【文章內(nèi)容簡(jiǎn)介】 he 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。s cost is very high. Moreover, its tree branch topology caused the user not to have the protection function or the protection function cost is high, has affected the largescale development. 2. APON AND BPON The early narrow band passive light work is based on TDM, the performance price pared not well, already naturally withers away. An ATM passive light work (APON/BPON) may use ATM the centralism and the statistics multiplying, the rebination passive shunt to the optical fiber and the light line terminal sharing function, enable the performance price pared to have the important improvement, at present in countries and so on US and Japan already started mercial. However, the actual APON/BPON service adaptive provides at present very plex, provision of service ability is limited, the data transmission rate and the efficiency are not high, the cost is high, but its market prospect as a result of ATM decline dim. Finally, looking from the longterm service trend of development that, the APON available band width was still insufficient. Take FTTC as the example, although the typical branch downward speed may reach 622Mb/s, after but because the bypass, actual as separable greatly will reduce as each user39。s band width. According to 32 groups’ putations, each branch available band width only remains , again presses 10 user sharing, then each user only can obtain approximately the 2Mb/s band width. Obviously, such performance price pared to is unable to satisfy the work and the service longterm development needs. 3. EPON/GEPON Along with IP rising with the development, some people proposed the EPON concept, namely in with APON and the BPON similar structure and in the foundation, tries to retain its essence part physics level PON。 But replaces ATM by the Ether to take the link level agreement, constitutes one to be possible to provide a greater band width, the Low cost and wider professional ability new marriage EPON. This thought obtained the positive response in the Ether。 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, thus reduced the initial cost and the movement cost。 The downward service speed reaches as high as 1Gb/s, the permission support multiuser, each user39。s band width may be higher, and can provide video frequency professional ability and good QOS The hardware is simple, does not need outdoor electronic installation, and enables the installment deployment work to simplify。 May use the Ether technology mature chip massively, the realization is simple, the cost low improved the electric circuit to refer to the coordination service nimbly provision with the reshuffle ability. IEEE the standard GEPON technology standards is good, on the downward wave length is 1310 and 1490nm, on the downward spee