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North-South Security Calculator

Derate a perimeter inspection stack stage by stage to find real capacity, added latency and unmonitored public endpoints.

About North-South Security Calculator

Service chains compound multiplicatively, not additively: four stages each costing 15% leave 0.85⁴, or about 52% of rated capacity — not 40%. Latency, by contrast, is additive, so each stage adds its full delay to every session in both directions. The endpoints bypassing the stack matter more than the capacity number: one internet-facing service that routes around the perimeter makes the whole chain irrelevant for that path.

Formula

North-South Security

effective capacity = rated capacity × (1 − per-stage derate)^stages; added latency = stages × latency per stage.

per-stage derate
Throughput lost to each inspection function in the chain
stages
Number of chained inspection functions traffic traverses

Worked example

With the default values below, North-South Security Calculator returns Effective Perimeter Capacity of 41.76. Change any input above and every figure here is recalculated in your browser.

Inputs used

Peak ingress trafficaccepts 0–100,000 Gbps
12 Gbps
Peak egress trafficaccepts 0–100,000 Gbps
18 Gbps
Inspection stages in the chainaccepts 1–12 stages
4 stages
Throughput lost per stageaccepts 0–90 %
15 %
Rated perimeter capacityaccepts 0.1–100,000 Gbps
80 Gbps
Latency added per stageaccepts 0–100 ms
0.4 ms
Internet-facing endpointsaccepts 1–1,000,000 endpoints
120 endpoints
Endpoints behind the inspection stackaccepts 0–1,000,000 endpoints
96 endpoints

Results

Effective Perimeter Capacity
41.76 Gbps
Total North-South Traffic
30.00 Gbps
Perimeter Utilisation
71.8%
Headroom
11.76 Gbps
Latency Added by the Chain
1.60 ms
Endpoint Inspection Coverage
80.0%
Endpoints Bypassing Inspection
24

Step by step

  1. 1Values used
  2. 2North-South Security
  3. 3Effective Perimeter Capacity= 41.76 Gbps
  4. 4Total North-South Traffic= 30.00 Gbps
  5. 5Perimeter Utilisation= 71.8
  6. 6Headroom= 11.76 Gbps
  7. 7Latency Added by the Chain= 1.60 ms
  8. 8Endpoint Inspection Coverage= 80.0

Assumptions and limits

  • The result is derived only from the 8 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 Security calculated?

effective capacity = rated capacity × (1 − per-stage derate)^stages; added latency = stages × latency per stage. Service chains compound multiplicatively, not additively: four stages each costing 15% leave 0.85⁴, or about 52% of rated capacity — not 40%. Latency, by contrast, is additive, so each stage adds its full delay to every session in both directions.

Why does North-South Security matter?

The endpoints bypassing the stack matter more than the capacity number: one internet-facing service that routes around the perimeter makes the whole chain irrelevant for that path.

What values do I need to enter?

This calculator takes 8 inputs: Peak ingress traffic, Peak egress traffic, Inspection stages in the chain, Throughput lost per stage, Rated perimeter capacity, Latency added per stage, Internet-facing endpoints, Endpoints behind the inspection stack. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

Is a longer inspection chain always better security?

No. Each stage adds latency, a failure domain and an operational owner, and overlapping stages often detect the same things twice while nobody owns the gaps between them. Consolidating four single-function appliances into one platform that runs the same four engines usually gives better coverage at lower latency, provided you size the derate honestly.

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