Raws li tau hais ua ntej, SDH yog sib xws, txhais tau hais tias cov teeb liab los ntawm txhua theem ntawm PDH series tuaj yeem muab tso rau hauv SDH kis tau tus mob modules, tso cai rau cov cuab yeej PDH uas twb muaj lawm txuas ntxiv mus siv yam tsis muaj pov tseg. Ib txhij, SDH kuj tau sib xws nrog ntau yam kev pabcuam tshiab tau muab tso rau hauv nws cov kis tau tus mob. Cov txheej txheem ntawm kev thauj khoom PDH teeb liab thiab ntau yam kev pabcuam tshiab rau hauv SDH teeb liab qhov chaw los tsim SDH thav ntawv yog hu ua daim ntawv qhia thiab multiplexing.
Mapping yog hais txog tus nqi hloov pauv thiab hloov pauv. Hauv SDH, daim ntawv qhia txhais tau tias muab PDH teeb liab bytes rau hauv cov haujlwm meej hauv SDH ntim raws li qee cov ntawv xov xwm. Nws lub ntsiab lus yog los synchronize tus nqi ntawm ntau yam tributary teeb liab nrog tus nqi ntawm cov khoom ntim khoom sib xws, ua kom cov ntim virtual los ua cov koom haum muaj peev xwm ntawm kev sib kis, kev sib txuas, thiab hla -kev sib txuas. Piv txwv li, kev hloov pauv tus lej code, ntxiv cov nyiaj siv ua haujlwm channel, suav nrog lub thawv virtual. Daim ntawv qhia tau muab faib ua ob pawg loj: synchronous map thiab asynchronous map. Asynchronous daim ntawv qhia siv tus lej hloov pauv rau tus nqi hloov pauv; SDH siv ob qho tib si zoo/zero/negative code tus nqi hloov thiab zoo code tus nqi hloov. Synchronization daim ntawv qhia tsis xav tau tus nqi hloov pauv. Synchronization muab faib ua me ntsis synchronization thiab byte synchronization. SDH siv byte synchronization, uas tuaj yeem muab faib ntxiv rau hauv hom ntab thiab kaw hom.
Multiplexing yog hais txog cov txheej txheem ntawm kev sib txuas ntau lub teeb liab byte-by-byte los yog me ntsis-by- ntsis rau hauv ib lub teeb liab. SDH siv byte-by-byte multiplexing.
Multiplexing muaj ntau txoj kev siv. Piv txwv li, nyob rau hauv European tus qauv PDH system, nws tau teev tias 30 lub suab raws tau multiplexed rau hauv 2048 kbit / s thawj pab pawg teeb liab, 4 2048 kbit / s tributary signals yog multiplexed rau hauv 8448 kbit / s teeb liab, thiab 4 8448 kbit / s signals yog multiplexed rau 8 kbit / s, thiab lwm yam. yog li-hu ua PDH multiplexing structure lossis multiplexing route. Tus thawj ITD-T tau tsim cov kev cai nruj rau cov qauv multiplexing mapping lossis multiplexing route ntawm SDH, raws li qhia hauv daim duab. PDH cov teeb liab ntawm ntau tus nqi tuaj yeem ua rau SDH kis tau tus mob modules raws li txoj kev multiplexing.
Raws li pom nyob rau hauv daim duab, nyob rau hauv lub multiplexing qauv pom zoo los ntawm G.709, txoj kev multiplexing los ntawm txhua PDH tus nqi teeb liab mus rau STM-N tsis yog tshwj xeeb; Txawm li cas los xij, rau ib lub teb chaws los yog cheeb tsam, txoj kev multiplexing yuav tsum yog qhov tshwj xeeb. kuv lub teb chaws optical synchronous kis tau tus mob network technology system qhia tias 2 Mbit / s -raws li PDH series yog siv raws li SDH payload, thiab AU-4 multiplexing txoj kev yog xaiv. Nws qhov yooj yim multiplexing mapping qauv yog qhia nyob rau hauv daim duab. Raws li tau pom los ntawm daim duab, kuv lub teb chaws SDH multiplexing mapping qauv muaj peb PDH tributary teeb liab input interfaces: 139,264 kbit / s, 34,368 kbit / s,
2,048 kbit / s. Vim tias ib qho STM-1 tsuas tuaj yeem ua daim ntawv qhia rau hauv peb 34 Mbit / s tributary signals, kev siv channel tsawg dhau. Yog li, 34 Mbits tributary interfaces feem ntau tsis siv. Nyob rau hauv lub neej yav tom ntej, rau qee yam kev siv, xws li cov kev pab xauj tsev thoob ntiaj teb, yuav tsum muaj 1.544 Mbit / s pob tshab tributary, uas tuaj yeem ua raws li C-11 txog VC-12 rau TU-12. Rau cov kev pab cuam duab thiab LAN cov kev pab cuam, compression encoding ntawm cov duab tseem tsis tau tiav. SDH tuaj yeem muab txoj hauv kev sib kis xws li VC-2 thiab VC-2 concatenation.
