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Feature Article
February 2005

Media Gateways… Oh How Far They’ve Come! (Sidebar)

BY Thomas Howe, Chief Technology Officer, Versatel Networks

What came first, the chicken or the egg? The answer in VoIP is clear: it was the gateway. In 1996, at the beginning of the VoIP revolution, VoIP gateways were the first available commercial product. The business model was very simple and lucrative. Two gateways were attached to traditional phone lines, and then they were connected in a point-to-point network. At first, a single clear channel T1 line was used to connect the boxes. Using the compression from the gateways, service providers could fit six times the phone calls into the bandwidth required by one, resulting in a large cost savings. At that time, gateways were pretty stupid devices, but that was fine since they were connected in static routes. No intelligence required.

About four years later, sometime around 2000, it became clear that adding intelligence in the middle would be a good idea. The intelligent thing in the middle was called a softswitch, and provided large amounts of intelligence to the network. You could intelligently route calls between the gateways, choosing destinations based on cost, quality, or anything else you can imagine. The gateways were easier to configure now, too — you didn’t have to set up a dozen static routes. All you had to do was to point each gateway towards the softswitch. Billing was better as well. Billing could be done at one place, in the center of the network, easing deployments. This model also worked well for adding applications, as the softswitch would direct calls to some central device that would provide the service.

Today, as we start the first real deployments of large VoIP networks, a new complication is appearing. Service globalization demands network infrastructures that optimize not only network performance, but politics, organizational structure, and legal considerations. Instead of a one size fits all solution, service providers need flexible solutions that fit their unique needs. Standard solutions don’t always work from a business or technical angle. Far from making networks simpler, VoIP has added yet another set of protocols, making the alphabet soup of telecom a little thicker. Flexibility is required to optimize today’s networks, and handling intelligence at any point in the network is a key ingredient. As an example, a simple modification in tariffs may change termination and origination strategies overnight. International long-distance providers may see tremendous incentive to replace TDM connections with IP. A flexible solution that makes VoIP and TDM terminations transparent could mean the difference between a decent profit and a hefty loss.

Intelligent media gateways are the natural evolution of first-generation VoIP gateways, except that they are more flexible, they handle media processing functions and can host small VoIP applications. With them, the network planner has a powerful tool to handle dynamic and complex networks.

So what makes an intelligent media gateway intelligent?
To understand intelligent media gateways, a quick discussion of first-generation media gateways is in order. A media gateway is used to connect older, PSTN networks and equipment to VoIP networks. The role of the first-generation gateway is simply one of conversion. Calls from a T1 line are converted into VoIP calls such as SIP or H.323. Inbound VoIP calls are converted into traditional T1 calls. There are two distinct parts of any phone call: the signaling and the media. Gateways are responsible for converting both sides of the calls. First-generation gateways typically work with application servers or switches. In addition, media gateways tend to be “closed” devices. That is, their architecture doesn’t lend itself to simple upgrades, upwards or downwards scalability or integration of third-party technology. In fact, you had to choose your gateway very carefully since you may not be able to upgrade them easily, if at all.

Intelligent media gateways bring us into the second generation of gateway, and solve some real world operational issues that could simply not be solved with first-generation gateways. They can be used any place a traditional media gateway would, and will provide the same functions. But, unlike first-generation gateways, they have features that give them a much greater degree of flexibility. The most important feature of intelligent media gateways is that they depend on open standards as much as possible. This not only includes call control and management protocols, but also extends to hardware chassis and backplanes. By having an entirely open gateway platform, service providers can easily choose third party technologies to include in the gateway. In the future, you may even be able to mix and match line cards from two intelligent media gateway vendors. This openness naturally solves another pressing problem of gateways: scalability. Scalability is a critical feature because it reduces business risk — service providers no longer need to guess about network growth patterns, and overspend on initial purchases.

Another important function is the ability to handle any combination of protocol conversion. First-generation gateways are fairly limited in what they can do: convert TDM to IP, and IP back to TDM. They cannot handle IP to IP or TDM to TDM conversions. When added to a gateway, the ability to convert any protocol lets the network administrator keep his internal network clean and consistent while accepting anyone else’s VoIP traffic, without regard to formats. This is critical for larger service providers, who want to have clean G.711 and SIP-based internal networks, but must accept H.323 or G.729 traffic from smaller providers.

Intelligence is not something you would expect to see in a media gateway. However, when it is added, you add a whole new world of flexibility. Instead of depending on a single vendor, physical location, or source for application intelligence, you can easily mix and match. Here’s an example: imagine that your long-distance traffic from Mexico will be heavily tarriffed if you don’t terminate the call in the country. The rest of your operation is located in New York. If you use an intelligent media gateway in Mexico to route the local calls, and terminate there as well, you can optimize your network expenditures without reproducing your large infrastructure in some far-off land.

Media servers typically have the responsibility of processing voice. Intelligent media gateways can perform this task as well. They can conference calls, play prompts, record audio and collect digits. Although it might seem like a useful but optional feature, it is really very important. The ability to process voice directly allows a VoIP application to be housed in a single device, without sending the call back into the core for processing. From a technical perspective, this reduces the bandwidth required between the remote sites and the central facility. From an operations standpoint, you can clearly tie the application to a certain geography or a facility.

Once you have one, what do you do with it?
You can use an intelligent media gateway any place you could use a first-generation gateway. There’s no need to change any other network element. The benefit is that you have a cost effective, scalable, and robust platform. Over time, you may need to add intelligence around your network, and then you will have the option of distributing that intelligence to wherever it needs to go. A fantastic example is that as your business grows you decide to go to a distributed network model to increase stability and performance. With the right equipment selection today, your network is future proofed.

Another common use is to extend legacy equipment. Many rural local exchange carriers use older TDM switches to provide telephony service. They often find that their options are quite limited when they wish to go to VoIP. They can replace their entire infrastructure (AKA the “forklift strategy”), or they can set up a parallel infrastructure (AKA the “double your op-ex strategy”). Using an intelligent media gateway, they can add a simple VoIP service and place it next to their legacy switch. Because it’s scalable, they can start it small and grow it with revenue. Because it handles all protocols, their existing TDM customers can take advantage of the new service, just as if they were VoIP based.

Just as minicomputers empowered smaller groups inside large corporations, intelligent media gateways will do the same inside large service providers. Since they don’t require a complete infrastructure, and they are scalable, they provide the perfect platform for smaller, niche service offerings. Just like minicomputers, they can be used to overcome issues of performance, geography, politics, or legacy.

What do you look for? What should you avoid?
When it comes to purchasing intelligent media gateways, there are a growing number of vendors to choose from. Each has some variation in their offerings, but all provide the basic functionality in their platform. Here are the questions you want to ask:

  1. Openness: Is the device based on open standards? Remember that openness refers not only to call control standards, but to hardware ones as well. Pick a solution that uses common technologies such as CompactPCI, so that you don’t limit yourself from selecting other third-party technology components such as ASR or line cards.
  2. Interoperability: How much interoperation has the device been through? Could you drop it in to replace a standard first-generation gateway?
  3. Application Support: What applications are available now? Are they in use and will they generate immediate revenue? How do you create new ones? What partners are available for custom development?
  4. Traction: How many are in the field? What large companies or organizations have standardized on the device? What industry awards has it received?
  5. Carrier Class: Is it fault tolerant? Scalable? What are the management interfaces? IT

Thomas Howe is chief technology officer at Versatel Networks. For more information, please visit the company online at

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