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Versions: (RFC 4938) 00 RFC 5578

Internet-Draft                                         B. Berry (Editor)
Intended status: Informational                                S. Ratliff
Obsoletes: 4938                                              E. Paradise
Expires: October 24, 2008                                          Cisco
                                                                T.Kaiser
                                                      Harris Corporation
                                                                M. Adams
                                                       L3 Communications
                                                          April 24, 2008

                 PPP Over Ethernet (PPPoE) Extensions
                   for Credit Flow and Link Metrics

                    draft-bberry-rfc4938bis-00.txt



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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This document extends the Point-to-Point over Ethernet (PPPoE)
   Protocol with an optional credit-based flow control mechanism and
   an optional Link Quality Metric report.  These optional extensions
   improve the performance of PPPoE over media with variable bandwidth
   and limited buffering, such as mobile point-to-point radio links.

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Table of Contents

   1.0  Introduction .................................................2
   2.0  Terminology ..................................................3
   3.0  Overview of Protocol Extensions ..............................3
   3.1  TLVs..........................................................4
   3.1.1. Credit TLV .................................................5
   3.1.2. Metric TLV .................................................5
   3.1.3. Sequence Number TLV ........................................7
   3.1.4. Credit Scale Factor TLV ....................................7
   3.2  Discovery Stage Extensions ...................................8
   3.2.1. PPPoE Active Discovery Request (PADR) ......................8
   3.2.2. PPPoE Active Discovery Session-confirmation (PADS) ........10
   3.2.3. PPPoE Active Discovery Session-Grant (PADG) ...............12
   3.2.4. PPPoE Active Discovery Session-Credit Response (PADC) .....14
   3.2.5. PPPoE Active Discovery Quality (PADQ) .....................15
   3.3  PPP Session Stage Extensions ................................17
   4.0  Credit Flow Considerations ..................................18
   5.0  PADG and PADC Retransmission ................................19
   6.0  Other Considerations ........................................19
   7.0  IANA Considerations .........................................20
   8.0  Security Considerations .....................................20
   9.0  References ..................................................21
   10.0  Appendix ...................................................22



1.0  Introduction

   PPP over Ethernet (PPPoE) [2] is a protocol for establishing and
   encapsulating sessions between hosts (clients) and traffic access
   aggregators (servers) for PPP [1] transport over real or emulated
   Ethernet. PPPoE works well when both session endpoints have similar
   bandwidth, forwarding, and buffering capabilities that do not vary
   over time. However, improvements can be made for applications with
   variable bandwidth and limited buffering. This document addresses
   these improvements with optional extensions to PPPoE that support
   credit-based session flow control and session-based link metric
   quality reports.

   These extensions are designed to support radio systems that exhibit
   point-to-point waveforms.  The diagram below is used to illustrate
   the improvement that these extensions address. When the local
   client (radio) detects the presence of a remote radio neighbor, it
   initiates a PPPoE session with its local server (router). The radio
   also establishes a radio link connection with the remote radio over
   the point-to-point RF link (which is beyond the scope of this
   document). The remote radio is also establishing a PPPoE session



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   with its local server (router). The radios associate the two PPPoE
   sessions and the point-to-point radio link protocol (RLP) creating
   a complete data path. Now a PPP session is established via the PPP
   IP Control Protocol (IPCP) as described in RFC 1661.  Included in
   this IPCP exchange is the router IP address. With the exchange of
   the IPCP IP addresses, each router inserts the remote IP address
   into its local routing tables.  Note that the radio IP information
   is not inserted into the routing tables.


   |-----Local Neighbor-----|          |-----Remote Neighbor----|

   +--------+       +-------+          +-------+       +--------+
   | Router |=======| Radio |{~~~~~~~~}| Radio |=======| Router |
   | Server |       | Client|          | Client|       | Server |
   +--------+       +-------+          +-------+       +--------+

            |       |       |          |       |       |
            |-PPPoE-|       |----RLP---|       |-PPPoE-|
            |                                          |
            |-----------PPP IPCP  (IP Address)---------|
            |                                          |
            |-------------PPP Data Session-------------|

                     Figure 1. PPPoE Network

   The capabilities of the RF links between RLP neighbors will vary
   over time due to mobility, changes in the RF waveforms and encoding
   as well as environmental conditions.  To reflect these dynamic
   changes, the radio may periodically generate Link Quality Metrics
   to the router. The router uses the link metric to update route
   costs and influence route selection. The influence upon the routing
   protocols is beyond the scope of this document.

