Bandwidth Delay Product

Bandwidth Delay Product (BDP) is a measurement of how many bits can fill up a network link. It gives the maximum amount of data that can be transmitted by the sender at a given time before waiting for acknowledgment. Thus it represents the maximum amount of unacknowledged data that can be "in flight" on the network.

Calculation Formula

Bandwidth delay product is calculated as the product of the link capacity of the channel and the round-trip delay time of transmission:

BDP = Bandwidth × Round Trip Time

• Bandwidth (Link Capacity) − The number of bits transmitted per second, measured in bps (bits per second)

• Round Trip Time (RTT) − The sum of the time taken for a signal to travel from sender to receiver plus the time for acknowledgment to return, including all propagation delays

The unit of bandwidth delay product is bits or bytes.

Example Calculation

Consider a channel with link capacity of 512 Kbps and round-trip delay time of 1000ms:

BDP = 512 × 10³ bits/sec × 1000 × 10?³ sec
    = 512,000 bits
    = 64,000 bytes
    = 62.5 KB

Long Fat Networks (LFN)

A Long Fat Network (LFN) is a network having high bandwidth delay product which is greater than 10? bits. These networks are characterized by either high bandwidth, high latency, or both.

Examples of LFN

• Ultra-high-speed LANs − Local area networks with very high bandwidth

• Satellite connections − WANs through geostationary satellite links with high propagation delay

• Transcontinental fiber links − Long-distance connections with significant round-trip times

Practical Implications

Understanding BDP is crucial for network optimization because it determines the minimum buffer size needed at the sender and affects window sizing in protocols like TCP. Networks with high BDP require larger send windows to maintain efficient throughput.

Conclusion

Bandwidth Delay Product represents the maximum amount of data that can be in transit on a network link before acknowledgment is required. It is calculated as the product of bandwidth and round-trip time, and is essential for understanding network capacity and optimizing protocol performance, especially in Long Fat Networks.