Media and ISUP Signaling Transition for IMS and Next-Gen Networks

James Rafferty, Cantata TechnologyJraff@cantata.com

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Agenda

• Introduction: Networks in Transition• Needs for Translation

– Signaling– Media

• How Does it Work Now?• How will it Work in the IMS? • The Way Forward• Summary

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Introduction: Networks in Transition

• IP has excellent momentum in both carriers and enterprises

• Voice and other services will run over IP in the future• The transition is underway…

– But it will take many years

• SIP has won the IP standards war– But it needs to interwork with the current networks– Traditional circuit based signaling is still prevalent for both

landline and wireless networks

• IP Multimedia Subsystem has won mind share as a next-gen service architecture

– But implementations are still at the trial stage

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Network Evolution for Service Delivery

Network TraditionalTDM

TransitionHybrid

Next-GenIP

Architecture Centralized • Integrated Design

Open & distributed• TDM-IP Migration

Open & distributed• Pure IP (IMS)

Signaling/Functions SS7, ISDN, CAS SS7-SIP

ISDN-SIP

CAS-SIP

SIP-SIP

H.323-SIP

Media/Functions TDM – TDM“circuit to circuit”

TDM - IP conversion

“circuit to packet”

IP - IP

“packet to packet”

Applications • TDM enhanced services

• Discrete applications

• IP-based transport• SS7 services over IP• IP services over TDM• IP-enable/extend TDM

services

• Multimedia services on common service platform (IMS)

• Blended SIP services

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Needs for Translation

Signaling:• SIP is likely to be the protocol of choice for next generation IP

communications• It will need to interwork with other signaling methods

– Circuit: • SS7 network overlays for Intelligent Network services

– ISDN User Part (ISUP) for call control

– TCAP for Database Services like Caller ID

• ISDN PRI• Channel Associated Signaling (tonal)

– IP• H.323 was rolled out starting in 1998

– Still found in many carriers and enterprises

• MGCP is the gateway protocol of choice for Cable networks• H.248 is used for gateway control in the IP Multimedia Subsystem

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Needs for Translation (2)

Media:• Next generation IP architectures envision end-to-end

trancoding-free voice operations– This is the ideal / Reality is messier

• Why?– Most common VoIP voice codecs:

• G.711, G.729A, G.723.1

– Up and coming• iLBC

– Most common Wireless codecs: • CDMA, GSM-FR, GSM-EFR, AMR

– Fax• Both T.38 and G.711 IP coding are common

• Result: – Need to translate media across network boundaries

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Needs for Translation (3)

• Situation is not much better for video• H.324-3G translates media between IP and first gen

3G phones– Special gateways needed to multiplex the media for

transmission to the handset

• A variety of different video codecs in use– H.263 (2000), H.263++– MPEG-4 Advanced Simple Profile– H.264 (aka MPEG-4 Advanced Video Coding)– And more are being produced all the time…

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How Does it Work Now?

• VoIP relies strongly on a variety of network elements– Media Gateways

• Translate media and typically some signaling

– Signaling Gateways• Usually translate from circuit signaling to IP signaling

– Session Border Controllers• May translate between IP signaling protocols

– For example, H.323 to SIP

– Softswitches• Provide control over media and signaling gateways in a

distributed architecture

• Sometimes these elements are combined– For example, media + signaling ->

• Integrated Media Gateway

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Typical VoIP Architecture

IMG 1010 Media Gateway

SS7

ISDN / CAS

IP Network

Class 5 Switch

SIP / H.323SIP / H.323

SS7

ISDN / CAS

IMG 1010 Media Gateway

End UsersEnd Users

Class 5 Switch

Media Gateway Functions:PSTN-to-IP Connection >Media >Signaling >Routing

Media Gateway Functions:PSTN-to-IP Connection >Media >Signaling >Routing

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VoIP Using Softswitch Architecture

Softswitch

SS7

IP Network

SIP - TSIP - T

SS7

End User End Users

Class 5 Switch

TDM / IMT

MediaGW

SignalingGW

MediaGW

H.248 / MGCP H.248 / MGCP

SS7 / M3UA

IP NetworkTDM / IMTRTP RTP

Softswitch

Media Gateway Functions:PSTN-to-IP Connection >Media

Media Gateway Functions:PSTN-to-IP Connection >Media

Signaling GW Functions:TDM-to-IP connection >SS7 to SS7 over SIGTRAN

Signaling GW Functions:TDM-to-IP connection >SS7 to SS7 over SIGTRAN

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Voice over Broadband

IP Backbone

IP Phone

SIP

RTP

SIP

RTP

TDM Phone

TelcoClass 5Switch

Media Gateway Functions:PSTN-to-IP Connection >Media >Signaling >Routing

Media Gateway Functions:PSTN-to-IP Connection >Media >Signaling >Routing

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VoIP Peering

IMG 1010

Media Gateway

TDM Carrier

SS7 + TDM

ISDN / CAS

IP Carrier1

Media Gateway Functions:PSTN-to-IP Connection >Media >Signaling >RoutingIP to IP Connection>Transcoding> ENUM address translation

Media Gateway Functions:PSTN-to-IP Connection >Media >Signaling >RoutingIP to IP Connection>Transcoding> ENUM address translation

IP Carrier2

Session Border Controller

SIP / H.323

SIP

SBC Functions:IP-to-IP connection >Firewall and NAT traversal >Policy enforcement >Security >Signaling Interwork (SIP, H.323)

SBC Functions:IP-to-IP connection >Firewall and NAT traversal >Policy enforcement >Security >Signaling Interwork (SIP, H.323)

