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March 2007 SIP Magazine
Volume 2 / Number 2


By Richard "Zippy" Grigonis, Feature Articles


SIP (Session Initiation Protocol) and IMS (IP Multimedia Subsystem) are huge topics these days, the subjects of endless discussion. SIP defeated its rival, H.323, in the call control signaling area for IP Communications, but it was the harbinger of more grandiose things to come — namely, the grandiose IMS architecture, which is based on SIP and started out as a small part of the 3G wireless world. Both wireless and wireline operators soon realized that IMS could become a universal service architecture for the world’s communications services, and that IMS enabled operators to hatch new services by the dozen in a multi-vendor friendly network. In an IMS universe, such services can roam with users, which leads us to the Shangri-La of fixed-mobile communications (FMC).

Over at the legendary telephony hardware/software vendor (news - alert) Dialogic (http://www.dialogic.com), the Director of Product Management for Media Products for the Service Provider Markets, Chris Fullam, says, “We’ve bought into both SIP and IMS, no question about it. We’ve pretty much built our product strategy around allowing people to migrate from the current networks to IMS. We don’t think it will happen overnight. Indeed, things seem to be moving slower than was originally forecast. Still, our strategy that we formulated a few years ago about using host media processing [HMP] as our basic media engine and SIP for call control, has worked out very well. Both HMP and SIP really provide a good foundation so that we can evolve with the market. We’ve been tuning that architecture so that by adding DSP [Digital Signal Processor] offload to HMP, we think that we’ve got a really good combination of factors: First we have the best performance. Second, the price is good because we can really take advantage of off-the-shelf servers.”

“So, we’re buying into SIP, IMS and HMP,” says Fullam, “and that’s the basis for our product strategy. It seems to be playing out really well too, though as I said things are moving a bit slower than we expected. The whole rollout on IMS and 3G networks takes time. A year ago we thought that we’d see a lot of deployments in 2007. As it happens, we’re seeing pilot projects, but it now looks like the big deployments will start occurring in 2008 or 2009. In China, for example, there are some pilots, and the 2008 Olympics is acting as a sort of driver to get things rolled out.”

“Some of the key benefits that IMS provides makes sense to everybody,” says Fullam. “Lowering your costs, being able to rollout new applications more quickly, having a distributed environment and modularizing components — those are all really great benefits that no one can argue with. Everybody plans to move toward IMS but the realities of the situation are that operators have to keep their revenues flowing and they need to leverage existing investments. Still, our approach seems to be working in this environment. We have network operator customers that have deployed things such as color ring back, the Short Messaging Service, or just a media solution in today’s network. They can move to our newer platforms, such as our Multi Media Platform [MMP] that uses HMP with the DSP offload, and they can keep using the same APIs. Essentially, they can leverage the vast majority of their existing application development work. Over time, they can move to some of the other standard protocols such the Media Sessions Markup Language [MSML] or H.248 and use the same servers. That’s a key piece of our approach, to provide a migration strategy that allows people to leverage their existing infrastructure.”

“The ‘M’ in IMS is Multimedia, and for years we’ve felt pretty good about HMP as an excellent approach to handling media processing. I think most of our competitors and many people in the industry have said, ‘Yes, it’s a great idea, but it doesn’t scale, and it will only work for small-scale deployments or where there’s extreme cost pressure’. And I think we’ve now seen people recognize that our combination of HMP and DSP boards is highly scalable. In particular, if you take the most MIPS-intensive functions, such as the transcoding processes for wireless, and you move them to a DSP board, now you’ve got the best of both worlds. You do the majority of the media processing — playing prompts and call control activity and all that — on an off-theshelf, high-end server, and you relegate the processing-intensive transcoding processes to the DSPs. That mix gives you the best overall price performance in building equipment that will function in the greater SIP and IMS environment.”


The Great IMS Migration
So, companies known for their telephony hardware, such as Dialogic, are gearing up and jockeying for position in preparation for the upcoming Great Migration to IMS.

At (news - alert) AudioCodes (http://www.audiocodes.com) VP of Systems Yehuda Hershkovits says: “IMS uses a common IP core with SIP-controlled endpoints. SIP is used to set up, maintain and terminate multimedia sessions. Key elements in the IMS architecture are media gateways for interconnection with the PSTN, MRF [Media Resource Function] for advanced multimedia services, and SBCs [Session Border Controllers]. AudioCodes provides all key elements.”

“AudioCodes’ media gateways have been inherently designed as IP-based systems to support wireline [carrier VoIP & enterprise VoIP], wireless [CDMA, UMTS, GSM, WiFi, & WiMAX] and cable access networks, making the transition to a combined, converged IMS-based core network a relatively simple task,” says Hershkovits.

