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Versions: 00 01 02 03

Network Working Group                                           B. Cheng
Internet-Draft                                                D. Wiggins
Intended status: Standards Track                  MIT Lincoln Laboratory
Expires: December 28, 2018                                     L. Berger
                                                 LabN Consulting, L.L.C.
                                                           June 26, 2018


         DLEP Credit-Based Flow Control Messages and Data Items
              draft-ietf-manet-dlep-credit-flow-control-02

Abstract

   This document defines new DLEP protocol Data Items that are used to
   support credit-based flow control.  The Data Items enable separate
   but related functions: traffic classification and credit window
   control.  Traffic classification information is used to identify
   traffic flows based on frame/packet content such as destination
   address.  Credit window control is used to regulate when data may be
   sent to an associated virtual or physical queue.  The Data Items are
   defined in an extensible and reusable fashion.  Their use will be
   mandated in other documents defining specific DLEP extensions.  This
   document also introduces DLEP sub data items.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 28, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Key Words . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Traffic Classification  . . . . . . . . . . . . . . . . . . .   4
     2.1.  Traffic Classification Data Item  . . . . . . . . . . . .   5
       2.1.1.  Traffic Classification Sub Data Item  . . . . . . . .   6
     2.2.  DiffServ Traffic Classification Sub Data Item . . . . . .   7
       2.2.1.  Router Receive Processing . . . . . . . . . . . . . .   8
     2.3.  Ethernet Traffic Classification Sub Data Item . . . . . .   9
       2.3.1.  Router Receive Processing . . . . . . . . . . . . . .  10
   3.  Credit Window Control . . . . . . . . . . . . . . . . . . . .  10
     3.1.  Data Plane Considerations . . . . . . . . . . . . . . . .  12
     3.2.  Credit Window Messages  . . . . . . . . . . . . . . . . .  12
       3.2.1.  Credit Control Message  . . . . . . . . . . . . . . .  12
       3.2.2.  Credit Control Response Message . . . . . . . . . . .  13
     3.3.  Credit Window Control Data Items  . . . . . . . . . . . .  14
       3.3.1.  Credit Window Initialization  . . . . . . . . . . . .  14
       3.3.2.  Credit Window Associate . . . . . . . . . . . . . . .  16
       3.3.3.  Credit Window Grant . . . . . . . . . . . . . . . . .  17
       3.3.4.  Credit Window Status  . . . . . . . . . . . . . . . .  19
       3.3.5.  Credit Window Request . . . . . . . . . . . . . . . .  20
     3.4.  Management Considerations . . . . . . . . . . . . . . . .  21
   4.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .  22
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     6.1.  Message Values  . . . . . . . . . . . . . . . . . . . . .  22
     6.2.  Data Item Values  . . . . . . . . . . . . . . . . . . . .  22
     6.3.  DLEP Traffic Classification Sub Data Item Registry  . . .  23
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  24
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  24
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   The Dynamic Link Exchange Protocol (DLEP) is defined in [RFC8175].
   It provides the exchange of link related control information between
   DLEP peers.  DLEP peers are comprised of a modem and a router.  DLEP



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   defines a base set of mechanisms as well as support for possible
   extensions.  DLEP defines Data Items which are sets of information
   that can be reused in DLEP messaging.  The base DLEP specification
   does not include any flow identification beyond DLEP endpoints or
   flow control capability.  There are various flow control techniques
   theoretically possible with DLEP.  For example, a credit-window
   scheme for destination-specific flow control which provides aggregate
   flow control for both modem and routers has been proposed in
   [I-D.ietf-manet-credit-window], and a control plane pause based
   mechanism is defined in [I-D.ietf-manet-dlep-pause-extension].

   This document defines DLEP Data Items and Messages which provide flow
   identification, and 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.  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.  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.  (For general background on traffic
   classification see [RFC2475] Section 2.3.)  Credit windows may be
   shared or dedicated on a per flow basis.  The Data Items are
   structured to allow for reuse of the defined traffic classification
   information with non-credit window applications as well as reuse of
   the credit window based flow control with different traffic
   classification techniques.

   This document defines traffic classification based on a DLEP
   destination and flows identified by either DiffServ [RFC2475] DSCPs
   (differentiated services codepoints) or IEEE 802.1Q
   [IEEE.802.1Q_2014] Ethernet Priority Code Points (PCP).  The defined
   mechanism allows for credit windows to be shared across traffic sent
   to multiple DLEP destinations and flows, or used exclusively for
   traffic sent to a particular destination and/or flow.  The extension
   also supports the "wildcard" matching of any flow (DSCP or PCP).
   Traffic classification information is provided such that it can be
   readily extended to support other traffic classification techniques,
   or be used by non-credit window related extensions, such as
   [I-D.ietf-manet-dlep-pause-extension] or even 5-tuple IP flows.

