1. Introduction

This section preserves the RFC text for the DLEP IEEE 802.1Q Aware Credit Window extension, including Extension Type 5, VLAN identifiers, PCPs, traffic classification, credit windows, IANA registration, and normative behavior.

Original RFC Text

1.  Introduction

   The Dynamic Link Exchange Protocol (DLEP) is defined in [RFC8175].
   The protocol provides the exchange of link-related control
   information between DLEP peers.  DLEP peers consist of a modem and a
   router.  DLEP defines a base set of mechanisms as well as support for
   possible extensions.  This document defines one such extension.

   The DLEP specification does not define any flow control mechanisms.
   While in theory various flow control techniques could be implemented
   with DLEP, this document specifies a DLEP extension that introduces
   an Ethernet-based flow control mechanism for traffic transmitted from
   a router to a modem.  This mechanism utilizes one or more logical
   "credit windows", each of which is typically associated with a
   virtual or physical queue.  The router leverages traffic flow
   classification information provided by the modem to determine the
   appropriate credit window for a given traffic flow.  Credit windows
   may be shared across multiple flows or used on a per-flow basis.  For
   a Diffserv-based approach to credit window flow control, refer to
   [RFC9894].  As specified in Section 2.3.1 of [RFC9892], when both
   Diffserv and Ethernet traffic classification are applied to a flow,
   Ethernet-based classification takes precedence.

   This document leverages the traffic classification and credit window
   flow control mechanisms defined in [RFC9892] and [RFC9893] to enable
   credit-window-based flow control based on DLEP destinations, Ethernet
   Virtual Local Area Networks (VLANs), and Priority Code Points (PCPs).
   Ethernet PCP support is specified as part of the IEEE 802.1Q tag
   format [IEEE8021Q], which includes a 3-bit "PCP" field.  The tag
   format also incorporates a 12-bit "VLAN Identifier (VID)" field.

   The defined mechanism allows credit windows to be shared across
   traffic destined for multiple DLEP destinations, VLANs, and PCPs, or
   to be dedicated exclusively to traffic associated with a specific
   destination, VLAN, and/or PCP.  Additionally, this extension supports
   "wildcard" matching for any PCP or VID.

   The extension defined in this document is referred to as the "IEEE
   802.1Q Aware Credit Window" or, more simply, the "Ethernet Credit"
   extension.  The reader should be familiar with both the traffic
   classification and credit window flow control mechanisms defined in
   [RFC9892] and [RFC9893].

   This document defines a new DLEP Extension Type value that is used to
   indicate support for the extension.  See Section 2.

1.1.  Key Words

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.