Network Working Group Luca Martini(Editor)
Internet Draft Eric C. Rosen
Expiration Date: August 2005 Cisco Systems, Inc.
Nasser El-Aawar Giles Heron
Level 3 Communications, LLC. Tellabs
February 2005
Encapsulation Methods for Transport of Ethernet Over MPLS Networks
draft-ietf-pwe3-ethernet-encap-09.txt
Status of this Memo
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patent or other IPR claims of which we are aware have been disclosed,
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Abstract
An Ethernet Pseudowire (PW) is used to carry Ethernet/802.3 Protocol
Data Units over an MPLS network. This enables service providers to
offer "emulated" ethernet services over existing MPLS networks. This
document specifies the encapsulation of Ethernet/802.3 PDUs within a
pseudo wire. It also specifies the procedures for using a PW to
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provide a "point-to-point ethernet" service.
Table of Contents
1 Specification of Requirements .......................... 3
2 Introduction ........................................... 3
3 Details Specific to Particular Emulated Services ....... 6
3.1 Ethernet Tagged Mode ................................... 6
3.2 Ethernet ............................................... 6
3.3 Ethernet Specific Interface Parameters ................. 7
3.4 Generic Procedures ..................................... 7
3.4.1 Raw Mode vs. Tagged Mode ............................... 8
3.4.2 MTU Management on the PE/CE Links ...................... 9
3.4.3 Frame Ordering ......................................... 9
3.4.4 Frame Error Processing ................................. 9
3.4.5 IEEE 802.3x Flow Control Interworking .................. 9
3.5 PW Setup and Maintenance ............................... 10
3.6 Management ............................................. 10
3.7 The Control Word ....................................... 10
3.7.1 Setting the sequence number ............................ 11
3.7.2 Processing the sequence number ......................... 11
3.8 QoS Considerations ..................................... 12
4 Security Considerations ................................ 13
5 PSN MTU Requirements ................................... 13
6 IANA Considerations .................................... 13
7 Full Copyright Statement ............................... 14
8 Intellectual Property Statement ........................ 14
9 Normative References ................................... 15
10 Informative References ................................. 15
11 Editor Information ..................................... 16
12 Author Information ..................................... 16
13 Significant Contributors ............................... 17
Ap A Interoperability Guidelines ............................ 19
Ap B QoS Details ............................................ 21
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1. Specification of Requirements
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 RFC 2119
2. Introduction
An Ethernet Pseudowire (PW) allows Ethernet/802.3 Protocol Data Units
(PDUs) to be carried over an MPLS network. In addressing the issues
associated with carrying an Ethernet PDU over a Public Switched
Network (PSN), this document assumes that a Pseudowire (PW) has been
set up by using the LDP protocol as described in [PWE3-CRTL]. This
may be via manual configuration, or a signaling protocol such as LDP,
as defined in [PWE3-CTRL].
In addition to the Ethernet PDU format used within the pseudo wire,
this document discusses:
- Procedures for using a PW in order to provide a pair of CEs with
an emulated (point-to-point) ethernet service, including the
procedures for the processing of PE-bound and CE-bound ethernet
PDUs. [RFC3985]
- Ethernet-specific QoS and security considerations
- Inter-domain transport considerations for Ethernet PW
The following two figures describe the reference models which are
derived from [RFC3985] to support the Ethernet PW emulated services.
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|<-------------- Emulated Service ---------------->|
| |
| |<------- Pseudo Wire ------>| |
| | | |
| | |<-- PSN Tunnel -->| | |
| PW End V V V V PW End |
V Service +----+ +----+ Service V
+-----+ | | PE1|==================| PE2| | +-----+
| |----------|............PW1.............|----------| |
| CE1 | | | | | | | | CE2 |
| |----------|............PW2.............|----------| |
+-----+ ^ | | |==================| | | ^ +-----+
^ | +----+ +----+ | | ^
| | Provider Edge 1 Provider Edge 2 | |
| | | |
Customer | | Customer
Edge 1 | | Edge 2
| |
| |
Attachment Circuit (AC) Attachment Circuit (AC)
native ethernet service native ethernet service
Figure 1: PWE3 Ethernet/VLAN Interface Reference Configuration
The "emulated service" shown in Figure 1 is, strictly speaking, a
bridged LAN; the PEs have MAC interfaces, consume MAC control frames,
etc. However, the procedures specified herein only support the case
in which there are two CEs on the "emulated LAN". Hence we refer to
this service as "emulated point-to-point ethernet". Specification of
the procedures for using pseudo wires to emulate LANs with more than
two CEs are out of scope of the current document.
