It became a thing because Asterisk and eventually others have used that range as their default range. The 16384-32767 range is a Cisco thing which is what was used in the write up from a random website that voip-info.org linked to.
Neither IANA or the RTP RFC have any official port ranges for RTP. RTP can use any of the ephemeral ports from 1024-65535. Different vendors will have different port ranges they use for RTP communications on their devices.
Yealink - 11780-11800
Grandstream - 5004 (increments as needed) but accepts 1024-65535 as acceptable range.
Poly/Polycom - 2222 (increments as needed)
Snom - 18000 (increments as needed)
Freeswitch - 10000-50000
Cisco SPAs - 30000-50000
Cisco Devices - 16384 - 32767, however UCM only uses 24576-32767
Kamailio RTP Engine - 30000-40000
Kamailio RTP Proxy - 35000-60000
So trying to bang your head to figure out why Asterisk isn’t using “official” (when there are none) RTP ports is pointless. Because the range is basically as wide as the ephemeral port range and its vendors choice when picking their desired RTP range for their devices.
