A designation assigned to describe the service treatment and privileges given to a particular terminal. 2. A subgrouping of telephone users for the purpose of rate distinction. Note: Examples of class of service subgrouping include distinguishing between (a) individual and party lines, (b) Government and non-Government lines, (c) those permitted to make unrestricted international dialled calls and those not so permitted, (d) business, residence, and coin-operated, (e) flat rate and message rate, and (f) restricted and extended area service. 3. A category of data transmission provided by a public data network in which the data signalling rate, the terminal operating mode, and the code structure, are standardized. Note: Class of service is defined in ITU-T Recommendation X. 1. Synonym user service class.