wdiff draft-ietf-manet-dlep-da-credit-extension-01.txt draft-ietf-manet-dlep-da-credit-extension-02.txt

Network Working Group B. Cheng
Internet-Draft D. Wiggins
Intended status: Standards Track Lincoln Laboratory
Expires: September 14, 2017 May 3, 2018 L. Berger
LabN Consulting, L.L.C.
March 13,
October 30, 2017

DLEP DiffServ Aware Credit Windowing Extension
draft-ietf-manet-dlep-da-credit-extension-01
draft-ietf-manet-dlep-da-credit-extension-02

Abstract

This document defines an extension to the DLEP protocol that enables
a DiffServ aware credit-windowing scheme for destination-specific and
shared flow control.

Status of This Memo

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provisions of BCP 78 and BCP 79.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Extension Overview . . . . . . . . . . . . . . . . . . . . . 3
3. Extension Usage and Identification . . . . . . . . . . . . . 4 5
4. Data Plane Considerations . . . . . . . . . . . . . . . . . . 4 5
5. Extension Messages . . . . . . . . . . . . . . . . . . . . . 4 5
5.1. Credit Control Message . . . . . . . . . . . . . . . . . 4 5
5.2. Credit Control Response Message . . . . . . . . . . . . . 5 6
6. Extension Data Items . . . . . . . . . . . . . . . . . . . . 5 6
6.1. Queue Parameters Credit Window Initialization . . . . . . . . . . . . . . 7
6.2. Credit Window Traffic Classification . . . . . . . 6
6.2. . . . 9
6.2.1. Traffic Classification Sub Data Item . . . . . . . . 11
6.2.2. DiffServ Aware (DA) Traffic Classification Sub Data Item . . . . 11
6.3. Credit Window Associate . . . . . . . . . . . . . . . . . 13
6.4. Credit Window Credit Grant . . . . . . . . . . . . 8
6.3. DiffServ Aware (DA) . . . 14
6.5. Credit Window Status . . . . . . . . 10
6.4. DiffServ Aware (DA) . . . . . . . . . . 15
6.6. Credit Window Request . . . . . . . . . . . 12 . . . . . . . 17
7. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 13 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 18
9.1. Extension Type Value . . . . . . . . . . . . . . . . . . 13 18
9.2. Message Values . . . . . . . . . . . . . . . . . . . . . 14 19
9.3. Data Item Values . . . . . . . . . . . . . . . . . . . . 14 19
9.4. DLEP Sub Data Item Registry . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 20
10.1. Normative References . . . . . . . . . . . . . . . . . . 15 20
10.2. Informative References . . . . . . . . . . . . . . . . . 15 21
Appendix A. Open and Resolved Issues . . . . . Acknowledgments . . . . . . . . . 15
A.1. Merge with [I-D.ietf-manet-credit-window] . . . . . . . . 15
A.2. Credit Windows Shared Across Destinations . . 21
Appendix B. Open and Resolved Issues . . . . . . 16
A.3. Supporting Router Limits . . . . . . . . 21
B.1. Merge with [I-D.ietf-manet-credit-window] . . . . . . . . 16
A.4. Absolute vs Increment 21
B.2. Supporting Router Limits . . . . . . . . . . . . . . . . 22
B.3. Absolute vs Increment . . 16
A.5. Alternate Format Encoding . . . . . . . . . . . . . . . . 16
A.6. 22
B.4. Bidirectional Flow
Control (closed) . . . . . . . . . . . . . . . . . . . . 17 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 22

1. Introduction

The Dynamic Link Event Protocol (DLEP) is defined in
[I-D.ietf-manet-dlep]. [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. This document defines one such extension.

The base DLEP specification does not include any flow control
capability. There are various flow control theoretically possible
with DLEP. For example, a credit-windowing 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].

This document defines a DLEP extension which provides an alternate
flow control mechanism for DiffServ [RFC2475] traffic sent from a router to a modem.
Flow control is provided for multiple DSCPs (differentiated services
codepoint), which are grouped into provide using one or more logical sets "Credit Windows",
each of logical queues.
The extension defined in this document is referred to as "DiffServ
Aware Credit Windowing" or, more simply, the "DA Credit" extension.

