Layer 2 Tunneling Protocol (L2TP) Access Line Information Attribute Value Pair (AVP) Extensions
Cisco Systems181 Bay Street, Suite 3400TorontoM5J 2T3ONCanadavince@cisco.comCisco Systems7200 Kit Creek RoadPO Box 14987Research Triangle Park27709NCUSAcpignata@cisco.comRedback Networks300 Holger WaySan Jose95134CAUSAparberg@redback.comJuniper Networks 10 Technology Park DriveWestford01886MAUSAjgibbons@juniper.nethowsoft@mindspring.comL2TPAccess Line InformationDSLAM
This document describes a set of Layer 2 Tunneling Protocol (L2TP)
Attribute Value Pair (AVP) extensions designed to carry the subscriber
Access Line identification and characterization information that
arrives at the Broadband Remote Access Server (BRAS) with L2TP Access
Concentrator (LAC) functionality. It also describes a mechanism to
report connection speed changes, after the initial connection speeds
are sent during session establishment. The primary purpose of this
document is to provide a reference for DSL equipment vendors wishing
to interoperate with other vendors' products. The L2TP AVPs defined
in this document are applicable to both L2TPv2 and L2TPv3.
Access Nodes (ANs), referred to as Digital Subscriber Line Access Multiplexers (DSLAMs) in DSL, are adding
enhancement features to forward, via in-band signaling, subscriber Access Line
identification and characterization information to their connected upstream
Broadband Remote Access Server (BRAS) with L2TP Access Concentrator
(LAC) functionality.
The Access Node/DSLAM may forward the information via one or more of the
following methods:
Vendor-Specific Point-to-Point Protocol over Ethernet (PPPoE) Tags
.
DHCP Relay Options
and Vendor-Specific Information Suboptions
.
Access Node Control Protocol .
Currently, this information is been collected on the BRAS and
forwarded to a radius server via .
This document describes the new additional L2TP AVPs that were created to
forward the subscriber line identification and characterization information
received at the BRAS/LAC to the terminating L2TP Network Server (LNS).
It also
describes a mechanism by which the LAC may report connection speed
changes to the LNS, after the initial connection speeds are sent
by the LAC during session establishment.
The L2TP AVPs defined in this document MAY be used with either an L2TPv2
or L2TPv3
implementation.
The information acquired may be used to provide authentication, policy, and
accounting functionality. It may also be collected and used for management
and troubleshooting purposes.
The following sections define the usage and meaning of certain specialized
terms
in the context of this document.
The key words "MUST", "MUST NOT",
"REQUIRED", "SHALL",
"SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED",
"MAY", and "OPTIONAL" in this document
are to be interpreted as described in .
Access Node/DSLAM
The Access Node/DSLAM is a DSL signal terminator that contains a
minimum of one Ethernet or ATM interface that serves as its upstream
interface into which it aggregates traffic from several ATM-based
(subscriber ports) or Ethernet-based downstream interfaces.
BNG
Broadband Network Gateway. A BNG is an IP edge router where
bandwidth and Quality-of-Service (QoS) policies are applied; the functions performed by
a BRAS are a superset of those performed by a BNG.
BRAS
Broadband Remote Access Server. A BRAS is a BNG and is the
aggregation point for the subscriber traffic. It provides
aggregation capabilities (e.g., IP, PPP, Ethernet) between the
access network and the core network. Beyond its aggregation
function, the BRAS is also an injection point for policy
management and IP QoS in the access network.
DSL
Digital Subscriber Line. DSL is a technology that allows digital
data transmission over wires in the local telephone network.
DSLAM
Digital Subscriber Line Access Multiplexer. DSLAM is a device
that terminates DSL subscriber lines. The data is aggregated and
forwarded to ATM- or Ethernet-based aggregation networks.
IWF
Interworking Function. The set of functions required for
interconnecting two networks of different technologies (e.g., ATM
and Ethernet). IWF is utilized to enable the carriage of Point-to-Point Protocol over ATM (PPPoA) traffic over PPPoE.
LAC
L2TP Access Concentrator.
If an L2TP Control Connection Endpoint (LCCE) is being used to
cross-connect an L2TP session directly to a data link, we refer to
it as an L2TP Access Concentrator (LAC).
(See and
.)
LCCE
L2TP Control Connection Endpoint.
