RFC relevance of indicate

As per Relevance of the word indicate, we have this rfc below:

Network Working Group C.
Request for Comments: 2125 Shiva
Category: Standards Track K.
Ascend Communications, Inc
March 1997

The PPP Bandwidth Allocation Protocol (BAP
The PPP Bandwidth Allocation Control Protocol (BACP

Status of this

This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited

This document proposes a method to manage the dynamic
allocation of implementations supporting the PPP multilink
[2]. This is done by defining the Bandwidth Allocation
(BAP), as well as its associated control protocol, the
Allocation Control Protocol (BACP). BAP can be used to manage
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
regarding managing bandwidth during a multilink connection

Table of

1. Introduction .......................................... 2
1.1 Specification of Requirements ................... 2
1.2 Terminology ..................................... 3
2. New LCP Configuration Option .......................... 3
2.1 Link Discriminator .............................. 3
3. BACP Operation ........................................ 4
4. BACP Configuration Options ............................ 5
4.1 Favored-Peer .................................... 5
5. BAP Operation ......................................... 7
5.1 Link Management ................................. 7
5.2 Bandwidth Management ............................ 8
5.3 BAP Packets ..................................... 8
5.4 Race Conditions ................................. 9
5.5 BAP Datagram Format ............................. 9
5.5.1 Call-Request .................................... 12
5.5.2 Call-Response ................................... 12

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RFC 2125 PPP BACP March 1997

5.5.3 Callback-Request ................................ 13
5.5.4 Callback-Response ............................... 13
5.5.5 Link-Drop-Query-Request ......................... 13
5.5.6 Link-Drop-Query-Response ........................ 13
5.5.7 Call-Status-Indication .......................... 14
5.5.8 Call-Status-Response ............................ 14
6. BAP Datagram Options .................................. 14
6.1 Link-Type ....................................... 15
6.2 Phone-Delta ..................................... 17
6.2.1 Phone-Delta Sub-Options ......................... 18
6.3 No-Phone-Number-Needed .......................... 19
6.4 Reason .......................................... 20
6.5 Link-Discriminator .............................. 21
6.6 Call-Status ..................................... 21
Appendix - List of BAP datagrams and associated fields ....... 23
ACKNOWLEDEMENTS .............................................. 23
SECURITY CONSIDERATIONS ...................................... 23
REFERENCES ................................................... 24
CHAIR'S ADDRESS .............................................. 24
EDITORS'S ADDRESSES .......................................... 24

1.

As PPP multilink implementations become increasingly common, there
a greater need for some conformity in how to manage bandwidth
such links. BACP and BAP provide a flexible yet robust way
managing bandwidth between 2 peers. BAP does this by defining Call
Control packets and a protocol that allows peers to co-ordinate
actual bandwidth allocation and de-allocation. Phone number
may be passed in the Call-Control packets to minimize the end user'
configuration

1.1. Specification of

In this document, several words are used to signify the
of the specification. These words are often capitalized

MUST This word, or the adjective "required", means that
definition is an absolute requirement of the specification

MUST NOT This phrase means that the definition is an
prohibition of the specification

SHOULD This word, or the adjective "recommended", means that
may exist valid reasons in particular circumstances
ignore this item, but the full implications must
understood and carefully weighed before choosing
different course

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MAY This word, or the adjective "optional", means that
item is one of an allowed set of alternatives.
implementation which does not include this option MUST
prepared to interoperate with another implementation
does include the option

1.2.

This document frequently uses the following terms

peer The other end of the point-to-point

silently
This means the implementation discards the packet
further processing. The implementation SHOULD provide
capability of logging the error, including the contents of
silently discarded packet, and SHOULD record the event in
statistics counter

BOD (bandwidth on demand
BOD refers to the ability of a system to allocate and
links in a multilink system to change the bandwidth of
multilink bundle. This may be done in response to
line conditions and it also may be done in response to
resource conditions. In either case, changing
dynamically during a multilink connection is referred to
BOD

2. New LCP Configuration

Implementations MUST implement LCP as defined in [1]. LCP MUST be
the Network-Layer Protocol phase before BACP can be negotiated

