ADSL????·???????ADSL2??ADSL2+
?? ?? ±??????ò?÷?é????ITU×??ü?¨????????ADSL????????±ê×???G.992.3??G.992.4??G.992.5????????????ADSL???????????????ù???????????ú?ü???????ó?ê???é?????????úADSL????????????????????????????????????????×??????????????°???í??·??????????????????????ò???é?????????ú??ADSL???????úADSL?????????ù×?????????????×??ó?????????????úADSL±????????ó???í??????·???·????ü?ó??×÷????

???????ü?? ADSL ADSL2 ADSL2+ ITU ????±ê×?

????1 ADSL2 ??ADSL2+??????±ê×?

????2002?ê7????ITU??????ADSL????????±ê×??¨G.992.3??G.992.4???????????ù????ADSL2??2003?ê3???????????úADSL±ê×????ù??????ITU???¨??G.992.5????????ADSL2plus???ò??ADSL2+??

?????????ú??ADSL???????§?????ü?????????????????ü?????????±???????í?à?????????????????????????¤??????????10?ê????ADSL???á?ü???????????????????????????????????á???????????????????¤×÷???????í??????????????·??????°???????????§????????°ü?¨?????????á??????????????????????????±?????????·?????ADSL2+??5000???????à??????????20 Mbit/s??????????????????±???????ADSL2+??ADSL2??±??¤???ò????????

????ADSL2+?á??·????á?????????????????????????ü??????·?????±????????????????????·?·???¤?·?·?á????????????·?°????????????±???????????????ù?????????ü?????????????????????????????????è±????????è±????????????ú?ü????

2 ADSL2???÷???????????°??ADSL??±???

2.1 ????????????????

?????????????????????é??????ADSL2?????á???????????¤?à????????±?ADSL?ü??????????ADSL2????????12Mbit/s??????????1Mbit/s??????????????????????ADSL2???????ü?????§???÷???????????????ú???????ü????±à?????????á????????×????ú???????????????????????????í??·¨???á????ADSL2???ù??·???±ê×????è±??á?????ü??????????

????ADSL2??????????16??????×?±à????1bit??QAM????×ù????????????ANR???????é???????·?????????????????????????ù???????ú???????????????????ú????????????AM?????????ú?ú?????·?¨??????????Viterbi?????÷?????ü??????????

????ADSL2???????????????ú???¨????????????±à???????ú±????????ò?????????????ú??ADSL±ê×???32kbit/s???????????????ú?????¨????????ADSL2??????????4kbit/s??32kbit/s±à????

???????????úADSL?????????¤?à???????????????????????¨?ó????128kbit/s???????????¨??32kbit/s?¨×?????????????25%????????ADSL2???????????ú????????????????????4kbit/s?????????????§????????????????28kbit/s??

???????¤?à????????????±????????±?ò??ADSL2??RS±à?????????ü????±à??????????????????????RS??×????±?ò??ADSL2?????÷?á?????ü?à??????????????±à?????????±????????×????ú?ó?ó???á????ADSL2????????????????±??????????·?????????????????????????ù?????°???¨???????ú???????????¨???????í????????±???????????AM?¨???ì???????????????????????ú?ú???????§?§??

?????¨???????ú??·????ú???·?¨?????ü×???????×????????????????????????????????ú??·????ú???????í?????????·???¨???????ú?????????????????????????·?¨??????±???????AM?¨???ì???????????????????????ú?ú???????§?§?????????ú???·?±??????????±?·?????????????????????·?????·????ú???·?à?????????±?????×??????

??????????????????????????????RFI??

???????????úADSL?à±???ADSL2?ù?????????????????¤?à???????°??????ADSL2?????????????????·???á??50kbit/s???????????????????????????????à??600????????????????????????????6%???ó??2.5??·???????

2.2 ????

??????ADSL???????????????±???·?¨???????ù???????????ó????????????????????????ADSL2+?????÷???????????¤?????????¤???á??????°?×°?±??????????·?°??????°??·????×?????à?????????????????¤????°?±??????ü????????

