Service providers have a great deal to gain through VoP implementations. They envision new revenue opportunities in leveraging the open architecture of packet-based services to quickly bring to market new and enhanced services while reducing operating costs through the deployment of packet-based networks. Service providers, however, will not sacrifice the tradition of toll-quality voice for the benefit of deploying a single converged infrastructure.

The solution density concept can help service providers and platform developers more clearly understand and implement high density VoP. VoP solutions cannot be evaluated merely for the number of channels on a chip. From a system engineering perspective, a solution must be evaluated on how the combination of system elements deliver a complete solution with lowest power and smallest area without compromising voice quality and features. Solution density then, refers to the optimization of channel density, power, architecture, integration of system functions, and I/O with the required software-based features for the targeted application (i.e., high density, carrier-class gateways).

The solution density concept provides a framework to evaluate solutions based on the integration of all major system elements and features by considering factors beyond just the number of channels and area for any single component. The following areas are important to service providers as they move to implement packet-based voice networks:

• Quality and reliability
• Scalability
• Flexibility

Quality and Reliability

Standards for VoP quality and network reliability are the same as for traditional telephone networks. Customers expect service quality to be consistent with traditional telephone networks. Packet-based voice is transparent to the customer. High-density VoP implementations are often discussed in terms of carrier class or toll quality, which are universally associated with the high-quality voice services. These terms set the expectation for quality of service providers and more important, their customers.

Features such as tone processing, packet play-out, voice activity detection (with comfort noise generation), and echo cancellation are key in meeting quality expectations. These features require a robust and in-service-hardened implementation to be considered toll quality. The absence of any of these features will result in less than toll-quality voice service.

Scalability

The ability to scale VoP networks to large volumes of traffic is critical to service providers justifying deployment of a packet-based infrastructure. Scalability requires VoP gateways to support very high volumes of traffic without degradation of voice quality. This places increased pressure on gateway vendors to support thousands of voice channels on a single platform driving the need for a system-level evaluation of density.

In most cases, density will be limited by the power requirements for the total system. Service providers must maintain power and cooling within industry guidelines (i.e., NEBS specifies a maximum of 1275 watts for a 23-inch bay with forced air cooling). For platform developers, this important design criterion can only be met with a solution that optimizes the design for power and area while maintaining carrier-class features. Therefore, the most important performance specification is not channels per chip but power per channel. It is possible that a service provider will run out of power-budget before shelf space in a bay. This would result in underutilization of central office space driving higher operational costs. Power per channel is the key metric.

Flexibility

Flexibility includes the ability to add new services and to react to standards evolution. VoP gateway platforms based on solutions that support features beyond pulse code modulation (PCM) voice (features such as low bit-rate CODECs and fax relay) enable service providers to add services without the disruption and expense of replacing equipment. These software-based features allow platform developers to distinguish their gateways from the competition. From a solution density perspective, architectural considerations, such as sizing of DSP resources and memory, will determine a solution's level of flexibility.

Key Solution Density Criteria for High-Density Applications

RISC/DSP Processor	Integration of System Functions	Integration of System Interfaces	Power Consumption	Channel Density	Voice Features	Cost
Multicore DSP	Medium	Medium	High	High	High	High

Table 1 summarizes the key criteria for high density solutions from a solution density perspective.

The architecture of a high density VoP gateway is discussed in the following section with focus on power, channel density, and voice features supporting true carrier-class voice.