Here are a few typical scenarios using VOCAL’s ED-137 module for both GRS and VCS. These modules need not only be used for ATM purposes; any RoIP implementation may benefit from tools that ED-137 supplies.
Scenario 1: Summing audio for transmission
For multiple audio streams of equal priority, the GRS sums(conferences) the audio sources and sends the combined result to the radio transmitter. The ptt-id sent back in R2S matches previous assigned values so each VCS knows it’s transmitting.
Scenario 2: Prioritizing audio for transmission
All VCSs send their audio to GRS but only VCS-3 audio is transmitted due to its higher priority. VCS-1 and VCS-2 are locked out and this is indicated in the R2S RTP header with a ptt-id assigned to VCS-3 and the ptt-summation bit set. VCS-3 knows it is transmitting as the received ptt-id matches its previously assigned value.
When VCS-3 stops sending, the scenario becomes like scenario 1 with VCS-1 & 2 audio being transmitted.
A VCS can change its audio priority simply by altering the PTT mode using the send PTT API.
Scenario 3 – GRS multicasts audio to VCSs
The VCS sets up a multicast call with the GRS-RX/TXRX whose audio can be shared with other VCSs. The VCSs send unicast R2S while GRS sends multicast RTP.
Scenario 4 – Sending SELCAL tones
VCS sends SIP INFO requests with SELCAL tones to be transmitted to aircraft.
Scenario 5 – Sending and Receiving RTP Header extensions
Sample of the sequence of APIs used for sending and receiving RTP extensions across the RTP link between the VCS and GRS.
VOCAL’s optimized RoIP software is available for the following platforms. Please contact us for specific RoIP supported platforms.