2.1. Link

This LCP Configuration Option is used to declare a
discriminator for the link that the option is sent over.
option MUST be negotiated by LCP on every link. BAP uses the
discriminator to differentiate the various links in a
bundle. Each link in a multilink bundle MUST have a
discriminator. The discriminator is independent for each peer,
each link may have 2 different LCP Link Discriminator values,
for each peer. When the Link Discriminator is sent in a
packet, the transmitter sends the Link Discriminator Option
received from its peer in the peer's LCP Configure Request packet

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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

23 for Link Discriminator option

4

Link

The Link Discriminator field is 2 octets in Length, and
contains a unique identifier used to indicate a particular link
a multilink bundle. The Link Discriminator for a link MUST
unique among the Link Discriminators assigned by this endpoint
this bundle. The Link Discriminator MAY be assigned in
sequential, monotonically increasing manner

3. BACP

BACP uses the same packet exchange mechanism as the Link
Protocol defined in [1]. BACP packets MUST NOT be exchanged
PPP has reached the Network-Layer Protocol phase. BACP
received before this phase is reached should be silently discarded

BACP is negotiated once per multilink bundle. If BACP is
on any of the links in a multilink bundle, it is opened for all
the links in the bundle

The Bandwidth Allocation Control Protocol is exactly the same as
Link Control Protocol [1] with the following exceptions

Data Link Layer Protocol

Exactly one BACP packet is encapsulated in the
field of PPP Data Link Layer frames where the Protocol
indicates Type hex c02b (Bandwidth Allocation
Protocol).

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Code

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
as unrecognized and should result in Code-Rejects

Configuration Option

BACP has a distinct set of Configuration Options, which
defined in the next section

4. BACP Configuration

BACP Configuration Options allow negotiation of desirable
parameters. These options are used in Config-Request, Config-Ack
Config-Nak, and Config-Reject packets. BACP uses the
Configuration Option format defined for LCP [1], with a seperate
of Options

Current values of BACP Configuration Options are assigned as follows

1 Favored-

4.1. Favored-

This Configuration Option is used to determine which peer
favored in the event of a race condition in which 2
simultaneously transmit the same BAP request. Each
negotiates a 4 octet magic number, which is
negotiated when the 2 Magic-Numbers are different. The
peer is the peer that transmits the lowest Magic-Number in
Favored-Peer Configuration Option

The Favored-Peer Configuration Option MUST be implemented

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BACP will usually be negotiated after only one link of a
bundle has reached the Network-Layer Protocol phase. In
situation, it is acceptable for the peer that initiated
connection to use a Magic-Number of 1, and the peer that
to the connection to use a Magic-Number of 0xFFFFFFFF. If
multilink bundle has been established with links that
originated by each peer, or if it is not clear which peer
initiated a link (on a leased line, for example), then a
number MUST be used for the Magic-Number. Refer to
description of the LCP Magic-Number Configuration Option in [1]
for an explanation of how to create a useful random number

When a Configure-Request is received with a Favored-
Configuration Option, the received Magic-Number is compared
the Magic-Number of the last Configure-Request sent to the peer
If the two Magic-Numbers are different, then the Favored-
negotiation has been successful, and the Favored-Peer
SHOULD be acknowledged. If the two Magic-Numbers are equal,
Configure-Nak MUST be sent specifying a different Magic-
value. A new Configure-Request SHOULD NOT be sent to the
until normal processing would cause it to be sent (that is,
a Configure-Nak is received or the Restart timer runs out).

A summary of the Favored-Peer Option format is shown below.
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 | Magic-
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Magic-Number (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

1 for Favored-

6

Magic-

The Magic-Number field is four octets, and indicates a
which is very likely to be unique to one end of the link.
Magic-Number of zero is illegal and MUST always be Nak'd

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5. BAP

5.1. Link

BAP defines packets, parameters and negotiation procedures to
two endpoints to negotiate gracefully adding and dropping links
a multilink bundle. An implementation can

o Request permission to add a Link to a bundle (Call-Request

o Request that the peer add a link to a bundle via a
(Callback-Request

o Negotiate with the peer to drop a link from a bundle (
implies that the peer can refuse) (Link-Drop-Query-Request

After BACP reaches the opened state, either peer MAY request
another link be added to the bundle by sending a BAP Call-
Callback-Request packet. A Call-Request packet is sent if
implementation wishes to originate the call for the new link, and
Callback-Request packet is sent if the implementation wishes its
to originate the call for the new link. The implementation
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
link be dropped from the bundle. A BAP Link-Drop-Query-
packet is sent to the peer to negotiate dropping a link. The
MUST respond with a Link-Drop-Query-Response. If the peer
agreeable to dropping the link the implementation MUST issue an
Terminate-Request to initiate dropping the link

If an implementation wishes to force dropping a link
negotiation, it should simply send an LCP Terminate-Request packet
the link (without sending any BAP Link-Drop-Query-Request).

