Bandwidth Delay Product Calculator

Welcome to the bandwidth delay product calculator! The following text will help you to understand what the bandwidth delay product (BDP) is and how to calculate it. The text explains the meaning of the formula's variables, bandwidth, round-trip delay time (RTT), and how you can find their values. We go through an example calculation and look at different communication technologies to understand why and when the BDP needs to be determined. Start calculating now, or keep reading for additional information! 🛜

The short definition: The bandwidth delay product is the maximum amount of data that can be in transit in a network, measured in bits. What does that mean? The information we want to send to a server must first be transformed into bit sequences (a sequence of 0's and 1's; take a look at our binary converter if you need a refresh on that topic).

To send these bit packages between the client and the server, we need a communication network consisting of physical and technical components such as wires, radio antennas, and routers. We determine their capacity and speed to send data with the bandwidth delay product. It tells us how many bits the sender can send before the first bit reaches the receiver. To determine the BDP, we look especially for the communication network's bandwidth (the data link's capacity) and latency, also known as round-trip delay time (RTT).

The bandwidth is the maximum amount of data transmitted over an internet connection in a given time, expressed in bits per second (bps). For example, if the bandwidth of a network is 50 Mbps, it means that the network cannot transmit data faster than 50 Mbps in any given case. Knowing the bandwidth-delay product is especially important when dealing with high-performance networks with very high bandwidth, such as Long Fat Networks (LFN), e.g., connections to satellites or LAN/ Fast Ethernet. Later in the text, we examine why the BDP value is essential for these connections.

The round-trip delay time (RTT) is the total time it takes a network to send a request from you (the client) to the server, the server processing the data, and the network sending the server's answer back to you that your device can display. Very simply, it is analogous to the total time it would take a friend to throw a ball at you and you throwing it back to him. The lower the RTT, the more responsive your application will be.

Now that we understand what the bandwidth delay product and its variables are, let's calculate it! The bandwidth delay product formula is relatively easy and only takes two variables: The bandwidth B in bits per second (bps) and the round-trip time RTT in seconds (s). Once you have these values, you can calculate the BDP in bits using the following formula:

To calculate the bandwidth delay product with this calculator:

1. Enter your bandwidth in megabits per second. If you don't know it, you can use an online speed test for your local network, e.g., Google's free internet speed test. Let's say we run a speed test and get a good download rate of 220 Mbps.

2. Enter the round-trip delay time. Let's say we get a value of 14 ms (this is the ping value on the Google internet speed test). Otherwise, you can also find it out with the ping command in your command line/ terminal: Open your command line or terminal and type ping and a domain name such as google.com.

3. That's all! The calculator will show us that our bandwidth-delay product is 3.08 Mbits. Alternatively, you can calculate 220 Mbps × 14 ms × 1000 = 3,080,000 bits = 3.08 megabits (Mbit) or 0.385 megabytes (MB).

4. What does this result tell us? It means that when the sender has sent 3,080,000 bits, the receiver has just started to receive the first bit. After, there can be 3,080,000 bits "in-flight" in the network before the sender can expect to hear back from the receiver.

We are interested in the BDP, especially when dealing with high-performance networks like Long Fat Networks (LFN). They have a very high bandwidth but also a very high delay. Examples are connections to satellites or LAN/ Fast Ethernet.

The BDP is of particular interest in the design of the Transmission Control Protocol (TCP) of these networks. These protocols track the transmitted data: a sender will send data segments, and the receiver will acknowledge the segments. If all segments pass without problems, the sender increases the data size (called window size) of the following package it sends. If the receiver acknowledges this bigger package, the sender will send an even bigger package with the next send. But when the receiver doesn’t send an acknowledgment within a specific time (called the round-trip time), the window size will be reduced again. You see, the sender always has to wait to send the following data package until he gets the acknowledgment from the receiver.

Now, imagine we want to communicate with a satellite that is 22,000 miles (35,405 km) away. The sender has to wait a very long time for an acknowledgment from the receiver before sending the next data packet, and the size of the sent data packets stays relatively small. While waiting, nothing happens, so we don’t use the total bandwidth of our link. By calculating the bandwidth-delay product, we can find the perfect window size to fill the network stream with the maximum data segments to minimize the waiting time.

So, the bandwidth-delay product tells us the needed data window size to let one stream of the transmission control protocol utilize the complete bandwidth of the connection, which results in faster communication.