PPP Working Group Craig Richards
Internet Draft Shiva Corporation
expires August 1996 Kevin Smith
Ascend Communications, Inc.
February 1996
The PPP Bandwidth Allocation Protocol (BAP)
The PPP Bandwidth Allocation Control Protocol (BACP)
draft-ietf-pppext-bacp-01.txt
Status of this Memo
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Group of the Internet Engineering Task Force (IETF). Comments should
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Abstract
This document proposes a method to manage the dynamic bandwidth
allocation of implementations supporting the PPP multilink protocol
[2]. This is done by defining the Bandwidth Allocation Protocol
(BAP), as well as its associated control protocol, the Bandwidth
Allocation Control Protocol (BACP). BAP can be used to manage the
number of links in a multilink bundle. BAP defines 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 have had
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, they also provide a flexible yet robust way of
managing bandwidth between 2 peers. BAP does this by defining Call-
Control packets and a protocol that allows peers to co-ordinate the
actual bandwidth allocation and de-allocation. Phone numbers may be
passed in the Call-Control packets to minimize 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
capability of logging the error, including the contents of
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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
Implementations MUST implement LCP as defined in [1]. LCP MUST be in
the Network-Layer Protocol phase before BACP can be negotiated.
2.1. 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. BAP uses the link discriminator to
differentiate the various links in a multilink bundle. If this
option is negotiated on one link of a bundle, 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.
When the Link Discriminator is sent in a BAP packet, it is the
peer's Link Discriminator which is sent.
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
23 for Link Discriminator option.
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Length
The Length field is one octet, and indicates the Length of this
LCP Option including the Type, Length, and Link Discriminator
fields.
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. The Link Discriminator for a link MUST be
unique among the Link Discriminators assigned by this endpoint for
this bundle. The Link Discriminator SHOULD be assigned in a
sequential, monotonically increasing manner. It MUST be unique
among the Link Discriminators assigned by this endpoint for this
bundle.
3. BACP Operation
BACP uses the same packet exchange mechanism as the Link Control
Protocol defined in [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 8071 (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
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defined in the next section. BACP uses only those options
defined in the BACP Configuration Options section. Any other
option SHOULD not be sent and SHOULD be silently discarded if
received.
3.1. BACP Configuration Options
BACP Configuration Options allow negotiation of 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 separate set of Options.
Current values of BACP Configuration Options are assigned as follows:
1 Datagrams-Supported
2 Base-Phone-Number
3.2. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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
corresponding Response datagram. Bit 0 of the Datagrams Supported
field corresponds to bit 16 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.
3.3. Base-Phone-Number
Description
An implementation informs its peer of its base phone number by
sending the Base-Phone-Number option in the Config-Request packet.
The base phone number indicates the primary phone number used to
call that implementation. The base phone number MAY be used with
or without the BAP Phone-Number Option to indicate the phone
number to be used for setting up additional links. Each endpoint
MAY include this option in the Config-Request. An implementation
that originated the call to create the multilink bundle SHOULD
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include this option if it intends to receive calls during the
lifetime of the bundle (e.g., originate a Callback-Request or Ack
a Call-Request).
If an answering implementation does not receive the Base-Phone-
Number Option in a Config-Request, it SHOULD set the default to no
base phone number for its peer; however, it MAY use a
preconfigured default of the Calling Party ID if received from the
phone network. If an originating implementation does not receive
the Base-Phone-Number Option in a Config-Request, it SHOULD set
the default to the phone number used to make the call. If the
multilink bundle is initiated with a callback connection, then the
callback phone number MAY be used as the default Base Phone
Number.
Since this configuration option is used to inform the peer, and
can not be negotiated, an implementation SHOULD NOT transmit this
option in a Config-Nak or Config-Rej packet and MUST include this
option in a Config-Ack in response to a Config-Request including
this option.
A summary of the Base-Phone-Number 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 | Base Phone Number...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
2 for Base-Phone-Number.
Length
The Length field is one octet and is binary encoded. It indicates
the Length of this BACP Option in bytes including the Type, Length
and Base Phone Number fields.
Base Phone Number
The Base Phone Number field is an ASCII string consisting of
digits in the range 0-9 inclusive and SHOULD denote a valid phone
number. It MAY 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
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line, long distance prefix, national destination code, country
prefix and/or country code, as well as the phone number to be
dialed. It MAY be similar to the format of a phone number used
when performing a callback connection.
