1. Introduction
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Original RFC Text
1. Introduction
The Dynamic Link Exchange Protocol (DLEP), defined in [RFC8175],
provides the exchange of link-related control information between
DLEP peers. DLEP peers are comprised of a modem and a router. DLEP
defines a base set of mechanisms as well as support for future
extensions. DLEP defines Data Items, which are sets of information
that can be reused in DLEP messaging. The DLEP specification does
not include any flow identification beyond DLEP endpoints, nor does
it address flow control capability. Various flow control techniques
are theoretically possible with DLEP. For example, a credit window
scheme for destination-specific flow control that provides aggregate
flow control for both modems and routers has been proposed in
[Credit-Window-Extension], and a mechanism referred to as the
Control-Plane-Based Pause Extension is defined in [RFC8651]. The use
of other flow control mechanisms simultaneously with credit-based
flow control is not within the scope of this document.
Credit-based flow control, as a result of its proactive nature, may
offer some advantages over a pause mechanism. Packet loss resulting
from insufficient buffer space is less likely, as a transmitter does
not send packets until the receiver has indicated that there is
sufficient buffer space available.
Figure 1 illustrates a local node consisting of a router and a modem
implementing DLEP. DLEP messages optionally contain a number of Data
Items and Sub-Data Items. The Traffic Classification Data Item
provided by the modem is defined in [RFC9892]. In this case, a flow
is identified based on information found in a data plane header, and
one or more matches are associated with a single flow. As stated in
[RFC9892], more than one Data Item MAY be included in a message to
provide information on multiple traffic classifiers. Refer to
Section 2.3 of [RFC2475] for general background on traffic
classification.
|--------------------Local Node--------------------|
| |
+-----------------------------+ +-------+
| Router | |Modem |
| | |Device |{~~~~~~~~} Remote
| | | | Link Nodes
| Traffic Classification: | | | Protocol
| Per TID: | | | (e.g.,
| DSCPs to FID / PCPs to FID | | | 802.11)
| | Data Items | |
| Per Modem: (list of TIDs) |<---------->| |
| FID to Credit Window Queues |============| |
| | | |
+-----------------------------+ +-------+
| |
|----DLEP--- |
DSCP: Differentiated Services Code Point
FID: Flow Identifier
PCP: Priority Code Point
TID: Traffic Classification Identifier
Figure 1: Router and Modem DLEP Exchange
This document defines DLEP Data Items that provide a flow control
mechanism for traffic sent from a router to a modem. Flow control is
provided using one or more logical "credit windows", each of which
will typically be supported by an associated virtual or physical
queue. Credit windows may be shared or dedicated on a per-flow
basis. The Data Items are structured to allow for the reuse of the
defined credit-window-based flow control with different traffic
classification techniques. A router logically consumes credits for
each credit window matching packet sent.
Note that this document defines common messages, Data Items, and
mechanisms that are reusable. They are expected to be required by
DLEP extensions defined in other documents, such as the extension
defined in [RFC9894].
This document introduces support for credit window flow control by
defining two new DLEP messages (Section 2.2) and five new DLEP Data
Items (Section 2.3).
Various conditions described in this document cause a message to be
logged. In all cases, the log message results from the contents of a
received Data Item defined here. No messages are logged in response
to activity in the data plane.