+-------------+ +-------------+
| Emulated | | Emulated |
| Ethernet | | Ethernet |
| (including | Emulated Service | (including |
| VLAN) |<==============================>| VLAN) |
| Services | | Services |
+-------------+ Pseudo Wire +-------------+
|Demultiplexer|<==============================>|Demultiplexor|
+-------------+ +-------------+
| PSN | PSN Tunnel | PSN |
| MPLS |<==============================>| MPLS |
+-------------+ +-------------+
| Physical | | Physical |
+-----+-------+ +-----+-------+
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Figure 2: Ethernet PWE3 Protocol Stack Reference Model
For the purpose of this document, PE1 will be defined as the ingress
router, and PE2 as the egress router. A layer 2 PDU will be received
at PE1, encapsulated at PE1, transported, decapsulated at PE2, and
transmitted out on the attachment circuit of PE2.
An Ethernet PW emulates a single Ethernet link between exactly two
endpoints. The mechanisms described in this document are agnostic to
that which is beneath the "Pseudo Wire" level in Figure 2, concerning
itself only with the "Emulated Service" portion of the stack.
The following reference model describes the termination point of each
end of the PW within the PE:
+-----------------------------------+
| PE |
+---+ +-+ +-----+ +------+ +------+ +-+
| | |P| | | |PW ter| | PSN | |P|
| |<==|h|<=| NSP |<=|minati|<=|Tunnel|<=|h|<== From PSN
| | |y| | | |on | | | |y|
| C | +-+ +-----+ +------+ +------+ +-+
| E | | |
| | +-+ +-----+ +------+ +------+ +-+
| | |P| | | |PW ter| | PSN | |P|
| |==>|h|=>| NSP |=>|minati|=>|Tunnel|=>|h|==> To PSN
| | |y| | | |on | | | |y|
+---+ +-+ +-----+ +------+ +------+ +-+
| |
+-----------------------------------+
^ ^ ^
| | |
A B C
Figure 3: PW reference diagram
The PW terminates at a logical port within the PE, defined at point A
in the above diagram. This port provides an Ethernet MAC service that
will deliver each Ethernet frame that is received at point A,
unaltered, to the point A in the corresponding PE at the other end of
the PW.
The Native Service Processing (NSP) function includes frame
processing that is required for the Ethernet frames that are
forwarded to the PW termination point. Such functions may include
stripping, overwriting or adding VLAN tags, physical port
multiplexing and demultiplexing, PW-PW bridging, L2 encapsulation,
shaping, policing, etc. These functions are specific to the native
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frame technology , and may not be required for the PW emulation
service.
The points to the left of A, including the physical layer between the
CE and PE, and any adaptation (NSP) functions between it and the PW
terminations, are outside of the scope of PWE3 and are not defined
here.
"PW Termination", between A and B, represents the operations for
setting up and maintaining the PW, and for encapsulating and
decapsulating the Ethernet frames as necessary to trasmit them across
the MPLS network.
An ethernet PW operates in one of two modes: "raw mode" or "tagged
mode". In tagged mode, each frame MUST contain an 802.1Q VLAN tag,
and the tag value is meaningful to the NSPs at the two PW termination
points. That is, the two PW termination points must have some
agreement (signaled or manually configured) on how to process the
tag. On a raw mode PW, a frame MAY contain an 802.1Q VLAN tag, but if
it does, the tag is not meaningful to the NSPs, and passes
transparently through them.
3. Details Specific to Particular Emulated Services
3.1. Ethernet Tagged Mode
The Ethernet frame will be encapsulated according to the procedures
defined in this document "tagged mode". It should be noted that if
the VLAN identifier is modified by the egress PE, the Ethernet
spanning tree protocol might fail to work properly. If the PE detects
a failure on the Ethernet physical port, or the port is
administratively disabled, it MUST send PW status notification
message for all PWs associated with the port. This mode uses
service-delimiting tags to map input ethernet frames to respective
PWs and is corresponds to PW type 0x0004 "Ethernet Tagged Mode"
[IANA].
