Mobile Ad hoc Networks Working Group S. Ratliff Internet-Draft VT iDirect Intended status: Standards Track March 21, 2016 Expires: September 22, 2016 Credit Windowing extension for DLEP draft-ietf-manet-credit-window-03 Abstract This draft describes an extension to the DLEP protocol to provide a credit-windowing scheme analogous to that in RFC5578 for destination- specific 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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 22, 2016. Copyright Notice Copyright (c) 2016 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 (http://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. Ratliff Expires September 22, 2016 [Page 1] Internet-Draft Credit Windowing extension for DLEP March 2016 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5. DLEP Messages for Credit-Window Extension . . . . . . . . . . 4 6. DLEP Status Codes for Credit-Window Extension . . . . . . . . 5 7. DLEP Data Items for Credit-Window Extension . . . . . . . . . 5 7.1. DLEP Destination Up Message . . . . . . . . . . . . . . . 5 7.2. DLEP Destination Announce Message . . . . . . . . . . . . 6 7.3. DLEP Destination Up Response Message . . . . . . . . . . 6 7.4. DLEP Destination Announce Response Message . . . . . . . 6 7.5. DLEP Destination Update Message . . . . . . . . . . . . . 7 7.6. DLEP Link Characteristics Request Message . . . . . . . . 7 8. Credit Window Data Item Definitions . . . . . . . . . . . . . 7 8.1. Credit Grant . . . . . . . . . . . . . . . . . . . . . . 7 8.2. Credit Window Status . . . . . . . . . . . . . . . . . . 8 8.3. Credit Request . . . . . . . . . . . . . . . . . . . . . 10 9. Security Considerations . . . . . . . . . . . . . . . . . . . 10 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 10.1. Registrations . . . . . . . . . . . . . . . . . . . . . 10 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 12.1. Normative References . . . . . . . . . . . . . . . . . . 11 12.2. Informative References . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction In the world of radio-based networking, there are modems that need fine-grained flow control over traffic ingressing from a LAN connection, bound for transmission over the RF. The need for such fine-grained control can exist for multiple reasons. For example, radio devices are typically connected to the network by Ethernet. The capacity of an Ethernet link is normally far superior to that of the RF, leading to the possibility of overruns and dropped traffic. This is exacerbated by the fact that RF link capacity can vary from moment to moment, for an indeterminate amount of time. Additionally, the capacity of the link can vary greatly depending on the destination, due to factors such as obstructions or multipath fading. Ratliff Expires September 22, 2016 [Page 2] Internet-Draft Credit Windowing extension for DLEP March 2016 These challenges motivate the requirement for a fine-grained flow control in radio-based communications - one that can support different window sizes for each destination accessed across the RF network. To address this requirement, this document describes an extension to the Dynamic Link Event Protocol ([DLEP]), allowing for a Credit windowing scheme to be implemented on a destination-by- destination basis. 2. Overview This protocol extension to DLEP describes a credit windowing scheme analogous to the one documented in [RFC5578]. In this scheme, data plane traffic flowing between the router and modem is controlled by the availability of credits. Credits are expressed as if two unidirectional windows exist between the modem and router. This document identifies these windows as the 'Modem Receive Window', or MRW, and the 'Router Receive Window', or RRW. The responsibility of granting credits lies with the receiver on a window - that is, on the MRW, the modem is responsible for granting credits to the router, allowing it (the router) to send data plane traffic to the modem. Likewise, the router is responsible for granting credits on the RRW, which allows the modem to send data plane traffic to the router. Credits represent the number of data plane octets, or an increment in the number of data plane octets, that can be sent on a given window at the MAC layer to the receiver. 3. Terminology In general, the draft uses the same terminology as specified in the core DLEP draft [DLEP]. In addition, the draft uses the following terms: o Modem Receive Window, or MRW. The MRW represents a logical, unidirectional window for traffic flowing from the router to the modem. o Router Receive Window, or RRW. The RRW represents a logical, unidirectional window for traffic flowing from the modem to the router. 