HDLC vs SDLC
HDLC thiab SDLC yog kev sib txuas lus raws tu qauv. SDLC (Synchronous Data Link Control) yog ib qho kev sib txuas lus raws tu qauv siv ntawm cov ntaub ntawv txuas txheej ntawm lub computer network, tsim los ntawm IBM. HDLC (High-Level Data Link Control) yog dua cov ntaub ntawv txuas raws tu qauv, tsim los ntawm ISO (International Organization for Standardization), thiab tau tsim tawm ntawm SDLC.
SDLC tau tsim los ntawm IBM hauv xyoo 1975 los siv rau hauv Systems Network Architecture (SNA) ib puag ncig. Nws yog synchronous thiab me ntsis-oriented thiab yog ib qho ntawm thawj ntawm nws hom. Nws tshaj qhov synchronous, tus cwj pwm-oriented (piv txwv li Bisync los ntawm IBM) thiab synchronous byte-count-oriented raws tu qauv (i.e. DDCMP los ntawm DEC) hauv kev ua tau zoo, yoog raws thiab nrawm. Ntau yam kev sib txuas thiab thev naus laus zis xws li kev sib txuas ntawm taw tes rau taw tes thiab ntau qhov sib txuas, kev sib txuas thiab tsis muaj kev sib txuas lus, ib nrab-duplex thiab puv-duplex kis tau tus mob thiab cov kev sib txuas hauv Circuit Court thiab pob ntawv hloov pauv tau txais kev txhawb nqa. SDLC txheeb xyuas hom "primary" node, uas tswj hwm lwm qhov chaw, uas yog hu ua "thib ob" nodes. Yog li cov nodes thib ob yuav raug tswj los ntawm lub hauv paus. Cov thawj coj yuav sib txuas lus nrog cov thib ob uas siv kev xaiv tsa. Secondary nodes tsis tuaj yeem kis tau yam tsis muaj kev tso cai los ntawm thawj. Plaub qhov kev teeb tsa yooj yim, uas yog, Point-to-point, Multipoint, Loop thiab Hub mus-ua ntej tuaj yeem siv los txuas thawj zaug nrog rau theem nrab. Point-to-point suav nrog tsuas yog ib qho tseem ceeb thiab theem nrab thaum Multipoint txhais tau tias yog ib qho tseem ceeb thiab ntau qhov thib ob. Loop topology koom nrog Loop, uas yog qhov tseem ceeb txuas thawj zaug rau thawj theem nrab thiab lub xeem thib ob txuas ntxiv mus rau thawj zaug kom cov neeg nruab nrab nruab nrab hla cov lus los ntawm ib leeg thaum lawv teb rau qhov kev thov ntawm thawj. Thaum kawg, Hub mus tom ntej koom nrog txoj hauv kev sab hauv thiab sab nraud rau kev sib txuas lus mus rau lwm qhov chaw.
HDLC tuaj rau hauv lub neej tsuas yog thaum IBM xa SDLC rau ntau pawg tswj hwm tus qauv thiab ib qho ntawm lawv (ISO) hloov SDLC thiab tsim HDLC raws tu qauv. Nws yog ib qho me ntsis-oriented synchronous raws tu qauv. Txawm tias muaj tseeb hais tias ob peb yam ntxwv siv nyob rau hauv SDLC raug tshem tawm, HDLC yog suav tias yog ib tug tshaj superset ntawm SDLC. SDLC Ncej hom yog sib koom los ntawm HDLC. Cov teb ntawm HDLC muaj tib lub luag haujlwm ntawm cov hauv SDLC. HDLC ib yam nkaus, txhawb synchronous, ua haujlwm puv duplex li SDLC. HDLC muaj kev xaiv rau 32-ntsis checksum thiab HDLC tsis txhawb lub Loop lossis Hub mus-ua ntej teeb tsa, uas yog qhov txawv me me ntawm SDLC. Tab sis, qhov sib txawv tseem ceeb los ntawm qhov tseeb tias HDLC txhawb nqa peb hom kev hloov pauv uas tsis yog ib qho hauv SDLC. Ua ntej ib qho yog hom lus teb ib txwm (NRM) uas cov kab nruab nrab tsis tuaj yeem sib txuas lus nrog thawj zaug kom txog rau thaum thawj zaug tau tso cai. Qhov no yog qhov tseeb hloov hom siv hauv SDLC. Qhov thib ob, Asynchronous teb hom (ARM) tso cai rau cov nodes thib ob los tham yam tsis muaj kev tso cai thawj zaug. Thaum kawg nws muaj Asynchronous balanced mode (ABM) uas qhia txog kev sib koom ua ke, thiab txhua qhov kev sib txuas lus ABM tshwm sim ntawm cov nodes nkaus xwb.
Hauv cov ntsiab lus, SDLC thiab HDLC yog ob qho tib si cov ntaub ntawv txuas txheej txheej txheej txheem network. SDLC tau tsim los ntawm IBM thaum HDLC tau txhais los ntawm ISO siv SDLC ua lub hauv paus. HDLC muaj kev ua haujlwm ntau dua, txawm hais tias, qee qhov nta ntawm SDLC tsis nyob hauv HDLC. SDLC tuaj yeem siv nrog plaub qhov kev teeb tsa thaum HDLC tuaj yeem siv nrog ob qho xwb. HDLC muaj kev xaiv rau 32-ntsis checksum. Qhov sib txawv loj ntawm ob qho no yog cov kev hloov pauv uas lawv muaj. SDLC tsuas muaj ib hom kev hloov pauv, uas yog NRM tab sis, HDLC muaj peb hom suav nrog NRM.
