Which two media encryptions should be used when configuring SRTP between Cisco UCM and Cisco VCS Expressway? (Choose two.)

While conceptually an 'optional' setting might exist in some systems, 'Mandatory' and 'None' are explicit, distinct settings for SRTP encryption policy in Cisco UCM and VCS Expressway configurations, often with 'Best Effort' as a middle ground.

'Pass-through' refers to how media (or signaling) traverses a device without modification, typically in firewall or NAT scenarios, not a specific media encryption setting for SRTP.

'Priority' is typically used for ordering preferences, such as codec priority or call routing, and is not a direct setting for SRTP media encryption.

The 'mandatory' setting for SRTP ensures that media encryption is strictly enforced; if the receiving endpoint or device cannot establish an SRTP encrypted stream, the call will not be permitted.

The 'none' setting for SRTP explicitly disables media encryption, allowing the media stream to be sent using standard RTP without any encryption. This is used when SRTP is not desired or supported by one of the endpoints.