An L2TP node that exists at either end of an L2TP control
connection. May also be referred to as an LAC or LNS, depending
on whether tunneled frames are processed at the data link (LAC) or
network layer (LNS).
(See
.)
LNS
L2TP Network Server.
If a given L2TP session is terminated at the L2TP node and the
encapsulated network layer (L3) packet processed on a virtual
interface, we refer to this L2TP node as an L2TP Network Server
(LNS).
(See and
.)
When the BRAS with LAC functionality receives the Access Line information from
the Access Node and has determined that the session will be
established with an LNS,
the LAC will forward the information that it has collected in the newly
defined
L2TP AVPs. The LAC will only forward the Access Line Information
AVPs that have populated values.
Access Line information from any of the above methods must be available
at the BRAS prior to the start of session negotiation by the LAC.
This ensures Access Line parameters are reliably provided to the LNS and
avoids additional call set-up delays. Under the condition that the LAC
has not received any Access Line information from any of the methods, as
default behavior the LAC SHOULD establish the L2TP session without waiting
for the Access Line information. In this case, the LAC MUST NOT send
any of the Access Line AVPs to the LNS. The LAC MAY, as local policy,
wait for the Access Line information from one or more of the methods
before forwarding the information in the Access Line L2TP AVPs to the LNS.
It is possible that the Access Node will only send a subset of the currently
available line information defined.
The LAC MUST be able to limit
and/or filter which AVPs, if any, are sent to the LNS.
It is also possible that the LAC may receive Access Line information from multiple
sources and at different time intervals. Local policy SHOULD determine which
source(s) the LAC will accept. The LAC SHOULD default to accepting ANCP-sourced
parameters.
The Access Line AVPs are sent as part of the L2TP Incoming-Call-Request (ICRQ)
control message.
Connect Speed Update AVPs are sent as part of
the Connect-Speed-Update-Notification (CSUN)
or Connect-Speed-Update-Request
(CSURQ) L2TP messages
(see Sections ,
, and
).
It is possible for the LAC to send updated Connect Speed characteristics
to the LNS via the Connect Speed Update AVP in an
L2TP Connect-Speed-Update-Notification (CSUN)
control message (see ).
To avoid unnecessary L2TP Connect-Speed-Update-Request and
Connect-Speed-Update-Notification message exchanges between
the LAC and LNS (e.g., during failover
protocol recovery and resynchronization), the LAC signals in the
session establishment exchange its
ability and desire to provide speed updates during the life of the session.
This is achieved using
a new AVP, Connect Speed Update Enable (see ),
sent in the L2TP Incoming-Call-Request (ICRQ) control message.
The absence
of this AVP in the ICRQ message implies that the LAC will not
be sending any speed
updates during the life of the session.
If the LAC is configured to accept ANCP-sourced parameters,
and supports providing speed updates during the life of a session,
it MUST send the Connect Speed Update Enable AVP in the ICRQ, since
this implies that speed updates may occur over
the life of the connection.
If the
LAC is configured to only accept PPPoE vendor-specific tags, it MUST NOT send
the Connect Speed Update Enable AVP in the ICRQ, since
the connection speed is only sent during
PPPoE discovery
and no further updates will occur during the life of the
connection.
If the Access Line information changes while the session is still maintained,
connection speed updates MAY be sent from the LAC to the LNS via an L2TP
Connect-Speed-Update-Notification (CSUN) Message
(see ). A new AVP,
Connect Speed Update AVP (see ),
is included in the CSUN message to report connect
speed updates for a specific session
after the initial connection speeds are established (i.e.,
at session establishment
via the Tx Connect Speed and Rx Connect Speed AVPs,
Attribute Types 24 and
38, respectively, for L2TPv2 and 74 and 75, respectively, for L2TPv3).
The values established in the Connect Speed Update AVP (as well as the
values for the initial Tx/Rx
Connect Speeds AVPs) are based on LAC local policy.
For example, the LAC's local policy may use the
Actual-Data-Rate-Upstream and Actual-Data-Rate-Downstream as its
policy to report connection speed updates. For consistency, the same
local policy SHOULD equally apply both to the initial connect speeds
(conveyed during session establishment) and to the (optional) connect
speed updates (sent after the establishment of the session).
The CSUN message MAY be
sent periodically to
the LNS based on local policy and may include more than one
Connect Speed Update
AVP. The bulking of more than one Connect Speed Update AVP into the CSUN
message serves the following purposes:
Dampens the rate of changes sent to the LNS when Access Line parameter
updates are received at a high rate for a given line.
