Internet DRAFT - draft-richards-bacp
draft-richards-bacp
PPP Working Group Craig Richards
Internet Draft Shiva Corporation
expires July 1996 Kevin Smith
Ascend Communications, Inc.
January 1996
The PPP Bandwidth Allocation Protocol (BAP)
The PPP Bandwidth Allocation Control Protocol (BACP)
draft-richards-bacp-00.txt
Status of this Memo
This document is a submission to the Point-to-Point Protocol Working
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the ietf-ppp@merit.edu mailing list.
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Abstract
This document proposes a method to manage the dynamic bandwidth
allocation of implementations supporting the PPP multilink protocol
[1]. This is done by defining the Bandwidth Allocation Protocol
(BAP), as well as its associated control protocol, the Bandwidth
Allocation Control Protocol (BACP). BAP will manage the number of
links in a multlink bundle. This includes defining datagrams to co-
ordinate adding and removing individual links in a multilink bundle,
as well as specifying which peer is responsible for which decisions
regarding managing bandwidth during a multilink connection.
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1. Introduction
As PPP multilink implementations become increasingly common, there is
a greater need for some conformity in how to manage bandwidth over
such links. Interoperable implementations of PPP multilink may have
problems such as thrashing, when links are repeatedly brought up and
torn down in a short amount of time. BACP and BAP provide a means of
solving problems associated with interoperable thrashing
implementations, as well as providing a flexible yet robust way of
managing bandwidth between 2 peers. BAP does this by defining rules
governing bandwidth on demand allocation and by defining Call-Control
packets that co-ordinate the actual bandwidth allocation and de-
allocation. Phone numbers may be passed in the Call-Control packets
to improve dynamic bandwidth decisions, as well as minimizing the end
user's configuration.
1.1. Specification of Requirements
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized.
MUST This word, or the adjective "required", means that the
definition is an absolute requirement of the specification.
MUST NOT This phrase means that the definition is an absolute
prohibition of the specification.
SHOULD This word, or the adjective "recommended", means that there
may exist valid reasons in particular circumstances to
ignore this item, but the full implications must be
understood and carefully weighed before choosing a
different course.
MAY This word, or the adjective "optional", means that this
item is one of an allowed set of alternatives. An
implementation which does not include this option MUST be
prepared to interoperate with another implementation which
does include the option.
1.2. Terminology
This document frequently uses the following terms:
peer The other end of the point-to-point link
silently discard
This means the implementation discards the packet without
further processing. The implementation SHOULD provide the
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capability of logging the error, including the contents of
the silently discarded packet, and SHOULD record the event
in a statistics counter.
BOD (bandwidth on demand)
BOD refers to the ability of a system to allocate and
remove links in a multilink system to change the bandwidth
of a multilink bundle. This may be done in response to
changing line conditions and it also may be done in
response to changing resource conditions. In either case,
changing bandwidth dynamically during a multilink
connection is referred to as BOD.
2. New LCP Configuration Option - Link Discriminator
Description
This option is used to declare a unique discriminator for the link
that the option is sent over. This option may be in an LCP
configure request packet. The link discriminator is used to
differentiate the various links in a multilink bundle. If this
option is used, each link in a multilink bundle MUST have a unique
discriminator. The discriminator is independent for each peer, so
each link may have 2 different LCP Link Discriminator values, one
for each peer.
A summary of the Link Discriminator LCP Option format is shown below.
The fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Link Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
?? for Link Discriminator option.
Length
The Length field is one octet, and indicates the length of this
LCP Option including the Type, Length, and Link Discriminator
fields.
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Link Discriminator
The Link Discriminator field is 2 octets in length, and it
contains a unique identifier used to indicate a particular link in
a multilink bundle.
3. BACP Packet Format
BACP uses the same packet exchange mechanism as the Link Control
Protocol [1]. BACP packets MUST NOT be exchanged until PPP has
reached the Network-Layer Protocol phase. BACP packets received
before this phase is reached should be silently discarded.
BACP is negotiated once per multilink bundle. If BACP is negotiated
on any of the links in a multilink bundle, it is opened for all of
the links in the bundle.
The Bandwidth Allocation Control Protocol is exactly the same as the
Link Control Protocol [1] with the following exceptions:
Data Link Layer Protocol Field
Exactly one BACP packet is encapsulated in the Information
field of PPP Data Link Layer frames where the Protocol field
indicates type hex 80?? (Bandwidth Allocation Control
Protocol).
Code field
Only Codes 1 through 7 (Configure-Request, Configure-Ack,
Configure-Nak, Configure-Reject, Terminate-Request, Terminate-
Ack and Code-Reject) are used. Other Codes should be treated
as unrecognized and should result in Code-Rejects.
Configuration Option Types
BACP has a distinct set of Configuration Options, which are
defined in the next section.
4. BACP Configuration Options
BACP Configuration Options allow negotiation of desirable BACP
parameters. These options are used in Config-Request, Config-Ack,
Config-Nak, and Config-Reject packets. BACP uses the same
Configuration Option format defined for LCP [1], with a seperate set
of Options.