This document defines a new DLEP Extension Type Value in Section 3 which is used to indicate the will typically be supported by an associated virtual or
physical queue. Traffic sent by a router will use of traffic
classification information provided by the extension. modem to identify which
traffic is associated with each credit window. (For general
background on traffic classification see [RFC2475] Section 2.3.)
This document supports traffic classification based on DLEP
destination and DiffServ [RFC2475] DSCPs (differentiated services
codepoints). Credit windows may be shared or dedicated on a per
{destination, DSCP} tuple basis. Said another way, the defined
mechanism allows for credit windows to be shared across traffic sent
to multiple DLEP destinations and DSCPs, or used exclusively for
traffic sent to a particular destination and/or DSCP. The extension
also supports the "wildcard" matching of any DSCP.

The extension defined in this document is referred to as "DiffServ
Aware Credit Windowing" or, more simply, the "DA Credit" extension.
The extension is structured to allow for reuse of the defined credit
window based flow control with traffic classification techniques
other than DiffServ, e.g., IEEE 802.1 Q priority code points or even
5-tuple IP flows.

This document defines a new DLEP Extension Type Value in Section 3
which is used to indicate the use of the extension. Two new messages
are defined in Section 5, and four six new DLEP Data Items in Section 6.

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, RFC 2119 [RFC2119].
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

2. Extension Overview

The DA Credit extension can be used to support credit based flow
control of traffic sent from a router to a modem. The extension can
be used to support DiffServ and non-DiffServ based flow control.
Both types of DLEP endpoints, i.e., a router and a modem, negotiate
the use of extension during session initialization, see Section 5.2
[I-D.ietf-manet-dlep].

[RFC8175]. When using this extension, data is allowed to be sent by
the router to the modem only when there are credits available.

When the extension is to be used,

Credits are managed on a modem passes per logical "Credit Windows" basis. Each
credit window can be thought of as corresponding to a queue within a
modem. Modems pass to the router information on its
known DSCPs, if any. DSCPs are grouped by logical queues, credit windows
and identify each of
which are given via a logical queue index. The queue index zero (0) is
special and is used for any DSCP value, including 0, which is not
otherwise identified by "Credit Window Identifier", or "CID". In
addition to the modem. The modem also provides a CID, credit window information includes an initial
credit window size,
in bytes, as well as the maximum size of the logical queue
associated with each CID. The maximum size is included for
informative and, potential, future uses. Currently, only DSCP to logical queue index value mapping is
used in flow control operation.

The DA Credit extension supports credit based flow control

As mentioned above, traffic classification supported by this document
is performed on a per
MAC address destination, per queue index {destination, DSCP} tuple basis. Modems provide This means
that, routers need the
initial size combination of the DLEP identified destination
and DSCP associated "Credit Window", i.e., with a CID in order to match traffic it sends to
specific credit windows. Modems provide the amount mapping of DSCPs to CIDs
in
octets (bytes) that may sets, each of which is identified via a "Traffic Classification
Identifier" or "TID". When a destination becomes reachable, a modem
"Associates" (identifies) the TID to be used for traffic sent by the
router to the modem, when that destination. This use of CIDs, TIDs and association
of a
MAC TID to a DLEP destination becomes reachable and, optionally, when enables modem to share or dedicate
resources as needed to match the specifics of its implementation and
its attached transmission technology.

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 Increments", Grants", i.e., increases in a
increments to Credit Window size, are provided using a Destination Up
or the new "Credit Control" messages. Message. A router provides its view of
the Credit Window, which is known as
"status", "Status", in Destination Up
Response and the new "Credit Control Response" messages. Messages. Routers can
also request credits using the new "Credit Control" message.

Credit information, both grants and status, is provided in new credit
grant related data items. Each data item contains Message.

When modems provide credits to a single credit
value that applies router, they will need to one or more queue indexes. Different (grant take into
account any overhead of their attached transmission technology and status) values for different queue indexes can be provided
map it into the credit semantics defined in a
single message by including multiple grant data items. The values
indicate a number of octets (bytes), including this document. In
particular, the credit window is defined below to include per frame
(packet) MAC headers on and this may not match the actual overhead of
the
router to modem link, attached transmission technology. In that may case a direct
mapping or an approximation will need to be sent.

