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PaC
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...
PPTP divides these functions between the PAC and PNS. The PAC is
responsible for functions 1, 2, and possibly 3. The PNS may be
...
... PPTP divides these functions between the PAC and PNS. The PAC is
responsible for functions 1, 2, and possibly 3. The PNS may be
responsible for function 3 and is responsible for functions 4, 5, and
...
... protocol data units (PDUs) between
the PAC and PNS, as well as call control and management is addressed
by PPTP ...
...
The PPTP protocol is implemented only by the PAC and PNS. No other
systems need to be aware of PPTP. Dial networks ...
... PPTP. Dial networks may be connected to a
PAC without being aware of PPTP. Standard PPP client software ...
...
It is envisioned that there will be a many-to-many relationship
between PACs and PNSs. A PAC may provide service to many PNSs. For
example, an Internet service provider ...
... provided on the tunnels used to carry user data between PAC and PNS.
This mechanism allows for efficient use of the bandwidth available
...
... PPP
operation and of handling the PPTP protocol. The PAC need only
implement TCP/IP to pass traffic ...
... PPTP is connection-oriented. The PNS and PAC maintain state for
each user that is attached to a PAC ...
... PPTP: 1) a Control Connection
between each PAC-PNS pair operating over TCP and 2) an IP tunnel
...
... TCP and 2) an IP tunnel
operating between the same PAC-PNS pair which is used to transport
GRE ...
... Before PPP tunneling can occur between a PAC and PNS, a control
connection must be established between them. The control connection
...
... the means by which a PNS is notified of an incoming call at an
associated PAC, as well as the means by which a PAC is instructed to
place an outgoing dial call.
...
... incoming call at an
associated PAC, as well as the means by which a PAC is instructed to
place an outgoing dial call.
...
...
A control connection can be established by either the PNS or the PAC.
Following the establishment of the required TCP connection, the PNS
...
... Following the establishment of the required TCP connection, the PNS
and PAC establish the control connection using the Start-Control-
...
... Connection-Request and -Reply messages. These messages are also used
to exchange information about basic operating capabilities of the PAC
and PNS. Once the control connection is established, the PAC ...
... PAC
and PNS. Once the control connection is established, the PAC or PNS
may initiate sessions by requesting outbound calls or responding to
...
... Link-Info message. Individual sessions may be released by either the
PAC or PNS, also through Control Connection messages.
...
... echo
messages. This ensures that a connectivity failure between the PNS
and the PAC can be detected in a timely manner. Other failures can be
reported via the
...
... management
related messages in the future, such as a message allowing the PNS to
request the status of a given PAC; these message types have not yet
been defined.
...
... PPTP requires the establishment of a tunnel for each communicating
PNS-PAC pair. This tunnel is used to carry all user session PPP ...
... PPP
packets for sessions involving a given PNS-PAC pair. A key which is
present in the GRE header ...
... PPP packets are multiplexed and demultiplexed over a
single tunnel between a given PNS-PAC pair. The value to use in the
key field is established by the call establishment procedure which
takes place on the control connection ...
... PPTP defines a set of messages sent as TCP data on the control
connection between a PNS and a given PAC. The TCP session for the
control connection ...
... control connection itself. The control connection is
initiated by either the PNS or PAC after they establish the
underlying TCP connection. The procedure and configuration
information ...
... user data
on the established TCP connection between a given PNS-PAC pair. Note
that care has been taken to ensure that all word (2 octet) and
...
... control message used
to establish the control connection between a PNS and a PAC. Each
PNS-PAC pair requires a dedicated control connection ...
... control connection between a PNS and a PAC. Each
PNS-PAC pair requires a dedicated control connection to be
established. A control connection ...
... other PPTP messages can be issued. The establishment of the control
connection can be initiated by either the PNS or PAC. A procedure
which handles the occurrence of a collision between PNS and PAC
...
