IETF RFC 5578 PDF

Introduction

PPP over Ethernet (PPPoE) [2] is a protocol for establishing and encapsulating sessions between Hosts (Clients) and traffic-access aggregators (Servers) for PPP [1] transport over real or emulated Ethernet. PPPoE works well when both session endpoints have similar bandwidth, forwarding, and buffering capabilities that do not vary over time. However, improvements can be made for applications with variable bandwidth and limited buffering. This document addresses these improvements with optional extensions to PPPoE that support credit-based session flow control and session-based link metric quality reports.

These extensions are designed to support radio systems that exhibit point-to-point waveforms. The diagram below is used to illustrate the improvement that these extensions address. When the local Client (Radio) detects the presence of a remote Radio neighbor, it initiates a PPPoE session with its local Server (router). The Radio also establishes a radio link connection with the remote Radio over the point-to-point RF (radio frequency) link (which is beyond the scope of this document). The remote Radio is also establishing a PPPoE session with its local Server (router). The Radios associate the two PPPoE sessions and the point-to-point radio link protocol (RLP), creating a complete data path. Now a PPP session is established via the PPP IP Control Protocol (IPCP) as described in RFC 1661. Included in this IPCP exchange is the router IP address. With the exchange of the IPCP IP addresses, each router inserts the remote IP address into its local routing tables.

The capabilities of the RF links between RLP neighbors will vary over time due to mobility and environmental conditions as well as changes in the RF waveforms and encoding. To reflect these dynamic changes, the Radio may periodically generate Link Quality Metrics to the router. The router uses the link metric to update route costs and influence route selection. The influence upon the routing protocols is beyond the scope of this document.

A PPPoE Client implementation can be found at [3]. It is open source (GNU GPLv2 -- General Public License).