   An open source (GPLv2) pppoe client implementation can be found
   at [4].

2.0  Terminology

    Access Concentrator
             The RFC 2516 term used to describe the server. This
             document uses the terms Router or Server.

    BCN      Backward Credit Notification, The BCN represent the
             local node remaining credits that were granted from
             the peer node.  The local node uses these credits
             to transmit payload back to the peer node.  BCN
             ranges from 0-65535.

    CDR      Current Data rate

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    FCN      Forward Credit Notification. The FCN represents the
             credits that the local node is granting to the peer node.
             The peer node uses these granted credits to transmit
             payload back to the local node.  FCN ranges from 0-65535.

    gbps     gigabits (1,000,000,000) per second

    Host     The RFC 2516 term used to describe the server. This
             document uses the terms Radio or Client.

    kbps     kilobits (1,000) per second

    LCP      PPP Link Control Protocol, RFC 1661

    mbps     megabits (1,000,000) per second

    MDR      Maximum Data rate

    NCP      PPP Network Control Protocol, RFC 1661

    RLP      Radio Link Protocol

    TAG      Is the RFC 2516 PPPoE Synonym for TLV. This document
             uses TLV.

    tbps     terabits (1,000,000,000,000) per second

    TLV      Type-Length-Value



3.0  Overview of Protocol Extensions

   The extensions consist of optional TLVs, enhanced and newly defined
   Discovery packets.  The enhancements are applied to the Discovery
   Stage and the PPP Session Stage.

3.1  TLVs
   The new TLVs are listed in the table below:

           TLV      TLV
           Value    Description
           =========================================
           0x0106   Credit TLV
           0x0107   Metric TLV
           0x0108   Sequence Number TLV
           0x0109   Credit Scale Factor TLV



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3.1.1   Credit TLV

   This TLV contains the Forward Credit Notification (FCN) and the
   Backward Credit Notification (BCN).  The Credit TLV is optional
   with the PADR and PADS and required in the PADG and PADC Discovery
   Packets (ETHER_TYPE=8863).

   The Credit TLV is optionally carried in the PPPoE data payload
   packet of the PPP Stage (ETHER_TYPE=8864).

   The FCN represents the number of credits being granted by the
   local node to the peer node. The BCN represents the number of
   credits remaining at the local node that were granted by the
   peer node.

   The Credit TLV is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Credit TLV = 0x0106       |       TLV Length = 0x04       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              FCN              |              BCN              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.1.2   Metric TLV

   The Metric TLV is used to report the link quality parameters. The
   Metric TLV is required with the PADQ Discovery Packet.

   The Metric TLV contains the following fields:

       Resources - a percentage, 0-100, representing the amount of
       remaining or available resources, such as battery power. If
       resources cannot be calculated, a value of 100 should be
       reported.

       Relative Link Quality (RLQ) - a non-dimensional number, 0-100,
       representing the relative link quality.  A value of 100
       represents a link of the highest quality. If the RLQ cannot
       be calculated, a value of 100 should be reported.

       Receive only - a bit that indicates whether the link is bi-
       directional or receive only.  A value of -1- indicates that
       the link is receive-only.

       Reserved - Reserved fields are zeroed unless otherwise
       specified.


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       CD - Two bits that designate the units of the current data rate.

                CD Scale:  00 == kbps (default)
                           01 == mbps
                           10 == gbps
                           11 == tbps

       MD - Two bits that designate the units of the maximum data rate.

                MD Scale:  00 == kbps (default)
                           01 == mbps
                           10 == gbps
                           11 == tbps

       Current data rate - the current data rate, in un scaled units
       per second, achieved on the RLP link. If the radio makes no
       distinction between maximum data rate and current data rate,
       current data rate should equal the maximum data rate.  When
       metrics are reported, the current data rate must be reported.
       The current data rate must be less than or equal to the maximum
       data rate.