Note that credit information related made by the modem to different destination MAC
addresses is always passed in different DLEP messages.
provide appropriate credit values.

3. Extension Usage and Identification

The use of the extension defined in this document SHOULD be
configurable. To indicate that the DiffServ Aware Credit Windowing
Extension is to be used, an implementation MUST include the DiffServ
Aware Credit Windowing Type Value in the Extensions Supported Data
Item. The Extensions Supported Data Item is sent and processed
according to [I-D.ietf-manet-dlep]. [RFC8175].

The DiffServ Aware Credit Windowing Extension Type Value is TBA1, see
Section 9.

4. Data Plane Considerations

When the use of the extension defined in this document is agreed upon
per standard DLEP processing, see Section 3, a router MUST NOT send
data to a modem for forwarding when there are no credits available in
the associated Credit Window.

5. 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. The definitions support
identification based on DLEP destination and, at the modem's
discretion, DSCPs. Note that routers will typically view a DLEP
destination as the next hop.

5. Extension Messages

Two new messages are defined by this extension: the Credit Control
and the Credit Control Response message. Message. Sending and receiving both
message types MUST be supported by any implementation that advertises
use of this extension per Section 3.

5.1. Credit Control Message

Credit Control Messages are sent by modems to provide Credit
Increments. credit window
increases. For messages sent by modems, only one message per MAC
address can be
outstanding at one time. That is, a modem MUST NOT send a second (or
any subsequent) message containing the same MAC
Address Credit Control Message until a Credit Control
Response message Message is received from its peer router with that MAC address. router.

Credit Control Messages MAY be sent by routers, e.g., to request
credits or provide window status. No specific response message is
required from a modem from a message transaction perspective. There
is no restriction on when a router can send a Credit Control Message.

[TBD: Should anything be said about sending, or limiting, multiple
credit requests?]

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

The message MUST contain a DLEP MAC Address Data Item.

A message sent by a modem, MUST contain one or more DiffServ Aware Credit Window
Grant data items Data Items as defined below in Section 6.2. 6.4. A router receiving
this message MUST respond with a Credit Control Response Message.

A message sent by a router, MUST contain the DiffServ Aware Credit Window Request data item
Data Item defined below in Section 6.4. 6.6. A modem receiving this
message MUST provide a Credit Increment for process the indicated MAC
address received message and queue indexes data item as defined
below, which will result in credit window increments being provided
via a Credit Window Grant Data Items carried in one more more new
Credit Control Message.

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

5.2. Credit Control Response Message

Credit Control Response Messages are sent by routers to report the
current Credit Window for a destination.

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

The message MUST contain a DLEP MAC Address Data Item.

A message sent by a router, MUST contain one or more DiffServ Aware Credit Window
Status data items as defined below in Section 6.3. 6.5.

Specific processing associated with the DA Credit Window Window Status data
item
Data Item is provided below.

6. Extension Data Items

Four

Six data items are defined by this extension. The Queue Parameters Credit Window
Initialization Data Item is used by a modem to provide information on the DSCPs it
uses in forwarding. identify a credit
window and set its size. The DA Credit Grant Window Traffic Classification
Data Item is used by a modem to
provide credits identify a set which identifies which
DSCPs are mapped to a router. credit window. The Credit Window Association
Data Item is used by a modem to identify which traffic classification
set 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 DA Credit Request is
used by a router to request additional credits. The DA 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.

The defined data items and operations are have similar to objectives as
those found in [I-D.ietf-manet-credit-window]. One notable
difference from this extension is that in this document credits are
never provided by the router to the modem.

6.1. Queue Parameters Credit Window Initialization

The Queue Parameters Credit Window Initialization Data Item is used by a modem to indicate DSCP
values that may be independently controlled.
identify a credit window and set its size. This data item MUST SHOULD be
included in a any Session Initialization Response Message that also
contains the DiffServ Aware Credit Windowing Extension Type Value in
the Extensions Supported Data Item. Updates to these parameters 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 Queue Parameters Credit Window Initialization Data Item identifies DSCPs based on groups of
logical queues. The number of logical queues is variable as is a credit window
using a Credit Window Identifier, or CID. It also provides the
number size
of DSCPs associated with each queue. A the identified credit window. Finally, a queue size (in bytes) is
provided for informational purposes. An implementation that does
not support DSCPs would indicate 1 queue with 0 DSCPs, and the number
of bytes Note that may to be used, a CID
must be listed in its associated link transmit queue. a Credit Window Traffic Classification Data Item.

