GTP Overview

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LTE:Afeaturebasedintroduction

LTECoreFeatures

Annex.GTPPrimer

Irfan Ali

Video at youtube: https://www.youtube.com/watch?v=FPfExr9bEEg&list=PLgQvzsPaZX_bimBc5Wu4m6-cVD4bZDav9&index=9

Irfan Ali 2İki Teknoloji 2

WhatisGTP?

• GTP=GPRSTunneling Protocol

• WhatisTunneling intheIPWorld?Ø TunnelingintheIPworldmeansputtinganIPpacketinsideanotherIPpacket.

IP_src -> IP_dst PayloadIP_a->

IP_b

InnerIPPacket

OuterIPPacket

GPRS General Packet Radio Service


WhatisthepurposeofGTPTunneling?

• RouteanIPpacketalongapaththatisnottopologicallycorrectforthepacket.

Mehmet’s IP address46.1.78.189 ->10.40.40.12 Internet

S-GW

P-GW

eNB

Ayse

Mehmet

10.10.10.1

10.10.10.2

10.10.10.0/24

10.10.20.1

10.10.20.0/24

10.10.20.2 GTP

Tun

nel

IP_sgw -> IP_enb

UDP_dst=2152

TEID_x

IP_pgw -> IP_sgw

IP

UDP_dst=2152

UDP

TEID_k

GTP-U header

Mehmet’s IP address10.40.40.12

DHCP

GTP is IP-in-UDP Tunneling

HiIP_a -> IP_m

HiIP_a -> IP_m

HiIP_a -> IP_m

HiIP_a -> IP_m


HowdoestheGTP-UTunnelgetsetup?

• GTPProtocolhastwopartsØ SignalingpartcalledGTP-C(GTP-Control)Ø UserdatapartcalledGTP-U(GTP-User)

• GTP-CisusedtosetupGTP-Utunnel• BothGTP-CandGTP-UrunontopofUDP• IP-in-UDPtunnelingisonlyusedforGTP-U• GTP-Ccarriescontrol/signalingmessages

IP_pgw -> IP_sgw

IP_a -> IP_m

UDP_dst=2152

TEID_a IP_pgw -> IP_sgw

UDP_dst=2123

TEID_k

IP UDP GTP-U header IP UDP GTP-C

header

GTP-C message


SGW PGW

TEID

21232123

2152

TEID

IPc,sgw

2152

IPu,pgwIPu,sgw

TxRx Tx Rx

TEIDTEID

TxRx Tx Rx

TEIDas

TEIDbs

TEIDcs

IPc,pgw

SGW PGW

TEID

2123

2152

2123

2152

TEID

IPc,sgw

IPu,sgw

IPc,pgw

IPu,pgw

TxRx Tx Rx

TxRx Tx Rx

TEIDTEID

HowdoesGTP-UTunnelgetsetup:Example

TEIDas

TEIDas

0

C.S. Req (IMSIa, C: IPc,sgw,TEIDas, EBID5:IPu,sgw,TEIDas) C.S. Rsp (C:IPu,pgw,TEIDap,

EBID5:IPu,pgw, TEIDxp)

TEIDbs

TEIDcs

TEIDap

TEIDbp

TEIDcp

TEIDap

TEIDbs

TEIDcs

TEIDbp

TEIDcp


PacketTrace:CreateSessionRequest(S11);MME->SGW

MMESGW/PGW

0

212321230x1

eNBSGW/PGW

21522152

S11

S1U


PacketTrace:CreateSessionResponse(S11);SGW->MME

MMESGW/PGW

212321230x1

eNBSGW/PGW

21522152

S11

S1U

0x80..01

0xc0..1


PacketTrace:ModifyBearerRequest(S11);MME->SGW

MMESGW/PGW

212321230x1

eNBSGW/PGW

21522152

S11

S1U

0x80..01

0xc0..1

0x800..001

0x3ea


PacketTrace:GTP-U:S1-U;eNB ->SGW/PGW

eNBSGW/PGW

21522152

S1U

0x010000

UE Server10.255.1.111 10.0.0.10010.1.2.11 10.1.1.12

TxRx Tx Rx


PacketTraceGTP-U:S1-U;eNB <- SGW/PGW

eNBSGW/PGW

21522152

S1U

0x010000

UE Server10.255.1.111 10.0.0.10010.1.2.11 10.1.1.12

TxRx


GTPPathandPathManagement

• Pathisbetweentwoendpoints.EachendpointisIP_address+UDP_Port#

• TherecanbeseveralGTPtunnelsonapath(eachwithdifferentTEIDs).

