1. User guide
   1. 1 Overview
   2. 2 Getting started
      1. 2.1 Connecting
      2. 2.2 A simple overlay
      3. 2.3 Moving an overlay
      4. 2.4 Canceling an overlay
      5. 2.5 Overlaying multiple numbers
      6. 2.6 What next
   3. 3 A more advanced overlay
      1. 3.1 Call announcements
      2. 3.2 Call recordings
      3. 3.3 Advertisers
      4. 3.4 Expiry options
         1. 3.4.1 Setting an expiry
         2. 3.4.2 Enforcing the expiry
         3. 3.4.3 The called extension
      5. 3.5 Restricting calls
         1. 3.5.1 Who can call
         2. 3.5.2 The length of calls
         3. 3.5.3 The number of calls
   4. 4 Advertisers functions
      1. 4.1 Create an advertiser
      2. 4.2 List advertisers
      3. 4.3 Edit an advertiser
   5. 5 Sound file functions
      1. 5.1 Pre-call anouncements
         1. 5.1.1 Create an announcement
         2. 5.1.2 List announcements
         3. 5.1.3 Edit an announcement
         4. 5.1.4 Delete an announcement
      2. 5.2 Call recordings
         1. 5.2.1 Get recordings
   6. 6 Statistical functions
      1. 6.1 Call statistics
         1. 6.1.1 Raw statistics
         2. 6.1.2 Grouped statistics
      2. 6.2 Overlay statistics
         1. 6.2.1 Count your overlays
         2. 6.2.2 List your overlays
      3. 6.3 Real time reporting
   7. 7 Miscellaneous functions
      1. 7.1 Check values
         1. 7.1.1 List number types
         2. 7.1.2 List number classes
         3. 7.1.3 Check a parameter
      2. 7.2 Check settings
         1. 7.2.1 Check your permissions
         2. 7.2.2 Check your settings
         3. 7.2.3 Check call costs
         4. 7.2.4 Check costs for a call
      3. 7.3 Check previous requests
         1. 7.3.1 Count previous requests
         2. 7.3.2 List previous requests
         3. 7.3.3 View request details
   8. 8 Glossary

3.4 Expiry options

When you create an overlay it will remain assigned for a period of time even if it is not called and for even longer if it is called. If an overlay expires, the number is still allocated to the destination and calls will be put through if it is dialled. The allocation is only broken when a new overlay request reuses an expired number and points it to a new destination. This system allows the highest level of availability for numbers and maximises the chance that the overlaying number for a destination will not change. However, in some circumstances it is advantageous to cycle through overlaying numbers more swiftly. These parameters allow you to control this process.