Packet-Switched Network Delays

There are four major types of delays on each node of a packet-switched network:

Processing Delay

When a packet reaches a router, the router reads the header, locates its final destination, and decides which outbound link to send it on. It also may do some transmission error checking. These account for the processing delay.

Queueing Delay

Most routers utilize a first-come-first-serve queue for packet traffic. If traffic on the router is busy, then the packet will have to wait in a queue for its turn to be transmitted by the router. This accounts for the queueing delay.

Transmission Delay

The amount of time it takes a router to push out the next packet on to the link is the transmission delay. This delay is a function of the size of the packet and the transmission rate of the link.

L = packet length
R = transmission rate of link 
delay_trans = L / R

Propagation Delay

The amount of time it takes to propagate the packet from the beginning of the link to the next link is the propagation delay. It is a function of the length of the link and the speed of the link.

d = distance of the link
s = speed of the distance
delay_prop = d / s

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