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Current values of BACP Configuration Options are assigned as follows:
1 Datagrams-Supported
2 Base-Phone-Number
4.1. Datagrams-Supported
Description
This option is used to inform the peer of which Bandwidth
Allocation Protocol datagrams this implementation supports. This
option MUST be included in every BACP Configure-Request packet.
An implementation MUST NOT send its peer any packets which it does
not support, as indicated by this option. If an implementation
receives a packet that it does not support, it MUST silently
discard it.
Since this configuration option is used to inform the peer, and
can not be negotiated, an implementation SHOULD NOT transmit a
Config-Nak or a Config-Rej in response to this configuration
option.
A summary of the Datagrams-Supported Option format is shown below.
The fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Datagrams Supported |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
1 for Datagrams-Supported.
Length
The Length field is one octet, and indicates the length of this
BACP Option including the Type, Length and Datagrams Supported
fields.
Datagrams Supported
The Datagrams Supported field is a bit mask. It is 2 octets long.
If a bit is set, it indicates support of both a Bandwidth
Allocation Protocol Request or Indication datagram as well as the
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corresponding Response datagram. Bit 0 of the Datagrams Supported
field corresponds to bit 31 of the Datagrams-Supported Option as
diagrammed above.
Bit Datagram Supported
--- ------------------
0 Call-Request & Call-Response
1 Callback-Request & Callback-Response
2 Link-Drop-Request & Link-Drop-Response
3 Link-Drop-Query-Request & Link-Drop-Query-Response
4 Bundle-Drop-Request & Bundle-Drop-Response
5 Link-Type-Request & Link-Type-Response
6 Available-Link-Indication & Available-Link-Response
7 Call-Fail-Indication & Call-Fail-Response
If the Length field contains more bits than are defined by this
specification, then any bits that are not defined should be
ignored. If the Length field is shorter than the number of bits
defined, then the implementation should set all bits not received
to 0.
4.2. Base-Phone-Number
Description
This Configuration Option provides a way to inform the peer of an
implementation's base phone number. The base phone number can be
used in conjunction with the unique-digits sub-option of the
phone-number BAP option to create a valid phone number string to
be dialed. This option would be needed if an answering
implementation wishes to make a callback call to initiate a
subsequent link in a bundle.
By default, the answerer's base phone number is the original
number used to make the call that creates the first link in a
multilink bundle, and the originator does not have a base phone
number. However, if a callback protocol is used during link
establishment of the first link of a bundle, then the callback
phone number would be the default base number for the originator's
implementation.
Since this configuration option is used to inform the peer, and
can not be negotiated, an implementation SHOULD NOT transmit a
Config-Nak or a Config-Rej in response to this configuration
option.
A summary of the Base-Phone-Number Option format is shown below. The
fields are transmitted from left to right.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Base Phone Number...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
2 for Base-Phone-Number.
Length
The Length field is one octet, and indicates the length of this
BACP Option including the Type, Length and Base Phone Number
fields.
Base Phone Number
The Base Phone Number field is an ASCII phone number string. It
will contain the complete set of digits that must be dialed by the
calling implementation to reach the called implementation. This
might include a code to reach an outside line, long distance
prefix, area code, country prefix and/or country code, as well as
the phone number to be dialed. It should be similar to the format
of a phone number used when performing a callback connection.
5. BAP Overview
5.1. Link Management
After BACP reaches the opened state, either peer may request that
another link be added to the bundle by sending a BAP Call- or
Callback-Request packet. A Call-Request packet is sent if the
implementation wishes to originate the call for the new link, and a
Callback-Request packet is sent if the implementation wishes to
answer the call for the new link. The implementation receiving Call-
and Callback-Requests must respond with the appropriate Request-Ack
or Request-Nak Response Code.
5.2. Bandwidth Management
In order to discuss bandwidth management, it is first necessary to
define some terms. For the purposes of this specification, Bandwidth
on Demand (BOD) is divided into 2 different types - throughput BOD
and resource BOD. Throughput BOD refers to BOD decisions made based
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on the amount of data being sent, received or queued to be sent over
a multilink bundle. An example of this is when a link is added to a
bundle due to a large file being transferred across the bundle.
Resource BOD refers to dynamic bandwidth decisions based on the
equipment available to an implementation. For example, a link might
be removed from a multilink bundle to allow an incoming voice call to
be answered, or a link might be added when a line becomes free due to
the termination of a seperate PPP call on another port. A system
implementing BACP may be capable of implementing neither, one or both
types of dynamic bandwidth management.
Resource BOD support is an optional part of BAP. An implementation
does not have to locally make resource based BOD decisions as part of
BAP. However, any system implementing BAP must handle resource BOD
management by its peer. When links are removed due to resource BOD
decisions, an implementation MUST use a Link-Drop-Request. A Link-
Drop-Request is used to inform the peer that the implementation is
going to drop a link from the multilink bundle. The peer MUST reply
to this request with a Link-Drop-Response with the Response Code set
to Request-Ack. No other response is allowed. The peer that decides
to drop a link MAY choose to drop the link even if a Request-Ack has
not been received. This SHOULD only be done if there is a time
critical quality to dropping the link. An example of this is when
there is an incoming call on a line in use by the multilink bundle,
and the line must be dropped quickly before the incoming call goes
away.