Hershkovits elaborates: “AudioCodes’ enterprise gateways [Mediant 1000/2000/3000], access gateways [Mediant™ 5000/8000] and media servers [IPmedia™ 2000/3000/5000/8000] fit into any IMS-compliant network on which fixed-mobileconvergence [FMC] is based. Since the inception of VoIP, the company’s gateways have operated in distributed networks, recently adopted by IMS. In addition, its field-proven, IMScompliant H.248 control protocol supports those functions necessary for IMS deployment — IMS uses H.248 as the transport call control. AudioCodes products already have a choice of multiple vocoders — GSM-EFR, AMR, EVRC, iLBC, G.729A, and so forth — needed to build a truly converged core network supporting GSM, UMTS, CDMA, cable and wireline access networks, to enable interoperability with an IMS core network.

In addition to standards — or multi-standards — compliance, AudioCodes teamed up with NEPs [Network Equipment Providers], SIs [System Integrators] and Service Providers, offering VoIP equipment with a full commitment to open interfaces and interoperability with third party network elements, which is at the heart of IMS philosophy. AudioCodes is closely following 3GPP SIP standardization, assuring IMS compliance with no hardware changes, thereby protecting infrastructure investment.”


Will SIP Keep Evolving?

One wonders if, after all of this ramping-up to deal with SIP and IMS, whether SIP is in fact suited to working in an IMS environment as it is, or whether there may be any more official, major extensions to the protocol.

AudioCodes’ Yossi Kurzman, Director, Product Marketing, Systems, says, “SIP is an evolving standard, making interoperability a challenging task. The IMS is an IP-based core network used with multiple access networks — wireline, wireless and cable— to provide a converged service to wireless, wireline and cable subscribers. Each new access type brings along a whole new set of standard activities that impact the IMS core network. Access agnostic is the goal, but not yet the reality. Each new access type presents a different set of requirements and challenges. It will take time to overcome them, but, as with what happened following the early days of VoIP, standards eventually stabilize and reach equilibrium.”

“All customers seek unique applications to justify their large investment in IMS deployments,” says Kurzman. “Voice is still the leader application, generating a significant portion of revenues. Video could play a definite role in the future.”

“MSOs [Multiple System Operators] are now offering subscribers mobility,” says Kurzman, “such as quadruple play, in addition to the converged voice, video and data services over IP [triple play] offered by wireline, cellular and VOBB [Voice over Broadband] operators.”

“IMS, with its SIP architecture,” says Kurzman, “enables video over IP communications, presence services, Instant Messaging, Multimedia services and mobility, such as handoff between VoIPoWiFi to GSM/CDMA. IMS is the architecture that will help MSOs offer quadruple play services, secure their competitive status, expand their subscriber base and increase the ARPU [Average Revenue per User]. IMS’ SIP architecture needs to continuously adapt to these market forces and changes.”


Where the Legacy PSTN Meets the IMS Future

SIP and IMS will be stuck with legacy PSTN technologies for some time to come. Mindful of Dialogic’s HMP/DSP offload combination to handle MIPS-intensive tasks such as transcoding, Yours Truly asked Rich Poole, AudioCodes’ Director of Business Development whether he thought extensive interworking and transcoding would be needed for SIP and IMS to interoperate with legacy PSTN technologies.

Says Poole, “A fundamental asset of the IMS framework is its ability to transparently interconnect different types of network access, viz., cellular access [AMR coders, EVRC coders] wireline access [G.711, G.729], PacketCable access, WiFi access and WiMAX access, each of which uses different coders. To perform interworking with the PSTN, intensive, high-quality, high-capacity transcoding capabilities are required, so extensive transcoding is a given.”

“In the case of AudioCodes,” says Poole, “our gateways are at the heart of media/bearer processing within IMS-based networks, providing the appropriate voice processing required to complete and handover calls between divergent access networks and the existing PSTN, if required.”

“These divergent access networks typically require different vocoders, protocol and signaling support,” says Poole, “so maximizing voice quality will naturally dictate minimizing the number of vocodings required in a given call and naturally increase the number of vocoders required to be supported on a given IMS media gateway.”

Poole proudly notes that, “In the 3rd Annual ETSI [European Telecommunications Standards Institute] Speech Quality Test Event, AudioCodes was the only vendor out of 10 who participated which did not score below the standard on a single test and exceeded the standard significantly on a number of tests. AudioCodes submitted a Mediant™ 2000 digital gateway for the testing. The Mediant 2000 shares core enabling technology with a wide range of AudioCodes gateway and media server platforms, testing the core of a large number of AudioCodes products.”




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