Network Working Group B. Cheng
Internet-Draft D. Wiggins
Intended status: Standards Track Lincoln Laboratory
Expires: May 3, 2018 L. Berger
LabN Consulting, L.L.C.
October 30, 2017
DLEP DiffServ Aware Credit Windowing Extension
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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on May 3, 2018.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Extension Overview . . . . . . . . . . . . . . . . . . . . . 3
3. Extension Usage and Identification . . . . . . . . . . . . . 5
4. Data Plane Considerations . . . . . . . . . . . . . . . . . . 5
5. Extension Messages . . . . . . . . . . . . . . . . . . . . . 5
5.1. Credit Control Message . . . . . . . . . . . . . . . . . 5
5.2. Credit Control Response Message . . . . . . . . . . . . . 6
6. Extension Data Items . . . . . . . . . . . . . . . . . . . . 6
6.1. Credit Window Initialization . . . . . . . . . . . . . . 7
6.2. Credit Window Traffic Classification . . . . . . . . . . 9
6.2.1. Traffic Classification Sub Data Item . . . . . . . . 11
6.2.2. DiffServ Traffic Classification Sub Data Item . . . . 11
6.3. Credit Window Associate . . . . . . . . . . . . . . . . . 13
6.4. Credit Window Credit Grant . . . . . . . . . . . . . . . 14
6.5. Credit Window Status . . . . . . . . . . . . . . . . . . 15
6.6. Credit Window Request . . . . . . . . . . . . . . . . . . 17
7. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9.1. Extension Type Value . . . . . . . . . . . . . . . . . . 18
9.2. Message Values . . . . . . . . . . . . . . . . . . . . . 19
9.3. Data Item Values . . . . . . . . . . . . . . . . . . . . 19
9.4. DLEP Sub Data Item Registry . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 21
Appendix B. Open and Resolved Issues . . . . . . . . . . . . . . 21
B.1. Merge with [I-D.ietf-manet-credit-window] . . . . . . . . 21
B.2. Supporting Router Limits . . . . . . . . . . . . . . . . 22
B.3. Absolute vs Increment . . . . . . . . . . . . . . . . . . 22
B.4. Bidirectional Flow
Control (closed) . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
The Dynamic Link Event Protocol (DLEP) is defined in [RFC8175]. It
provides the exchange of link related control information between
DLEP peers. DLEP peers are comprised of a modem and a router. DLEP
defines a base set of mechanisms as well as support for possible
extensions. This document defines one such extension.
The base DLEP specification does not include any flow control
capability. There are various flow control theoretically possible
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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 traffic sent from a router to a modem.
Flow control is provide 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
classification information provided by the 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 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 [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
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[RFC8175]. When using this extension, data is allowed to be sent by
the router to the modem only when there are credits available.
Credits are managed on a per logical "Credit Windows" basis. Each
credit window can be thought of as corresponding to a queue within a
modem. Modems pass to the router information on its credit windows
and identify each via a "Credit Window Identifier", or "CID". In
addition to the CID, credit window information includes an initial
credit window size, 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.
As mentioned above, traffic classification supported by this document
is performed on a per {destination, DSCP} tuple basis. This means
that, routers need the combination of the DLEP identified destination
and DSCP associated with a CID in order to match traffic it sends to
specific credit windows. Modems provide the mapping of DSCPs to CIDs
in 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 that destination. This use of CIDs, TIDs and association
of a TID to a DLEP destination 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 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.
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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 [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. 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. 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 window
increases. For messages sent by modems, only one message can be
outstanding at one time. That is, a modem MUST NOT send a second (or
any subsequent) Credit Control Message until a Credit Control
Response Message is received from its peer router.
Credit Control Messages MAY be sent by routers, e.g., to request
credits or provide window status. No specific response message is
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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.
A message sent by a modem, MUST contain one or more Credit Window
Grant Data Items as defined below in Section 6.4. A router receiving
this message MUST respond with a Credit Control Response Message.
A message sent by a router, MUST contain the Credit Window Request
Data Item defined below in Section 6.6. A modem receiving this
message MUST process the received message and data item as defined
below, which will result in credit window increments being provided
via Credit Window Grant Data Items carried in one more more new
Credit Control Message.
Specific processing associated with each Credit 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.
