atm交換技術(shù)與bisdn原理(已修改)
2025-05-27 22:55 本頁面
【正文】 1 ATM業(yè)務(wù)分類和 ATM業(yè)務(wù)適配的思想 ITU－ T標準委員會根據(jù)以下三個參數(shù)對用戶平面高層業(yè)務(wù)進行分類： ?Timing relation between source and destination(required or not required) ?Bit rate (constant or variable) ?Connection mode(connectionoriented or connectionless) 基于以上三個參數(shù)，用戶高層業(yè)務(wù)可被劃分成四類： ?Class A: Connectionoriented constant bit rate (BCR)service, such as circuit emulation and CBR video ? Class B: Connectionoriented variable bit rate (VBR) service with a timing relation between the source and the destination, such as VBR video and audio ? Class C: Connectionoriented VBR service without a timing relation between the source and the destination, such as connectionoriented file(., data) transfer ? Class D: Connectionless VBR service, such as LAN data 2 ATM Adaptation Layer Traffic Types ? AAL1－ ATM Adaptation Layer Type 1: CBR service, which allows ATM to emulate voice or DSn(n=0,1,or 3) traffic. 舉例： PCM 64kb/s Voice, coded video transmission,etc. ? AAL2－ ATM Adaptation Layer Type 2: VBR service with timing relation between the source and destinationUnder studying. 舉例：可變比特率分組傳輸，可變比特率視頻編碼 MPEG1/2 etc. RtVBR/nrtVBR ? AAL3/4－ ATM Adaptation Layer Type 3/4:VBR service without timing relation between source and destination. 舉例：幀中繼， etc. AAL3是面向連接的業(yè)務(wù)， AAL4是 無連接數(shù)據(jù)業(yè)務(wù) ? AAL5－ ATM Adaptation layer Type 5: Connectionless traffic. 舉例： IP， SMDS AAL3/4 (SEAL: Simple and Efficient Adaptation Layer ) 3 ATM ITU ATM/BISDN Service Classes S e r vi c e C l assA t t r i b u t e C l ass A C l ass B C l ass C C l ass DT i m i n g r e l at i on b e t w e e nS o u r c e an d d e st i n at i o nR e q u i r e d N ot R e q u i r e dB i t R at e C on st a n t V ar i ab l eC on n e c t i on M od e C on n e c t i on O r i e n t e d C on n e c t i on l e ssA A L ( s ) A A L 1 A A L 2A A L 3/ 4or A A L 5A A L 3/ 4or A A L 5E x am p l e A p p l i c at i on s D S 1,E 1, n x 64 kbps e m u l at i o nP ac k e tV i d e o,A u d i o F r am e R e l ay , X .25IP , S M D S4 Applications of AAL and ATM Layer Service Category A T M L aye r Ser vic e c at e gor yAAL C B R r t V B R n r t V B R A B R U B RA A L 1 C i r c u i te m u l at i o n ,N I S D N ,voi c e o ve rA T MA A L 2 V ar i ab l e b i tr at e voi c ean d vi d e oA A L 3/ 4 A T M / S M D SA A L 5 L A N E V i d e o on F r am e r e l ay , L A N E C l as s i c al I PP N N I d e m an d A T M / S M D S , P N N I ove r A T M ,L A N E , L A N E L A N EP N N I P N N I P N N I M P O AN u l l P N N I P N N I P N N I P N N I P N N I 5 高層、 AAL層和 ATM層 1 2 3 4User Data(用戶數(shù)據(jù))1n ByteHeader Trailer高層AAL 層CS子層 Hamp。T:640Byte4447THTHTHTHH H H HSAR子層ATM CellATM 層6 Generic AAL Protocol Sublayer Model Service SpecificConvergence Sublayer(SSCS)May be NullSegmentation AndReassembly(SAR)Common PartConvergence Sublayer
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