defining the time it takes to do something (latency, throughput, bandwidth)

I unders开发者_如何学JAVAtand latency - the time it takes for a message to go from sender to recipient - and bandwidth - the maximum amount of data that can be transferred over a given time - but I am struggling to find the right term to describe a related thing:

If a protocol is conversation-based - the payload is split up over many to-and-fros between the ends - then latency affects 'throughput'¹.

¹ What is this called, and is there a nice concise explanation of this?

Surfing the web, trying to optimize the performance of my nas (nas4free) I came across a page that described the answer to this question (imho). Specifically this section caught my eye:

"In data transmission, TCP sends a certain amount of data then pauses. To ensure proper delivery of data, it doesn’t send more until it receives an acknowledgement from the remote host that all data was received. This is called the “TCP Window.” Data travels at the speed of light, and typically, most hosts are fairly close together. This “windowing” happens so fast we don’t even notice it. But as the distance between two hosts increases, the speed of light remains constant. Thus, the further away the two hosts, the longer it takes for the sender to receive the acknowledgement from the remote host, reducing overall throughput. This effect is called “Bandwidth Delay Product,” or BDP."

This sounds like the answer to your question. BDP as wikipedia describes it

To conclude, it's called Bandwidth Delay Product (BDP) and the shortest explanation I've found is the one above. (Flexo has noted this in his comment too.)

Could goodput be the term you are looking for?

According to wikipedia: In computer networks, goodput is the application level throughput, i.e. the number of useful bits per unit of time forwarded by the network from a certain source address to a certain destination, excluding protocol overhead, and excluding retransmitted data packets.

Wikipedia Goodput link

The problem you describe arises in communications which are synchronous in nature. If there was no need to acknowledge receipt of information and it was certain to arrive then the sender could send as fast as possible and the throughput would be good regardless of the latency.

When there is a requirement for things to be acknowledged then it is this synchronisation that cause this drop in throughput and the degree to which the communication (i.e. sending of acknowledgments) is allowed to be asynchronous or not controls how much it hurts the throughput.

'Round-trip time' links latency and number of turns.

Or: Network latency is a function of two things:

(i) round-trip time (the time it takes to complete a trip across the network); and

(ii) the number of times the application has to traverse it (aka turns).