INTERNET-DRAFT B. Berry
Category: Informational H. Holgate
Expires: October 26, 2005 Cisco Systems,Inc.
10 March 2004
PPP Over Ethernet (PPPoE) Extensions
for Credit Flow and Link Metrics
draft-bberry-pppoe-credit-03.txt
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed, or
will be disclosed, and any of which I become aware will be disclosed,
in accordance with RFC 3668.
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Abstract
The Point-to-Point Over Ethernet (PPPoE) Protocol [2] provides a
standard method for encapsulating Point-to-Point Protocols (PPP) [1]
over Ethernet.
This document extends the PPPoE protocol with a credit based flow
control mechanism and Link Quality Metric report. The PPPoE
specification is also extended to allow TLV Tags in the PPP Session
Stage. These extensions are optional to retain backwards
compatibility and at the same time provide for future extendibility.
Internet-Draft PPPoE with Credit Flow and Metrics March 2004
Table of Contents
1. Introduction................................................3
2. Payload.....................................................4
3. Overview of Protocol Extensions.............................4
4. Discovery Stage.............................................4
5.1 PPPoE Active Discovery Request (PADR)...................4
5.2 PPPoE Active Discovery Session-confirmation (PADS)......5
5.3 PPPoE Active Discovery Session-Grant (PADG).............5
5.4 PPPoE Active Discovery Session-Credit Response (PADC)...6
5.5 PPPoE Active Discovery Quality (PADQ)...................7
5. PPP Session Stage...........................................8
6. Credit Flow Considerations..................................8
7. Other Considerations........................................9
8. Security Considerations.....................................9
9. Appendix A: Tag Values.....................................10
10. Appendix B: Example Message Formats.......................12
11. Normative References......................................19
12. Contributorªs Information.................................19
13. Contact Information.......................................19
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1. Introduction
PPP over Ethernet (PPPoE) [2] is a method of establishing and
encapsulating sessions between hosts and traffic aggregators (Access
Concentrators) for PPP transport. This method of transporting PPP
traffic works well when both session endpoints have similar
bandwidth, forwarding, and buffering capabilities that do not vary
over time. It is insufficient for applications with variable
bandwidth and limited buffering. This document describes a method
for extending PPPoE to support credit based session flow control and
session based metrics exchanges for mobile radio network
applications.
In the diagram below PPPoE sessions between and access concentrator
(IP routers) and a radio transmission system are used to represent
individual radio neighbors. The radio transmission system
establishes point to point Radio Link Protocol (RLP) sessions with
its neighbors and establishes a corresponding PPPoE session for each
neighbor with the transmission system's associated access
concentrator (router).
+--------+ +-------+ +-------+ +---- ---+
| Access | | Host | | Host | | Access |
| Conc. |=======| Radio |~~~~~~~| Radio |=======| Conc. |
+--------+ +-------+ +-------+ +--------+
| | | | | |
|-PPPoE-| |--RLP--| |-PPPoE-|
| |
|-------------PPP Session---------------|
The capabilities of the RF links between RLP neighbors may vary over
time due to mobility and environmental conditions. In many
instances, the radio transmission system has limited buffering
capability to handle capacity changes in the RLP sessions. To limit
buffering in the radio transmission system, a session flow control
mechanism is necessary to provide dynamic buffering feedback to the
router.
From the router's perspective in the diagram, each PPPoE session
between it and the radio transmission system represents a link to a
routable peer. For efficient routing, a mechanism of assigning and
dynamically updating a cost for each link (PPPoE session) is
required. When a modified PPPoE session between the router and the
radio is established, link metrics must be exchanged. When the RLP
session capabilities change, link metric feedback is provided to the
router.
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2. Payload
The Ethernet payload version field retains its value of 0x01. The
extensions for credit flow control and link quality metrics are
optional and backward compatible.
3. Overview of Protocol Extensions
PPPoE has two distinct stages. There is a Discovery Stage and a PPP
Session Stage. During the Discovery Stage, the Host can optionally
request a flow controlled PPP Session Stage. Once the Access
Concentrator acknowledges the Host flow control request, all PPP
Session Stage traffic must be flow controlled.
4. Discovery Stage
The packet exchange of the Discovery Stage is unchanged by this
specification. The specifications of the Session Request (PADR) and
the Session Confirmation (PADS) packets are extended to include the
optional Credit Tag TLV.