4. Operation DLEP peers supporting this extension MUST include a DLEP 'Extensions Supported' data item, including the value TBD representing this extension in the appropriate DLEP Session Initialization and Session Initialization Response messages. Ratliff Expires September 22, 2016 [Page 3] Internet-Draft Credit Windowing extension for DLEP March 2016 Credits are managed on a destination-specific basis - separate credit counts MUST be maintained for each destination requiring the service. Credits MUST NOT be applied to the DLEP session that exists between routers and modems; they are applied only to the data plane traffic. There are no default values for either the initial credit window or the credit increments. When DLEP peers desire to employ the credit-windowing extension, the peer originating the Destination Up or Destination Announce message MUST supply a Credit Grant data item with an initial, non-zero value as the increment of the window the originator controls (i.e., the MRW, or RRW). When receiving a Credit Grant data item on a Destination Up or Destination Announce message, the receiver MUST take one of the following actions: 1. Reject the use of credits for this destination, via the Destination Up Response or Destination Announce Response message containing a Status data item with a status code of 'Credit Use Rejected', or 2. Initialize the appropriate window value of zero, then apply the increment specified in the Credit Grant data item. If the initialization completes successfully, the receiver MUST respond to the Destination Up/Destination Announce message with a response message that contains a Credit Grant data item, initializing its receive window. Data plane traffic would then flow between the DLEP peers, with said peers accounting for the traffic sent/received by decrementing the appropriate credit counts. The number of credits needed for a given transmission is the length of the data portion of the packet at the MAC layer. When sending data to a credit enabled peer, the sender MUST decrement the appropriate window by the size of the data being sent, prior to encapsulation at the MAC layer. When traffic is received, the receiver MUST decrement its own window after decapsulation at the MAC layer. When the number of available credits to the destination reaches 0, the sender MUST stop sending data plane traffic to the destination, until additional credits are granted by the receiver. 5. DLEP Messages for Credit-Window Extension Ratliff Expires September 22, 2016 [Page 4] Internet-Draft Credit Windowing extension for DLEP March 2016 The credit-windowing extension does not introduce any additional DLEP signals or messages. 6. DLEP Status Codes for Credit-Window Extension The credit-windowing extension introduces two additional DLEP status code: +--------------+----------+------------+----------------------------+ | Status Code | Value | Failure | Reason | | | | Mode | | +--------------+----------+------------+----------------------------+ | Credit | TBD | Continue | Credit counts are out-of- | | Window Out | | | sync between sender and | | of Sync | | | receiver on the | | | | | destination. | | Credit Use | TBD | Continue | Credit counts cannot be | | Rejected | | | used for the destination. | +--------------+----------+------------+----------------------------+ 7. DLEP Data Items for Credit-Window Extension The extension introduces 3 DLEP data items: +------------+-------------------------------------+ | Type Code | Description | +------------+-------------------------------------+ | TBD | Credit Grant (Section 8.1) | | TBD | Credit Window Status (Section 8.2) | | TBD | Credit Request (Section 8.3) | +------------+-------------------------------------+ Descriptions of the data items are included below. The credit- windowing data items are inserted into DLEP messages as follows: 7.1. DLEP Destination Up Message If use of credits is required for the destination, then the Destination Up message MUST contain one Credit Grant (Section 8.1) data item. The value of the credit increment is at the discretion of the implementation. The receiver of the Destination Up message MUST use the value in Credit Grant as the initial value for the appropriate window. If the Destination Up message does not contain the Credit Grant data item, credits MUST NOT be used for that destination. Ratliff Expires September 22, 2016 [Page 5] Internet-Draft Credit Windowing extension for DLEP March 2016 7.2. DLEP Destination Announce Message If use of credits is required for the destination, then the Destination Announce message MUST contain one Credit Grant (Section 8.1) data item. The value of the credit increment is at the discretion of the implementation. The receiver of the Destination Announce message MUST use the value in Credit Grant as the initial value for the appropriate window. If the Destination Announce message does not contain the Credit Grant data item, credits MUST NOT be used for that destination. 7.3. DLEP Destination Up Response Message If the corresponding Destination Up message contained a Credit Grant (Section 8.1) data item, the Destination Up Response message MUST also contain a Credit Grant (Section 8.1) data item. Likewise, if the corresponding Destination Up message did not contain a Credit Grant (Section 8.1) data item, the Destination Up Response message MUST NOT contain a Credit Grant (Section 8.1) data item. The receiver of Destination Up Response MUST use the received Credit Grant value to initialize the appropriate window (e.g., the MRW value for routers, the RRW value for modems). When an implementation detects a mismatch in the presence or absence of credit window data items between the DLEP Destination Up and Destination Up Response messages, the implementation detecting the mismatch MUST terminate the session by issuing a Peer Termination message with a status code of 'Credit Window Out of Sync', and transition to the Session Termination state. 