Network Working Group B. Cheng
Internet-Draft D. Wiggins
Intended status: Standards Track Lincoln Laboratory
Expires: December 17, 2018 L. Berger
LabN Consulting, L.L.C.
June 15, 2018
DLEP Credit-Based Flow Control Messages and Data Items
draft-ietf-manet-dlep-credit-flow-control-01
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
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on December 17, 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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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 . . . . . . . . . . . . . . . . . . . . . . . . 21
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 .
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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 (8) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow Identifier (FID) |NumPCPs| VLAN Identifier (VID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pri. 1| Pri. 2| Pri. 3| Pri. 4| Pri. 5| Pri. 6| Pri. 7| Pri. 8|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length: Variable
Length is defined above. For this Sub Data Item, it is equal to
eight (8).
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 16-bit unsigned integer representing the data plane information
carried in the sub Data Item that is to be used in identifying a
flow.
VLAN identifier (VID):
A 12-bit unsigned integer field indicating the VLAN to be used in
traffic classification. A value of zero (0) indicates that the
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VID is to be ignored and any VID is to be accepted during traffic
classification.
Priority:
Each Priority Field is an 4-bit whose definition includes the PCP
field defined in [IEEE.802.1Q_2014]
0 1 2 3
+---+---+---+---+
| PCP |DEI|
+---+---+---+---+
PCP: Priority code point
DEI: currently unused, MUST be zero
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.
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.
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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
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
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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
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.
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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.
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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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.
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.
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:
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 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:
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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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.
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.
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:
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.
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
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.
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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:
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+---------------------------------+------------------------+
| Type Code | Description |
+---------------------------------+------------------------+
| 0 | N/A |
| | |
| Reserved | 1 |
| | |
| DiffServ Traffic Classification | 2 |
| | |
| Ethernet Traffic Classification | 3-65407 |
| | |
| | Specification Required |
| | |
| 65408-65534 | |
| | |
| Private Use | 65535 |
| | |
| | Reserved |
+---------------------------------+------------------------+
Table 3: Initial Registry Values
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.
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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-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>.
[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
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Bow-Nan Cheng
Lincoln Laboratory
Massachusetts Institute of Technology
244 Wood Street
Lexington, MA 02421-6426
Email: bcheng@ll.mit.edu
David Wiggins
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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