1.What is GPON?
　　GPON is the latest generation broadband passive optical integrated access standard based on the ITU-TG.984.x standard.Its technical feature is that it adopts GFP(framing procedure)defined by ITU-T to encapsulate and map various services such as Ethernet,TDM and ATM at the second layer,and has strong OAM function.
　　2.System structure of GPON
　　Since GPION is a kind of PON,its composition is the same as that of PON,consisting of ONU(optical network unit),OLT(optical line terminal)and passive optical distribution network.
　　3.Basic performance parameters of GPON network
　　0.15552Gbps upstream 1.24416Gbps downstream
　　0.62208Gbps upstream 1.24416Gbps downstream
　　1.24416Gbps upstream 1.24416Gbps downstream
　　0.15552Gbps upstream 2.48832Gbps downstream
　　0.62208Gbps upstream 2.48832Gbps downstream
　　1.24416Gbps upstream 2.48832Gbps downstream
　　2.48832Gbps upstream 2.48832Gbps downstream
　　Among them,1.24416Gbps uplink and 2.48832Gbps downlink are the main rates currently supported
　　It should be noted that unlike EPON,GPON is not completely asynchronous.
　　The maximum logical distance supported is:60km
　　The maximum physical distance supported is:20km
　　The maximum distance difference supported is:20km
　　The splitting ratio is generally 1:64.At present,the splitting ratio of mainstream manufacturers'products can be smoothly upgraded to 1:128.
　　4.Features of GPON
　　(1)High bandwidth and high transmission efficiency,the downlink rate is as high as 2.488Gbit/s,and the uplink rate is 1.244Gbit/s,which can meet the operator's access bandwidth requirements for future services.When using the GEM encapsulation method,the comprehensive transmission efficiency is 93%.%above.
　　(2)Single-fiber access,using a single fiber can meet the intervention requirements of ONT users,which can greatly save the fiber resources of operators in the feeder section of the access layer.
　　(3)It can support longer access distance.The GPON system developed for FTTB can reach the farthest access distance from OLT to ONT up to 60km.
　　(4)As a carrier-class technical standard,it has detailed requirements for the interoperability of equipment,and can provide corresponding QoS guarantees for various types of services.GPON also specifies the protection mechanism and complete protection mechanism at the access network level.OAM function,the automatic fiber switching time is less than 50ms.
　　(5)In the outdoor optical distribution network,there are only optical fibers and passive optical splitters with very stable physical medium characteristics,without any active equipment,which makes the network highly reliable.
　　(6)Provide a unified access platform at the access network level to save the cost of maintenance and troubleshooting by power operators.