3.2. Ethernet
The Ethernet frame will be encapsulated according to the procedures
defined in this document "raw mode". If the PE detects a failure on
the Ethernet input port, or the port is administratively disabled,
the PE MUST send an appropriate PW status notification message to the
corresponding remote PE. In this mode all ethernet frames received
on the attachment circuit of PE1 will be transmitted to PE2 on a
single PW.This service corresponds to PW type 0x0005 "Ethernet"
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[IANA].
3.3. Ethernet Specific Interface Parameters
This field specifies interface specific parameters. When applicable,
it MUST be used to validate that the PEs, and the ingress and egress
ports at the edges of the circuit, have the necessary capabilities to
interoperate with each other. The Interface parameter TLV is defined
in [CONTROL], the IANA registry with initial values for interface
parameter types is defined in [IANA], but the ethernet specific
interface paramenters are specified as follows:
- 0x06 Requested VLAN ID.
An Optional 16 bit value indicating the requested VLAN ID. This
parameter MUST be used by a PE that is incapable of rewriting the
802.1Q ethernet VLAN tag on output. If the ingress PE receives
this request, it MUST rewrite the VLAN ID tag at the input to
match the requested VLAN ID. If this is not possible, and the
VLAN ID does not already match the configured ingress VLAN ID,
the PW MUST not be enabled. This parameter is applicable only to
PW type 4.
3.4. Generic Procedures
When the NSP/Forwarder hands a frame to the PW termination function:
- The preamble (if any) and FCS are stripped off.
- The control word as defined in the "The Control Word" section is,
if necessary, prepended to the resulting frame. The conditions
under which the control word is or is not used are specified
below.
- The proper Pseudowire demultiplexor ( PW Label ) is prepended to
the resulting packet.
- The proper tunnel encapsulation is prepended to the resulting
packet.
- The packet is transmitted.
The way in which the proper tunnel encapsulation and pseudo wire
demultiplexor are chosen depends on the procedures that were used to
set up the pseudo wire.
When a packet arrives over a PW, the tunnel encapsulation and PW
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demultiplexor are stripped off. If the control word is present, it is
processed and stripped off. The resulting frame is then handed to the
Forwarder/NSP. Regeneration of the FCS is considered to be an NSP
responsibility.
3.4.1. Raw Mode vs. Tagged Mode
When the PE receives an ethernet frame, and the frame has a VLAN tag,
we can distinguish two cases:
1. The tag is "service-delimiting". This means that the tag was
placed on the frame by some piece of service provider-operated
equipment, and the tag is used by the service provider to
distinguish the traffic. For example, LANs from different
customers might be attached to the same service provider
switch, which applies VLAN tags to distinguish one customer's
traffic from another's, and then forwards the frames to the PE.
2. The tag is not service-delimiting. This means that the tag was
placed in the frame by a piece of customer equipment, and is
not meaningful to the PE.
If an ethernet PW is operating in raw mode, service-delimiting tags
are NEVER sent over the PW. If a service-delimiting tag is present
when the frame is received from attachment circuit by the PE, it MUST
be stripped (by the NSP) from the frame before the frame is sent to
the PW.
If an ethernet PW is operating in tagged mode, every frame sent on
the PW MUST have a service-delimiting VLAN tag. If the frame as
received by the PE from the attachment circuit does not have a
service-delimiting VLAN tag, the PE must prepend the frame with a
dummy VLAN tag before sending the frame on the PW. This is the
default operating mode. This is the only REQUIRED mode.
In both modes, non-service-delimiting tags are passed transparently
across the PW as part of the payload. It should be noted that a
single ethernet packet may contain more then one tag. None of these
tags maybe service-delimiting, otherwise only one of these tags maybe
be service-delimiting. In any case the NSP function may only inspect
the outer most tag for the purpose of adapting the ethernet frame to
the pseudo wire.
In both modes, the service-delimiting tag values have only local
significance, i.e., are meaningful only at a particular PE-CE
interface. When tagged mode is used, the PE that receives a frame
from the PW may rewrite the tag value, or may strip the tag entirely,
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or may leave the tag unchanged, depending on its configuration. When
raw mode is used, the PE that receives a frame may or may not need to
add a service-delimiting tag before transmitting the frame on the
attachment circuit; however it MUST not rewrite or remove any tags
which are already present.