After an LCP Terminate-Request is sent an implementation SHOULD
transmitting data packets on that link, but still continue to
and process data packets normally until receipt of a Terminate-
from the peer. The receiver of an LCP Terminate-Request SHOULD
transmitting packets before issuing the Terminate-Ack.
procedure will insure that no data is lost in either direction

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5.2. Bandwidth

BAP allows two peer implementations to manage the bandwidth
to the protocols using the multilink bundle by negotiating when
add and drop links (See Link Management). Use of the
features of BAP makes it unnecessary to require a 'common'
for determining when to add and remove links in a multilink bundle

BOD decisions can be based on link utilization. A BAP
may monitor its transmit traffic, both transmit and receive traffic
or choose not to monitor traffic in either direction. If a
system implements bi-directional monitoring, it will allow
operation with a client that does not monitor traffic in
direction, which will minimize the end-user's configuration. When
implementation decides that it is time to remove a link due
traffic monitoring, it MUST transmit a Link-Drop-Query-Request
inquire if the peer agrees to drop a link from the current
bundle. When an implementation receives a Link-Drop-Query-Request
it SHOULD base its response on the traffic it is monitoring. It
NOT base its response solely on its receive data heuristics

The operation of the Link-Drop-Query-Request and -Response
causes a link in a multilink bundle to be left up as long as
implementation that is monitoring link utilization determines that
is necessary

BOD decisions can also be based on the resources (e.g.,
port, B-channel, etc.) available to an implementation. For example
an implementation might remove a link from a multilink bundle
answer an incoming voice call, or might add a link when a
becomes free due to the termination of a separate PPP call on
port. An implementation MUST use an LCP Terminate-Request to
a link due to a resource condition

5.3. BAP

All of the BAP Request and Indication packets require a
packet in response before taking any action

An implementation MUST set a timer when sending a Request
Indication packet. The value of this timer SHOULD depend on the
and speed of the link or links in use. Upon expiration of
timer, the implementation MUST retransmit the request or indication
with an identical identification number. This procedure will
that the peer receives the proper request or indication even if
packet is lost during transmission. If a response packet is lost
peer will realize that this is not a new request or
packet

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If the number of retransmissions exceeds the number supported by
implementation for this packet, the implementation MAY
appropriate recovery action. For example, if no response to a Link
Drop-Query-Request is received after 2 retransmissions,
implementation MAY initiate dropping the link by sending an
Terminate-Request for that link

Since BAP packets help determine the amount of bandwidth available
an implementation, PPP SHOULD give them priority over other
packets when transmitting. This will help insure the prompt
and removal of links in a multilink bundle. This is
important when adding links to a bundle due to bandwidth constraints

5.4. Race

In order to resolve race conditions, an implementation MUST
the BACP Favored-Peer Configuration Option

A race condition can occur if both implementations send a Call
Request, Callback-Request or Link-Drop-Query-Request at the
time. These race conditions should be solved as follows

If each implementation sends a Call-Request or Callback-Request
the same time, the implementation with the lowest BACP Favored
Peer Magic-Number value SHOULD be favored

If each implementation sends a Link-Drop-Query-Request at the
time, the same scheme SHOULD be used as for Call-Requests

5.5. BAP Datagram

Before any BAP packets may be communicated, PPP MUST reach
Network-Layer Protocol phase, and BACP MUST reach the
state

Exactly one BAP packet is encapsulated in the Information field
PPP Data Link Layer frames where the Protocol field indicates
hex c02d (Bandwidth Allocation Protocol).