... control
connection can be initiated by either the PNS or PAC. A procedure
which handles the occurrence of a collision between PNS and PAC
Start-Control-Connection ...
... Connection-Requests issued by the PNS, this
value SHOULD be set to 0. It MUST be
ignored by the PAC.
Firmware Revision This field contains the firmware revision
...
...
Firmware Revision This field contains the firmware revision
number of the issuing PAC, when issued by
the PAC, or the version ...
... 64 octet field containing the DNS name of
the issuing PAC or PNS. If less than 64
octets in length, the remainder of this
field SHOULD be filled with octets of value
...
... 64 octet field containing a vendor
specific string describing the type of PAC
being used, or the type of PNS software
being used if this request is issued by the
...
... Connection-Reply issued by the PNS, this
value SHOULD be set to 0 and it must be
ignored by the PAC. The PNS MUST NOT use
this value to try to track the remaining
number of PPP ...
...
Firmware Revision This field contains the firmware revision
number of the issuing PAC, or the version of
the PNS PPTP ...
... 64 octet field containing the DNS name of
the issuing PAC or PNS. If less than 64
octets in length, the remainder of this
field SHOULD be filled with octets of value
...
... 64 octet field containing a vendor
specific string describing the type of PAC
being used, or the type of PNS software
being used if this request is issued by the
...
... PPTP control message sent by
one peer of a PAC-PNS control connection to inform the other peer
that the control connection ...
... PPTP control message sent by
one peer of a PAC-PNS control connection upon receipt of a Stop-
Control-Connection ...
... PPTP control message sent by either peer of a
PAC-PNS control connection. This control message is used as a "keep-
...
... PPTP control message sent by either peer of a
PAC-PNS control connection in response to the receipt of an Echo-
...
... PPTP control message sent by the PNS
to the PAC to indicate that an outbound call from the PAC is to be
established. This request provides the PAC ...
... control message sent by the PNS
to the PAC to indicate that an outbound call from the PAC is to be
established. This request provides the PAC with information required
...
... PAC to indicate that an outbound call from the PAC is to be
established. This request provides the PAC with information required
to make the call. It also provides information to the PAC that is
...
... established. This request provides the PAC with information required
to make the call. It also provides information to the PAC that is
used to regulate the transmission of data to the PNS for this session
...
... Call ID A unique identifier, unique to a particular
PAC-PNS pair assigned by the PNS to this
session. It is used to multiplex and
...
... session in logged session
information. Unlike the Call ID, both the
PNS and PAC associate the same Call Serial
Number with a given session. The combination
...
... packet processing delay
that might be imposed on data sent to the
PNS from the PAC. This value is specified
in units of 1/10 seconds. For the PNS this
number should be very small. See section
...
... The Outgoing-Call-Reply is a PPTP control message sent by the PAC to
the PNS in response to a received Outgoing-Call-Request message. The
...
... provides information to the PNS about particular parameters used for
the call. It provides information to allow the PNS to regulate the
transmission of data to the PAC for this session.
...
... unique identifier for the tunnel, assigned
by the PAC to this session. It is used to
multiplex and demultiplex data sent over the
...
... multiplex and demultiplex data sent over the
tunnel between the PNS and PAC involved in
this session.
...
... Outgoing Call was not
established within time allotted by
PAC
7 (Do Not Accept) - Outgoing Call ...
...
Packet Recv. Window Size The number of received data packets the PAC
will buffer for this session ...
... packet processing delay
that might be imposed on data sent to the
PAC from the PNS. This value is specified
in units of 1/10 seconds. For the PAC, this
...
... PAC from the PNS. This value is specified
in units of 1/10 seconds. For the PAC, this
number is related to the size of the buffer
...
... client. This value should be set to the
maximum delay that can normally occur
between the time a packet arrives at the PAC
and is delivered to the client. See section
...
... Physical Channel ID This field is set by the PAC in a vendor-
specific manner to the physical channel ...