       Latency - the transmission delay that a packet encounters as
       it is transmitted over the link. This is reported in absolute
       delay, milliseconds.  If latency cannot be calculated, a value
       of 0 should be reported.  The calculation of latency is radio
       dependent.  For example, the latency may be a running average
       calculated from the internal queuing.

       Maximum data rate - the maximum theoretical data rate, in
       un scaled units per second, that the RLP link is capable of
       providing.  When metrics are reported, the maximum data rate
       must be reported.

   The Metric TLV is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Metric TLV = 0x0107       |       TLV Length = 0x0A       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Reserved        | MD| CD|R|      RLQ      |    Resources  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Latency (MS)          |   Current Datarate            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Maximum Datarate           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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3.1.3   Sequence Number TLV

   This TLV is used to carry a unique 16-bit sequence number in order
   to identify a specific request and the associated response.  The
   sequence number should be initialized to zero and incremented by one
   for each new request.  For retransmitted packets, the same sequence
   number that was used in the previous packet transmission is repeated.
   The PADG and PADC packets require the Sequence Number Tag.

   The Sequence Number TLV is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Sequence Number TLV = 0x0108  |        TLV Length = 0x02      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Sequence Number         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.1.4   Credit Scale Factor TLV

   This TLV contains the scale factor value that is to be applied to
   the session credit calculations.  The Credit Scale Factor TLV is
   optional with the PADR, PADS packets.  Once the session is
   established with specified scale factors, the scale factors are
   set for the entire session.   The scale factor value represents
   the units that the local node grants to the remote node.  The
   remote node is responsible for maintaining the credit accounting
   relative to the data flow back to the local node.

   The Credit Scale Factor TLV can be used to change from the
   default 64-byte credit unit during the PADR-PADS exchange. The
   credit scale factor value can range from 1-byte to 65535-bytes.
   A zero value is ignored and the default 64-byte unit remains set.
   The scale factor is set per each payload flow: peer-to-local and
   local-to-peer.

   The Credit Scale Factor TLV is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Credit Scale Factor = 0x0109 |       TLV Length = 0x02       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Scale Factor Value      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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3.2  Discovery Stage Extensions

   The specifications of the Session Request (PADR) and the Session
   Confirmation (PADS) packets are extended to include the optional
   Credit TLV and the Credit Scale Factor TLV. The Credit Grant (PADG)
   packet, the Grant Confirmation (PADC) packet and the Quality packet
   are newly defined Discovery Stage Packets.

           Discovery
           Packet                 Status
           =======================================================
           PADR        Enhanced   Optionally includes the Credit
                                  TLV and the Credit Scale Factor
                                  TLV

           PADS        Enhanced   Optionally includes the Credit
                                  TLV and the Credit Scale Factor
                                  TLV

           PADG        New        Includes the Credit TLV and the
                                  Sequence Number TLV

           PADC        New        Includes the Credit TLV and the
                                  Sequence Number TLV

           PADQ        New        Includes the Metric TLV


3.2.1   PPPoE Active Discovery Request (PADR)

   The PADR packet is extended to optionally contain a single Credit
   TLV, indicating that the Client requests credit flow control for
   this session. The Credit TLV contains the Forward Credit Notification
   (FCN) and the Backward Credit Notification (BCN) to be applied to
   the PPP Session Stage.  The FCN provides the initial credits granted
   to the Server by the Client.  The BCN value is set to 0 as the Client
   has not yet been granted credits from the Server.

   The PADR packet is enhanced to optionally contain a single Credit
   Scale Factor TLV.  The Credit Scale Factor TLV defines the credit
   scale factor value. If the Credit Scale Factor TLV is omitted, the
   default 64-byte value is used for the session.  When the client
   includes the optional Credit Scale Factor TLV in the PADR, this
   credit scale factor value is applied to all credit grants associated
   with the client credits that are granted to the server.