   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 found in
   [I-D.ietf-manet-dlep-da-credit-extension].

   This document defines support for traffic classification using a
   single new Data Item in Section 2.1 for general support and two new



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   sub Data Items are defined to support identification of flows based
   on DSCPs and PCPs.  The document supports credit window control by
   introducing two new DLEP messages in Section 3.2, and five new DLEP
   Data Items in Section 3.3.

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.

2.  Traffic Classification

   The Traffic Classification Data Item is used to represent a list of
   flows that may be used at the same time for traffic sent from a
   router to a modem.  The data plane information used to identify each
   flow is represented in a separate sub Data Item.  The Data Item and
   Sub Data Item structure is intended to be independent of any specific
   usage of the flow identification, e.g., flow control.  The Sub Data
   Item structure is also intended to allow for future traffic
   classification types, e.g., 5-tuple flows.  While the structure of
   the Data Items is extensible, actual flow information is expected to
   be used in an extension dependent manner.  Support for DSCP and PCP-
   based flows are defined via individual sub Data Items below.  Other
   types of flow identification, e.g., based on IP protocol and ports,
   may be defined in the future via new sub Data Items.

   The list of flows contained in the Data Item can be used per sender
   or shared across multiple senders.  Each list of flows is identified
   using a "Traffic Classification Identifier" or "TID" and is expected
   to represent a valid combination of data plane identifiers that may
   be used at the same time.  Each flow is identified via a "Flow
   Identifier" or "FID".  Each FID is defined in a sub Data Item which
   carries the data plane identifier or identifiers used to associate
   traffic with the flow.  A DLEP destination address is also needed to
   complete traffic classification information used in extensions such
   as flow control.  This information is expected to be provided in an
   extension specific manner.  For example, this address can be provided
   by a modem when it identifies the traffic classification set in a
   Destination Up Message using the Credit Window Associate Data Item
   defined in Section 3.3.2.  The scope of TID and FID values is a
   modem.







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2.1.  Traffic Classification Data Item

   This sections defines the Traffic Classification Data Item.  This
   Data Item is used by a modem to provide a router with traffic
   classification information.  When an extension requires use of this
   Data Item the Traffic Classification Data Item SHOULD be included by
   a modem in any Session Initialization Response Message that also
   indicates support for an extension that requires support for the
   credit window control mechanisms defined in this document, e.g., see
   [I-D.ietf-manet-dlep-da-credit-extension].  Updates to previously
   provided traffic classifications or new traffic classifications MAY
   be sent by a modem by including the Data Item in Session Update
   Messages.  More than one Data Item MAY be included in a message to
   provide information on multiple traffic classifiers.

   The set of traffic classification information provided in the data
   item is identified using a Traffic Classification Identifier, or TID.
   The actual data plane related information used in traffic
   classification is provided in a variable list of Traffic
   Classification Sub Data Items.

   The format of the Traffic Classification Data Item is:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Data Item Type                | Length                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Traffic Class. Identifier (TID)|   Num SDIs    |   Reserved    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Traffic Classification Sub Data Item 1              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :                                ...                            :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Traffic Classification Sub Data Item n              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBA1

   Length:  Variable

      Per [RFC8175] Length is the number of octets in the Data Item,
      excluding the Type and Length fields.

    Traffic Classification Identifier (TID):






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      A 16-bit unsigned integer identifying a traffic classification
      set.  There is no restriction on values used by a modem, and there
      is no requirement for sequential or ordered values.

   Num SDIs:

      An 8-bit unsigned integer indicating the number of Traffic
      Classification Sub Data Items included in the Data Item.  A value
      of zero (0) is allowed and indicates that no traffic should be
      matched against this TID.

   Reserved:

      MUST be set to zero by the sender (a modem) and ignored by the
      receiver (a router).

   Traffic Classification Sub Data Item:

      Zero or more Traffic Classification Sub Data Items of the format
      defined below MAY be included.  The number MUST match the value
      carried in the Num SDIs field.

   A router receiving the Traffic Classification Data Item MUST locate
   the traffic classification information that is associated with the
   TID indicated in each received Data Item.  If no associated traffic
   classification information is found, the router MUST initialize a new
   information set using the values carried in the Data Item.  When
   associated traffic classification information is found, the router
   MUST update the information using the values carried in the Data
   Item.  In both cases, a router MUST also ensure that any data plane
   state, e.g., see Section 3.1, that is associated with the TID is
   updated as needed.

2.1.1.  Traffic Classification Sub Data Item

   All Traffic Classification Sub Data Items share a common format that
   is patterned after the standard DLEP Data Item format, see [RFC8175]
   Section 11.3.  There is no requirement on, or meaning to sub Data
   Item ordering.  Any errors or inconsistencies encountered in parsing
   sub Data Items are handled in the same fashion as any other Data Item
   parsing error encountered in DLEP.