The format of the Queue Parameters Credit Window Initialization Data Item is:

Data Item Type: TBA4

Length: Variable 16

Per [I-D.ietf-manet-dlep] [RFC8175] Length is the number of octets in the data item,
excluding the Type and Length fields.

Num Queues:

An 8-bit

Credit Window Identifier (CID):

A 16-bit unsigned integer indicating the number of queues
represented in the data item. This field MUST contain identifying a credit window. The value
of
at least one (1). Note that 0xFFFFFFFF is reserved and MUST not be used in this number Data Item.
There is one larger than no other restriction on values used by a modem, and there
is no requirement for sequential or ordered values.

Reserved:

MUST be set to zero by the
largest queue index value included 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 data item. Credit Window. This value includes MAC headers
as seen on the link between the modem and router.

Scale:

An 4-bit 8-bit unsigned integer indicating the scale used in the Queue 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)

Reserved:

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

Num DSCPs Qn:

An 8-bit unsigned integer indicating the number of DSCPs
associated with the indexed queue. Other than the special case
covered in the next paragraph, this field MUST contain a value of
at least one (1). Queue indexes start at zero (0) and the maximum
queue index "Qn" is one less than the value carried in the Num
Queues field. Queue indexes are implicit in the position in the
data item.

Queue index zero "Q0" is a special case. It is used for any
traffic that does not carry a DSCP value represented in the data
item. Therefore the value of the Queue index zero field, "Num
DSCPs Q0", field MUST be zero (0).

Queue Size Qn:

Credit Window Size:

A 24-bit unsigned integer representing the maximum size, in the
octet scale indicated by the Scale field, of the queue supporting
traffic with the DSCPs associated with the queue index.

DS Field Qn:

The data item credit
window.

A router that receives a Credit Window Initialization Data Item MUST
locate the credit window that is associated with the CID 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 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.

6.2. Credit Window Traffic Classification

The Credit Window Traffic Classification Data Item is used by a modem
to provide information to enable router to identify the credit window
associated with traffic the router sends. Each data item includes a
set of credit windows and provides traffic classification for each
window. The data item is defined to support classification based on
DSCPs, but is designed to be extensible for future traffic
classification types. The data item is not required to provide full
traffic classification information. In the context of the definition
included in this document, the DLEP destination address needed to
complete the traffic classification information is provided by a
modem when it identifies the traffic classification set in a
Destination Up message using the Credit Window Associate Data Item
defined below.

The Credit Window Traffic Classification Data Item SHOULD be included
by a modem in any Session Initialization Response Message that also
contains the DiffServ Aware Credit Windowing Extension Type Value in
the Extensions Supported Data Item. 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.
Addition information, e.g., the list DSCPs associated with a credit
window, is provided in a variable series of Queue Parameter sub-data
items. Note that to be used, a TID must be listed in a Credit Window
Associate Data Item.

The format of the Credit Window 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: TBA5

Length: Variable

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

Traffic Classification Identifier (TID):

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, see Section 4, that is associated with the TID is updated as
needed.

6.2.1. 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:

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 data item's Value field. Sub Data
Item Types are managed according to the IANA registry described in
Section 9.4.

Length: Variable

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

6.2.2. DiffServ Traffic Classification Sub Data Item

The DiffServ Traffic Classification Sub Data Item is used to identify
the DSCPs associated with a specific credit window. Credit windows
are identified using CID 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 sub data item. DSCPs are
identified in a list of DiffServ fields. An implementation that does
not support DSCPs, and wants to use credit window flow control for
all traffic to a destination or destinations, would indicate with 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 two (2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Window Identifier (CID)| Num DSCPs | DS Field 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DS Field 2 | ... | DS Field n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Length: Variable

Length is the number of octets in the sub data item. It is equal
to seven (7) plus the value of the Num DSCPs field.

