A label interpreted by each network
DSCP is a field used to identify differentiated-service treatment. Devices can classify, mark, preserve or rewrite it under policy. The marking alone does not create a queue or reserve bandwidth.
Match policy to behavior
Check the endpoint's documented media and signaling settings, the switch trust boundary and the router's class mapping. A common voice marking is not a reason to assume every network uses the same policy. Read the configured behavior at the actual egress interface.
Inspect both sides of tunnels
A VPN can introduce an outer header whose treatment differs from the inner voice packet. Determine whether the tunnel preserves or maps markings as intended. A capture inside the tunnel does not automatically show what the upstream network sees.
Validate with counters and calls
Confirm that marked packets enter the expected queue during a bounded call. Check for remarking across boundaries and test under contention. Avoid accepting arbitrary endpoint markings from untrusted devices. Keep the mapping documented so a replacement router does not silently remove the voice policy.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.