One document matched: draft-ietf-l2tpext-pwe3-atm-02.txt
Differences from draft-ietf-l2tpext-pwe3-atm-01.txt
Network Working Group Sanjeev Singh
Internet-Draft W. Mark Townsley
Category: Standards Track Jed Lau
<draft-ietf-l2tpext-pwe3-atm-02.txt> Cisco Systems, Inc.
October 2004
ATM Pseudo-Wire Extensions for L2TP
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
The Layer 2 Tunneling Protocol, Version 3, (L2TPv3) defines an
extensible tunneling protocol, how to transport layer 2 services over
IP network. This document describes the specifics of how to use the
L2TP control plane for Asynchronous Transfer Mode (ATM) Pseudo-Wires
and guidelines for transporting various ATM services over an IP
network.
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Contents
Status of this Memo.......................................... 1
1. Introduction.............................................. 3
1.1 Abbreviations......................................... 3
2. Control Connection Establishment.......................... 4
3. Session Establishment and ATM Circuit Status Notification. 4
3.1 L2TPv3 Session Establishment.......................... 4
3.2 L2TPv3 Session Teardown............................... 6
3.3 L2TPv3 Session Maintenance............................ 6
4. Encapsulation............................................. 7
4.1 ATM-Specific Sublayer................................. 7
4.2 Sequencing............................................ 9
5. ATM Transport............................................. 9
5.1 ATM AAL5-SDU Mode..................................... 10
5.2 ATM Cell Mode......................................... 10
5.2.1 ATM VCC Cell-Relay Service....................... 11
5.2.2 ATM VPC Cell-Relay Service....................... 11
5.2.3 ATM Port Cell-Relay Service...................... 12
5.3 OAM Cell Support...................................... 12
5.3.1 VCC switching.................................... 12
5.3.1 VPC switching.................................... 12
6. ATM Maximum Concatenated Cells AVP........................ 12
7. OAM Emulation Required AVP................................ 13
8. ATM defects mapping and status notification............... 14
8.1 ATM Alarm Status AVP.................................. 14
9. Security Considerations................................... 15
10. IANA Considerations...................................... 15
10.1 L2-Specific Sublayer Type............................ 16
10.2 Control Message Attribute Value Pairs (AVPs)........ 16
10.3 Result Code AVP Values.............................. 16
10.4 ATM Alarm Status AVP Values......................... 17
11. Acknowledgments.......................................... 18
12. References............................................... 18
12.1 Normative References................................. 18
12.2 Informative References............................... 18
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13. Authors' Addresses....................................... 19
Specification of Requirements
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized. 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 [RFC2119].
1. Introduction
This document describes the specifics of how to use the L2TP for ATM
pseudo-wires, including encapsulation, carrying various ATM services,
such as, AAL5 SDU, ATM VCC/VPC/Port cell-relay over L2TP, and mapping
ATM defects to L2TP SLI message to notify the peer LCCE.
Any ATM specific AVPs or other L2TP constructs for ATM pseudo-wire
(ATMPW) support will be defined here as well. Support for ATM
Switched Virtual Path/Connection (SVP/SVC) and Soft Permanent Virtual
Path/Connection (SPVP/SPVC) are outside the scope of this document.
The reader is expected to be very familiar with the terminology and
protocol constructs defined in [L2TPv3].
1.1 Abbreviations
AIS Alarm Indication Signal
ATMPW ATM Pseudo-wire
AVP Attribute Value Pair
CC Continuity Check OAM Cell
CE Customer Edge
HEC Header Error Control
LAC L2TP Access Concentrator (See [L2TPv3])
LCCE L2TP control connection endpoint (See [L2TPv3])
MSB Most Significant Byte
OAM Operation, Administration, and Management
PE Provider Edge
PSN Packet Service Network
PWE3 Pseudo-wire Edge-to-edge emulation
RDI Remote Defect Indicator
SDU Service Data Unit
SLI Set Link Info, an L2TP control message
SVC Switched Virtual Connection
SVP Switched Virtual Path
SPVC Soft Permanent Virtual Connection
SPVP Soft Permanent Virtual Path
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VC Virtual Circuit
VCC Virtual Channel Connection
VCI Virtual Channel Identifier
VPC Virtual Path Connection
VPI Virtual Path Identifier
2. Control Connection Establishment
To emulate, ATM pseudo-wires using L2TP, an L2TP Control Connection
as described in Section 3.3 of [L2TPv3] MUST be established.