Credit Window Identifier (CID):

A 16-bit unsigned integer identifying a credit window that has
been identified in a Credit Window Initialization Data Item, see
Section 6.1. Unknown CID values SHOULD be reported and result in
associated traffic being dropped.

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

A router receiving the DiffServ Traffic Classification Sub Data Item
MUST validate the information on receipt prior to the information and
data plan update described earlier in this section. The credit
window associated with the CID indicated in each Data Item must be
located. It is important to note that the CID value may be present
in a Credit Window Initialization Data Item carried in the same
message as the Sub Data Item. If the CID is not located, the it MUST
be treated as an error as described above.

In the case there are no unknown CIDs, the receiver MUST ensure that
each DS Field value is listed only once across the whole Credit
Window 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 Credit Window
Traffic Classification Data Item, the Data Item MUST be treated as an
error as described above.

6.3. Credit Window Associate

The Credit Window Associate Data Item is used by a sequence of 8 bit DS Fields. modem to associate
traffic classification information with a destination. The
position traffic
classification information is identified using a TID value that has
been previously been sent by the modem or is listed in a Credit
Window Traffic Classification Data Item carried in the sequence identifies same message
as the associated queue index.
The number of DS Fields present should equal 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 sum use of all Num
DSCPs field values.

The DS Field structure the extension defined in this document is agreed upon, see
Section 3.

The format of the same as [RFC2474]. Credit Window 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DSCP Data Item Type | CU Length (2) |
+---+---+---+---+---+---+---+---+

DSCP: differentiated services codepoint
CU: currently unused,
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Traffic Class. Identifier (TID)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Data Item Type: TBA6

Length: 2

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

Traffic Classification Identifier (TID):

A 16-bit unsigned integer identifying a traffic classification set
that has been identified in a Credit Window Traffic Classification
Data Item, see Section 6.2. Unknown TID values SHOULD be reported
and result in associated traffic being dropped.

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 zero

6.2. DiffServ Aware (DA) 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 4, that is associated with the TID is updated as
needed.

6.4. Credit Window Credit Grant

The DiffServ Aware, or DA, Credit Window Credit Grant data item is used by a modem to
provide credits to a router. One or more DA Credit Window Grant data
items Data
Items MAY be carried in the DLEP Destination Up, Destination Announce
Response, Destination Update, and Credit Control messages. Messages. Multiple
DA
Credit Window Grant data items Data Items in a single message are used to indicated
indicate different credit values for different logical queues. credit windows. In Destination type messages, this data item provides the total
number of octets available in the Credit Window to the destination
indicated in the
all message for the specified logical queues. In the
Credit Control message, types, this data item provides an additional number of
octets to be added to the Credit Window to the destination indicated in the message for the specified logical queues.

Logical queues credit window. Credit window are
identified via using a Queue Index as defined above in
Section 6.1. Multiple Queue Indexes MAY be present to allow for using CID values that have been previously been
sent by the
case where same credit information applies to multiple queues. As
mentioned above, multiple DA modem or are listed in a Credit Grant Window Initialization
Data Items MAY be present
to provide different queue-specific credit information Item carried in one
message. The special Queue Index value of 255 is used to indicate
that the credit information applies to all queues. same messages as the Data Item.

The format of the DA 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit value Window Identifier (CID)| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Queue Index | ... Additional Credits :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... | Queue Index Additional Credits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Data Item Type: TBA5 TBA7

Length: Variable 12
Per [I-D.ietf-manet-dlep], [RFC8175], Length is the number of octets in the data item,
excluding the Type and Length fields. It will equal 8 plus the
number of Queue Index CID fields carried in the data item and MUST be at least
9.

Credit Value: Window Identifier (CID):

A 16-bit unsigned integer identifying a credit window that has
been identified in a Credit Window Initialization Data Item, see
Section 6.1. Unknown CID values SHOULD be reported and ignored.

Additional Credit:

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

Queue Index:

One or more 8-bit fields used to indicate a queue index defined by
a Queue Parameters Data Item. The special value of 255 indicates
that includes MAC headers as
seen on the information in link between the data item applies to all queue
indexes.

Receive processing of modem and router.