Efficiently forwards speed updates when Access Line parameter updates
are received for many lines at the same time.
Supports failover protocol recovery and
resynchronization.
During failover recovery and resynchronization, to ensure the correct speeds
have been applied to outstanding sessions on each tunnel, the LNS MAY issue a
Connect-Speed-Update-Request (CSURQ) message
(see ) to the LAC containing one or more
Session IDs. In response to the CSURQ message, the LAC MUST issue a
Connect-Speed-Update-Notification (CSUN) message
(see )
containing a Connect Speed Update AVP
for each of the Session IDs requested in the CSURQ.
Note:
In the CSUN response to the CSURQ, the LAC MUST NOT respond to
unknown sessions, or to known sessions for which it did not issue a
Connect Speed Update Enable AVP in the prior Incoming-Call-Request
(ICRQ) control message for the session
(see Sections
and ).
This section defines two new Messages that are used
with the IETF Vendor ID of 0 in the Message Type AVP.
The following message types will be assigned to these new messages
(see ):
28: (CSUN) Connect-Speed-Update-Notification29: (CSURQ) Connect-Speed-Update-Request
The Mandatory (M) bit within the Message Type AVP SHOULD be clear
(i.e., not set) for the CSUN and CSURQ control messages,
to allow for an
L2TP Control Connection Endpoint (LCCE)
to maintain the control connection if the
message type is unknown.
The Connect-Speed-Update-Notification (CSUN) is an
L2TP control message sent by the LAC
to the LNS to provide transmit and receive
connection speed updates for one or more sessions. The
connection speed may change at any time during the life of the call; thus, the
LNS SHOULD be able to update its connection speed on an active
session.
The following AVPs MUST be present in the CSUN:
Message TypeConnect Speed Update (more than one may be present in the CSUN)
Note that the LAC MUST NOT include a Connect Speed Update AVP for which it did
not send a Connect
Speed Update Enable AVP in the prior Incoming-Call-Request (ICRQ)
control message for the session.
The Connect-Speed-Update-Request (CSURQ)
is an L2TP control message sent by the LNS to
the LAC to request the current transmit and receive
connection speed for one or more sessions. It
MAY be issued at any time during the life of the tunnel and MUST only be issued
for each outstanding session on each tunnel on which the LNS has already
received a Connect
Speed Update Enable AVP in the prior Incoming-Call-Request (ICRQ)
control message for the session. It is typically used as part of failover
recovery and resynchronization to allow the LNS to verify it has the correct
speeds for each outstanding session on each tunnel.
The following AVPs MUST be present in the CSURQ:
Message TypeConnect Speed Update (more than one may be present in the CSURQ)
The Current Tx Connect Speed and Current Rx Connect Speed fields in
the Connect Speed Update AVP MUST be set to 0 when this AVP
is used in the CSURQ message.
In the CSUN response to the CSURQ, the LAC MUST NOT respond to
unknown sessions or to known sessions for which it did not issue a
Connect Speed Update Enable AVP in the prior Incoming-Call-Request
(ICRQ) control message for the session.
The Access Line information was initially defined in the DSL Forum Technical
Report TR-101 .
TR-101 defines the line characteristic that are sent from an
Access Node.
The following sections contain a list of the Access Line Information L2TP AVPs.
Included with each of the listed AVPs is a short description of the purpose of
the AVPs.
The M bit for all the AVPs defined in this document SHOULD be set to 0
to allow
for backwards compatibility with LNSs that do not support the Access Line
Information AVP extensions hereby defined. However, if it is desired to prevent
the establishment of the L2TP session if the peer LNS does not support the
Access Line Information AVP extensions, the M bit MAY be set to 1. See Section
4.2 of
and Section 5.2 of
.
All the AVPs defined in this document MAY be hidden (the H bit MAY be 0 or 1).
The Length (before hiding)
of all the listed AVPs is 6 plus the length of the Attribute Value,
if one is required, in octets.
The Vendor ID for all the listed AVPs
(Sections through )
is that of the IANA assigned ADSL Forum
Vendor ID, decimal 3561
.
All the listed AVPs ( through )
MAY be present in the following messages unless otherwise
stipulated:
Incoming-Call-Request (ICRQ)
The Value of the AVP contains information about
the Access Line to which the subscriber is attached.
