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Industry Insight
May 2001

Jim Machi

The Next-Generation Network


We've all heard buzzwords like softswitch, media gateway, media server, and signaling gateway. Maybe we've even read articles or heard presentations about them. I've certainly written about them in this column over the last two years. But I often get asked: "How do they fit together?" "Why are they important?" And perhaps the most interesting question: "What are these things?" Here's the big picture. Together, these components form what is commonly referred to as the next-generation network (NGN), which also just happens to be a key concept in the IP telephony industry. I want to explain the context of these elements by describing how they fit into the NGN.

Before we look at the elements of the NGN, we need to understand its scope. It's easy to think the NGN is simply the cure-all IP network of the future. After all, that's what we hear about all the time. It's like a radio station with the tagline, "All IP, All the Time!" But we have existing, functioning networks today. The NGN is actually the convergence of four of these networks: The ever popular circuit-switched network, the cable telephony network, the wireless network, and the Internet service provider networks (the group of networks most often associated with the NGN).

It Takes A Tradition To Start A Revolution
Let's start by looking at traditional circuit-switched networks. A circuit-switched network actually consists of two distributed networks, one for transport and one for signaling. The CO (central office) carries and switches the media. The STPs (signal transfer points) route the SS7 messages. SCPs (signaling control points) are databases for enabling traditional enhanced services. Actually, a circuit-switched network looks similar to the wireless network -- after all, it was designed by the same telecommunications companies.

Circuit-switched networks interface to the IP and packet networks over trunking media gateways, access media gateways, and signaling gateways. The most common is the SS7 signaling gateway, which is used to provide certain SS7 information to the IP network. The access media gateway (also known as a generic "gateway," since it was the first type of gateway) transcodes traditional telephony to IP telephony. This gateway also provides the interface to consumers -- that is, to a business' CPE (customer premise equipment) and/or to residential subscribers over traditional analog or digital ISDN lines. Finally, the trunking media gateway transcodes the circuit network telephony stream to an IP network media stream, where the media simply stays in the IP network domain for some kind of action on it later. These relatively new types of gateways evolved once it was clear that IP telephony was here to stay.

Life At The Edge
There are also signaling gateways and media gateways to connect one IP network to another IP network. In this case, a signaling gateway provides IP-to-IP signaling conversion, necessary today since we have several IP signaling protocols including MGCP, H.323, SIP, and Megaco. The packet media gateway is also necessary, since it can be used as a firewall from one IP network to another.

The current stars of the NGN are softswitches and media servers, which reside in an all-IP world providing the application interfaces. I've written about softswitches before, but since I haven't written about media servers per se, let's spend some time on them.

Special Treat Included Inside!
Media servers are the real rising stars of the NGN. This is where the action takes place to and from the all-IP telephony media stream. By "action" I mean some kind of enhanced service like an announcement, IVR (interactive voice response), conferencing, messaging, text-to-speech, or speech recognition. For instance, one type of pure IP media server is an Internet voice portal where a customer browses a Web site over an IP session and hears content spoken back. Just two years ago routing these services over an all-IP media stream was just not possible -- and even downright alien. But no more. The NGN has truly taken the next step beyond the gateway and arbitrage. Applications are here today. Why do you read about softswitches and hosting together? Because the softswitches control and enable the media server, which handles the very cool work on the IP media stream.

It's also important to understand that these networks have a CPE component. They need to interface with a CPE switch, such as a PBX, and with its clients. Increasingly, the CPE needs to actually understand the NGN infrastructure since, as we already noted, there are multiple networks and multiple ways in which the CPE communicates to the outside world.

In short, the NGN is a complex and ever-evolving creature. However, some basic elements have emerged to help us contextualize it. Next month I will discuss applications the NGN can enable and the direction in which the elements we have just discussed -- many still in their infancy -- are headed. 

Jim Machi is director, product management, CT Server and IPT Products, for Dialogic Corporation (an Intel company). Dialogic is a leading manufacturer of high-performance, standards-based computer telephony components. Dialogic products are used in fax, data, voice recognition, speech synthesis, and call center management CT applications. 

[ Return To The May 2001 Table Of Contents ]

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