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

James Rafferty, Cantata Technology [email protected]

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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

Network Architecture

Network Evolution for Service Delivery

Traditional TDM

•

Centralized Integrated Design Transition Hybrid

•

Open & distributed TDM-IP Migration Next-Gen IP

•

Open & distributed Pure IP (IMS) Signaling/Functions Media/Functions Applications SS7, ISDN, CAS TDM – TDM “circuit to circuit”

• •

TDM enhanced services Discrete applications SS7-SIP ISDN-SIP CAS-SIP TDM - IP conversion “circuit to packet”

• • • •

IP-based transport SS7 services over IP IP services over TDM IP-enable/extend TDM services SIP-SIP H.323-SIP IP - IP “packet to packet”

• •

Multimedia services on common service platform (IMS) Blended SIP services 5

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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

Class 5 Switch IMG 1010 Media Gateway

SIP / H.323

SS7 ISDN / CAS

IP Network

SIP / H.323

IMG 1010 Media Gateway

SS7 ISDN / CAS

Class 5 Switch

End Users

Media Gateway Functions:

PSTN-to-IP Connection >Media >Signaling >Routing End Users

VoIP Using Softswitch Architecture

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Softswitch

SIP - T SIP - T

Softswitch

SS7 / M3UA

Signaling GW

IP Network

H.248 / MGCP

Media GW

H.248 / MGCP SS7 RTP

IP Network

RTP End User TDM / IMT

Media Gateway Functions:

PSTN-to-IP Connection >Media

Signaling GW Functions:

TDM-to-IP connection >SS7 to SS7 over SIGTRAN SS7

Class 5 Switch Media GW

TDM / IMT End Users

Voice over Broadband

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SIP SIP IP Backbone RTP RTP Telco Class 5 Switch

Media Gateway Functions:

PSTN-to-IP Connection >Media >Signaling >Routing IP Phone TDM Phone

TDM Carrier

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

VoIP Peering

Session Border Controller

SS7 + TDM ISDN / CAS SIP

IMG 1010 Media Gateway

SIP / H.323

SIP / H.323

RTP Peering Fabric SIP SIP

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

IP Carrier 1 IP Carrier 2 13

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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

Mb Mb MRFP

IP Multimedia Networks CS Network Legacy mobile signalling Networks

Mm Mb CS Mb CS BGCF Mj IM MGW Mc MGCF Mk BGCF Mg Mr Mk I-CSCF Mw Mm ISC Cx AS Mi Cx Sh C, D, Gc, Gr HSS S-CSCF Dx Mw Dx SLF MRFC P-CSCF Mb Mp Mb Gm UE IMS Subsystem Ut 3GPP TS 23.228 V7.2.0 (2005-12)

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IMS for the Rest of US

MRFC MRFP MRF SIP S-CSCF I-CSCF P-CSCF CSCF Application Servers SCIM BGCF MGCF HSS/HLR Key Elements:



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

MGW RTP

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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 1 st 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!