Hi all,


1) can any one give me a more precise explanation/practical example
which clarifies the concept of latency and throughput

2) how can we measure the latency in a LAN using the httping utility

the following definitions from this site http://www.tcpipguide.com/free/t_Per...ghputand-2.htm

seems to be more confusing

throughput

Throughput is a specific measure of how much data flows over a channel in a given period of time. It is usually a practical measurement.


Latency

refers to the timing of data transfers on a communications channel or network. One important aspect of latency is how long it takes from the time a request for data is made until it starts to arrive. Another aspect is how much control a device has over the timing of the data that is sent, and whether the network can be arranged to allow for the consistent delivery of data over a period of time. Low latency is considered better than high latency.

These seem to be good definitions; the only thing I can add, in a practical manner is that latency is pragmatically taken as a measure of how long before something happens.

Let's say that you want to use 5 gallons of water to take a 5 minute shower. Would you rather that all 5 gallons be dumped on you at the end of 5 minutes, or that it flowed at a linear rate for the whole 5 minutes? In both cases the throughput would be the same over 5 minutes, but in one case, the latency would be 5 minutes.

After going through the book "Linux Networking Cookbook" by Carla Schroder i found the following explanation


there is often confusion between bandwidth,latency, and throughput. Broadband means fat pipe, not necessarily a fast pipe. As us folks out here in the sticks say, “Bandwidth is capacity, and latency is response time.

Bandwidth is the diameter of your irrigation line.

Latency is waiting for the water to come out.”

Throughput is the amount of data transferred per unit of time, like 100 Kbps.

So, you could say throughput is the intersection of bandwidth and latency.

Bandwidth is generally understood to mean the maximum data transfer rate of a given link. A 6-meg satellite internet connection has much greater bandwidth than a 56k dial-up modem does.

Latency means delay -- in networking, it refers to how long it takes to send one packet from one host to another -- often measured with ping, and therefore the time is for the round trip. Due to the 44,000-mile trip to and from the satellite -- 88,000 for your ping to get to the other system and then back -- the latency for the satellite link is MUCH MUCH WORSE than for the dial-up modem. You cannot possibly ping anything over the satellite link in less than 500ms -- light can only go 186,000 miles/sec. You can ping the other end of your dial-up connection is something under 50ms.

The kicker comes when you want to transfer a file. The modem will be slow due to the low bandwidth. But it will also be far less than 6 megabits over the satellite link, due to the nature of TCP. (The transfer will flow, then stop while the receiving host acknowledges receiving the data, which takes 1/4 second in this example, over and over.) You can improve the behavior of the transfer over satellite by dramatically increasing the tcp window size on both hosts involved in the transfer.

doc