atm交換技術與bisdn原理-資料下載頁
2025-05-11 22:55本頁面
【正文】 t o A T M l a y e r u s e r i n d i c a t i o n = 1100 O A M F 5 s e g m e n t a s s o c i a t e d c e l l101 O A M F 5 e n d t o e n d a s s o c i a t e d c e l l1 1 0 R e s o u r c e m a n a g e m e n t c e l l111 R e s e r v e d f o r f u t u r e f u n c t i o n s36 Illustration of the need for segment marking to correctly delineate CSPDUs CSPDUsCSPDUs segments into thepayload of SAR_PDUs1 2 3 4 5 1 2 3 4 5 1 2 3 4 5received segmentswith one missingbecause of cell loss1 2 3 4 5 1 2 3 4 5 1 2 3 4 51 2 3 4 5 11 2 3 5reconstructed CSPDUsall erroredbecause of the 1segment slipa)without lastsegment indicationCSPDUsCSPDUs segments into the payload ofSAR_PDUslast segment indication present1 2 3 4 5 1 2 3 4 5 1 2 3 4 5received segmentswith one missingbecause of cell loss1 2 3 4 5 1 2 3 4 5 1 2 3 4 51 2 3 4 5 11 2 3 5reconstructed CSPDUsonly the first errored because the lastsegmentindication corrects the aligment of the segmenta)with lastsegment indication37 (4)AAL5 CS子層 CPCS:Common part convergence sublayer PAD: padding CPI: Common part indicator PDU: Protocol data unit CRC: Cyclic redundancy cheek UU: cpcs usertouser indication Length: Length of CPCSPDU payload CRCLengthCPIUUPADCPCSPDUPayloac32 bits0...47Octets8 bits 8 bits 16 bitsCPCSPDU trailerCPCSPDU38 － 用戶數(shù)據(jù)幀： 1~65, 536 Bytes － CPCSPDU沒有頭，但 CPCSPDU尾占 8個字節(jié) － PAD：實現(xiàn) 48 Octets 對準 (即：使整個 CPCSPDU長度為 48字節(jié)的 整倍數(shù) ) － UU： CPCS用戶到用戶指示， 8 bits, 用于 CPCS用戶信息的透明傳輸 － CPI：公共部分指示， 8 bits, 同 AAL3/4，此處只用作使 CPCSPDU 尾部長 8個字節(jié) － L：長度指示， 16 bits 指示最大＝ 216 CPCSPDU凈荷長度 (L=0表示中止現(xiàn)有的 CPCSPDU傳送 ) － CRC32 x32+x26+x23+x22 + x16+ x12+ x11+ x10+ x9+ x7+ x6+ x4+ x3+ x+1 (4)AAL5 CS子層 39 (5)AAL5 與 AAL3/4比較 A A L 3 / 4 AAL5段屬性判斷 用 ST 判斷 B O M / C O M / E O M / S S ， 用 A T M 層中 PT I 來判斷S A R P D U 校驗 C R C 1 0 無AAL 復接 用 M I D 不支持S A R P D U 凈荷 約每信元 44 字節(jié) 約每信元 48 字節(jié)C P C S P D U 檢驗 無 C R C 3 2緩存分配 用 B A S i z e 不支持40 －應用于信令控制平面 (6)SAAL(Signaling AAL) (UNI )SAALATM LayerPhysical Layer41 SAAL結(jié)構(gòu) SSCFCPAAL(5)SSCOPPhysical LayerATM LayerATM－SignalingApplication()SSCFCPAAL(5)SSCOPPhysical LayerATM LayerATM－SignalingApplication()ATM NetworkPeertoPeer MessagesPeertoPeer MessagesSAALServiceSpecificFunctions42 － PAD: 03 octets are used to make the CPCS PDU an integral multiple of 4 octets － PL: (Length of PAD in octets): 2 bits － RSVD:(Reserved): 2 bits － PDU Type: 4 bits, Used to describe the type of message being transported － SN (sequence number) 24 bits SAAL處理過程 SNPDUTYPERSVDPLPAD(03B)Information(0~65,535B)User data(0~65,535B)SAPSAPCPCS SublayerSAR SublayerATM LayerCPCSPDUSARPDUATM CellInformation Field(48 bytes)2 bits 2 bits 24 bits4 bitsHeader(5 Bytes)43 MPEG2 Transport stream over ATM 188byte PacketsAAL5 PDU (8byte Trailer added)8 840 5 48 5 48 5 48 5 48 5 48 5MPEG2 Encoderor Video ServerMPEG2 Transport StreamATM Cells Transported across ATM Nework(5byte ATM Cell header Added)
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