???????????????·?¨?í?ó??ADSL2?????÷?????·???????á???????????·???ù???·?·??????SNR??·?·¨??????????·?·¨?????????·???????????é?????¨???????????????????????é???ê??ADSL??????????????ADSL2°ü???????±???????à???????á???????·?????????????ù×??????????????????????í?????í??·????á??????????????????????ADSL?????????????¤·???????·??????§°????????????????·?¨??·??????????????§?á???ü??????????·?????

2.3 ????????

?????????úADSL?????÷??????????±????????±?ò?????±?¤×÷??????????????????ADSL Modem???¤×÷?????ú/????×????????ú?????ú???ù????????????°??ò?¨??Modem???????????????????????????????±?????????¤×÷????????ADSL??·??÷?????????????????????¤×÷?·???????????ó??????DLC????????????

??????????????????????ADSL2?á???????????????í???????????????§±???ADSL?°???±?????±???????????±??????×?????????????????????°ü?¨??

????????????L2??

????????????????ATU-C???????ù??Internet???÷??ADSL???÷?????ì??????????????????????????????L2??????ADSL2±ê×???×???????????????????

????????????L3??

?????±?????????????????????????????¨?????è±?????????×???????????ATU-C??ATU-R????×???????????????

????ADSL2??·??÷?????ù??ADSL???·?????÷???????ò????L2???????????±?????ó???????±??ADSL2?¤×÷??????????????????L0????????????±??¤×??ì?????????????±?????÷???????±??±????±???????§???????????¤??TXT?????±??ADSL2????????L2?????????????±???????ó?ó??????×??????????????????????±??L2?????±?????????§??????????????????ADSL2????????????????L0????????????×??ó????????????L2×??????????????????ê???????°?ì·????????á?ì??·???????????????????±??????í?ó???ò???????á±????§×???????L3?????????????????????±???§????????ADSL???·???????÷???±?????????????±???§????????×????±??ADSL??·??÷?è???ó??3s???±?????????????????????ó???????¨???¨????????

2.4 ????×?????

???????°?????????????????á?????????ù???°?????????????????????????????ü???í???ù???°??????

???????????ó±???×÷???°???á?ó?ó?°?ìADSL???????????á?????????°??????±????á????ADSL??????????????????ADSL?????????ò??×??????????????°??????±??????ò°ü?¨AM????????????????±??????±??????

????ADSL2?¨????????·ì?????±????×???????·?·¨??????????????????????????????×÷SRA??????ADSL2???????????¤×÷???±?ò????????·?????????±????í?ó????±?????????????

????ADSL2?????ì????????????±?????±???????±???AM·????????í????±??ü??·?????????±??ü?????????????????????????????????????§?????÷????SRA???ù????ADSL2???????÷???????????????????????????????????÷????????????????????????????±?????????????????????±??¤Modem???§?????????????§???á?????????ü????±????í?ó????????????SRA??????*??ADSL2?????????????????????ò????·ì????±?????????????

????SRA?????¤×÷?????é??????

?????¨1???????ú?à????????SNR?????¨????????????????±????ù?è????????±?????

?????¨2???????ú·?????????????·????ú??????????????????????±???????????°ü?????ù??±?????????????????????????????????????????°ü?¨????ADSL2?à???¨??????±??÷????±???????·?????????

?????¨3??·????ú·????????°Sync Flag?±??????????????×÷??????±ê????????±ê????????????????????·??????·???±?????ù?????????????????????¨4???????°Sync Flag?±????±??????ú?ì?????????ù??·????ú???????ú????????????×÷??????·ì?????÷????????

2.5 ???????????ü????????

???????????????¨?????ó???á????????·??????????¨??°??à?·???°???????????????????ó?ó?????????§?á??????????????????·?????????????????????????ADSL2 ?§??ATM??????IMA±ê×???????±ê×???????????ATM?????è???????¨??IMA??ADSL2??????????°????ù?ò?ü?à?????°???????????ùADSL???·?????????á?????????·???????????ü???é??????

