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RFC1934 - Ascends Multilink Protocol Plus (MP+)

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

Network Working Group K. Smith

Request For Comments: 1934 Ascend Communications

Category: Informational April 1996

Ascend's Multilink Protocol Plus (MP+)

Status of This Memo

This memo provides information for the Internet community. This memo

does not specify an Internet standard of any kind. Distribution of

this memo is unlimited.

Abstract

This document proposes an extension to the PPP Multilink Protocol

(MP) [1]. Multilink Protocol Plus (MP+) is a new control protocol for

managing multiple data links that are bundled by MP.

Table Of Contents

1. IntrodUCtion.................................................2

1.1 Functional Description...............................2

1.2 Conventions..........................................3

2. General Overview.............................................3

2.1 Operation............................................4

3. MP+ Frame Formats............................................4

3.1 Error Control (EC) Layer.............................6

3.1.1 Error Control State Machine..................7

3.2 Multilink Plus Control Messages......................9

3.3 Multilink Plus Message Formats......................10

3.3.1 VERSION_EXCHANGE_REQ Message Format.........10

3.3.2 VERSION_EXCHANGE_RSP Message Format.........12

3.3.3 ADD_REQ Message Format......................13

3.3.4 ADD_RSP Message Format......................15

3.3.5 ADD_COMPLETE Message Format.................16

3.3.6 REMOVE_REQ Message Format...................17

3.3.7 REMOVE_RSP Message Format...................17

3.3.8 REMOVE_COMPLETE Message Format..............18

3.3.9 CLOSE_REQ Message Format....................19

3.3.10 CLOSE_RSP Message Format....................19

3.3.11 REMOTE_MGMT_REQ Message Format..............20

3.3.12 REMOTE_MGMT_RSP Message Format..............20

3.3.13 REMOTE_MGMT_RX_REQ Message Format...........21

3.3.14 REMOTE_MGMT_TX_REQ Message Format...........22

3.3.15 REMOTE_MGMT_TX_RSP Message Format...........22

3.3.16 CLEAR_REQ Message Format....................23

3.4 Events..............................................23

3.5 State Machine.......................................25

3.5.1 States......................................25

3.5.2 Common Actions..............................26

3.5.3 MP+STATE_INITIAL state machine..............32

3.5.4 MP+STATE_IDLE state machine.................35

3.5.5 MP+STATE_ADD state machine..................37

3.5.6 MP+STATE_REMOVE state machine...............41

3.5.7 MP+STATE_CLOSE state machine................44

4. PPP LCP Extensions..........................................46

5. Security Considerations.....................................47

6. References..................................................47

7. Author's Address............................................47

1. Introduction

The PPP Multilink Protocol (MP), is a set of features that provide

inverse multiplexing at the packet/fragment level by bundling

multiple independent links between a fixed pair of systems, providing

a virtual link with greater bandwidth than any of the constituent

members.

Once multiple channels have been established MP is responsible for

managing channel use to insure in-sequence delivery of user packets.

MP+ is an extension to MP that adds an inband control channel to

provide a new level of session management and control.

MP+ also allows remote device management of (unconfigured) systems.

This feature allows a network operations center to dial into an

unconfigured system and remotely manage it, before ethernet

interface, IP address, and other LCP and system configuration

information is entered. (This does require local configuration of

the WAN interfaces to the extent required to answer an incoming

call).

1.1 Functional Description

The features of MP+ include:

* Ability to negotiate to add and suBTract channels when bandwidth

needs change.

* Phone number management so calling stations need not know every

possible number; answering stations can manage their own resources.

* A simple remote management interface.

To perform the above functions MP+ is split into a call management

layer and a reliable delivery layer. The call management layer is

the source and sink of MP+ control messages. The reliable delivery

layer adds a simple acknowledge and retry mechanism.

MP+ only takes network bandwidth when in the process of performing a

user request, e.g. adding and subtracting bandwidth.

NOTE: Neither MP, or MP+ define the process that makes the bandwidth

requirement determination. That is outside the scope of either of

these protocols and will likely be implementation dependent.

1.2 Conventions

The following language conventions are used in the items of

specification in this document:

MUST, SHALL or MANDATORY -- the item is an absolute requirement

of the specification.

SHOULD or RECOMMENDED -- the item should generally be followed

for all but exceptional circumstances.

MAY or OPTIONAL -- the item is truly optional and may be followed

or ignored according to the needs of the implementor.

2. General Overview

PPP

In order to establish communications over a point-to-point link,

each end of the PPP [2] link must first send LCP packets to

configure the data link during link establishment phase. After

the link has been established, PPP provides for an authentication

phase.

MP The goal of multilink operation is to bundle multiple

independent links between a fixed pair of systems, providing a

virtual link with greater bandwidth than any of the constituent

members.

MP+ MP+ is also negotiated during initial LCP option negotiation. A

system indicates to its peer that it is willing to do MP+ by

sending the MP+ option as part of the initial LCP option

negotiation. The MP+ option MUST NOT be negotiated unless MP is

also negotiated. When used, MP+ adds a virtual unit-to-unit

control channel.

A peer may elect to:

Acknowledge both the MP and MP+ options, indicating that both MP and

MP+ will be used.

Acknowledge the MP option and reject the MP+ option. Operation will

fall back to MP.

Reject both options. Standard PPP will be used for this connection.

2.1. Operation

Standard PPP

In standard PPP the LCP negotiation phase is followed by an

optional authentication phase, and then one or more NCPs are

initiated.

PPP with MP The LCP negotiation phase and authentication phase are

identical to standard PPP. The ability to initiate an MP

aggregate data link is indicated by sending an MP option - as

described in [1].

PPP with MP and MP+ When MP+ is negotiated at LCP startup, the same

procedures are followed as when MP is negotiated alone. The MP+

LCP option is negotiated to indicate the ability to use the MP+

feature.The first connection between endpoints causes the MP+

process to be started for the connection.

3. MP+ Frame Formats

+---------------+---------------+

PPP Header: Address 0xff Control 0x03

+---------------+---------------+

PID(H) 0x00 PID(L) 0x73

+-+-+-+-+-------+---------------+

MP Header: 11000001 seq # high

+-+-+-+-+-------+---------------+

sequence number low bits

+---------------+---------------+

control data

.

.

.

+---------------+---------------+

PPP FCS: FCS

+---------------+---------------+

Figure 1: Multilink Plus Frame Format (long sequence number format)

+---------------+---------------+

PPP Header: Address 0xff Control 0x03

+---------------+---------------+

PID(H) 0x00 PID(L) 0x73

+-+-+-+-+-------+---------------+

MP Header: 1101 sequence number

+-+-+-+-+-------+---------------+

control data

.

.

.

