October 2001
 

Softswitch Emergence

BY KEVIN MAYER

The trouble is, the softswitch makes sense only when you describe the constellation of next-gen elements with which it interoperates. So, you end up trying to describe several things at once, waving your arms around as you quickly exhaust the patience of your audience. Perhaps, when describing a softswitch, the last place to start is the softswitch itself.

Some people describe the softswitch as part of an evolving ecosystem of network elements, which may include new, packet-oriented elements as well as legacy, circuit-switched devices. Ecosystem. That's the interesting word. An ecosystem emerges out of the complex interplay of its constituents, which may evolve themselves while the overall system evolves.

An emergent system, any emergent system, be it an ant colony or urban neighborhood or communications network, may begin with relatively simple constituents, and even a limited number of them, and yet evolve into something of considerable complexity, and exhibit considerable variety, provided the constituents may interact freely. In the case of communications networks, evolving complexity is the whole point. To date, the public switched telephony network has demonstrated limited capacity for evolving complexity, at least in part because of the limited interplay among its constituent parts. In fact, some potentially distinct functions are so deeply embedded within legacy elements that it may be hard to recognize them as constituents.

Service providers have depended on their equipment to allow them to create and deploy new services. However, legacy equipment has offered little flexibility. Since legacy equipment differs little among service providers, any one service provider will have difficulty differentiating itself from the others.

But what if service creation didn't depend so much on monolithic, legacy equipment? What if the constituent functionalities embedded in legacy equipment were extracted into more or less freestanding platforms, and allowed to interact with each other? You might create an evolving communications ecosystem from which complex differentiated services might emerge.

That, at least, is the idea. Whereas legacy equipment consolidates transport, call control, and application functionality into a monolithic switch, a next-generation constellation of network elements may specialize. Transport functionality may reside in media gateways; call control, in softswitches; and application functionality, in application servers. Finally, there's signaling, a function that has already been abstracted within the traditional network. In the next-generation network, signaling functionality may reside in a softswitch or a separate signaling gateway. (Some softswitches may attempt to combine call control and application functionality. But more about that later.)

Now comes the tricky part. All these next-gen elements have to interoperate. When interoperability is the issue, the usual answer is to rely on standardized protocols and interfaces. Between the application platform and the softswitch, you might find such protocols and interfaces as TAPI, PARLEY, JAIN, and SIP. Between the softswitch and the media gateway (or gateways), you might find MGCP, H.248, and MEGACO. Between the softswitch and the signalling platform, you might find M3UA/SCTP (Sigtran). Within the transport layer itself, you might find TDM, RTP/IP, and ATM. Within the signalling layer, you mind find ISUP, Q.931, and CAS (with TDM); SIP-T, H.323, and BICC (with VoIP); and BICC (with VoATM).

Ideally, with sufficient interoperability, new applications and services could be created that would run over different types of networks. The emergence of such applications and services would indicate that the migration from legacy, circuit-switched networks to next-generation, packet-based networks was underway. However, when asked about interoperability, softswitch vendors frequently limit their answers to describing the protocols they support, as though it could be taken for granted that any vendor's implementation or interpretation of a protocol would compatible with another's. As for actual interoperability tests, these are usually limited to demonstrating a media gateway's support for multiple integrated access devices (IADs).

Interoperability, however, is just one of the challenges for softswitches and other next-gen network elements. Doubts linger as to scalability and reliability. Some complain that when next-gen equipment vendors claim "five-nines" reliability, they are construing reliability as a hardware issue, glossing over issues of software design and fine points such as fault prevention, fault detection, fault avoidance, fault isolation, fault location, and fault recovery. Another issue is compatibility with business support systems and operation support systems. (For more on this issue, see this month's cover story on billing and mediation.)

Perhaps the biggest challenge facing the next-gen network is to maintain a degree of flexibility, even as next-gen equipment vendors attempt to match the capabilities of (and interact with) legacy equipment. Some influential voices warn against simply creating a packet-based version of the traditional network. For example, some suggest that application functionality shouldn't reside in the softswitch, but should be "distributed," in keeping with the spirit of the Internet. According to Jonathan Rosenberg of dynamicsoft, softswitches should be considered access platforms: "They [should be used to] provide critical connectivity to the PSTN in a highly scalable and reliable fashion. Placing applications on the softswitch ties access to services; the assumption is that these services are available only to those users who enter the carrier network through the softswitch." Such an assumption would be inconsistent with the idea of a communications ASP hosting and running its own applications, outside of any particular network.