... The Incoming-Call-Request is a PPTP control message sent by the PAC
to the PNS to indicate that an inbound call is to be established from
the PAC ...
... PAC
to the PNS to indicate that an inbound call is to be established from
the PAC. This request provides the PNS with parameter information
for the incoming call.
...
... PPTP
for establishing incoming calls. The PAC may defer answering the
call until it has received an Incoming-Call-Reply from the PNS
indicating that the call should be established. This mechanism allows
...
... unique identifier for this tunnel,
assigned by the PAC to this session. It is
used to multiplex and demultiplex data sent
...
... used to multiplex and demultiplex data sent
over the tunnel between the PNS and PAC
involved in this session.
...
... Call Serial Number An identifier assigned by the PAC to this
session for the purpose of identifying this
...
... session in logged session
information. Unlike the Call ID, both the
PNS and PAC associate the same Call Serial
Number to a given session. The combination
...
... Physical Channel ID This field is set by the PAC in a vendor-
specific manner to the number of the
physical ...
... PPTP control message sent by the PNS to
the PAC in response to a received Incoming-Call-Request message. The
reply indicates the result of the incoming call ...
... reply indicates the result of the incoming call attempt. It also
provides information to allow the PAC to regulate the transmission of
data to the PNS for this session.
...
... PPTP
for establishing incoming calls. It indicates to the PAC whether the
call should be answered or not.
...
... multiplex and demultiplex data sent over the
tunnel between the PNS and PAC involved in
this session.
...
... Request message. It is used by
the PAC to match the Incoming-Call-Reply
with the Incoming-Call-Request it issued.
This value is included in the GRE ...
...
Packet Recv. Window Size The number of received data packets the PAC
will buffer for this session ...
... packet processing delay
that might be imposed on data sent to the
PAC from the PNS. This value is specified
in units of 1/10 seconds.
...
... PPTP control message sent by
the PAC to the PNS in response to a received Incoming-Call-Reply. It
provides information to the PNS about particular parameters used for
the call. It also provides information to allow the PNS to regulate
...
... provides information to the PNS about particular parameters used for
the call. It also provides information to allow the PNS to regulate
the transmission of data to the PAC for this session.
...
... the PNS with additional information about the call that cannot, in
general, be obtained at the time the Incoming-Call-Request is issued
by the PAC.
0 1 2 3
...
...
Packet Recv. Window Size The number of received data packets the PAC
will buffer for this session ...
... packet processing delay
that might be imposed on data sent to the
PAC from the PNS. This value is specified
in units of 1/10 seconds.
...
... PPTP control message sent by the PNS to
the PAC indicating that a particular call is to be disconnected. The
call being cleared can be either an incoming or outgoing call, in any
...
... outgoing call, in any
state. The PAC responds to this message with a Call-Disconnect-
Notify message.
...
... PPTP control message sent by
the PAC to the PNS. It is issued whenever a call is disconnected,
due to the receipt by the PAC of a Call-Clear-Request or for any
...
... the PAC to the PNS. It is issued whenever a call is disconnected,
due to the receipt by the PAC of a Call-Clear-Request or for any
other reason. Its purpose is to inform the PNS of both the
disconnection and the reason for it.
...
... Reserved0 This field MUST be 0.
Call ID The value of the Call ID assigned by the PAC
to this call. This value is used instead of
the Peer's Call ID because the latter may
...
... PPTP control message sent by the
PAC to the PNS to indicate WAN error conditions (conditions that
...
... PPTP control message sent by the PNS
to the PAC to set PPP-negotiated options. Because these options can
change at any time during the life of the call, the PAC ...
... PAC to set PPP-negotiated options. Because these options can
change at any time during the life of the call, the PAC must be able
to update its internal call ...
... Reserved0 This field MUST be 0.
Peer's Call ID The value of the Call ID assigned by the PAC
to this call.
...
