DLEP Control Plane Based Pause Extension
draft-ietf-manet-dlep-pause-extension-05

Abstract

This document defines an extension to the DLEP protocol that enables a modem to use DLEP messages to pause and resume data traffic coming from its peer router.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on September 12, 2019.

Copyright Notice

Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• 1. Introduction
• 1.1. Key Words
• 2. Extension Usage and Identification
• 3. Extension Data Items
• 3.1. Queue Parameters
• 3.1.1. Queue Parameter Sub Data Item
• 3.2. Pause
• 3.3. Restart
• 4. Security Considerations
• 5. IANA Considerations
• 5.1. Extension Type Value
• 5.2. Data Item Values
• 5.3. Queue Parameters Sub Data Item Values
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Appendix A. Acknowledgments
• Authors' Addresses

1. Introduction

The Dynamic Link Exchange Protocol (DLEP) is defined in [RFC8175]. It provides the exchange of link related control information between DLEP peers. DLEP peers are comprised of a modem and a router. DLEP 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 data plane flow control capability. Various flow control methods are possible, e.g., see [I-D.ietf-manet-dlep-da-credit-extension]. The extension defined in this document supports flow control of data traffic based on explicit messages sent via DLEP by a modem to indicate when a router should hold off sending traffic, and when it should resume. The extension also optionally supports DSCP (differentiated services codepoint) aware, see [RFC2475], flow control. The extension defined in this document is referred to as "Control Plane Based Pause". Note that this mechanism only controls traffic that is to be transmitted on the modem's attached data channel and not to DLEP control messages themselves.

This document defines a new DLEP Extension Type Value in Section 2 which is used to indicate the use of the extension, and three new DLEP Data Items in Section 3.

1.1. Key Words

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2. Extension Usage and Identification

The use of the Control Plane Based Pause Extension SHOULD be configurable. To indicate that the Control Plane Based Pause Extension is to be used, an implementation MUST include the Control Plane Based Pause Extension Type Value in the Extensions Supported Data Item. The Extensions Supported Data Item is sent and processed according to [RFC8175].

The Control Plane Based Pause Extension Type Value is TBA1, see Section 5.

3. Extension Data Items

Three data items are defined by this extension. The Queue Parameters Data Item is used by a modem to provide information on the DSCPs it uses in forwarding. The Pause Data Item is used by a modem to indicate when a router should cease sending packets and the Restart Data Item is used by a modem to indicate when a router can resume sending packets.

3.1. Queue Parameters

The Queue Parameters Data Item is used by a modem to indicate DSCP values that may be independently paused. This data item MUST be included in a Session Initialization Response Message that also contains the Control Plane Based Pause Extension Type Value in the Extensions Supported Data Item. Updates to these parameters MAY be sent by a modem by including the data item in Session Update Messages.

The Queue Parameters Data Item identifies DSCPs based on groups of logical queues, each of which is referred to via a "Queue Index". The number of logical queues, or queue indexes, is variable as is the number of DSCPs associated with each queue. A queue size (in bytes) is provided for informational purposes. Queue Indexes are numbered sequentially from zero, where queue index zero is a special case covering DSCPs which are not otherwise associated with Queue Index.

An implementation that does not support DSCPs would indicate 1 queue with 0 DSCPs, and the number of bytes that may be in its associated link transmit queue. Additional logical queues are represented in a variable series of Queue Parameter sub data items.

The format of the Queue Parameters 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                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Num Queues  | Scale |              Reserved                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Reserved     |             Queue Size Q0                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Queue Parameter Sub Data Item 1                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                ...                            :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Queue Parameter Sub Data Item n                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Value  Scale
      ------------
          0   B - Bytes     (Octets)
          1  KB - Kilobytes (B/1024)
          2  MB - Megabytes (KB/1024)
          3  GB - Gigabytes (MB/1024)
        

Data Item Type:

TBA2

Length:

Variable

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

Num Queues:

An 8-bit unsigned integer indicating the number of queues represented in the data item. This field MUST contain a value of at least one (1), and is equal to one greater than the number of included Queue Parameter Sub Data Items.

Scale:

An 4-bit unsigned integer indicating the scale used in the Queue Size fields. The valid values are:

Reserved:

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

Queue Size Q0:

A 24-bit unsigned integer representing the size, in the octet scale indicated by the Scale field, of queue index zero.

3.1.1. Queue Parameter Sub Data Item

Queue Parameter Sub Data Items are an unordered list composed of sub data items with a common format. The first sub data item is assigned a Queue Index value of 1, and subsequent data items are numbered incrementally. The format of the Queue Parameter Sub Data Item is patterned after the standard DLEP data item format, see [RFC8175] Section 11.3. 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 Queue Parameter 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 (1)        | Length                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Value...                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

and Value has the format:

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Queue Index  |             Queue Size Qn                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Num DSCPs Qn  |  DS Field Qn  |              ...              :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                          ...                  |  DS Field Qn  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        0   1   2   3   4   5   6   7
      +---+---+---+---+---+---+---+---+
      |         DSCP          |  CU   |
      +---+---+---+---+---+---+---+---+

        DSCP: differentiated services codepoint
        CU:   currently unused, MUST be zero
        

Sub Data Item Type:

A 16-bit unsigned integer that indicates the type and corresponding format of the Sub Data Item's Value field. Sub Data Item Types are scoped within the Data Item in which they are carried, i.e., the Sub Data Item Type field MUST be used together with the Queue Parameters Data Item Type to identify the format of the Sub Data Item. This field MUST be set to one (1) for the Queue Parameter Sub Data Item.