+---------------+---------------+

PPP FCS: FCS

+---------------+---------------+

Figure 2: Multilink Plus Frame Format (short sequence number format)

MP+ frames use a similar structure to MP fragments.

The MP+ assigned PID is designated 00 73.

MP+ control uses the following two rules:

- MP+ control frames have their own sequence number space,

controlled by MP+.

- MP+ control frames MUST NOT be fragmented.

NOTE: Implementations of this protocol prior to the date of submission

of this specification to the IETF use the same PID as MP, but

sets the LSB of the reserved bits in the MP header to 1 - this

is how the MP+ packets are discriminated from MP fragments.

So the header of the MP+ packet looks like:

00 3d c1 ......

As compared to an MP packet that looks like:

00 3d c0 ...... or

00 3d 80 ...... or

00 3d 40 ......

3.1. Error Control (EC) Layer (MP+ control only)

The error control layer that runs over the virtual inband channel is

as simple as it can get, while handling the possibility of errors on

the line.

An assumption is made that errors are infrequent, and that at the

same time messages are rarely, if ever, dropped on the floor. The

implication of this is that "timing out" on retransmission of

messages does no harm. If a message cannot get through, then it

simply is retried some number of times. After giving up, the only

recourse is to notify the call management layer (of MP) that the

session has died.

+---------------+---------------+

PPP Header: Address 0xff Control 0x03

+---------------+---------------+

PID(H) 0x00 PID(L) 0x73

+-+-+-+-+-------+---------------+

MP+ Header: 11000001 seq # high

+-+-+-+-+-------+---------------+

sequence number low bits

+---------------+---------------+

EC Header: Error Control Message Type

32 bits reserved

+---------------+---------------+

MP+ Data: MP+ Message May not be

present.

Figure 3: MP+ control message format (shown long sequence number

format)

Error Control Message Type:

1 DATA_MSG: This message contains MP+ data transferred

between the peers.

2 ACK_MSG: An acknowledgement of a previous data message.

When set to DATA_MSG, the remainder of the frame contains an MP+

Control message.

When set to ACK_MSG, the remainder of the frame consists only of the

PPP Frame Check Sum (FCS).

3.1.1. Error Control State Machine

This layer is controlled by a simple state machine. There are three

states:

Stopped There is no connection between peers.

Idle There is a connection between peers;

no unacknowledged messages pending.

Pending There is a connection between peers;

awaiting an acknowledgement to the

last message sent.

Messages from the call management layer are queued for transmission

whenever the link is in the pending state. For simplicity, only

one outstanding message may be in the link at any given time. The

entire procedure is defined in table 1.

Event State

______________________________________________________________________

Stopped Idle Pending

======================================================================

Start 1,Idle -,* -,*

______________________________________________________________________

Received ACK_MSG ** 2,Start 5,IdlePending

current tx sequence number

______________________________________________________________________

Received ACK_MSG ** -,* -,*

last tx sequence number

______________________________________________________________________

Received ACK_MSG ** 2,Start 2,Start

other tx sequence number

______________________________________________________________________

Received DATA_MSG ** 6,* 6,*

current rx sequence number

______________________________________________________________________

Received DATA_MSG ** 7,* 7,*

previous rx sequence number

______________________________________________________________________

Received DATA_MSG ** 2,Start 2,Start

other rx sequence number

______________________________________________________________________

Receive Invalid Frame ** 2,Start 2,Start

______________________________________________________________________

Retransmit Timer EXPire ** ** 4,Start*

______________________________________________________________________

______________________________________________________________________

Transmit Request from call -,* 3,Pending 8,*

management layer

______________________________________________________________________

Stop 9,Start 9,Start 9,Start

______________________________________________________________________

Table 1: Error Control State Machine

Legend:

- No action

* Stay in same state

** Invalid or meaningless event for state, ignored.

Notes:

[1] Data from the call management layer will always be copied before

being queued for transmission. The call management layer is

responsible for its own buffers.

[2] MP always copies data for transmission and returns immediately.

Any buffers allocated to build control messages MUST be released

immediately upon return from MP transmission requests.

Actions:

1 Reset rx sequence number

Reset tx sequence number

Reset tx retransmit count

Stop retransmit timer

2 Report error to user

Stop retransmit timer

Stop frame transmit timer

Free buffers

3 Save call management message in pending transmit queue

Build DATA_MSG from first message in pending transmit

queue using current tx sequence number.

Send message to MP for transmission.

Reset tx retransmit count

4 Increment tx retransmit count

If tx retransmit count >= RETRANSMIT_COUNT

Action 2 (followed by state change to the Start state)

else

Build DATA_MSG from first message in pending

transmit queue using current tx sequence number.

Send message to MP for transmission.

5 Dequeue first element on pending transmit queue and release

its buffer

Increment the tx sequence number

Stop the retransmit timer

if pending transmit queue not empty

Build DATA_MSG from first message in pending

transmit queue using current tx sequence number.

Send message to MP for transmission.

Reset tx retransmit count

6 Build ACK_MSG using the current rx sequence number

Send ack message to MP for transmission

Pass message to call managment layer

Increment rx sequence number

7 Build ACK_MSG using the previous rx sequence number

Send the ack message to MP for transmission

8 Add the message to the end of the pending transmit queue

9 Stop retransmit timer

Free buffers

3.2. Multilink Plus Control Messages

Message Type Value

VERSION_EXCHANGE_REQ 1

VERSION_EXCHANGE_RSP 2

ADD_REQ 3

ADD_RSP 4

ADD_COMPLETE 5

REMOVE_REQ 6

REMOVE_RSP 7

REMOVE_COMPLETE 8

CLOSE_REQ 9

CLOSE_RSP 10

REMOTE_MGMT_REQ 11

REMOTE_MGMT_RSP 12

REMOTE_MGMT_RX_REQ 13

REMOTE_MGMT_TX_REQ 14

REMOTE_MGMT_TX_RSP 15

CLEAR_REQ 16

3.3. Multilink Plus Message Formats

The fields of all messages defined here MUST be encoded/decoded in

Network Byte Order (big endian).

3.3.1. VERSION_EXCHANGE_REQ Message Format

The version exchange message is sent by the call originator to inform

the answerer the version of the MP+ protocol being used as well as

any other information that may need to be conveyed outside of the

normal PPP parameter negotiation.

+---------------+---------------+

Message type

0x00000001

+---------------+---------------+

Protocol Version

+---------------+---------------+

Protocol Revision

+---------------+---------------+

Session Identifier

+---------------+---------------+

Hardware Type

+---------------+---------------+

Nailed Mode

+---------------+---------------+

Use Multiple Trunk Groups

+---------------+---------------+

Descriptor Length

+---------------+---------------+

Descriptor

+---------------+---------------+

Figure 4: Version Exchange Request

A message sent from call originator to call answerer specifying the

callers protocol version and other state info and requesting the

answerer to respond with its version info.