Because ISDN Terminal Adapters sometimes are used to do
with a non-multilink aware client, BAP datagrams MUST NOT
compressed or encrypted. Otherwise, the ISDN TA may not be
to properly intercept BAP datagrams needed to control
multilink connection. This refers to compression of the
datagram; Address-and-Control-Field-Compression and Protocol
Field-Compression are allowed if properly negotiated

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The maximum length of a BAP packet transmitted over a PPP link
the same as the maximum length of the Information field of a
data link layer frame

Bandwidth Allocation Protocol datagrams can be catagorized
either Request, Indication or Response packets. Every Request
Indication datagram has a corresponding Response packet.
and Indication datagrams have a slightly different format
Response datagrams, as the Response datagrams include a
Code octet

All of the BAP datagrams MUST be supported by an implementation
However, that does not mean an implementation must support all
datagram actions. An implementation MAY send a Request-Rej to
Request that it does not implement

A summary of the Bandwidth Allocation Protocol datagram Request
Indication packet format is shown below. The fields are
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
packet format is shown below. The fields are transmitted from
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Type field is one octet and identifies the type of
datagram packet. Datagram types are defined as follows.
field is coded in binary coded hexadecimal

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01 Call-
02 Call-
03 Callback-
04 Callback-
05 Link-Drop-Query-
06 Link-Drop-Query-
07 Call-Status-
08 Call-Status-

The various types of BAP datagrams are explained in the
sections

The Identifier field is one octet and is binary coded. It aids
matching Requests and Indications with Responses. Call-Status
Indication packets MUST use the same Identifier as was used by
original Call-Request or Callback-Request that was used
initiate the call. All other Request or Indication packets
use a unique Identifier for each new Request or Indication.
Response packets MUST use the same Identifier as the Identifier
the Request or Indication packet being responded to. When re
transmitting a request or indication, the Identifier MUST be
same as the Identifier used on the previous transmission of
request or indication

The Length field is two octets and indicates the length of
packet including the Type, Identifier, Length and Options fields
It is binary encoded. Octets outside the range of the Length
should be treated as Data Link Layer padding and should be
on reception

Response

The Response Code is only present in Response datagrams. It
binary coded and can have the following values

00000000 Request-
00000001 Request-
00000010 Request-
00000011 Request-Full-

The Request-Ack Response Code is sent to indicate that the
or Indication command is valid and was successfully received by
implementation. The Request-Nak Response Code is sent to
that the Request command was received, but an implementation

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RFC 2125 PPP BACP March 1997

not want the requested action performed at this time. If
Response containing a Request-Nak Response Code is received,
original Request MAY be retried after an implementation
that sufficient time has elapsed. The Request-Rej Response
is sent to indicate that the Request command received by
implementation is not implemented (i.e., if reception of
particular request type is not supported by the peer.)
Request-Full-Nak Response Code is sent to indicate that
Request command was received, but an implementation does not
the requested action performed. The Request-Full-Nak is used
indicate that an implementation has reached the maximum (for
Call- or Callback-Request) or the minimum (for a Link-Drop-Query
Request) bandwidth configured or available for this
bundle. If a Response containing a Request-Full-Nak Response
is received, the original Request SHOULD NOT be retried until
total bandwidth of the multilink bundle has changed

The Data field is variable in length, and will usually contain
list of zero or more BAP Options that the sender desires
transmit. The format of BAP Options is described in a
chapter

5.5.1. Call-

Before originating a call to add another link to a multilink bundle
an implementation MUST transmit a Call-Request packet. This
inform the receiver of the request to add another link to the
and give the receiver a chance to inform the implementation of
phone number of a free port that can be called

The options field MUST include the Link-Type option. The
field MAY include the No-Phone-Number and/or the Reason options

Upon reception of a Call-Request, a Call-Response datagram MUST
transmitted

5.5.2. Call-

An implementation MUST transmit a Call-Response datagram in
to a received Call-Request datagram. If the Call-Request
acceptable, the Call-Response MUST have a Response Code of Request
Ack. The Phone-Delta option MUST be included in a Call-
packet with a Response Code of Request-Ack unless the Call-
included the No-Phone-Number option. The options field MAY
the Reason and/or Link-Type options

