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Network Working Group                                           B. Cheng
Internet-Draft                                                D. Wiggins
Intended status: Standards Track                  MIT Lincoln Laboratory
Expires: September 7, 2019                                     L. Berger
                                                 LabN Consulting, L.L.C.
                                                              S. Ratliff
                                                              VT iDirect
                                                           March 6, 2019


         DLEP Credit-Based Flow Control Messages and Data Items
              draft-ietf-manet-dlep-credit-flow-control-04

Abstract

   This document defines new DLEP protocol Data Items that are used to
   support credit-based flow control.  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.

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 September 7, 2019.

Copyright Notice

   Copyright (c) 2019 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   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 . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Credit Window Control . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Data Plane Considerations . . . . . . . . . . . . . . . .   5
     2.2.  Credit Window Messages  . . . . . . . . . . . . . . . . .   5
       2.2.1.  Credit Control Message  . . . . . . . . . . . . . . .   5
       2.2.2.  Credit Control Response Message . . . . . . . . . . .   6
     2.3.  Credit Window Control Data Items  . . . . . . . . . . . .   7
       2.3.1.  Credit Window Initialization  . . . . . . . . . . . .   7
       2.3.2.  Credit Window Associate . . . . . . . . . . . . . . .   9
       2.3.3.  Credit Window Grant . . . . . . . . . . . . . . . . .  10
       2.3.4.  Credit Window Status  . . . . . . . . . . . . . . . .  12
       2.3.5.  Credit Window Request . . . . . . . . . . . . . . . .  13
     2.4.  Management Considerations . . . . . . . . . . . . . . . .  14
   3.  Compatibility . . . . . . . . . . . . . . . . . . . . . . . .  14
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     5.1.  Message Values  . . . . . . . . . . . . . . . . . . . . .  15
     5.2.  Data Item Values  . . . . . . . . . . . . . . . . . . . .  15
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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
   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].



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   This document defines DLEP Data Items and Messages which 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.  Traffic sent by a router will use traffic flow
   classification information provided by the modem as defined in
   [I-D.ietf-manet-dlep-traffic-classification].  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 credit
   window based flow control with different traffic classification
   techniques.

   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 supports credit window control by introducing two new
   DLEP messages in Section 2.2, and five new DLEP Data Items in
   Section 2.3.

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.  Credit Window Control

   This section defines additions to DLEP used in credit based flow
   control.  Two new messages and five Data Items are defined to support
   credit window control.  The use of credit window control impacts the
   data plane.

   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
   [I-D.ietf-manet-dlep-traffic-classification].  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



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   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
   [I-D.ietf-manet-dlep-traffic-classification].  This data item
   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.





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   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.

2.1.  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.

2.2.  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.

2.2.1.  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
   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



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   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 2.3.3.  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 2.3.5 and SHOULD contain
   a Credit Window Status Data Item, defined in Section 2.3.4,
   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.

2.2.2.  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 2.3.4.  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.
   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.



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2.3.  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.

2.3.1.  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.

   The format of the Credit Window Initialization 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 (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:

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



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   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.

2.3.2.  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:

        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



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   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 [I-D.ietf-manet-dlep-traffic-classification].

   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 2.1, that is associated with the TID and its
   corresponding FIDs is updated as needed.

2.3.3.  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:

       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                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   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).

   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.








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2.3.4.  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.

   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].





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   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.

2.3.5.  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 2.3.1.  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:

       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




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   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.

2.4.  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
   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.

3.  Compatibility

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







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4.  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.

5.  IANA Considerations

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

5.1.  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

5.2.  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                  |
               +-----------+------------------------------+
               | 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.  References

6.1.  Normative References

   [I-D.ietf-manet-dlep-traffic-classification]
              Cheng, B., Wiggins, D., and L. Berger, "DLEP Traffic
              Classification Data Item", August 2018.

   [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>.

6.2.  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.







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   [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-06 (work in progress), August 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-04 (work in progress), June 2018.

   [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>.

Appendix A.  Acknowledgments

   Many useful comments were received from contributors to the MANET
   working group, notably Rick Taylor.  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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   Stan Ratliff
   VT iDirect
   13861 Sunrise Valley Drive, Suite 300
   Herndon, VA  20171
   USA

   Email: sratliff@idirect.net












































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