4. BAP Operation
4.1. Link Management
BAP defines packets, parameters and negotiation procedures to allow
two endpoints to negotiate gracefully adding and dropping links from
a multilink bundle. An implementation can:
Request permission to add a Link to a bundle (Call-Request)
Request that the peer add a link to a bundle via a callback
(Callback-Request)
Notify the peer that it is going to drop a link from a bundle
(whether the peer agrees or not) (Link-Drop-Request)
Negotiate with the peer to drop a link from a bundle (this implies
that the peer can refuse) (Link-Drop-Query-Request)
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 its peer
to originate the call for the new link. The implementation receiving
a Call- or Callback-Request MUST respond with a Call- or Callback-
Response with a valid Response Code.
After BACP reaches the opened state, either peer MAY request that a
link be dropped from the bundle by sending a BAP Drop-Link-Request or
a Drop-Link-Query-Request. A Drop-Link-Request packet is sent if the
implementation wishes to force dropping a link with no negotiation
and a Drop-Link-Query-Request packet is sent if the implementation
wishes to negotiate dropping a link with its peer. The
implementation receiving a Drop-Link-Request or Drop-Link-Query-
Request MUST respond with a Drop-Link-Response or a Drop-Link-Query-
Response. The Drop-Link-Response MUST have the Response Code set to
Request-Ack.
A Link-Drop-Request is used to inform the peer that the
implementation is going to drop a link from the multilink bundle.
Originating a Link-Drop-Request is an optional part of BAP. A system
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implementing BAP MUST support receiving a Link-Drop-Request from its
peer. The peer MUST reply to a Link-Drop-Request with a Link-Drop-
Response with the Response Code set to Request-Ack. No other
response is allowed. The endpoint that originates a Link-Drop-
Request 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.
A Link-Drop-Query-Request is used to inquire if the peer agrees to
drop a link from the current multilink bundle. Origination of a
Link-Drop-Query-Request is an optional part of BAP. A system
implementing BAP MUST support the receipt of Link-Drop-Query-Request
from its peer. When an implementation wants to negotiate dropping a
link, it MUST transmit a Link-Drop-Query-Request. When an
implementation receives a Link-Drop-Query-Request, it MUST base its
response on its transmit heuristics or on its configuration (e.g., 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). If the implementation receiving a Link-Drop-Query-Request
is not monitoring its transmit data and is not configured otherwise,
it MUST accept the request to drop a link.
4.2. Bandwidth Management
BAP allows two peer implementations to manage the bandwidth available
to the protocols using the multilink bundle by negotiating when to
add and drop links (See Link Management). The Bandwidth Allocation
Protocol does not include an algorithm for determining when to add
and remove links in a multilink bundle. These algorithms are left to
the implementors. 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.
This section defines two important Types of BOD: Resource BOD and
Throughput BOD. This does not preclude other Types of BOD from being
implemented (e.g., Time of Day). The rest of this specification
refers to actions to take when implementing these types of BOD.
Throughput BOD refers to BOD decisions made based 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.
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Resource BOD refers to BOD decisions based on the resources (e.g.,
physical port, B-channel, etc.) available to an implementation. For
example, an implementation might remove a link from a multilink
bundle to answer an incoming voice call, or might add a link when a
line becomes free due to the termination of a separate PPP call on
another port. A system implementing BACP/BAP MAY support neither,
either, both or some other Type of Bandwidth On Demand. Regardless
of the Type of BOD implemented, if it uses BAP it must use the
procedures in this specification for adding and dropping links.
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 support resource BOD
management by its peer (i.e., support receipt of Link-Drop-Request).
An implementation MUST use a Link-Drop-Request to remove a link due
to Resource BOD. An implementation sends a Link-Drop-Request to
inform the peer that it 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 or if the implementation does not receive a response (e.g.,
after 2 retransmissions). An example of this is when there is an
incoming call on a link in use by the multilink bundle, and the link
must be dropped quickly to answer the incoming call 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 (i.e., receipt of Link-Drop-Query-
Request). 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 to inquire if the peer agrees 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 (if it implements Throughput BOD)
or on its configuration (e.g., 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). If the implementation
receiving a Link-Drop-Query-Request is not monitoring its transmit
data and is not configured otherwise, it MUST accept the request to
drop a link. It MUST NOT base its response on its receive data
heuristics. 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.