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   The Server must echo the Credit Scale Factor TLV in the PADS
   response to confirm the credit scaling session and to designate the
   server credit scaling factor.  This PADS Credit Scaling Factor TLV
   represents the scale factor value that is applied to all credits
   granted from the Server to the Client.

   Once the session is established during the PADR-PADS exchange, the
   credit scale factor value can not be changed.

   A Discovery PADR packet with optional Credit TLV is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Access_Concentrator_mac_addr                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Access_Concentrator_mac_addr(c)|        Host_mac_addr          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Host_mac_addr (cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8863        | v = 1 | t = 1 |  CODE = 0x19  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = 0x0C            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       TLV Type = 0x0101       |  Metric TLV Length = 0x00     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Credit TLV = 0x0106        |      TLV Length = 0x04        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              FCN              |              BCN = 0          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The credit units are expressed in the default 64-byte units.



















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   A Discovery PADR packet with the optional Credit TLV and the optional
   Credit Scale Factor TLV is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Access_Concentrator_mac_addr                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Access_Concentrator_mac_addr(c)|        Host_mac_addr          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Host_mac_addr (cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8863        | v = 1 | t = 1 |  CODE = 0x19  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = 0x0C            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       TLV Type = 0x0101       |        TLV Length = 0x00      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Credit TLV = 0x0106       |       TLV Length = 0x04       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              FCN              |             BCN = 0           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Credit Scale Factor = 0x0109  |       TLV Length = 0x02       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       scale factor value      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Credit TLV FCN value is expressed in units of the session
   credit scale factor value.


3.2.2   PPPoE Active Discovery Session-confirmation (PADS)

   The Server PADS is extended to optionally contain a single Credit
   TLV, indicating the Forward Credit Notification (FCN) and the
   Backward Credit Notification (BCN) of the PPP Session Stage.

   If the Client PADR contained a Credit TLV, then the Server PADS
   must indicate support for credit flow control by including
   a Credit TLV. The PADS Credit TLV FCN represents the number of
   credits initially granted to the Client.  The Credit TLV BCN is an
   echo of the number of credits that the Client had granted to the
   Server in the originating PADR packet.

   Exchange of the Credit TLV in the PADR and PADS indicates that
   credit flow control is supported by both the Server and the Client
   for the designated PPP Session Stage.  This is binding and must




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   be followed for the entire duration of the PPP Session Stage. A
   session's credit binding must be established prior to any other
   credit indications can be exchanged.

   The Server PADS should only include the Credit TLV in response to
   a Client PADR which included the Credit TLV.  If the Server does
   not support credit flow, it should not include the Credit TLV in
   its PADS response. The Client must terminate a credit-based session
   that cannot be supported by the Server. A Credit TLV transmitted
   outside an established credit based session must be ignored.

   The Server PADS is enhanced to optionally contain a single Credit
   Scale Factor TLV.  The Credit Scale Factor TLV defines the credit
   scale unit value. The Credit Scale Factor TLV must be included if
   it was included in the Client PADR. If the Credit TLV was not
   included in the originating PADR, it must be omitted, indicating
   that the 64-byte default is used for the directional flow. This
   credit scale factor is applied to Server grants to the Client.

   A Discovery PADS packet with the optional Credit TLV is shown
   below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Access_Concentrator_mac_addr                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Access_Concentrator_mac_addr(c)|        Host_mac_addr          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Host_mac_addr (cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8863        | v = 1 | t = 1 |  CODE = 0x65  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = 0x0C            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       TLV Type = 0x0101       |       TLV Length = 0x00       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Credit TLV = 0x0106        |       TLV Length = 0x04       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              FCN              |              BCN              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The BCN is expressed in the default 64-byte units.








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   A Discovery PADS packet with the optional Credit TLV and the optional
   Credit Scale Factor TLV is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Access_Concentrator_mac_addr                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Access_Concentrator_mac_addr(c)|        Host_mac_addr          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Host_mac_addr (cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8863        | v = 1 | t = 1 |  CODE = 0x65  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = 0x0C            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       TLV Type = 0x0101       |       TLV Length = 0x00       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Credit TLV = 0x0106       |        TLV Length = 0x04      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              FCN              |              BCN              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Credit Scale Factor = 0x0109 |       TLV Length = 0x02       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      scale factor value       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Credit TLV BCN value is expressed in units of the session
   scale factor value received in the PADR.