Throughput BOD support is an optional part of BAP. An implementation
does not have to locally make throughput based BOD decisions as part
of BAP. However, any system implementing BAP must handle throughput
BOD management by its peer. When an implementation decides that it's
time to remove a link due to a throughput BOD decision, an
implementation MUST transmit a Link-Drop-Query-Request. A Link-
Drop-Query-Request is used to inquire if the peer agrees that it is
okay to drop a link from the current multilink bundle. When an
implementation receives a Link-Drop-Query-Request, it MUST base its
response on its transmit heuristics (unless it is not monitoring its
transmit data, in which case it MUST accept the request to drop a
link.) It MUST NOT base its response on its receive data heuristics.
It MAY base its decision on its configuration, for example if the
request would cause the number of active links to fall below the
allowable minimum number of links configured for the active multilink
bundle. By making the decision to respond to a Link-Drop-Query-
Request based on transmit heuristics only, BAP maximizes
interoperability of various types of throughput BOD implementations.
An implementation may monitor its transmit traffic, both transmit and
receive traffic, or choose not to monitor traffic in either direction
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when implementing BACP. It is recommended that server systems
implement at least transmit monitoring, and that single-user dialin
servers implement bi-directional monitoring. This will allow clients
implementations that require a minimum amount of end-user
configuration in order to implement BOD successfully.
The Bandwidth Allocation Protocol does not include an algorithm for
determining when to add and remove links in a multilink bundle. It is
not necessary to include such an algorithm in the protocol, and
including it may limit the abilities of implementations to work
optimally. Leaving out the bandwidth on demand algorithm also
improves chances for interoperability and makes the protocol more
flexible.
6. BAP Packets
All of the BAP Request and Indication packets require a Response
packet in response before taking any action, except the Link-Drop-
Request packet. The sender of the Link-Drop-Request packet is not
required to receive a response to this packet before dropping a link,
because there may be a time critical event depending on dropping the
link. However, when possible, the sender of a Link-Drop-Request
packet SHOULD wait for a response before dropping the link.
With the exception of the Link-Drop-Request packet, an implementation
MUST set a timer when sending a request or indication packet. Upon
expiration of this timer, the implementation MUST retransmit the same
request or indication, with the identical identification number.
This will insure that the peer receives the proper request or
indication even if it is lost during transmission. If a Response
packet is lost, this retransmission scheme will insure that the
original Request or Indication will be retransmitted with the same
identification number, so the peer will realize that the response was
lost, and that this is not a new request or indication packet.
Since BAP packets help determine the amount of bandwidth available to
an implementation, they SHOULD be given priority over other data
packets when transmitting. This will help insure the prompt addition
and removal of links in a multilink bundle. This is especially
important when adding links to a bundle due to bandwidth constraints.
A race condition can occur if both implementations send a Call-
Request at the same time, or if both implementations send a Link-
Drop-Request at the same time. A race condition SHOULD be solved by
favoring the implementation with the lowest username value. If both
implementations are using the same username, then the lowest
Multilink Endpoint Discriminator SHOULD be favored. This means that
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the favored peer's request should be acked by its peer, and the
unfavored peer's request should be naked by the favored peer.
6.1. BAP Datagram Format
Description
Before any BAP packets may be communicated, PPP must reach the
Network-Layer Protocol phase, and the BA Control Protocol must
reach the opened state.
Exactly one BAP packet is encapsulated in the Information field of
PPP Data Link Layer frames where the Protocol field indicates type
hex 00?? (Bandwidth Allocation Protocol).
The maximum length of a BAP packet transmitted over a PPP links is
the same as the maximum length of the Information field of a PPP
data link layer frame.
Bandwidth Allocation Protocol datagrams can be catagorized as
either Request, Indication or Response packets. Every Request and
Indication datagram has a corresponding Response packet. Request
and Indication datagrams have a slightly different format from
Response datagrams, as the Response datagrams include a Response
Code octet.
A summary of the Bandwidth Allocation Protocol datagram Request and
Indication packet format is shown below. The fields are transmitted
from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-+-+-+-+
A summary of the Bandwidth Allocation Protocol datagram Response
packet format is shown below. The fields are transmitted from left
to right.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Response Code | Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
The Type field is one octet and identifies the type of BAP
datagram packet. Datagram types are defined as follows:
00 Call-Request
01 Call-Response
02 Callback-Request
03 Callback-Response
04 Link-Drop-Request
05 Link-Drop-Response
06 Link-Drop-Query-Request
07 Link-Drop-Query-Response
08 Bundle-Drop-Request
09 Bundle-Drop-Response
0A Link-Type-Request
0B Link-Type-Response
0C Available-Link-Indication
0D Available-Link-Response
0E Call-Failure-Indication
0F Call-Failure-Response
The various types of BAP datagrams are explained in the following
sections.