... 1 (Not-Connected) - No control connection exists yet for this
PAC-PNS pair
2 (Bad-Format) - Length is wrong or Magic Cookie ...
... PPTP control connection protocol is not distinguishable
between the PNS and PAC, but is distinguishable between the
originator and receiver. The originating peer is the one which first
...
... receiver. The originating peer is the one which first
attempts the TCP open. Since either PAC or PNS may originate a
connection, it is possible for a TCP ...
... Control Connection Originator (may be PAC or PNS) ...
...
A PAC and PNS must have only one control connection between them. It
is possible, however, for a PNS and a PAC ...
... PAC and PNS must have only one control connection between them. It
is possible, however, for a PNS and a PAC to simultaneously attempt
to establish a control connection to each other. When a Start ...
... telephone signaling, both the PNS
and PAC should be implemented with multi-threaded architectures such
that messages related to multiple calls are not serialized and
...
... architectures such
that messages related to multiple calls are not serialized and
blocked. The transit delay between the PAC and PNS should not exceed
one second. The call and connection state ...
... accepts. This Call ID value MUST be unique for the tunnel between the
PNS and PAC to which it belongs. Tunnels to other peers can use the
same Call ID number so the receiver ...
...
An Incoming-Call-Request message is generated by the PAC when an
associated telephone line rings. The PAC ...
... PAC when an
associated telephone line rings. The PAC selects a Call ID and serial
number and indicates the call bearer type. Modems should always
...
... telephone network.
Once the PAC sends the Incoming-Call-Request, it waits for a response
from the PNS but does not answer the call from the telephone network.
...
... If the PNS chooses to accept the call, it responds with an Incoming-
Call-Reply which also indicates window sizes (see section 4.2). When
the PAC receives the Outgoing-Call-Reply, it attempts to connect the
call, assuming the calling party has not hung up. A final call
connected message from the PAC ...
... PAC receives the Outgoing-Call-Reply, it attempts to connect the
call, assuming the calling party has not hung up. A final call
connected message from the PAC to the PNS indicates that the call
states for both the PAC and the PNS should enter the established
...
... connected message from the PAC to the PNS indicates that the call
states for both the PAC and the PNS should enter the established
state.
...
... When the dialed-in client hangs up, the call is cleared normally and
the PAC sends a Call-Disconnect-Notify message. If the PNS wishes to
clear a call, it sends a Call-Clear-Request message and then waits
...
... PAC Incoming Call States ...
... /Send Call Disconnect Notify
The states associated with the PAC for incoming calls are:
...
... TE has
detected an incoming Q.931 SETUP message. The PAC sends an
Incoming-Call-Request message and moves to the wait_reply state ...
...
wait_reply
The PAC receives an Incoming-Call-Reply message indicating non-
willingness to accept the call (general error or don't accept) and
...
... idle state. If the reply message indicates
that the call is accepted, the PAC sends an Incoming-Call-
Connected message and enters the established state.
...
...
An event on the telco connection. The PAC sends a
Call-Disconnect-Notify message
...
... Call-Disconnect-Notify message
Receipt of a Call-Clear-Request. The PAC sends a
Call-Disconnect-Notify message
...
... Call-Disconnect-Notify message
A local reason. The PAC sends a Call-Disconnect-Notify message.
...
... An Incoming-Call-Request message is received. If the request is
not acceptable, an Incoming-Call-Reply is sent back to the PAC and
the PNS remains in the idle state. If the Incoming-Call-Request
message ...
... wait_connect
If the session is connected on the PAC, the PAC sends an incoming
call connect message to the PNS which then moves into established
...
... If the session is connected on the PAC, the PAC sends an incoming
call connect message to the PNS which then moves into established
state ...
... incoming
call connect message to the PNS which then moves into established
state. The PAC may send a Call-Disconnect-Notify to indicate that
the incoming caller could not be connected. This could happen,
...