Protocol Version:

caller MP+ protocol version number.

2 octets fixed length (initially 1)

Protocol Revision:

caller MP+ protocol revision number.

2 octets fixed length (initially 4)

Session Identifier:

A non-zero identifier unique to the caller.

2 octets fixed length.

Hardware Type:

caller hardware type (can be vendor defined).

2 octets fixed length.

Nailed Mode:

caller nailed mode from the session profile.

2 octets fixed length.

Use Multiple Trunk Groups:

non-zero if the call may use channels from multiple trunk

groups.

2 octets fixed length

Descriptor Length:

length of the end point descriptor.

2 octets fixed length

Descriptor:

the end point descriptor. This field allows for vendor

specific identification of the peer.

Variable length as defined above.

3.3.2. VERSION_EXCHANGE_RSP Message Format

The version exchange response message is sent by the call answerer in

response to a version exchange request message. The answerer uses

the message to inform the caller the version of the MP+ protocol

being used as well as any other information that needs to be conveyed

outside of the normal PPP parameter negotiation.

+---------------+---------------+

Message type

0x00000002

+---------------+---------------+

Protocol Version

+---------------+---------------+

Protocol Revision

+---------------+---------------+

Session Identifier

+---------------+---------------+

Hardware Type

+---------------+---------------+

Nailed Mode

+---------------+---------------+

Use Multiple Trunk Groups

+---------------+---------------+

Descriptor Length

+---------------+---------------+

Descriptor

+---------------+---------------+

Figure 5: Version Exchange Response

A message sent from call answerer to the call originator specifying

the answerers protocol version and other state info. Sent in

response to receiving a version exchange request.

Protocol Version:

caller MP+ protocol version number.

2 octets fixed length (initially 1)

Protocol Revision:

caller MP+ protocol revision number.

2 octets fixed length (initially 4)

Session Identifier:

A non-zero identifier unique to the answerer.

2 octets fixed length.

Hardware Type:

caller hardware type (can be vendor defined).

2 octets fixed length.

Nailed Mode:

caller nailed mode from the session profile.

2 octets fixed length.

Use Multiple Trunk Groups:

non-zero if call may use channels from multiple trunk groups.

2 octets fixed length

Descriptor Length:

length of the remote descriptor in 4-octet units.

2 octets fixed length

Descriptor:

the remote unit descriptor. This field allows for vendor

specific identification of the peer.

Variable length Nx4 octets long - total length defined above.

3.3.3. ADD_REQ Message Format

A message of this type is sent by either caller or answerer to

initiate an increase of bandwidth. When sent by the caller the

request is aSKINg for permission to dial a certain number of

channels; the response will contain permission and the phone numbers

of the channels to dial. When sent by the answerer, this message

contains the phone numbers to dial. The message looks like:

+---------------+---------------+

Message type

0x00000003

+---------------+---------------+

Number of channels requested

+---------------+---------------+

Number of phone numbers

+---------------+---------------+

A phone number list for

each phone number

.

.

.

+---------------+---------------+

Figure 6: Add Request

A message sent by either caller or answerer to request that additional

bandwidth be added to a session.

Number of channels requested:

The maximum number of channels to add.

2 octets fixed length.

Number of phone numbers:

The number of phone numbers provided. This

value will always be zero when the caller

initiates an add and will be at least

Number of channels requested when the answerer

initiates the add.

2 octets fixed length.

Phone number list:

A list of up to 32 phone number lists

containing the phone numbers to call.

Each description is of fixed length as described below:

Each phone number is represented by a phone number list.

The format of a phone number list is:

+---------------+---------------+

in use flag

+---------------+---------------+

call service type

+---------------+---------------+

Phone number

20 octets

plus null terminator

(21 octet total)

+---------------+

Must be 0

+---------------+---------------+

must be 0

+---------------+---------------+

Figure 7: Phone number list

A structure containing information about a connection within the

system.

in use flag:

non-zero if the phone number indicated

in this descriptor is currently in use.

2 octets fixed length

call service type:

Defines the type of service, switched, nailed,

or other, associated with a phone number.

1 Nailed

2 Switched

>=3 Undefined

Phone number:

The null terminated phone number of this channel.

Fixed length 21 octets. Each octet contains IA5 character

representation of a digit (or #, *).

Must be 0:

Filler to force alignment to 32-bit boundary.

3.3.4 ADD_RSP Message Format

A message of this type gives permission to dial some number of

channels and, when sent by the answerer of the original call, gives

the phone numbers of channels to dial.

+---------------+---------------+

Message type

0x00000004

+---------------+---------------+

Number of channels allowed

+---------------+---------------+

Number of phone numbers

+---------------+---------------+

A phone number list for

each phone number

.

.

.

+---------------+---------------+

Figure 8: Add Response

A message sent by either caller or answerer to indicate the number of

channels that may be added to a session.

Number of channels allowed:

The actual number of channels to add. This

may be less than the number requested.

2 octets fixed length.

Number of phone numbers:

The number of phone numbers provided. This

value will always be zero when sent by the

caller and will be at least channelCount

when sent by the answerer.

2 octets fixed length.

Phone number list:

A list of up to 32 phone number lists

containing the phone numbers to call.

Each description is of fixed length as described above.

3.3.5. ADD_COMPLETE Message Format

This message is sent by the caller to the answerer after all calls

have been placed. The message is used to notify the answerer that

the add transaction is complete and it may return to the idle state.

+---------------+---------------+

Message type

0x00000005

+---------------+---------------+

Channels added

+---------------+---------------+

Must be zero

+---------------+---------------+

Figure 9: Add Complete

A message sent by caller to indicate the number of channels that were

added successfully. This message was added in MP+ Version 1.1.

Channels added:

The actual number of channels added.

2 octets fixed length

Must be zero:

Padding to 32-bit boundary.

2 octets fixed length

3.3.6. REMOVE_REQ Message Format

A message of this type is sent when a peer decides, for any reason,

to remove channels from use. The purpose of the message is to tell

the remote end of the remove and give it a chance to adjust the

number of channels to remove.

+---------------+---------------+

Message type

0x00000006

+---------------+---------------+

Number of channels to remove

+---------------+---------------+

Must be zero

+---------------+---------------+

Figure 10: Remove Request

A message sent by either caller or answerer to request that bandwidth

be removed from a session.

Number of channels to remove:

The maximum number of channels to remove.

2 octets fixed length

Must be zero:

Padding to 32-bit boundary.

