The table below lists the cache lifetime options that you can choose after selecting the Allow caching downstream caching option. The cache lifetime is determined based on the Expires header; each option listed below sets the Expires header to a specific value.

Name	Description
Smaller value: origin header or remaining edge TTL	Sets caching lifetime to a value that is lesser of the remaining edge cache lifetime and origin header value (Cache-Control:max-age or Expires, if both are present, Cache-Control:max-age takes precedence).
Greater value: origin header or remaining edge TTL	Sets caching lifetime to a value that is greater of the remaining edge cache lifetime and origin header value (Cache-Control:max-age or Expires, if both are present, Cache-Control:max-age takes precedence).
Remaining edge TTL	Sets caching lifetime to the remaining edge cache lifetime.
Full edge TTL (max-age)	Sets caching lifetime to the full edge cache lifetime as represented by the max-age parameter.
Fixed value	Sets caching lifetime to a fixed value that you can define.
Calculate Expires from origin Cache-Control	Sets caching lifetime to the origin’s Cache-Control:max-age header value.