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.
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