According to End-To-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs book, there are four available standard PHBs (Per-Hop Behavior) and are listed below:
- Expedited Forwarding (EF) – Provides a strict-priority service. This is similar to the Express Mail service of USPS.
- Assured Forwarding (AF) – Provides a qualified delivery guaranteee and makes the provision for oversubscription to this service (specifically, markdown and dropping schemes for excess traffic). This is similar to Registered Mail service of USPS.
- Class Selectors (CS) – Provides code points that can be used for backward compatibility with IP Precedence models.
- Default PHB (Best-Effort Service) – Provides a “delivery when possible” or best effort service. This is similar to Regular Mail service of USPS.
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