INTERNET-DRAFT B. Berry
Category: Informational H. Holgate
Expires: October 10, 2004 Cisco Systems,
Inc.
10 March 2004
A Method for Terminating PPP Over Ethernet (PPPoE) Sessions
on Radio Modems
with Optional Extensions for
Credit Based Flow and Link Metrics
draft-bberry-pppoe-credit-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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Abstract
This document defines an optional credit based flow control
mechanism for PPP over Ethernet (PPPoE) Discovery and PPP Session.
It also defines a Link Quality Metric packet that can use to report
link status, which in turn can be used to influence traffic flow.
Applicability
The application of these extensions can be employed when PPP traffic
is transported by radio modems. In this architecture, the Access
Concentrator connects to a radio modem using Ethernet. Traffic
across the Ethernet link can be flow controlled using the PPPoE
extensions defined in this document.
Internet-Draft PPPoE with Credit Flow and Metrics March 2004
The link quality metric packet provides a mechanism that the radio
modem can use to report status and quality of the RF link to the
concentrator.
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Table of Contents
1. Introduction................................................4
2. Conventions used in this document...........................4
3. Overview of Protocol Extensions.............................4
4. Payload.....................................................5
5. Discovery Stage.............................................5
5.1 PPPoE Active Discovery Request (PADR)...................5
5.2 PPPoE Active Discovery Session-confirmation (PADS)......5
5.3 PPPoE Active Discovery Session-Grant (PADG).............6
5.4 PPPoE Active Discovery Session-Credit Response (PADC)...7
5.5 PPPoE Active Discovery Quality (PADQ)...................7
6. PPP Session Stage...........................................8
7. Credit Flow Considerations..................................9
8. Other Considerations.......................................10
9. Security Considerations....................................10
10. Appendix A: Tag Values....................................11
11. Appendix B: Example Message Formats.......................13
12. Normative References......................................20
13. ContributorËs Information.................................20
14. Contact Information.......................................20
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1. Introduction
PPP over Ethernet (PPPoE) provides the ability to connect a network
of hosts over a simple bridging access device to a remote Access
Concentrator. With this model, each host utilizes its own PPP stack
and the user is presented with a familiar user interface. Access
control, billing and type of service can be done on a per-user,
rather than a per-site, basis. This document focuses on a point-to-
point connection using radio.
PPPoE with Credit Flow Control is used between the Access
Concentrator and the Radio Modem. The Radio Modem terminates the
PPPoE and forwards the PPP data over the airwaves using a Radio Link
Protocol (RLP). The remote radio terminates the RLP and forwards
the PPP packets over the PPPoE path to its local Access
Concentrator. The PPP session is Access Concentrator to Access
Concentrator.
+------------+ +-------+ +-------+ +------------+
| Access | | Host | | Host | | Access |
|Concentrator|=======| Radio |~~~~~~~| Radio |=======|Concentrator|
+------------+ +-------+ +-------+ +------------+
| | | | | |
|-PPPoE-| |--RLP--| |-PPPoE-|
| |
|-------------PPP Session---------------|
In this example, the Host Radio initiates the PPPoE session with its
local Access Concentrator.
This document should be read with A Method for Transmitting PPP
Over Ethernet (PPPoE)÷, RFC 2516.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [2].
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. Once the Access Concentrator
acknowledges the Host flow control request, all session traffic MUST
be flow controlled.
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The Credit Flow control feature allows proper management of
resources in both the Host and Access Concentrator. This is
important when throughput capabilities of one are much greater that
the other.
When transmission facilities include radio modems, the quality of
the radio RF link can be reported through the Link Quality Metric
packet. Given this information, a node can make traffic decisions.
4. 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.
5. 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 have been 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.
5.1 PPPoE Active Discovery Request (PADR)
The PADR packet may 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. 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.
5.2 PPPoE Active Discovery Session-confirmation (PADS)
The PADS packet may optionally 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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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. This is binding and must
be followed for the entire duration of the PPP Session. A sessionËs
credit binding MUST be established prior to any other credit
indications can be exchanged.
The Access Concentrator PADS SHOULD ONLY contain 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. In this case the Host should terminate the
session. Credit Tags transmitted outside an established credit
based session MUST be ignored.
An example packet is shown in Appendix B.
5.3 PPPoE Active Discovery Session-Grant (PADG)
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 PPP 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.
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.
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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.
5.4 PPPoE Active Discovery Session-Credit Response (PADC)
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 PADG packet MUST contain a single Sequence Number Tag. The
sequence number should be the sequence number associated with the
PADG.
An example packet is shown in Appendix B.
5.5 PPPoE Active Discovery Quality (PADQ)
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.
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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.
6. PPP Session Stage
The packet exchange of the PPP Session Stage is unchanged by this
specification. The specification does define the optional use of
the Credit Tag TLV during the PPP Session. The Credit Tag TLV is
used to support flow control.
When the PPP Session is a flow controlled session, the first field
following the Payload Field MUST be checked. If the value of the
PPP Protocol identifier is that of the Credit Tag TLV (0x0106), then
the credit tag must be processed. In this case, the Credit Tag TLV
length is subtracted from the overall payload length. If the value
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of the PPP Protocol identifier is not that of the Credit Tag TLV
(0x0106), normal processing occurs.
The Credit Tag is the only optional tag permitted in the PPP Session
Stage.
An example packet is shown in Appendix B.
7. 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 must manage 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 must be 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 must
maintain a running counter. With each PPP Session Stage packet
received from the peer, the running counter must be decremented.
When the running counter reaches zero, no additional packets are
expected. The node must incrementally grant more credits to the
peer to enable packet flow. Packets received when granted credits
have been exhausted are discarded.
For a given session, credit grants exchanged in the Discovery Stage
are referred to as out-of-band. Credit grants exchanged in the PPP
Session Stage are referred to as in-band. In-band credit management
allows credits to be incrementally granted with each PPP Session
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Stage packet. This offers the greatest efficiency with less
opportunity for credit exhaust. Out-of-band credit management is
handled by periodic exchange of the PPPoE Active Discovery Grant
PADG and PPPoE Active Discovery Credit (PADC) packets.
The largest possible credit limit is 0x0ffff. If an incremental
credit grant ever 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.
8. 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 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.
The rate of autonomously generated PADQ packets may need to be
throttled by the radio modem so not to overrun the node.
9. Security Considerations
No new security considerations are provided in this document.
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10 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 radio RF link 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 PADM
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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11. 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 RF 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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12.
Normative References
[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD
51, RFC 1661, July 1994
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Mamakos L., et. al., A Method for Transmitting PPP Over
Ethernet (PPPoE)÷, RFC 2516, February 1999.
13. ContributorËs Information
The authors would like to acknowledge the influence and
contributions from Billy Moon and Fred Baker.
14. 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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Internet-Draft PPPoE with Credit Flow and Metrics March 2004
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