CSMA/CD efficiency is governed by the equation shown. There are two ways to improve the efficiency of a CSMA/CD network 1) increase the transmission delay or 2) decrease the propagation delay. Explain how each of these could be achieved in an actual network without changing the medium of the link (ie you can’t change from optical fibre to copper). efficiency = 1/1 + 5tprop/ttrans
Try an answer before revealing the guidance below.
Key Concepts
- t_trans = L/R
- t_prop = d/s
- Frame size
- Cable length / collision domain
- Ratio t_prop / t_trans
Answer Approach
- Write t_trans and t_prop in terms of frame size, rate, distance and speed.
- Identify which quantities you can change without changing the medium.
- Give a practical action for each.
Full Answer
Answer status: Draft answer (unofficial). Revision notes, not an official marking scheme.
Efficiency = 1 / (1 + 5 t_prop/t_trans), so it rises as t_prop/t_trans falls. 1) Increase t_trans = L/R: send larger frames (raise the minimum/maximum frame size or aggregate data into bigger frames); lowering the bit rate also increases t_trans, though it reduces raw capacity. 2) Decrease t_prop = d/s: since the propagation speed s is fixed by the medium, reduce the distance d — use shorter cables, limit the network diameter, or split the network into smaller collision domains with switches/bridges so that colliding stations are closer together.
efficiency = 1 / (1 + 5 · t_prop / t_trans)t_trans = L / Rt_prop = d / sShortcuts: K concepts · A approach · F answer · R reviewed · B bookmark · ← / → previous / next