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6 ADSL NETWORK ARCHITECTURE,PROTOCOLS,AND EQUIPMENT the UNI signaling message or by convention (e.g.,odd VPI/VCI for fast path; even for interleave path)has yet to be determined by the ADSL or ATM Forums Once the latency path mapping has been determined,a new ATM layer function must assign each cell to be transmitted to the designated latency path. The VPI/VCI in each cell becomes an index to a 1-bit lookup table that specifies the correct path(ADSL channel).In addition to selecting a latency path for user data,one must also be assigned for both signaling and ILMI(ATM access via SNMP)messages.If we have dual latency downstream and single latency upstream,which downstream path should be selected for these control and management protocols?This assignment has yet to be standardized. In a dual latency environment,the ability to reassign bandwidth from one latency path to another after modem startup is known as rate repartitioning (RR).Since bandwidth usage is not static,RR would be highly desirable.It is optional in T1.413-II,and specified in informative Annex K.However,the means for the ATM layer to request RR and notify of its completion has yet to be standardized (see WT-21 open issues in Section 2.6). 2.5 UNIQUE ADSL REQUIREMENTS FOR ATM Many of the ATM over ADSL issues are addressed in ADSL Forum WT-21 [ADSLF,1998]: Specific reference models:functional blocks and interfaces Transport of ATM over ADSL,including the problems presented by dynamic rate change: DRA and RR (dual latency mode)for full-rate ADSL (T1.413 and G.992.1) Fast retrains and full retrains/restart for G.992.2 .QOS and traffic management Functional block definitions ATM Forum and ITU-T signaling (for SVCs) Management:including use of OAM cells according to ITU Recommen- dation I.610 ATM virtual circuit assignment ·Annexes on Relationship to other reference models Standards work cross reference SVC call load analysis ATM VP/VC assignment in dual latency mode 5 None of the commercially available ATM SAR chips has this capability today:they will need to be modified for dual latency full-rate ADSL. !"# $%&' ( ) $% ' ' $ * +, -' . !"# / ' ' #% $% "% ) ' ) ' )) ' 0$ 1 ' ) ' - ) 23452563247478979: ;; " )' ;;)' $+<+=, . *>?) $% @';; 1A$,B+ ' " BC DEF GHIJGKLMNOPKJGIPKQKHRNSTP LRQ % $% !"#' !"#&' A$,B+ U !"#&+VVWXY Z " . Y ' - Z $ $% !"# ' Y Z !; ;;' ' , !"#$+<+= [VVB+ Z & ' [VVBB Z \(" . Z &' -. Z $% &' $,$ " Z % Y ' ' ( % $; , C+] Z $% ' ' Z * Y Z ; Z " )- Z " Z $% ' / $%" ; ) . ' ' , !"# ^_ `abcdefghij`iklmfekfnieopihfhkhcbo`daeqnmpredf