Internet DRAFT - draft-bberry-pppoe-scaled-credits-metrics
draft-bberry-pppoe-scaled-credits-metrics
Internet-Draft B. Berry, Editor
Intended status: Informational S. Ratliff
Expires: February 28, 2008 E. Paradise
Cisco
T.Kaiser
Harris Corporation
M. Adams
L3 Communications
September 10, 2007
PPP Over Ethernet (PPPoE) Extensions
for Scaled Credits and Link Metrics
draft-bberry-pppoe-scaled-credits-metrics-01.txt
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document specifies a method for optional flow control credit
scaling and link quality metric scaling for Point-to-Point over
Ethernet (PPPoE). Credit and metric scaling is required when
connecting to high performance devices that employ the PPPoE credit
flow control and link metric reports as defined in RFC 4938.
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1. Introduction
PPP over Ethernet (PPPoE) [2] is a protocol for establishing and
encapsulating sessions between hosts and traffic aggregators for
PPP [1] transport over Ethernet. PPPoE [2] was extended by RFC 4938
[3], which provides Credit Flow and Link Metrics.
This document specifies an enhancement to RFC 4938 [3] credit flow
and metric reports to support high performance (radio) traffic
aggregators. The enhancements are backward compatible to maintain
the functionality of RFC4938.
2 Terminology
BCN Backward Credit Notification
CDR Current Data rate
FCN Forward Credit Notification
gbps gigabits (1,000,000,000) per second
kbps kilobit (1,000) bits per second
mbps megabits (1,000,000) per second
MDR Maximum Data rate
tbps terabits (1,000,000,000,000) per second
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3. Overview of Credit and Metric Enhancements
RFC 4938 defined credits in 64-byte units of PPP payload. This
document specifies a new optional Credit Scalar Tag that can be
used in the PADR-PADS exchange to modify the credit unit value.
RFC 4938 defined the metrics maximum data rate and the current data
rate in units of kilobits per second. With high performance devices,
the need to express data rates greater than kilobits per second is
needed. To support the dynamic nature of high performance radio
devices, two bits for each data rate, the maximum data rate and the
current data rate, are allocated from the Reserved field to specify
the data rate units.
The tables below show the impact of the new Credit Scalar Tag and
the enhanced Metric Tag.
Packet Types
Packet Status
=======================================================
PADR Enhanced, optionally includes
the Credit Scalar Tag
PADS Enhanced, optionally includes
the Credit Scalar Tag
PADG Unchanged
PADC Unchanged
PADQ Enhanced, metrics are expressed
in the default units or scalar
the units.
Tag_Types and Tag_Values
Tag Tag
Value Description Status
=======================================================
0x0106 Credits Unchanged
0x0107 Metrics Modified, MD and CD bits defined
0x0108 Sequence Number Unchanged
0x0109 Credit Scalar New
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4. Packet Enhancements
4.1. PPPoE Active Discovery Request (PADR)
The PADR packet is enhanced to optionally contain a single Credit
Scalar Tag TLV. The Credit Scalar Tag defines the credit unit
value. If the Credit Scalar tag is omitted, the default value of
64-bytes is used for the session. When the client includes the
Credit Tag in the PADR, the server MUST send the PADS with the
Credit Tag. This PADR credit scalar value is applied to all
credit values associated with the client.
An example packet is shown in Appendix B.
4.2. PPPoE Active Discovery Session-confirmation (PADS)
The PADS packet is enhanced to optionally contain a single Credit
Tag Scalar Tag TLV. The Credit Scalar Tag defines the credit unit
value. The Credit Scalar Tag MUST be included when it was included
in the PADR. If the Credit Tag was not included it MUST be omitted,
indicating that the 64-bytesdefault is used for the session. This
credit scalar value is applied to all credit values associated with
the server.
An example packet is shown in Appendix B.
4.3. PPPoE Active Discovery Session-Grant (PADG)
The PADG 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 FCN and BCN values must be scaled by the value established
during session establishment in the Credit Scalar Tags or by the
default 64-byte value prior to processing.
An example packet is shown in Appendix B.
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4.4. PPPoE Active Discovery Session-Credit Response (PADC)
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, and any number of other
Tag types.
The FCN and BCN values must be scaled by the value established
during session establishment in the Credit Scalar Tags or by the
default 64-byte value prior to processing.
An example packet is shown in Appendix B.
4.5. PPPoE Active Discovery Quality (PADQ)
The PADQ must carry a single Metric Tag TLV. When processing the
data rates, the values must be converted using the indicated
data rate units. This document ehances the Metric Tag as described
below.
An example packet is shown in Appendix B.
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5 TAG Enhancements
5.1 Metric Tag TLV
The Metric Tag TYPE, contains the following fields:
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.
MD - Two bits that designate the units of the maximum data rate.
MD Scale: 00 == kbps
01 == mbps
10 == gbps
11 == tbps
CD - Two bits that designate the units of the current data rate.
CD Scale: 00 == kbps
01 == mbps
10 == gbps
11 == tbps
Reserved - Reserved fields are zeroed unless otherwise specified.
Maximum data rate - the maximum theoretical data rate, in
scalar units per second, that the link is capable of
providing. When metrics are reported, the maximum data rate
must be reported.
