Queueing Delay

networking

Definition

Queueing Delay

Let a packet arrive at a node $v$ and be assigned to an output link $e$. Let $Q_e$ be the queue of packets already waiting for transmission on $e$.

The queueing delay $d_{\text{queue}}$ is the time the packet waits in $Q_e$ before its first bit is transmitted onto $e$.

Unlike other delay components, $d_{\text{queue}}$ is variable: it depends on the number and size of packets ahead in the queue, the link rate, and the arrival pattern of competing traffic.

Let $L_a$ be the total length (in bits) of all packets ahead in $Q_e$ and $R$ the link rate. Under first-come-first-served queuing:

$$d_{\text{queue}}\approx \frac{L_a}{R}$$

$d_{\text{queue}}$ is a component of the total packet delay. It is often the dominant and most unpredictable component.