Transmission Delay Calculator & Simulation

Q: What is the formula for transmission delay?

d_trans = (L)/(R), where L is the packet length in bits and R is the link rate (bandwidth) in bits per second. Convert bytes to bits (× 8) and Mbps to bits per second (× 1 000 000) before dividing.

About this simulator

Transmission delay is the time a sender needs to push every bit of a packet onto the link. It is one of the four components of nodal delay in computer networks, and it is the one that depends on packet size and bandwidth rather than distance. Use the calculator above to try your own numbers and watch the packet drain onto the wire.

How it works

A packet of $L$ bits waits at the sending node; the link can push $R$ bits onto the wire every second.
Bits leave one after another at rate $R$ , so the last bit is on the wire after $L / R$ seconds.
Doubling the packet size doubles the delay; doubling the bandwidth halves it.

Formulas used

$d_{\text{trans}} = \dfrac{L}{R}$
$L$ = packet length (bits), $R$ = link rate (bits per second)

Worked example

A 1,500-byte Ethernet frame is $1500 \times 8 = 12000$ bits. On a 10 Mbps link the transmission delay is $\dfrac{12000}{10\,000\,000} = 0.0012\ \text{s} = 1.2\ \text{ms}$ . On a 100 Mbps link the same frame takes $0.12\ \text{ms}$ — ten times faster, because the rate $R$ is ten times larger.

Enter these numbers in the simulator above to see every step.

When to use it

Checking answers to computer-networks homework on nodal delay and end-to-end delay.
Understanding why larger packets or slower links increase latency.
Preparing for exams such as GATE, university computer-networks papers and NTS/HEC computer-science tests.

Frequently asked questions

What is the formula for transmission delay?

$d_{\text{trans}} = \dfrac{L}{R}$ , where $L$ is the packet length in bits and $R$ is the link rate (bandwidth) in bits per second. Convert bytes to bits ( $\times 8$ ) and Mbps to bits per second ( $\times 1\,000\,000$ ) before dividing.

Does distance affect transmission delay?

No. Distance affects propagation delay, not transmission delay. Transmission delay depends only on how many bits the packet has and how fast the link can send them.

How is transmission delay different from propagation delay?

Transmission delay is the time to put the packet's bits on the link ( $L/R$ ). Propagation delay is the time for a bit to travel along the link ( $d/s$ ). A packet is sent at once but travels over the whole distance.