Four layers, four boundaries. A failure in one does not reach the next.

Skinshells Voice in layers Request access
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Access

Request access

Describe the estate and what is prompting the change. Specificity in, specificity out.

Worth including

  • Sites, and simultaneous call volume at each if you know it
  • What handles calls today — make, model and firmware, or provider
  • Whether numbers must be retained
  • Which layer you think is failing, if you have a view
  • Any fixed date: circuit withdrawal, contract end, end of support

Describe the estate

Twenty characters or more. Sites, numbers and any fixed date are the useful parts.
Before writing

It may be documented already

Layer one

Connectivity

The outermost layer. Whether a call can happen at all.

Open Layer two

Control

Where a call goes, and what happens when nobody answers.

Open Layer three

Numbering

What a caller dials, and whether it can ever be unreachable.

Open Layer four

Operation

Change, treated as a layer because it causes more incidents than failure does.

Open

Questions answered