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5.5.3. Callback-

An implementation that wants its peer to originate another link
add to the multilink bundle MUST transmit a Callback-Request
to its peer. This will inform the receiver of the request to
another link to the bundle along with the number to be called

The options field MUST include the Link-Type and Phone-Delta options
The Reason option MAY also be included

Upon reception of a Callback-Request, a Callback-Response
MUST be transmitted

5.5.4. Callback-

An implementation MUST transmit a Callback-Response datagram
response to a received Callback-Request datagram. If the Callback
Request is acceptable, the Callback-Response MUST have a
Code of Request-Ack. A Callback-Response packet MAY include
Link-Type option

5.5.5. Link-Drop-Query-

An implementation that determines that a link is no longer needed
wishes to negotiate dropping it (e.g., based on a throughput
decision), MUST transmit a Link-Drop-Query-Request packet.
options field MUST include the Link-Discriminator option (
the receiver's Link-Discriminator), and MAY include the
option

Upon reception of a Link-Drop-Query-Request, an implementation
transmit a Link-Drop-Query-Response datagram. The Response-Code
be Request-Ack if it agrees to drop the link; if it does not agree
drop the link the Response-Code will be Request-Nak or Request-Full
Nak. After the receipt of a Link-Drop-Query-Response with a
Code of Request-Ack, the transmitter of the Link-Drop-Query-
MUST initiate tear down of the indicated link by sending an
Terminate-Request packet on the designated link

5.5.6. Link-Drop-Query-

An implementation transmits a Link-Drop-Query-Response datagram
response to a received Link-Drop-Query-Request datagram. If
implementation agrees (e.g., based on its throughput BOD algorithm
to reduce the bandwidth of the multilink bundle, then the
Code MUST be set to Request-Ack

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The Reason option MAY be included in the Link-Drop-Query-
packet

The Link-Drop-Query-Request datagram MUST be supported, as well
the underlying implementation to respond to it. This means that
Link-Drop-Query-Response with a Response Code of Request-Rej MUST
be transmitted in response to a Link-Drop-Query-Request

5.5.7. Call-Status-

After an implementation attempts to add a link to a bundle as
result of a Call-Request or a Callback-Request, it MUST send a Call
Status-Indication packet to its peer to indicate if the attempt
add the link succeeded or failed. One Indication MUST be sent
each attempt made. For each Call-Status-Indication packet
with the Call-Status Option Action octet set to Retry, a
Call-Status-Indication packet MUST be sent to indicate the success
failure of the retry. The Call-Status option MUST be included
inform the receiver of the status of the attempt to add a link
the action the implementation will take in case of failure.
reason option MAY also be included in the Call-Status-
packet

Upon reception of a Call-Status-Indication packet which indicates
failure, an implementation may log the failure and reason code.
reception of any Call-Status-Indication packet, a Call-Status
Response datagram MUST be transmitted

5.5.8. Call-Status-

An implementation transmits a Call-Status-Response datagram
response to a received Call-Status-Indication datagram. The
Code field MUST be set to Request-Ack in this packet. The
option MAY be included in this packet

6. BAP Datagram

BAP Datagram Options are used in various BAP packets. Their use
various packets is as defined below. The format of these
loosely follows the formatting conventions of LCP
Options. When there are multiple BAP Options in one BAP packet,
options MAY be transmitted in any order

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A summary of the BAP Option format is shown below. The fields
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The type field is one octet, and indicates the type of the
Datagram Option. This field is binary coded Hexadecimal.
following options are currently defined

01 Link-
02 Phone-
03 No-Phone-Number-
04
05 Link-
06 Call-

The Length field is one octet, and indicates the length of
BAP Option including the Type, Length, and Data fields

The Data field is zero or more octets, and contains
specific to the BAP Option. The format and length of the
field is determined by the Type and Length fields

6.1. Link-

This option indicates the general type of link indicated for
operation being performed. This option does not indicate
specific link type, rather it gives some general
of the desired link type. This option MAY be used along
other knowledge (i.e., the type of the other link(s) in the
or user configuration) to determine the type of link desired to
used in the operation. It MUST be included in a Call-
Callback-Request, and MAY be included in a Call- or Callback
Response

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A summary of the Link-Type BAP Option format is shown below.
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 Speed (kbps) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Type |
+-+-+-+-+-+-+-+-+