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A BAP implementation may monitor its transmit traffic, both transmit
and receive traffic, or choose not to monitor traffic in either
direction. Server systems SHOULD implement bi-directional monitoring
and single-user dialin clients MAY implement any type of monitoring.
This will allow client BOD implementations that require minimal end-
user configuration.
4.3. 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. An
implementation MAY set a timer for the Link-Drop-Request packet. The
value of this timer SHOULD depend on the type and speed of the link
or links in use. Upon expiration of this timer, the implementation
MUST retransmit the same request or indication, with the identical
identification number unless the implementation has exceeded the
maximum number of retransmissions it supports for this packet. If
the number of retransmissions exceeds the number supported by the
implementation for this packet, the implementation MAY take
appropriate recovery action. For example, if no response to a Link-
Drop-Request is received after 2 retransmissions, an implementation
MAY initiate dropping the link by sending an LCP Terminate-Request
for that link.
This procedure will insure that the peer receives the proper request
or indication even if a packet 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 this is not
a new request or indication packet.
Since BAP packets help determine the amount of bandwidth available to
an implementation, PPP SHOULD give them 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.
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4.4. Race Conditions
A race condition can occur if both implementations send a Call-
Request, Callback-Request, Link-Drop-Request, or Link-Drop-Query-
Request at the same time. These race conditions should be solved as
follows:
If each implementation sends a Call-Request (or Callback-Request)
at the same time, the implementation with the lowest username
value SHOULD be favored. A username value is compared by
converting the ASCII bytes into hexadecimal octets to create a
number. If both implementations are using the same username, then
the lowest Multilink Endpoint Discriminator SHOULD be favored.
Once again, each Multilink Endpoint Discrininators is first
converted into hexadecimal octets starting with the Class octet,
before being compared. This means that the favored peer's request
SHOULD be acked by its peer, and the unfavored peer's request
SHOULD be naked by the favored peer.
If each implementation sends a Link-Drop-Request at the same time,
the same scheme SHOULD be used as for Call-Requests.
If each implementation sends a Link-Drop-Query-Request at the same
time, the same scheme SHOULD be used as for Call-Requests.
4.5. BAP Datagram Format
Description
Before any BAP packets may be communicated, PPP MUST reach the
Network-Layer Protocol phase, and BACP 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 0071 (Bandwidth Allocation Protocol).
The maximum length of a BAP packet transmitted over a PPP link 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.
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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.
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. This
field is coded in binary coded hexadecimal.
01 Call-Request
02 Call-Response
03 Callback-Request
04 Callback-Response
05 Link-Drop-Request
06 Link-Drop-Response
07 Link-Drop-Query-Request
08 Link-Drop-Query-Response
09 Bundle-Drop-Request
0A Bundle-Drop-Response
0B Link-Type-Request
0C Link-Type-Response
0D Available-Link-Indication
0E Available-Link-Response
0F Call-Failure-Indication
10 Call-Failure-Response
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The various types of BAP datagrams are explained in the following
sections.
Identifier
The Identifier field is one octet and is binary coded. It 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 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.
It is binary encoded. 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 is
binary coded and can have the following values:
00000000 Request-Ack
00000001 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.
4.5.1. 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 request to add another link to the bundle and
give the peer a chance to inform the implementation of the phone
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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.
4.5.2. Call-Response
An implementation MUST transmit a Call-Response datagram in response
to a received Call-Request datagram. If the Call-Request is
acceptable, the Call-Response MUST have a Response Code of Request-
Ack; otherwise the Response Code MUST 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-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.
4.5.3. 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 request 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.
4.5.4. Callback-Response
An implementation MUST transmit a Callback-Response datagram in
response to a received Callback-Request datagram. If the Callback-
Request is acceptable, the Callback-Response MUST have a Response
Code of Request-Ack; otherwise the Response Code MUST be Request-Nak.
In a Callback-Response packet with a Response Code of "Request-Nak",
the implementation MUST include the Nak-Code option and MAY include
the Time-Until-Retry option.
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4.5.5. 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 may be due to Resource BOD decisions. The options field MUST
include the Link-Type option and MAY include the Drop-Code option.
If the Link-Discriminator was negotiated in LCP, it MUST be included.
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. The
implementation SHOULD initiate tear down of the 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. An implementation MAY
drop a link from the multilink bundle without receiving a response
from its peer (e.g., if there are time constraints).
4.5.6. Link-Drop-Response
An implementation transmits 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.
