IEC 80000-13
IEC 80000-13:2008 is an international standard that defines quantities and units used in information science, and specifies names and symbols for these quantities and units. The standard is published by the International Electrotechnical Commission (IEC) and is part of the group of standards called ISO/IEC 80000, published jointly by the IEC and the International Organization for Standardization (ISO).
It is divided into the following chapters:
Scope
Normative references
Names, definitions and symbols
Prefixes for binary multiples
Names, definitions and symbols
Quantities defined by the standard include
traffic intensity (symbol A): number of simultaneously busy resources in a particular pool of resources
traffic offered intensity (symbol A0): traffic intensity ... of the traffic that would have been generated by the users of a pool of resources if their use had not been limited by the size of the pool
traffic carried intensity (symbol Y): traffic intensity ... of the traffic served by a particular pool of resources