The SCCRQ and corresponding SCCRP MUST include the supported ATM PW
types (See Section 3.1), in the Pseudo-Wire Capabilities List as
defined in Section 5.4.3 of [L2TPv3]. This identifies the control
connection as able to establish L2TP sessions in support of the ATM
Pseudo-Wires.
An LCCE MUST be able to uniquely identify itself in the SCCRQ and
SCCRP messages via a globally unique value. By default, this is
advertised via the structured Router ID AVP [L2TPv3], though the
unstructured Hostname AVP [L2TPv3] MAY be used to identify LCCEs via
this value.
3. Session Establishment and ATM Circuit Status Notification
This section describes how L2TP ATM PW or sessions are established
between two LCCEs. This includes what will happen when an ATM Circuit
(e.g. AAL5 PVC) is created, deleted or changes state when circuit is
in alarm.
3.1 L2TPv3 Session Establishment
ATM Circuit (e.g. an AAL5 PVC) creation triggers establishment of a
L2TP session using three-way handshake described in Section 3.4.1 of
[L2TPv3]. An LCCE MAY initiate the session immediately upon ATM
circuit creation, or wait until the Circuit state transitions to
ACTIVE before attempting to establish a session for the ATM circuit.
It MAY be preferred to wait until Circuit status transitions to
ACTIVE in order to avoid wasting L2TP resources.
The Circuit Status AVP (see Section 8) MUST be present in the ICRQ
and ICRP messages, and MAY be present in the SLI message for ATM PWs.
The following figure shows how L2TP messages are exchanged to setup
an ATM PWs after ATM Circuit (e.g. an AAL5 PVC) becomes ACTIVE.
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LCCE (LAC) A LCCE (LAC) B
------------------ --------------------
ATM Ckt Provisioned
ATM Ckt Provisioned
ATM Ckt ACTIVE
ICRQ (status = 0x03) ---->
ATM Ckt ACTIVE
<----- ICRP (status = 0x03)
L2TP session established
OK to send data into PW
ICCN ----->
L2TP session established
OK to send data into PW
The following signaling elements are required for the ATM PW
establishment.
a. Pseudo-Wire Type: One of the supported ATM related PW Types as
defined in section 2 of [IANA] should be present in PW Type AVP of
[L2TPv3].
0x0002 ATM AAL5 SDU VCC transport
0x0003 ATM transparent cell transport
0x0009 ATM n-to-one VCC cell transport
0x000A ATM n-to-one VPC cell transport
The above Cell-Relay mode can also signal the ATM Cell Concatenation
AVP as described in Section 6. Other ATM PW types are outside the
scope of this document.
b. PW Remote End ID: Each PW is associated with a PW Remote End ID
akin to the VC-ID in [PWE3ATM]. Two LCCEs of a PW would have the
same PW Remote End ID and its format is described in Section 5.4.4
of [L2TPv3].
This Remote End ID AVP MUST be present in the ICRQ in order for
the remote LCCE to associate the session to the ATM Circuit. The
Remote End Identifier AVP defined in [L2TPv3] is of opaque form,
though ATMPW implementations MAY simply use a four-octet value
that is known to both LCCEs (either by direct configuration, or
some other means). The exact method of how this value is
configured, retrieved, discovered, or otherwise determined at
each LCCE is outside the scope of this document.
As with the ICRQ, the ICRP is sent only after the ATM Circuit
transitions to ACTIVE. If LCCE B had not been provisioned yet for the
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ATM Circuit identified in the ICRQ, a CDN would have been immediately
returned indicating that the circuit was either not provisioned or is
not available at this LCCE. LCCE A should then exhibit a periodic
retry mechanism. The period and maximum number of retries MUST be
configurable.
An Implementation MAY send an ICRQ or ICRP before a PVC is ACTIVE, as
long as the Circuit Status AVP reflects that the ATM Circuit is
INACTIVE and an SLI is sent when the ATM Circuit becomes ACTIVE (see
Section 8).
The ICCN is the final stage in the session establishment. It confirms
the receipt of the ICRP with acceptable parameters to allow
bidirectional traffic.
3.2 L2TPv3 Session Teardown
When an ATM Circuit is unprovisioned (deleted) at either LCCE, the
associated L2TP session MUST be torn down via the CDN message defined
in Section 3.4.3 of [L2TPv3].
