Making IMS Work: Current Realities, Challenges and Successes
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NETWORK ARCHITECTURES Making IMS Work: Current Realities, Challenges And Successes Jeff Fried and Duane Sword IMS is real, and it is This article will survey the current state of IMS proceeding. Enterprises readiness and touch on some current issues and should be prepared. alternatives. The Premise And Promise Of IMS he IP Multimedia Subsystem (IMS) is IP Multimedia Subsystem (IMS) is an emerging steadily progressing from concept to reality. reference architecture for carrier-class networks But significant real-world issues remain. that is evolving through several standards groups, T All major equipment providers have com- research labs, vendors and carriers. IMS allows Jeff Fried mitted to the IMS architecture and are implement- wireless and wireline carriers to use a common IP ([email protected]) ing parts of it—as are a selection of major IT ven- application core to deliver a host of new, content- is chief technology dors and a variety of specialists. Many vendors rich multimedia services combined with legacy officer for Empirix Inc. and carriers now tout IMS as the single most sig- services across a variety of access technologies. Duane Sword nificant technology change of the decade. New (For more background on IMS, see BCR, June ([email protected]) product announcements, reports, newsletters and 2005, pp. 18–23). The basic idea behind IMS is to is vice president of articles are continually appearing. So what is the shift the network architecture from “silos” to “lay- product management current reality, and how can you prepare for the ers” in delivering services across different access for Empirix Inc. inevitable challenges? networks (Figure 1). FIGURE 1 The Premise Of IMS Silos Layers Service IMS Control Transport Fixed Mobile Wireless Fixed Mobile Wireless Use BCR’s Acronym Directory at www.bcr.com/bcrmag BUSINESS COMMUNICATIONS REVIEW / MAY 2006 43 IMS promises to accelerate convergence in spearheaded by Tier-1 operators in the U.S. and many dimensions (technical, business-model, ven- Europe. Many of these have already announced dor and access network) and make “anything over IMS contracts, including Cingular, Sprint, Bell- IMS’s primary IP and IP over everything” a reality. However, the South, AT&T, France Telecom, Telecom Italia stratification of the transport layer, control/session Mobile, Vodaphone, O2, Swisscom Mobile, and advantage for plane and applications—a key change to the net- more. These carriers are faced with flat or decreas- enterprises will work with IMS—creates unique challenges from a ing average revenue per unit (ARPU), increased be in fixed-mobile service quality-assurance perspective. competition and a desire to roll out a large variety To some, IMS is “simply” a flavor of Service of compelling services to increase customer convergence Oriented Architecture (SOA–also see this issue, “stickiness.” pp. 58–64), and is fueled by the same forces that For enterprises, IMS could provide advantages drive SOA in enterprises and service provider net- in fixed-mobile convergence (FMC), enabling works. Many also hearken back to the Intelligent increased mobility at lower costs, as well as the Network (IN) initiative of the 1980s that delivered potential for access and control of services in the many real benefits but fell short of the dream of network. rapid application delivery. Of course, for this promise to be realized, Some call IMS the “last gasp of the smart net- progress has to happen on many fronts: Standards, work” and predict that it will be circumvented products from vendors, infrastructure rollouts, even as it collapses of its own weight (see BCR, new applications, business models, etc. IMS is a October 2005, pp. 54–58). Others truly regard it as complex architectural framework, and itself is an the culmination of major forces and the realization enabler and part of a larger picture as network ser- of convergence on a global scale. But no matter vices converge and evolve. how you look at it, a few premises in IMS are now This article touches on some of the current very well accepted: realities and lessons, to shed some light on how ■ Decouple access from applications. things are unfolding and what can be done to pre- ■ Provide functions as modules. pare for the inevitable challenges. ■ Use standardized interfaces, reusing as much as possible (e.g., SIP). IMS Standards—Surprisingly Fast Progress, These may sound simple, but there are wide- But Still Unfolding ranging implications, many of which are already IMS began in the 3GPP group as an effort by wire- evident in early IMS products and trials. less carriers to standardize service delivery. It has Currently, the move to IMS is primarily being gained remarkable steam (and a remarkable alpha- FIGURE 2 IMS Standards Players Services and Service Enablers Open Mobile Alliance Defining IMS services; not strictly mobile Liberty Alliance => OASIS oriented, driving wireline services also (Federated Identify Mgmt) The Parlay Group WS-I (Web