   The format of the Traffic Classification Sub Data Item is:








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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Sub Data Item Type            | Length                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Value...                            :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sub Data Item Type:

      A 16-bit unsigned integer that indicates the type and
      corresponding format of the Sub Data Item's Value field.  Sub Data
      Item Types are scoped within the Data Item in which they are
      carried, i.e., the Sub Data Item Type field MUST be used together
      with the Data Item Type to identify the format of the Sub Data
      Item.  Traffic Classification Sub Data Item Types are managed
      according to the IANA registry described in Section 6.3.

   Length:  Variable

      Copying [RFC8175], Length is a 16-bit unsigned integer that is the
      number of octets in the sub Data Item, excluding the Type and
      Length fields.

2.2.  DiffServ Traffic Classification Sub Data Item

   The DiffServ Traffic Classification Sub Data Item is used to identify
   the set of DSCPs that should be treated as a single flow, i.e.,
   receive the same traffic treatment.  DSCPs are identified in a list
   of DiffServ fields.  An implementation that does not support DSCPs
   and wants the same traffic treatment for all traffic to a destination
   or destinations would indicate 0 DSCPs.

   The format of the DiffServ Traffic Classification Sub Data Item is:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Must be one (1)               | Length                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Flow Identifier (FID)         |   Num DSCPs   |   DS Field 1  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   DS Field 2  |      ...      |   DS Field n  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length:  Variable





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      Length is defined above.  For this Sub Data Item, it is equal to
      three (3) plus the value of the Num DSCPs field.

   Flow Identifier (FID):

      A 16-bit unsigned integer representing the data plane information
      carried in the sub Data Item that is to be used in identifying a
      flow.  The value of 0xFFFF is reserved and MUST NOT be used in
      this field.

   Num DSCPs:

      An 8-bit unsigned integer indicating the number of DSCPs carried
      in the sub Data Item.  A zero (0) indicates a (wildcard) match
      against any DSCP value.

   DS Field:

      Each DS Field is an 8-bit whose definition is the same as
      [RFC2474].

               0   1   2   3   4   5   6   7
             +---+---+---+---+---+---+---+---+
             |         DSCP          |  CU   |
             +---+---+---+---+---+---+---+---+

               DSCP: differentiated services codepoint
               CU:   currently unused, MUST be zero

2.2.1.  Router Receive Processing

   A router receiving the Traffic Classification Sub Data Item MUST
   validate the information on receipt, prior to using the carried
   information, including potentially updating the data behavior as
   determined by the extension requiring the use of the Sub Data Item.
   Validation failures MUST be treated as an error as described above.

   Once validated, the receiver MUST ensure that each DS Field value is
   listed only once across the whole Traffic Classification Data Item.
   Note, this check is across the Data Item and not the individual sub
   Data Item.  If the same DS Field value is listed more than once
   within the same Traffic Classification Data Item, the Data Item MUST
   be treated as an error as described above.








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2.3.  Ethernet Traffic Classification Sub Data Item

   The Ethernet Traffic Classification Sub Data Item is used to identify
   the VLAN and PCPs that should be treated as a single flow, i.e.,
   receive the same traffic treatment.  Ethernet Priority Code Point
   support is defined as part of the IEEE 802.1Q [IEEE.802.1Q_2014] tag
   format and includes a 3 bit "PCP" field.  The tag format also
   includes a 12 bit VLAN identifier (VID) field.  PCPs are identified
   in a list of priority fields.  An implementation that does not
   support PCPs and wants the same traffic treatment for all traffic to
   a destination or destinations would indicate 0 PCPs.  Such an
   implementation could identify a VLAN to use per destination.

   The format of the Ethernet Traffic Classification Sub Data Item is:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Must be two (2)               | Length                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Flow Identifier (FID)         |NumPCPs| VLAN Identifier (VID) |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Pri. 1| Pri. 2| ..... | ..... | ..... |  Pad  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length:  Variable

      Length is defined above.  For this Sub Data Item, it is equal to
      four (4) plus the number of octets needed to carry the carried
      Priority fields is indicated by the NumPCPs field.  Note that as
      length is in octets and each Priority field is 4 bits, the
      additional length is the value carried in the NumPCPs field
      divided by two and rounded up to the next higher integer quantity.

   Flow Identifier (FID):

      A 16-bit unsigned integer representing the data plane information
      carried in the sub Data Item that is to be used in identifying a
      flow.  The value of 0xFFFF is reserved and MUST NOT be used in
      this field.

   Num PCPs:

      A 4-bit unsigned integer indicating the number of Priority fields
      carried in the sub Data Item.  A zero (0) indicates a (wildcard)
      match against any PCP value.

   VLAN identifier (VID):



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      A 12-bit unsigned integer field indicating the VLAN to be used in
      traffic classification.  A value of zero (0) indicates that the
      VID is to be ignored and any VID is to be accepted during traffic
      classification.

