Ditech Networks' Solutions
Codec Normalization for VoIP Service Providers
The ability to use a common infrastructure to deliver multiple services is a strong driver for VoIP, but as VoIP becomes more prevalent, new network issues are appearing. A major problem is the choice of a coder-decoder (codec) to convert voice signals from analog to digital. The Time Division Multiplex (TDM) de facto standard is G.711 for fixed-access solutions, but for many new VoIP applications, G.711 is too bandwidth intensive. Where bandwidth may not be a concern, network operators may want to differentiate service quality by offering wideband codecs for better-than-PSTN voice quality. Because of the advantages of specific codecs for specific applications, the industry is seeing an increasing number of codecs in the network, including G.711A/µ, G.726, G.729a/b/e/g, G.722, G.723.1, EVRC, GSM-HR, GSM-FR, iLBC, Speex, and many others.
| Supported Codecs | Ditech Platform | ||
*Future Capability |
Ditech’s Codec Normalization solution is available on the Packet Voice Processor:
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The Need for VoIP Codec Normalization
Network operators now face a dilemma. How do they choose codecs that are interoperable with all network equipment, across multiple operators, and still meet the need for flexibility within an acceptable economic model? Today, adding codecs requires support for each codec on all nodes in the call path. From the operations point of view, this can be a significant commitment to test, deploy, and administer. From a capital standpoint, the costs become prohibitive as the network grows, because each supported codec adds cost in the media gateways, media servers, and application servers. Not only is the addition of a new codec an expensive proposition, but it also reduces channel density because of the increase in MIPS required by more complex codecs. For these reasons, most providers are forced to deploy additional networking equipment (Figure 1).
Figure 1 – Equipment Required by Various Codecs
The Codec Normalization Solution
The most straightforward way to increase the number of supported codecs is to perform codec normalization at the access border of the VoIP network. This allows a diverse set of application-specific codecs in the access network to operate with a single codec in the core. The codec for the core remains G.711 because it requires the lowest processing effort, has a reasonable cost-to-density ratio, and is universally supported by the various network elements.
Ditech Networks’ Packet Voice Processor™ is an ideal solution for supporting diverse codecs in the access network. The Packet Voice Processor provides codec transcoding on up to 13,440 channels in a shelf, and over 40,000 channels per telco rack. It is available as a fully redundant, NEBS-compliant chassis for central office deployment.
The Packet Voice Processor offers significant savings compared to media gateway or media server based solutions, where additional codec options can increase equipment cost by as much as 75%. The benefits of the Packet Voice Processor include a reduced codec burden on application and feature servers and the ability to add or upgrade codecs without affecting equipment in the core.
For Codec Normalization, the Packet Voice Processor is placed at the network border as shown in Figure 2. At the defined boundary between the aggregation/access network and the core VoIP network, the Packet Voice Processor normalizes all media traffic to a chosen codec, since all media must traverse this aggregation point. The core VoIP network can then consist of equipment that only supports one or two key codec types (e.g., narrowband G.711 and wideband G.722), while the access network can support any codec type that is desired.
Figure 2 – Ditech’s Codec Normalization Solution at the VoIP Border
Conclusion
Implementing Ditech’s Codec Normalization solution at the VoIP border establishes a consistent codec interface between users and all core network elements. This consistent interface reduces equipment costs, improves interoperability, and allows network growth to occur quickly and cost effectively.