Identifier
The Identifier field is one octet and aids in matching Requests
and Indications with Responses, as well as which links are added
or removed. Call-Failure-Indication packets MUST use the same
Identifier as was used by the original Call-Request or Callback-
Request that was used to initiate the call that failed. All other
Request or Indication packets MUST use a unique Identifier for
each new Request or Indication. All Response packets MUST use the
same identifier as the Identifier in the Request or Indication
packet being responded to. When re-transmitting a request or
indication, the Identifier MUST be the same as the Identifier used
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on the previous transmission of the request or indication.
Length
The Length field is two octets and indicates the length of the
packet including the Type, Identifier, Length and Options fields.
Octets outside the range of the Length field should be treated as
Data Link Layer padding and should be ignored on reception.
Response Code
The Response Code is only present in Response datagrams. It can
have the following values:
0 Request-Ack
1 Request-Nak
Data
The Data field is variable in length, and will usually contain the
list of zero or more BAP Options that the sender desires to
transmit. The format of BAP Options is described in a later
chapter.
6.1.1. Call-Request
Before originating a call to add another link to a multilink bundle,
an implementation MUST transmit a Call-Request packet. This will
inform the peer of the intention to add another link to the bundle,
and give the peer a chance to inform the implementation of the phone
number of a free port that can be called.
The options field MUST include the Link-Type option. The options
field MAY include the No-Phone-Number and/or the Call-Add-Code
options.
Upon reception of a Call-Request, a Call-Response datagram MUST be
transmitted.
6.1.2. Call-Response
An implementation transmits a Call-Response datagram in response to a
received Call-Request datagram. If the Call-Request is acceptable,
the Call-Response will have a Response Code set to Request-Ack,
otherwise the Response Code will be Request-Nak. The Phone-Number
option MUST be included in a Call-Response packet with a Response
Code of Request-Ack unless the Call-Request included the No-Phone-
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Number option. The Nak-Code option MUST be included in a Call-
Response packet with a Response Code of Request-Nak, and the Time-
Until-Retry and Link-Types options MAY be included in such a packet.
6.1.3. Callback-Request
An implementation that wants its peer to originate another link to
add to the multilink bundle MUST transmit a Callback-Request packet
to its peer. This will inform the peer of the intention to add
another link to the bundle, and will also inform the peer of the
number to be called.
The options field MUST include the Link-Type and Phone-Number
options. The Call-Add-Code option MAY also be included.
Upon reception of a Callback-Request, a Callback-Response datagram
MUST be transmitted.
6.1.4. Callback-Response
An implementation transmits a Callback-Response datagram in response
to a received Callback-Request datagram. If the Callback-Request is
acceptable, the Callback-Response will have a Response Code of
Request-Ack, otherwise the Response Code will be Request-Nak. The
Nak-Code option MUST be included in a Callback-Response packet with a
Response Code of Request-Nak, and the Time-Until-Retry option MAY
also be included in such a packet.
6.1.5. Link-Drop-Request
An implementation that requires that a link be removed from the
current multilink bundle MUST transmit a Link-Drop-Request packet.
This will usually be due to resource BOD decisions. If an
implementation wants to remove a link due to a throughput BOD
decision, it MUST send a Link-Drop-Query-Request (see section below)
The options field MUST include the Link-Type option and MAY include
the Drop-Code option and MAY include the Link-Discriminator option.
Upon reception of a Link-Drop-Request, a Link-Drop-Response datagram
with a Response Code of Request-Ack MUST be transmitted. After the
receipt of the Link-Drop-Response datagram, the transmitter of the
Link-Drop-Request MUST initiate tear down of the indicated link by
sending an LCP Terminate-Request packet.
The Link-Drop-Request is the only BAP Request packet that does not
require a response before an action is taken. If there are time
constaints, an implementation may go ahead and drop a link from the
multilink bundle without receiving a response from its peer.
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6.1.6. Link-Drop-Response
An implementation transmit a Link-Drop-Response datagram in response
to a received Link-Drop-Request datagram. The Response Code MUST be
set to Request-Ack in this packet.
6.1.7. Link-Drop-Query-Request
An implementation that determines that a link is no longer needed
based on a throughput BOD decision MUST transmit a Link-Drop-Query-
Request packet. The remote implementation will respond with a
Response Code of Request-Ack if it agrees that there is too much
bandwidth in the current multilink bundle based on a throughput BOD
algorithm, or a Request-Nak if its own throughput BOD management
determines that current load conditions warrent keeping all links of
the bundle. The options field MUST include the Link-Type option and
MAY include the Drop-Code option and MAY include the Link-
Discriminator option.
Upon reception of a Link-Drop-Query-Request, a Link-Drop-Query-
Response datagram MUST be transmitted. After the receipt of a Link-
Drop-Query-Request with a Response Code of Request-Ack, the
transmitter of the Link-Drop-Query-Request MUST initiate tear down of
the indicated link by sending an LCP Terminate-Request packet.