When receiving this data item item, a router MUST identify the credit
window indicated by the CID. If the CID is based on not known to the message in which router,
it SHOULD report or log this information and discard the Data Item.
It is carried. When important to note that while this data item is can be received in
a Destination type destination specific message, credit windows are managed
independently from the Credit Window of the indicated destination MAC address identified in the message carrying
this Data Item, and the indicated queue indexes MUST CID MAY even be set to disjoint from the value contained in
identified destination.

Once the
Credit Value field.

When this data item credit window is received in a Credit Control message, the
Credit Window of identified, the indicated destination MAC address and indicated
queue indexes credit window size MUST be
increased by the value contained in the Credit
Value Additional Credits field. If
the increase results in a window overflow, i.e., the
Credit Window resulting size of the
credit window after the increase is smaller than the original Credit Window, credit
window size, the Credit Window must be set to its maximum
(0xFFFFFFFFFFFFFFFF).

Independent of the received message, the receiving router MUST send a
DA
Credit Window Window Status data item or items reflecting the
resulting Credit Window value of each modified queue index. the updated credit window. When the
Credit Grant data item is received in a Destination Up message, Message, the DA
Credit Window Window Status data item(s) MUST be sent in the
corresponding Destination Up Response message. Message. In all other cases, the a
Credit Control message Message MUST be sent.

6.3. DiffServ Aware (DA)

6.5. Credit Window Status

The DiffServ Aware, or DA, Credit Window Status data item is used by a router to report the
current Credit Window credit window size to its peer modem. One or more DA Credit
Window Status data items MAY be carried in a Destination Up Response message
Message or a Credit Control Response message. Message. As discussed above,
the Destination Up Response message Message is used when the data item is
sent in response to a Destination Up message, Message, and the Credit Control
Response message Message is sent in response to a Credit Control message. Message.
Multiple DA Credit Window Window Status data items in a single message
are used to indicated different credit window values
for different logical queues.

Similar to the DA Credit Grant, logical queues are identified using a
Queue Index as defined above in Section 6.1. Multiple Queue Indexes
MAY be present to allow for the case where same credit information
applies to multiple queues. Multiple DA Credit Window Status Data
Items are used to provide sizes of different queue-specific credit window
information in one message. The special Queue Index value of 255 is
used to indicate that windows.
Similar to the Credit Window information applies to all
queues. Grant, credit windows are identified
using CID values that have been previously been sent by the modem.

The format of the DA Credit Window 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Window :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Credit Window Identifier (CID)| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Queue Index | ... Credit Window Size :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... | Queue Index Credit Window Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Data Item Type: TBA6 TBA8

Length: Variable 12

Per [I-D.ietf-manet-dlep] [RFC8175] Length is the number of octets in the data item,
excluding the Type and Length fields. It will equal 8 plus the
number of Queue Index CID fields carried in the data item and MUST be at least
9.

Credit Window: Window Identifier (CID):

A 16-bit unsigned integer identifying a credit window that has
been identified in a Credit Window Initialization Data Item, see
Section 6.1.

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].

Queue Index:

One or more 8-bit fields used to indicate

When receiving this data item, a queue index defined modem MUST identify the credit
window indicated by
a Queue Parameters the CID. If the CID is not known to the modem,
it SHOULD report or log this information and discard the Data Item. The special value of 255 indicates
that
As with the information in Credit Window Grant Data Item, the data item applies CID MAY be unrelated
to all queue
indexes.

The receiving 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 credits
credit window's available credits at the time the last most Credit
Increment Window
Initialization or Grant data item associated with the indicated MAC address and Queue Indexes
were CID
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 Destination Update message carrying a DA Credit Grant
data item Window Initialization Data Item to reset the associated Credit Window(s)
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 item
indicated value. Multiple values and queue indexes items need
to be sent, they SHOULD be combined into a single Destination Update Control message when
possible. Alternatively, and also in cases where there are small
differences, the modem MAY adjust the values sent in DA Credit Window
Grant data items to account for the reported Credit Window.

6.4. DiffServ Aware (DA)

6.6. Credit Window Request

The DiffServ Aware, or DA, Credit Window Request Data Item data item is used by a router to
request additional credits for a specific destination
and Queue Index associated Credit window. DA particular credit windows. Credit
Window Request data
items Data Items are carried in Credit Control messages, Messages, and
only one DA Credit Window Request data item SHOULD be present in a
message.

