When to use: Design QoS traffic policies for enterprise WAN or campus LAN. Assign DSCP values and bandwidth percentages per traffic class, verify allocations sum to 100%, and document queuing strategy for router/switch policy maps. Follows RFC 4594 per-hop behavior guidelines.
| Traffic Class | DSCP Value | Bandwidth % | Mbps | Queuing Mechanism |
|---|---|---|---|---|
% | 15.0 | |||
% | 20.0 | |||
% | 5.0 | |||
% | 20.0 | |||
% | 30.0 | |||
% | 10.0 |
This tool maps DSCP values to traffic classes, allocates percentage bandwidth per class, and validates that all allocations sum to 100% of link capacity. Network engineers use it to document QoS policy maps for router and switch configuration before deploying enterprise WAN or campus LAN policies.
Differentiated Services Code Point (DSCP) is a 6-bit field in the IP header that marks each packet's per-hop behavior (PHB). Routers and switches read the DSCP field and place packets into corresponding queues with different scheduling priorities and bandwidth guarantees. The standard DiffServ model (RFC 2474, RFC 4594) defines a hierarchy: EF (DSCP 46) for voice requiring minimum delay, AF (Assured Forwarding, DSCP 10–43) for video and business-critical data with protected bandwidth, CS (Class Selector) values for legacy IP Precedence compatibility, and BE (DSCP 0) for best-effort data.
Bandwidth allocation defines what percentage of the link each class is guaranteed during congestion. Voice (EF) is typically capped at 15–33% via a policer, video at 20–30%, and best-effort data receives the remainder. The allocations must sum to 100% to ensure no bandwidth is unaccounted for.
RFC 4594 provides configuration guidelines for DiffServ service classes covering voice, video, signaling, and data. RFC 3246 defines EF (DSCP 46) for voice per-hop behavior. RFC 2597 defines AF (Assured Forwarding) classes AF1x through AF4x with drop precedences. RFC 2475 defines the overall DiffServ architecture. IEEE 802.1p maps Layer 2 CoS values (0–7 PCP bits) to DSCP when traffic transitions between L2 and L3. Cisco's SRND (Solution Reference Network Design) for enterprise QoS recommends the 8-class model used in this calculator as a best practice baseline.
Trust boundaries must be established at the network edge: mark traffic with correct DSCP at the source (IP phone, video endpoint) and configure switches to trust those markings only from known endpoints. Reclassify or re-mark untrusted hosts at the access switch ingress to prevent users from self-marking their traffic as EF. Voice policing is critical — without a policer on the EF queue, any application that marks itself DSCP 46 can consume the priority queue and starve legitimate voice traffic. Document the classification policy in a QoS MQC (Modular QoS CLI) policy map and verify with DSCP-aware traffic generators after deployment.
Set the link capacity in Mbps to match your WAN circuit or uplink. Adjust the DSCP value and bandwidth percentage for each traffic class. The visual bandwidth bar at the top shows proportional allocation across the link. The total allocated percentage must reach exactly 100% — the counter turns green when balanced. Use the per-class Mbps column as input to your router QoS policy-map bandwidth statements. Export the table to document the QoS design in your network design specifications.
AF41 (DSCP 34) is the recommended marking for interactive video conferencing per RFC 4594. Some vendors mark both audio and video flows with the same class; others use EF for audio streams and AF41 for video. Verify against your UC platform documentation (Cisco, Microsoft Teams, Zoom).
IP Precedence is the legacy 3-bit ToS marking (RFC 791) preserved for backward compatibility. DSCP uses all 6 bits and provides 64 possible values versus 8 for IP Precedence. All modern enterprise equipment supports DSCP; IP Precedence should only be used when interoperating with very old network equipment.
RFC 4594 and Cisco's enterprise QoS SRND recommend capping EF (voice) at 33% of link bandwidth to prevent starvation of lower-priority classes. The actual required voice bandwidth is calculated as simultaneous calls × 80–100 kbps (G.711) or 28–32 kbps (G.729).
The Scavenger class (CS1, DSCP 8) is assigned below best-effort priority and is used for bulk file transfers, backup jobs, and peer-to-peer applications. It is the first class to be dropped during congestion and ensures background transfers do not impact production traffic.
Create a class-map matching each DSCP value, a policy-map assigning bandwidth percentages to each class, and apply the policy-map to the interface egress direction using "service-policy output <name>". On WAN-edge routers, also apply a traffic shaping policy for fair bandwidth sharing across SD-WAN paths.
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