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