This Recommendation describes relationships among the following ITU-T Recommendations: G.781, G.783, G.798, G.803, G.810, G.811, G.812, G.813, G.821, G.822, G.823, G.824, G.825, G.826, G.827, G.828, G.829, G.921, G.8201, G.8251, I.350, I.352, I.353, I.354, I.355, I.356, I.357, I.358, I.359, I.381, Y.1530, Y.1540, Y.1541, Y.1560 and Y.1561. Collectively, these Recommendations provide the basis for the specification and apportionment of performance in narrow-band and broadband ISDNs, Internet Protocol (IP)-based networks, and digital layers of transport networks. They include jitter, wander, and network synchronization and timing performance. These Recommendations are intended to be used in describing performance between the measurement points that delimit and apportion international ISDNs, IP-based networks, and digital layers of transport networks.

The relevant Recommendations and their relationships are illustrated in Figure 1. The 3 × 3 performance description framework defined in ITU-T Rec. I.350 is used to illustrate the relationships among particular Recommendations. Three protocol-independent telecommunication functions are identified in the matrix: access, user information transfer, and disengagement. These general functions correspond to specified aspects of ISDN, IP-based network, and transport network digital layer services conforming to ITU-T standardized protocols¹. Each function is considered with respect to three general performance concerns (or "performance criteria"): speed, accuracy, and dependability. These express, respectively, the delay or rate, degree of correctness, and degree of certainty with which the function is performed. Recommendations shown within the matrix define sets of protocol-specific parameters ("primary parameters") that describe performance relative to each function and criterion. An associated model provides a basis for describing overall service availability. A specified availability function compares the values for a subset of the primary parameters with corresponding outage thresholds to classify the services as "available" (no service outage) or "unavailable" (service outage) during scheduled service time. Figure 1 presents the Recommendations that specify availability functions and define availability parameters associated with ISDN, IP-based network, and transport network digital layer services. Recommendations concerning jitter, wander, and timing and synchronization performance of digital networks are illustrated in Figure 1 by their relationships to the complementary aspects of network level jitter, wander, and synchronization performance and related timing equipment performance.

This Recommendation is organized as follows. The scope of the Recommendation is provided in clause 1. A list of abbreviations is provided in clause 2. The general scope and content of each Recommendation illustrated in Figure 1 is described in clause 3². Annex A contains information on the history of the G-series physical layer error performance Recommendations. An index listing key concepts and associated Recommendations is also provided.

¹ For B-ISDN, these general functions include multiparty and multipoint connection types.

² The most recent editions of draft and approved Recommendations should be consulted.