Packet transfer delay is a concept in packet switching

Packet switching

Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...

 technology.

The sum of store-and-forward delay that a packet experiences in each router gives the transfer or queuing delay of that packet across the network

Computer network

A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

. Packet transfer delay is influenced by the level of network congestion

Network congestion

In data networking and queueing theory, network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates. Typical effects include queueing delay, packet loss or the blocking of new connections...

 and the number of routers along the way of transmission

Transmission (telecommunications)

Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...

.

There are four sources of packet transfer delay:

1. Nodal processing:
   1. Check bit errors
   2. Determine output link
2. Queuing:
   1. Time waiting at output link for transmission
   2. Depends on congestion level of router
3. Transmission delay
   Transmission delay
   In a network based on packet switching, transmission delay is the amount of time required to push all of the packet's bits into the wire. In other words, this is the delay caused by the data-rate of the link....
   
   :
   1. R=Link bandwidth (bit/s)
   2. L=Packet length (bits)
   3. Time to send bits into link = L/R
4. Propagation delay
   Propagation delay
   Propagation delay is a technical term that can have a different meaning depending on the context. It can relate to networking, electronics or physics...
   
   :
   1. d = Length of physical link
   2. s = Propagation speed in medium
   3. Propagation delay = d/s