2.3.5. Credit Window Request

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Original RFC Text

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 are identified using a FID as defined in
   Section 2.3.1.  Multiple FIDs MAY be present to allow for the case
   where the router determines that credits are needed in multiple
   credit windows.  A special FID value, as defined below, is used to
   indicate that a credit window request is being made across all
   queues.

   The format of the Credit Window Request Data Item is as follows:

       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) [1]     | Flow Identifier (FID) [2]     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               ...             | Flow Identifier (FID) [n]     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Data Item Type:
      34

   Length:
      Variable

      As specified in [RFC8175], Length is the number of octets in the
      Data Item, excluding the Data Item Type and Length fields.  It is
      equal to the number of FID fields carried in the Data Item times 2
      and MUST be at least 2.  If it is less than 2, the Data Item is
      corrupt, so the message in which it appears cannot be reliably
      parsed and is ignored.

   Flow Identifier (FID):
      A 2-octet flow identifier as defined by the Traffic Classification
      Data Item.  The FID also uniquely identifies a credit window.  The
      special value 0xFFFF indicates that the request applies to all
      FIDs.  When this special value is included, all other FID values
      included in the Data Item are redundant, as the special value
      indicates all FIDs.

   A modem receiving this Data Item MUST provide a credit window
   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 logged and then
   ignored by the modem.  The method of logging is left to the modem
   implementation.