Break down total network delay into propagation, transmission, processing and queuing delay.
Total network delay is the sum of four components: propagation delay (time for a signal to travel the physical distance), transmission delay (time to push all bits onto the link), processing delay (time for routers to examine and forward the packet), and queuing delay (time spent waiting in router buffers).
Total delay
total = propagation + transmission + processing + queuing
On long-distance links (WAN/internet), propagation delay typically dominates. On short-distance, low-bandwidth links, transmission delay may dominate. Queuing delay dominates under congestion regardless of distance.
Queuing delay depends on the current traffic load — when a router's output buffer is empty, queuing delay is zero; when many packets compete for the same output link, each waits behind those ahead of it, making queuing delay highly variable and load-dependent.