3.2.3   PPPoE Active Discovery Session-Grant (PADG)

   The PPPoE Active Discovery Session-Grant (PADG) is a new packet
   defined in this specification.  The local node (Server or Client)
   may send a PADG at any time after the PADR/PADS exchange to grant
   incremental flow control credits to a peer. The CODE field is set
   to 0x0A and the SESSION_ID must be set to the unique value
   generated for this PPPoE Session.


   Each flow control credit corresponds to the amount of PPP payload
   bytes that can be sent or received.  For example, if the default
   credit scale factor of 64-bytes is used, and 128 bytes of PPP
   payload data is sent, then 2 credits would be consumed. When
   calculating credits to consume, all credit calculations must be
   rounded up. If in the previous example 130 bytes of PPP payload
   data was sent, 3 credits would have been consumed.



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   When the peer receives a PADG packet, it adds the incremental
   credits to its working credit count and responds with a PPPoE
   Active Discovery Session-Credit (PADC) packet indicating the
   accumulation of the credits.  The FCN and BCN values must be
   scaled by the value established during session establishment
   in the Credit Scale Factor TLV or by the default 64-byte
   value prior to processing.

   The PADG packet must contain a single Credit TLV, indicating
   the Forward Credit Notification (FCN) and the Backward Credit
   Notification (BCN) of the PPPoE Session.

   The Credit TLV FCN indicates the number of incremental credits
   being granted to the peer by the node.  A value between 1 and
   0xffff represents an incremental credit grant.  The peer must
   multiply the credits units by the credit scale factor  and add
   these credits to its accumulated transmit credit count. A value
   of 0x0000 represents a NULL grant, meaning that there are no
   additional credits being granted.

   The Credit Tag BCN indicates the remaining absolute credits that
   have been granted by the peer to the local node.  When the local
   node exhausts the BCN, it must stop transmitting payload packets.

   Once a credit has been granted, it must be honored. The largest
   number of incremental credits at any time is 0xffff.

   The PADG packet must contain a single Sequence Number TLV. This
   tag is used to carry a unique 16-bit sequence number to uniquely
   to identify each request. The sequence number should be
   initialized zero and incremented by one for each new PADG. For
   retransmitted PADGs, the same sequence number that was used in
   the previous packet transmission is repeated.


















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   A Discovery PADG packet with the Sequence Number and Credit TLVs
   is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination_mac_addr                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Destination_mac_addr(c)    |       Source_mac_addr         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Source mac_addr (cont)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8863        | v = 1 | t = 1 |  CODE = 0x0A  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = 0x0E            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Sequence Number TLV = 0x0108  |       TLV Length = 0x02       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Sequence Number         |     Credit TLV = 0x0106       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       TLV Length = 0x04       |               FCN             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              BCN              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.2.4   PPPoE Active Discovery Session-Credit Response (PADC)

   The PPPoE Active Discovery Session-Credit Response (PADC) is a new
   packet defined in this specification.  A Server or Client must send
   a PADC in response to a PADG.  The CODE field is set to 0x0B, and
   the SESSION_ID must be set to the unique value generated for this
   PPPoE session.

   The PADC packet must contain a single Credit Tag TLV, indicating
   the Forward Credit Notification (FCN) and the Backward Credit
   Notification (BCN) of the PPPoE session.

   The Credit TLV FCN represents the absolute credits remaining that
   have been granted to the peer by the node.  The Credit TLV BCN
   represents the remaining absolute credits that have been granted
   to the local node from the peer.  The FCN and BCN values must be
   scaled by the value established during session establishment in
   the Credit Scale Factor TLV or by the default 64-byte value prior
   to processing.

   The PADC packet must contain a single Sequence Number Tag.The
   sequence number must be the sequence number associated with the
   PADG.