With the exception of the Connect
Speed Update AVP (see ),
all new AVPs specifying a data rate or speed expressed in bits per second (bps)
will be sent as 64-bits to provide
extensibility to support future increases in subscriber connection
speeds. These new AVPs that specify a 64-bit "Data-Rate" are defined from
to , both inclusive.
Whenever a speed value sent in an AVP fits within 32 bits, the
upper 32 bits MUST be transmitted as 0s.
The various Data-Rates and Interleaving-Delays used in the subsequent
Sections
through
are defined in Section 3.9.4 of .
The qualifiers used with these Data-Rates and Interleaving-Delays
have the following meanings:
Actual rate or delay of an access loopMaximum value that can be achieved by the equipmentMinimum value configured by the operatorMaximum value configured by the operator
The Access Line Agent-Circuit-Id AVP, Attribute Type 1, contains information
describing the subscriber agent circuit ID corresponding to the logical access
loop port of the Access Node/DSLAM from which a subscriber's requests are
initiated.
The Agent-Circuit-Id is of arbitrary length, but MUST be greater than 1 octet
and not greater than 63 octets.
The Length (before hiding) of this AVP
is 6 plus the length of the Agent-Circuit-Id.
The Agent-Circuit-Id contains information about the Access Node/DSLAM to which
the subscriber is attached, along with a unique
identifier for the subscriber's DSL
port on that Access Node/DSLAM.
The Agent-Circuit-Id contains a locally administered string representing
the access loop logical port, and its
syntax is defined in Section 3.9.3 of .
The text string is encoded in the UTF-8
charset .
An exemplary description of the Agent-Circuit-Id string format follows
for background purposes. The LAC MUST treat the string as an opaque
value and MUST NOT manipulate or enforce the format of the string based
on the description here or in TR-101 .
Default syntax for the string is defined in .
The examples in this section are included only for illustrative purposes.
The exact syntax of the string is implementation dependent; however, a typical
practice is to subdivide it into two or more space-separated components, one to
identify the Access Node and another the subscriber line on that node, with
perhaps an indication of whether that line is Ethernet or ATM. Example formats
for this string are shown below.
"Access-Node-Identifier atm slot/port:vpi.vci"
(when ATM/DSL is used)
"Access-Node-Identifier eth slot/port[:vlan-id]"
(when Ethernet/DSL is used)
The syntax for the string is defined in .
An example showing the slot and port field encoding is given below:
"Relay-identifier atm 3/0:100.33"
(slot = 3, port = 0, vpi = 100, vci = 33)
The Access-Node-Identifier is a unique ASCII string that does not include
'space' characters. The syntax of the slot and port fields reflects typical
practices currently in place. The slot identifier does not exceed 6 characters
in length, and the port identifier does not exceed 3 characters in length using
a '/' as a delimiter.
The exact manner in which slots are identified is Access Node/DSLAM implementation dependent. The vpi, vci, and vlan-id fields (when applicable)
are related to a given access loop (U-interface).
The Access Line Agent-Remote-Id AVP, Attribute Type 2, contains an
operator-specific, statically configured
string that uniquely identifies the subscriber
on the associated access loop of the Access Node/DSLAM.
The Agent-Remote-Id is of arbitrary length, but MUST be greater than
1 octet and
not greater than 63 octets.
The Length (before hiding)
of this AVP is 6 plus the length of the Agent-Remote-Id.
The Agent-Remote-Id contains information sent from the Access Node/DSLAM from
which the subscriber is attached, to further refine the access loop
logical port identification with a user.
The content of this message is entirely open
to the service provider's discretion. For example, it MAY contain a subscriber
billing ID or telephone number.
The LAC MUST treat the string as an opaque
value and MUST NOT manipulate or enforce its format.
The text string is defined in , and is
encoded in the UTF-8 charset .
The Access Line Actual-Data-Rate-Upstream AVP, Attribute Type 129, contains the
actual upstream train rate of a subscriber's synchronized Access link.
The Actual-Data-Rate-Upstream is an 8-octet value.
The Actual-Data-Rate-Upstream AVP contains an 8-octet unsigned integer,
indicating the subscriber's actual data rate upstream of a synchronized Access
link. The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Actual-Data-Rate-Downstream AVP, Attribute Type 130, contains
the actual downstream train rate of a subscriber's synchronized Access link.
