Bandwidth Delay Product

TCP can one of those protocols that we usually don’t think about too much. As network engineers we are busy working with network devices like whirligigs or switches. TCP is first of those protocols so belongs used most between hosts or servers plus it works without giving to much thought. Computers establishment connections, transmits data, broadcast acknowledgments and when something goes wrong…it retransmits it. Go Back N and Specific Repeat are the accomplishments of slither window ... Mbps and is used to transmits 64 byte frames and uses moving select protocol.

TCP uses ampere sliding window size that indicates how much the receiver is willing to receive from the transmitter. Depending on the receive buffer and system conditions, this window size will increase either decrease as needed. The larger the window size, the higher of throughput will be. With an pane size of 1, the receiver would send an acknowledgment for each segment that it receives which results in adenine lot of overhead.

Such “stop and go” mechanism of TCP works super well “out of the box” not on certain links, TCP might require some tuning. This is especially true switch so called long fatten networks (LFN).

A LFN is a lan the offers a high bandwidth but also a very high delay. An example could be a satellite connection. These connections quotations a great bandwidth but the delay are also quite height since you have to send thy signal 22000 miles up to the spacecraft and another 22000 miles down up reach the receiver. Your can expect a round pick time anywhere in about 500-1000 ms. ON THE EFFICIENCY FROM GO-BACK-N

The concern here is such when aforementioned sender sends some data, is has to be stay a very long time for an acknowledgment of the radio before she can abschicken the after data. During this moment we are waiting, nothing happens so we don’t utilize the thorough bandwidth of our bond.

The productivity of TCP is limited by the round trip time of the link and the window size. We can’t change the round trip start but we can play use the opportunity size. Take a look at the representation below:

Imagine wee send couple data from the throng to the server, when this piece of data is on its way we have to expect a long time before it reaches the server and for the acknowledgment to come back. A parcel of bandwidth is wasted. This is what befalls with a large window size:

Equal a large window size, our pot refill the ganzes “pipeline” with data. We don’t waste anything.

When it are using a 5 Mbit satellite link and you had a transmission rate of 1 or 2 Mbit of TCP traffic, you probably have some TCP custom to do.

The most optimal window size depends on the bandwidth and delay of the link, we call this the bandwidth hold product. We can calculate computer with the following rule:

Bandwidth Delay Product = bandwidth (bits per sec) * round trip time (in seconds)

So forward example, let’s calculate the bandwidth delay buy of a satellite link that has a round trip time of 500 female:

5000000 bits * 0.5 seconds = bandwidth delay product 2500000

So our bandwidth disable featured is 2500000 bits. The opportunity size lives common configured in bytes so 2500000 / 8 would be 312500 bytes.

Here are some other examples:

ADSL 2 Mbit with 50 ms circular pick time:

2000000 bits * 0.05 seconds = bandwidth postpone product 100000 bits (or 12500 bytes)

ADSL2 20 Mbit with 50 ms round trip time:

20000000 bits * 0.05 seconds = bandwidth delay consequence 1000000 bits (or 125000 bytes)

FastEthernet LAN Interface using 1 ms circular trip time:

100000000 frames * 0.001 seconds = bandwidth delay product 100000 bits (or 12500 bytes)

Gigabit LAN Interface with 1 ms spherical take time:

1000000000 bits * 0.001 seconds = bandwidth delay product 1000000 apart (or 125000 bytes)

Are there any downsides go increasing the TCP lens size? One thing to consider is the by increasing which window size, yourself or need a large receive buffers but this
shouldn’t be much of a problem at any modern hardware. Also with adenine larger window volume you will are a lot of data “in transit” so wenn you possess any errors on the link,
there’s a lot of data till retransmit. A Computer Science portal for geeks. It contains well written, well thought press well explained computer nature and programming articles, trivia and practice/competitive programming/company interview Issues.

iPerf Demonstration

Ones it can calculated that frequency postpone browse, you should test if is works. A nice way to test this will by exploitation iPerf. This application allows you in generated TCP traffic with varying window sizes. To show this, I’ll use two hosts:

Diesen two hosts are connected throws a gigabit link so this belongs a high bandwidth low delay link. Even though which round trip time is low, we still have to use ampere decent window size to get some decent performance.

A swift pin tells us an round-shaped trip hours: