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Transmission Delay Independence Question (Length vs Distance vs Rate)

Transmission Delay Independence Question (Length vs Distance vs Rate)

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Sep 12, 2026

In packet-switched networks, “network delay” is commonly decomposed into multiple components: keyword processing, queuing, transmission, and propagation delays. The question asks specifically about transmission delay and which factors it does not depend on. In standard models, transmission delay is the time required to “push” all bits of a packet onto the link, and is modeled as

Ttx=LR,T_{tx}=\frac{L}{R},

so it depends on packet length LL and transmission rate RR, and it is independent of distance between routers (that independence belongs to propagation delay, not transmission delay).2

Key takeaway: for transmission delay, distance between routers is not a variable in L/RL/R.2

Footnotes

  1. Transmission delay - Wikipedia - States transmission delay equals N/RN/R and is independent of distance. ↩ ↩2

  2. Propagation Delay Calculator - Gives propagation delay formula as distance/speed between routers. ↩

  3. Transmission Delay - Defines transmission delay as TD=L/RTD=L/R (time to push bits onto the link). ↩

Network Delay - Transmission and Propagation Delay

What “transmission delay” means

Transmission delay is the serialization time to send a packet of LL bits over a link with rate RR (bits/s). The formula Ttx=L/RT_{tx}=L/R directly shows its dependencies.2

Packet length LL increases transmission delay linearly.
Transmission rate RR decreases transmission delay as 1/R1/R.
Distance between routers does not appear in the transmission delay expression, because distance affects propagation delay instead.2

Transmission delay vs propagation delay (the source of confusion)

Propagation delay depends on distance dd and propagation speed ss, typically:

Tprop=ds.T_{prop}=\frac{d}{s}.

So “distance between routers” is tied to propagation delay, not transmission delay.2

Footnotes

  1. Transmission delay - Wikipedia - States transmission delay equals N/RN/R and is independent of distance. ↩ ↩2 ↩3

  2. Transmission Delay - Defines transmission delay as TD=L/RTD=L/R (time to push bits onto the link). ↩ ↩2

  3. Propagation Delay Calculator - Gives propagation delay formula as distance/speed between routers. ↩ ↩2

  4. Propagation delay - Wikipedia - Defines propagation delay as ratio of distance to wave propagation speed (d/sd/s). ↩

Decide which option is correct for: Transmission delay does not depend on?

  1. 1
    Step 1

    Use Ttx=L/RT_{tx}=L/R (packet length divided by transmission rate).2

    Footnotes

    1. Transmission delay - Wikipedia - States transmission delay equals N/RN/R and is independent of distance. ↩

    2. Transmission Delay - Defines transmission delay as TD=L/RTD=L/R (time to push bits onto the link). ↩

  2. 2
    Step 2

    Since dd (distance) is not in L/RL/R, transmission delay is independent of distance.2

    Footnotes

    1. Transmission delay - Wikipedia - States transmission delay equals N/RN/R and is independent of distance. ↩

    2. Propagation Delay Calculator - Gives propagation delay formula as distance/speed between routers. ↩

  3. 3
    Step 3

    Therefore, the correct choice is (ii) distance between the routers.

Dependencies of Transmission vs Propagation Delay

Transmission delay uses L/R; propagation delay uses d/s.

Common FAQ checks

Pro Tip: Use variable presence

If the factor doesn’t appear in Ttx=L/RT_{tx}=L/R, then transmission delay doesn’t depend on it. Distance appears in Tprop=d/sT_{prop}=d/s, not in TtxT_{tx}. 2

Footnotes

  1. Transmission delay - Wikipedia - States transmission delay equals N/RN/R and is independent of distance. ↩

  2. Propagation Delay Calculator - Gives propagation delay formula as distance/speed between routers. ↩

Warning: Don’t mix units/interpretations

Transmission delay is based on pushing bits into the link (serialization). Propagation delay is based on how long the signal takes to travel through the medium. They can be similar in magnitude on some links, but the formulas—and the dependencies—are different.2

Footnotes

  1. Propagation Delay Calculator - Gives propagation delay formula as distance/speed between routers. ↩

  2. Transmission Delay - Defines transmission delay as TD=L/RTD=L/R (time to push bits onto the link). ↩

Final answer

Transmission delay does not depend on (ii) distance between the routers.2

Footnotes

  1. Transmission delay - Wikipedia - States transmission delay equals N/RN/R and is independent of distance. ↩

  2. Propagation Delay Calculator - Gives propagation delay formula as distance/speed between routers. ↩

Knowledge Check

Question 1 of 3
Q1Single choice

Transmission delay in packet switching is given by which relation (in the basic model)?

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