6.1.8. Link-Drop-Query-Response
An implementation transmits a Link-Drop-Query-Response datagram in
response to a received Link-Drop-Query-Request datagram. If the
implementation determines, based on its BOD algoritm, that it would
be acceptable to reduce the bandwidth of the multilink bundle, then
the Response Code should be set to Request-Ack. Otherwise, the
Response Code should be set to Request-Nak.
If the Response Code is Request-Nak, the Nak-Code option MUST be
included, and the Time-Until-Retry option MAY be included.
6.1.9. Bundle-Drop-Request
An implementation that wishes to terminate a multilink bundle MAY
transmit a Bundle-Drop-Request to its peer. This packet indicates
that the peer is going to terminate all the links in the current
bundle. This packet can be used instead of sending Link-Drop-
Requests for each link in a multilink bundle. The options field MAY
include a Drop-Code option.
Upon reception of a Bundle-Drop-Request, a Bundle-Drop-Response with
a Response Code of Request-Ack MUST be transmitted. After the receipt
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of the Bundle-Drop-Response, the transmitter of the Bundle-Drop-
Request MUST initiate tear down of all links in the bundle by sending
an LCP Terminate-Request packet on each link.
6.1.10. Bundle-Drop-Response
An implementation transmits a Bundle-Drop-Response datagram in
response to a received Bundle-Drop-Request datagram. The Response
Code MUST be set to Request-Ack in this packet.
6.1.11. Link-Type-Request
If an implementation desires to know which types of links its peer
supports for the current multilink bundle, it MAY send a Link-Type-
Request to its peer.
Upon reception of a Link-Type-Request, a Link-Type-Response datagram
MUST be transmitted.
6.1.12. Link-Type-Response
An implementation transmits a Link-Type-Response datagram in response
to a received Link-Type-Request datagram. The Response Code MUST be
set to Request-Ack in this packet. The Link-Types option MUST be
included in this datagram, so the peer will be informed of which link
types this implementation supports.
6.1.13. Available-Link-Indication
Whenever an implementation transmits a Call-Response or a Callback-
Response with the Response Code set to Request-Nak and the Nak Code
set to "link not currently available", that implementation enters a
link denied state. While an implementation is in a link denied state
and a link of the type previously requested becomes available, and if
the implementation and its peer both support the Available-Link
packets, then the implementation MUST send an Available-Link-
Indication packet to the peer. When an Available-Link-Indication
packet is sent to the peer, the link denied state is cleared for that
link type. Each independent link type has an independent link denied
state.
When an implementation receives an Available-Link-Indication packet,
it MUST transmit an Available-Link-Response packet in response so
that the peer knows that the indication was received. The Link-Type
option MUST be included in the Available-Link-Indication datagram.
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6.1.14. Available-Link-Response
An implementation transmits an Available-Link-Response datagram in
response to a received Available-Link-Indication datagram. The
Response Code MUST be set to Request-Ack in this packet.
6.1.15. Call-Failure-Indication
After an implementation fails an attempt to add a link to a bundle as
the result of a Call-Request or a Callback-Request, it MUST send a
Call-Failure-Indication packet to its peer. The options field MUST
include the Call-Failure-Code option to indicate why the call failed
as well as whether or not the implementation will retry the call.
The Link-Type option MAY be included and the Phone-Number option
indicating the phone number of the attempted call MAY be included.
Upon reception of a Call-Failure-Indication packet, an implementation
MAY log the failure and reason code, and a Call-Failure-Response
datagram MUST be transmitted.
6.1.16. Call-Failure-Response
An implementation transmits a Call-Failure-Response datagram in
response to a received Call-Failure-Indication datagram. The
Response Code field MUST be set to Request-Ack in this packet.
7. BAP Datagram Options
BAP Datagram Options are used in various BAP packets. Their use in
various packets is as defined below. The format of these options
loosely follows the formatting conventions of LCP Configuration
Options.
A summary of the BAP Option format is shown below. The fields are
transmitted from left to right.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
The type field is one octet, and indicates the type of the BAP
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Datagram Option. The following options are currently defined:
0 Link-Type
1 Link-Types
2 Phone-Number
3 No-Phone-Number-Needed
4 Call-Add-Code
5 Nak-Code
6 Drop-Code
7 Call-Failure-Code
8 Time-Until-Retry
9 Link-Discriminator
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length, and Data fields.
Data
The Data field is zero or more octets, and contains information
specific to the BAP Option. The format and length of the Data
field is determined by the Type and Length fields.
7.1. Link-Type
Description
This option indicates the type of link supported for the operation
being performed. Exactly one bit MUST be set in the Link Type
field. This option MUST be included in all Bandwidth Allocation
Protocol datagrams except Bundle-Drop- Request/Response and Link-
Type- Request/Response datagrams.
A summary of the Link-Type BAP Option format is shown below. The
fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Link Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
0 for Link-Type.
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Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length and Link Type fields.