Logical queues are

Credit windows identified using a Queue Index CID as defined above in
Section 6.1. Multiple Queue Indexes CIDs MAY be present to allow for the
case where the credit request applies to case
where the router identifies that credits are needed in multiple queues.
credit windows. The special Queue Index CID value of 255 0xFFFFFFFF is used to
indicate that a credit request is being made across all queues.

The format of the DA 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Queue Index | Credit Window Identifier (CID)| ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... | Queue Index | Credit Window Identifier (CID)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

[LB note: a list of Queue Indexes CIDs is now supported as is special value 255.]

Data Item Type: TBA7 TBA9

Length: Variable
Per [I-D.ietf-manet-dlep] [RFC8175] Length is the number of octets in the data item,
excluding the Type and Length fields. It will equal the number of Queue Index
CID fields carried in the data item and MUST be at least 1.

Queue Index:

Credit Window Identifier (CID):

One or more 8-bit 16-bit fields used to indicate a queue index defined by credit window that
has been identified in a Queue Parameters Credit Window Initialization Data Item. Item,
see Section 6.1. The special value of 255 0xFFFFFFFF indicates that
the request applies to all queue indexes. CIDs.

A modem receiving this data item MUST provide a Credit Increment for
the indicated MAC address and queue indexes credit windows via a DA 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 Message when
possible. Unknown CID values SHOULD be reported or logged and then
ignored by the modem.

7. Compatibility

Sessions established with both peers identified as supporting the
DiffServ Aware Credit Windowing Extension Type, see Section 3, SHOULD MUST
NOT use the [I-D.ietf-manet-credit-window] defined Credit data items.
If a node supporting the extension defined in this document, receives
a [I-D.ietf-manet-credit-window] defined data item, the recipient
MUST treat ignore the received credit information as applying to Queue Index
zero (0). information.

8. Security Considerations

The extension introduces a DiffServ awareness to the mechanisms
defined in [I-D.ietf-manet-credit-window]. The extension does not
inherently introduce any additional threats above those documented in
[I-D.ietf-manet-dlep].
[RFC8175]. The approach taken to Security in that document and
[I-D.ietf-manet-credit-window] apply equally when running the
extension defined in this document.

9. IANA Considerations

This document requests the assignment of 5 values by IANA. All
assignments are to registries defined by [I-D.ietf-manet-dlep]. [RFC8175].

9.1. Extension Type Value

This document requests 1 new assignment to the DLEP Extensions
Registry named "Extension Tyoe Type Values" in the range with the
"Specification Required" policy. The requested value is as follows:

+------+---------------------------------+
| Code | Description |
+------+---------------------------------+
| TBA1 | DiffServ Aware Credit Windowing |
+------+---------------------------------+

Table 1: Requested Extension Type Value

9.2. 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 2: Requested Message Values

9.3. Data Item Values

This document requests 4 the following new assignments to the DLEP Data
Item Registry named "Data Item Values" in the range with the
"Specification Required" policy. The requested values are as
follows:

+-----------+-------------------------+

+-----------+--------------------------------------+
| Type Code | Description |
+-----------+-------------------------+
+-----------+--------------------------------------+
| TBA4 | Queue Parameters Credit Window Initialization |
| | |
| TBA5 | DA Credit Grant Window Traffic Classification |
| | |
| TBA6 | DA Credit Window Status Association |
| | |
| TBA7 | DA Credit Request Credit Window Grant |
| | |
| TBA8 | Credit Window Status |
| | |
| TBA9 | Credit Window Request |
+-----------+--------------------------------------+

Table 3: Requested Data Item Values

9.4. DLEP Sub Data Item Registry

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

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

+-------------+-----------------------------+-----------------------+
| Type Code | Valid Data Items | Description |
+-------------+-----------------------------+-----------------------+
| 0 | N/A | Reserved |
| | | |
| 1 | N/A | Reserved (for pause |
| | | sub-DI) |
| | | |
| 2 | (TBD4) Credit Window | DiffServ Traffic |
| | Traffic Classification | Classification |
| | | |
| 2-65407 | | Specification |
| | | Required |
| | | |
| 65408-65534 | | Private Use |
| | | |
| 65535 | | Reserved |
+-----------+-------------------------+
+-------------+-----------------------------+-----------------------+

Table 3: Requested Data Item 4: Initial Registry Values

10. References

10.1. Normative References

[I-D.ietf-manet-dlep]
Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
Berry, "Dynamic Link Exchange Protocol (DLEP)", draft-
ietf-manet-dlep-28 (work in progress), March 2017.