• Thereistypicallya“softwareprocess”thatbindstoeachend-point.

• PathManagementmessages:Toensurethatapathisalive(boththephysicallinkandprocessattheendpoint),periodicecho-request andecho-response aresent.

• Failure-detectionanderror-recoverymechanismsaredefined.

SGW PGW

TEID

2123

2152

2123

2152

TEIDas

TEIDbs

TEIDcs

TEIDxs

TEIDys

TEIDzs

TEID

IPc,sgw

IPu,sgw

IPc,pgw

IPu,pgw

TxRx Tx Rx

Path

Path


PacketTraces:GTP-UEcho-request&EchoResponse

In GTP-Cv2 Echo request/response messages

do not contain TEID field

In GTP-Cv2 Echo request/response messages

do not contain TEID field


InterfacesonwhichGTPisused

• GTP-Cv2isusednotonly formobilitymanagement,butalsoforgeneralsignalingpurposes, eg providing UE’scellinformation tothePGWandfromtheretooperator’sservicenetwork.

Internet

MME

S-GW

P-GWHSS

eNB

UE’s IP address

S1-MME

S11

S6a

S5

S1-UMME

S10

S1AP

GTP C

GTP C


Specifications

• GTPCv2 TS29.274• GTPUv1 TS29.281

• GTPCv1 TS29.060

• Historically(beforeRel-8,i.e.before2009Q1),TS29.060usedtobethekeyGTPspecification(bothGTPCv1andGTPUv1).ButsinceRel-8,TS29.060isonlyapplicableto3Ginterfaces(Gn/Gp,betweenSGSN<->GGSNandbetweenSGSNs)andnottoEPCinterfaces.ItsspecificationonlyappliestoGTPCv1Ø Ignoreanythingthat29.060saysaboutGTPU.

İki Teknoloji 15

Annex


RulesforGTP-CIPaddressandportnumbers• Threetypesofmessages

• RulesforPort#andIPaddresses

Ø InitialMessage:1. TheUDPDestination PortnumberforGTPv2Initial messagesshallbe21232. TheUDPSourcePort foraGTPv2Initialmessageisalocallyallocatedport number.3. Duringtheestablishment oftheGTPtunnel, theGTPv2entityselectsandcommunicates tothepeerGTPv2entitytheIPDestination Addressat

whichitexpects toreceivesubsequent control planeInitialmessagesrelatedtothatGTPtunnel viathe "SenderF-TEIDforControl Plane"IE

Ø Triggeredmessage1. TheIPSourceAddressofaGTPv2TriggeredmessageandforaTriggeredReplymessageshallbecopied fromtheIPdestination addressofthe

messagetowhich thisGTPv2entityisreplying2. TheIPDestination AddressofaGTPv2TriggeredmessageandforaTriggeredReplymessageshallbecopied fromtheIPSourceAddressofthe

messagetowhich thisGTPv2entityisreplying3. TheUDPSourcePort ofaGTPv2TriggeredmessageshallbethevaluefromtheUDPDestination Portofthecorresponding messagetowhich

thisGTPv2entityisreplying4. TheUDPDestination Port valueofaGTPv2Triggered messageshallbethevalueoftheUDPSourcePort ofthecorresponding messagetowhich

thisGTPv2entityisreplying

Ø TriggeredReplymessage1. Samerulesastriggeredmessage.

• RulesforTEID#Ø Thefirst CreateSession RequestmessageonS11foraUEshallhaveTEID=0x0Ø The(firstandsubsequent) CreateSession RequestmessageonS5foraUEshallhaveTEID=0x0

GTP-C Peer A

GTP-C Peer B

Initial Message

Triggered Message

Triggered Reply Message

Technology

GTP Overview