Link Type
The Link Type field is a bit mask. It is 2 octets in length. Bit
0 of the Link Type field corresponds to bit 31 of the Link-Type
BAP Option as described above. If a bit is set, it indicates
support of the corresponding link type:
Bit Link type
--- -------------
0 Sync ISDN 64K
1 Sync ISDN 56K
2 Sync ISDN Data over voice
3 V.120 on Sync ISDN 64K
4 V.120 on Sync ISDN 56K
5 V.120 on Sync ISDN Data over voice
6 V.110 on Sync ISDN 64K
7 V.110 on Sync ISDN 56K
8 V.110 on Sync ISDN Data over voice
9 ISDN PRI H0 Channel
10 X.25
11 Asynchronous analog modem
12 Synchronous analog modem
13 Analog modem over ISDN
If the Length field contains more bits than are defined by this
specification, then any bits that are not defined should be
ignored. If the Length field is shorter than the number of bits
defined, then the implementation should set all bits not received
to 0.
7.2. Link-Types
Description
This option indicates the types of links capable of being
supported in this multilink bundle. This option has a similar
format to the Link-Type option, except that the Link Type field is
a bit mask instead on having exactly one bit set.
This option MUST be included in the Link-Type-Response datagram.
A summary of the Link-Types BAP Option format is shown below. The
fields are transmitted from left to right.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Link Types |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
1 for Link-Types.
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length and Link Types fields.
Link Types
The Link Types field is a bit mask. It is 2 octets long. See the
bit definitions in the previous section (Link-Type Option) for a
definition of the bits in the Link Types field. If a bit is set,
it indicates support of the corresponding link type.
If the Length field contains more bits than are defined by this
specification, then any bits that are not defined should be
ignored. If the Length field is shorter than the number of bits
defined, then the implementation should set all bits not received
to 0.
7.3. Phone-Number
Description
This option is used to transmit an implementation's phone number
to its peer. This phone number should be either the phone number
of a hunt group for this device, or the specific phone number of a
free port on this device. If there are no free ports on this
device, a Response with a Response Code of Request-Nak should be
sent, and this option would not be used.
Note that an implementation may include more than one Phone-Number
option in a response. This means that there is more than one
phone number that can be used for the requested operation.
The Phone-Number option MUST appear in a Callback-Request. It also
MUST appear in a Call-Response if the Call-Request did not contain
the No-Phone-Number option. It MAY appear in the Call-Failure-
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Indication datagram.
A summary of the Phone-Number BAP Option format is shown below. The
fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |Sub-Option Type| Sub-Option Len|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sub-Option...
+-+-+-+-+-+-+-+-+
Type
2 for Phone-Number.
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length, and Sub-Option fields.
Sub-Option Type
The following Sub-Options Types are defined for the Phone-Number
option.
0 Unique Digits
1 Phone Number
2 Area Code
3 Country Code
4 Phone Number Sub Address
7.3.1. Phone-Number Sub-Options
Unique Digits
This byte is a count of the number of unique digits in the phone
number. The Unique Digits byte indicates the number of rightmost
digits of the complete phone number that are different from port
to port on the given device. (For example, if all phone numbers
on a given device are 617/555-89XX, the Unique Digits byte is 2,
if all phone numbers are 617/55X-XXXX, then the Unique Digits byte
will be 5). This field is required.
The purpose of the unique digits sub-option is to aid the
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originating implementation in phone number parsing. With this
information, the implementation that originates a call does not
have to know which combination of access codes, country codes,
dialing codes, area codes and extension numbers are necessary. It
just takes the digits contained in the original phone number
dialed, and replaces the rightmost unique digits with the
rightmost unique digits of the new phone number. For example, if
the original number dialed is 9,16175512345, and the new phone
number has an area code of 617, a phone number of 5598765, and a
unique digits value of 5, then the number to be dialed will be
created by replacing the rightmost 5 digits of the original number
(12345) with the rightmost 5 digits of the new number (98765),
which results in a new phone number to be dialed of 9,16175598765.
Phone Number
This field is the phone number of the port that should be called
by the peer. It MUST NOT include the area code and country code
fields IF they are defined in seperate sub-options. This field is
an ASCII string and only contains valid phone number digits. This
field is required.
Area Code
This field is the area code of the port that should be called by
the peer. This field is an ASCII string and only contains valid
phone number digits. This field is optional.
Country Code
This field is the country code of the port that should be called
by the peer. This field is an ASCII string and only contains valid
phone number digits. This field is optional.
Phone Number Sub Address
This field is the sub address of the port to be called by the
peer. This sub-option will only be used for an ISDN call. This
field is an ASCII string and only contains valid phone number
digits. This field is optional.
7.4. No-Phone-Number-Needed
Description
The No-Phone-Number option is used to indicate that the calling
peer is already configured with the phone number of its multilink
peer. This may be for security reasons, for configuration
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reasons, or for any other reason.
This option MAY be used in a Call-Request packet.
A summary of the No-Phone-Number BAP Option format is shown below.
The fields are transmitted from left to right.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
3 for No-Phone-Number.
