Your deployment design should account for network growth over the expected life of the design. The network growth rate will relate to the vertical market environment and the organization’s plans, so the organization must provide you with growth estimates:
Total ports and interfaces (P&I) 
= 
Current P&I 
+ 
Additional P&I due to growth 
Total managed ports and interfaces (P&I) 
= 
Current managed P&I 
+ 
Additional managed P&I due to growth 
Network growth planning can involve very complex calculations, but this is beyond the scope of this guide. For illustrative purposes, a simple method based on percentages is used here.
For example, if a network has a total of 5000 interfaces and 20000 ports. Using the method for calculating the percentage of managed ports and interfaces from these totals, there are 4500 managed interfaces and 1000 managed ports. The network is expected to grow by 10 percent per year, to calculate the size after 1 year:
Total ports and interfaces (P&I) 
= 
Current P&I 
+ 
Additional P&I due to growth 
= 
25,000 
+ 
(10/100) * 25,000 

= 
25,000 
+ 
2,500 

= 
27,500 after 1 year 

Total managed ports and interfaces (P&I) 
= 
Current managed P&I 
+ 
Additional managed P&I due to growth 
= 
5,500 
+ 
(10/100) * 5,500 

= 
5,500 
+ 
550 

= 
6,050 after 1 year 
To continue this example, if the design life is 2 years, then recalculate to add an additional 10 percent growth of the deployment over the second year:
Total ports and interfaces (P&I) 
= 
27,500 
+ 
(10/100) * 27,500 
= 
27,500 
+ 
2750 

= 
30,250 after 2 years 

Total managed ports and interfaces (P&I) 
= 
6,050 
+ 
(10/100) * 6,050 
= 
6,050 
+ 
605 

= 
6,655 after 2 years 