Delay bandwidth product

from Wikipedia, the free encyclopedia

The delay bandwidth product ( English bandwidth-delay product , BDP ) is a term from network technology and is a property of a data connection. It is calculated as the product of the delay (unit: second) and the data transmission rate (unit: bits per second). The result, a data volume specified in bits or bytes, corresponds to the number of data that are on the way when one or more transmitters fill the transmission channel .

A network with a large delay bandwidth product is referred to as a long fat network (LFN, German  long, wide network ). RFC 1072 defines a network as LFN if the delay bandwidth product is greater than 10 5 bits (12500 bytes).

The delay-bandwidth product plays a role especially in the design of reliable transport protocols such as TCP . Acknowledgments of receipt are used to ensure that the data sent has been received successfully. A high throughput can only be achieved if the sender can send sufficiently large amounts of data before it has to pause and wait for an acknowledgment of receipt by the recipient . If the amount of data sent is low compared to the delay bandwidth product, then the protocol cannot achieve maximum efficiency. In this context, the delay bandwidth product is also calculated as the product of the data transmission rate and the packet round-trip time.

In the case of a connection to a geostationary satellite, for example Internet access via satellite , the delay and possibly the bandwidth are very large. The resulting delay-bandwidth product may require adjustments in stop-and-wait protocols in order to be able to utilize the maximum bandwidth.

example

For a channel with a data transmission rate of 100 Mbit / s (such as with Fast Ethernet ) and a delay of 20 ms, the following calculation results for the product:

Delay × data transmission rate = 20 ms × 100 Mbit / s = 20 × 10 −3  s × 100 × 10 6  bit / s = 2 × 10 6  bit, or 2 Mbit, or 250 kbytes.

Slow satellite network: 512 kbit / s, 900 ms packet cycle time

Delay × data transmission rate = 900 × 10 −3  s × 512 × 10 3  bit / s = 460,800 bit, / 8 = 57,600 B (56.25 KiB)

Individual evidence

  1. ↑ Christoph Meinel, Harald Sack: Digital Communication: Networking, Multimedia, Security , Springer, 2009
  2. ↑ Medhi, Deepankar: Network Routing: Algorithms, Protocols, and Architectures , Morgan Kaufmann, 2010 (English source)
  3. ↑ TecChannel: Basic Network Knowledge, Part 1 , accessed: March 7, 2014.

See also