0 votes
575 views
asked in Estimation by (14 points) | 575 views

2 Answers

+2 votes

Lets start with a few assumptions:

1. Is this only about initial setup cost or also ongoing operational cost?

Assumption: Only initial cost

2. Is wifi only at street level or also inside the subway systems, at multiple floor levels of local government buildings, etc.?

Assumption: Street level only

3. What is the size of the city?

Assumption: A simple 50km by 50 km square city. So 2250 sq km.

4. What is the range of each router being installed?

Assumption: 100 sq meters

5. What is the max bandwidth supported by each router?

Assumption: 1 GBPS

6. Is this free wifi or paid wifi?

Assumption: Its FREE!

7. Maximum # of devices that will be using free wifi?

Assumption: (Population size) X (% of users who will choose to use free wifi vs their paid data plans) X Avg. number of devices per user. Lets assume population size is 5M. 90% choose to use the wifi and at an average there are 1.5 devices per user.

= 5M X 90% X 1.5 = 6.75M devices.

8. Any per device usage restrictions?

Assumption: Yes. 1 GB/device/day

9. Total bandwidth that needs to be supported daily?

Answer: Max # of devices X daily usage restriction = 6.75M GB/day

10. What is the cost of a single leaf node (router + wiring + labor )?

Assumption: router - $100, wiring - $50, labor - $200. Cost per node is 350$

11. Any booster nodes needs to mesh with the leaf nodes?

Assumption: 1 per 50 nodes. Cost: booster - $200, wiring - $50, labor - $300. Cost per booster node is $550.

12. Any sat link costs or underground cabling costs, to coonect this network to the internet?

Assumption: Use existing cable infrastructure. No extra cost.

13. Any other set up cost?

Assumption: No.

Based on a simple : (Max daily total bandwidth)/ (bandwidth per router per day), we can get an answer but that would be inaccurate since it doesnt take into account the sheer size of the city. Lets take the city size into account.

Few more assumptions:

14. Is the population evenly distributed? 

Assumption: Yes. if no, then we need to go into max number of concurrent devices that can be supported per node and if the density of the population is higher than can be supported per node, we would need more node in certain areas vs others. 

Now, 

City size: 2250 sq. km.

Per node range: 100 sq meters.

Total number of nodes needed: 2250 sq. km / 100 sq. meters = 22.5M Nodes
Total number of booster nodes needed: 22.5M / 50 nodes = 450K booster nodes
Total cost of wifi set up is therefore: 350$ X 22.5M nodes + 550$ X 450K booster nodes =  $7.875B +  $247.5M = $8.1225B give or take a few hundred million :)
answered by (22 points)
0 votes

Assumptions:

Q is about the setup cost without ny other cosiderations. this means HW only setup for equipment and installation to have a city wide WiFi system.

City Area= 50 sqkm * 50 sqkm = 2,500 sqkm

 

City area [sq. km to sqm]2,500,000,000               
coverage area of each AP [sqm]             100  
   
How many APs are needed? 25,000,000
   
   
Cost to install each AP  $   500.00
AP $          200  
wiring $          100  
labor $          200  
   
total cost of AP installation  $   12,500,000,000
   
Infrastructure [Backend spine and leaf switches]  
Need a leaf switch for every 10APs [inc. wiring] $          200                       2,500,000
Need a leaf switch for every 100 leaf switches [inc. wiring] $      2,000                             25,000
   
total cost leaf switches  $  500,000,000
total cost spine switches  $    50,000,000
   
Grant Total $  13,050,000,000

A: The installation cost is roughly $13B.

answered by (13 points)
0

Errata:

WAS: Need a leaf switch for every 100 leaf switches [inc. wiring]    $      2,000

Should be: Need a spine switch for every 100 leaf switches [inc. wiring] $      2,000

 

Post answer and get feedback

Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
To avoid this verification in future, please log in or register.