01 for Link-Type

The Length field is one octet, and indicates the length of
BAP Option including the Type, Length and Link Type fields

Link

The Link Speed field is 2 octets, and indicates the
speed of the desired link in kilobits per second. This field
coded as 2 binary coded hexadecimal octets, with the
significant octet sent first

Link

The Link Type field is a bit mask. It is 1 octet in length.
0 of the Link Type field corresponds to bit 39 of the Link-
BAP Option as described above. If a bit is set, it
support of the corresponding link type. If the link indicated
different than the supported link types, no bit will be set
Otherwise, at least one bit MUST be set. If an
supports more than one link type, more than one bit MAY be set

Bit Link
--- -------------
0
1 X.25
2
3 switched digital (non-ISDN
4 ISDN data over
5-7

If the Length field contains more bits than are defined by
specification, then any bits that are not defined should

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RFC 2125 PPP BACP March 1997

ignored. In order to allow for future expansion of this field,
is important to properly support receiving a Link Type
longer than what is defined by this specification. If the
field is shorter than the number of bits defined, then
implementation should set all bits not received to 0.

6.2. Phone-

The BAP Phone-Delta Option is used by an implementation to
its peer the information needed to make a call. Due to
difficulty of determining which dialing prefixes (if any)
necessary to dial a given phone number/national
code/country code combination, the phone number to be dialed
be based on a previously known number. This MAY be the
number used to establish the first link of the multilink bundle,
number configured by the user, the phone number used to make
callback connection, or a number determined in some other way
The Phone-Delta Option will consist of a Subscriber-Number Sub
Option along with a Unique-Digits Sub-Option that indicates
many of the digits of the Subscriber-Number are unique among
ports in use, previously used, and to be used in the
bundle. There is also an optional Phone-Number-Sub-Address Sub
Option

An implementation MAY include more than one Phone-Delta option
a response. This indicates that there is more than one
number that can be used for the requested operation. The Phone
Delta option MUST appear in a Callback-Request. It also
appear in a Call-Response with a Response Code set to Request-
if the Call-Request did not contain the No-Phone-Number option
It MAY be included in the Call-Status-Indication packet

A summary of the Phone-Delta BAP Option format is shown below.
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...
+-+-+-+-+-+-+-+-+

02 for Phone-Delta

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RFC 2125 PPP BACP March 1997

The Length field is one octet, and indicates the length of
BAP Option including the Type, Length, and Sub-Option fields

Sub-Option

The following Sub-Option Types are defined for the Phone-
option

01 Unique-
02 Subscriber-
03 Phone-Number-Sub-

Sub-Option

The Sub-Option Length field is one octet, and indicates the
of this BAP Sub-Option including the Sub-Option Type, Sub-
Length, and Sub-Option fields

6.2.1. Phone-Delta Sub-

Unique-

The Unique-Digits Sub-Option field consists of one octet that is
count of the number of rightmost digits of the Subscriber-
that are different from the set of phone numbers of the ports
in this multilink connection. (For example, if the first port
a multilink bundle has a phone number of 123456789, and
implementation wanted its peer to call a port with a phone
of 123456888, the Unique-Digits octet would be 3.) If the Phone
Number-Sub-Address Sub-Option is present, the Unique-Digits Sub
Option MUST NOT include any of the Sub Address digits in its
of different rightmost digits

This field is required

Subscriber-

This field is the phone number of the port that should be
by the peer. Any digits that precede the rightmost unique
of the Subscriber-Number are provided for informational
only, and do not need to be included in this field. This field
an ASCII string and MUST contain only ASCII characters
valid phone number digits. This field is required

Richards & Smith Standards Track [Page 18]

RFC 2125 PPP BACP March 1997

Phone-Number-Sub-

This field is the sub address of the port to be called by
peer. This sub-option SHOULD only be used for an ISDN call.
field is an ASCII string and only contains valid phone
digits. This field is optional

6.3. No-Phone-Number-

The No-Phone-Number option indicates that the
implementation is already configured with the phone number of
multilink peer and the answering implementation MUST NOT
the Phone Number option in the response. This may be for
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

03 for No-Phone-Number

2

Richards & Smith Standards Track [Page 19]

RFC 2125 PPP BACP March 1997

6.4.

