SIP and IMS Enabled Residential Gateway

Sergio Romero Telefónica I+DJan Önnegren Ericsson ABAlex De Smedt Thomson Telecom

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Index

Introduction

Existing issues SIP & the CPN 3GPP vs IETF SIP

Proposed architecture SIP B2BUA Auxiliary file and DBs Complete architecture

Functional examples

Conclusions

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Introduction

IP multimedia services are becoming more and more demanded by residential users. Within this scenario: SIP protocol has been designed for controlling IP multimedia

sessions and is talented to replace previous signalling protocols like H.323 or the aged SS7

IMS has been presented as the framework able to provide a better service provisioning and control for IP multimedia services in a NGN architecture

the CPN needs to be “SIP&IMS-friendly”

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Existing issues – SIP & the CPN

Legacy terminals do not support SIP Legacy terminals (e.g. POTS or DECT phones) need a terminal adapter to

translate dated signalling protocols and to act as SIP UA

Private IP addressing at the CPN NA(P)T binding mechanisms at the RGW do not take into account that

SIP messages take transport address information in their payload. To provide an effective NA(P)T traversal solution other techniques must be applied (e.g. STUN, ICE, or ALG)

Traffic blocking at the RGW Firewall at the RGW needs to be configured to open signalling and media

ports (e.g. 5060/UDP for SIP signalling and 8000/UDP for RTP media)

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Existing issues – 3GPP vs IETF SIP

SIP profile 3GPP specifies a greater number of

compulsory messages 3GPP requires a greater number of

compulsory headers and has its own private headers (P-Headers)

SIP UA 1 IMS Core SIP UA 2

INVITE

INVITE100 Trying

100 Trying

183 Session Progress

183 Session Progress

PRACKPRACK

200 OK200 OK

200 OK200 OK

UPDATEUPDATE

180 Ringing180 Ringing

ACKACK

200 OK200 OK

INVITE tel:+1-212-555-2222 SIP/2.0Via: SIP/2.0/UDP [5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp;branch=z9hG4bKnashds7Max-Forwards: 70Route: <sip:pcscf1.visited1.net:7531;lr;comp=sigcomp>, <sip:scscf1.home1.net;lr>P-Preferred-Identity: "John Doe" <sip:user1_public1@home1.net>P-Access-Network-Info: 3GPP-UTRAN-TDD; utran-cell-id-3gpp=234151D0FCE11Privacy: noneFrom: <sip:user1_public1@home1.net>;tag=171828To: <tel:+1-212-555-2222>Call-ID: cb03a0s09a2sdfglkj490333 Cseq: 127 INVITERequire: sec-agreeSupported: precondition, 100rel Proxy-Require: sec-agreeSecurity-Verify: ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; ealg=aes-cbc; spi-c=98765432; spi-s=87654321; port-c=8642; port-s=7531Contact: <sip:[5555::aaa:bbb:ccc:ddd]:1357;comp=sigcomp>Allow: INVITE, ACK, CANCEL, BYE, PRACK, UPDATE, REFER, MESSAGEContent-Type: application/sdp Content-Length: (…)

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Existing issues – 3GPP vs IETF SIP

Identities and security mechanisms 3GPP terminals require an ISIM application that stores public

identities (IMPUs), but also the private identity (IMPI) and the authentication key that are used during the complex Digest AKA mechanism. IETF RFCs only provides an HTTP Digest based authentication mechanism

3GPP uses IPsec ESP to provide integrity and confidentiality between the terminal and the IMS core . IETF RFCs do not cover the establishment of any kind of SAs

IMS Subscription

IMPI

Default IMPU#1

IMPU#2

IMPU#5

IMPU#4

Service Profile B

Service Profile A

Service Profile D

IMPU#3

Service Profile C

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Proposed architecture – SIP B2BUA

Definition A B2BUA is a signalling control and handling entity that after

receiving a SIP request/response can reformulate and send it out as a new request/response according to some given rules

A SIP B2BUA is able to manage and monitor the entire session state and parameters

Signalling handling and control

SIP UA SIP UA

Dialog #1

SIP UA SIP UA SIP UE SIP UE SIP UA

Dialog #2

SIP B2BUA

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Proposed architecture – SIP B2BUA

NA(P)T and firewall support For signalling flows, a B2BUA can change when necessary the IP

addresses and ports in the incoming or outgoing SIP messages For media streams, a B2BUA can interact with the NA(P)T

mechanism to provide the required bindings In both cases, a B2BUA can ask the firewall to open the required

ports

QoS assurance The B2BUA can obtain from the SDP payload what codecs are

going to be used in a multimedia session and interact with the CAC to check if there are enough resources to support the session

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Proposed architecture – SIP B2BUA

SIP interworking The B2BUA can generate, drop or modify different SIP messages

in order to provide the required interoperability between a 3GPP network and those SIP UAs located at the CPN that only can understand the simpler IETF SIP profile

The B2BUA is able to use the information stored in an ISIM to be authenticated against the IMS network and it also can establish the required SAs

Multimedia PBX The B2BUA can forward any SIP message at any time according

to some rules. Hence, it is able to route all the incoming and outgoing SIP calls as a traditional PBX

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Proposed architecture – Routing File