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   A Discovery PADC packet with the Sequence Number and Credit TLV
   is shown below.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination_mac_addr                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Destination_mac_addr(c)    |       Source_mac_addr         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Source mac_addr (cont)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8863        | v = 1 | t = 1 |  CODE = 0x0B  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = 0x0E            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Sequence Number TLV = 0x0108  |        TLV Length = 0x02      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Sequence Number         |     Credit TLV = 0x0106       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       TLV Length = 0x04       |               FCN             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              BCN              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The FCN and BCN values are expressed in the respective units
   defined by the Credit Scale Factor TLV or the 64-byte default.


3.2.5   PPPoE Active Discovery Quality (PADQ)

   The PPPoE Active Discovery Quality (PADQ) is a new packet defined
   in this specification.  An Server or Client may send an optional
   PADQ at any time to query or report link quality metrics.

   When transmitting PPP [1] streams over wireless links through radio
   modems, the quality of the RF link directly affects the throughput.
   The PPPoE Active Discovery Quality (PADQ) packet can be used by the
   radio modem to report RF link metrics.  The CODE field is set to
   0x0C, and the SESSION_ID must be set to the unique value generated
   for this PPPoE session.

   The PPPoE Active Discovery Quality (PADQ) packet can be used to
   query link metrics by setting the PADQ Metric Tag Length to zero.

   The PADQ must carry a single Metric TLV. When processing the
   data rates, the values must be converted using the indicated
   data rate units.  This document enhances the Metric Tag as
   described below.


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   The PPPoE Active Discovery Quality (PADQ) packet can be used to
   query link metrics by setting the PADQ Metric Tag Length to zero.


   A Discovery PADQ packet with the required Metric TLV is shown
   below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Access_Concentrator_mac_addr                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Access_Concentrator_mac_addr(c)|        Host_mac_addr          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Host_mac_addr (cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8863        | v = 1 | t = 1 |  CODE = 0x0C  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = 0x12            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       TLV Type = 0x0101       |        TLV Length = 0x00      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Metric TLV = 0x0107        |        TLV Length = 0x0A      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Reserved      | MD| CD|R|      RLQ      |    Resources  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Latency (MS)          |        Current Datarate       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Maximum Datarate       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The maximum datarate and the current datarate are expressed in
   units determined by the MD and CD bits, respectively.


















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   A Discovery PADQ packet with a Metric TLV Length=0 to query for
   is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Access_Concentrator_mac_addr                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Access_Concentrator_mac_addr(c)|        Host_mac_addr          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Host_mac_addr (cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8863        | v = 1 | t = 1 |  CODE = 0x0C  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = 0x08            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       TLV Type = 0x0101       |       TLV Length = 0x00       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Metric TLV = 0x0107      |       TLV Length = 0x00       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.3  PPP Session Stage Extensions

   The PPP Session Stage Extensions define the optional use of Credit
   TLV.  Use of the Credit TLV in the PPP Session Stage is referred
   to as an in-band credit grant.

   The first field following the PPP Session Stage LENGTH must be
   checked.  If the value is equal to the PPP Protocol identifier
   (0xc021), then normal packet (payload) processing occurs.
   When the field following the PPP Session Stage LENGTH is not
   the PPP Protocol identifier (0xc021), a TLV is assumed.  In
   this case, the TLV length is subtracted from the overall payload
   length.
















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   A PPP LCP packet with optional Credit TLV is shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Access_Concentrator_mac_addr                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Access_Concentrator_mac_addr(c)|        Host_mac_addr          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Host_mac_addr (cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ETHER_TYPE = 0x8864        | v = 1 | t = 1 |  CODE = 0x00  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     SESSION_ID = 0x1234       |      LENGTH = (payload)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Credit TLV = 0x0106       |       TLV Length = 0x04       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              FCN              |              BCN              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    PPP PROTOCOL = 0xc021      |        PPP payload           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



4.0  Credit Flow Considerations

   For a given session, credit grants exchanged in the Discovery Stage,
   PADG-PADC, are referred to as out-of-band.  Credit grants exchanged
   in the PPP Session Stage are referred to as in-band.  Credit
   accounting is only applied to the packets transmitted in the PPP
   Session Stage.