The Actual-Data-Rate-Downstream AVP contains an 8-octet unsigned integer,
indicating the subscriber's actual data rate downstream of a synchronized
Access link. The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Minimum-Data-Rate-Upstream AVP, Attribute Type 131,
contains the
subscriber's operator-configured minimum upstream data rate.
The Minimum-Data-Rate-Upstream AVP contains an 8-octet unsigned integer,
indicating the subscriber's minimum upstream data rate (as configured by the
operator). The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Minimum-Data-Rate-Downstream AVP, Attribute Type 132, contains
the subscriber's operator-configured minimum downstream data rate.
The Minimum-Data-Rate-Downstream AVP contains an 8-octet unsigned integer,
indicating the subscriber's minimum downstream data rate (as configured by the
operator). The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Attainable-Data-Rate-Upstream AVP, Attribute Type 133, contains
the subscriber's actual attainable upstream data rate.
The Attainable-Data-Rate-Upstream AVP contains an 8-octet unsigned integer,
indicating the subscriber's Access Line actual attainable upstream data rate.
The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Attainable-Data-Rate-Downstream AVP, Attribute Type 134,
contains the subscriber's actual attainable downstream data rate.
The Attainable-Data-Rate-Downstream AVP contains an 8-octet unsigned integer,
indicating the subscriber's Access Line actual DSL attainable downstream data rate.
The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Maximum-Data-Rate-Upstream AVP, Attribute Type 135, contains
the subscriber's maximum upstream data rate, as configured by the operator.
The Maximum-Data-Rate-Upstream AVP contains an 8-octet unsigned integer,
indicating the numeric value of the subscriber's Access Line maximum upstream
data rate. The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Maximum-Data-Rate-Downstream AVP, Attribute Type 136, contains
the subscriber's maximum downstream data rate, as configured by the operator.
The Maximum-Data-Rate-Downstream AVP contains an 8-octet unsigned integer,
indicating the numeric value of the subscriber's Access Line maximum downstream
data rate. The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Minimum-Data-Rate-Upstream-Low-Power AVP, Attribute Type 137,
contains the subscriber's minimum upstream data rate in low power state, as
configured by the operator.
The Minimum-Data-Rate-Upstream-Low-Power AVP contains an 8-octet unsigned
integer, indicating the numeric value of the subscriber's Access Line minimum
upstream data rate when in low power state (L1/L2). The rate is coded in bits
per second.
The Length (before hiding) of this AVP is 14.
The Access Line Minimum-Data-Rate-Downstream-Low-Power AVP, Attribute Type 138,
contains the subscriber's minimum downstream data rate in low power state, as
configured by the operator.
The Minimum-Data-Rate-Downstream-Low-Power AVP contains an 8-octet unsigned
integer, indicating the numeric value of the subscriber's Access Line minimum
downstream data rate when in low power state (L1/L2).
The rate is coded in bits per second.
The Length (before hiding) of this AVP is 14.
The Access Line Maximum-Interleaving-Delay-Upstream AVP, Attribute Type 139,
contains the subscriber's maximum one-way upstream interleaving delay, as
configured by the operator.
The Maximum-Interleaving-Delay-Upstream AVP contains a 4-octet unsigned
integer, indicating the numeric value in milliseconds of
the subscriber's Access
Line maximum one-way upstream interleaving delay.
The Length (before hiding) of this AVP is 10.
The Access Line Actual-Interleaving-Delay-Upstream AVP, Attribute Type 140,
contains the subscriber's actual one-way upstream interleaving delay.
The Actual-Interleaving-Delay-Upstream AVP contains a 4-octet unsigned
integer, indicating the numeric value in milliseconds of the
subscriber's Access
Line actual upstream interleaving delay.
The Length (before hiding) of this AVP is 10.
The Access Line Maximum-Interleaving-Delay-Downstream AVP, Attribute Type 141,
contains the subscriber's maximum one-way downstream interleaving delay, as
configured by the operator.
The Maximum-Interleaving-Delay-Downstream AVP contains a 4-octet unsigned
integer, indicating the numeric value in milliseconds of the
subscriber's Access
Line maximum one-way downstream interleaving delay.
The Length (before hiding) of this AVP is 10.
The Access Line Actual-Interleaving-Delay-Downstream AVP, Attribute Type 142,
contains the subscriber's actual one-way downstream interleaving delay.
The Actual-Interleaving-Delay-Downstream AVP contains a 4-octet unsigned
integer, indicating the numeric value in milliseconds of the subscriber's
Access
Line actual downstream interleaving delay.