This option is used to indicate a reason for the Request
Response. It is meant to be used for informational purposes only
This option MAY be used in any BAP packet

A summary of the Reason BAP Option format is shown below. The
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 String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

04 for Reason

The Length field is one octet, and indicates the length of
BAP Option including the Type, Length and Reason String fields

Reason

This is an ASCII string. The content of the field
implementation dependent. An implementation MAY ignore the
String field

Richards & Smith Standards Track [Page 20]

RFC 2125 PPP BACP March 1997

6.5. Link-

The Link-Discriminator option MUST be used in a Link-Drop-Query
Request datagram. This option is used to inform the receiver of
Link-Drop-Query-Request of which link will be dropped

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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

05 for Link-

4

Link

The Link Discriminator field is 2 octets in length. It
the Link Discriminator that was contained in the LCP Link
Discriminator Configuration Option sent by the receiver of
packet containing the Link Discriminator

6.6. Call-

The Call-Status option MUST be used in a Call-Status-
datagram. This option is used to inform the receiver of
Call-Status-Indication datagram of the status of the
call attempt, as well as a possible action that will be taken (
the call failed).

Richards & Smith Standards Track [Page 21]

RFC 2125 PPP BACP March 1997

A summary of the Call-Status BAP Option format is shown below.
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 | Status | Action |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

06 for Call-Status

4

The Status field is 1 octet in length. If the call
successful, the value MUST be set to 0. A non-zero
indicates a call failure. A value of 255 indicates a non-
failure, and a more specific call status MAY be indicated by
the same number as the Q.931 cause value (i.e., 1 is
number, 17 is user busy, etc.)

The Action octet indicates what action the calling implementation
taking after a failed call. If the call was sucessful, the
octet MUST be set to 0.

The Action octet can have the following values

0 - No
1 -

Richards & Smith Standards Track [Page 22]

RFC 2125 PPP BACP March 1997

List of BAP datagrams and associated fields

datagram mandatory fields allowed
-------- ----------------- ---------------
Call-Request Link-Type No-Phone-
Call-Response Phone-
Link-
Callback-Request Link-
Phone-
Callback-Response Link-
Link-Drop-Query-Request Link-
Link-Drop-Query-
Call-Status-Indication Call-Status Phone-
Call-Status-

The Reason option is allowed to be included with any BAP datagram

History of

The first version of BACP was written by Craig Richards of
Corporation. This version was enhanced and improved by the
Working Group, a collaborative effort of 3Com, Ascend, Bay Networks
Cisco, Microsoft, Shiva, US Robotics and Xylogics

Kevin Smith of Ascend for his contributions based on his work on
MP+ Specification. Gerry Meyer and Robert Myhill of Shiva for
early comments and improvements. Andy Nicholson of Microsoft for
improvements to the bandwidth management scheme. Dana Blair and
Valencia of Cisco, Cheng Chen and Dan Brennan of 3Com for their
ideas as part of the MPCP Working Group. All of the members of
MPCP working group for their ability to work with their
with enthusiasm to produce a better protocol for the industry

Security

Security issues are not discussed in this memo

Richards & Smith Standards Track [Page 23]

RFC 2125 PPP BACP March 1997

[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)",
51, RFC 1661, Daydreamer, July 1994.

[2] Sklower, Lloyd, McGregor, Carr & Coradetti, "The PPP
Protocol", RFC 1990, University of California, Berkeley,
Internetworking, Newbridge Networks Corporation,
Software, August 1996.

Chair's

The working group can be contacted via the current chair

Karl
Ascend
3518 Riverside Drive, Suite 101
Columbus, Ohio 43221

(614)451-1883

EMail: karl@ascend.

Editors'

Craig
Shiva
28 Crosby
Bedford, MA 01730
VOICE +1 617 270 8419
FAX +1 617 270 8599

EMail: crich@us.shiva.

Kevin
Ascend Communications, Inc
1275 Harbor Bay
Alameda, CA 94501

EMail: kevin@ascend.

Richards & Smith Standards Track [Page 24]

if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.

RFC documents can be found at I.E.T.F.

Relevance System Copyright © 2002 Spectrum WorldResearch
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