9.7.1. Mt phng ngi s dng, UP T gc mng khng dy (bao gm c mng li v mng truy nhp) mt phng khng ch gm s liu ca ngi s dng nh cc gi thoi hoc ni dung Web m cn c cc bo hiu lin quan n dch v ng dng nh SIP hay RTCP. Mc d c coi l thng tin iu khin ca cc lp ng dng, bo hiu mc cao c truyn qua mt phng ngi s dng. Mt phng ngi s dng u cui u cui c m t trn hnh 9.20 t thit b u cui n server ng dng. Trn hnh v ny ta thy lp ng dng ch tn ti trong thit b u cui v server ng dng v c xy dng da trn truyn ti IP. Cc gi ng dng c nh tuyn qua P-GW trc khi n ni nhn. Trong th d ny, lp ng dng c th bao gm mt tp ln giao thc nh cc giao thc truyn ti u cui u cui (chng hn TCP hay UDP) v RTP (Real Time Protcol) truyn ti s liu cng nh cc giao thc bo hiu mc ng dng (SIP, SDP, RTCP,).

GTP-U (GPRS Tunnelling Protocol for User Plane: giao thc truyn tunel GPRS cho mt phng ngi s dng): truyn tunel s liu ca ngi s dng gia eNodeB v S-GW cng nh gia S-GW v P-GW. MME iu khin thit lp tunel mt phng ngi s dng v thit lp cc knh mang gia eNodeB v S-GW UDP/IP l cc giao thc mng ng trc c s dng nh tuyn s liu ca ngi s dng v bo hiu iu khin Hnh 9.20. Ngn xp giao thc mt phng ngi s dng L1 v L2 trn hnh v tng ng vi cc giao din vt l v lin kt s liu ca cc giao din ca mng c nh S1, S5 v SGi. i vi cc lp ny, chun EPS hon ton linh hot v a ra nhiu ty chn ph hp cc mng IP.

TS. Nguyn Phm Anh Dng Trong thi gian mt phin, nh tuyn gi t P-GW n UE c th phi tri qua nhiu thay i khi UE di ng: chng hn thay i eNodeB phc v, thay i S-GW c th xy ra khi truyn lung video hoc duyt Web. gii quyt di ng UE, c th s dng MIP hoc GTP. 3GPP chn gii php GTP. Cng ging nh MIP, mi khi eNodeB thay i nt phc v, cc nt phc v hay P-GW c cp nht v thit lp tunnel n nt phc v mi. Tt c cc gi IP cho UE u c ng bao trong mt giao thc c th EPC v c truyn tunnel gia P-GW v eNodeB n UE. Cc giao thc truyn tunnel khc nhau c s dng trn cc giao din khc nhau. Giao thc truyn tunnel c th 3GPP c gi l GTP (GPRS tunnelling Protcol: giao thc truyn tunnel GPRS) c s dng trn cc giao din S1 v S5/S8. Trong nh ngha ca 3GPP, truyn tunnel cho s liu ngi s dng c m bo bi lp GTP (GPRS Tunnelling Protocol: giao thc truyn tunnel GPRS) c trong chun 2G GPRS. Giao thc ny gm hai phn: Phn mt phng ngi s dng (GTP-U): m bo ng v tho bo s liu ca ngi s dng gia hai nt Phn mt phng iu khin (GTP-C): c s dng trong EPC m bo tt c cc th tc, cc bn tin qun l tunnel (thit lp, thay i v gii phong tunnel) v qun l v tr (trao i thng tin di ng ca ngi s dng gia hai nt). Hnh 9.21 cho thy cc ng bao ca GTP. Gi IP c b sung thm tiu GTP (cha cc s nhn dng u cui tunnel v s trnh t GTP PDU ty chn) pha thu c th nhn dng gi truyn lin quan n tunnel no. Gi c ng bao GTU c truyn gia hai im cui ca tunnel bng cc s dng ngn xp UDP/IP truyn thng.

Hnh 9.21. Qu trnh ng bao GTP (s dng IPv4 truyn ti GTP) Nu ly truyn s liu VoIP lm th d, gi IP gc c di khong 72 byte (gm 20 byte tiu IP, 8byte tiu UDP, 12 byte tiu RTP v 32 byte ting c m ha AMR 12,2kbps). Nh vy chi ph cho truyn tunnel GTP trn cc giao din truyn ti l 36 byte chim 33% ton b gi: qu ln. Tuy nhin ti phn v tuyn bc tranh ny hon ton khc. Khng cn truyn GTP tunnel na v cc tiu ca gi IP gc gim ng k nh nn tiu trong giao thc PDCP.

TS. Nguyn Phm Anh Dng Thit lp tunnel l mt b phn ca thit lp phin. i vi mt UE cho trc, mng to lp nhiu tp cc tunnel nh l cc knh mang EPS hay cc PDP context. Qu trnh truyn tunnel hon ton trong sut i vi u cui v server ng dng v mc ch ca n ch cp nht tuyn trung gian gia cc nt mng EPC v mng E-UTRAN. Ngn xp giao thc mt phng ngi s dng trn giao din v tuyn ca E-UTRAN trn hnh 9.21 c t m. N bao gm cc lp v lp con sau y: PDCP (Packet Data Convergence Protcol: giao thc hi t s liu gi): m bo nn tiu giao thc v thc hin mt m ho s liu RLC (Radio Link Control: iu khin lin kt v tuyn): chu trch nhim truyn s liu tin cy, lp con ca lp 2 MAC (Medium Access Control: iu khin mi trng): chu trch nhim lp biu v pht li nhanh, lp con ca lp 2 PHY: lp vt l.