????IMA±ê×???ADSL???í????ATM?????????¨??????????×???????·???????????×?????×÷IMA×??????ü??ATM??????????????ATM?÷??°??????÷·?????ADSL???í??????????????IMA×???????????ATM???í????????ATM????????????????ATM?÷??IMA×??????¨??IMA???????????é?????í?????????????í?????????í??·??ú±????í?ó???§???????????????±??×÷?????????????????????¤×÷??IMA±ê×??????ó??????ADSL???í??????????????????±????????????????????????í?ó?????????ú????ADSL2°ü?¨????IMA?¤×÷???????á??±????????í??????????ADSL?????¤×÷??

2.6 DSL???·????????????

????ADSL2?á???????????????·??????°????í??·??????????????????????????????á??·?????±?????ADSL2???????????á???????§??????????±????????·???????ó???????????????±?????ó??????????????·????????±?????ó????????±????????·?????ó??????

????ADSL2????·???????????????CVoDSL?á?????§??????????????????DSL???í?????÷??????TDM??????????CVoDSL????DSL?÷?????÷?÷????PCM DS0???????ò???????¨?????¨????POTS??±?????64kbit/s?????????????????è±??¨??PCM?±??°?????DS0·????????·??????

3 ADSL2?????í????????

???????????????????÷??????????ADSL2????????????????????

????1. ???????????¤×÷????

?????ò????×????ú??????????????????????????????????ADSL??·??÷???±?ò?????????¤×÷?????á??????????

????2. ?ì??????

????ADSL2?á?????????ì???????????????????±????ADSL??10s??????3s??

????3. ????×???????

????ADSL2??????????????????????????????????ADSL?????????í????????????????256kbit/s?????????????????????????????°????????????????·?????·???????×????ó???ü?????????????????????????????í??????????

????4. ?§???ù??°ü??·???

????ADSL2°ü?¨????°ü??????????????????????????????????ADSL2???????ù??°ü??????·?????

4 ????ADSL2+

????ADSL2+??2003?ê??1???????¨????×÷?? G.992.5??????ADSL2±ê×???ADSL2+?¨?é??±????????í???ò????????5000???????à?????????????°????????????????

????ADSL2±ê×???×??÷×????¨????????????????1.1MHz??552kHz??ADSL2+???¨??????2.2MHz?????????????????á???????????°???·?????????ó????????ADSL2+???????????ó????1Mbit/s?????????????·?·??×?????

????ADSL2+???????????????°??????????1.1MHz??2.2MHz?±??ADSL2+?¨????????????????1.1MHz????????????????????????????CO??RT??ADSL·??????????§???±?ò???????????????????±??±?????????ADSL·???????RT?????·?????°?????ó?ó?÷????CO?????·??????????

????ADSL2+?????¨????????????????????????????????1.1MHz????????????????????????????????????1.1MHz??2.2MHz???????????????????????á??????·??????????????????·????±??¤?????????????ó??·????°??

5 ?á????

???????????¨??ADSL2?°ADSL2+±????á?????ó?í????????????·???·??ò???????ü×÷??ADSL???????ú±ê×???????????ADSL??????????????????*??·????ó?ó????ADSL???????°???????§???????á???????????°???????????°???é??????????ADSL2?°ADSL2+×÷???í??????????????????????????????????????°????ü?ó????????

?? ?? ?? ?×

[1] ITU??ADSL2/ADSL2plus??White Paper

[2] ITU G.992.3??ITU G.992.4??ITU G.992.5

[3] ?ù???? . ADSL?í???????? . ±±?????????ó?§??°???

[4] ???÷?÷ . ?í?????????? . ±±???????§??°???

????????°???????1972?ê?ú????·??ü?????¤???ó?§???????¤??????

?????????ù??????1952?ê?ú????·??ü?????¤???ó?§???????????ú??????

?????? ?á??????1977?ê?ú????·??ü?????¤???ó?§????????


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