"Introduction The purpose of this standard is to define a set of parameters that may be used in specifying and measuring the performance of packet switched data communication services provided in accordance with ITU-T Recommendations X.25 and X.75. The defined parameters are applicable to switched virtual-call services. Some parameters pertain to permanent virtual-circuit services as well. They describe four general service performance characteristics: speed@ accuracy@ dependability@ and availability. The parameters defined in this standard may be used to specify or measure the performance of any entity delimited by the boundaries defined in ITU-T Recommendations X.25 and X.75. This standard specifies the boundaries@ described in ITU-T Recommendations X.25 and X.75@ at which performance can be measured. The specification of these boundaries is not intended to imply any specific allocation of performance responsibility. The organization of this standard is summarized in figure 1. For comparability and completeness@ packet switched network performance is considered in the context of the 3x3 performance matrix defined in American National Standard for Information systems - Data communication systems and services - Useroriented performance parameters@ ANSI X3.102-1992. Three protocol-independent data communication functions are identified in the matrix: access@ user information transfer@ and disengagement. Each function is considered with respect to three general performance concerns (or ""performance criteria""): speed@ accuracy@ and dependability. A two-state model provides a basis for describing service availability. Clause 2 presents normative references. Clause 3 defines sections of a virtual connection whose boundaries are associated with the interfaces described in ITU-T Recommendations X.25 and X.75@ and defines a set of packet layer reference events (PEs) that provide a basis for performance parameter definition. Clause 4 defines protocol-specific speed-of-service parameters associated with each of the three data communication functions. Clause 5 defines protocol-specific accuracy and dependability parameters associated with each function. Clause 6 specifies the availability function and defines availability parameters. Clause 7 defines measurement methods to be used in assessing and comparing the performance of packet-switched data communications services. Clause 8 specifies worst-case design objectives for the packet-switched performance parameters defined in clauses 4@ 5@ and 6."