One document matched: draft-ietf-l2tpext-pwe3-atm-00.txt
Network Working Group Sanjeev Singh
Internet-Draft W. Mark Townsley
Category: Standards Track Jed Lau
<draft-ietf-l2tpext-pwe3-atm-00.txt> Cisco Systems, Inc.
March 2004
ATM Pseudo-Wire Extensions for L2TP
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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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............... 13
8.1 ATM Alarm Status AVP.................................. 14
9. Security Considerations................................... 15
10. IANA Considerations...................................... 15
7. Acknowledgments........................................... 15
12. References............................................... 16
12.1 Normative References................................. 16
12.2 Informative References............................... 16
13. Contacts................................................. 17
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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 Switched/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 Switched Permanent Virtual Connection
SPVP Switched Permanent Virtual Path
VC Virtual Circuit
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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 specific ATM PW
type of TBA1 (See IANA Considerations Section), 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 if both endpoints
support an application (as defined by the Application Code AVP
[L2TPv3]) 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
alarmed.
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 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 figures shows how the 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 following four attribute types can be
present in PW Type AVP of [L2TPv3].
- ATM AAL5 SDU attribute type, TBA1
- ATM VCC Cell-Relay attribute type, TBA2
- ATM VPC Cell-Relay attribute type, TBA3
- ATM Port Cell-Relay attribute type, TBA4
The above Cell-Relay mode can also signal the ATM Cell-Packing AVP as
described in Section 6. Other ATM PW types are outside the scope of
this document.
b. PW End ID: Each PW is associated with a PW End ID akin to the
VC-ID in [PWE3ATM]. Two LCCEs of a PW would have the same PW
End ID and its format is described in Section 5.4.4 of [L2TPv3].
This End ID AVP MUST be present in the ICRQ in order for the
remote LCCE to associate the session to the ATM Circuit. The 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 as well. If LCCE B had not been provisioned
that ATM Circuit identified in the ICRQ, a CDN would have been
immediately returned indicating that the circuit was not provisioned
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or 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, confirming
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 any time there is a status change which
may be reported by any values identified in the Circuit Status AVP.
The only exception to this is 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).
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
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8.
4. Encapsulation
The 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 non-zero 32-bit session ID and 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 the Section 4.1 for more details.
4.1 ATM-Specific Sublayer
An alternative to default L2-Specific Sublayer as mentioned in
Section 4.6 of [L2TPv3], the ATM-Specific Sublayer is defined here.
Four new flag bits (T,G,C,U) are defined which concurs with the
Section 8.2 of [PWE3ATM]. The bit positions, 6 & 7 of MSB have
already been defined in Section 4.5 of [L2TPFRAG] for fragmentation
but are mutually exclusive with bits defined below.
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|x|x|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 as per Section 4.6 of [L2TPv3].
* xx (Reserved)
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
transported in the packet is set to 1. Otherwise this bit
SHOULD be set to 0. The egress LCCE device SHOULD set the CLP
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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 L2-Specific Sublayer:
0 - There is no L2-Specific Sublayer present.
1 - The default L2-Specific Sublayer (defined in Section 4.6)
is used.
TBA5 - The ATM L2-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 for signaling
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-
byte ATM Cell Header and 48-byte ATM Cell-payload.
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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) is carried in ATM Specific
sublayer across ATMPW to egress LCCE. The processing of these bits on
ingress and egress 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 PW then AAL5 SDU should be discarded. 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 cell is not maintained.
Performance Monitoring OAM, as specified in ITU-T 610 [I610-1],
[I610-2], [I610-3] and security OAM cells as speicified in [ATMSEC],
should not be used in combination with AAL5 SDU mode and these cells
MAY be dropped at ingress LCCE because cell sequence integrities is
not maintained.
5.2 ATM Cell Mode
In this mode, ATM cells skip the reassembly process at ingress LCCE
and 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 required. It is left to
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 detail 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 one other ATM port. All ATM cells that are received at the
ingress ATM port on the LCCE, is 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 an 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 reproting
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 intesrted 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 TBA6,
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
direction 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 given ATM cell-relay Circuit.
7. OAM Emulation Required AVP
An "OAM Emulation Required AVP" Attribute type, TBA7 MAY be needed to
signal OAM Emulation in AAL5 SDU mode if LCCE does 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, TBA8.
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.
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.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |A|N|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Value is a 16 bit mask with the two least significant bits
defined and the remaining bits 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, TBA9 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:
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
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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
assignment of a ATM Pseudowire Type for ATM AAL5 SDU, ATM VCC Cell-
relay, ATM VPC Cell-Relay, ATM Port Cell-Relay. IANA assignment of
this value should take place within the PWE3 WG.
This document defines a new ATM-Specific Sublayer and enumeration for
L2-Specific Sublayer AVP to identify the ATM-Specific Sublayer.
Two additional AVP Attribute (ATM Maximum Concatenated Cells AVP, OAM
Emulation Required AVP) are specified in this document. These are
required to be defined by IANA as described in Section 9.1 of
[BCP0068].
This document defines one L2TP Result Codes in Section 7 and 8, which
will be defined by IANA as described in Section 9.1 of [BCP0068].
7. Acknowledgments
Thanks for the contribution from Pony Zhu, Prasad Yaditi, Durai, Jaya
Kumar,
Sanjeev, et al. Standards Track [Page 15]
INTERNET DRAFT ATM over L2TPv3 March 2004
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-11.txt, October 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-00.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
[I610-1] ITU-T Recommendation I.610 (1999): B-ISDN operation and
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
Sanjeev, et al. Standards Track [Page 16]
INTERNET DRAFT ATM over L2TPv3 March 2004
13. Contacts
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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INTERNET DRAFT ATM over L2TPv3 March 2004
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Sanjeev, et al. Standards Track [Page 18]
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