3.3 L2TPv3 Session Maintenance
All sessions established by a given control connection utilize the
L2TP Hello facility defined in Section 4.4 of [L2TPv3] for session
keepalive. This gives all sessions basic dead peer and path detection
between LCCEs.
If the control channel utilizing the Hello message is not in-band
with data traffic over PSN, then other method MAY be used to detect
the Session failure and it is left for further study.
ATMPW over L2TP uses the Set Link Info (SLI) control message as
defined in [L2TPv3] to signal ATM Circuit Status between LCCEs after
initial session establishment. This includes ACTIVE or INACTIVE
notifications of the ATM Circuit, or any other parameters that may
need to be shared between the LCCEs in order to provide proper PW
emulation.
The SLI message MUST be sent whenever there is a status change which
may be reported by any values identified in the Circuit Status AVP.
The only exception to this are the initial ICRQ, ICRP and CDN
messages which establish and teardown the L2TP session itself when
ATM circuit is created or deleted. The SLI message may be sent from
either LCCE at any time after the first ICRQ is sent (and perhaps
before an ICRP is received, requiring the peer to perform a reverse
Session ID lookup).
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The other application of the SLI message is to map the ATM OAM or
physical layer alarms into Circuit Status AVP as described in Section
8.
4. Encapsulation
This section describes the general encapsulation format for ATM
services over L2TP.
Figure 1: General format for ATM encapsulation over L2TPv3 over IP
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PSN Transport Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ATM-Specific Sublayer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ATM Service Payload |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The PSN Transport header is specific to IP and its underlying
transport header. This header is used to transport the encapsulated
ATM payload through the IP network.
The Session Header is a non-zero 32-bit session ID with optional
cookies upto 64-bits. This Session ID is exchanged during session
setup.
The ATM Specific Sublayer is REQUIRED for AAL5 SDU mode and OPTIONAL
for ATM Cell mode. Please refer to Section 4.1 for more details.
4.1 ATM-Specific Sublayer
This section defines a new ATM-specific sublayer as, an alternative
to default L2-Specific Sublayer as mentioned in Section 4.6 of
[L2TPv3]. Four new flag bits (T,G,C,U) are defined which concur with
Section 8.2 of [PWE3ATM].
Figure 2: ATM-Specific Sublayer Format
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x|S|B|E|T|G|C|U| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Definition of these four bits are as per Section 8.2 of [PWE3ATM] and
also included here for reference.
* S bit
Definition of this bit is as per Section 4.6 of [L2TPv3].
* B and E bits
Definition of these bits as per Section 5.5 of [L2TPFRAG]
These bits are reserved and MUST be set to 0 upon transmission
and ignored upon reception, unless otherwise, these bits are
used as per [L2TPFRAG].
* T (Transport type) bit
Bit (T) of the control word indicates whether the packet
contains an ATM admin cell or an AAL5 payload. If T = 1, the
packet contains an ATM admin cell, encapsulated according to
the VCC cell relay encapsulation of Section 5.2.
If not set, the PDU contains an AAL5 payload. The ability to
transport an ATM cell in the AAL5 SDU mode is intended to
provide a means of enabling administrative functionality over
the AAL5 VCC (though it does not endeavor to preserve user-cell
and admin-cell arrival/transport ordering).
* G (EFCI) Bit
The ingress LCCE device SHOULD set this bit to 1 if the EFCI bit
of the final cell of the incoming AAL5 payload is set to 1, or
if the EFCI bit of the single ATM cell to be transported in
the packet is set to 1. Otherwise this bit SHOULD be set to
0. The egress LCCE device SHOULD set the EFCI bit of all the
outgoing cells that transport the AAL5 payload to the value
contained in this field.
* C (CLP) Bit
The ingress LCCE device SHOULD set this bit to 1 if the CLP bit
of any of the incoming ATM cells of the AAL5 payload are set
to 1, or if the CLP bit of the single ATM cell that is to be
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transported in the packet is set to 1. Otherwise this bit
SHOULD be set to 0. The egress LCCE device SHOULD set the CLP
bit of all outgoing cells that transport the AAL5 CPCS-PDU to
the value contained in this field.
* U (Command/Response) Bit
When FRF.8.1 Frame Relay / ATM PVC Service Interworking (see
[FRF8.1]) traffic is being transported, the CPCS-UU Least
Significant Bit (LSB) of the AAL5 CPCS-PDU may contain the
Frame Relay C/R bit.