7.4. DLEP Destination Announce Response Message If the corresponding Destination Announce message contained a Credit Grant (Section 8.1) data item, the Destination Announce Response message MUST also contain a Credit Grant (Section 8.1) data item. Likewise, if the corresponding Destination Announce message did not contain a Credit Grant (Section 8.1) data item, the Destination Announce Response message MUST NOT contain a Credit Grant (Section 8.1) data item. The receiver of Destination Announce Response MUST use the received Credit Grant value to initialize the appropriate window (e.g., the MRW value for routers, the RRW value for modems). Ratliff Expires September 22, 2016 [Page 6] Internet-Draft Credit Windowing extension for DLEP March 2016 When an implementation detects a mismatch in the presence or absence of credit window data items between the DLEP Destination Announce and Destination Announce Response messages, the implementation detecting the mismatch MUST terminate the session by issuing a Peer Termination message with a status code of 'Credit Window Out of Sync', and transition to the Session Termination state. 7.5. DLEP Destination Update Message If the corresponding Destination Up or Destination Announce message contained the Credit Grant data item, the Destination Update message MAY contain one of each of the following data items: o Credit Grant (Section 8.1) o Credit Window Status (Section 8.2) o Credit Request (Section 8.3) DLEP peers supporting the extension MAY format and send a DLEP Destination Update message solely for the purposes of maintaining the credit windows. In cases where a peer already has information requiring a Destination Update message, (e.g., a change in Latency on the link), the credit data items MAY be included in addition to that information. 7.6. DLEP Link Characteristics Request Message If the corresponding Destination Up or Destination Announce message contained the credit Grant data item, the Link Characteristics Request message MAY contain the following data item: o Credit Request (Section 8.3) DLEP peers supporting the extension MAY format and send a DLEP Link Characteristics Request message solely for the purposes of maintaining the credit windows. In cases where a peer already has information requiring a Link Characteristics Request message, the Credit Request data MAY be included in addition to that information. 8. Credit Window Data Item Definitions 8.1. Credit Grant The Credit Grant data item is sent from a DLEP participant to grant an increment to credits on a window. The Credit Grant data item MAY appear in the DLEP Destination Up, Destination Announce, and Destination Update messages. The value in a Credit Grant data item Ratliff Expires September 22, 2016 [Page 7] Internet-Draft Credit Windowing extension for DLEP March 2016 represents an increment to be added to any existing credits available on the window. Upon successful receipt and processing of a Credit Grant data item, the receiver MUST respond with a message containing a Credit Window Status data item to report the updated aggregate values for synchronization purposes, and if initializing a new credit window, granting initial credits. The Credit Grant data item contains the following fields: 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 Increment | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Credit Increment | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Data Item Type: TBD Length: 8 Credit Increment: A 64-bit unsigned integer representing the additional credits, in octets, to be assigned to the credit window. Since credits can only be granted by the receiver on a window, the applicable credit window (either the MRW or the RRW) is derived from the sender of the grant. The Credit Increment MUST NOT cause the window to overflow; if this condition occurs, implementations MUST set the credit window to the maximum value contained in a 64-bit quantity. 