The Length (before hiding) of this AVP is 10.
The Access Line Access-Loop-Encapsulation AVP, Attribute Type 144,
describes the
encapsulation(s) used by the subscriber on the access loop.
The Length (before hiding) of this AVP is 9.
The Access-Loop-Encapsulation value is comprised of
three 1-octet values representing the Data Link, Encapsulation 1, and
Encapsulation 2, respectively.
The Access-Loop-Encapsulation value is 3 octets in length, logically divided
into three 1-octet sub-fields, each containing its own enumeration value, as
shown in the following diagram:
Valid values for the sub-fields are as follows:
Data Link
0x00 ATM AAL5
0x01 Ethernet
Encaps 1
0x00 NA - Not Available
0x01 Untagged Ethernet
0x02 Single-Tagged Ethernet
Encaps 2
0x00 NA - Not Available
0x01 PPPoA LLC
0x02 PPPoA Null
0x03 IP over ATM (IPoA) LLC
0x04 IPoA Null
0x05 Ethernet over AAL5 LLC with Frame Check Sequence (FCS)
0x06 Ethernet over AAL5 LLC without FCS
0x07 Ethernet over AAL5 Null with FCS
0x08 Ethernet over AAL5 Null without FCS
The ANCP Access Line Type AVP, Attribute Type 145, describes the transmission
systems on access loop to the subscriber.
The Length (before hiding)
of this AVP is 10.
The ANCP Access Line Type AVP
defines the type of transmission system used.
The ANCP Access Line Type AVP contains a 1-octet field encoding
the Transmission System, followed
by a 3-octet reserved field (MUST be zero), and is 4 octets in length.
It indicates
the transmission systems on access loop to the subscriber. The current valid
values only utilize the 1-octet field.
Valid values are as follows:
Transmission system:
0x01 ADSL1
0x02 ADSL2
0x03 ADSL2+
0x04 VDSL1
0x05 VDSL2
0x06 SDSL
0x07 UNKNOWN
The Access Line IWF-Session AVP, Attribute Type 254, indicates if an
Interworking Function has been performed with respect to the subscriber's
session.
The Inter-Working Function is a 4-octet value.
Valid values for this field are as follows:
0x00 IWF not performed
0x01 IWF performed
The Length (before hiding) of this AVP is 10.
The following sections define Connect Speed Update related AVPs.
These AVPs
( and )
use the
IETF Vendor ID of 0.
The M bit for these AVPs SHOULD be set to 0.
However, if it is desired to prevent the establishment or tear down
the established L2TP session if the peer LNS does not support the
Connect Speed Update AVP extensions, the M bit MAY be set to 1. See Section
4.2 of
and Section 5.2 of
.
The Connect Speed Update AVP, Attribute Type 97, contains the updated
connection speeds for this session.
The format is consistent
with
that of the Tx Connect Speed and Rx Connect Speed AVPs for L2TPv2 (Attribute Types
24 and 38, respectively) and L2TPv3 (Attribute Types 74 and 75, respectively).
Hence, there is a separate format defined for L2TPv2 and L2TPv3.
The Remote Session Id is the remote session id relative to the sender
(i.e., the identifier that was assigned to this session by the peer). The
Current Tx Connect Speed is a 4-octet value (L2TPv2) or an 8-octet value
(L2TPv3) representing the current
transmit connect speed, from the perspective of the LAC (e.g., data flowing from
the LAC to the remote system). The rate is encoded in bits per second. The
Current Rx Connect Speed is a 4-octet value (L2TPv2) or an 8-octet value
(L2TPv3) representing the current
receive connect speed, from the perspective of the LAC (e.g., data flowing from
the remote system to the LAC). The rate is encoded in bits per second.
The Length (before hiding) of this AVP is 18 (L2TPv2) or 26 (L2TPv3).
The Connect
Speed Update Enable AVP, Attribute Type 98, indicates whether the
LAC intends to send speed updates to the LNS during the life of the session.
The Connect Speed Update Enable AVP is a boolean AVP.
Presence of this AVP indicates that the LAC MAY send speed updates
using CSUN (see ) during the life of the session,
and the LNS SHOULD query for the current connection speed
via the CSURQ (see )
during failover synchronization. Absence of this AVP indicates
that the LAC will not be sending speed updates using
CSUN (see ) during the life of the session,
and the LNS MUST NOT query for the current connection speed via the CSURQ
(see ) during
failover synchronization.