   Priority:

      Each Priority Field is 4-bits long and indicates a PCP field
      defined in [IEEE.802.1Q_2014].  Note that zero (0) is a valid
      value for either PCP or DEI.

           0   1   2   3
           +---+---+---+---+
           |    PCP    |DEI|
           +---+---+---+---+

           PCP: Priority code point
           DEI: currently unused, MUST be zero

   Pad:

      A 4-bit long field included when NumPCPs is an odd number.  This
      field MUST be set to zero when added, and MIST be ignored on
      receipt.

2.3.1.  Router Receive Processing

   A router receiving the Traffic Classification Sub Data Item MUST
   validate the information on receipt, prior to the using the carried
   information, including potentially updating the data behavior as
   determined by the extension requiring the use of the Sub Data Item.
   Validation failures MUST be treated as an error as described above.

   Once validated, the receiver MUST ensure that each Priority Field
   value is listed only once across the whole Traffic Classification
   Data Item.  Note, this check is across the Data Item and not the
   individual sub Data Item.  If the same Priority Field value is listed
   more than once within the same Traffic Classification Data Item, the
   Data Item MUST be treated as an error as described above.

3.  Credit Window Control

   This section defines additions to DLEP used in credit based flow
   control.  In addition to the Traffic Classification Data Item, two
   new messages and five Data Items are defined to support credit window
   control.  The use of credit window control impacts the data plane.





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   The credit window control mechanisms defined in this document support
   credit based flow control of traffic sent from a router to a modem.
   The mapping of specific flows of traffic to a particular credit
   window is based on the Traffic Classification Data Item defined in
   Section 2.1.  Both types of DLEP endpoints, i.e., a router and a
   modem, negotiate the use of extension during session initialization,
   e.g., see [I-D.ietf-manet-dlep-da-credit-extension].  When using
   credit windows, data traffic is only allowed to be sent by the router
   to the modem when there are credits available.

   Credits are managed on a per logical "Credit Windows" basis.  Each
   credit window can be thought of as corresponding to a queue within a
   modem.  Credit windows may be shared across, or dedicated to,
   destinations and data plane identifiers, e.g., DSCPs, at a
   granularity that is appropriate for a modem's implementation and its
   attached transmission technology.  As defined below, there is a
   direct one-for-one mapping of credit windows to flows as identified
   by FIDs carried within the Traffic Classification Data Item.  Modems
   pass to the router information on their credit windows and FIDs prior
   to a router being able to send data when an extension requiring the
   use of credit window control is used.  In addition to the traffic
   classification information associated with an FID, routers provide an
   initial credit window size, as well as the maximum size of the
   logical queue associated with each credit window.  The maximum size
   is included for informative and potential future uses.

   Modems provide an initial credit window size at the time of "Credit
   Window Initialization".  Such initialization can take place during
   session initiation or any point thereafter.  It can also take place
   when rate information changes.  Additional "Credit Grants", i.e.,
   increments to Credit Window size, are provided using a Destination Up
   or the new "Credit Control" Message.  A router provides its view of
   the Credit Window, which is known as "Status", in Destination Up
   Response and the new "Credit Control Response" Messages.  Routers can
   also request credits using the new "Credit Control" Message.

   When modems provide credits to a router, they will need to take into
   account any overhead of their attached transmission technology and
   map it into the credit semantics defined in this document.  In
   particular, the credit window is defined below to include per frame
   (packet) MAC headers, and this may not match the actual overhead of
   the modem attached transmission technology.  In that case a direct
   mapping, or an approximation will need to be made by the modem to
   provide appropriate credit values.

   Actual flows of traffic are mapped to credit windows based on flow
   identification information provided by modems in the Traffic
   Classification Data item defined in Section 2.  This data item



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   supports traffic classification on a per destination or more fine
   grain level.  Routers use the combination of the DLEP identified
   destination and flow information associated with a credit window in
   order to match traffic they send to specific credit windows.

   When a destination becomes reachable, a modem "Associates"
   (identifies) the appropriate traffic classification information via
   the TID to be used for traffic sent by the router to that
   destination.  As defined, each credit window has a corresponding FID.
   This means that the use of FIDs, TIDs and the association of a TID to
   a DLEP destination enables a modem to share or dedicate resources as
   needed to match the specifics of its implementation and its attached
   transmission technology.

   The defined credit window control has similar objectives as the
   control found in [I-D.ietf-manet-credit-window].  One notable
   difference from that credit control is that in this document, credits
   are never provided by the router to the modem.

3.1.  Data Plane Considerations

   When credit windowing is used, a router MUST NOT send data traffic to
   a modem for forwarding when there are no credits available in the
   associated Credit Window.  This document defines credit windows in
   octets.  A credit window value MUST be larger than the number of
   octets contained in a packet, including any MAC headers used between
   the router and the modem, in order for the router to send the packet
   to a modem for forwarding.  The credit window is decremented by the
   number of sent octets.