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

10.2. 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.

[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,
<http://www.rfc-editor.org/info/rfc2474>.
<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,
<http://www.rfc-editor.org/info/rfc2475>.
<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.

Appendix B. Open and Resolved Issues

This section captures issues that are open or have been addressed
since the document has become a WG draft. This section will be
removed before submission for publication.

A.1.

B.1. Merge with [I-D.ietf-manet-credit-window]

There has been discussion within the WG that this document should be
merged with [I-D.ietf-manet-credit-window]. The timing of this is
TBD. The authors would like to reach closure on some of the
remaining open issues before embarking on this merge, but are open to
discussion with the WG and other authors.

A.2. Credit Windows Shared Across Destinations

The DA Credit Extension supports credit windows per mac destination.
Some media technologies share queues across all, or even some set of,
destinations and supporting an associated set of credit windows isn't
currently supported.

Supporting credit windows per modem, i.e., for a single transmit
channel, is clearly required and needs to be supported.

Credit windows for sets of mac addresses should also be considered
and discussed within the working group, both from a requirements and
support perspective.

This issue was reported by Stan Ratliff <ratliffstan@gmail.com>.

A.3.

B.2. Supporting Router Limits

Routers may have limits on the number of queues that they can support
and, perhaps, if per destination queues can even be supported at all.
There is no current way for a router to communicate these limits to a
modem or for a router to indicate that the identified queue
information cannot be supported. Support for these cases clearly
needs to be addressed.

This issue was reported by Stan Ratliff <ratliffstan@gmail.com>.

A.4.

B.3. Absolute vs Increment

Stan Ratliff <ratliffstan@gmail.com> suggested an approach to
simplify credit synchronization and re-synchronization by always
passing the credit window size rather than credit window increments.
This is an interesting idea that needs to be explored and perhaps
experimented with.

A.5. Alternate Format Encoding

The format of the Queue Parameters Data Item is a bit cumbersome and
there has been some discussion of a possible better way of encoding
lists and optional information elements within Data Items. There has
been some discussion of developing a generic mechanisms for use by
DLEP and future DLEP Data Items. Such a definition is beyond the
scope of this document, but if such becomes available there is every
reason for this document to leverage this improved encoding. This
issue will remain open until such a time as there is a such a
definition within the WG or this document is otherwise ready for
publication.

This issue was independently raised by both David Wiggins (co-author)
and Rick Taylor <rick@tropicalstormsoftware.com>.

A.6.

B.4. Bidirectional Flow Control (closed)

One of the key differences between this draft and
[I-D.ietf-manet-credit-window] is that this document only supports
flow control in one direction, i.e., for traffic sent from a router
to a modem, while the other credit-window draft supports it in both
directions.

This was a conscious choice, made out of the desire to keep the
extension as simple as possible and to provide what is really
expected to be used. Clearly the reason for being able to control
traffic that is sent from the router to the modem/radio is pretty
easily understood. Also, while bidirectional flow control existed in
pre-dlep solutions, it wasn't really used. There is also no reason
why router to modem flow control can't be defined at a later time -
once there is an actual need.

Based on a brief discussion on the WG list, and the absence of any
advocates for bidirectional flow control, there is no current plan to
add bidirectional flow control to this document.

Authors' Addresses
Bow-Nan Cheng
Lincoln Laboratory
Massachusetts Institute of Technology
244 Wood Street
Lexington, MA 02420-9108 02421-6426

Email: bcheng@ll.mit.edu

David Wiggins
Lincoln Laboratory
Massachusetts Institute of Technology
244 Wood Street
Lexington, MA 02420-9108 02421-6426

Email: David.Wiggins@ll.mit.edu

Lou Berger
LabN Consulting, L.L.C.

Email: lberger@labn.net