Length:

Variable

Length is the number of octets in the sub data item, excluding the Type and Length fields.

Queue Index:

An 8-bit field indicating the queue index of the queue parameter represented in the sub data item. Only the first instance of a particular Queue Index value is meaningful. Subsequent sub data items containing the same Queue Index values, if present, MAY be logged via a management interface and MUST otherwise be ignored.

Queue Size Qn:

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

Num DSCPs Qn:

An 8-bit unsigned integer indicating the number of DSCPs associated with the queue index associated with the sub data item. This field MUST contain a value of at least one (1).

DS Field Qn:

The data item contains a sequence of 8 bit DS Fields. The position in the sequence identifies the associated queue index. The number of DS Fields present MUST equal the sum of all Num DSCPs field values.

The DS Field structure is the same as [RFC2474].

3.2. Pause

The Pause Data Item is used by a modem to indicate to its peer that traffic is to be suppressed. An example of when a modem might send this data item is when an internal queue length exceeds a particular threshold.

A modem can indicate that traffic is to be suppressed on a device wide or destination specific basis. An example of when a modem might use device wide indications is when output queues are shared across all destinations, and destination specific might be used when per destination queuing is used. To indicate that suppression applies to all destinations, a modem MUST send the Pause Data Item in a Session Update Message. To indicate that suppression applies to a particular destination a modem MUST send the Pause Data Item in a Destination Update Message.

Each Pause Data Item identifies the traffic to be suppressed by the Queue Index defined by Section 3.1, which in turn indicates a set of traffic identified by DSCPs. The special value of 255 is used to indicate that all traffic is to be suppressed.

While there is no restriction on the number of Messages containing Pause Data Item that may be sent by a modem, a modem SHOULD include multiple queue indexes in the same message when possible.

A router which receives the Pause Data Item MUST cease sending the identified traffic to the modem. This may of course translate into the router's queues exceeding their own thresholds. If a received Pause Data Item contains a Queue Index value other than 0, 255, or a queue index established by a Session Initialization or Session Update Message, the router MUST terminate the session with a Status Data Item indicating Invalid Data.

The format of the Pause 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  |               ...                             :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                ...            |  Queue Index  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Data Item Type:

TBA3

Length:

Variable

Per [RFC8175] Length is the number of octets in the data item, excluding the Type and Length fields. It will equal the number of Queue Index fields carried in the data item.

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 all traffic is to be suppressed to the modem, when the data item is carried in a Session Update Message, or a destination, when the data item is carried in Destination Update Message.

3.3. Restart

The Restart Data Item is used by a modem to indicate to its peer that transmission of previously suppressed traffic may be resumed. An example of when a modem might send this data item is when an internal queue length drops below a particular threshold.

The sending of this data item parallels the Pause Data Item, see the previous section, and follows the same rules. This includes that to indicate that transmission can resume to all destinations, a modem MUST send the Restart Data Item in a Session Update Message. It also includes that to indicate that transmission can resume to a particular destination a modem MUST send the Pause Restart Item in a Destination Update Message. Finally, the same rules apply to queue indexes.

A router which receives the Restart Data Item SHOULD resume transmission of the identified traffic to the modem.

The format of the Restart Data Item matches the Pause Data Item and 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  |               ...                             :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                ...            |  Queue Index  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Data Item Type:

TBA4

Length:

See Section 3.2.

Queue Index:

See Section 3.2.

4. Security Considerations

The extension introduces a new mechanism for flow control between a router and modem using the DLEP protocol. The extension does not inherently introduce any additional threats above those documented in [RFC8175]. The approach taken to Security in that document applies equally when running the extension defined in this document.

Note that this extension does allow a compromised or impersonating modem to suppress transmission by the router, but this is not a substantively different threat by such a compromised modem simply dropping all traffic destined to, or sent by a router. [RFC8175] defines the use of TLS to protect against the impersonating attacker.

5. IANA Considerations

This document requests the assignment of 4 values by IANA. All assignments are to registries defined by [RFC8175].

5.1. 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:

5.2. Data Item Values

This document requests 3 new assignments to the DLEP Data Item Registry named "Data Item Type Values" in the range with the "Specification Required" policy. The requested values are as follows:

5.3. Queue Parameters Sub Data Item Values

Upon approval of this document, IANA is requested to create a new DLEP registry, named "Queue Parameters Sub Data Item Type Values".

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

6. References

6.1. Normative References

6.2. Informative References

Appendix A. Acknowledgments

The sub data item format was inspired by Rick Taylor's "Data Item Containers" idea.

Authors' Addresses