A message sent by a router, MUST contain one or more Credit Window
Status data items as defined below in Section 6.5.
Specific processing associated with the Credit Window Window Status
Data Item is provided below.
6. Extension Data Items
Six data items are defined by this extension. The Credit Window
Initialization Data Item is used by a modem to identify a credit
window and set its size. The Credit Window Traffic Classification
Data Item is used by a modem to identify a set which identifies which
DSCPs are mapped to a 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 Credit Request is
used by a router to request additional credits. The Credit Window
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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 have similar 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. 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
contains the DiffServ Aware Credit Windowing Extension Type Value in
the Extensions Supported Data Item. 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 Credit Window Identifier, or CID. 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 CID
must be listed in a Credit Window Traffic Classification Data Item.
The format of the Credit Window Initialization 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 (16) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Window Identifier (CID)| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Value :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Credit Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Scale | Credit Window Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Data Item Type: TBA4
Length: 16
Per [RFC8175] Length is the number of octets in the data item,
excluding the Type and Length fields.
Credit Window Identifier (CID):
A 16-bit unsigned integer identifying a credit window. The value
of 0xFFFFFFFF is reserved and MUST not be used in this Data Item.
There is 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 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)
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
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,
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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:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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
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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
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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
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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 modem to associate
traffic classification information with a destination. The 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 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 use of the extension defined in this document is agreed upon, see
Section 3.
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 (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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.
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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 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 Credit Window Credit 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, and Credit Control 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 window are
identified via using 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 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Window Identifier (CID)| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Additional Credits :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Additional Credits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Data Item Type: TBA7
Length: 12
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Per [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 CID fields carried in the data item and MUST be at least
9.
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 ignored.
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.
When receiving this data item, a router MUST identify the credit
window indicated by the CID. If the CID 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 CID 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).
Independent of the received message, the receiving router MUST send a
Credit Window 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 Window Status data item(s) MUST be sent in the
corresponding Destination Up Response Message. In all other cases, a
Credit Control Message MUST be sent.
6.5. 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
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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 Window Status data items in a single message
are used to indicated different sizes of different credit windows.
Similar to the Credit Window Grant, credit windows are identified
using CID values that have been previously been sent by the modem.
The format of the 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 Identifier (CID)| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Window Size :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Credit Window Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Data Item Type: TBA8
Length: 12
Per [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 CID fields carried in the data item and MUST be at least
9.
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.
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].
When receiving this data item, a modem MUST identify the credit
window indicated by the CID. If the CID 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 CID MAY be unrelated
to the Destination indicated in the message carrying the Data Item.
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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 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 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.
6.6. Credit Window Request
The Credit Window Request Data Item 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
only one Credit Window Request data item SHOULD be present in a
message.
Credit windows identified using a CID as defined above in
Section 6.1. Multiple CIDs MAY be present to allow for the case
where the router identifies that credits are needed in multiple
credit windows. The special CID value of 0xFFFFFFFF 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Credit Window Identifier (CID)| ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... | Credit Window Identifier (CID)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[LB note: a list of CIDs is now supported as is special value 255.]
Data Item Type: TBA9
Length: Variable
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Per [RFC8175] Length is the number of octets in the data item,
excluding the Type and Length fields. It will equal the number of
CID fields carried in the data item and MUST be at least 1.
Credit Window Identifier (CID):
One or more 16-bit fields used to indicate a credit window that
has been identified in a Credit Window Initialization Data Item,
see Section 6.1. The special value of 0xFFFFFFFF indicates that
the request applies to all CIDs.
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 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, 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 ignore the received 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
[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 [RFC8175].
9.1. Extension Type Value
This document requests 1 new assignment to the DLEP Extensions
Registry named "Extension Type Values" in the range with the
"Specification Required" policy. The requested value is as follows:
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+------+---------------------------------+
| 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 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 | Credit Window Initialization |
| | |
| TBA5 | Credit Window Traffic Classification |
| | |
| TBA6 | Credit Window Association |
| | |
| TBA7 | Credit Window Grant |
| | |
| TBA8 | Credit Window Status |
| | |
| TBA9 | Credit Window Request |
+-----------+--------------------------------------+
Table 3: Requested Data Item Values
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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 4: Initial Registry Values
10. References
10.1. 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>.
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[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,
<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.
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.
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.
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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>.
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.
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
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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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