RFC 3247 (rfc3247) - Page 2 of 24
Supplemental Information for the New Definition of the EF PHB (Expedited Forwarding Per-Hop Behavior)
Alternative Format: Original Text Document
RFC 3247 Supplemental Information March 2002 Table of Contents 1 Introduction ........................................... 2 2 Definition of EF PHB ................................... 3 2.1 The formal definition .................................. 3 2.2 Relation to Packet Scale Rate Guarantee ................ 6 2.3 The need for dual characterization of EF PHB ........... 7 3 Per Packet delay ....................................... 9 3.1 Single hop delay bound ................................. 9 3.2 Multi-hop worst case delay ............................. 10 4 Packet loss ............................................ 10 5 Implementation considerations .......................... 11 5.1 The output buffered model with EF FIFO at the output. .. 12 5.1.1 Strict Non-preemptive Priority Queue ................... 12 5.1.2 WF2Q ................................................... 13 5.1.3 Deficit Round Robin (DRR) .............................. 13 5.1.4 Start-Time Fair Queuing and Self-Clocked Fair Queuing .. 13 5.2 Router with Internal Delay and EF FIFO at the output ... 13 6 Security Considerations ................................ 14 7 References ............................................. 14 Appendix A. Difficulties with the RFC 2598 EF PHB Definition .. 16 Appendix B. Alternative Characterization of Packet Scale Rate Guarantee ......................................... 20 Acknowledgements .............................................. 22 Authors' Addresses ............................................ 22 Full Copyright Statement ...................................... 24 1. Introduction The Expedited Forwarding (EF) Per-Hop Behavior (PHB) was designed to be used to build a low-loss, low-latency, low-jitter, assured bandwidth service. The potential benefits of this service, and therefore the EF PHB, are enormous. Because of the great value of this PHB, it is critical that the forwarding behavior required of and delivered by an EF-compliant node be specific, quantifiable, and unambiguous. Unfortunately, the definition of EF PHB in the original RFC 2598 [10] was not sufficiently precise (see Appendix A and [4]). A more precise definition is given in [6]. This document is intended to aid in the understanding of the properties of the new definition and provide supplemental information not included in the text of [6] for sake of brevity. This document is outlined as follows. In section 2, we briefly restate the definition for EF PHB of [6]. We then provide some additional discussion of this definition and describe some of its properties. We discuss the issues associated with per-packet delay Charny, et. al. Informational