3.4.2. MTU Management on the PE/CE Links
The Ethernet PW MUST NOT be enabled unless it is known that the MTUs
of the CE-PE links are the same at both ends of the PW.
3.4.3. Frame Ordering
In general, applications running over Ethernet do not require strict
frame ordering. However the IEEE definition of 802.3 [802.3] requires
that frames from the same conversation are delivered in sequence.
Moreover, the PSN cannot (in the general case) be assumed to provide
or to guarantee frame ordering. An ethernet PW can, through use of
the control word, provide strict frame ordering. If this option is
enabled, any frames which get misordered by the PSN will be dropped
by the receiving PW endpoint. If strict frame ordering is a
requirement for a particular PW, this option MUST be enabled.
3.4.4. Frame Error Processing
An encapsulated Ethernet frame traversing a psuedo-wire may be
dropped, corrupted or delivered out-of-order. As described in [PWE3-
REQ], frame-loss, corruption, and out-of-order delivery is considered
to be a "generalized bit error" of the psuedo-wire. PW frames that
are corrupted will be detected at the PSN layer and dropped.
At the ingress of the PW the native Ethernet frame error processing
mechanisms MUST be enabled. Therefore, if a PE device receives an
Ethernet frame containing hardware level CRC errors, framing errors,
or a runt condition, the frame MUST be discarded on input. Note that
defining this processing is part of the NSP function and is outside
the scope of this document.
3.4.5. IEEE 802.3x Flow Control Interworking
In a standard gigabit Ethernet network, the flow control mechanism is
optional and typically configured between the two nodes on a point-
to-point link (e.g. between the CE and the PE). IEEE 802.3x PAUSE
frames MUST NOT be carried across the PW. See Appendix A for notes on
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CE-PE flow control.
3.5. PW Setup and Maintenance
This document assumes that a mechanism exists to set up the ethernet
PW. Maintenance of the PW (e.g. keepalives, status updates, etc) is
generally tied closely to the PW Setup mechanisms. [PWE3-CTRL] and
[L2TPv3] define two mechanisms for setup and maintenance of Ethernet
PWs.
3.6. Management
The Ethernet PW management model follows the general management
defined in [RFC3985] and [PWE3-MIB]. Many common PW management
facilities are provided here, with no additional Ethernet specifics
necessary. Ethernet-specific parameters are defined in an additional
MIB module, [PW-MIB].
3.7. The Control Word
When carrying Ethernet over an MPLS backbone, sequentiality may need
to be preserved. The OPTIONAL control word defined here addresses
this requirement. Implementations MUST support sending no control
word, and MAY support sending a control word.
In all cases the egress router must be aware of whether the ingress
router will send a control word over a specific virtual circuit. This
may be achieved by configuration of the routers, or by signaling, as
defined in [PWE3-CRTL].
The control word is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0| Reserved | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the above diagram the first 4 bits MUST be set to 0 to indicate PW
data. The rest of the first 16 bits are reserved for future use.
They MUST be set to 0 when transmitting, and MUST be ignored upon
receipt.
The next 16 bits provide a sequence number that can be used to
guarantee ordered frame delivery. The processing of the sequence
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number field is OPTIONAL.
The sequence number space is a 16 bit, unsigned circular space. The
sequence number value 0 is used to indicate that the sequence number
check alghorithm is not used.
3.7.1. Setting the sequence number
For a given PW, and a pair of routers PE1 and PE2, if PE1 supports
frame sequencing then the following procedures should be used:
- the initial frame transmitted on the PW MUST use sequence number
1
- subsequent frames MUST increment the sequence number by one for
each frame
- when the transmit sequence number reaches the maximum 16 bit
value (65535) the sequence number MUST wrap to 1
If the transmitting router PE1 does not support sequence number
processing, then the sequence number field in the control word MUST
be set to 0.
3.7.2. Processing the sequence number
If a router PE2 supports receive sequence number processing, then the
following procedures should be used:
When a PW is initially set up, the "expected sequence number"
associated with it MUST be initialized to 1.
When a frame is received on that PW, the sequence number should be
processed as follows:
- if the sequence number on the frame is 0, then the sequence
number check is skipped. ( sequence check disabled )
- otherwise if the frame sequence number >= the expected sequence
number and the frame sequence number - the expected sequence
number < 32768, then the frame is in order.
