Next gen networks, open architectures: a "plane" and simple way

Then the Internet exploded on the scene causing a catalytic reaction that has, by necessity, created completely new architectural models with matching sets of new infrastructure equipment. Dealing with data paths in addition to the growing volume of voice traffic became the issue. New packet-based networks were put in place and the concept of converging usage models and encoding and transmitting voice calls around the data network evolved.

Equipment suppliers supported this converged or next generation network, but it also spawned a new breed of equipment suppliers looking to contribute their technologies to the melting pot. With so many interested parties, standardization and interoperability is crucial to success.

Today, using an open standards approach is imperative to encourage adoption and accelerate deployment, the goal of the Multiservice Switching Forum (MSF).

The MSF is a global association with representatives from the world's leading telecommunications companies committed to developing and promoting open-architecture, multiservice switching systems. Founded in 1998, the MSF's activities include developing implementation agreements, promoting worldwide compatibility and interoperability, and encouraging input to appropriate national and international standards bodies.

There are three main working groups in the MSF:

* The Architecture Working Group is the primary working group within the MSF that has created and continues to develop the overall architecture aimed at delivering the vision of the MSF.

* The Protocol and Control Working Group focuses on call and bearer control protocols and how they interface to the various reference points as defined within the MSF architecture. The Media Control Working Group looks at the interrelationship of Media Gateways and Media Gateway Controllers creating requirements and implementation agreements. MEGACO or H.248 is the primary protocol involved here and the MSF works closely with the IETF in reviews of this protocol helping to refine the ongoing requirements.

*The Interoperability working group focuses on the fact that architecture success depends to a great extent on its adoption by multiple vendors and how all the equipment developed interoperates. Developing methodologies and procedures with the aim of ensuring this compatibility is the mandate of this group. Demonstrations and testing forums or events are coordinated between MSF members and related industry groups to forward the goal of full interoperability.

The fundamentals of the MSF are founded on the adoption and development of their architectural vision. The work of the architecture group is therefore a major focus for the MSF representing the efforts to create and standardize the architecture for the functional model of the next generation network.

There are four key features of this architecture. First, there is a separation of specific functionality into "planes", with each element having defined open interfaces and reference points. Second, the architecture is agnostic from a bearer services perspective, supporting multiple traffic types (ATM, FR, IP, MPLS). Third, it clearly defines and separates the control and switching functionality into distinct planes. Fourth, new multimedia services additions and enhancements have been made to the service interfaces to support new revenue generation.

Historically telecom and data communication equipment could be seen as vertical silos of technology, associated with individual switching architectures. In this way equipment was designed with one primary usage in mind and the software and protocol models, although based on the appropriate related layering would have been a single "top-to-bottom" style stack. This model provided limited access, if any, to the layer boundaries and made decomposed architectures difficult if not impossible.

The MSF architecture is structured in planes where the various layered elements can coexist. This allows for separate evolution of services/application functionality, network controller capability, switching technology and media transport. The interconnections of these planes have strict definitions this allows for the development of systems where one or more layers can be implemented independently. This provides the ability to add functionality and/or technology easily without significant impact on the layers above or below. The architecture defines four planes for adaptation, switching, control, application and management.

The adaptation plane provides technological linkage of the disparate client types. A wide variety of network interfaces would need to be supported within the adaptation plane with real-time service functions translating or transcoding the various streams into a format ready to pass on to the switching functions. Front-end services such as filtering or firewalling would also be available in this plane. The switching plane allows for interconnection of the various media streams using matrix style cross connects between the various logical ports. Individual subsets can be created using a virtual switching function which can operate standalone or in groups.

Basically, the control plane manages the routing of traffic between the other planes allocating adaptation and switching resources, facilitating set up and tear down of connections. Signaling is a major component of this plane and support for multiple protocols is essential. Various QoS levels are enabled through the use of specific resources, selected per session. Packet forwarding functions are part of the control plane. The application plane enables the rapid introduction of new services via standardized open interfaces to the service logic and data. The goal is for a wide variety of applications to be capable of being supported within this architecture. Classic voice and data service could coexist with newer ones such as, real-time gaming, video on demand or multimedia groupware.

And, the management plane allows configuration of various planes to create multiservice switching environments. Typical functions would also include: fault, performance, security and accounting management. Service creation is also handled here.

The "planes" of the MSF model encapsulate functional elements rather than physical ones. There are no specific guidelines that dictate how one might build products so this leaves appropriate freedoms to the equipment manufacturers.

The true realization of the architecture is how effectively it translates into real products. Although one could create a system that encompasses all elements, the architectural definition of the planes allows for certain functions to be separated into a distributed physical architecture. A good example of this is the softswitch architecture that creates a new network infrastructure for interconnecting the older TDM voice networks with the new packet world. The main elements of these packet-voice style networks are a number of different types of gateways for media, access, signaling, media controllers, and media and application.

Media Gateways are network elements providing conversion between circuit-switched voice and data packets carried over IP networks with two main types defined. Access gateways provide traditional analog or primary rate (PRI) interfaces to a VoP network. The inverse function is also applicable in VoB (voice over broadband) applications where calls are digitally encoded before entering the access network and need routing via conventional telephony once inside. Trunking gateways interface directly between the telephone network and a voice over packet (VoP) network in the core. Such gateways typically manage large numbers of digital virtual circuits.

Signaling Gateways provide functionality that interconnects established protocols and signaling methods such as SS7 with the technology of the converged network. Working groups such as Sigtran (IETF) are defining standards that will allow IP telephony interworking with PSTN through the transport of signaling between the various gateway and control entities within the network.

Essentially, Media Gateway Controllers (Softswitches) provide the intelligent call control within the network, supporting protocols such as MGCP, H.248 (Megaco), SIP, H.323. Signaling, protocol mediation and service creation within a converged network is also handled by the softswitch. Intelligent call handling for media gateways can be independent of the access method or medium type. Essentially, a softswitch enables highly customizable IP-based services.

Media and Application Servers have a wide range of definitions. A media server adds processing functionality to a gateway for functions such as transcoding. Application servers essentially terminate traffic and provide services to the network or end user. Examples include unified messaging, video servers, voice recording, announcement servers.

Many other standards bodies and forums are collaboratively working on elements of this next generation architecture. For example, long established organizations such as the ITU and ETSI (European Telecom Standard Institute) are playing their parts along with open community groups such as the IETF (Internet Engineering Task Force). The International Softswitch Consortium (ISC) is another key organization promoting open standards.

As this new wave of equipment, designed for voice over packet networks, continues to evolve and be deployed, the work of standards bodies and forums becomes increasingly important. Success depends upon open standards and their ability to interoperate with each other. When added to open computer architectures, form factors and software standards like CompactPCI and Linux, complete platforms can be created virtually off the shelf - meaning less time, fewer resources, and fewer headaches for telecom equipment manufacturers.

Look for vendors to bring together open standard hardware and software components to create open and flexible, application-ready products such as media gateway platforms on which developers can quickly build their call control and application solutions. Openness equals rapid development, compatibility, interoperability and ultimately, choice.

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