The ingress LCCE device SHOULD copy this bit to the U bit of
the control word. The egress LCCE device SHOULD copy the
U bit to the CPCS-UU Least Significant Bit (LSB) of the AAL5
payload.
The Sequence Number fields are described in Section 4.3
In case of a reassembly timeout, the encapsulating LCCE should
discard all component cells of the AAL5 frame.
An additional enumeration is added to the L2-Specific Sublayer AVP
to identify the ATM-Specific Sublayer:
0 - There is no L2-Specific Sublayer present.
1 - The default L2-Specific Sublayer (defined in
Section 4.6) is used.
TBA-1 - The ATM-Specific Sublayer is used.
The first two values are already defined in the L2TPv3 base draft
[L2TPv3].
4.2 Sequencing
Data Packet Sequencing MAY be enabled for ATMPWs. The sequencing
mechanisms described in [L2TPv3] MUST be used to signal sequencing
support. ATMPW over L2TPv3 MUST request the presence of the ATM-
Specific Sublayer when sequencing is enabled, and MAY request its
presence at all times.
5. ATM Transport
There are two encapsulations supported for ATM transport as described
below.
ATM Specific Sublayer is prepended to AAL5-SDU. The other Cell-mode
encapsulation consists of the OPTIONAL ATM-Specific Sublayer and 4-
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byte ATM Cell Header and 48-byte ATM Cell-payload.
5.1 ATM AAL5-SDU Mode
In this mode each AAL5 VC is mapped to an L2TP session. Ingress LCCE
reassembles AAL5 CPCS-SDU without AAL5 trailer and any padding bytes.
Incoming EFCI, CLP and C/R (if present) are carried in ATM Specific
sublayer across ATMPW to egress LCCE. The processing of these bits on
ingress and egress are LCCE defined in Section 4.1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x|S|x|x|T|G|C|U| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| AAL5 CPCS-SDU |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If ingress LCCE determines that an encapsulated AAL5 SDU exceeds the
MTU size of the L2TPv3 session, then AAL5 SDU may be fragmented as
per [L2TPFRAG] or underneath Transport layer (IP, etc). F5 OAM cells
that arrive during the reassembly of an AAL5 SDU are sent immediately
on the PW followed by the AAL5 SDU payload. In this case OAM cell's
relative order with respect to user data cells is not maintained.
Performance Monitoring OAM, as specified in ITU-T 610 [I610-1],
[I610-2], [I610-3] and security OAM cells as specified in [ATMSEC],
should not be used in combination with AAL5 SDU mode. These cells MAY
be dropped at ingress LCCE because cell sequence integrity is not
maintained.
5.2 ATM Cell Mode
In this mode, ATM cells skip the reassembly process at ingress LCCE.
These cells are transported over an L2TP session, either as a single
Cell or as concatenated cells, into a single packet. Each ATM Cell
consists of 4 byte ATM cell header and 48-byte ATM Cell-payload, HEC
is not included.
In ATM Cell Mode encapsulation, ATM-Specific Sublayer is OPTIONAL.
It can be included, if sequencing support is required. It is left to
the implementation to choose to signal Default L2-Specific Sublayer
or ATM-Specific Sublayer.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x|S|x|x|x|x|x|x| Sequence Number (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VPI | VCI |PTI |C|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ATM Cell Payload (48-bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
"
"
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VPI | VCI |PTI |C|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ATM Cell Payload (48-bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the simplest case, this encapsulation can be used to transmit
a single ATM cell per Pseudo Wire PDU. However, in order to
provide better Pseudo Wire bandwidth efficiency, several ATM cells
may be optionally encapsulated into single Pseudo Wire PDU.
The maximum number of concatenated cells in a packet is limited by
the MTU size of the session and also by the ability of egress
LCCE to process them. For more details about ATM Maximum Concatenated
cells, please refer to Section 6.
5.2.1 ATM VCC Cell-Relay Service
A VCC cell relay service may be provided by mapping an ATM Virtual
Channel Connection to a single Pseudo-Wire using cell mode
encapsulation as defined in section 5.2.
An LCCE may map one or more VCCs to a single PW. However, a service
provider may wish to provision a single VCC to a PW in order to satify
QOS or restoration requirement.
5.2.2 ATM VPC Cell-Relay Service
A Virtual Path Connection cell relay service may be provided by
mapping an ATM Virtual Path Connection to single Pseudo Wire using
cell mode encapsulation as defined in section 5.2.