Uncertainty over this issue prompted us to survey a number of softswitch vendors. We asked them to describe the functional configuration of their offerings, describing whether the application was co-resident with the softswitch itself, or whether it resided on a separate platform, or whether there was potential for either approach. Potential, of course, is a key word. The softswitch is still a work in progress. Regardless, softswitches are being deployed in an increasingly wide array of situations, by ILECs coping with lengthy Internet hold times, by data CLECs hoping to offer voice services to small and medium-sized businesses, to service providers offering limited applications to consumers. Gradually, service providers are moving from Class 4-style applications to Class 5-style applications, from Internet offload and Tandem replacement, to virtual PBX and IP Centrex. As the evolution continues, we're bound to hear more about interoperability tests, application development partnerships, interfaces to back office support systems, and "customer wins."

THE VENDORS SPEAK
While the softswitch is often described as occupying the control plane between the transport and application (or services) plane, individual softswitches exhibit considerable diversity. For example, sometimes softswitch functionality is co-resident with the media gateway, and sometimes the softswitch platform includes tightly integrated service creation and application functionality. And some softswitch vendors may work with third-party "application server" specialists. We asked vendors to describe how their platforms were configured, with respect to the various functional planes.

Alcatel: The Alcatel Softswitch is the central control element for a converged, data-centered network. It provides a standard interface to the SS7 network, and directs voice traffic to media gateways, which are located at the interface between the PSTN and the packet network. The gateways convert voice traffic between circuit- and packet-switching formats, resulting in seamless convergence at the network level and transparent service integration at the subscriber level.

Cirilium: Cirilium's High-Availability Softswitch occupies the call control plane and is sold as part of a complete solution along with our VoIP media gateways, IP phones, network control software, and enhanced applications. The softswitch hardware platform is a CompactPCI chassis or industrial-grade server with an NT, HP-UX operating system. The architecture is modular, distributive, and scalable. The dual 8-slot cPCI backplane allows CPU modules to be added for increased processing capability, and application servers for feature support. Added modules for IVR, voice mail, voice recognition, and SS7 are available. Duplicates Class 4 and 5 features. Also offers the following redundancy capabilities: softswitch CPU, Ethernet switches, power supplies, fans, hot-swappable CPI and I/O boards, and four hot-swappable drive bays.

Cisco: The standards-based Cisco BTS 10200 softswitch enables new, innovative, and easily differentiated services for a one-stop broadband services offering. Services are quickly deployed without time-consuming and costly upgrades to each transport element, since the Cisco BTS 10200 softswitch extracts and centralizes the call-control and service applications from the transport network. In addition to telecommunications services, service providers can offer a wider range of services, including virtual private networks (VPNs), Web hosting, and Internet access.

These content-rich services not only improve overall customer satisfaction, but also result in increased online time for subscribers. The Cisco BTS 10200 softswitch enables IP and ATM to PSTN calling using SS7 and MGCP. The system integrates call control and services software on an open UNIX platform. All Cisco BTS 10200 softswitch equipment and paths are fully redundant with an architecture that eliminates single-point failures and is designed for 99.999 percent reliability. The unit can be rack-mounted or configured in its own cabinet and delivers the call throughput capabilities required for even very large subscriber bases.

Three elements comprise the Cisco BTS 10200 softswitch:

• The call agent component serves as a call management system and media gateway controller. Each Cisco BTS 10200 Softswitch System incorporates multiple call agents to handle capacity and redundancy requirements.
   
• The element management system (EMS) serves as a mediation device between a network management system (NMS) and one or more call agents. The EMS facilitates the provisioning, administration, reporting, and billing features.
   
• The feature server provides an open protocol and flexible framework for the introduction of both new and innovative features into the network, allowing service providers to take advantage of multi-vendor products. It provides various plain old telephone service (POTS), Centrex, Tandem, and Advanced Intelligent Network (AIN) services to the calls controlled by the call agents. It also processes POTS features such as call forwarding and call waiting.

Clarent: The Clarent NGN softswitch infrastructure builds and expands upon the basic call control layer and delivers the essential Tandem (Class 4) and Class 5 internet offload functionality via three elements: the Clarent Command Center (provides the intelligent network control), the Clarent BHCM (Backbone High-density Call Manager), and the SS7/C7 Clarent MPSS (Multipoint Signaling Server). The Clarent OpenAccess softswitch is a combination of the Clarent Call Manager and the Clarent Command Center. It provides a highly scalable, standards-based service and application platform with the essential elements of a traditional Class 5 telecommunications switch. The softswitch also includes a comprehensive set of tools to enable the development of next-generation service applications by third parties.