- otherwise if the frame sequence number < the expected sequence
number and the expected sequence number - the frame sequence
number >= 32768, then the frame is in order.
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- otherwise the frame is out of order.
If a frame passes the sequence number check, or is in order then, it
can be delivered immediately. If the frame is in order, then the
expected sequence number should be set using the algorithm:
expected_sequence_number := frame_sequence_number + 1 mod 2**16
if (expected_sequence_number = 0) then expected_sequence_number := 1;
Packets which are received out of order MAY be dropped or reordered
at the discretion of the receiver.
If a PE router negotiated not to use receive sequence number
processing, and it received a non zero sequence number, then it
SHOULD send a PW status message indicating a receive fault, and
disable the PW.
3.8. QoS Considerations
The ingress PE MAY consider the user priority (PRI) field [802.1Q] of
the VLAN tag header when determining the value to be placed in a QoS
field of the encapsulating protocol (e.g., the EXP fields of the MPLS
label stack). In a similar way, the egress PE MAY consider the QoS
field of the PSN's encapsulating protocol when queuing the frame for
CE-bound.
A PE MUST support the ability to carry the Ethernet PW as a best
effort service over the PSN. PRI bits are kept transparent between
PE devices, regardless of the QoS support of the PSN.
If an 802.1Q VLAN field is added at the PE, a default PRI setting of
zero MUST be supported, a configured default value is recommended, or
the value may be mapped from the QoS field of the PSN, as referred to
above.
A PE may support additional QoS support by means of one or more of
the following methods:
-i. One COS per PW End Service (PWES), mapped to a single COS PW
at the PSN.
-ii. Multiple COS per PWES mapped to a single PW with multiple
COS at the PSN.
-iii. Multiple COS per PWES mapped to multiple PWs at the PSN.
Examples of the cases above and details of the service mapping
considerations are described in Appendix B.
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The PW guaranteed rate at the PSN level is PW provider policy based
on agreement with the customer, and may be different from the
Ethernet physical port rate.
4. Security Considerations
The ethernet pseudo wire type is subject to all of the general
security considerations discussed in [RFC3985][PWE3-CRTL].
The ethernet pseudo wire is transported on a MPLS PSN, therefore the
security of the pseudo wire itself will only be as good as the
security of the MPLS PSN. The MPLS PSN can be secured by various
methods, as described in [RFC3031].
Security achieved by access control of MAC addresses is out of scope
of this document. Additional security requirements related to the use
of PW in a switching (virtual bridging) environment are not discussed
here as they are not within the scope of this document.
5. PSN MTU Requirements
The PSN MUST be configured with an MTU that is large enough to
transport a maximum sized ethernet frame which has been encapsulated
with a control word, a pseudo wire demultiplexor, and a tunnel
encapsulation. If MPLS is used as the tunneling protocol, for
example, this is likely to be 8 or more bytes greater than the
largest frame size. Other tunneling protocols may have longer headers
and require larger MTUs. If the ingress router determines that an
encapsulated layer 2 PDU exceeds the MTU of the tunnel through which
it must be sent, the PDU MUST be dropped. If an egress router
receives an encapsulated layer 2 PDU whose payload length (i.e., the
length of the PDU itself without any of the encapsulation headers),
exceeds the MTU of the destination layer 2 interface, the PDU MUST be
dropped.
6. IANA Considerations
This document has no IANA Actions.
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7. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78 and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
8. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
or will be disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668.
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9. Normative References
[PWE3-CW] "PWE3 Control Word for use over an MPLS PSN", S. Bryant,
G. Swallow, D. McPherson, draft-ietf-pwe3-cw-01.txt, ( work in
progress ), December 2004.
[IANA] "IANA Allocations for pseudo Wire Edge to Edge Emulation
(PWE3)" Martini,Townsley, draft-ietf-pwe3-iana-allocation-08.txt
(work in progress), April 2004
[PWE3-CRTL] "Transport of Layer 2 Frames Over MPLS", Martini L.,et al
draft-ietf-pwe3-control-protocol-09.txt, ( work in progress ),
September 2004.
[RFC3031] E. Rosen, et al., RFC 3031, MPLS Architecture, January
2001.
10. Informative References
[RFC3985] "PWE3 Architecture" Bryant, et al., RFC3985.