An LCCE may map one or more VPCs to a single Pseudo Wire.
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5.2.3 ATM Port Cell-Relay Service
ATM port cell relay service allows an ATM port to be connected to
only another ATM port. All ATM cells that are received at the
ingress ATM port on the LCCE, are encapsulated as per section 5.2,
into Pseudo wire PDU and sent to peer LCCE.
Each LCCE MUST discard any idle/unassigned cells received on an ATM
port associated with ATM PW.
5.3 OAM Cell Support
The OAM cells are defined in [I610-1], [I610-2], [I610-3] and [ATMSEC]
can be categoried as:
a. Fault Management
b. Performance monitoring and reporting
c. Activation/deactivation
d. System Management (e.g. security OAM cells).
OAM Cells are always encapsulated using cell mode encapsulation,
regardless of the encapsulation format used for user data.
5.3.1 VCC switching
The LCCEs SHOULD be able to pass the F5 segment and end-to-end Fault
Management, Resource Management (RM cells), Performance Management,
Activation/deactivation and System Management OAM cells.
F4 OAM cells are inserted or extracted at the VP link termination.
These OAM cells are not seen at the VC link termination and are
therefore not sent across the PW.
5.3.1 VPC switching
The LCCEs MUST be able to pass the F4 segment and end-to-end Fault
Management, Resource Management (RM cells), Performance Management,
Activation/deactivation and System Management OAM cells transparently
according to [I610-1].
F5 OAM cells are not inserted or extracted at the VP cross-connect.
The LCCEs MUST be able to pass the F5 OAM cells transparently across
the PW.
6. ATM Maximum Concatenated Cells AVP
The "ATM Maximum Cells Concatenated AVP", Attribute type AVP-TBA-1,
indicates that the egress LCCE node can process a single PDU with
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concatenated cells upto a specified number of cells. An LCCE
node transmitting concatenated cells on this PW MUST not exceed
the maximum number of cells as specified in this AVP. This AVP
is applicable only to ATM Cell-Relay PW types (VCC, VPC, Port
Cell-Relay). This Attribute value may not be same in both
directions of the specific PW.
The Attribute Value field for this AVP has the following format:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ATM Maximum Concatenated Cells|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This AVP MAY be hidden (the H bit MAY be 0 or 1). The M bit for this
AVP MAY be set to 0, but MAY vary (see Section 5.2 of [L2TPv3]). The
length (before hiding) of this AVP is 8.
This AVP is sent in an ICRQ, ICRP during session negotiation or via
SLI control messages when LCCE changes the maximum number of
Concatenated Cells configuration for a given ATM cell-relay Circuit.
This AVP is OPTIONAL. If egress LCCE is configured with maximum
number of cells to be concatenated by ingress LCEE, it should signal
to ingress LCCE.
7. OAM Emulation Required AVP
An "OAM Emulation Required AVP" Attribute type, AVP-TBA-2 MAY be
needed to signal OAM Emulation in AAL5 SDU mode, if LCCE can not
support transport of OAM cells across L2TP session. If OAM Cell
Emulation is configured or detected via some other means on one side,
the other LCCE MUST support OAM Cell Emulation as well.
This AVP is exchanged during session negotiation (in ICRQ, ICRP) or
during life of the session via SLI control message. If the other LCCE
can not support the OAM Cell Emulation, the associated L2TP session
MUST be torn down via CDN message with result code, RC-TBA-1.
OAM Emulation AVP is a boolean AVP, having no Attribute Value. Its
absence is FALSE and its presence is TRUE. This AVP MAY be hidden
(the H bit MAY be 0 or 1). The M bit for this AVP SHOULD be set to 0,
but MAY vary (see Section 5.2 of [L2TPv3]). The Length (before
hiding) of this AVP is 6.
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8. ATM defects mapping and status notification
ATM OAM alarms or circuit status is indicated via Circuit Status AVP
as defined in Section 5.4.5 of [L2TPv3]. For reference, usage of
this AVP is shown below.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |N|A|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Value is a 16 bit mask with the two least significant bits
defined and the remaining bits are reserved for future use. Reserved
bits MUST be set to 0 when sending, and ignored upon receipt.
The A (Active) bit indicates whether the ATM Circuit is ACTIVE (1) or
INACTIVE (0).
