A company wants to prioritize voice traffic at their network edge and ensure that it has reserved some minimum bandwidth and treated with priority in the core. QoS is not currently implemented in…

Configuring PHB queuing policies on every core node based on DSCP requires touching each core device individually, which contradicts the minimal-changes requirement and is the scenario the solution is trying to avoid.

Creating GRE tunnels and configuring PBR adds significant complexity and does not leverage the existing MPLS/RSVP infrastructure already in place, violating the minimal-changes constraint.

RSVP-TE tunnel creation with minimum bandwidth reservation leverages the already-enabled RSVP infrastructure to guarantee bandwidth for voice in the core without requiring per-node QoS policy changes.

Class-based tunnel selection allows the head-end router to forward packets matching a specific class (voice DSCP marking) into dedicated RSVP-TE tunnels, providing differentiated treatment without modifying every core node.

Enabling LDP and configuring PHB policies based on MPLS EXP bits still requires deploying queuing policies on every core node, which is not a minimal change and does not use the existing RSVP-TE capability.

Marking voice traffic with a DSCP value at the network edge is the foundational step that enables all downstream classification and tunnel selection - without edge marking, class-based steering cannot function.