ATM END-TO-END NETWORK ARCHITECTURES AND PROTOCOL STACKS 3 2.3.1 New Equipment Needed for ADSL In addition to the ADSL central site and remote site modems.the key new network infrastructure equipment required to make ADSL a commercial reality is the digital subscriber-line access multiplexer (DSLAM).This equipment aggregates a large number of ADSL subscribers into one or a few uplink ports to a frame relay or ATM backbone network (edge switch or router).The uplink interface is formally known as the V reference point.It is typically a DS3/E3 facility,but could also be n x DS1/E1 with inverse multiplexing,or even SONET OC3c/STM-1 (155 Mbit/s). NOTE:The architecture of the DSLAM may determine the entire design of the ADSL network.Some DSLAMs handle only ATM over ADSL (e.g.,Alcatel); others support a variety of DSLs with both ATM and frame-based transport(e.g., Ascend). The DSLAM acts as a VPI/VCI cross-connect for PVCs (the VPI/VCI "labels"have only local significance for a particular point-to-point ATM link). It must aggregate traffic from ADSL links and map to uplink.Conversely,the DSLAM must distribute traffic from the uplink to the appropriate ADSL port (more than one,if multipoint virtual circuits are supported).UPC/policing of ATM traffic contracts will also be required in the DSLAM. For SVCs,UNI signaling messages could be passed transparently through the DSLAM in configurations known as virtual UNI and SVC tunneling.However, there are major problems with these methods that will greatly restrict their use. More likely,the DSLAM will terminate UNI signaling messages(as the network side of the UNI)and map them over the V reference point,as either the user side of the UNI or an access node-to-node interface (ANNI).In this scenario, there are independent signaling state machines,each of which has intimate knowledge of the link(s)to which they are connected.Hence connection admission control(CAC)and QoS parameter negotiation can be done properly at call setup time. With the great interest in PPP over ATM,there is a perceived need for new adjunct equipment(behind the DSLAM)for concentrating or terminating PPP sessions at the boundary between the network service provider (NSP)and the access network:for example,either an L2 access concentrator (LAC)or a broadband access server(BAS).The LAC concentrates multiple PPP sessions into a smaller number of PVCs to the NSP's broadband network.The BAS terminates the PPP sessions and probably handles authentication,billing,and security functions (if needed).The LAC and BAS may be colocated with the DSLAM in a central office,or many DSLAMs can be connected to a single LAC/ BAS.It is expected that one or the other of these adjuncts will be deployed in either an access provider or ISP network. The formal specification of these and other network equipment adjuncts will be done by the ADSL Forum under core network architecture.￾   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`abcde59??=73?4Ff- P &*  & & )g&1&I' )(- ( ) (-''H& ',& (&% &/( F D& '+ ',* "#$!D-'' &) ]S(H'H) ((H (C(  -&+ ( . ]SE)1 )P & J& . & % 1*(  & /( & ( . ]S&6;;=88?h2=>5h>?h2=3?5=<i6;=C!SSEF((% &*  & &  1  (H'H( )% (* %.-%() +-' H . '+C(E-% ,& % % Ff % ;h??=;53h? 62@3883h?;h?5<h7CT!TEj#1&)  & H%I  1&1 &', %''( /1) F k H&  & (YYYP &!GD* & (1 &% P  .& - g/% 0/1) CI  "#$!DE.&%% &H& &)HYYY ( ((( I/&,I -   -&+( &P% 1&P &CS#YE %% (( -&+W.& Q)1' *  &lm6;;=88;h?;=?5<65h<C$!TE& :<h62:6?26;;=888=<_=<Cn!#EFG $!T%% & ()/'1' YYY( ((( ()'' &/)I &.YJT( S#Y[(I&I -&+FG n!#  &) ( YYY( (((1&II',' (/ %*I''H* ( %/&,./%(C.  EFG $!Tn!#),I %'% - "#$!D% &'.\% *&),"#$!D(%I % % (H' $!TL n!#F( Q1 %  &  &. ( g/%(-''I  1',   &%% ((1&P &&#Y -&+F G .&)'(1 %\%. (  & -&+ 0/1) g/%(-'' I  I, !"#$^&/)/ &;h<=?=5oh<p6<;q35=;59<=F rst uvwxsyxuvwvuszy{|r{}~su}s€{urvw‚{ysy}yƒsr}|