The Length (before hiding) of this AVP is 6.
The Access Line information that is obtained from the Access Node/DSLAM is
required to be mapped into the Access Line AVPs. The Access Line
information can be obtained via:
Vendor-Specific PPPoE Tags
.
DHCP Relay Options
and Vendor-Specific Information Suboptions
.
ANCP .
summarizes the Access Line AVPs
defined in Sections
through .
Access Line AVPName1 (0x01)Agent-Circuit-Id 2 (0x02)Agent-Remote-Id 129 (0x81)Actual-Data-Rate-Upstream 130 (0x82)Actual-Data-Rate-Downstream 131 (0x83)Minimum-Data-Rate-Upstream 132 (0x84)Minimum-Data-Rate-Downstream 133 (0x85)Attainable-Data-Rate-Upstream 134 (0x86)Attainable-Data-Rate-Downstream135 (0x87)Maximum-Data-Rate-Upstream136 (0x88)Maximum-Data-Rate-Downstream137 (0x89)Minimum-Data-Rate-Upstream-Low-Power138 (0x8A)Minimum-Data-Rate-Downstream-Low-Power139 (0x8B)Maximum-Interleaving-Delay-Upstream140 (0x8C)Actual-Interleaving-Delay-Upstream141 (0x8D)Maximum-Interleaving-Delay-Downstream142 (0x8E)Actual-Interleaving-Delay-Downstream144 (0x90)Access-Loop-Encapsulation145 (0x91)ANCP Access Line Type254 (0xFE)IWF-Session
Sections
and
describe request for new values
in , for registries
already managed by IANA assignable through Expert Review
according to .
describes number spaces not managed by IANA.
This number space is managed by IANA as per .
There are two new message types, defined in Sections
and
,
to be allocated for this specification.
Message Type AVP (Attribute Type 0) Values
28: (CSUN) Connect-Speed-Update-Notification29: (CSURQ) Connect-Speed-Update-Request
This number space is managed by IANA as per .
There are two new AVPs, defined in Sections
and
,
to be allocated for this specification.
Control Message Attribute Value Pairs (AVPs)
97: Connect Speed Update AVP98: Connect Speed Update Enable AVP
The Access Line Information AVPs use the Vendor ID of 3561 for the ADSL Forum
(now Broadband Forum). The number spaces in these Values and their new allocations
(e.g., enumerated values for
the Access Line Access-Loop-Encapsulation AVP and ANCP Access Line Type AVP)
are managed by the Broadband Forum.
The security of these AVP relies on an implied trust relationship between the
Access Node/DSLAM and the BRAS/LAC, and between the LAC and the LNS.
The identifiers that
are inserted by the Access Node/DSLAM are unconditionally trusted; the
BRAS does
not perform any validity check on the information received before
forwarding the information.
These AVPs are intended to be used in environments in which the network
infrastructure (the Access Node/DSLAM, the BRAS/LAC, the LNS, and the entire
network in which those devices reside) is trusted and secure.
Careful consideration should be given to the potential security
vulnerabilities that are present in this model before deploying this option in
actual networks.
The AVPs described in this document are used to carry identification and
characterization of subscriber Access Line, and to report connection speed
changes. If used in a non-secure environment, they could reveal such
information. The Tunnel (Control Connection) security considerations are
covered in Section 9.1 of and Section 8.l
of . Additionally, the hiding of AVP attribute values
mechanism can be used to hide the value of the AVPs described in this
document, if they are deemed sensitive in some environments. AVP hiding is
described in Section 4.3 of and Section 5.3
of .
The Attributes described in this document neither increase nor decrease the
security of the L2TP protocol.
It is possible to utilize
"Securing L2TP with IPsec" to increase the
security by utilizing IPsec to provide for tunnel authentication, privacy
protection, integrity checking and replay protection.
Many thanks to Wojciech Dec and the others of the
Broadband Forum (previously the DSL Forum) Architecture
and Transport Working Group for their help in putting together this
document.
Migration to Ethernet-Based DSL AggregationDSL Forum
PRIVATE ENTERPRISE NUMBERS
Internet Assigned Numbers Authority
Layer Two Tunneling Protocol 'L2TP'
Internet Assigned Numbers Authority
Protocol for Access Node Control Mechanism in Broadband Networks