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type and Length fields.
7.5. Call-Add-Code
Description
This option is used to indicate the primary reason for requesting
that a link be added to a bundle. This option MAY be used in a
Call-Request or a Callback-Request packet.
A summary of the Call-Add-Code BAP Option format is shown below. The
fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reason | Description
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
String (Optional)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
4 for Call-Add-Code.
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Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length, Reason and optional
Description String fields.
Reason
The reason code byte can have the following values:
0 - unlisted reason
1 - link has been freed up
2 - other resources freed up
3 - transmit queue length exceeds limit
4 - receive traffic exceeds limit
5 - transmit traffic exceeds limit
Description String
The Description String field is optional. If the length field
indicates that the option continues past the Reason field, then
the remaining octets in the option are the Description String.
This is an ASCII string. The content of the field is
implementation dependent. An implementation MAY ignore the
Description String field.
7.6. Nak-Code
Description
This option is used to transmit a Nak code to the peer. This
option MUST be included in every Call-Response and Callback-
Response with a Response Code of Request-Nak.
A summary of the Nak-Code BAP Option format is shown below. The
fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reason | Description
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
String (Optional)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type
5 for Nak-Code.
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length, Reason and optional
Description String fields.
Reason
The reason code byte can have the following values:
0 - unlisted reason
1 - link not currently available
2 - multilink bundle has reached its maximum capacity
3 - invalid phone number
4 - no resources
5 - peer does not have sufficient privilege
Description String
The Description String field is optional. If the length field
indicates that the option continues past the Reason field, then
the remaining octets in the option are the Description String.
This is an ASCII string. The content of the field is
implementation dependent. An implementation MAY ignore the
Description String field.
7.7. Drop-Code
Description
This option is used to indicate the primary reason for requesting
that a link be removed from the bundle. This option MAY be used
in a Link-Drop-Request, Link-Drop-Query-Request or a Bundle-Drop-
Request packet.
A summary of the Drop-Code BAP Option format is shown below. The
fields are transmitted from left to right.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reason | Description
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
String (Optional)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
6 for Drop-Code.
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length, Reason and optional
Description String fields.
Reason
The reason code byte can have the following values:
0 - unlisted reason
1 - incoming call
2 - outgoing call
3 - transmit data dropped below threshold
4 - receive data dropped below threshold
5 - transmit queue dropped below threshold
6 - higher priority connection requested line
7 - user initiated disconnect
Description String
The Description String field is optional. If the length field
indicates that the option continues past the Reason field, then
the remaining octets in the option are the Description String.
This is an ASCII string. The content of the field is
implementation dependent. An implementation MAY ignore the
Description String field.
7.8. Call-Failure-Code
Description
This option is used to indicate the action that will be taken
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after a call failed, as well as a reason code for the failure.
This option MUST be included in a Call-Failure-Indication packet.
A summary of the Call-Failure-Code BAP Option format is shown below.
The fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Action | Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Description String (Optional)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
7 for Call-Failure-Code.
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length, Action, Reason and optional
Description String fields.
Action
The Action octet indicates what action the calling implementation
is taking after a failed call.
The Action octet can have the following values:
0 - No retry
1 - Will retry same number
2 - Will retry next number in list
Reason
The reason code byte can have the following values:
0 - unlisted reason
1 - no dial tone
2 - no answer
3 - no carrier
4 - unable to negotiate LCP
5 - unable to authenticate
6 - call canceled
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Description String
The Description String field is optional. If the length field
indicates that the option continues past the Reason field, then
the remaining octets in the option are the Description String.
This is an ASCII string. The content of the field is
implementation dependent. An implementation MAY ignore the
Description String field.
7.9. Time-Until-Retry
Description
The Time-Until-Retry option MAY be used in Nak's of Call-Response,
Callback-Response, and Link-Drop-Query-Response datagrams with the
Response Code set to Request-Nak. This option is used to inform
the peer that the previous Request will not be accepted until the
time indicated by the option. This retry time only applies to the
link type or types being requested.
A summary of the Time-Until-Retry BAP Option format is shown below.
The fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Time (seconds)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Time (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
8 for Time-Until-Retry.
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length and Time fields.
Time
The Time field is 4 octets in length (network byte order), and
indicates the time in seconds before the Request being Nak'd may
be retried.
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7.10. Link-Discriminator
Description
The Link-Discriminator option MAY be used in a Link-Drop-Request
or a Link-Drop-Query-Request datagram. This option is used to
inform the peer of which link will be dropped. If the peer did
not send the LCP Link Discriminator Configuration Option during
the LCP link negotiation phase, then this option MUST NOT be sent.
A summary of the Link-Discriminator BAP Option format is shown below.
The fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Link Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
9 for Time-Until-Retry.
Length
The Length field is one octet, and indicates the length of this
BAP Option including the Type, Length and Link Discriminator
fields.
Link Discriminator
The Link Discriminator field is 2 octets in length. It contains
the Link Discriminator that was contained in the LCP Link-
Discriminator Configuration Option sent by the peer.