CopperCom: The LeXSS platform includes the CSX 2100 media gateway and the CopperController softswitch. The CSX handles the transport plane and provides an advanced switching matrix. The CopperController provides an integrated call agent, application server and service creation environment call control, signaling (including SS7), and custom calling features.

ipGen: The Genovation-MSP is a standalone softswitch which provides functionality in both the control and application plane. Depending on the customer requirement, it is supplied with intrinsic feature server functionality (usually for Class 4 and 5 features), or customers use the APIs or SIP to interact with external applications and application servers. Unique to the Genovation-MSP is a programmable call model built within the architecture to allow dynamic granular control of the call flow under direction of the application, enabling the implementation of creative multimedia, non traditional, enhanced services. The Genovation-ACT (Applications Creation Toolkit) is available to create applications to run on the Genovation-MSP. This tool provides an intuitive graphical drag-and-drop interface for rapid application development and deployment.

ipVerse: ipVerse ControlSwitch is an open, carrier-class call control and application platform that offers traditional toll, Tandem, and local (that is, Class 4/5) voice services, as well as new, converged voice-data services. The ipVerse ControlSwitch offers open, standards-based interfaces to media gateways, application servers, and back-office systems from multiple vendors.

Lucent: The Lucent Softswitch (LSS) is built in line with the industry direction of open functional layers. LSS is physically separated from gateways and application platforms. LSS can work with any voice gateway conforming to industry standard H.323, H.248, or IPDC protocols. LSS can work with any external application platform using JTAPI, JAIN, and PARLAY, as well as SIP.

MetaSwitch: The first MetaSwitch VP3000 release (available now) is an integrated system, comprising media gateway, softswitch, and feature server in one carrier-class chassis. MetaSwitch will offer a distributed product suite in 2002, when the relevant IETF/ITU-T standards are more stable/mature.

Mockingbird: The Mockingbird SIP Server (MSS) is a stand-alone, telco-grade SIP proxy server, location server, and registration server that can work with any third-party application servers. Addition major telco-grade features include: 1. Trunk group based routing; 2. DNIS digit manipulation; 3. ANI digit manipulation; 4. DNIS-based routing; 5. ANI-based routing; source IP address based routing; 7. least-cost routing based on carrier cost tables; 8. multiple route attempts to reach a destination; 9. dynamically block and unblock inbound calls when the destination is unreachable and reachable again. (Immediately block inbound calls when the destination is unreachable, eliminating the 32-second wait for 7 INVITE messages retransmission to the destination. Unblock the inbound calls when the destination becomes reachable again.); 10. propagate cause code of failed calls to upstream media gateways and softswitches; 11. export CORBA IDL for any CORBA client to manage the MSS; 12. Provide console program interface to dynamical provisioning and monitoring of the MSS locally; 13. provide EMS GUI to dynamically provisioning and monitoring the MSS, both locally and remotely; 15. provide high availability. This capability allows established calls to be maintained during changeover between an active and standby MSS.

NetCentrex: The NetCentrex CCS Softswitch was created with a purpose-built modular architecture to deliver unmatched scalability and functionality to support multiple VoIP protocols and a variety of network implementations. The CCS Softswitch is a core component of the NetCentrex product line that also includes the SVI Media Server, a Service Creation Environment, the Application Server, and customizable applications including VoIP VPN, IP Centrex, and Personal Call Manager. In addition, the CCS Softswitch is based on open standards and open APIs to support third-party applications as well as interoperability with products from market leading vendors.

The CCS Softswitch is positioned in the call control plane, separate from, but supporting call signaling from third-party network devices (gateways, gatekeepers, standard phones, IP phones, IADs, etc.) in the transport layer that are based on H.323, MGCP, or SIP. The CCS Softswitch provides the core technology to support the application plane through deployment of the NetCentrex Application Server with NetCentrex customizable applications or with third-party applications. In addition, the SVI Media Server provides IVR and announcement capabilities as well as a service creation environment for the development of advanced applications by third parties.

Nuera: The Nuera SSC softswitch provides the call processing and signaling for the media gateway. It uses MGCP to control the gateway and SIP to communicate with feature servers and SIP devices such as convergent messaging systems, follow-me route servers, interactive voice response servers, and announcement servers. The SSC supports multiple variants of SS7, ISDN, and channel associated signaling (R1, R2, feature group D, etc.) for interworking with the PSTN.

