Notification-Delay:= "Notification-Delay:" 1*DIGIT
If the client explicitly requested a notification delay, the server must include in its response an identical header containing the notification delay that it will use. The server may return a value that is greater or less than the value requested by the client, allowing the server to dictate a minimum delay, a maximum delay, or to return a less granular delay. For example, the server may round up a request from 0.24 to 0.25.
The header is also valid in a subscription refresh and indicates a request to change the notification delay. If the server does not support changing the notification delay but otherwise will refresh the subscription, it must respond with a 200 (OK) response, and include the Notification-Delay header with the original value.
The following subscription will coalesce events for 400 seconds before sending a notification to the User Datagram Protocol (UDP) server that was specified in the Call-Back header.
SUBSCRIBE /public/subtest HTTP/1.1 Host: www.contoso.com Notification-type: update Notification-Delay: 400 Call-Back: httpu://www.fourthcoffee.com:8080/510