DLEP DiffServ Aware Credit Window
Extension
MIT Lincoln Laboratory
Massachusetts Institute of Technology
244 Wood Street
Lexington
MA
02421-6426
bcheng@ll.mit.edu
MIT Lincoln Laboratory
Massachusetts Institute of Technology
244 Wood Street
Lexington
MA
02421-6426
David.Wiggins@ll.mit.edu
LabN Consulting, L.L.C.
lberger@labn.net
This document defines an extension to the Dynamic Link Exchange Protocol (DLEP) that enables a
DiffServ aware credit-window scheme for destination-specific and
shared flow control.
The Dynamic Link Exchange Protocol (DLEP) is defined in . It 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 possible extensions. This
document defines one such extension.
The base DLEP specification does not include any flow control
capability. There are various flow control techniques theoretically possible
with DLEP.
This document defines a DLEP extension which provides a DiffServ-based
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. Traffic sent by a router will use traffic flow classification
information provided by the modem to identify which traffic is
associated with each credit window.
Credit windows may be shared or dedicated on a per flow basis.
See for
an Ethernet-based version of credit window flow control.
This document uses the traffic classification and credit window
control mechanisms defined in and to provided credit
window based flow control based on on DLEP destination and DiffServ
DSCPs (differentiated services codepoints).
The defined mechanism allows for credit windows to be shared across
traffic sent to multiple DLEP destinations and DSCPs, or used
exclusively for traffic sent to a particular destination and/or DSCP.
The extension also supports the "wildcard" matching of any DSCP.
The extension defined in this document is referred to as "DiffServ
Aware Credit Window" or, more simply, the "DA Credit" extension. The
reader should be familiar with both the traffic classification and
credit window control mechanisms defined in and .
This document defines a new DLEP Extension Type Value in which is used to indicate support for the
extension.
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 when, and
only when, they appear in all capitals, as shown here.
The extension defined in this document is composed of the mechanisms
and processing defined in and . To indicate that the
DiffServ Aware Credit Window Extension is to be used, an
implementation MUST include the DiffServ Aware Credit Window Type
Value in the Extensions Supported Data Item. The Extensions
Supported Data Item is sent and processed according to . Any implementation that indicates use of the
DiffServ Aware Credit Window Extension MUST support all Messages,
Data Items, the DiffServ Traffic Classification Sub Data Item, and all
related processing defined in and .
The DiffServ Aware Credit Window Extension Type Value is TBA1, see
.
This section provides several network management guidelines
to implementations supporting the DiffServ Aware Credit Window
Extension.
The use of the extension defined in this document SHOULD be
configurable on both modems and routers.
Modems SHOULD support the configuration of DSCP to credit
window (queue) mapping.
Modems MAY support the configuration of the number of credit
windows (queues) to advertise to a router.
Routers may have limits on the number of queues that they can
support and, perhaps, even limits in supported credit window
combinations, e.g., if per destination queues can even be
supported at all. When modem-provided credit window information
exceeds the capabilities of a router, the router MAY use a subset of
the provided credit windows. Alternatively, a router MAY reset the
session and indicate that the extension is not supported. In either
case, the mismatch of capabilities SHOULD be reported to the user via
normal network management mechanisms, e.g., user interface or error
logging.
This document defines a DLEP extension that uses base DLEP
mechanisms and the credit window control and flow mechanisms defined
in and
. The use of
those mechanisms, and the introduction of a new extension, do not
inherently introduce any additional vulnerabilities above those documented
in . The approach taken to Security in that
document applies equally to the mechanism defined in this document.
This document requests one assignment by IANA. All
assignments are to registries defined by .
This document requests 1 new assignment to the DLEP Extensions
Registry named "Extension Type Values" in the range with the
"Specification Required" policy. The requested value is as follows:
Code Description
TBA1 DiffServ Aware Credit Window
DLEP Traffic Classification Data Item
MIT Lincoln Laboratory
Massachusetts Institute of Technology
244 Wood Street
Lexington
MA
02421-6426
bcheng@ll.mit.edu
MIT Lincoln Laboratory
Massachusetts Institute of Technology
244 Wood Street
Lexington
MA
02421-6426
David.Wiggins@ll.mit.edu
LabN Consulting, L.L.C.
lberger@labn.net
The sub data item format was inspired by Rick Taylor's "Data Item
Containers". He also proposed the separation of credit windows from
traffic classification at IETF98. Many useful comments were
received from contributors to the MANET working group.