2 octets fixed length

3.3.7. REMOVE_RSP Message Format

This message is sent in response to a remove request. The responder

specifies the number of channels that can be removed. If the

response specifies 0 channels the remove is cancelled.

+---------------+---------------+

Message type

0x00000007

+---------------+---------------+

Number of channels to remove

+---------------+---------------+

Must be zero

+---------------+---------------+

Figure 11: Remove Response

A message sent in response to a remove request specifying the number

of channels that the peer agrees can be removed.

Number of channels to remove:

The maximum number of channels to remove.

May be zero, in which case the remove is

cancelled.

2 octets fixed length

Must be zero:

Padding to 32-bit boundary.

2 octets fixed length

3.3.8. REMOVE_COMPLETE Message Format

This message is sent by the initiator of a remove transaction when

the agreed upon number of channels have been removed. The message is

used to notify the peer that the remove transaction is complete and

it may return to the idle state.

+---------------+---------------+

Message type

0x00000008

+---------------+---------------+

Number of channels removed

+---------------+---------------+

Must be zero

+---------------+---------------+

Figure 12: Remove Complete

A message sent by the caller or answerer to indicate how many channels

were actually removed. This message was added in MP+ CM version 1.1.

Number of channels removed:

The number of channels that were removed.

2 octets fixed length

Must be zero:

Padding to 32-bit boundary.

2 octets fixed length

3.3.9. CLOSE_REQ Message Format

This message is sent when the peer requests to close the whole

session. This is typically due to a configuration option that

indicates when a system should request to close the session (an

example being, a link has been idle for greater than a preconfigured

time period).

+---------------+---------------+

Message type

0x00000009

+---------------+---------------+

Figure 13: MP+ close request.

There are no data fields associated with this message.

3.3.10. CLOSE_RSP Message Format

If the peer agrees that closing the session is acceptable based on

it's own configuration (an example reject reason would be that the

peer is configured with a *minimum* number of channels to keep

active).

+---------------+---------------+

Message type

0x0000000a

+---------------+---------------+

OK To Close

+---------------+---------------+

Must be zero

+---------------+---------------+

Figure 14: MP+ close response

The response to a close request. May be sent by caller or answerer.

OK To Close:

If non-zero, peer said I can close all channels.

2 octets fixed length

Must be zero:

Padding to 32-bit boundary.

2 octets fixed length

3.3.11. REMOTE_MGMT_REQ Message Format

This message is sent from a master station to a slave station when

the master wishes to manage the remote station. The message is also

used to cancel remote management once it's been started.

+---------------+---------------+

Message type

0x0000000b

+---------------+---------------+

Mode

+---------------+---------------+

Must be zero

+---------------+---------------+

Figure 15: Remote Management Request

A message sent from master to slave to initiate or clear a remote

management session.

Mode:

One to start session. Zero to stop session.

2 octets fixed length

Must be zero:

Padding to 32-bit boundary.

2 octets fixed length

3.3.12. REMOTE_MGMT_RSP Message Format

The slave side of a remote management session has the opportunity to

reject remote management. The master side is informed of accept/deny

status via the remote management response.

+---------------+---------------+

Message type

0x0000000c

+---------------+---------------+

Mode

+---------------+---------------+

Figure 16: Remote Management Response

A message sent from slave to master to allow or deny initiation of a

remote management session.

Mode:

One to accept session. Zero to deny session.

2 octets fixed length

Must be zero:

Padding to 32-bit boundary.

2 octets fixed length

3.3.13. REMOTE_MGMT_RX_REQ Message Format

This message type is used to convey keyboard input from the

management master to be processed by the management slave. The

message format consists of an octet count (in network byte order) and

then an array of octets to be processed. It looks like:

+---------------+---------------+

Message type

0x0000000d

+---------------+---------------+

character count

+---------------+---------------+

array of characters

.

.

.

+---------------+---------------+

Figure 17: Remote Management Receive Request

A message sent from master to slave, conveying keystrokes typed on the

masters keyboard that will be processed by the slave.

character count:

Number of characters to process.

2 octets fixed length

array of characters:

Array of characters to process.

3.3.14. REMOTE_MGMT_TX_REQ Message Format

The remote management slave conveys output to be displayed on the

masters terminal with a remote management transmit request message.

Only one message may be outstanding. The next transmit request may

not be sent until the previous has been acknowledged.

+---------------+---------------+

Message type

0x0000000e

+---------------+---------------+

character count

+---------------+---------------+

array of characters

.

.

.

+---------------+---------------+

Figure 18: Remote Management Transmit Request

A message sent from slave to master, conveying output to be output on

the master's display.

Character count:

Number of characters to process.

2 octets fixed length

array of characters:

Array of characters to process.

3.3.15. REMOTE_MGMT_TX_RSP Message Format

This message is used to acknowledge remote management transmit

requests. The slave may send the next transmit request once this

message has been received.

+---------------+---------------+

Message type

0x0000000f

+---------------+---------------+

Figure 19: Remote Management Transmit Response

There are no data fields associated with this message.

3.3.16. CLEAR_REQ Message Format

A message sent to initiate a friendly shutdown of an MP+ link. The

sender will stop sending data immediately. The receiver of the

message will also stop sending user data and start a clean shutdown

of all NCPs and the LCP of each member link of the bundle. When the

last member link terminates, the session is completely closed.

+---------------+---------------+

Message type

0x00000010

+---------------+---------------+

Figure 20: Clear Request

There are no data fields associated with this message.

3.4. Events

The MP+ state machine is event driven. Reception of an event triggers

an action and possibly a state change. The events processed by the

MP+ state machine can be roughly classed into two types:

Events that originate within the unit, e.g. notification that a

call has cleared, an MP+ session may be started, etc.

Events that originate with the reception of an MP+ control

message from the peer unit.

Both types are processed by the state machine in the sequence they

occurred. The events processed are:

MP+START_SESSION: Notification from PPP/MP that an

MP+ session is starting.

MP+SESSION_DOWN: Notification from the error-control

layer that end-to-end connectivity

has been lost and control messages can

not be delivered.

MP+SESSION_TERM: Session termination notification from

PPP/MP. This event is not sent until

the last channel of a multi-channel

session is cleared.

MP+TIMER_EXPIRED: Timers are used in various states and

sub-states. This event is signaled whenever

a timer expires.

MP+CALL_COMPLETE: A call placed during an add request has

completed. The call may have succeeded or

failed.

MP+UTILIZATION: Notification from MP/PPP that link

utilization has crossed a threshold and that

channels may need to be added/removed.

(The number of channels to add/remove will be

passed with the notification).

MP+RX_VERSION_REQ: A Version Exchange request message has

been received from the peer.

MP+RX_VERSION_RSP: A Version Exchange response message has

been received from the peer.

MP+ADD_REQ: An Add request message has been received

from the peer.