Routing File Rules to control the multimedia sessions that are managed by the

RGW. According to them, the B2BUA decides how outgoing or incoming sessions must be routed

<cpl> <incoming> <time-switch> <time dtstart=“20070703T090000” duration”PT8H”> <location url="sip:my_secretary@telefonica.es"> <proxy/> </location> </time> </time-switch> </incoming></cpl>

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Proposed architecture – Auxiliary Databases

Credentials DB Local credentials that must be used

at the registration to authenticate home users against the B2BUA

Location DB Location information (bindings of

contact addresses and SIP URIs) used by the B2BUA to route the messages

Local Credentials: Users’ credentials for

SIP services [AoR, Username,

Password]

Location Info: Addresses of registered SIP

devices [Contact Address,

AoR]

Location DB

Credentials DB

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Proposed architecture – Auxiliary Databases

Service DBA. General B2BUA parameters

like status, supported SIP methods, etc.

B. SIP and IMS services parameters like servers addresses, listening ports, global credentials, etc.

This DB can be remotely managed via TR-069 by extending TR-098 data model

InternetGatewayDevice.B2BUA.SIPService.{i}.

Service parameters required for accessing a concrete SIP service

GlobalAoR User's identity for the corresponding SIP network. This address will be included in the location database of the service provider.

AuthenticationMethod HTTP Digest authentication or none authentication required for accessing the service provider network.Values: “None”, “Digest”Default: “Digest”

DigestUsername Username for digest authentication.

DigestPassword Password for digest authentication.

RegistrationPeriod Period over which the registration must be refreshed, in seconds.

RegisterExpires Register request Expires header value, in seconds.

ProxyServer Host name or IP address of the SIP proxy server.

ProxyServerPort Destination port when connecting to the SIP proxy server.Values: [0,65535]Default: 5060

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Proposed architecture – Signalling handling

SIP/IMS Handling and Control Routing & Control module modifies the

SIP signalling (according to the routing rules), and can interact with the CAC, the NA(P)T and the Firewall

SIP/IMS Interworking module adapts different SIP profiles and uses the IMS identities (IMPI and IMPUs) and the key stored in the ISIM

SIP/IMS Interworking

Routing & Control

IMS B2BUA

SIP UA SIP UA

ISIM

Credentials DB

Routing File

CAC, NAT, Firewall

IMS-Enabled RGW

SIP signalling

Other interactions

SIP/IMS Handling and Control

Service DB

Admin Service Provider

Location DB

TR-069

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Proposed architecture – General scenario

RGW

IETF SIP UE

IMS UE SIP UA

SIP UA

IMS B2BUA

Non-SIP UE SIP UA

Sign Conv TA SIP/IMS Handling and Control

No Security Association

Security Association

ISIM

IMS server(s)

P/I/S-CSCF

IMS UE SIP UA

ISIM

LAN WAN

FXS POTs or DECT BS

SIP UA

Sign Conv TA Sign Conv

SIP UA TA

FXO

CAC, NAT, Firewall

IETF SIP server(s)

SIP Server

IETF SIP UE

SIP UA

PSTN

Credentials DB

Routing File

Service DB

Location DB

SIP UA SIP UA

ISIM

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Functional examples – IMS registration

REGISTER

401 Unauthorized

REGISTER

REGISTERREGISTER

IMPIAuthentication

DIAMETER

401 Unauthorized401 Unauthorized

REGISTERREGISTER

200 OK200 OK

Waiting for firstlocal registration

Step 1

Step 2

Step 3

IETF SIP Profile 3GPP SIP Profile

S-CSCF AssignationDIAMETER

REGISTER

401 Unauthorized

Locate S-CSCFDIAMETER

REGISTER

User ProfileIMPU Registration

DIAMETER

200 OK

200 OK

SIP TerminalIMS RGW

B2BUA P-CSCF I-CSCF HSS S-CSCF

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Functional examples – IMS session

INVITE

200 OK

3GPP SIP ProfileIETF

SIP Profile

INVITE

100 Trying

100 TryingINVITE

INVITEINVITE

100 Trying100 Trying

100 Trying

183 Session Progress

183 Session Progress

183 Session Progress

PRACK

QoS Reservation

PRACKPRACK

PRACK

200 OK200 OK

200 OK

UPDATEUPDATE

UPDATEUPDATE

200 OK200 OK

200 OK200 OK 180 Ringing

180 Ringing180 Ringing

180 Ringing

PRACKPRACK

PRACKPRACK

200 OK (PRACK)

200 OK (INVITE)200 OK (PRACK)

200 OK (PRACK)200 OK (PRACK)

200 OK (INVITE)200 OK (INVITE)

200 OK (INVITE)

200 OK (INVITE)

ACKACK

ACKACK

ACK

Authorize QoS

Authorize QoS

183 Session Progress

QoS Reservation

180 Ringing

RTP

SIP Terminal

IMS RGWB2BUA P-CSCF S-CSCF I/S/P-CSCF IMS Terminal

IMS network #1 IMS network #2

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Conclusions

The proposed architecture pushes the incorporation of the CPN to the IMS/NGN...

It contributes to ensure the viability of the multimedia sessions interacting automatically with other blocks of the RGW

It provides a total control of the ongoing multimedia sessions to the RGW administrator

It is able to adapt the signalling and the security mechanisms to fulfil 3GPP requirements