North-South Traffic Calculator
Size the data centre border from north-south traffic volume, growth allowance and uplink speed.
Inputs
Projected North-South Load
520.0Gbps
North-South Today
400.0Gbps
Border Utilisation when Projected
65.00%
Border Uplinks Needed
6links
Headroom Remaining
280.0Gbps
Step by step
Values used
Servers in the fabric = 400 servers; Busy-hour traffic per server = 4 Gbps; Share that is north-south = 25 %; Border capacity installed = 800 Gbps; Growth allowance = 30 %; Border uplink speed = 100 Gbps
North-South Traffic
north-south = total traffic × north-south share; projected = that × (1 + growth); uplinks = projected ÷ uplink speed, rounded up.
Projected North-South Load
= 520.0 Gbps
North-South Today
= 400.0 Gbps
Border Utilisation when Projected
= 65.00
Border Uplinks Needed
= 6 links
Headroom Remaining
= 280.0 Gbps
How it works
North-south traffic is what the border routers, firewalls and load balancers have to carry, and it grows with user demand rather than with internal chatter. The uplink count is the projected load divided by the speed of one border link. Border devices are the most expensive per gigabit in the data centre, so knowing the projected figure prevents both a congested edge and a heavily over-built one.
Formula
North-South Traffic
north-south = total traffic × north-south share; projected = that × (1 + growth); uplinks = projected ÷ uplink speed, rounded up.
- north-south share
- Traffic entering or leaving the data centre
- growth
- Allowance over the planning horizon, typically 12–36 months
Frequently Asked Questions
How is North-South Traffic calculated?
north-south = total traffic × north-south share; projected = that × (1 + growth); uplinks = projected ÷ uplink speed, rounded up. North-south traffic is what the border routers, firewalls and load balancers have to carry, and it grows with user demand rather than with internal chatter. The uplink count is the projected load divided by the speed of one border link.
Why does North-South Traffic matter?
Border devices are the most expensive per gigabit in the data centre, so knowing the projected figure prevents both a congested edge and a heavily over-built one.
What values do I need to enter?
This calculator takes 6 inputs: Servers in the fabric, Busy-hour traffic per server, Share that is north-south, Border capacity installed, Growth allowance, Border uplink speed. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
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