Peering Fabric offers simpler connections among carriers

Peering Fabric offers simpler connections among carriers

SIP / H.323

RTP

SIP

SIP

PeeringFabric

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What’s Next: IMS

• Wireless Vendors worked to produce standards for Multimedia Services over SIP

• Design Criteria: – Provide common architecture for multiple services– IP at the core– Offer access to users on existing networks– Need to interwork between IP and circuit switched at the

edges

• Result: IP Multimedia Subsytem (IMS) – Developed by Third Generation Partnership Project (3GPP)– Endorsed by both wireless and wireline industry groups

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IMS Architecture

P-CSCF

S-CSCFMGCFHSS

Cx

IP Multimedia Networks

IM-MGW

CS Network

Mc

Mb

Mg

Mm

MRFP

Mr

Mb

Legacy mobile signalling Networks

I-CSCF

Mw

Mw

Gm

BGCFMjMi

BGCF

Mk Mk

C, D, Gc, Gr

UE

Mb

Mb

Mb

MRFC

SLFDx

Mp

CS

CS

IMS Subsystem

Cx

Mm

AS

ISCSh

Ut

Mb

Dx

3GPP TS 23.228 V7.2.0 (2005-12)

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IMS for the Rest of US

AS – Application Server

SCIM - Service Capability Interaction Manager

MRFC - Multimedia Resource Function Controller

MRFP - Multimedia Resource Function Processor

MRF – Media Resource Function

CSCF- Call Session Control Function

BGCF - Breakout Gateway Control Function

MGCF - Media Gateway Control Function

MGW - Media Gateway

HSS - Home Subscription Server

HLR - Home Location Register

Key Elements:

HSS/HLR

MRFC

MRFP

CSCF

MGW

SCIM

S-CSCF

I-CSCF

P-CSCF

BGCF

MGCF

MRF

SIP

RTP

ApplicationServers

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IMS and Signaling Translation

• All signaling converted from circuit to IP at the edges– Integrated Approach:

• Convert SS7 ISUP, PRI, CAS directly to SIP– Follows TS 29.163 which is based on ITU-T Q.1912.5

– Distributed Approach• Signaling GW: Convert SS7 ISUP and PRI to run over IP

– Use the SIGTRAN suite of adaption layers that run over SCTP» For example, ISUP runs over M3UA

• Media Gateway Control Function– Terminates SS7 over IP and converts to SIP

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IMS and Media Translation

• Ideally, media is NOT converted from end to end– For example, use AMR codec for voice over entire 3G

UTMS network from end to end

• Conversions needed to connect to existing networks– Media Gateways

• Landline Connection - Will convert G.711 to AMR or EVRC

• 2G to 3G Wireless– Will convert GSM series to AMR

• Voice over Broadband to Wireless IP – May need conversions such as G.729A, iLBC, or G.723.1 to AMR

or EVRC

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State of the Standards

• SIP is a many splendored thing…– Core 3261 specification and many, many others

• Hitchhiker’s Guide to SIP outlines the “Core SIP” (draft)

• IMS is standardized on SIP, But:– Several different versions, each offering its own profile of

SIP and other related specifications• Release 5: First real specs for IMS in 2003; introduces the

architecture

• Release 6: More complete IMS specs in late 2004, but still incomplete

• Release 7: Just being standardized now; Rollout probably 2 years away

– More complete, but some areas are very immature» For example, no standard for media control between

application servers and Media Resource Functions

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State of the Marketplace

• VoIP Rollout is not waiting for IMS• SIP has overtaken H.323 for new VoIP deployments

– SIP enabled Media Gateways very popular– H.323 mainly needed to tie into legacy deployments

• Distributed Gateway model– Many of the large gateways use the distributed approach

• Media Gateway controlled by Softswitch

• Softswitch Protocols of choice are MGCP and H.248

• Usually have separate signaling gateways to terminate SS7 and convert to IP signaling

• Integrated Media Gateway Model– Incorporate both signaling and media translation in GW– Include SS7 termination and conversion to SIP or SIP-T in

one box for better economics

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The Way Forward

• IMS will continue to mature and is well regarded by Tier 1 carriers

– Pressures on Landline vendors such as BT will be the early IMS implementors

– Wireless vendors have less incentive to make the investment except for new applications

• Voice over Cable vendors start transition to IMS as well, but currently using SIP and MGCP

• Tier 2 and below vendors will continue to use SIP and only convert to IMS if obvious advantages

• Peer to Peer models will also compete with the IMS Client – Server approach

– Skype is the 1st big success story– SIP PTP is being standardized

• Slow transition from hybrid to all-IP networks

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Resources

• Internet Engineering Task Force: www.ietf.org– Provides RFCs for SIP, RTP and some aspects of SS7 / IP

interworking– Hitchhiker’s Guide to SIP:

• http://www.ietf.org/internet-drafts/draft-ietf-sip-hitchhikers-guide-02.txt

• International Telecommunications Union: www.itu.int– Develops H.248 / Megaco and SS7 series of

recommendations

• Third Generation Partnership Program (3GPP): www.3GPP.org

– Develops IP Multimedia Subsystem and related standards

• Cablelabs: www.cablelabs.org– Develops standards for Cable use of IMS and MGCP

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Summary

• Transition underway from Circuit to IP communications networks

• SIP is the IP Communications protocol of choice• Both Signaling and Media Conversion needed today

and for years to come• IMS has good mind share, but still at early stage of

deployments• In the meantime, a variety of network elements will

fuel the transition to IP• Both distributed and integrated models popular

methods for signaling and media translation

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Thank You!