Quality Control Because OCS voice and video calls are encrypted by default, network administrators will only be able to glean a limited amount of QOS (quality of service) information from standard network-based VOIP monitoring tools. To overcome this shortcoming, Microsoft produced the OCS Quality of Experience Monitoring Server role to help administrators monitor ongoing network experience with insight gleaned from within the system.The reports are broken out according to avenue (PC-to-PC calls, PSTN-to-PC calls, PC-to-PSTN calls, and conference calls) and provide several different MOS (mean opinion scores) to represent incoming and outgoing sound quality, among other assessments. The reports also provide information on metrics like codec used, packet loss, packet reorder, packet errors, jitter and even the end-point device in use. Since OCS by default uses Microsoft's RTAudio codec-which operates as either a high-definition wideband or narrowband codec, depending on network conditions-all reported MOS are based on the richer experience expected from a wideband call. Therefore, an in-network call between two people on the same subnet may get the maximum MOS of 4.1 (using a wideband codec), while a call to the PSTN using a narrowband codec (as that's all the PSTN will support) will only get a score of about 2.5. Consequently, network administrators will need to be re-trained in the new scoring criteria applicable for high-definition audio.
Instead of viewing packets strictly from a network perspective, the Monitoring Server aggregates data from the primary call control servers (which cull data from the endpoints) and from the Mediation Servers (to monitor calls to and from the PSTN). This data is collected in the Monitoring Servers' SQL Server database, which can be queried using prepackaged Web-based reports.
Senior Analyst Andrew Garcia can be reached at firstname.lastname@example.org.