   Out-of-band credit management is handled by periodic exchange of
   the PPPoE Active Discovery Grant (PADG) and PPPoE Active Discovery
   Credit (PADC) packets.

   In-band credit management allows credits to be incrementally
   granted with each PPP Session Stage packet.  These in-band
   incremental credit grants are not explicitly acknowledged.
   However, they are reflected in the in-band credit flow from
   the peer node.  This offers the greatest credit granting efficiency
   when traffic rates are high.

   Once agreed upon during the Discovery Stage, credit grants are
   required to transmit packets in the PPP Session Stage.  A node must
   grant credits to its peer, before the peer can transmit packets to
   the granting node.




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   Credits are granted incrementally in the forward direction. Locally,
   a node manages the credits that it has granted to a peer, as well
   as the credits that a peer has granted to it.

   Grants received from a peer are added to a local running credit
   counter.  The accumulated credits are decremented with each packet
   the node transmits to the peer.  When the running counter reaches
   zero, the node must stop transmitting packets to the peer.

   To manage the credits that a node has granted, the node maintains a
   running counter.  With each PPP Session Stage packet received from
   the peer, the running counter is decremented.  When the running
   counter reaches zero, no additional packets are expected.  The node
   incrementally grants more credits to the peer to maintain packet
   flow.  Packets received when granted credits have been exhausted
   are discarded.


5.0  PADG and PADC Retransmission

   When a node does not receive a PADC packet in response to a PADG
   within a specified amount of time, it should transmit a new PADG
   packet with zero credits, using the same sequence number and double
   the waiting period.  A PADC response with the associated sequence
   number will indicate whether or not the previously granted credits
   were accumulated.  If they were not, a PADG with credits, with an
   incremented sequence number, should be transmitted.  This process
   should be repeated until granted credits are properly acknowledged
   or as many times as desired.

   When a node does not receive a PADQ metric packet in response to a
   query within a specified amount of time, it should resend the PADQ
   query packet and double the waiting period.  This can be repeated
   as many times as desired.

6.0  Other Considerations

   A node may autonomously generate PADQ metric packets.  The rate of
   autonomously generated PADQ metric packets may need to be throttled
   so as not to overrun the peer.

   The sending and receiving of PPPoE Discovery packets are
   independent of credit counts.  For example, a node must always
   be able to  receive a PADG and send a PADC.







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   During normal operation, nodes may disagree about the number of
   credits.  Operational credit mismatches would occur due to packets
   in transit on the wire.  Much larger credit mismatches can occur if
   there are transmission errors.  To correct these larger errors, the
   BCN fields of the PADG and PADC packets and in-band credit grants
   from a peer can be used by the receiving node to reset the credit
   values of its peer.

7.0  IANA Considerations

   IANA has assigned the following PPPoE TLV Values as noted in [3]:

   TLV Value     TLV Name             Description         Reference
   -----------   -------------------  -----------------   ---------
   262  0x0106   Credits              See the reference   [RFC4938bis]
   263  0x0107   Metrics              See the reference   [RFC4938bis]
   264  0x0108   Sequence Number      See the reference   [RFC4938bis]
   265  0x0109   Credit Scale Factor  See the reference   [RFC4938bis]

   IANA has assigned the following PPPoE Code fields as noted in [3]:

   Code      PPPoE Packet Name        Description         Reference
   --------  ----------------------   -----------------   ---------
   10  0x0a  PADG, Session-Grant      See the reference   [RFC4938bis]
   11  0x0b  PADC, Session-Credit     See the reference   [RFC4938bis]
                    Response
   12  0x0c  PADQ, Quality            See the reference   [RFC4938bis]


8.0  Security Considerations

   This memo defines a mechanism for adding flow control to the
   existingPPP Over Ethernet (PPPoE) sessions.  These extensions
   are subsequent to the existing PPPoE security mechanisms as
   described in RFC 2516 [2].  It is required that the Service TLV
   and Session ID  always be validated prior to processing credits.