   A router MUST identify the credit window associated with traffic sent
   to a modem based on the traffic classification information provided
   in the Data Items defined in this document.  Note that routers will
   typically view a DLEP destination as the next hop MAC address.

3.2.  Credit Window Messages

   Two new messages are defined in support for credit window control:
   the Credit Control and the Credit Control Response Message.  Sending
   and receiving both message types is REQUIRED to support the credit
   window control defined in this document.

3.2.1.  Credit Control Message

   Credit Control Messages are sent by modems and routers.  Each sender
   is only permitted to have one message outstanding at one time.  That
   is, a sender (i.e., modem or router) MUST NOT send a second or any




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   subsequent Credit Control Message until a Credit Control Response
   Message is received from its peer (i.e., router or modem).

   Credit Control Messages are sent by modems to provide credit window
   increases.  Modems send credit increases when there is transmission
   or local queue availability that exceeds the credit window value
   previous provided to the router.  Modems will need to balance the
   load generated by sending and processing frequent credit window
   increases against a router having data traffic available to send, but
   no credits available.

   Credit Control Messages MAY be sent by routers to request credits and
   provide window status.  Routers will need to balance the load
   generated by sending and processing frequent credit window requests
   against a having data traffic available to send, but no credits
   available.

   The Message Type value in the DLEP Message Header is set to TBA2.

   A message sent by a modem, MUST contain one or more Credit Window
   Grant Data Items as defined below in Section 3.3.3.  A router
   receiving this message MUST respond with a Credit Control Response
   Message.

   A message sent by a router, MUST contain one or more Credit Window
   Request Data Items defined below in Section 3.3.5 and SHOULD contain
   a Credit Window Status Data Item, defined in Section 3.3.4,
   corresponding to each credit window request.  A modem receiving this
   message MUST respond with a Credit Control Response Message based on
   the received message and Data Item and the processing defined below,
   which will typically result in credit window increments being
   provided.

   Specific processing associated with each Credit Data Item is provided
   below.

3.2.2.  Credit Control Response Message

   Credit Control Response Messages are sent by routers to report the
   current Credit Window for a destination.  A message sent by a router,
   MUST contain one or more Credit Window Status Data Items as defined
   below in Section 3.3.4.  Specific receive processing associated with
   the Credit Window Status Data Item is provided below.

   Credit Control Response Messages sent by modems MUST contain one or
   more Credit Window Grant Data Items.  A Data Item for every Credit
   Window Request Data Item contained in the corresponding Credit
   Control Response Message received by the modem MUST be included.



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   Each Credit Grant Data Item MAY provide zero or more additional
   credits based on the modem's transmission or local queue
   availability.  Specific receive processing associated with each Grant
   Data Item is provided below.

   The Message Type value in the DLEP Message Header is set to TBA3.

3.3.  Credit Window Control Data Items

   Five new Data Items are defined to support credit window control.
   The Credit Window Initialization Data Item is used by a modem to
   identify a credit window and set its size.  The Credit Window
   Association Data Item is used by a modem to identify which traffic
   classification identifiers (flows) should be used when sending
   traffic to a particular DLEP identified destination.  The Credit
   Window Grant is used by a modem to provide additional credits to a
   router.  The Credit Request is used by a router to request additional
   credits.  The Credit Window Status is used to advertise the sender's
   view of number of available credits for state synchronization
   purposes.

   Any errors or inconsistencies encountered in parsing Data Items are
   handled in the same fashion as any other data item parsing error
   encountered in DLEP, see [RFC8175].  In particular, the node parsing
   the Data Item MUST terminate the session with a Status Data Item
   indicating Invalid Data.

3.3.1.  Credit Window Initialization

   The Credit Window Initialization Data Item is used by a modem to
   identify a credit window and set its size.  This Data Item SHOULD be
   included in any Session Initialization Response Message that also
   indicates support for an extension that requires support for the
   credit window control mechanisms defined in this document, e.g., see
   [I-D.ietf-manet-dlep-da-credit-extension].  Updates to previously
   identified credit windows or new credit windows MAY be sent by a
   modem by including the Data Item in Session Update Messages.  More
   than one data item MAY be included in a message to provide
   information on multiple credit windows.

   The Credit Window Initialization Data Item identifies a credit window
   using a Flow Identifier, or FID.  It also provides the size of the
   identified credit window.  Finally, a queue size (in bytes) is
   provided for informational purposes.  Note that to be used, a FID
   must be defined within a Traffic Classification Data Item and the
   associated TID must be provided via a Credit Window Association Data
   Item.