Open Telecommunications: As you suggest, the openCallAgent accommodates only the control plane, and is largely independent of the transport and application plane. It uses MGCP for control of Media Gateways, Media Servers, and IADs, and incorporates the PacketCable NCS and DCS specifications. The openCallAgent provides access to Intelligent Network (IN) services via CS-1/CS-2 INAP or OT's proprietary INAP/IP. In addition, an open industry-standard Parlay API is provided to an Application Server for development of enhanced voice services capabilities, either by OT or third-party vendors. The openCallAgent uses the industry standard SIGTRAN protocol to communicate with Signalling Gateways (such as OT's openSignallingGateway) for interworking with the PSTN via SS7.

The openCallAgent has also been extended to support the functionality necessary for second- and third-generation mobile telephony by merging the latest wireless architecture with a software distributed switching and control platform to produce the openMobileCallAgent. This platform provides the functionality of a third-generation cellular mobile switching center integrated with an IP-based switching fabric while still providing high reliability and functionality. Deployed in a mobile network, the openMobileCallAgent supports cdma2000 third-generation MSC functions (3GPP2), and also 3GPP GSM-derived standards. Additionally IS-664 Cellular Features (Supplementary Services) and Wireless Intelligent Network are supported. By extension, the interfaces and protocols supported by openMobileCallAgent are the same as the openCallAgent.

Oresis: The ISIS-700 will offer an integrated or co-resident softswitch providing Class 4/Tandem capabilities. As portrayed above, the ISIS-700 will be a carrier-grade media gateway supporting ATM, frame relay, and on-board digital cross-connect capabilities. Additionally the integrated Tandem softswitch which resides on a single blade or slot enables the carrier to have a next generation Tandem voice switch in a single chassis, with the associated benefits of an integrated architecture: higher reliability, simpler network management and control, and easier operational management.

The ISIS-700 will also have an MGCP/Megaco interface to an external softswitch, which would provide control plane signaling. The ISIS-700 will provide bearer level connections and switching for carrier edge devices and applications.

Santera: The SanteraOne is based upon the softswitch model -- it consists of: a media gateway which is responsible for media processing and switching; and a media gateway controller which is responsible for call control, signaling, service selection, and routing. The MG and MGC can be collocated in the same frame or geographically distributed to bring the MG closer to the edge of the network. The SanteraOne components support open interfaces such as MEGACO/H.248, SIP, SIP-T, and BICC and as such can interoperate with other vendor's media gateways, media gateway controllers, and application servers.

Siemens: As the intelligence of the SURPASS next generation network, the hiQ 9200 softswitch provides call control and feature delivery for voice over packet (VoP), as well as signaling interworking to both traditional SS7 networks and new packet networks. Media gateway control capabilities are provided to manage voice over IP (VoIP) or voice over ATM (VoATM) trunk gateways and access devices. Using Siemens' patent-pending Soft Circuit Call Model, the hiQ 9200 softswitch delivers today's revenue-rich legacy voice feature set into a packet network environment, to both existing TDM-based and new packet-based subscribers. Additionally, the hiQ 9200 operates in conjunction with the SURPASS hiQ 4000 open services platform and SIP Application Servers to create and deliver next generation multimedia applications.

The architecture of the hiQ 9200 is split into the following co-located functional units, each optimized for a specific set of tasks:

• Call Feature Server: The Call Feature Server has a distributed architecture over multiple processors, and is the primary source for the 3000+ legacy voice services offered by the hiQ9200. Built-in redundancy ensures no single component failure can cause the server to fail, and in the case of a malfunction, switch-over is automatic. Multiprocessing and load-sharing capabilities, along with the patent-pending Soft Circuit Call Model, optimize throughput and resources. And the hiQ can scale to as many as one million busy-hour call attempts now, with up to 16 million in 2002.
   
• SS7 Signaling Gateway: The integrated SS7 Signaling Gateway provides the interface to the SS7 network. All three MTP (Message Transfer Part) layers are handled in this subsystem, which provides the means of sending ISUP (ISDN User Part) messages to a connecting office and TCAP (Transactional Capabilities Application Part) or other AIN messaging to and from service control points, service nodes and intelligent peripherals.
   
• Packet Manager: Responsible for providing the interface to media gateways, the hiQ Packet Manager is implemented on a commercial computing platform. Within this open software environment, the Packet Manager handles the protocols used in the IP and ATM networks, including MGCP, H.248/MEGACO and SIP.
   
• OAM&P Agent: The OAM&P functions provide the means to manage the hiQ 9200. Support for legacy interfaces saves the effort of having to convert to new interfaces for information reporting from the hiQ platform. In addition to legacy interfaces, new optional interfaces are provided to report Automatic Message Accounting and maintenance activities.
   