MP+ADD_RSP: An Add response message has been received

from the peer.

MP+ADD_COMP: An Add Complete message has been received

from the peer.

MP+REMOVE_REQ: A Remove request message has been received

from the peer.

MP+REMOVE_RSP: A Remove response message has been

received from the peer.

MP+REMOVE_COMP: A Remove Complete message has been received

from the peer.

MP+RX_RM_REQ: A Remote Management request has been received

from the peer.

MP+RX_RM_RSP: A Remote Management response has been received

from the peer.

MP+RX_RM_RX_REQ: A Remote Management Receive Request has been

received from the far end.

MP+RX_RM_TX_REQ: A Remote Management Transmit Request has

been received from the peer.

MP+RX_RM_TX_RSP: A Remote Management Transmit Response has

been received from the peer.

MP+RX_CLEAR: A request to shut down the session has been

received from the peer.

MP+CLOSE_REQ: A Close Request message has been received

from the peer.

MP+CLOSE_RSP: A Close Response message has been received

from the peer.

MP+START_RM Request to start a remote management session

with this station being the master.

MP+SEND_RMS: Request to send data to a remote management

master from a slave.

MP+SEND_RMM: Request to send data to a remote management

slave from a master.

MP+RECV_RMM: Request to send an ack to a remote management

slave for data received from the slave.

MP+STOP_RM: Request to stop a remote management session.

3.5. State Machine

3.5.1 States

To ease readability and understanding the major states are considered

as separate state machines, each having two to four sub-states. The

sub-states are named by the letters, A, B, C, and D. State

information is maintained for every interface.

The major states are:

MP+STATE_INITIAL: The state of an unused session. Session table

entries are intialized to this state at startup

and return to this state when sessions are

terminated.

MP+STATE_IDLE: The state of an active session that is not

performing any MP+ function.

MP+STATE_ADD: The state of a session when an add transaction is

in progress.

MP+STATE_REMOVE: The state of a session when a remove transaction is

in progress.

MP+STATE_CLOSE: The state of a session that is in the process of

being closed.

State transitions are triggered by the reception of an event. Tables

2 through 6 contain the state tables for the major states. All state

tables use the following symbols.

- No action

* Stay in same state

+ Target state is defined by the action taken

** An error has occurred, log an error message but no

state change.

States and sub-state transitions are noted as state:sub-state, e.g.,

initial:A. Alternative transitions are listed on separate lines.

3.5.2 Common Actions

Some actions are common to all states, they are defined here.

Error Close Action

Called to close a session when an error occurs. Actions are:

[1] Stop timer if running.

[2] Log an error message.

[3] Close the MP+EC layer for this session.

[4] Close MP for this session

[5] Clean up, restore state variables to their initial state.

Term Action

Processed when a MP+SESSION_TERM event occurs in most states.

Actions are:

[1] Stop timer if running.

[2] Close the MP+EC layer for this session.

[3] Call the passed termination callback function if not null.

[4] Clean up, restore state variables to their initial state.

Ignore Action

We don't care about this event in this state. Do nothing.

Timer Action

This action is called when a timer expires in one of the on-line

states. The timer is used to implement add and remove locks. A

lock is set when an add or remove fails and is not cleared until

a bandwidth change or the timer expires. This keeps us from

retrying add's and subtracts until there is a likelyhood that it

will succeed.

[1] Check add lock flag.

[1] If set an add lock occured last timeout period so

triple the timeout value (to a max of 81 minutes).

[2] If not set restore the timeout value to its initial

value of one minute.

[2] Clear the add lock flag.

[3] Clear the remove lock flag.

[4] Restart the retry timer.

Enter Remove [local] Action

The local unit is initiating a remove transaction. The desired

bandwidth is given.

[1] Restart the idle timer.

[2] Calculate number of channels to remove (difference between

number in use and number in desired).

[3] Build and send a remove request and send to remote.

[4] Go to REMOVE:A.

Enter Remove [remote] Action

The remote unit is initiating a remove transaction. The incoming

message contains the number of channels to remove.

[1] Restart the idle timer.

[2] Request the number of channels required. If greater than the

number available after removing the number of channels indicated

in the incoming message reduce the number of channels to remove

and set a remove lock.

[3] Build a remove response message indicating the number of

channels we will allow the requester to remove and send to the

remote.

[4] Go to REMOVE:B.

Enter Add [local] Action

The local unit is initiating an add transaction. We are given

the number of channels desired. The steps are:

[1] Restart the idle timer.

[2] Calculate number of channels to add (difference between

number desired and number in use).

[3] Reserve number of channels, retrieving their phone numbers.

[4] If number of channels reserved less than the number desired

set an add lock.

[5] If number of channels reserved greater than zero.

[1] Build an add request. If the answerer the request

includes the phone numbers for the caller to dial.

[2] If caller, go to ADD:A.

[3] If answerer, go to ADD:C.

[6] Go to IDLE state.

Enter Remove [remote] Action

The remote unit is initiating a remove transaction. The

incoming message contains the number of channels to remove.

[1] Clear the remove lock.

[2] Restart the idle timer.

[3] Request the number of channels required. If greater

than the number available after removing the number of

channels indicated in the incoming message reduce the

number of channels to remove.

[4] Build a remove response message indicating the number

of channels we will allow the requester to remove and

send to the remote.

[5] Go to REMOVE, sub-state B.

Enter Add [remote answerer] Action

We've received a message from the remote requesting that

bandwidth be added. The message contains the number of

channels to add. Since the remote is the answerer, the mes-

sage also contains the phone nubmers to dial. We may dial

less than the number requested.

[1] Restart idle timer.

[2] If the number of channels requested will put us over

the maximum number of channels allowed for the session

reduce the channel count.

[3] For each channel to add,

[1] Integrate the phone number returned from the

answerer with the original phone number dialed.

[2] Request that a session be extended by dialing

the integrated phone number. A callback is

passed with the request so call success or fail-

ure can be reported back to MP+.

[4] Go to ADD:B. Note: This change must actu-

ally occur before requesting the first outgoing call.

If not, the callback could be called (and ignored)

because the session is not in the correct state.

Enter Add [remote caller] Action

We've received a message from the remote requesting that

bandwidth be added. The message contains the number of

channels to add. Since the remote is the caller, it needs

us to send the phone numbers to dial. We may send fewer

phone numbers than requested

[1] Restart idle timer.

[2] If the number of channels requested will put us over

the maximum number of channels allowed for the session

reduce the channel count.

[3] Reserve the adjusted number of channels, retrieving

their phone numbers.

[4] If the number of channels reserved is less than the

adjusted number requested.

[5] Build an add response message, including the phone

numbers for the channels we will let the caller add

and send it to the far end.