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   The format of the Credit Window Initialization Data Item is:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Data Item Type                | Length (16)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Flow Identifier (FID)         |            Reserved           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Credit Value                          :
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       :                         Credit Value                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Scale      |         Credit Window Size                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBA4

   Length:  16

      Per [RFC8175] Length is the number of octets in the Data Item.  It
      MUST be equal to sixteen (16).

   Flow Identifier (FID):

      A flow identifier as defined by the Traffic Classification Data
      Item.  The FID also uniquely identifies a credit window.

   Reserved:

      MUST be set to zero by the sender (a modem) and ignored by the
      receiver (a router).

   Credit Value:

      A 64-bit unsigned integer representing the credits, in octets, to
      be applied to the Credit Window.  This value includes MAC headers
      as seen on the link between the modem and router.

   Scale:

      An 8-bit unsigned integer indicating the scale used in the Credit
      Window Size fields.  The valid values are:








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         Value  Scale
         ------------
             0   B - Bytes     (Octets)
             1  KB - Kilobytes (B/1024)
             2  MB - Megabytes (KB/1024)
             3  GB - Gigabytes (MB/1024)

   Credit Window Size:

      A 24-bit unsigned integer representing the maximum size, in the
      octet scale indicated by the Scale field, of the associated credit
      window.

   A router that receives a Credit Window Initialization Data Item MUST
   ensure that the FID field value has been provided by the modem in a
   Traffic Classification Data Item carried in either the current or
   previous message.  If the FID cannot be found the router SHOULD
   report or log this information.  Note that no traffic will be
   associated with the credit window in this case.  After FID
   validation, the router MUST locate the credit window that is
   associated with the FID indicated in each received Data Item.  If no
   associated credit window is found, the router MUST initialize a new
   credit window using the values carried in the Data Item.  When an
   associated credit window is found, the router MUST update the credit
   window and associated data plane state using the values carried in
   the Data Item.  It is worth noting, that such updates can result in a
   credit window size being reduced, for example, due to a transmission
   rate change on the modem.

3.3.2.  Credit Window Associate

   The Credit Window Associate Data Item is used by a modem to associate
   traffic classification information with a destination.  The traffic
   classification information is identified using a TID value that has
   previously been sent by the modem or is listed in a Traffic
   Classification Data Item carried in the same message as the Data
   Item.

   A single Credit Window Associate Data Item MUST be included in all
   Destination Up and Destination Update Messages sent by a modem when
   the credit window control defined in this document is used.  Note
   that a TID will not be used unless it is listed in a Credit Window
   Associate Data Item.

   The format of the Credit Window Associate Data Item is:






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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Data Item Type                | Length (2)                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Traffic Class. Identifier (TID)|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBA5

   Length:  2

      Per [RFC8175] Length is the number of octets in the Data Item.  It
      MUST be equal to two (2).

    Traffic Classification Identifier (TID):

      A 16-bit unsigned integer identifying a traffic classification set
      that has been identified in a Traffic Classification Data Item,
      see Section 2.1.

   A router that receives the Credit Window Associate Data Item MUST
   locate the traffic classification information indicated by the
   received TID.  If no corresponding information can be located, the
   Data Item MUST be treated as an error as described above.  Once the
   traffic classification information is located, it MUST be associated
   with the destination and the router MUST ensure that any data plane
   state, see Section 3.1, that is associated with the TID and its
   corresponding FIDs is updated as needed.

3.3.3.  Credit Window Grant

   The Credit Window Grant Data Item is used by a modem to provide
   credits to a router.  One or more Credit Window Grant Data Items MAY
   be carried in the DLEP Destination Up, Destination Announce Response,
   Destination Update, Credit Control Messages, and Credit Control
   Response Messages.  Multiple Credit Window Grant Data Items in a
   single message are used to indicate different credit values for
   different credit windows.  In all message types, this Data Item
   provides an additional number of octets to be added to the indicated
   credit window.  Credit windows are identified using FID values that
   have been previously been sent by the modem or are listed in a Credit
   Window Initialization Data Item carried in the same messages as the
   Data Item.

   The format of the Credit Window Grant Data Item is:





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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Data Item Type                | Length (12)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Flow Identifier (FID)         |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Additional Credits                        :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Additional Credits                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBA6

   Length:  12

      Per [RFC8175], Length is the number of octets in the Data Item.
      It MUST be equal to twelve (12).

   Flow Identifier (FID):

      A flow identifier as defined by the Traffic Classification Data
      Item.  The FID also uniquely identifies a credit window.

   Additional Credit:

      A 64-bit unsigned integer representing the credits, in octets, to
      be added to the Credit Window.  This value includes MAC headers as
      seen on the link between the modem and router.  A value of zero
      indicates that no additional credits are being provided.

   When receiving this Data Item, a router MUST identify the credit
   window indicated by the FID.  If the FID is not known to the router,
   it SHOULD report or log this information and discard the Data Item.
   It is important to note that while this Data Item can be received in
   a destination specific message, credit windows are managed
   independently from the destination identified in the message carrying
   this Data Item, and the indicated FID MAY even be disjoint from the
   identified destination.

