DLEP Control Plane Based Pause Extension
draft-ietf-manet-dlep-pause-extension-00

Abstract

This document defines an extension to the DLEP protocol that enables a simple control plane based flow control mechanism.

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 August 13, 2017.

Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

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

1. Introduction

The Dynamic Link Event Protocol (DLEP) is defined in [I-D.ietf-manet-dlep]. 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 possible, e.g., see [I-D.ietf-manet-credit-window]. The extension defined in this document supports flow control 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 Pause".

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, RFC 2119 [RFC2119].

2. Extension Usage and Identification

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

The Control Plane 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 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. The number of logical queues is variable as is the number of DSCPs associated with each queue. 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 that may be in its associated link transmit queue.

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                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Num DSCPs Q0(0)|             Queue Size Q0                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Num DSCPs Q1  |             Queue Size Q1                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Num DSCPs Q2  |             Queue Size Q2                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                ...                            :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Num DSCPs Qn  |             Queue Size Qn                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  DS Field Q1  |  DS Field Q1  |  DS Field Q1  |  DS Field Q2  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                ...            |  DS Field Qn  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

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

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

Data Item Type:

TBA2

Length:

Variable

Per [I-D.ietf-manet-dlep] 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). Note that this number is one larger than the largest queue index value included in the data item.

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).

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:

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.

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 should 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 may 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 MAY send the Pause Data Item in a Session Update Message. To indicate that suppression applies to a particular destination a modem MAY 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.

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  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

Data Item Type:

TBA3

Length:

Variable

Per [I-D.ietf-manet-dlep] 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 MAY 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 MAY 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 [I-D.ietf-manet-dlep]. The approach taken to Security in that document applies equally when running the extension defined in this document.

5. IANA Considerations

This document requests the assignment of 4 values by IANA. All assignments are to registries defined by [I-D.ietf-manet-dlep].

5.1. Extension Type Value

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