AudioCodes Mediant 800B User Manual page 328

Parameter
Web: MKI Size
CLI: mki-size
[IpProfile_MKISize]
Web: Reset SRTP Upon Re-key
CLI: reset-srtp-upon-re-key
[IpProfile_ResetSRTPStateUponRekey
]
User's Manual
Mediant 800B Gateway and E-SBC
Description
Vnh0kH|2^31
The first crypto line includes the MKI parameter "1:1".
In the 200 OK response, the device selects one of the
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
/QFuxw|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.
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.
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.
328 Document #: LTRT-10620