Which of the following is a MAJOR consideration in implementing a Voice over IP (VoIP) network?

Unified messaging is an application-layer feature that integrates voicemail and email but is not a fundamental network infrastructure consideration when implementing VoIP.

While VLAN separation for voice traffic is a best practice, it is a design recommendation rather than a 'major consideration' at the level of security enforcement that NAC provides during implementation.

Network Access Control (NAC) on switches is a major consideration for VoIP because it enforces endpoint compliance and authentication before devices are permitted onto the network, preventing unauthorized devices from accessing voice VLANs and disrupting call quality or security. NAC can also enforce QoS policies and ensure VoIP phones are placed into the correct voice VLAN automatically. Without NAC, rogue devices could impersonate IP phones, intercept voice traffic, or degrade network performance.

RFC 1918 private addressing is standard practice for internal networks and is not specific to VoIP implementation; VoIP networks can function with any IP addressing scheme and this is not a unique or major VoIP concern.