With major telcos and cable operators now competing for IP voice customers against pure-play providers like Vonage, SunRocket, and others, good voice quality is increasingly becoming a key differentiator between VoIP service providers. Recently though, a new trend is emerging. Carriers are looking to upgrade their technology arsenals with new wideband codecs to provide better-than-PSTN voice quality, thus upping the ante for defining total voice quality for subscribers. The benefits to the user are significant.

With wideband codecs and HD voice services, users experience enhanced fidelity when compared to standard POTS phone services. The calls sound more realistic and are more pleasing to the listener. But with this new approach, higher voice quality may require additional bandwidth and may add complexity in a customer's phone. These and other obstacles can be gating factors for deploying wideband codec support network-wide. Fortunately, new solutions for addressing these challenges are coming onto the market.                                                                             

Climbing the Quality Ladder

Carriers have used VoIP to increase capacity and reduce costs on long-distance lines for more than ten years, but in the past five years, we have seen a growing shift to VoIP services for business and consumer access services. In May of 2006, a report by Infonetics Research found that 36 percent of large, 23 percent of medium, and 14 percent of small North American organizations interviewed were using VoIP products and services by the end of 2005, and that VoIP adoption would triple by 2010 among small organizations in North America. In-Stat's 2006 Consumer Broadband Survey of some 1,200 households found that 23 percent used some form of VoIP service. In this environment of growing VoIP usage, voice quality will become a competitive edge.

In the beginning, VoIP was used by hobbyists who used crude soft-phones and limited-bandwidth connections to make scratchy calls overseas. There were no quality guarantees, and static, clicking, and dropped calls were commonplace.

Today, carriers use priority queuing and other IP QoS mechanisms to deliver packet streams with low packet loss and delay, offering a user experience that is nearly -- but not quite -- as good as wired (POTS) service. Users still experience reduced voice quality and unreliable service due to packet loss and jitter, but carriers have generally met a lower voice quality expectation that is commensurate with a heavily discounted phone service. 

So where does VoIP go from here? The next level of service will come with HD voice, based on rollouts of wideband coders/decoders (codecs) and enhanced end-user equipment. This "better-than-POTS quality will encode a wider spectrum of audible speech to offer a more natural sound with fuller fidelity. Users will hear lower lows, higher highs, and a more conversant natural speech that is easier to understand and much more pleasing to the ear. The comparisons between standard and HD voice services will be similar to comparisons between standard and HD television. Carriers who want to differentiate with high-quality enterprise services with clearer, more natural calling and high-definition audio conferencing will be the first to adopt wideband codec based equipment. 

HD Voice Requirements

Carriers use media gateways to convert TDM voice to VoIP packet streams. The deployment considerations must satisfy operational and service quality requirements to deliver reasonable voice quality with affordable levels of bandwidth and processing power. Each voice channel (or call) requires network bandwidth, while the encoding/decoding process requires processing horsepower. Ideally, a codec would encode speech to perfectly represent the original analog waveform (as spoken by the individual) while using virtually no bandwidth and very little processing power. 

Unfortunately, carriers must make tradeoffs. In the earlier years of the Internet and VoIP services, bandwidth was limited and simplicity was the key consideration. While there are more than twenty codecs in use today, the most popular one has continued to be G.711. This codec has low processing overhead (0.2 MIPS per channel) but requires a high amount of bandwidth (64Kbps per channel). The G.711 codec captures the majority of the audible voice spectrum, representing a range from 300-3400Hz. Other encoding technologies offer similar performance with lower bandwidth per call, but with much higher processing requirements: for example, the G.729a codec shrinks the per-call bandwidth requirement to 8Kbps, but requires 35 times as much processing horsepower (7.55 MIPS per channel).

As advances in core and metro networking have made more bandwidth available, carriers are now able to use more bandwidth to allow improvements in the representation of actual speech. New wideband codecs such as iSAC and AMR Wideband will encode a much larger spectrum (50-7000Hz), but with higher processing requirements than standard narrowband codecs. A common measure of transmitted voice quality is the Mean Opinion Score (MOS). While narrowband voice has a maximum potential MOS score of 4.2 with G.711, wideband codecs can surpass this level, increasing far beyond narrowband's quality potential.

Wideband Codec Implementation Challenges

Carriers that are looking to begin deploying wideband codecs in 2007 will face tradeoffs between bandwidth usage, available processing power, and voice quality. In addition, the migration to wideband codecs will also force considerations about how to manage equipment migrations while maximizing investments in existing media gateways and media servers. Carriers will also have to consider how to deliver high quality to end users via customer premises devices.

To date, media gateways and media servers have been designed to offer a low cost per channel; their architectures are optimized for the G.711 codec. As a result, these media gateways do not have the processing power to handle increasingly complex codecs, including wideband codecs. Naturally, carriers will want to avoid replacing hundreds or even thousands of media gateways throughout their networks, if possible.

Another significant issue to address is the topic of codec transcoding. Carriers already deploy equipment to translate traffic from TDM to G.711 based VoIP, but this capability must be upgraded to ensure transcoding for wideband codecs as well.

Finally, there's the issue of endpoint devices. To experience HD-level voice, end users must have PBXs, telephones, and soft-phones that support the wideband audio spectrum. In many cases, these devices will require additional signal processing horsepower, enhanced microphones, and the capability to encode and decode packet streams using wideband codecs.

Deployment Strategies and Decisions

When new wideband codecs are offered in carrier equipment in 2007, carriers will need to determine how to deploy wideband codec equipment as well as develop an appropriate network migration schedule. They will also need to decide how these services are made available to their subscribers. For example, will HD voice be offered as a premium service, or will it become an upgrade to existing subscriber services to further differentiate from the competition? 

Many of these decisions will depend on the importance of voice quality to each carrier's customer base, and whether the carrier feels it will gain differentiation by adding higher-quality voice services for business or residential customers. 

As for the actual deployment of wideband capable equipment, carriers should look for the best way to maximize existing media gateway investments. One strategy is to deploy a media processing platform that has been purpose-built to handle a full range of narrowband and wideband codec processing needs including codec transcoding. By deploying these platforms in the network, carriers can retain their existing media gateways for basic TDM-to-packet conversion using the G.711 codec while offloading processing and transcoding of wideband codecs to the new media processing platforms. 

When the carrier rolls out HD voice services to customers, it should offer a range of HD-capable PBXs or PBX upgrades, phones, and other devices to complete the end-to-end service delivery. This may also help carriers gain additional revenue through the sale of wideband capable equipment along with premium services.

Just as it is transforming the video world, HD quality will transform VoIP services, and ultimately wideband codecs will offer a new standard for business-grade voice. By considering the required changes and deployment strategies now, carriers can prepare themselves to make the right moves at the appropriate time.

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