Current data rate - the current data rate, in scalar units per
second, achieved on the link. If there is no distinction
between maximum data rate and current data rate, current data
rate should equal the maximum data rate.
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Latency - the transmission delay that a packet encounters as it
is transmitted over the Host 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 device
dependent. For example, the latency may be a running average
calculated from the internal queuing.
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.
The PPPoE Active Discovery Quality (PADQ) packet can be used to
query link metrics by setting the PADQ Metric Tag Length to zero.
An example tag is shown in Appendix A.
5.2 Credit Scalar Tag TLV
The Credit Scalar Tag can be used to change from the default
64-byte credit unit. The new credit scalar can range from
1-byte to 65535-bytes. A zero value is ignored and the
default 64-byte unit remains set.
For example, if a high performance device requires credit
grants in 512-bytes units, the new Credit Scalar TLV is
included in the PADR-PADS exchange to set its credit flow
to 512-byte units.
In another example, a high performance device requires credit
grants in 2048-bytes units. To set the new scalar value, the
high performance device must use the Credit Scalar in the
PADR-PADS exchange to set its credit flow to 2048-byte units.
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6. IANA Considerations
IANA has assigned the following PPPoE TAG Values as noted in [4]:
TAG Value TAG Name Tag Description Reference
----------- ------------------- --------------------- ---------
262 0x0106 Credits See the reference [RFC4938]
263 0x0107 Metrics See the reference [RFC4938]
264 0x0108 Sequence Number See the reference [RFC4938]
265 0x0109 Credit Scalar See the reference [RFCnnnn]
IANA has assigned the following PPPoE Code fields as noted in [4]:
Code PPPoE Packet Name Description Reference
-------- ----------------------------- ----------------- ---------
10 0x0a PADG, Session-Grant See the reference [RFC4938]
11 0x0b PADC, Session-Credit Response See the reference [RFC4938]
12 0x0c PADQ, Quality See the reference [RFC4938]
7. Security Considerations
This memo defines a mechanism to scale the credit grant units and
the link metrics to the existing credit-based flow control mechanism
and link quality metrics of Point-to-Point over Ethernet (PPPoE).
These extensions are subsequent to the existing PPPoE security
mechanisms as described in RFC 2516 [2].
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Appendix A: Tag Values
Feature Tag_Types and Tag_Values
Tag Tag
Value Description Status
===================================
0x0106 Credits Unchanged
0x0107 Metrics Modified
0x0108 Sequence Number Unchanged
0x0109 Credit Scalar New
0x0107 Metric Tag
This tag is used to report the link quality and performance. The
Metrics Tag contains the Receive Only indicator, Resource
status, Latency, Relative Link Quality (RLQ), Current data rate,
and Maximum data rate. The Metrics Tag is required by the PADQ
packet.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0107 | Tag Length=0x0A |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | MD| CD|R| RLQ | Resources |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latency (MS) | Current Datarate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Datarate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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0x0109 Credit Scalar Tag
This tag contains the scalar value that is to be applied to the
session credit manipulation. The Credit Scalar Tag is OPTIONAL
with the PADR, PADS packets. A value of zero is ignored and the
default scalar of 64 bytes is applied.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0109 | Tag Length=0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Scalar |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Appendix B: Example Packet Formats
A PADR packet with the Credit Tag Type 0x0106 and the OPTIONAL
Credit Scalar Tag Type 0x0109:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0101 | Tag Length=0x00 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0106 | Tag Length=0x04 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCN | BCN=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0109 | Tag Length=0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| scalar |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Credit Tag (0x106) FCN value is expressed in units of the
session credit scalar. If the Credit Scalar Tag is omitted,
the FCN is expressed in 64-byte units.
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A PADS packet with the Credit Tag Type 0x0106 and the OPTIONAL
Credit Scalar Tag Type:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0101 | Tag Length=0x00 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0106 | Tag Length=0x04 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCN | BCN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0109 | Tag Length=0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| scalar |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Credit Tag (0x106) FCN value is expressed in units of the
session metric scalar received in the PADR. If the PADR did not
contain the Credit Scalar Tag, the FCN is expressed in the default
64-byte units.
The Credit Tag (0x106) BCN value is expressed in units of the
session credit scalar contained in this PADS. If the Credit
Scalar Tag is omitted, the BCN is expressed in 64-byte units.
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A PADG packet with the Credit Tag Type 0x0106:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0108 | Tag Length=0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | Tag Type = 0x0106 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Length=0x04 | FCN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BCN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The FCN and BCN values are expressed in the respective units
of the session credit scalar.
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A PADC packet with the Credit Tag Type 0x0106:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0108 | Tag Length=0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | Tag Type = 0x0106 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Length=0x04 | FCN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BCN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The FCN and BCN values are expressed in the respective units
of the session credit scalar.
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A PADQ packet with Metric Tag Type 0x0107 showing the scalar bits:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0101 | Tag Length=0x00 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0107 | Tag 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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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.
[3] Berry, B., Holgate, H., "PPP Over Ethernet (PPPoE) Extensions
for Credit Flow and Link Metrics",
RFC 4938, June 2007.
[4] Arberg, P. and V. Mammoliti, "IANA Considerations for PPP over
Ethernet (PPPoE)", RFC 4937, June 2007.
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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Acknowledgements
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