This Technical Bulletin discusses absolute and differential delays in Mega-E applications.
Absolute delay is the total time that a signal takes to go from one end of a circuit to the other.
Differential delay is the difference in absolute delays between two circuits. Absolute delay is calculated by adding the delays introduced by each network component that the signal traverses. The one-way absolute delay for E1 circuits is approximately 5 milliseconds per 1000 miles. Differential delay between Mega-E circuits becomes a problem only if it exceeds 125 milliseconds.