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Circuit Switching Simulator: Set-up, TDM and Transfer Time

Circuit switching reserves resources along the whole path before any data is sent (like a phone call). The circuit then carries data at a guaranteed rate with no queuing, but it pays a set-up time and wastes capacity while idle.

About this simulator

Circuit switching reserves capacity along the whole path before any data moves — like a phone call. After a set-up phase the circuit carries data at a guaranteed rate with no queuing, but the capacity stays reserved even when nobody is talking. The simulation shows each phase and compares the total time with packet switching.

How it works

  1. Set-up: a signalling message travels to the destination and back, reserving a time slot (TDM) on every link.
  2. Transfer: with nn circuits sharing a link, each gets R/nR / n bits per second for the entire call.
  3. Tear-down releases the reservation. Total time == set-up +M/(R/n)++ M / (R/n) + propagation.

Formulas used

  • Circuit rate=Rn\text{Circuit rate} = \dfrac{R}{n} (TDM)
  • Tcircuit=Tsetup+MR/n+K dpropT_{\text{circuit}} = T_{\text{setup}} + \dfrac{M}{R/n} + K\,d_{\text{prop}}
  • Tsetup=2K (dprop+dproc)T_{\text{setup}} = 2K\,(d_{\text{prop}} + d_{\text{proc}})

Worked example

A 125,000-byte (1 Mbit) message crosses 3 links of 10 Mbps shared by 5 TDM circuits, so one call gets 10/5=210 / 5 = 2 Mbps. Set-up takes 2×3×(5+1) ms=36 ms2 \times 3 \times (5 + 1)\ \text{ms} = 36\ \text{ms}; transfer takes 1 Mbit2 Mbps=500 ms\dfrac{1\ \text{Mbit}}{2\ \text{Mbps}} = 500\ \text{ms}; propagation adds 3×5=15 ms3 \times 5 = 15\ \text{ms}. Total: 551 ms551\ \text{ms}.

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

When to use it

  • Solving circuit-switching delay problems that ask for set-up and transfer time.
  • Explaining why short bursts of data suit packet switching better.
  • Understanding TDM and FDM sharing of a link.

Frequently asked questions

How do you calculate transfer time in circuit switching?

Divide the message size by the circuit rate. With TDM on a link of rate RR shared by nn circuits, each circuit gets R/nR/n, so transfer time =MR/n= \dfrac{M}{R/n}; add the set-up time and the propagation delay.

What is the main drawback of circuit switching?

The reserved capacity is wasted when the sender is silent, and the call needs a set-up phase before any data can flow.

When is circuit switching better than packet switching?

For steady, long-lasting flows such as voice calls that need guaranteed bandwidth and constant delay.