8M083X25 R14
APX Series P25 Interface
DVRS Installation & Programming Guide
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PART II
January 2019
Page 109 of 153
Digital Audio Buffering
Audio buffering is supported by the DVRS in order to eliminate loss of messages / parts
of messages due to the inherent delays associated with acquiring system access. The
Digital Audio Buffer in the DVR is programmable up to 1800ms.
P25 Encryption
The DVRS transparently passes the P25 encrypted voice used by the subscriber and fixed
network equipment. Even though the DVRS can be programmed to support TG
translation, it cannot support encryption key translation.
When the DVR is on a P25 Digital channel, inbound digital audio from a Local PSU is
handled according to the following table:
Local PSU Call
MSU Secure
Strapping
Receiving Local
PSUs
Receiving FNE
P25 Clear
Clear or Secure
P25 Clear
P25 Clear
P25 Encrypted
Clear or Secure
P25 Encrypted
P25 Encrypted
Table 20 Inbound P25 Encryption Rules
While the DVR is on a digital channel, outbound digital audio originating from the FNE is
handled according to the following table:
Call from FNE
MSU Secure Strapping
Receiving Local PSUs
P25 Clear
Clear or Secure
P25 Clear
P25 Encrypted
Clear or Secure
P25 Encrypted
Table 21 Outbound P25 Encryption Rules
While the DVR is on a digital channel, outbound digital audio originating from the MSU is
handled according to the following table:
MSU Mode
MSU Secure Strapping
Receiving Local PSUs
Digital P25
Clear
P25 Clear
Digital P25
Secure
P25 Encrypted
Table 22 MSU MIC PTT P25 Encryption Rules
The MSU interfaced to the DVR will unmute to inbound or outbound encrypted P25 calls
ONLY if the MSU contains the key used for encryption in its encryption key list.