The N (New) bit indicates whether the ATM circuit status indication
is for a new Circuit (1) or an existing ATM Circuit (0).
8.1 ATM Alarm Status AVP
An "ATM Alarm Status AVP" attribute type, AVP-TBA-3 indicates the
reason for the ATM circuit status and specific alarm type, if any, to
its peer LCCE node. This OPTIONAL AVP MAY be present in SLI message
with Circuit Status AVP.
The Attribute Value field for this AVP has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Status Reason | Alarm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Circuit status reason is a 2-octets unsigned integer and Alarm
Type is also a 2-octets unsigned integer.
This AVP MAY be hidden (the H bit MAY be 0 or 1). The m bit for this
AVP SHOULD be set to 0, but MAY vary (see Section 5.2 of [L2TPv3]).
The Length (before hiding) of this AVP is 10 octets.
This AVP is sent in SLI message to indicate the additional
information about the ATM circuit status.
Circuit Status Reason values for the SLI message are as follows:
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0 - Reserved
CSR-TBA1 - No alarm or alarm cleared (default for Active Status)
CSR-TBA2 - Unspecified or unknown Alarm Received (default for
Inactive Status)
CSR-TBA3 - ATM Circuit received F1 Alarm on ingress LCCE
CSR-TBA4 - ATM Circuit received F2 Alarm on ingress LCCE
CSR-TBA5 - ATM Circuit received F3 Alarm on ingress LCCE
CSR-TBA6 - ATM Circuit received F4 Alarm on ingress LCCE
CSR-TBA7 - ATM Circuit received F5 Alarm on ingress LCCE
CSR-TBA8 - ATM Circuit down due to ATM Port shutdown on Peer LCCE
CSR-TBA9 - ATM Circuit down due to loop-back timeout on ingress
LCCE
The general ATM Alarm failures are encoded as below:
0 - Reserved
A-TBA1 - No Alarm type specified (default)
A-TBA2 - Alarm Indication Signal (AIS)
A-TBA3 - Remote Defect Indicator (RDI)
A-TBA4 - Loss of Signal (LOS)
A-TBA5 - Loss of pointer (LOP)
A-TBA6 - Loss of framer (LOF)
A-TBA7 - loopback cells (LB)
A-TBA8 - Continuity Check (CC)
9. Security Considerations
For generic security issues regarding PWs and ATMPWs, this document
will eventually refer to documents from the PWE3 WG.
10. IANA Considerations
The signaling mechanisms defined in this document rely upon the
allocation of following ATM Pseudowire Types (see Pseudo Wire
Capabilities List as defined in 5.4.3 of [L2TPv3] and L2TPv3
Pseudowire Types in 10.6 of [L2TPv3]) by the IANA (number space
created as part of publication of [L2TPv3]):
Pseudowire Types
----------------
0x0002 ATM AAL5 SDU VCC transport
0x0003 ATM transparent cell transport
0x0009 ATM n-to-one VCC cell transport
0x000A ATM n-to-one VPC cell transport
This document defines a number of "magic" numbers to be maintained by
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the IANA. This section explains the criteria to be used by the IANA
to assign additional numbers in each of these lists. The following
subsections describe the assignment policy for the namespaces defined
elsewhere in this document.
These sections are for new registries to be added to the existing
L2TP registry and maintained by IANA accordingly.
10.1 L2-Specific Sublayer Type
This number space is managed by IANA as per [BCP0068].
The L2-Specific Sublayer Type is a 2 octet unsigned integer. The
following enumeration value is to be assigned by Expert Review
[RFC2434].
L2-Specific Sublayer Type
-------------------------
TBA-1 - ATM L2-Specific Sublayer present
10.2 Control Message Attribute Value Pairs (AVPs)
This number space is managed by IANA as per [BCP0068].
New AVPs requiring assignment in this document are encoded with
"AVP-TBA-x," where "x" is 1, 2, 3...
A summary of the three new AVPs follows:
Control Message Attribute Value Pairs
Attribute
Type Description
--------- ----------------------------------
AVP-TBA-1 ATM Maximum Concatenated Cells AVP
AVP-TBA-2 OAM Emulation Required AVP
AVP-TBA-3 ATM Alarm Status AVP
10.3 Result Code AVP Values
This number space is managed by IANA as per [BCP0068].
New Result Code value for the CDN message is defined in section 7.
