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.155.52 Mbit/s/155.52 Mbit/s ·622.08Mbit/s/155.52Mbit/s .622.08 Mbit/s/622.08 Mbit/s ·1244.16Mbit/s/155.52Mbit/s ●1244.16Mbit/s/622.08Mbit/s. The B-PON standard defines specific wavelength allocation schemes for the downstream and upstream traffic.In the case of a dual fibre system,the older B- PON standard reserves the 1260-1360 nm wavelength window for both the downstream and the upstream traffic.In the case of a single fibre system,the 1480-1580 nm window is used for the downstream direction(see Figure 4).The new wavelength allocation was made to improve B-PON's support for broadcast and multicast of economical video delivery services,including possibility to have varied deployment scenarios and modulation schemes,and possibility to implement a wide range of high-speed digital services.In the new wavelength allocation scheme [6],the downstream wavelength window is divided into the normal downstream band (1480-1500 nm)and enhancement band.The enhancement band has two options,1539-1565 nm window for additional digital services and 1550-1560 nm window for video distribution and services alike. Separate guard bands are left between the reserved wavelength windows and some bands are reserved for the future use. UPSTREAM DOWNSTREAM (155.52Mb/s) (155.52or622.05Mbs) Basic wavelength allocation compliant with G.983.1 1200 1300 1400 11500 1600nm FUTURE USE FUTURE USE Enhanced wavelength allocation compliant with G.983.3 1200 1300 1400 1500 1600nm ENHANCEMENT BAND Figure 4.Wavelength allocation for a single fibre B-PON. 26 !"# ""$ $ % $ $ %& % ' $ &" ( %) $" ! *+% !"# $ $ $ $ % & % ' $ #" ( %) *% $ & $ $ % $, - #& . !"# ""$ $ % $ % $!/ & $ $ $ %&" $ $$% "! $" ! ( ! ) "& # $ " ( $ !! "$(% $ %$&" $ % ) $ " ( $ % "% #$ # # " ! ' !"# ""$ $ %01) $ % !"# $ ! $ $ %"$ % ,*%. % % $$ $ )+2*% $ $ $" # " ! *% $ $ ! $ & $ ! " 3 4 #& " ! !"# $ $% ! $ & & & + % + % 54678 , . 9:4678 ,$ . -5567547 -5567547 7;8<7789 7 !"# ""$ $ $% " =2++ !"# ""$ $ $% " =2+ >?@ABCDEFGHCICJ@KLGIIMNGK?MJOMBGP?J@ICO?QBCRSTUVE