[6] Go to ADD:C.

Enter Idle Action

The IDLE state is entered at the end of normal transactions.

At entry the current status of the connection should be

checked and new transactions initiated if necessary. To be

safe, we can also use this state as a catch all place to

release any bandwidth reserved for adds. The functions to

perform are:

[1] Restart the idle timer using the current retry value.

[2] Release any reserved bandwidth not actually in use.

[3] Check if bandwidth change reqested during last trans-

action. If change indicated:

[1] Query channel counts.

[2] If current bandwidth less than suggested band-

width and removes are not locked, store the

requested bandwidth and initiate a remove trans-

action (Enter Remove Action).

[3] If current bandwidth greater than suggested

bandwidth and adds are not locked:

[1] Store the requested bandwidth.

[2] Intiate an add transaction (Enter Add

[local] Action).

[4] Go to the IDLE state.

Remote Management Request Action

We received a request to start/stop remote management.

If this is a start request

If we can/allow remote management:

Build and send a Remote management response Allow

message.

Else

Build and send a Remote management response Deny

message.

Else (this is a stop)

Notify the remote management slave process to terminate.

Remote Management Response Action

We received a response to our remote management start request.

If the response was an Allow response

Notify the remote management master process, we can

start sending keystrokes/commands

Else

The peer denied the request, so notify the remote

management master process of failure.

Remote Management Receive Data Action

We (the slave) received data from the remote management master.

Pass the received data to the remote management slave process.

This is typically keystroke data received from the remote user

interface.

Remote Management Transmit Data Action

We (the master) received data from the remote management slave.

Pass the received data to the remote management master process.

This is typically screen-updates to be passed to the user

interface.

Remote Management Transmit Data Response Action

We (the slave) received an ack to data we previously sent to the

master. Notify the remote management slave process so that it

can queue further transmissions.

Remote management (Master) start Action

Build a REMOTE_MGMT_REQ start message and send to the far end.

Send a proceeding message to the RM master process.

Remote management (Slave) data Action

Build a REMOTE_MGMT_TX_REQ message with the data passed from

the remote management slave process, send it to the far end.

Remote management (Master) data Action

Build a REMOTE_MGMT_RX_REQ message with data passed from the

remote management master process, send it to the far end.

Remote management data acknowledgement Action

Build a REMOTE_MGMT_TX_RSP message and send it so the slave can

send the next block. There is no data associated with this

message.

Remote management (Master) stop Action

Build a REMOTE_MGMT_REQ stop message and send to the far end.

3.5.3. MP+STATE_INITIAL state machine

All sessions start from this state, sub-state A. The state is not

exited until version exchange succeeds.

The sub-states are:

A Initial state

B Sent version request, waiting for version response.

C Waiting for version request.

Event Sub-state

______________________________________________________________________

A B C

======================================================================

MP+START_SESSION 1,+ ** **

______________________________________________________________________

MP+SESSION_DOWN ** 2,Initial:A 2,Initial:A

______________________________________________________________________

MP+SESSION_TERM ** 3,Initial:A 3,Initial:A

______________________________________________________________________

MP+TIMER_EXPIRED ** 4,Initial:A 7,Initial:B

______________________________________________________________________

MP+RX_VERSION_REQ ** 8,Initial:A 5,+

______________________________________________________________________

MP+RX_VERSION_RSP ** 6,+ **

______________________________________________________________________

MP+START_RM 9,* 9,* 9,*

______________________________________________________________________

All other events ** ** **

______________________________________________________________________

Table 2: Initial State Machine

Actions:

1 Start timer, 60 seconds if originator, 30 seconds if answerer.

Start MP+

If originator

Build and send version exchange request

Go to INITIAL, sub-state B.

Go to INITIAL, sub-state C.

2 Do Error Close Action, go to INITIAL, sub-state A.

3 Do Term Action, go to INITIAL, sub-state A.

4 Do Error Close Action, go to INITIAL, sub-state A.

5 Stop the idle timer.

Compare protocol versions, if they do not match Do Error Close

Action, go to INITIAL, sub-state A.

Store off info received from remote.

Build a version exchange response and send to remote end.

Do Enter Idle Action which causes a state change.

6 Stop the retry timer.

Compare protocol versions, if they do not match Do Error Close

Action, go to INITIAL, sub-state A.

Store off info received from remote.

Check the base channel count in the callers profile.

If greater than 1

Set the requested bandwidth to the base channel count.

Do Enter Add Caller action which causes a state change.

Do Enter Idle Action which causes a state change.

7 Both sides think they are the answerer. This is possible if both

dial each other at the same time and the first channel that

completed PPP negotiation happened to be the channel associated

with the incoming call on both units. We resolve this by trying

to become the originator.

If both sides try to become the originator the one with the

largest endpoint discriminator will fall back to being the

answerer.

Restart Idle timer at 60 seconds

Build and send Version Exchange Request message

Go to Initial:B

8 Both sides think they are the originator. This can happen if

both dial each other at the same time and the first channel

that completed PPP negotiation happened to be the channel

associated with the originating call on both units. MP+

determines which will be the caller and which the answerer by

comparing the endpoind discriminator in the version exchange

request with the local endpoint discriminator. The unit with

the smaller endpoint is arbitrarily called the originator. The

actions are:

Compare local endpoint discriminator with endpoint discrimator

in message.

If local endpoint discriminator is less than the remote value

we are the caller, ignore the incoming message.

Otherwise, if local endpoint discriminator is greater than the

remote value we are the answerer:

Compare protocol versions, if they do not match

Do Error Close Action, go to INITIAL, sub-state A.

Store off info received from remote.

Build a version exchange response and send to remote end.

Do Enter Idle Action which causes a state change.

If the two values match, there is a problem, Do Error Close

Action,go to INITIAL, sub-state A.

9 Log an error message.

Notify the user interface of remote management failure.

3.5.4. MP+STATE_IDLE state machine

The Idle state is the state of an active session with no call

management activity in progress.

There are no sub-states.

