This is a read-only value reporting the length of time, in milliseconds, represented by the media in each packet for this active AMR-NB call, with the description noting 20 ms as the supported value, applicable only when the negotiated coder is AMR-NB. An admin checks this to confirm the actual packet timing negotiated for a live AMR-NB call, similar in purpose to the related maximum-payload-time object but describing the actual packet time rather than the maximum. For example, an admin comparing this value against the maximum-payload-time object on the same call would expect them to match given that 20 ms is documented as the only supported value.