In addition, the optional Credit Grant (PADG) packet, the Credit
Response (PADC) packet and the Link Quality Metric (PADQ) packets
are introduced.
4.1 PPPoE Active Discovery Request (PADR)
The PADR packet is extended to optionally contain a single Credit
Tag TLV, indicating that the Host requests credit flow control for
this session. The Credit Tag 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 Access Concentrator by the Host. The BCN
value is set to 0.
An example packet is shown in Appendix B.
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4.2 PPPoE Active Discovery Session-confirmation (PADS)
The PADS packet is extended to optionally contain a single Credit
Tag TLV, indicating the Forward Credit Notification (FCN) and the
Backward Credit Notification (BCN) of the PPP Session Stage.
If the PADR contained a Credit Tag, then the Access Concentrator
PADS packet indicates support for credit flow control by including a
Credit Tag. The PADS Credit Tag FCN represents the number of
credits being initially granted to the Host. The Credit Tag BCN is
an echo of the number of credits that the Host had granted to the
Access Concentrator in the previous PADR packet.
Exchange of the Credit Tag TLV in the PADR and PADS indicates that
credit flow control is supported by both the Access Concentrator and
the Host for the designated PPP Session Stage. This is binding and
must be followed for the entire duration of the PPP Session Stage.
A sessionªs credit binding must be established prior to any other
credit indications can be exchanged.
The Access Concentrator PADS SHOULD ONLY carry the Credit Tag in
response to a Host PADR with Credits. If the Access Concentrator
does not support credit flow, it should not include the Credit Tag
in its PADS response. The Host must terminate a credit based
session that can not be supported by the Access Concentrator.
Credit Tags transmitted outside an established credit based session
must be ignored.
An example packet is shown in Appendix B.
4.3 PPPoE Active Discovery Session-Grant (PADG)
The PPPoE Active Discovery Session-Grant (PADG) is a new packet
defined in this specification. An Access Concentrator or Host MAY
send a PADG at any time after the PADR/PADS exchange to grant
incremental flow control credits. The CODE field is set to 0x0A and
the SESSION_ID must be set to the unique value generated for this
PPPoE Session.
The peer may then transmit data until the credits are exhausted.
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 accumulated
credits.
The PADG packet must contain a single Credit Tag TLV, indicating the
Forward Credit Notification (FCN) and the Backward Credit
Notification (BCN) of the PPP Session.
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The Credit Tag FCN indicates the number of incremental credits being
granted to the peer. A value between 1 and 0x0ffff represent an
incremental credit grant. The peer must add these credits to its
accumulated transmit credit count. A value of 0x00 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.
Once a credit has been granted, it must be honored. The largest
number of outstanding credits at any time is 0xffff.
The PADG packet must contain a single Sequence Number Tag TLV. This
tag is used to carry a unique 16-bit sequence number to uniquely
identify each request. The sequence number SHOULD be initialized to
zero and incremented by one for each new PADG. For re-transmitted
PADGs, the same sequence number that was used in the previous packet
transmission is repeated.
An example packet is shown in Appendix B.
4.4 PPPoE Active Discovery Session-Credit Response (PADC)
The PPPoE Active Discovery Session-Credit Response (PADC) is a new
packet defined in this specification. An Access Concentrator or
Host 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, and any number of other Tag
types.
The Credit Tag FCN represents the absolute credits remaining that
have granted to the peer. The Credit Tag BCN represents the
remaining absolute credits that have been granted to the node from
the peer.
The PADC packet must contain a single Sequence Number Tag. The
sequence number must be the sequence number associated with the
PADG.
An example packet is shown in Appendix B.
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4.5 PPPoE Active Discovery Quality (PADQ)
The PPPoE Active Discovery Quality (PADQ) is a new packet defined in
this specification. An Access Concentrator or Host MAY send an
optional PADQ at any time to query or report link quality metrics.
When transmitting PPP 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 PADQ MUST carry a single Metric Tag TYPE, which contains the
following fields:
Receive only - is a bit that indicates if the link is bi-
directional or receive only. A value of -1- indicates that the
link is receive-only.
Maximum data rate - is the maximum theoretical data rate, in
kilobits per second (kbps), that the RF link is capable of
providing. When metrics are reported, the maximum data rate MUST
be reported.
Current data rate - is the current data rate, in kilobits per
second (kbps), achieved on the RF link. If there is no
distinction between maximum data rate and current data rate,
current data rate should equal to maximum data rate.