Following is a summary:
Result Code AVP (Attribute Type 1) Values
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-----------------------------------------
General Error Codes
RC-TBA-1 - Session not established due to other LCCE
can not support the OAM Cell Emulation,
10.4 ATM Alarm Status AVP Values
This number space is managed by IANA as per [BCP0068].
New Attribute values for the SLI message is defined in section 8.
Following is a summary:
ATM Alarm Status AVP (Attribute Type AVP-TBA-3) Values
------------------------------------------------------
Circuit Status Reason values for the SLI message are as follows:
0 - Reserved
CSR-TBA1 - No alarm or alarm cleared (default for Active Status)
CSR-TBA2 - Unspecified or unknown Alarm Received (default for
Inactive Status)
CSR-TBA3 - ATM Circuit received F1 Alarm on ingress LCCE
CSR-TBA4 - ATM Circuit received F2 Alarm on ingress LCCE
CSR-TBA5 - ATM Circuit received F3 Alarm on ingress LCCE
CSR-TBA6 - ATM Circuit received F4 Alarm on ingress LCCE
CSR-TBA7 - ATM Circuit received F5 Alarm on ingress LCCE
CSR-TBA8 - ATM Circuit down due to ATM Port shutdown on Peer LCCE
CSR-TBA9 - ATM Circuit down due to loop-back timeout on ingress
LCCE
The general ATM Alarm failures are encoded as below:
0 - Reserved
A-TBA1 - No Alarm type specified (default)
A-TBA2 - Alarm Indication Signal (AIS)
A-TBA3 - Remote Defect Indicator (RDI)
A-TBA4 - Loss of Signal (LOS)
A-TBA5 - Loss of pointer (LOP)
A-TBA6 - Loss of framer (LOF)
A-TBA7 - loopback cells (LB)
A-TBA8 - Continuity Check (CC)
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11. Acknowledgments
Thanks for the contribution from Pony Zhu, Prasad Yaditi, Durai, Jaya
Kumar, and razor sharp review by Carlos Pignataro.
Many Thanks to Srinivas Kotamraju for editorial review.
Thanks to Shoou Yiu and Fred Shu for their valuable time to review
this document.
12. References
12.1 Normative References
[L2TPv3] J. Lau, M. Townsley, A. Valencia, G. Zorn, I. Goyret,
G. Pall, A. Rubens, B. Palter, Layer Two Tunneling
Protocol a.k.a. "L2TPv3," work in progress,
draft-ietf-l2tpext-l2tp-base-10.txt, August 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
12.2 Informative References
[PWE3ATM] L. Martini., et al., "Encapsulation Methods for
Transport of ATM Cells/Frame Over IP and MPLS Networks",
work in progress, draft-ietf-pwe3-atm-encap-01.txt
[L2TPFRAG] A. Malis, W. M. Townsley, "PWE3 Fragmentation and
Reassembly", draft-ietf-pwe3-fragmentation-06.txt
[FRF8.1] "Frame Relay / ATM PVC Service Interworking
Implementation Agreement (FRF 8.1)", Frame Relay
Forum 2000.
[BCP0068] Townsley, W., "Layer Two Tunneling Protocol (L2TP)
Internet Assigned Numbers Authority (IANA)
Considerations Update" RFC3438, BCP0068, December 2002
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations section in RFCs", BCP 26, RFC 2434,
October 1998.
[IANA] L. Martini, W. M. Townsley, "IANA Allocations for pseudo
Wire Edge to Edge Emulation (PWE3)",
draft-ietf-pwe3-iana-allocation-07.txt
[I610-1] ITU-T Recommendation I.610 (1999): B-ISDN operation and
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INTERNET DRAFT ATM over L2TPv3 July 2004
maintenance principles and functions
[I610-2] ITU-T Recommendation I.610, Corrigendum 1 (2000): B-ISDN
operation and maintenance principles and functions
(corrigendum 1)
[I610-3] ITU-T Recommendation I.610, Amendment 1 (2000): B-ISDN
operation and maintenance principles and functions
(Amendment 1)
[ATMSEC] ATM Forum Specification, af-sec-0100.002 (2001): ATM
Security Specification version 1.1
13. Authors' Addresses
Sanjeev Singh
cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
sanjeevs@cisco.com
W. Mark Townsley
cisco Systems
7025 Kit Creek Road
PO Box 14987
Research Triangle Park, NC 27709
mark@townsley.net
Jed Lau
cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
jedlau@cisco.com
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