Cc lp con ny u kt cui ti eNodeB. Ging nh m hnh OSI, giao din v tuyn ca E-UTRAN bao gm lp 1 truyn thng (lp vt l) c thc hin bi phn PHY, lp 2 (hay lp lin kt s liu) c h tr bi cc phn RLC v MAC. Vic phn tch lp 2 xut pht t s cn thit phi thit k mt m hnh linh hot v chung p ng c cc thay i v pht trin trong lp vt l. y l l do m cc chc nng lp 2 thun ty c lp vi cc kha cnh vt l ca giao din (chng hn truyn s liu tin cy v truyn gi theo th t) c t vo lp RLC ring, trong khi cc chc nng ph thuc mi trng (nh lp biu hay HARQ) li l mt b phn ca MAC.

9.7.2. Mt phng iu khin, CP

Mt phng iu khin (CP) tng ng vi cc lung bo hiu ca E-UTRAN v EPC. Chng hn CP bao gm tt c bo hiu RRC (Radio Resource Control) ca E-UTRAN ( h tr cc chc nng nh qun l knh mang v tuyn, di ng v tuyn v tm gi ngi s dng) v bo hiu NAS (Non Access Stratum) lin quan n cc chc nng v cc dch v c lp vi cng ngh truy nhp. NAS bao gm: EMM (EPS Mobility Management: qun l di ng EPS). Giao thc chu trch nhim x l di ng UE trong h thng vi cc chc nng nhp, ri mng v cp nht v tr (TAU: Tracking Area Update) trong ch ri. Lu rng chuyn giao trong ch kt ni c x l bi lp thp hn, nhng EMM ng vai tr tch cc li UE trong ch ri. EMM cn c cc chc nng khc nh nhn thc, bo v nhn dng UE (n nh nhn dng tm thi GUTI cho UE) v iu khin cc chc nng an ninh lp NAS nh mt m v bo v ton vn.

TS. Nguyn Phm Anh Dng ESM (EPS Session Management: qun l phin EPS). Giao thc ny c s dng x l cc knh mang gia UE v MME cng nh cc th tc qun l knh mang E-UTRAN.

Tm li EMM (EPS Mobility Management: qun l di ng EPS) v SM (Session Management: qun l phin) chu trch nhim cc th tc bo hiu gia UE v MME ca EPC cho phin v qun l knh mang, iu khin an ninh v nhn thc EPS. Hnh 9.22a m t ngn xp giao thc CP. hnh 9.22b m t ngn xp giao thc gia UE v MME. Ngn xp dng ti MME v cc giao thc mc nh kt cui ti MME.

a) Ngn xp giao thc CP ca LTE/SAE eNodeB

X2-AP

UEeNodeBNASS1X2RRCRRC-AP-AP

PDCPPDCPSCTP

RLCRLCIPMACMACL2

L1L1L1

LTE Uub) Ngn xp giao thc CP gia UE v MME

SCTP

IP

L2

L1

X2C

S1-MME

MME

NAS

S1-AP

SCTP

IP

L2

L1

GTP-C

UDP

IP

L2

L1

S10

NAS

RRC

PDCP

RLCMAC

L1

LTE UuUE

Chuyn tipRRCS1-APPDCPSCTP

RLCIP

MACL2

L1L1S1-MMEeNodeB

NAS

S1-AP

SCTP

IP

L2

L1

MME

NAS: giao thc NAS h tr cc chc nng qun l di ng v tch cc knh mang cua rmt phng ngi s dng SCTP: Stream Control Transmission Protocol: Giao thc truyn dn iu khin lung Hnh 9.22. Ngn xp giao thc mt phng iu khin.

TS. Nguyn Phm Anh Dng

Cc giao thc tng truy nhp trn giao din v tuyn c biu th bng vng t m. Cc lp thp hn thc hin cc chc nng ging nh i vi mt phng ngi s dng vi ngoi tr l khng c chc nng nn tiu trong mt phng iu khin. Giao thc RRC thuc lp 3 trong ngn xp giao thc tng truy nhp. y l chc nng iu khin chnh trong tng truy nhp, chu trch nhim thit lp cc knh mang v tuyn v lp cu hnh tt c lp di bng cch s dng bo hiu RRC gia cc eNodeB v UE. Cng nh UP, trn giao din v tuyn, CP s dng cng ngn xp PDCP, RLC v PHY truyn ti RRC v bo hiu NAS. RLC, MAC v PHY h tr cng cc chc nng cho c CP v UP. Tuy nhin iu ny khng c ngha l thng tin ca UP v CP c truyn nh nhau. Mt s knh mang v tuyn c th c thit lp gia UE v mng, mi knh mang tng ng vi mt s truyn dn, bo v v tuy v x l u tin c th.