ARA-1 Operations Manual
1-8
INTEROPERABILITY NOW
1.8.2
Deriving COR from the Local Radio
Within the JPS ARA-1 SIP-to-Radio interface, there are two options at the radio interface for
deriving COR (determining that the associated radio is unsquelched).
See Figure 1-5 below; with ARA-1s on both sides of the link, it illustrates all aspects of COR/PTT
signaling. To simplify the explanation, consider Radio A the
Local Radio;
Radio B will be
referred to as the
Distant Radio
.
Figure 1-5
Radio to ARA-1 to IP Network to ARA-1 to Radio
Currently we’re discussing how the Local ARA-1 determines that the Local Radio cabled to it is
unsquelched. The options include:
•
A Hardwired COR signal – some radios supply a COR output line.
•
VOX: Active COR is triggered by any audio input above a configurable threshold.
For radio interface cables supplied by JPS, the Radio Application Note supplied with the cable
will explain which is best for the associated radio model.
1.8.3
Pushing the COR Indication across the IP Network
The Local ARA-1 in Figure 1-5 has various options for making the Distant ARA-1 aware that
the local radio is unsquelched. These include:
•
RTP Header: IP packets include an RTP extension header that JPS created for this
purpose. When the extension is detected by the distant ARA-1, it knows the local radio
is unsquelched. The local ARA-1 will send its COR status over the network as part of the
RTP extension header if its
Send Radio COR/AUX Status
function is enabled.
•
Silence Suppression: Very simply described – send audio packets to the distant ARA-1 if
the local radio is unsquelched, and if not, don’t send any. Silence suppression is invoked
when the
Silence Suppression
function is enabled via the SIP Settings web page.
These Active COR indicators are best understood in terms of how they are applied by the Distant
ARA-1. Operation at this unit is more complex as the Distant ARA-1 must also be able to
function properly if there are “non-JPS” devices playing the part of the Local ARA-1. This is
vital because many SIP devices, such as the SIP VoIP phones and computer-based Softphones
are Full Duplex, while radio systems are Half Duplex. If not handled properly, a Full Duplex
device that’s linked to a distant radio could cause that radio to remain continuously keyed. This
is not likely to be a desirable condition.
ARA-1
Local
Radio A
Local
ARA-1
Distant
Radio B
Distant