AudioCodes Mediant 500 E-SBC, User Manual

Page: 309 / 920

User's Manual 19. Coders and Profiles
Version 6.8 309 Mediant 500 E-SBC
Parameter Description
crypto lines (i.e., '2' or '3'). Typically, it selects the first line
that supports the crypto suite. However, for SRTP-to-
SRTP in SBC sessions, it can be determined by the
remote side on the outgoing leg. If the device selects
crypto line '2', it includes the MKI parameter in its answer
SDP, for example:
a=crypto:2 AES_CM_128_HMAC_SHA1_80
inline:R1VyA1xV/qwBjkEklu4kSJyl3wCtYeZLq1/Q
Fuxw|2^31|1:1
If the device selects a crypto line that does not contain
the MKI parameter, then the MKI parameter is not
included in the crypto line in the SDP answer (even if the
SRTPTxPacketMKISize parameter is set to any value
other than 0).
Note: The corresponding global parameter is
EnableSymmetricMKI.
Web: MKI Size
CLI: mki-size
[IpProfile_MKISize]
Defines the size (in bytes) of the Master Key Identifier (MKI)
in SRTP Tx packets.
The valid value is 0 to 4. The default is 0 (i.e., new keys are
generated without MKI).
Notes:

Gateway application: The device only initiates the MKI
size.

SBC application: The device can forward MKI size as is
for SRTP-to-SRTP flows or override the MKI size during
negotiation. This can be done on the inbound or
outbound leg.

The corresponding global parameter is
SRTPTxPacketMKISize.
Web: Reset SRTP Upon Re-key
CLI: reset-srtp-upon-re-key
[IpProfile_ResetSRTPStateUponRek
ey]
Enables synchronization of the SRTP state between the
device and a server when a new SRTP key is generated
upon a SIP session expire. This feature ensures that the roll-
over counter (ROC), one of the parameters used in the
SRTP encryption/decryption process of the SRTP packets, is
synchronized on both sides for transmit and receive packets.

[0] Disable = (Default) ROC is not reset on the device
side.

[1] Enable = If the session expires causing a session
refresh through a re-INVITE, the device or server
generates a new key and the device resets the ROC
index (and other SRTP fields) as done by the server,
resulting in a synchronized SRTP.
Notes:

If this feature is disabled and the server resets the ROC
upon a re-key generation, one-way voice may occur.

The corresponding global parameter is
ResetSRTPStateUponRekey.
Generate SRTP keys mode
CLI: generate-srtp-keys
[IpProfile_GenerateSRTPKeys]
Enables the device to generate a new SRTP key upon
receipt of a re-INVITE with this SIP entity.

[0] Only If Required= (Default) The device generates an
SRTP key only if necessary.

[1] Always = The device always generates a new SRTP