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Appendix
List of BAP datagrams and associated options.
datagram mandatory options possible options
-------- ----------------- ----------------
Call-Request Link-Type No-Phone-Number
Call-Add-Code
Call-Response Phone-Number
Nak-Code
Time-Until-Retry
Link-Types
Callback-Request Link-Type Phone-Number
Call-Add-Code
Callback-Response Nak-Code
Time-Until-Retry
Link-Types
Link-Drop-Request Link-Type Link-Discriminator
Drop-Code
Link-Drop-Response
Link-Drop-Query-Request Link-Type Link-Discriminator
Drop-Code
Link-Drop-Query-Response
Bundle-Drop-Request Drop-Code
Bundle-Drop-Response
Link-Type-Request
Link-Type-Response Link-Types
Available-Link-Indication Link-Type
Available-Link-Response
Call-Failure-Indication Call-Failure-Code Phone-Number
Link-Type
Call-Failure-Response
History of BACP
The first version of BACP was written by Craig Richards of Shiva
Corporation. This version was enhanced and improved by the MPCP
Working Group, a collaborative effort of 3Com, Ascend, Bay Networks,
Cisco, Microsoft, Shiva, US Robotics and Xylogics.
Acknowledgements
Kevin Smith of Ascend for his contributions based on his work on the
MP+ Specification. Gerry Meyer and Robert Myhill of Shiva for their
early comments and improvements. Andy Nicholson of Microsoft for his
improvements to the bandwidth management scheme. Dana Blair and Andy
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Valencia of Cisco, Cheng Chen and Dan Brennan of 3Com for their good
ideas as part of the MPCP Working Group. All of the members of the
MPCP working group for their ability to work with their competitors
with enthusiasm to produce a better protocol for the industry.
Security Considerations
Security issues are not discussed in this memo.
References
[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD
51, RFC 1661, Daydreamer, July 1994.
[2] Sklower, Lloyd, McGregor & Carr, "The PPP Multilink Protocol",
RFC 1717, PPP Extensions Working Group, Work in Progress.
Chair's Address
The working group can be contacted via the current chair:
Fred Baker
Cisco Systems
519 Lado Drive
Santa Barbara, California 93111
VOICE +1 408 526 4257
FAX +1 805 681-0115
EMail: fbaker@cisco.com
Editors' Addresses
Craig Richards
Shiva Corporation
63 Third Avenue
Burlington, MA 01803
VOICE +1 617 270 8419
FAX +1 617 270 8599
EMail: crich@shiva.com
Kevin Smith
Ascend Communications, Inc.
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1275 Harbor Bay Parkway
Alameda, CA 94501
CA
EMail: kevin@ascend.com
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Table of Contents
1. Introduction .......................................... 1
1.1 Specification of Requirements ................... 1
1.2 Terminology ..................................... 1
2. New LCP Configuration Option - Link Discriminator ..... 2
3. BACP Packet Format .................................... 3
4. BACP Configuration Options ............................ 3
4.1 Datagrams-Supported ............................. 4
4.2 Base-Phone-Number ............................... 5
5. BAP Overview .......................................... 6
5.1 Link Management ................................. 6
5.2 Bandwidth Management ............................ 6
6. BAP Packets ........................................... 8
6.1 BAP Datagram Format ............................. 9
6.1.1 Call-Request .................................... 11
6.1.2 Call-Response ................................... 11
6.1.3 Callback-Request ................................ 12
6.1.4 Callback-Response ............................... 12
6.1.5 Link-Drop-Request ............................... 12
6.1.6 Link-Drop-Response .............................. 13
6.1.7 Link-Drop-Query-Request ......................... 13
6.1.8 Link-Drop-Query-Response ........................ 13
6.1.9 Bundle-Drop-Request ............................. 13
6.1.10 Bundle-Drop-Response ............................ 14
6.1.11 Link-Type-Request ............................... 14
6.1.12 Link-Type-Response .............................. 14
6.1.13 Available-Link-Indication ....................... 14
6.1.14 Available-Link-Response ......................... 15
6.1.15 Call-Failure-Indication ......................... 15
6.1.16 Call-Failure-Response ........................... 15
7. BAP Datagram Options .................................. 15
7.1 Link-Type ....................................... 16
7.2 Link-Types ...................................... 17
7.3 Phone-Number .................................... 18
7.3.1 Phone-Number Sub-Options ........................ 19
7.4 No-Phone-Number-Needed .......................... 20
7.5 Call-Add-Code ................................... 21
7.6 Nak-Code ........................................ 22
7.7 Drop-Code ....................................... 23
7.8 Call-Failure-Code ............................... 24
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7.9 Time-Until-Retry ................................ 26
7.10 Link-Discriminator .............................. 27
Appendix - List of BAP datagrams and associated options ...... 28
ACKNOWLEDEMENTS .............................................. 28
SECURITY CONSIDERATIONS ...................................... 29
REFERENCES ................................................... 29
CHAIR'S ADDRESS .............................................. 29
EDITORS'S ADDRESSES .......................................... 29
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