2.3.3. Credit Window Grant
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Original RFC Text
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, and Credit Control Response
Messages. Multiple Credit Window Grant Data Items may be present in
a single message. Each item grants credits to a different credit
window and therefore references a different FID. 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 sent by the modem or are
listed in a Credit Window Initialization Data Item carried in the
same message as the Data Item.
The format of the Credit Window Grant 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 (12) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Identifier (FID) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Credits |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Data Item Type:
32
Length:
12
As specified in [RFC8175], Length is the number of octets in the
Data Item. It MUST be equal to twelve (12). If it is some other
value, 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 indicates a credit window.
Reserved:
For the Credit Window Grant Data Item, this reserved field is
currently unused. It MUST be set to all zeros for this version of
the Data Item and is currently ignored on reception. This allows
for future extensions of the Data Item if needed.
Additional Credits:
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 log this information and discard the Data Item. The method
of logging is left to the router implementation. It is important to
note that while this Data Item can be received in a destination-
specific message, credit windows are managed independently of 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, the credit window must be
set to its maximum as defined by the Credit Window Max Size carried
in the Credit Window Initialization Data Item.
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. For each Credit Window Grant Data Item received in other
message types, the receiving router MUST send a Credit Window Status
Data Item reflecting the resultant credit window value of the updated
credit windows. When the Credit Window 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.