services specifications) Integral to IMS architecture, define standard API frameworks OGC Legacy Wireline & Converged Architectures American National Standards Institute TISPAN—ETSI body on T1.679 covers internetworking between ANSI ISUP and SIP Next Generation Network International Telecommunication Union Agreement on reuse of 3GPP/3GPP2 Q.1912.SIP covers interworking between ITU-T ISUP and SIP IMS in comprehensive NGN plans H.248 for media control Alliance for Architecture Telecommunications Industry Solutions Wireless Driven (ATIS) Nearing agreement to use 3GPP/3GPP2 Third Generation Partnership Project IMS Third Generation Partnership Project2 Define IMS network elements and infrastructure CJK China Japan Korea Harmonization effort has kept definitions as similar Starting Focus Group on NGN as possible ITU-T NGN Focus Group Leveraging IMS in wireline Protocols Internet Engineering Task Force Defines SIP, SDP and other protocols underlying IMS Source: TISPAN IMS is driving some of the work in IETF 44 BUSINESS COMMUNICATIONS REVIEW / MAY 2006 bet soup of acronyms), and is now active in at least not specify packaging, so many products encom- 14 different standards forums in a major way pass more than one function. Different vendors (Figure 2), with more than 40 standards groups in package the functions differently, which compli- the picture. We won’t delve into the intricacies of cates the construction of a true multi-vendor sys- The carriers’ big these groups and the various versions of IMS and tem (see BCR, April 2006, pp. 40–45). “pre-IMS” standards here. It is, however, worth What is particularly interesting about IMS is vendors are commenting that the complexity of the that there are more than 12 “traditional IT ven- serving as standardization effort currently under way is pre- dors” involved, and many products and concepts their integrators dictably represented in the complexity of the IMS come from the IT world rather than the telecom standards framework. world. Application servers, Web services inter- IMS is not a standard; it is reference architec- faces, and several other IMS elements are new to ture that defines functions within a three-layer telecom but well established in the IT world. The architecture consisting of equivalence is not always direct; for example an 1.) The access/transport/device layer. “application server” in IMS runs the gamut from a 2.) The control layer. SIP proxy to a J2EE app server. 3.) The applications layer. Because of the sheer complexity of IMS Figure 3 shows a simplified view of the refer- deployments, integration is crucial. A breed of ence architecture. As much as possible, existing “Network Integrator” (NI) is emerging with the standards are incorporated into the architecture to expertise to make complex multi-vendor imple- specify functions. This re-use of existing stan- mentations work in demanding carrier environ- dards such as SIP and Parlay, plus a general sense ments—something many carriers have traditional- of urgency in these standards groups, has resulted ly done by themselves. in remarkable progress. For an industry that took To date, all the major network integrators are 12 years to standardize T1 and E1 and 15 years to part of network equipment manufacturers: Lucent, standardize AIN, getting to the current IMS Alcatel, Sonus and Siemens, for example. There is framework in 5 years is remarkable. overlap between “Network Integrators” and tradi- However, many issues remain, and standards tional “System Integrators” like IBM, Accenture, haven’t yet addressed several big areas. These include the definition of common security elements and security aspects such as han- dling denial of service, topology hiding, FIGURE 3 IMS Reference Architecture and overload protection. Legal require- ments for “lawful intercept” aren’t dealt Applications Applications Applications with yet, nor are the “transcoding” Server Server Server approaches that will be necessary when users roam between wireline and wireless networks. SCIM It’s already clear that the conformance and interoperability challenges with IMS Applications Plane will be huge. To date, there haven’t been any “interoperability” events or confor- MRFC S-CSCF mance test suites beyond those in place HSS with the existing protocols IMS adopted. The first such events are coming in I-CSCF mid-2006. As a result, most of the early trials have focused on single vendors’ product lines. But since no vendor covers P-CSCF BGCF SEG everything and carriers are pushing for Control Plane PDF standardization in order to have interoper- ability, you should expect much more MGCF SGW effort on interoperability testing. IMS Products—Early Implementation MRFP Challenges All major traditional telecom vendors are MGW MGW MGW IM-MGW IM-MGW IM-MGW committed to the development of a com- prehensive IMS solution. Figure 4, p. 46, SGSN GGSN provides an overview of the various types Wireless of products and vendors involved: There Internet PSTN Transport Plane Network/WLAN are at least 11 major “suite” vendors, 6 softswitch players, and 45–50 specialists.