Event State

_____________________________________________

A

=============================================

MP+SESSION_DOWN 1,Initial:A

_____________________________________________

MP+SESSION_TERM 2,Initial:A

_____________________________________________

MP+TIMER_EXPIRED 3,*

_____________________________________________

MP+UTILIZATION 4,+

_____________________________________________

MP+RX_ADD_REQ 5,+

_____________________________________________

MP+RX_REMOVE_REQ 6,Remove:B

_____________________________________________

MP+RX_RM_REQ 7,+

_____________________________________________

MP+RX_RM_RSP 8,+

_____________________________________________

MP+RX_RM_RX_REQ 9,+

_____________________________________________

MP+RX_RM_TX_REQ 10,+

_____________________________________________

MP+RX_RM_TX_RSP 11,+

_____________________________________________

MP+RX_CLOSE_REQ 12,+

_____________________________________________

MP+START_RM 13,*

_____________________________________________

MP+SEND_RMS 14,*

_____________________________________________

MP+SEND_RMM 15,*

_____________________________________________

MP+RECV_RMM 16,*

_____________________________________________

MP+STOP_RM 17,*

_____________________________________________

All other events **

_____________________________________________

Table 3: Idle State Machine

Actions:

1 Do Error Close Action, go to INITIAL, sub-state A.

2 Do Term Action, go to INITIAL, sub-state A.

3 Do Timer Action.

4 Note that a bandwidth change has been reqested.

Do Enter Idle Action which may cause a state change.

5 If we are the caller:

Do Enter Add [remote answerer] Action.

Else

Do Enter Add [remote caller] Action.

6 Do Enter Remove [remote] Action

7 Do Remote Management Request Action

8 Do Remote Management Response Action

9 Do Remote Management Receive Data Action

10 Do Remote Management Transmit Data Action

11 Do Remote Management Transmit Data Response Action

12 Clear remove lock.

If local recommended channels == 0, then:

send a Close Response message with OK To Close

set to TRUE.

Else

send a Close Response message with OK To Close

set to FALSE.

Do Enter Idle Action.

13 Do Remote management (Master) start Action

14 Do Remote management (Slave) data Action

15 Do Remote management (Master) data Action

16 Do Remote management data acknowledgement Action

17 Do Remote management (Master) stop Action

3.5.5. MP+STATE_ADD state machine

The add state is used by both caller and answerer when an add

transaction is in progress.

The sub-states are:

A Add request sent to answerer, waiting for add response

from the answerer.

B Caller waiting for call complete notification for calls

placed.

C Answerer waiting for add complete message from caller.

Event Sub-state

______________________________________________________________________

A B C

======================================================================

MP+SESSION_DOWN 1,Initial:A 7,Closing:A 1,Initial:A

______________________________________________________________________

MP+SESSION_TERM 2,Initial:A 7,Closing:B 2,Initial:A

______________________________________________________________________

MP+TIMER_EXPIRED 3,+ 3,+ 3,+

______________________________________________________________________

MP+UTILIZATION 4,* 4,* 4,*

______________________________________________________________________

MP+CALL_COMPLETE ** 8,Idle:A **

______________________________________________________________________

MP+RX_VERSION_REQ -,* ** **

______________________________________________________________________

MP+ADD_REQ 5,Add:B ** **

______________________________________________________________________

MP+ADD_RSP 6,+ ** **

______________________________________________________________________

MP+ADD_COMP ** ** 9,Idle:A

______________________________________________________________________

MP+RX_RM_REQ 10,+ 10,+ 10,+

______________________________________________________________________

MP+RX_RM_RSP 11,+ 11,+ 11,+

______________________________________________________________________

MP+RX_RM_RX_REQ 12,+ 12,+ 12,+

______________________________________________________________________

MP+RX_RM_TX_REQ 13,+ 13,+ 13,+

______________________________________________________________________

MP+RX_RM_TX_RSP 14,+ 14,+ 14,+

______________________________________________________________________

MP+RX_REMOVE_REQ -,* ** **

______________________________________________________________________

MP+START_RM 15,* 15,* 15,*

______________________________________________________________________

MP+SEND_RMS 16,* 16,* 16,*

______________________________________________________________________

MP+SEND_RMM 17,* 17,* 17,*

______________________________________________________________________

MP+RECV_RMM 18,* 18,* 18,*

______________________________________________________________________

MP+STOP_RM 19,* 19,* 19,*

______________________________________________________________________

All other events ** ** **

______________________________________________________________________

Table 4: Add State Machine

Actions:

1 Phone numbers (may) have been reserved, they must be released

before the normal error processing occurs.

Release all reserved phone numbers

Do Error Close Action.

2 Phone nubmers (may) have been reserved, they must be released

before the normal close processing occurs.

Release all reserved phone numbers

Do Term Action.

3 Do Timer Action

4 Note that a bandwidth change has been reqested. This will be

processed the next time IDLE state is entered.

5 An add collision has occured. Since the answerer has sent phone

numbers we will try to use what he as sent, within the limits of

the local system.

Compare local channels to add with current channels to

add.

If the local channels to add is less than the remote

channels to add

If the remote number of channels requested will

put us over the maximum number of channels

allowed for the session reduce the channel count

and set an add lock.

Re-reserve the channels. If the number reserved

are less than the number of phone numbers

provided by the far end, set an add lock and

reduce the number of channels to add to what we

could reserve.

Now treat the remote add request as if it were an add

response and process by:

Integrate the phone number returned from the

answerer with the original phone number dialed.

Request that a session be extended by dialing

the integrated phone number. A callback is

passed with the request so call success or

failure can be reported back to MP+.

Go to ADD:B. Note: This change must actually

occur before requesting the first outgoing call.

If not, the callback could be called (and

ignored) because the session is not in the

correct state.

6 If the answerer provided fewer phone numbers than requested set

an add lock.

If the number of channels is zero send an add complete message

(there's nothing to do) and go to the IDLE state.

For each phone number returned

Integrate the phone number returned from the answerer

with the original phone number dialed.

Request that a session be extended by dialing the

integrated phone number. A callback is passed with the

request so call success or failure can be reported back

to MP+.

Go to ADD:B. Note: This change must actually occur before

requesting the first outgoing call. If not, the callback could

be called (and ignored) because the session is not in the correct

state.

7 Restart idle timer for abort.

8 Increment the count of calls completed.

If the call succeeded, increment the count of calls that

succeeded.

If the count of calls completed equals the number of calls placed

If number of calls completed is not the same as the

nubmer that succeeded set an add lock.

Build an add complete message and send it to the far end.

If at least one channel was added clear any remove lock.

Go to the IDLE state.

9 If number of channels requested not equal to number connected

set add lock.

If at least one channel was added clear any remove lock.

Go to the IDLE state.

10 Do Remote Management Request Action

11 Do Remote Management Response Action

12 Do Remote Management Receive Data Action

13 Do Remote Management Transmit Data Action

14 Do Remote Management Transmit Data Response Action

15 Do Remote management (Master) start Action

16 Do Remote management (Slave) data Action

17 Do Remote management (Master) data Action

18 Do Remote management data acknowledgement Action

19 Do Remote management (Master) stop Action

3.5.6. MP+STATE_REMOVE state machine

The state of a session while processing a remove transaction.

