The propagation speed depends on the physical medium of the link (that is, fiber optics, twisted-pair copper wire, etc.)
Example: Ethernet communication over a UTP copper cable with maximum distance of 100 meter between computer and switching node results in: The packet delivery time or latency is the time from when the first bit leaves the transmitter until the last is received.
In the case of a physical link, it can be expressed as: In case of a network connection mediated by several physical links and forwarding nodes, the network delivery time depends on the sum of the delivery times of each link, and also on the packet queuing time (which is varying and depends on the traffic load from other connections) and the processing delay of the forwarding nodes.
It is affected by packet delivery time as well as the data processing delay, which depends on the load on the responding node.
If the sent data packet as well as the response packet have the same length, the roundtrip time can be expressed as: In case of only one physical link, the above expression corresponds to: If the response packet is very short, the link roundtrip time can be expressed as close to: The network throughput of a connection with flow control, for example a TCP connection, with a certain window size (buffer size), can be expressed as: In case of only one physical link between the sending and transmitting nodes, this corresponds to: The message delivery time or latency over a network depends on the message size in bit, and the network throughput or effective data rate in bit/s, as: