What’s in a name? The term "softswitch" has recently come to prominence as an essential element to enable convergence between PSTN and IP networks. This also makes it significant for 3G networks. Yet exactly what a softswitch is is open to some interpretation. For some it is a carrier class, next generation gateway which can handle anything up to 100,000 lines. For others, it’s just a big fast router. Others see it as a server-based device that controls real-time media streams over IP. Some see it as a marketing term, others as a technical description.

Do these differences matter?

Who’s running the show?

Public networks are now moving at a quickening pace towards a future where voice, video and data services are offered to fixed and mobile users on a single, packet-based infrastructure. How quickly a particular network gets there, though, depends on where it came from and what services it needs to offer in a particular timeframe. Whatever that is, an essential requirement is that phone calls across the network must be suitably managed, whether the end-to-end path is all packet network or a combination of packet and circuit-switched.

For the foreseeable future, the vast majority of phones will be connected via the traditional public phone network. If an IP network is going to be used as part of the route, a network resource (the softswitch) must clear a path across the packet network and complete it across the circuit-switched networks at either end. To do this, it needs to control other network elements (gateways) that either translate the data stream across the boundaries of the different networks (media gateway) or mediate between the different signalling streams (signalling gateway). Hence one of the alternative terms for a softswitch - media gateway controller (MGC) - which by definition controls a number of media and signalling gateways and is therefore physically remote from some or all of them. A virtual central office, in fact, that drives both IP and circuit-switched network routing and allows a wide variety of gateway and controller configurations to suit particular network requirements.

Opening the box

The International Softswitch Consortium (www.softswitch.org) limits the term softswitch to the media gateway controller. Some vendors and service providers however include the media gateway or signalling gateway, too, as part of the softswitch itself. Whatever it comprises though, in order to set up phone services, softswitches must tap into databases and application servers that define the services customers get. Because they do this via standard programming interfaces (APIs), third party developers other than the ones who make the softswitches will have the opportunity to write service programmes.

For a Java-based service creation environment, for example, just string together a few JavaBeans and a new service can be created and brought to users in a matter of weeks. If a service provider wants to implement prepaid calling cards, then, a JavaBean is selected that instructs the software to pick up the calling card calls. The next JavaBean activates a user greeting to the service and another, collecting account code information.

The speed and flexibility of this approach is in marked contrast to traditional circuit-switched voice switches, where applications and databases are typically based on proprietary software which have tended to lock service providers into one vendor.

SIP-ing the service opportunities

This illustrates a powerful advantage of the softswitch approach – an open service creation environment where new features incorporating voice/video/data streams can be brought into service quickly. It puts the softswitch structure in a position to drive a new Communications ASP market. It also puts SIP (Session Initiation Protocol) at centre stage because it tends to be used extensively: not only for softswitches communicating with each other, but also with feature servers and with network end points such as IP phones, although for this there is also the alternative H.323 standard.

What sort of services does SIP enable? For a start, a SIP device can be found wherever it’s connected to the network. Personal services can then be automatically routed to it. Then there are the possibilities from linking it with instant messaging.

For example, You want to discuss something urgently with Joe and your own device tells you he’s online somewhere – could be anywhere. You send a brief instant message that goes out to all the devices Joe is currently online with. He replies with another one back. This identifies what type of device he’s currently using, it’s address and Joe’s current preferences for receiving calls on it. You use SIP to initiate a phone call to his mobile from your desktop PC, creating an IP telephony call that is converted to a mobile switched-circuit call for delivery to his mobile. It would have worked the same way if he had been on a PC himself, or even a fixed line telephone.

What about interoperability?

In a truly open world, applications should be able to move across different networks, both fixed and wireless. But this is still early days. Protocols such as SIP are relatively new and some are still in a state of flux. So while there are plenty of standards, not everyone interprets them in quite the same way. This makes for greater complexity for interoperability in the meantime . . . but hopefully not for long.

© e-principles 2001

Robin Duke-Woolley

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