8.2. Credit Window Status During normal operation, DLEP session peers may disagree about the number of available credits. Operational credit mismatches can occur due to packets in transit on the wire. DLEP session peers MAY use the Credit Window Status data item to maintain synchronization of credit counts. This data item is informational only; it is used to inform the receiving peer of the current credit counts for both the MRW and RRW, from the perspective of the sender. Upon receipt of a Credit Window Status data item, an implementation SHOULD compare its own credit counts with that of the originator. If the receiver of Credit Window Status detects that the local credit counts are not synchronized with the originator, the receiving Ratliff Expires September 22, 2016 [Page 8] Internet-Draft Credit Windowing extension for DLEP March 2016 implementation MAY either: o Attempt resynchronization using an additional Credit Grant, if applicable, or o Issue a DLEP Destination Down message, to clear credit counts on the session. Implementations issuing Destinaton Down MUST supply a DLEP Status item, with the status code of 'Credit Window Out of Sync', as defined in this document. If a DLEP message contains both the Credit Grant (Section 8.1) data item and the Credit Window Status (Section 8.2) data item, implementations MUST first apply the Credit Grant (Section 8.1) data item before comparing the credit counts contained in Credit Window Status (Section 8.2). It is recommended that implementations issue a DLEP Destination Update with a Credit Window Status data item at a configurable multiple of the DLEP Heartbeat timer, to serve as a continuing check on synchronization of the credit windows for a destination. The Credit Window Status data item contains the following fields: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Modem Receive Window Value : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : Modem Receive Window Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router Receive Window Value : +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ : Router Receive Window Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Data Item Type: TBD Length: 16 Modem Receive Window Value: A 64-bit unsigned integer, indicating the current number of credits, in octets, available on the Modem Receive Window, for the destination referred to by the message. Router Receive Window Value: A 64-bit unsigned integer, indicating the current number of credits, in octets, available on the Router Receive Window, for the destination referred to by the message. Ratliff Expires September 22, 2016 [Page 9] Internet-Draft Credit Windowing extension for DLEP March 2016 8.3. Credit Request The Credit Request data item MAY be sent from either DLEP participant, as a data item in a DLEP Destination Update message, or a Link Characteristics Request message, to indicate the desire for the partner to grant additional credits in order for data transfer to proceed on the session. If the corresponding DLEP Destination Up or Destination Announce message for this session did not contain a Credit Grant data item, indicating that credits are to be used on the session, then receipt of the Credit Request data item MUST be considered as an error by the receiver, requiring termination of the DLEP peer session. The Credit Request data item contains the following fields: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Data Item Type: TBD Length: 0 9. Security Considerations The extension introduces a mechanism for destination-specific flow control between a router and modem supporting the DLEP protocol. The extension does not introduce any additional threats above those documented in [DLEP]. The mitigation strategy documented in that document is sufficient to secure operation of this extension. 10. IANA Considerations This section specifies requests to IANA. 10.1. Registrations This specification defines three (3) new entries in the repository entitled "Data Item Type Values for the Dynamic Link Event Protocol (DLEP)". Assignments from that registry are requested for: o Credit Grant o Credit Request Ratliff Expires September 22, 2016 [Page 10] Internet-Draft Credit Windowing extension for DLEP March 2016 o Credit Window Status The specification also defines an extension to the DLEP protocol. An assignment from the repository entitled "Extension Type Values for the Dynamic Link Event Protocol (DLEP)" is requested for: o Credit Windowing In addition, the specification defines two (2) new DLEP status codes. Assignments from the repository entitled "Status Code Values for the Dynamic Link Event Protocol (DLEP)" are requested for: o Credit Window Out of Sync o Credit Use Rejected 11. Acknowledgements The author would like to acknowledge and thank the members of the MANET working group, who have provided valuable insight. Specifically, the author would like to thank Lou Berger, David Wiggins, Justin Dean, Brian Amundson, Rick Taylor, John Dowdell, Shawn Jury, and Darryl Satterwhite. 12. References 12.1. Normative References [DLEP] Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B. Berry, "Dynamic Link Exchange Protocol (DLEP)", draft- ietf-manet-dlep-21 IETF draft, March 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ RFC2119, March 1997, . 12.2. Informative References [RFC5578] Berry, B., Ed., Ratliff, S., Paradise, E., Kaiser, T., and M. Adams, "PPP over Ethernet (PPPoE) Extensions for Credit Flow and Link Metrics", RFC 5578, DOI 10.17487/RFC5578, February 2010, . Author's Address Ratliff Expires September 22, 2016 [Page 11] Internet-Draft Credit Windowing extension for DLEP March 2016 Stan Ratliff VT iDirect 13861 Sunrise Valley Drive, Suite 300 Herndon, VA 20171 USA Email: sratliff@idirect.net Ratliff Expires September 22, 2016 [Page 12]