ATIS - Alliance for Telecommunications Industry Solutions
Scope
"Purpose and scope The purpose of this standard is to define a comprehensive basis for assessing the performance of Integrated Services Digital Networks (ISDNs) providing telecommunication service in accordance with the American National Standards and ITU-T Recommendations identified herein. This standard: (a) defines parameters that may be used to describe the performance of ISDN bearer services and (b) specifies worst-case objectives for the ISDN performance parameters. The parameters and objectives are applicable to circuit mode and packet mode ISDN bearer services. Unless noted otherwise in this standard@ the defined parameters and specified objectives apply to ISDN services using a single B channel and/or D channel; planned revisions to this standard will address other ISDN bearer services (e.g.@ n ?? 64 kbit/s). Practical methods for measuring ISDN parameter values will be specified in a planned supplement to this standard. For each ISDN bearer service@ performance is considered in the context of the 3??3 performance matrix defined in American National Standard for Information systems ?C Data communication systems and services ?C User-oriented performance parameters@ ANSI X3.102-1992 (see figure 1). 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. This standard defines a comprehensive set of primary parameters that describe performance relative to each function and criterion. The objectives specified for the primary parameters apply only to connections in the available state. A two-state model provides a basis for describing overall service availability. A specified availability function compares the values for a set of ""supported"" primary parameters with corresponding outage thresholds to classify the service as ""available"" (no service outage) or ""unavailable"" (service outage). This standard specifies the availability function and defines the availability parameters that characterize the resulting binary random process. The parameters defined in this standard may be used to specify or measure the performance of end-to-end ISDN connections or connection portions. This standard defines two general ISDN connection portion types: access portions and transit portions. These portions are delimited on the basis of jurisdictional boundaries between carriers and corresponding jurisdictional boundaries between carrier facilities and customer premises equipment. This standard defines worst-case objectives for each portion type. The measurement methods that will be defined in a supplement to this standard will be applicable in direct measurements at the defined jurisdictional boundaries or may be used to estimate performance at jurisdictional boundaries on the basis of observations made at adjunct functional boundaries (e.g.@ switch locations)@ taking account of known characteristics of the access or transit links that connect equipment in separate jurisdictions. All values specified in this standard (with the exception of table 14) are based on (and only apply under) the following assumptions: ?C values for primary performance parameters exclude performance observed during periods of unavailability; ?C for each connection portion type@ the ten worst-performing days in a calendar year are excluded. In the context of this standard@ the term@ worst-case@ means that the design objectives should be met by all portions of any end-to-end connection configured and used in accordance with the conditions and assumptions identified in this standard. The design objectives specified in this standard may not be achievable in all network configurations existing at the time of its publication. They represent agreements among service providers and end users applicable to the planned evolution of ISDN bearer services and their interconnection. The actual values achieved in a connection portion will depend on many factors@ including the traffic expected and actually offered@ the internal network topology@ and the signalling rates on the access and internetwork circuit sections. Variation away from the worst-case value for each factor can improve performance. In some cases@ two sets of values are specified for access portions depending on their interconnection to the transit portion. One set of values applies when the access portion is nominally interconnected to the transit portion. The other set applies when the access and transit portion providers cooperatively plan the interconnection. These two sets of values are called nominal interconnection values and cooperatively planned interconnection values@ respectively. An example of a cooperatively planned interconnection is one that reduces the number of switches between the NI and the INI. The organization of this standard is summarized in figure 2. Clause 2 identifies the normative references. Clause 3 defines an ISDN performance model that (a) specifies the boundaries and connection portion types and (b) defines a set of protocol-specific reference events that provide a basis for performance parameter definition. Clauses 4 and 5 provide a basis for performance assessment of ISDN circuit mode bearer services and packet mode bearer services@ respectively. These clauses define protocol-specific performance parameters and specify worst-case performance objectives. Annex A provides a bibliography."