standard stipulates that the TC sub layer can adopt the ATM and GFP two kinds of encapsulation mode, in which the GFP package is suitable for the IP/PPP and so on, but for the ATM package defined in order to support the ATM business is suitable for the Ethernet based Gpon system, has yet to be discussed.

The technology of carrying TDM service on Ethernet is immature and it is difficult to meet the QoS requirements of telecom class. So epon must design a new Mac mechanism and add new hardware and software in order to be able to host TDM business and voice services. Because of its TC substructure structure and ATM encapsulation method, Gpon adopts 125us frame length and timing mechanism, it can easily support TDM service and voice service.

At present, the industry about Epon and Gpon is a great controversy, but the access network has a distinct feature of technology diversification, so if the epon/gpon can reach the technical maturity, low-cost targets, the future should be applied, but in the next 1-2 years, Epon will walk in front of the gpon, Many operators in North America and Japan have started to adopt Epon technology to their FTTP/FTTH network.