The sub-states are:

A Remove request sent, waiting for remove response

B Remove response sent, waiting for remove complete

Event Sub-state

_________________________________________________________

A B

=========================================================

MP+SESSION_DOWN 1,Initial:A 1,Initial:A

_________________________________________________________

MP+SESSION_TERM 2,Initial:A 2,Initial:A

_________________________________________________________

MP+TIMER_EXPIRED 3,+ 3,+

_________________________________________________________

MP+UTILIZATION 4,* 4,*

_________________________________________________________

MP+RX_ADD_REQ 5,+ **

_________________________________________________________

MP+RX_REMOVE_REQ 6,+ **

_________________________________________________________

MP+RX_REMOVE_RSP 7,Idle:A **

_________________________________________________________

MP+RX_REMOVE_COMP ** 8,Idle:A

_________________________________________________________

MP+RX_CLOSE_REQ -,* **

_________________________________________________________

MP+RX_RM_REQ 9,* 9,*

_________________________________________________________

MP+RX_RM_RSP 10,* 10,*

_________________________________________________________

MP+RX_RM_RX_REQ 11,* 11,*

_________________________________________________________

MP+RX_RM_TX_REQ 12,* 12,*

_________________________________________________________

MP+RX_RM_TX_RSP 13,* 13,*

_________________________________________________________

MP+START_RM 14,* 14,*

_________________________________________________________

MP+SEND_RMS 15,* 15,*

_________________________________________________________

MP+SEND_RMM 16,* 16,*

_________________________________________________________

MP+RECV_RMM 17,* 17,*

_________________________________________________________

MP+STOP_RM 18,* 18,*

_________________________________________________________

All other events ** **

_________________________________________________________

Table 5: Remove State Machine

Actions:

1 Do Error Close Action

2 Do Term Action

3 Do Timer Action

4 Note that a bandwidth change has been reqested. This will be

processed the next time IDLE state is entered.

5 Our remove conflicted with the remote end Add. The add takes

preference.

Set a remove lock.

If we are the caller Do Enter Add [remote answerer] Action .

Otherwise Do Enter Add [remote caller] Action .

6 Two remove requests collided. We give preference to the caller

(an arbitrary decision).

If caller, ignore message.

Else

Check maximum number of channels needed by the local end.

Reduce the requested remove count and set a remove lock if

necessary.

Build and send a remove response to the remote.

Go to Remove:B.

7 Compare the number of channels requested with the number allowed

in the response. If fewer allowed set a remove lock.

Look at the current bandwidth. If the number to remove would

bring the current bendwidth below requirements reduce the number

of channels to remove.

If still channels to remove:

Remove the channels.

Clear any add lock.

Send a remove complete indicating the number of channels removed.

8 If at least one channel was removed clear any add lock.

9 Do Remote Management Request Action

10 Do Remote Management Response Action

11 Do Remote Management Receive Data Action

12 Do Remote Management Transmit Data Action

13 Do Remote Management Transmit Data Response Action

14 Do Remote management (Master) start Action

15 Do Remote management (Slave) data Action

16 Do Remote management (Master) data Action

17 Do Remote management data acknowledgement Action

18 Do Remote management (Master) stop Action

3.5.7. MP+STATE_CLOSE state machine

The close state is used when we are gracefully closing a session or

when we were notified that a session terminated mid-transaction.

The sub-states are:

A Waiting for call complete after session down notification

B Waiting for call complete after session terminate

notification.

C Waiting for close response after session close request

sent.

Event Sub-state

______________________________________________________________________

A B C

======================================================================

MP+SESSION_DOWN ** -,* 7,Initial:A

______________________________________________________________________

MP+SESSION_TERM 1,Close:B ** 8,Initial:A

______________________________________________________________________

MP+TIMER_EXPIRED 2,Initial:A 5,Initial:A 6,*

______________________________________________________________________

MP+UTILIZATION -,* -,* 9,*

______________________________________________________________________

MP+CALL_COMPLETE 3,+ 6,Initial:A **

______________________________________________________________________

MP+ADD_REQ ** -,* 10,+

______________________________________________________________________

MP+REMOVE_REQ ** ** 11,Remove:B

______________________________________________________________________

MP+CLOSE_REQ -,* -,* 12,*

______________________________________________________________________

MP+CLOSE_RSP -,* -,* 13,+

______________________________________________________________________

MP+START_RM 4,* 4,* 4,*

______________________________________________________________________

All other events ** ** **

______________________________________________________________________

Table 6: Close State Machine

Actions:

1 The session was closed while waiting for call completes.

Just go to Close:B.

2 We timed out waiting for completes. Just process the link down,

now.

Do Error Close Action.

3 Increment the number of calls complete.

If equal to the number of calls placed then:

Do Error Close Action, go to Initial:A.

Else

No state change.

4 Log an error message.

Notify the user interface of remote management failure.

5 We didn't get all the notifications that we expect. Give up and

close the session anyway. Do Term Action .

6 Increment the number of calls complete.

If equal to the number of calls placed then:

Do Term Action, go to Initial:A.

Else

No state change

7 Do Error Close Action

8 Do Term Action

9 Note that a bandwidth change has been reqested. This will be

processed the next time IDLE state is entered.

10 This is an Add & Close collision. Add wins. Perform current

remote add action.

If we are originator

Do Add [Remote Answerer] Action

else

Do Add [Remote Caller] Action

11 This is a Remove & Close collision, the Remove will win:

Set remove lock to FALSE

Do Remove [Remote] Action.

12 This is a Close collision. But since we both agree:

If we are originator

Send a Close Response with okToClose set to TRUE.

Else

Send a Close Response with okToClose set to FALSE.

13 If Close Response is received with okToClear is TRUE then:

Do Term Action

Else

set remove lock to TRUE and do Enter Idle Action.

4. PPP LCP Extensions

MP+ Configuration Option

The Multilink Protocol Plus introduces the use of an additional LCP

Configuration Option:

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 = 22 length = 4 Currently unused

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 21: MP+ Option

Type - 22.

NOTE: The current implementation uses option 0. This is not an

assigned number, so an IANA assigned official identifier has been

obtained (22).

The option, when sent to a peer, advises the peer that:

the unit is capable of running the MP+ protocol;

The peer can accept or reject the option.

NOTE: The MP+ option MUST NOT be included unless MP is also

negotiated.

5. Security Considerations

Security issues are not discussed in this memo.

6. References

[1] K. Sklower, B. Lloyd, G. McGregor, D. Carr, "The PPP Multilink

Protocol (MP)".

[2] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD

51, RFC1661, Daydreamer, July 1994.

7. Author's Address

Kevin Smith

Ascend Communications

1275 Harbor Bay Parkway

Alameda, CA 94502

Phone: (510) 769-6001

FAX: (510) 814-2300

EMail: ksmith@ascend.com

 
 
 
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2023年上半年GDP全球前十五强
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