Explanation:
The Differentiated Services (DiffServ) model for Quality of Service (QoS) enables traffic management based on predefined priorities. This involves classifying, policing, queuing, and scheduling traffic to ensure efficient network resource utilization.
Breakdown of Each QoS Processing Step:
# Step 1: Traffic Classification and Marking
* Purpose: Identifies and marks packets based on QoS attributes such as DSCP (Differentiated Services Code Point) or 802.1p priority bits.
* Function: Assigns a QoS label to packets for further processing.
* Example: Packets carrying voice traffic (EF - Expedited Forwarding) are marked for high-priority treatment.
# Step 2: Traffic Policing (CAR - Committed Access Rate)
* Purpose: Enforces bandwidth limits on specific traffic flows to prevent excessive usage.
* Function: Drops or re-marks packets exceeding the assigned bandwidth threshold.
* Example: If a video stream exceeds 10 Mbps, excess packets may be dropped or re-marked.
# Step 3: Congestion Management (Queuing and Scheduling)
* Purpose: Manages traffic flow through queues based on assigned QoS levels.
* Function: Places packets in appropriate priority queues (e.g., Strict Priority, Weighted Fair Queuing - WFQ, CBWFQ).
* Example: Voice packets are assigned to high-priority queues for low-latency forwarding.
# Step 4: Congestion Avoidance
* Purpose: Prevents network buffer overflows and excessive packet drops.
* Function: Uses mechanisms like WRED (Weighted Random Early Detection) to drop lower-priority packets before congestion occurs.
* Example: If a queue reaches 80% capacity, WRED may drop low-priority packets to maintain QoS.
# Step 5: Traffic Shaping
* Purpose: Smooths out traffic bursts to maintain a consistent transmission rate.
* Function: Buffers and delays packets to prevent excessive packet drops.
* Example: If outgoing traffic exceeds 50 Mbps, shaping ensures it does not exceed this limit while maintaining steady flow.
