Length in millisecond of the voice packets received or transmitted from/to this interface. For example, if the gateway intends to handle 20ms (160 bytes) RTP streams this value shall be set to 20. If the gateway intends to handle 30ms (240 bytes) RTP streams this value shall be set to 30. If the gateway inteads to handle 20 and 30ms RTP streams this value shall be set to 10. Note that, the gateway will consume more CPU when this value is small.