9.0 References

9.1 Normative References

   [1] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD 51,
       RFC 1661, July 1994.

   [2] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D., and R.
       Wheeler, "A Method for Transmitting PPP Over Ethernet (PPPoE)",
       RFC 2516, February 1999.



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   [3] Arberg, P. and V. Mammoliti, "IANA Considerations for PPP over
       Ethernet (PPPoE)", RFC 4937, June 2007.

9.2 Informative References

   [4] An open source (GPLv2) pppoe client implementation of
       RFC4938bis, PPP Over Ethernet (PPPoE) Extensions for Credit
       Flow and Link Metrics,
       http://rfc4938.sourceforge.net/










































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10.0  Appendix

  Session Credit Flow with the default 64-byte credit unit.

   Server                    Client
 ======================================================================
   <------------PADI--------------    Initiate
    ------------PADO-------------->   Offer

   <------------PADR--------------    Credit TLV:
                                      FCN represents the initial
                                      client credit grant to the
                                      server in  64-byte units.
                                      BCN is set to 0.

    ------------PADS-------------->   Credit TLV:
                                      FCN represents the initial
                                      server credit grant to the
                                      client in 64-byte units.
                                      BCN represents an echo of
                                      initial client credits.

   <==============================>   Data w/ optional inband
                                      Credit TLV

   <------------PADG--------------    Credit TLV: (out-of-band)
                                      FCN represents an incremental
                                      client credit grant to the
                                      server, in 64-byte units.
                                      BCN represents the remaining
                                      server credits that were granted
                                      to the client, in 64-byte units.

    ------------PADC-------------->   Credit TLV: (out-of-band)
                                      FCN represents an incremental
                                      server credit grant to the
                                      client, in 64-byte units.
                                      BCN represents the remaining
                                      client credits that were granted
                                      to the server, in 64-byte units.

   <==============================>   Data w/ optional inband Credit
                                      TLV

   <------------PADT-------------->   Terminate






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  Session Credit Flow with specific credit scale factor units for
  the Server and the Client.

   Server                    Client
 ======================================================================
   <------------PADI--------------    Initiate
    ------------PADO-------------->   Offer

   <------------PADR--------------    Credit TLV:
                                      FCN represents the initial
                                      client credit grant to the
                                      server, in Credit Scale Factor
                                      TLV units.
                                      BCN is set to 0.

    ------------PADS-------------->   Credit TLV:
                                      FCN represents the initial
                                      server credit grant to the
                                      client, in Credit Scale Factor
                                      TLV units.
                                      BCN represents an echo of the
                                      initial client credits, in
                                      Credit Scale Factor TLV units.

   <==============================>   Data w/ optional inband Credit
                                      TLV

   <------------PADG--------------    Credit TLV: (out-of-band)
                                      FCN represents an incremental
                                      client credit grant to the server,
                                      in Credit Scale Factor TLV units.
                                      BCN represents the remaining
                                      server credits that were granted
                                      to the client, in Credit Scale
                                      Factor TLV units.

    ------------PADC-------------->   Credit TLV: (out-of-band)
                                      FCN represents an incremental
                                      server credit grant to the client,
                                      in Credit Scale Factor TLV units.
                                      BCN represents the remaining
                                      client credits that were granted
                                      to the server, in Credit Scale
                                      Factor TLV units.

   <==============================>   Data w/ optional inband Credit
                                      TLV

   <------------PADT-------------->   Terminate


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Authors' Addresses

   Bo Berry, Editor
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   EMail: bberry@cisco.com

   Stan Ratliff
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   EMail: sratliff@cisco.com

   Ed Paradise
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134
   EMail: pdice@cisco.com

   Tim Kaiser
   Harris Corporation
   Government Communications System Division
   Mail Stop 25-11F
   P.O. Box 37
   Melbourne, FL 32902-0037
   EMail: timothy.kaiser@harris.com

   Mike D Adams
   640 N 2200 W MS F1J12
   Salt Lake City, Utah 84116
   801 594-2367
   EMail: Michael.D.Adams@L-3com.com


















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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on
   an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
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   The IETF invites any interested party to bring to its attention
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.






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