4.5.7. Link-Drop-Query-Request
An implementation that determines that a link is no longer needed and
wishes to negotiate dropping it (e.g., based on a throughput BOD
decision), MUST transmit a Link-Drop-Query-Request packet. The
options field MUST include the Link-Type option and MAY include the
Drop-Code option. If the Link-Discriminator was negotiated in LCP,
it MUST be included.
Upon reception of a Link-Drop-Query-Request, an implementation MUST
transmit a Link-Drop-Query-Response datagram. The Response-Code will
be Request-Ack if it agrees to drop the link, or Request-Nak if it
does not agree to drop the link. After the receipt of a Link-Drop-
Query-Response 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 on the
designated link.
4.5.8. 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
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implementation agrees (e.g., based on its throughput BOD algorithm)
to reduce the bandwidth of the multilink bundle, then the Response
Code MUST be set to Request-Ack. Otherwise, the Response Code MUST
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.
4.5.9. 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, an implementation MUST
transmit a Bundle-Drop-Response with a Response Code of Request-Ack.
After the receipt 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.
4.5.10. 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.
4.5.11. 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.
4.5.12. Link-Type-Response
An implementation MUST transmit 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. An implementation MUST
include the Link-Types option in this datagram informing the peer of
the link types supported by this implementation.
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4.5.13. 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" and if both peers support the
Available-Link-Indication packet (as negotiated in BACP), that
implementation enters a link denied state. While an implementation
is in a link denied state, if a link of the type previously requested
becomes available and if the implementation is ready to make the link
available, 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. The Available-Link-Indication datagram MUST include the
Link-Type.
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.
4.5.14. 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.
4.5.15. 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.
4.5.16. 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.
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5. 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. When there are multiple BAP Options in one BAP packet, the
options MAY be transmitted in any order.
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
Datagram Option. This field is binary coded Hexadecimal. The
following options are currently defined:
01 Link-Type
02 Link-Types
03 Phone-Number
04 No-Phone-Number-Needed
05 Call-Add-Code
06 Nak-Code
07 Drop-Code
08 Call-Failure-Code
09 Time-Until-Retry
0A 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.
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5.1. Link-Type
Description
This option indicates the type of link indicated 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link Type (continued)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link Type (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
01 for Link-Type.
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 8 octets in length. Bit
0 of the Link Type field corresponds to bit 16 of the Link-Type
BAP Option as described above. If a bit is set, it indicates
support of the corresponding link type:
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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 ISDN PRI H11 Channel
16 ISDN PRI H12 Channel
17-46 ISDN Multirate Channel, n=2-30
47 Switched 56 (4-wire)
48 Switched 56 over T1 with Robbed Bit Signaling
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.
5.2. 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
can have multiple bits set instead of instead of 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link Types (continued)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link Types (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
02 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 8 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.
5.3. Phone-Number
Description
This option is used to transmit an implementation's phone number
to its peer. For example, this phone number could 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 SHOULD not be sent.
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
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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 and if the Response Code is Request-
Ack. It MAY appear in the Call-Failure-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
03 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.
01 Unique Digits
02 Subscriber Number
03 National Destination Code
04 Country Code
05 Phone Number Sub Address
5.3.1. 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
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will be 5). This field is required.
The purpose of the unique digits sub-option is to aid the
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.
Subscriber 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 separate sub-options. This field is
an ASCII string and MUST contain only ASCII characters 0-9
inclusive (valid phone number digits). This field is required.
National Destination Code
This field is the national destination code (as defined in ITU-T
Recommendation E.164) of the port that should be called by the
peer. This field is an ASCII string and only contains a valid
national destination code. This field is optional. If the
National Destination Code is not included, the receiving endpoint
SHOULD assume that it is the same as the first link.
Country Code
This field is the country code (as defined in ITU-T Recommendation
E.164) of the port that should be called by the peer. This field
is an ASCII string and only contains a valid country code. This
field is optional. If the Country Code is not included, the
receiving endpoint SHOULD assume that it is the same as the first
link.
Phone Number Sub Address
This field is the sub address of the port to be called by the
peer. This sub-option SHOULD only be used for an ISDN call. This
field is an ASCII string and only contains valid phone number
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digits. This field is optional.
5.4. No-Phone-Number-Needed
Description
The No-Phone-Number option indicates that the calling
implementation is already configured with the phone number of its
multilink peer and the peer MUST NOT include the Phone Number
option in the response. This may be for security reasons, for
configuration 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
04 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.
