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North-South Traffic Calculator

Size the data centre border from north-south traffic volume, growth allowance and uplink speed.

About North-South Traffic Calculator

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

Worked example

With the default values below, North-South Traffic Calculator returns Projected North-South Load of 520.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Servers in the fabricaccepts 1–100,000 servers
400 servers
Busy-hour traffic per serveraccepts 0.01–800 Gbps
4 Gbps
Share that is north-southaccepts 0–100 %
25 %
Border capacity installedaccepts 1–400,000 Gbps
800 Gbps
Growth allowanceaccepts 0–300 %
30 %
Border uplink speedaccepts 1–800 Gbps
100 Gbps

Results

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

Step by step

  1. 1Values used
  2. 2North-South Traffic
  3. 3Projected North-South Load= 520.0 Gbps
  4. 4North-South Today= 400.0 Gbps
  5. 5Border Utilisation when Projected= 65.00
  6. 6Border Uplinks Needed= 6 links
  7. 7Headroom Remaining= 280.0 Gbps

Assumptions and limits

  • The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

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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