# Network Delay **The delay between the beginning of transmission of a [[Packet Switching#Packet|packet]] between nodes of a network.** ![[NetworkDelay.svg|550]] *A representation of the sources of network delay* **Network delay** refers to the delay between when a [[Packet Switching#Packet|packet]] is transmitted from a source node and when it is completely received by a destination node in a network. Network delay is typically divided into four parts that arise from different sources - processing, queueing, transmission, and propagation delay. > **Processing delay** is the delay introduced by the time taken for a node to *process the header* of a packet. This time is spent checking for errors and determining the output link to forward the packet to. > **Queuing delay** is the delay introduced by the *queue of packets* waiting to be transmitted by an output link. This delay is dependent on the amount of congestion present at the node. > **Transmission delay** is the delay caused by the time taken for the entire packet to be *pushed onto a link*. > > It is dependent on the *packet length* $L$ and the *link transmission rate* $R$. > $d_{\text{transmission}}=\frac{L}{R}$ > **Propagation delay** is the delay caused by the time taken for the packet to *propagate through a link*. > > It is dependent on the *physical distance of the link* $l$ and the *propagation speed* $s$ of the signal through the link. > $d_{\text{propagation}}=\frac{l}{s}$