5.5. 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.
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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
05 for Call-Add-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 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
6 - configuration change
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.
5.6. 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-
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Response with a Response Code of Request-Nak and MAY be included
in a Drop-Link-Query-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)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
06 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
6 - multilink bundle cannot drop below this minimum number
7 - dropping channel would cause thrashing in the local algorithm
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.
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5.7. 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.
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
07 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 - higher priority incoming call
2 - higher priority outgoing call
3 - transmit data dropped below threshold
4 - receive data dropped below threshold
5 - transmit queue dropped below threshold
6 - user initiated disconnect
7 - error threshold exceeded
Description String
The Description String field is optional. If the length field
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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.
5.8. Call-Failure-Code
Description
This option is used to indicate the action that will be taken
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
08 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 try next number in list
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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
7 - Q.931 Cause Information Element follows
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.
If the call failure is caused by receiving a Q.931
Disconnect/Release/ Release Complete from the network, thie field
SHOULD include the Cause Code received in the Cause Information
Element.
5.9. Time-Until-Retry
Description
The Time-Until-Retry option MAY be used in 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 it MUST NOT send a Request equivalent to the Request
being Nak'ed for the time period indicated in this option. This
retry time only applies to the link type or types being requested.
When an implementation receives this field in a Call-Response,
Callback-Response or a Link-Drop-Query-Response datagram with the
Response Code set to Request-Nak, it MUST NOT retry the same type
of Request again for the indicated time period.
A summary of the Time-Until-Retry 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 | Time (seconds)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Time (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
09 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.
5.10. Link-Discriminator
Description
The Link-Discriminator option SHOULD 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type
0A for Link-Discriminator
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 fields.
datagram mandatory fields allowed 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 Nak-Code
Time-Until-Retry
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
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improvements to the bandwidth management scheme. Dana Blair and Andy
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: fred@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
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Ascend Communications, Inc.
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 .......................... 2
2.1 Link Discriminator .............................. 2
3. BACP Operation ........................................ 3
3.1 BACP Configuration Options ...................... 4
3.2 Datagrams-Supported ............................. 4
3.3 Base-Phone-Number ............................... 5
4. BAP Operation ......................................... 7
4.1 Link Management ................................. 7
4.2 Bandwidth Management ............................ 8
4.3 BAP Packets ..................................... 10
4.4 Race Conditions ................................. 11
4.5 BAP Datagram Format ............................. 11
4.5.1 Call-Request .................................... 13
4.5.2 Call-Response ................................... 14
4.5.3 Callback-Request ................................ 14
4.5.4 Callback-Response ............................... 14
4.5.5 Link-Drop-Request ............................... 15
4.5.6 Link-Drop-Response .............................. 15
4.5.7 Link-Drop-Query-Request ......................... 15
4.5.8 Link-Drop-Query-Response ........................ 15
4.5.9 Bundle-Drop-Request ............................. 16
4.5.10 Bundle-Drop-Response ............................ 16
4.5.11 Link-Type-Request ............................... 16
4.5.12 Link-Type-Response .............................. 16
4.5.13 Available-Link-Indication ....................... 17
4.5.14 Available-Link-Response ......................... 17
4.5.15 Call-Failure-Indication ......................... 17
4.5.16 Call-Failure-Response ........................... 17
5. BAP Datagram Options .................................. 18
5.1 Link-Type ....................................... 19
5.2 Link-Types ...................................... 20
5.3 Phone-Number .................................... 21
5.3.1 Phone-Number Sub-Options ........................ 22
5.4 No-Phone-Number-Needed .......................... 24
5.5 Call-Add-Code ................................... 24
5.6 Nak-Code ........................................ 25
5.7 Drop-Code ....................................... 27
5.8 Call-Failure-Code ............................... 28
Richards & Smith expires August 1996 [Page ii]
RFC DRAFT PPP BACP February 1996
5.9 Time-Until-Retry ................................ 29
5.10 Link-Discriminator .............................. 30
Appendix - List of BAP datagrams and associated fields ....... 32
ACKNOWLEDEMENTS .............................................. 32
SECURITY CONSIDERATIONS ...................................... 33
REFERENCES ................................................... 33
CHAIR'S ADDRESS .............................................. 33
EDITORS'S ADDRESSES .......................................... 33
Richards & Smith expires August 1996 [Page iii]