   Once the credit window is identified, the credit window size MUST be
   increased by the value contained in the Additional Credits field.  If
   the increase results in a window overflow, i.e., the size of the
   credit window after the increase is smaller than the original credit
   window size, the Credit Window must be set to its maximum
   (0xFFFFFFFFFFFFFFFF).





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   No response is sent by the router to a modem after processing a
   Credit Window Grant Data Item received in a Credit Control Response
   Message.  In other cases, the receiving router MUST send a Credit
   Window Status Data Item or items reflecting the resulting Credit
   Window value of the updated credit window.  When the Credit Grant
   Data Item is received in a Destination Up Message, the Credit Window
   Status Data Item(s) MUST be sent in the corresponding Destination Up
   Response Message.  Otherwise, a Credit Control Message MUST be sent.

3.3.4.  Credit Window Status

   The Credit Window Status Data Item is used by a router to report the
   current credit window size to its peer modem.  One or more Credit
   Window Status Data Items MAY be carried in a Destination Up Response
   Message or a Credit Control Response Message.  As discussed above,
   the Destination Up Response Message is used when the Data Item is
   sent in response to a Destination Up Message, and the Credit Control
   Response Message is sent in response to a Credit Control Message.
   Multiple Credit Window Status Data Items in a single message are used
   to indicate different sizes of different credit windows.  Similar to
   the Credit Window Grant, credit windows are identified using FID
   values that have been previously been sent by the modem.

   The format of the Credit Window Status Data Item is:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Data Item Type                | Length (12)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Flow Identifier (FID)         |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Credit Window Size                      :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                       Credit Window Size                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBA7

   Length:  12

      Per [RFC8175] Length is the number of octets in the Data Item.  It
      MUST be equal to twelve (12).

   Flow Identifier (FID):

      A flow identifier as defined by the Traffic Classification Data
      Item.  The FID also uniquely identifies a credit window.



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   Credit Window Size:

      A 64-bit unsigned integer, indicating the current number of
      credits, in octets, available for the router to send to the modem.
      This is referred to as the Modem Receive Window in
      [I-D.ietf-manet-credit-window].

   When receiving this Data Item, a modem MUST identify the credit
   window indicated by the FID.  If the FID is not known to the modem,
   it SHOULD report or log this information and discard the Data Item.
   As with the Credit Window Grant Data Item, the FID MAY be unrelated
   to the Destination indicated in the message carrying the Data Item.

   Once the credit window is identified, the modem SHOULD check the
   received Credit Window Size field value against the outstanding
   credit window's available credits at the time the most Credit Window
   Initialization or Grant Data Item associated with the indicated FID
   was sent.  If the values significantly differ, i.e., greater than can
   be accounted for based on observed data frames, then the modem SHOULD
   send a Credit Window Initialization Data Item to reset the associated
   credit window size to the modem's current view of the available
   credits.  As defined above, Credit Window Initialization Data Items
   are sent in Session Update Messages.  When multiple Data Items need
   to be sent, they SHOULD be combined into a single message when
   possible.  Alternatively, and also in cases where there are small
   differences, the modem MAY adjust the values sent in Credit Window
   Grant Data Items to account for the reported Credit Window.

3.3.5.  Credit Window Request

   The Credit Window Request Data Item is used by a router to request
   additional credits for particular credit windows.  Credit Window
   Request Data Items are carried in Credit Control Messages, and one or
   more Credit Window Request Data Items MAY be present in a message.

   Credit windows identified using a FID as defined above in
   Section 3.3.1.  Multiple FIDs MAY be present to allow for the case
   where the router identifies that credits are needed in multiple
   credit windows.  A special FID value, as defined below, is used to
   indicate that a credit request is being made across all queues.

   The format of the Credit Window Request Data Item is:









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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Data Item Type                | Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Flow Identifier (FID)         |               ...             :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :               ...             | Flow Identifier (FID)         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:  TBA8

   Length:  Variable

      Per [RFC8175] Length is the number of octets in the Data Item,
      excluding the Type and Length fields.  It will equal the number of
      FID fields carried in the Data Item times 2 and MUST be at least
      2.

   Flow Identifier (FID):

      A flow identifier as defined by the Traffic Classification Data
      Item.  The FID also uniquely identifies a credit window.  The
      special value of 0xFFFF indicates that the request applies to all
      FIDs.

   A modem receiving this Data Item MUST provide a Credit Increment for
   the indicated credit windows via Credit Window Grant Data Items
   carried in a new Credit Control Message.  Multiple values and queue
   indexes SHOULD be combined into a single Credit Control Message when
   possible.  Unknown FID values SHOULD be reported or logged and then
   ignored by the modem.