Latency - is the transmission delay that a packet encounters as
it is transmitted over the RF link. This is reported in absolute
delay, milliseconds. If latency can not be calculated, a value
of 0 should be reported.
Resources - is a percentage, 0-100, representing the amount of
remaining or available resources, such as battery power. If
resources can not be calculated, a value of 100 should be
reported.
Relative Link Quality (RLQ) - is 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 can not 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 packet is shown in Appendix B.
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5. PPP Session Stage
This specification defines the optional use of TLV Tags in the PPP
Session Stage 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
Tag length is subtracted from the overall payload length.
The Credit Tag is the only optional TLV permitted in the PPP Session
Stage. The Credit Tag TLV is used to support in-band flow control.
A PPP Session Stage packet with Credits is shown in Appendix B.
6. 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
processing 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. 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.
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 stops 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
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incrementally grants more credits to the peer to maintain packet
flow. Packets received when granted credits have been exhausted are
discarded.
The largest possible credit limit is 0x0ffff. If an incremental
credit grant causes the accumulated count to exceed this value, the
max value is used.
One unit of credit represents 64-bytes, so a grant of 4 credits
translates to 256-bytes.
7. Other Considerations
When a node does not receive a PADC packet 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 if the
previously granted credits were accumulated or not. If not, the
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 within a specified
amount of time, it should resend the PADQ query packet and double
the waiting period. This is repeated as many times as desired.
A node may autonomously generate PADQ metric packets. The rate of
autonomously generate PADQ metric packets may need to be throttled
so not to overrun the peer.
8. Security Considerations
This memo defines a mechanism for adding flow control to the
existing PPP Over Ethernet (PPPoE). These extensions are
base upon an element of trust and upon the existing security
mechanisms provided by PPPoE. PPPoE is described in RFC 2516 [2].
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9. Appendix A: Tag Values
Feature Tag_Types and Tag_Values
0x0106 Credits
This tag contains the Forward Credit Notification (FCN) and the
Backward Credit Notification (BCN). The Credit Tag TLV is
OPTIONAL with the PADR, PADS and the PPPoE data payload packet
(ETHER_TYPE=8864).
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0106 | Tag Length=0x04 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCN | BCN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0x0107 Metrics
This tag is used to report the link quality and performance. The
Metrics Tag TLV contains the Receive Only indicator, Resource
status, Latency, Relative Link Quality (RLQ), Current data rate
and Maximum data rate. The Metrics TLV is required by the PADQ
packet.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0107 | Tag Length=0x0A |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |R| RLQ | Resource |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latency (MS) | Current Datarate (kbps) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Datarate (kbps) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0x0108 Sequence Number
This tag 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 sequence number. For re-transmitted
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.
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For example, the sequence number sent in the PADG request is
echoed in the PADC response. This ties a specific PADC response
to a specific PADG request.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0108 | Tag Length=0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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10. Appendix B: Example Message Formats
A PADR packet with OPTIONAL Credit Tag Type 0x0106:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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A PADS packet with OPTIONAL Credit Tag Type 0x0106:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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A PADG packet with Credit Tag Type 0x0106:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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A PADC packet with Credit Tag Type 0x0106:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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A PADQ packet to query for the link metrics: This is indicated by
the Metric Tag Length=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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0101 | Tag Length=0x00 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0107 | Tag Length=0x00 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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A PADQ packet with Metric Tag Type 0x0107:
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 |R| RLQ | Resource |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latency (MS) | Current Datarate (kbps) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Datarate (kbps) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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A PPP LCP packet with optional Credit Tag Type 0x0106:
While the PPP protocol value is shown (0xc021), the PPP payload is
left to the reader. This is a packet from the Host to the Access
Concentrator.
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 = 0x???? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Type = 0x0106 | Tag Length=0x04 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCN | BCN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPP PROTOCOL = 0xc021 | PPP payload ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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11. Normative References
[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD
51, RFC 1661, July 1994
[2] Mamakos L., et. al., "A Method for Transmitting PPP Over
Ethernet (PPPoE)", RFC 2516, February 1999.
12. Contributorªs Information
The authors would like to acknowledge the influence and
contributions from Billy Moon and Fred Baker.
13. Contact Information
Bo Berry
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
email: bberry@cisco.com
Howard Holgate
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
email: hholgate@cisco.com
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Berry, Holgate Expires April 10, 2005 [Page 20]