Voice over Internet Protocol (VoIP)

Introduction

The topology and behavior of circuit-switched networks and data networks are significantly different. Voice traffic carried over a system originally designed for data creates technical challenges that must be addressed to ensure a high quality of service (QoS). QoS refers to the ability of a network to satisfy voice traffic and service requirements. Circuit-switched networks sacrifice maintenance costs for a high QoS, and data networks sacrifice QoS for bandwidth efficiency. Circuit-switched networks have a high QoS because they dedicate bandwidth resources to each individual call for the duration of that call. However, dedicating permanent resources to an individual call creates significant cost disadvantages for circuit-switched networks. Additionally, because most voice conversation consists of “pauses” where no voice transmission takes place, circuit-switched networks cannot utilize available bandwidth efficiently, resulting in a cost disadvantage when compared to data networks.

Unlike circuit-switched networks, data networks do not dedicate permanent resources to an individual call between two locations. Instead, data is prepared for network transport by attaching classification information to the packet header, which is attached to the payload. The data network uses the path in the network that optimizes the utilization of available bandwidth.

Discussion

Currently, very couple of commerce standards lives for VOIP products. System implementations vary from complete software architectures to complete hardware architectures to combinations of both. Because a VOIP environment lacks defined standards, specifying and fabricating an ASIC device using a particular standard introduces significant risk as standards evolve. Altera programmable logic devices (PLDs) in VOIP-enabled products are ideal because they can be reconfigured and can provide fast time-to-market.

Altera provides a range of IP functions that give the designer access to a vast array of applications commonly used within VOIP applications. Parameterizable, shrink-wrapped solutions allow the designer to concentrate on system architecture optimization.

The VOIP gateway example network system provided in this section highlights the IP functions and APEX device features that can provide implementation-level benefits to VOIP developers. The VOIP gateway network system consists of a shelf, which contains three bus lines and two types of cards, each featuring an APEX device. The first type of card in the VOIP network interfaces with the Internet infrastructure and is referred to as the digital access card (DAC). The second kind of business card manages the interface between the phone hardware and the routing network. Because much of its functionality is based on standard telephony requirements, it is referred to ...