• Internal Message Distribution Subsystem: Since the hiQ softswitch is based on a distributed architecture, messages are sent between each subsystem and within a subsystem. The Internal Message Distribution Subsystem converts internal addresses to the IP address of the receiving subsystem.
   
• Integrated Management System (IMS): The optional IMS platform, when installed in lieu of a local management terminal, provides the full range of OAM&P capabilities for the hiQ 9200 via remote terminal access.

Sonus: The PSX6000 SoftSwitch platform can be configured in different ways: co-resident with the media gateway or as a standalone element, providing support for third-party media gateways. The PSX6000 provides Class 4, H.323 gatekeeper, and Internet-based services. The softswitch provides Class 5 feature server functionality, using SIP or MGCP to work with third-party application servers and endpoints. The softswitch comes with service creation capabilities, which allow service providers or third parties to develop and customize services.

Sylantro: Sylantro's Applications Switch tightly integrates a carrier-class softswitch with an applications server, allowing service providers to manage and deliver their end-user customers' telephony and PBX services. Additionally, Sylantro supplies a complete suite of ready-to-deploy telephony applications that provide hosted PBX and IP Centrex services, combining the best of mobile phone, call center, PBX and browser-based functionality.

Syndeo: The Syion 426 is a standalone softswitch with intrinsic feature server functionality from tightly integrated CLASS 5 applications. The Syion 426 is also capable of interfacing with third-party applications servers via SIP.

Taqua: The Taqua Systems Open Compact Exchange (OCX) is an integrated softswitch that includes media gateway, ATM gateway, softswitch, and signaling gateway functions along with imbedded Class 5 applications, PSTN interfaces, and third-party application interfaces.

Tekelec: Tekelec's softswitch is built on a distributed architecture model in which media gateways and application servers are separate, stand-alone elements. The VXi MGC interoperates with media gateways and application servers from multiple, third-party vendors. The primary function of the Tekelec?s softswitch is call control, PSTN connectivity, and resource control. Unbundling the switching fabric delivers economies of scale. A single softswitch can control multiple media gateways and application servers. Functions like billing, administration, and maintenance can be centralized in the network. Applications can be deployed easily in the field or on-site. This distributed approach allows carriers to expand their network footprint into new geographic regions or markets quickly and economically by simply deploying media gateways under control of a centralized MGC. This model also supports an open architecture in which best-in-breed products can be deployed.

Telcordia: The TelcordiaTM Call Agent is a Class 5 softswitch that resides in the control plane as part of a disaggregated architecture. Telcordia relies on associate-provided media gateways for the bearer path and will use SIP to provide access to third-party application servers that will enable feature-rich services.

Telica: Telica's Plexus 9000-based voice solutions are comprised of a media gateway (MG), media gateway controller (MGC)/softswitch, signaling gateway (SG), and services environment. These elements can be deployed in three different network models: as one integrated switching platform providing a simple and easy-to-manage node; using a traditional softswitch model where open intra-switch protocols such as MEGACO and SCTP/M3UA are used between switching sub-elements; or finally, using Telica's distributed architecture model where call control is truly distributed among several fault-tolerant platforms where the MG and MGC functions co-exist. The Plexus 9000 MGC also connects to third-party application/feature servers for additional services, using SIP.

Unisphere: SRX-3000 is an open service creation platform that enables the development and delivery of new voice services across the PSTN, cable modem access, wireless, and circuit-switched networks. The software-based switching platform offers highly scalable call processing; flexible platform for rapid deployment of enhanced services to end-users; service profiling and on-demand services; standards-based architecture for next-generation services; open API for service creation and feature server integration; uncomplicated integration with third party applications via standard protocol or programming inter-faces; meta-directory technology for back-office integration.

VocalData: VOISS is called a "service delivery softswitch" which means that it supports both elements of call control and the services and applications inherent to an application server. Call control elements include call state management, CPE control (IP phones and IADs), media resource control, and media gateway control. However, the VOISS platform contains intrinsic feature server functionality, including a rich set of typical Class 5 features. Service providers typically configure the VOISS value-added applications such as voice mail, unified messaging, and conferencing on a separate server for maximum performance. In addition to the VOISS server(s), the entire solution includes a VOISS proxy firewall, desktop portal, service administration, enterprise administration, and the front desk application, and VocalData and partner gateways. Other partner elements include SS7 signaling softswitch, integrated access devices, and IP phones. 

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