4.2 Cng ngh PPPoEPPPoE Point-to-point Protocol (PPP) over Ethernet Protocol. PPP l giao thc dng vn chuyn Internet ti ISP dc theo cc kt ni Moderm v ISDN. PPP kt hp cht ch cc yu t xc thc kim tra tn/mt khu v l l do chnh m ngi ta dng PPP vi ADSL. Mc d BRAS thc thi giao thc PPP v tin hnh vic xc thc, nhng thc ra vic c thc hin bng cch truy nhp vo cc c s d liu khch hng ti ISP. Bng cch , ISP bit c rng cc kt ni do BRAS nh tuyn ti c xc thc thng qua giao dch vi c s d liu ring ca ISP.4.2.1 Tng quan PPPoE l mt giao thc c hnh thnh bi s ng gi d liu ca gi tin PPP trong gi tin Ethernet. PPPoE gm hai giai on Discovery stage v PPP Session stage:a) Ti sao li c giai on Discovery stage ny:PPP l giao thc ng gi d liu truyn gia hai im Point to Point, trong khi mi trng Ethernet gi tin c rt nhiu im n nn giai on ny nhm xc nh im n duy nht cho gi tin PPP.b) Cch thc hot ngGi tin Ethernet bao gm cc thnh phn: DESTINATION_ADDR, SOURCE_ADDR, ETHER_TYPE, PAYLOAD, CHECKSUM. Ban u v cha xc nh c im truy cp ca nh cung cp dch v nn client s thc hin giai on discover xc nh im n bng cch gi gi tin Ethernet vi SOURCE_ADDR l a ch broadcast. PPPoE client s nhn c s tr li ca nhiu Server v s chn 1 thc hin kt ni PPP (PPP session stage). Sau khi PPP Session thit lp th PPPoE client v server s lin lc vi nhau qua 1 interface o c to trn my client.4.2.2 Qu trnh xc thc trong dch v ADSL/ADSL2+ Modem-------DSLAM--------BRAS---------ISPChc nng ca cc phn t khi tham gia vo qu trnh xc thc user: Modem: PPPoE client DSLAM: PPPoE forwarding BRAS: PPPoE server RADIUS client Router DHCP server (nu dng BRAS pht a ch cho modem) RADIUS server: AAA Billing server: traffic -> moneyQu trnh xc thc: Khi mt user mun vo mng n s gi mt bn tin yu cu c kt ni n BRAS. Bn tin ny i ngang qua DSLAM s c DSLAM forward tip m khng can thip vo hoc c can thip vo thay i mt s thng s ty theo yu cu cu hnh (v d thay i a ch MAC ca modem, thm tag option 82 vo). Khi n BRAS, BRAS l mt PPPoE server cn modem l PPPoE client (ti mi modem u c phn yu cu nhp username v password). Ti y BRAS s c bn tin yu cu thit lp kt ni m modem gi ln (bn tin bc 1), ni s ly nhiu tham s trong c 2 tham s chnh dng xc thc username v password. Cc thng s ny (username v pw) s c BRAS chuyn n RADIUS server lm nhim v AAA (xc thc, phn quyn, tnh cc). Lc ny BRAS ng vai tr l RADIUS client ni chuyn vi RADIUS server. RADIUS server s kim tra trong CSDL ca mnh (tc l cc thng s lin quan n khch hng khi ng k dch vu), CSDL thng l Oracle: Nu xc thc username v pw sai, hoc n cc th s khng vo c mng. Nu xc thc OK th RADIUS server s bo cho BRAS bit l cho php thit lp PPP section, ng thi s cp pht cho modem mt a ch IP public ra internet. BRAS s gi bn tin thit lp PPP tunel xung modem c km theo a ch IP, ng thi n cng s gi cc trng start time, stop time,cho RADIUS bt u m lu lng ca user. Mt ci na khng th thiu l BRAS s lm vic nh mt router bin (Edge router) nh tuyn a ch ny ra theo internet theo chnh sch ca ISP.RADIUS server s c kt ni vi Billing server tnh cc t lu lng ra tin