VoIP Gateways

The benefits of creating an infrastructure to support all forms of communication including data, voice and video are undeniable. Traditionally, voice data has been carried over circuit-committed protocols of the time division multiplexing (TDM) based public branch exchange (PBX). With this type of network, large amounts of unusable bandwidth occur during pauses in the conversation due to the TDM lines dedication of one pre-determined circuit/path for the duration of each call. With VoIP however, voice shares the same network with data and video effectively consolidating bandwidth by sending packets to any available path at any given time resulting in more efficient use of the network.

The objective of VoIP is to provide the same high-availability, high-quality voice service that users currently receive from the TDM based system. Nevertheless, the known systems and methods for managing and monitoring IP networks create several drawbacks with respect to VoIP. Numerous attributes negatively affect voice quality. VoIP consists of numerous components and moving parts as well as many protocols that may result in a loss of voice communication. In addition, because there are multiple vendors creating such parts, compatibility becomes an issue. Even when successful communication is achieved, voice quality must then be ensured. These issues need to be detected and isolated for better VoIP management.

Major Problems within VoIP Development
Outage Bringing many different systems and elements to deliver phone calls is not an easy task due to so many compatibility issues and possible interconnections. Any one of these VoIP elements can fail at any given time. Unfortunately, detecting an outage can become very cumbersome and time consuming and difficult to isolate the problem in an satisfactory time frame.

An event-driven alarm system detecting vital problems is one solution. By implementing an intelligent (management) server that is ready to receive alarms and send relevant information through elements like a SNMP trap, email/pager, carrier console, or an intelligent console, the finger-pointing should diminish as should the network managers workload.

The VoIP management server could also check vital signs by polling the connections. To determine whether a specific IP address is accessible, a ping sends a packet, or message, to another computer and waits for acknowledgment. The nature of acknowledgment received determines the IP address availability. Blind polling sends a ping to every element in the network a predetermined number of times per minute. This type of polling monitors the entire network at the expense of bandwidth. Therefore, a better polling option is severity-based. Severity-based polling transmits a ping to critical elements more often. Dynamic polling could also be introduced to babysit any failed pieces by increasing the number of pings to that particular piece. The number of pings would be recalculated based on the number of previous faults.

Voice Quality More vital to VoIP than outage problems are the characteristics that negatively affect voice quality. Since voice shares the same network with data, care must be taken to ensure that voice quality is preserved. Users demand the quality of VoIP match the business quality that PSTN voice routinely provides. Perceived voice quality is a function of many factors, including delay, line noise and echo, and jitter.

Obviously, each listener determines voice quality differently. As a result, a mean opinion score (MOS) was created by the International Telecommunication Union, Telecommunication Standardization Sector (ITU-T) as a benchmark to determine the quality of sound. A wide range of men and women rated the quality of pre-selected voice samples on a scale from 1 (bad) to 5 (excellent). The scores were averaged to provide the MOS for each sample. Communication quality is rated in the 3 - 4 range.

Given that the MOS is a highly subjective interpretation, the ITU-T created an automated scoring process (P. 861). The latest standard for assessing voice quality is Perceptual Evaluation of Speech Quality (PESQ, ITU-T P.862). PESQ builds on the PSQM and PAMS algorithms by adding additional processing steps to account for signal-level differences and the identification of errors associated with packet loss.

The Right Tools for the Job
Data network management tools are not readily adaptable to VoIP. Therefore, a system and method are needed for managing VoIP systems providing real-time performance monitoring of VoIP and other IP network components in a way that is relevant to voice communications.

A total quality management and measurement tool is needed to not only detect but also isolate any voice quality problems. Both real-time and trend information are essential to management views and reports. A central server can be created to dynamically collect performance/delay data from various sources to continuously calculate variable polling periods and inject active packets as necessary. The server can analyze the importance of each problem and report them to a console via an alarm. The console would send instructions back to the server to inject appropriate active test packets into the VoIP network to pinpoint the trouble spots. The console can then display overall call quality with display drill down to detail elements with MOS and R-Factor. VoIP users need a single, comprehensive and consolidated view of call quality and VoIP infrastructure behavior. Therefore, a complete, sophisticated tool is a must-have to perform enterprise-strength monitoring and management.

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Choon B. Shim is CTO and Senior VP of Engineering of Qovia, Inc., a market leader in monitoring and management products for enterprise IP phone systems. For more information please visit www.qovia.com.