The equation for determining the download time for a peer-to-peer file sharing is given below. Dpsp ≥ max(F/us, F/dmin, NF/(us + Σ_{i=1}^{N} ui)) Explain what each of the following terms represents (for example: ”The time for one peer to download a single copy of the file”) α) F/us β) F/dmin γ) NF/(us + Σ_{i=1}^{N} ui)
Try an answer before revealing the guidance below.
Key Concepts
- F: file size
- us: server upload rate
- dmin: slowest peer download rate
- Aggregate upload capacity
- Lower bound
Answer Approach
- Identify what each symbol means (F, us, dmin, ui, N).
- Read each term as “amount of data ÷ rate”.
- Decide who is sending or receiving in each term and how many copies are involved.
Full Answer
Answer status: Verified against study notes. Revision notes, not an official marking scheme.
α) F/us: the minimum time for the server to upload one copy of the file (at least one copy must leave the server). β) F/dmin: the time for the slowest peer (download rate dmin) to download one copy of the file. γ) NF/(us + Σui): the minimum time to deliver N copies (NF bits in total) when the server and all peers upload together at their combined upload capacity.
D_p2p ≥ max(F/us, F/dmin, NF/(us + Σui))Shortcuts: K concepts · A approach · F answer · R reviewed · B bookmark · ← / → previous / next