Digital transmission network models are hypothetical entities of a defined length and composition for use in the study of digital transmission impairments (e.g. bit errors, jitter and wander, transmission delay, availability, slip, etc.). The diversity of possible network situations requires that individual models can only represent a small portion of typical real entities. However, a limited number of such models (e.g. 2 or 3) together may be sufficiently representative to provide a useful tool upon which studies may be based.