Voice Call in LTE

Contents

LTE - Registration/Establishment of EPS bearer

SIP/VoIP call flows

SIP messages

Packet filter

LTE Network Attach

UE MME

Attach ReqPDN Connectivity Req

Network Registration

Est Default Bearer

Ready for service PDN address

assigned

Attach AcceptActivate Default EPS Bearer Context Req

Attach CompleteActivate Default EPS Bearer Context Accept

Dedicated EPS Bearer Setup

UE MME

Bearer Resource Modification Request

-QOS, Agg TFT for APN

Activate Dedicated EPS Bearer Context Req

- QOS, TFT, BearerId

Creates additional bearer with

QOS- QCI, MBR, GBR

TFT Bearer Id Agg TFT for APN – All

Packet filter for APN, media Auth token

Activate Dedicated EPS Bearer Context Accept

IMS – IP Multimedia System

Architectural framework for delivering Internet Protocol (IP) multimedia services

Designed by 3GPP,to evolve mobile networks beyond GSM

Isolates Access network from Service layer Aids fixed mobile convergence (FMC)

Uses IETF protocols for control functions SIP, SDP, RTP

SIP - Session Initiation Protocol

SIP – Session Signaling create, manage and terminate sessions in an IP

based network.

SDP – Media Signaling RTP – carries compressed voice 2 streams one in each direction

Signaling and Media can be on different paths

SIP - Advantages

Intelligence in end devices

Networks simple and robust

Adding a new SIP application does not take change to network infrastructure

SIP servers relay any application requests they receive

Key components of SIP network

SIP Phones (User-Agents)

SIP Servers (registrar+proxy+redirect; usually combo)

SIP PSTN gateways

Applications servers (such as media servers)

IMS VoIP Call: Preamble

Assuming Access Network is LTE

LTE Network Attach - Default EPS bearer activation, - UE gets IP address

Create Dedicated bearer for SIP signaling

SIP Registration Different from LTE NW Registration SIP UA Identity, reachability, contact

SIP Media Session

UE #1 P-CSCF #2 UE #2

Invite

100 Trying

183 Progress

RTP/RTCP

P-CSCF # 1IMS CN Entities

Invite Invite Invite100 Trying 100 Trying 100 Trying

183 Progress

183 Progress

Authorize QOS

Authorize QOS

Establish Bearer

EstablishBearer

PRACK PRACK

200 OK200 OK

Update Update

200 OK200 OK

183 Progress

180 Ringing

200 OK180 Ringing

200 OK

180 Ringing

200 OK

180 Ringing

200 OK

ACK ACK ACKACK

12

4

3

56

1.SIP Invite (Origination)

INVITE tel:+1-212-555-2222 SIP/2.0 From: <sip:user1_public1@home1.net>;tag=171828 To: <tel:+1-212-555-2222> Call-ID: cb03a0s09a2sdfglkj490333 Cseq: 127 INVITE

c=IN IP6 5555::aaa:bbb:ccc:ddd m=audio 3456 RTP/AVP 97 a=rtpmap:97 AMR a=inactive

2.SIP Invite (Termination)

INVITE tel:+1-212-555-2222 SIP/2.0 From: <sip:user1_public1@home1.net>;tag=171828

To: <tel:+1-212-555-2222>

Call-ID: cb03a0s09a2sdfglkj490333

Cseq: 127 INVITE

P-Media-Authorization: SOME HEX TOKEN

c=IN IP6 5555::aaa:bbb:ccc:ddd m=audio 3456 RTP/AVP 97

a=rtpmap:97 AMR

a=inactive

3 & 4. 183 Progress

SIP/2.0 183 Session Progress

From: To: <tel:+1-212-555-2222>;tag=314159 Call-ID: CSeq: Require: 100rel, precondition P-Media Authorization: Some Hex token

c=IN IP6 5555::eee:fff:aaa:bbb t=0 0 m=audio 6544 RTP/AVP 97 a=inactive a=rtpmap:97 AMR

5 & 6. Establish EPS Bearer

Info available Media Auth token Destination Address:Port Source Address:Port

Specify these in TFT IE UE request EPS bearer activation Could use this bearer for both send and recv

5. Bearer Activation Complete

Send Update UPDATE <sip:[5555::eee:fff:aaa:bbb]:8805;comp=sigcomp

From: <sip:user1_public1@home1.net>; tag=171828

To: <tel:+12125552222> tag=314159

Call-ID: cb03a0s09a2sdfglkj490333

Cseq: 129 UPDATE

c=IN IP6 5555::aaa:bbb:ccc:ddd

m=audio 3456 RTP/AVP 97 96

a=curr:qos local sendrecv

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=sendrecv

a=rtpmap:97 AMR

6.Bearer Activation Complete

200 OK (response to UPDATE) SIP/2.0 200 OK

From: <sip:user1_public1@home1.net>;tag=171828

To: <tel:+12125552222>;tag=314159

Call-ID: cb03a0s09a2sdfglkj490333

Cseq: 129 UPDATE

Content-Type: application/sdp

c=IN IP6 5555::eee:fff:aaa:bbb

m=audio 6544 RTP/AVP 97 96

a=curr:qos local sendrecv

a=curr:qos remote sendrecv

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=rtpmap:97 AMR

Handling IP Packets > 1 Dedicated EPS Context

Each EPS context is associated with a QOS & TFT Default EPS context not attached withTFT

Identify IP packets for a particular EPS context

Packet inspection, Match parameters against TFT packet filter setup for a EPS context Use matched EPS Context for that packet > 1 Packet filter per EPS context

On UL UE does this

On DL PDN-GW does this.

Packet Filter Contents Evaluation Precedence

Src & Dest Address and Subnet mask

Protocol Number(IPv4)/Next Header (Ipv6)

Destination Port Range

Source Port Range

IPSec Security parameter Index

TOS/Traffic Class and Mask

Flow label Ipv6

Atleast one of attribute present

Example UE #1 UL PF

Beared Id #3: Precedence:2

Addr 5555::eee:fff:aaa:bbb/120

Port Range: 6544-6545

Bearer Id #2: Precedence:1

Addr: P-CSCF/120

Port Range: 5060-5060

UE #1 DL PF

Bearer Id #3: Precedence:2

Addr: 5555::aaa:bbb:ccc:ddd/120

Port Range: 3456-3457

Bearer Id #2: Precedence:1

Addr: 5555::aaa:bbb:ccc:ddd/120

Port Range: 5060-5060

IP packet inspection Check header UL IP packet, Pickup dest and

source fields from IP header Compare with packet filter using

precedence Found match, use DRB id to

route this packet. Here, Only Dest Addr & Port

used. Src is don’t care.

Packet Filter Interfaces

Message based Interface specs Static binding

Functionality Store TFT to EPS

Bearer Id Map Deep packet

inspection to find bearer id

No match-use default EPS bearer.

PacketFilter

To PDCP:Bearer Id, Packet

From AP: IP Packet

From ESM: TFT, EPS Bearer

Packet Filter

Set of associative maps – container/storage

Match using Evaluation precedence

Extract src/dest IP addr & port # from IP packets

Dynamic View Single thread, wait on Q Process message

Reference

3gpp: TS 36.300, 24.008, 24.301, 23.228

3gpp: TS 24.229

3gpp: TR 24.930

RFC 3261, 3311, 3313, 4566