... telephone user accidently places a standard
voice call to a PAC resulting in a handshake failure on the called
modem ...
... The session is terminated either by receipt of a Call-Disconnect-
Notify message from the PAC or by sending a Call-Clear-Request.
Once a Call-Clear-Request has been sent, the session enters the
...
...
Outgoing messages are initiated by a PNS and instruct a PAC to place
a call on a telco interface. There are only two messages for outgoing
calls ...
... an Outgoing-Call-Request specifying the dialed party phone number and
subaddress as well as speed and window parameters. The PAC MUST
respond to the Outgoing-Call-Request message with an Outgoing-Call-
...
... Request message with an Outgoing-Call-
Reply message once the PAC determines that:
The call has been successfully connected
...
... PAC Outgoing Call States ...
... Call Disconnect Notify
The states associated with the PAC for outgoing calls are:
...
... idle
An Outgoing-Call-Request message is sent to the PAC and the
session moves into the wait_reply state ...
... idle state. If the PNS chooses to
terminate the session, it sends a Call-Clear-Request to the PAC
and then enters the wait_disconnect state.
...
... wait_disconnect
A session disconnection is waiting to be confirmed by the PAC.
Once the PNS receives the Call-Disconnect-Notify message, the
session ...
... tunnel. The IP packets transmitted over the tunnels between a PAC
and PNS has the following general structure:
...
... overhead of the adaptive time-out algorithm is reduced. The
PAC is not required to transmit multi-packet acknowledgments; it can
instead acknowledge each packet individually as it is delivered to
the PPP ...
... Occasionally packets lose their sequencing across a complicated
internetwork. Say, for example that a PNS sends packets 0 to 5 to a
PAC. Because of rerouting in the internetwork, packet 4 arrives at
the PAC ...
... PAC. Because of rerouting in the internetwork, packet 4 arrives at
the PAC before packet 3. The PAC acknowledges packet 4, and may
assume packet 3 is lost. This acknowledgment grants window credit
...
... rerouting in the internetwork, packet 4 arrives at
the PAC before packet 3. The PAC acknowledges packet 4, and may
assume packet 3 is lost. This acknowledgment grants window credit
beyond packet 4.
...
... beyond packet 4.
When the PAC does receive packet 3, it MUST not attempt to transmit
it to the corresponding PPP client ...
... PPP does properly deal with the loss of packets, but
not with reordering so out of sequence packets between the PNS and
PAC MUST be silently discarded, or they may be reordered by the
receiver. When packet 5 comes in, it is acknowledged by the PAC ...
... PAC MUST be silently discarded, or they may be reordered by the
receiver. When packet 5 comes in, it is acknowledged by the PAC
since it has a higher sequence number than 4, which was the last
...
... since it has a higher sequence number than 4, which was the last
highest packet acknowledged by the PAC. Packets with duplicate
sequence numbers should never occur since the PAC ...
... PAC. Packets with duplicate
sequence numbers should never occur since the PAC and PNS never
retransmit GRE packets. A robust implementation will silently
discard ...
... flow-control across the internetwork and to perform efficient data
buffering to keep the PAC-PNS data channels full without causing
receive buffer ...
...
Independent time-outs for each session. A device (PAC or PNS) will
have to maintain and calculate time-outs for every active session ...
... each side to process the maximum amount of data buffered in their
receive packet sliding window. The PPD is the value exchanged
between the PAC and PNS when a call is established. For the PNS,
this number should be small. For a PAC making modem ...
... between the PAC and PNS when a call is established. For the PNS,
this number should be small. For a PAC making modem connections,
...
... MTU is the overall MTU for the internetwork link between the PAC and
PNS. WindowSize represents the number of packets in the sliding
window, and is implementation-dependent. The latency ...
... in bytes per second, omit the 8. PACFudge is not required but can be
used to take overall processing overhead of the PAC into account.
The value of PPD is used to seed the adaptive algorithm ...