3.4.  Management Considerations

   This section provides several network management guidelines to
   implementations supporting the credit window mechanisms defined in
   this document.

   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



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   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.

4.  Compatibility

   The data items defined in this document will only be used when
   extensions require their use.

5.  Security Considerations

   This document introduces credit window control and flow mechanisms to
   DLEP.  These mechanisms do not inherently introduce any additional
   threats above those documented in [RFC8175].  The approach taken to
   Security in that document applies equally to the mechanism defined in
   this document.

6.  IANA Considerations

   This document requests the assignment of several values by IANA.  All
   assignments are to registries defined by [RFC8175].

6.1.  Message Values

   This document requests 2 new assignments to the DLEP Message Registry
   named "Message Values" in the range with the "Specification Required"
   policy.  The requested values are as follows:

                  +-----------+-------------------------+
                  | Type Code | Description             |
                  +-----------+-------------------------+
                  | TBA2      | Credit Control          |
                  |           |                         |
                  | TBA3      | Credit Control Response |
                  +-----------+-------------------------+

                     Table 1: Requested Message Values

6.2.  Data Item Values

   This document requests the following new assignments to the DLEP Data
   Item Registry named "Data Item Type Values" in the range with the
   "Specification Required" policy.  The requested values are as
   follows:







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               +-----------+------------------------------+
               | Type Code | Description                  |
               +-----------+------------------------------+
               | TBA1      | Traffic Classification       |
               |           |                              |
               | TBA4      | Credit Window Initialization |
               |           |                              |
               | TBA5      | Credit Window Association    |
               |           |                              |
               | TBA6      | Credit Window Grant          |
               |           |                              |
               | TBA7      | Credit Window Status         |
               |           |                              |
               | TBA8      | Credit Window Request        |
               +-----------+------------------------------+

                    Table 2: Requested Data Item Values

6.3.  DLEP Traffic Classification Sub Data Item Registry

   Upon approval of this document, IANA is requested to create a new
   DLEP registry, named "Traffic Classification Sub Data Item Type
   Values".  The registry shall identify the type code value, the Data
   Item which may use the value, and a description of the value.  While
   the same value may be reused in different Data Items, this is not
   recommended at this time.

   The following table provides initial registry values and the
   [RFC8126] defined policies that should apply to the registry:

             +-------------+---------------------------------+
             | Type Code   | Description                     |
             +-------------+---------------------------------+
             | 0           | Reserved                        |
             |             |                                 |
             | 1           | DiffServ Traffic Classification |
             |             |                                 |
             | 2           | Ethernet Traffic Classification |
             |             |                                 |
             | 3-65407     | Specification Required          |
             |             |                                 |
             | 65408-65534 | Private Use                     |
             |             |                                 |
             | 65535       | Reserved                        |
             +-------------+---------------------------------+

                     Table 3: Initial Registry Values




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7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8175]  Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
              Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175,
              DOI 10.17487/RFC8175, June 2017,
              <https://www.rfc-editor.org/info/rfc8175>.

7.2.  Informative References

   [I-D.ietf-manet-credit-window]
              Ratliff, S., "Credit Windowing extension for DLEP", draft-
              ietf-manet-credit-window-07 (work in progress), November
              2016.

   [I-D.ietf-manet-dlep-da-credit-extension]
              Cheng, B., Wiggins, D., and L. Berger, "DLEP DiffServ
              Aware Credit Window Extension", draft-ietf-manet-dlep-da-
              credit-extension-05 (work in progress), May 2018.

   [I-D.ietf-manet-dlep-pause-extension]
              Cheng, B., Wiggins, D., and L. Berger, "DLEP Control Plane
              Based Pause Extension", draft-ietf-manet-dlep-pause-
              extension-03 (work in progress), March 2018.

   [IEEE.802.1Q_2014]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks--Bridges and Bridged Networks", IEEE 802.1Q-2014,
              DOI 10.1109/ieeestd.2014.6991462, December 2014,
              <http://ieeexplore.ieee.org/servlet/
              opac?punumber=6991460>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.




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   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
              <https://www.rfc-editor.org/info/rfc2475>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Appendix A.  Acknowledgments

   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.  This document was
   derived from [I-D.ietf-manet-dlep-da-credit-extension] as a result of
   discussions at IETF101.

Authors' Addresses

   Bow-Nan Cheng
   MIT Lincoln Laboratory
   Massachusetts Institute of Technology
   244 Wood Street
   Lexington, MA  02421-6426

   Email: bcheng@ll.mit.edu


   David Wiggins
   MIT Lincoln Laboratory
   Massachusetts Institute of Technology
   244 Wood Street
   Lexington, MA  02421-6426

   Email: David.Wiggins@ll.mit.edu


   Lou Berger
   LabN Consulting, L.L.C.

   Email: lberger@labn.net








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