Defects Per Million (DPM) Metric for Transaction Services Such as VoIP
|Publication Date:||1 May 2007|
This document provides definitions for a metric that can be used to gauge the ability of an IP network to deliver transaction services in an acceptable manner. A transaction is defined as an IP network session involving a sequence of related information exchanges and processing operations designed to accomplish a specified service function. Examples of transactions include Voice over IP (VoIP) phone calls, web page access, file downloads, and or e-mail services. Transactions are either successfully completed by an IP network or encounter conditions that prohibit their successful completion. Such failed transactions are called defects. The proposed metric defines the ratio of "defective" transactions to the total number of attempted transactions and normalizes them by a factor of one million - Defects per Million (DPM).
As IP networks evolve, transaction-based services may span several network domains. For example, a VoIP call may originate over an IP network and complete over the Public Switched Telephone Network (PSTN). The scope for estimating the DPM metric is restricted to the traversal over the IP network domain1. The scope of this document is also restricted to the definition of whether a transaction is "successfully" completed over the IP network portion or not. Thus, transaction quality issues such as degraded VoIP call quality caused by delay and jitter are not considered for the moment. A properly completed transaction is considered to be "successful" irrespective of the transmission quality.
This document provides an illustrative example on the use of the DPM metric for VoIP services. Examples on DPM usage for other transaction services over IP networks (e.g., Virtual Private Network services) will be discussed in future documents.
1 This limitation has been recognized in previous discussions in PRQC, and will be addressed in future documents.