【正文】 nature production。 SBC in the plan plans in 2020 in its huge “speed of light” to reach 18,000,000 FTTN, each household has speed 2039Mb/s, provides the endtoend tertiary service colligation (trite play) the service. Japan is in the world advances the FTTH most radical country, years its optical fiber on already understood more than 18,000,000 households families, but the user development lag, probably was 2,000,000, in 2020 plans develops 10,000, quite is steady conservatively, FTTH altogether has laid to 2020 500,000, some 167 small projects or the experimental project are carrying on. Our country broadband access work extremely is also rapid in the near two year development, according to the preliminary statistics, to 2020 year39。s mace application”, promoted application. In fact, looking from the telemunication development history, when the work number of users achieved certain scale, each kind of application meets the nature production。 But the cost the linearity increases along with the number of users actual growth, does not need to plan, the investment risk is low, thus disperses the local cost in the low density user to be low. The shorting is the both sides equipment and the optical fiber facility specialpurpose, the user cannot share the bureau end equipment and the optical fiber, when the demand fast growth also the user are very crowded, optical fiber and both sides equipment quantity and cost as well as spatial demand also along with it rapid increase, thus not too suits the high crowded user region. The influence choice Ether technology another factor is the traditional video frequency service provides the way, for example American Place Bell Company all pledged provides the tradition to simulate the RF video frequency program, but the Ether and the simulated video program mix is very difficult. This aspect PON technology quite is easy. Because the cost, the quality, the management, the security and so on many kinds of factors, the Ether still had further to improve as the public work turning on way. Mainly is the Ether technology inherent mechanism does not provide the endtoend package time delay, the package loss rate, the band width control, supports the realtime service with difficulty the grade of service, lacks the safety mechanism guarantee and so on. Pointmultipoint passive, light work system Along with IP rising with the development, some people proposed the EPON concept, this thought obtained the positive response in the Ether, has already formed the GEPON standard in under the IEEE flag. 1. Passive light working Passive light work (PoN) is one pure medium work, its main characteristic has removed the active equipment in the access work, thus has avoided the electromagic interference and the thunder and lightning influence, reduced line and the external instrumentation failure rate, reduced correspondingly has transported the Augur cost. Next, the PON service transparency is good, the band width is wide, suitably in any service pattern and the speed signal, can support the simulation broadcast television service quite economically, has tertiary service function (tripleplay).Finally, as a result of its game of end equipment and optical fiber by user sharing, thus the line cost pares other pointtopoint mailing address to have to be low, the construction cost also may reduce obviously. Especially day by day advances along with the optical fiber to the user, its synthesis superiority is more and more obvious. But the PON each user cost along with shares OLT the user quantity increase to drop rapidly, thus most suits in the dispersible small business and the inhabitant user, these user region is specially dispersible, but each region user relative centralism small area crowded user area, in particular newly built region. Finally, after considered uses the PON technology quite to be easy to continue to provide traditional the simulated video program, thus, most American Place Bell Company favors the PON technology, but is not the light Ether technology. The PON main shorting is the disposable investment cost is high, because bureau end light line terminal OLT is very expensive, the optical fiber and the shunt and so on the passive infrastructure must an arriving, when like this the number of users are few or the user distribution surpasses some definition is away from, each user39。 in the 3ah flag has already formed the GEPON standard. In reality, EPON and the GEPON basic difference is the standardization, the former often Refers to the nonsign equipment, the latter refers conforms to IEEE , standard equipment. Moreover, the GEPON transmitting range and the bypass pare have pared to EPON reduce. EPON/GEPON and the traditional pointtopoint Ether main different place lies in the work in the pointmultipoint mailing address. Its downward direction work in the TDM way, the data stream changes the long Ether frame way to broadcast ONU, each ONU basis ether frame MAC address, decision choices. The upward direction work in the TDMA way, Comes from the different time slot ONU data stream to gather the public optical fiber facility and OLT. In addition, the traditional Ether work in the continual optical transmission pattern, is receiving and dispatching two directions both is the continual bit class, therefore receives the end fixed time easily to realize with the decision. But the EPON/GEPOkI ONUpward bit class is the sharpedged data packet which transmits in turn, the OLT receive timing recovery, the decision threshold establishment, the range finder and the time delay pensation quite is plex. Looked from the EPON/GEPON structure that, its essential merit Enormously simplified the traditional multilayered overlapping work Structure, the main characteristic included: Eliminated ATM and the SDH level, th