[PWE3-REQ] "Requirements for Pseudo Wire Emulation Edge-to-Edge",
Xiao, X., McPherson, D., Pate, P., White, C., Kompella,
K., Gill, V., Nadeau, T., draft-ietf-pwe3-requirements-08.txt,
(work in progress), September 2003.
[PW-MIB] "Pseudo Wire (PW) Management Information Base
using SMIv2", Zelig, D., Mantin, S., Nadeau, T., Danenberg,
D., draft-ietf-pwe3-pw-mib-04.txt, (work in progress),
February 2004.
[802.3] IEEE, ISO/IEC 8802-3: 2000 (E), "IEEE Standard
for Information technology -- Telecommunications and
information exchange between systems -- Local and metropolitan
area networks -- Specific requirements -- Part 3: Carrier
Sense Multiple Access with Collision Detection (CSMA/CD)
Access Method and Physical Layer Specifications", 2000.
[802.1Q] ANSI/IEEE Standard 802.1Q, "IEEE Standards for
Local and Metropolitan Area Networks: Virtual Bridged
Local Area Networks", 1998.
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11. Editor Information
Luca Martini
Cisco Systems, Inc.
9155 East Nichols Avenue, Suite 400
Englewood, CO, 80112
e-mail: lmartini@cisco.com
12. Author Information
Nasser El-Aawar
Level 3 Communications, LLC.
1025 Eldorado Blvd.
Broomfield, CO, 80021
e-mail: nna@level3.net
Giles Heron
Tellabs
Abbey Place
24-28 Easton Street
High Wycombe
Bucks
HP11 1NT
UK
e-mail: giles.heron@tellabs.com
Eric C. Rosen
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
e-mail: erosen@cisco.com
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13. Significant Contributors
Andrew G. Malis
Tellabs
90 Rio Robles Dr.
San Jose, CA 95134
e-mail: Andy.Malis@tellabs.com
Dan Tappan
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA 01719
e-mail: tappan@cisco.com
Steve Vogelsang
Laurel Networks, Inc.
Omega Corporate Center
1300 Omega Drive
Pittsburgh, PA 15205
e-mail: sjv@laurelnetworks.com
Vinai Sirkay
Reliance Infocomm
Dhirubai Ambani Knowledge City
Navi Mumbai 400 709
India
e-mail: vinai@sirkay.com
Vasile Radoaca
Nortel Networks
600 Technology Park
Billerica MA 01821
e-mail: vasile@nortelnetworks.com
Chris Liljenstolpe
Alcatel
11600 Sallie Mae Dr.
9th Floor
Reston, VA 20193
e-mail: chris.liljenstolpe@alcatel.com
Martini, et al. [Page 17]
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Kireeti Kompella
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
e-mail: kireeti@juniper.net
Tricci So
Nortel Networks 3500 Carling Ave.,
Nepean, Ontario,
Canada, K2H 8E9.
e-mail: tso@nortelnetworks.com
XiPeng Xiao
Riverstone Networks
5200 Great America Parkway
Santa Clara, CA 95054
e-mail: xxiao@riverstonenet.com
Christopher O. Flores
T-Systems
10700 Parkridge Boulevard
Reston, VA 20191
USA
e-mail: christopher.flores@usa.telekom.de
David Zelig
Corrigent Systems
126, Yigal Alon St.
Tel Aviv, ISRAEL
e-mail: davidz@corrigent.com
Raj Sharma
Luminous Netwokrs, Inc.
10460 Bubb Road
Cupertino, CA 95014
e-mail: raj@luminous.com
Martini, et al. [Page 18]
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Nick Tingle
TiMetra Networks
274 Ferguson Drive
Mountain View, CA 94043
e-mail: nick@timetra.com
Sunil Khandekar
TiMetra Networks
274 Ferguson Drive
Mountain View, CA 94043
email: sunil@timetra.com
Loa Andersson
TLA-group
e-mail: loa@pi.se
Ap A Interoperability Guidelines
Configuration Options
The following is a list of the configuration options for a point-to-
point Ethernet PW based on the reference points of Figure 3:
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--------------|---------------|---------------|------------------
Service and | Encap on C |Operation at B | Remarks
Encap on A | |ingress/egress |
--------------|---------------|---------------|------------------
1) Raw | Raw - Same as | |
| A | |
| | |
--------------|---------------|---------------|------------------
2) Tag1 | Tag2 |Optional change| VLAN can be
| |of VLAN value | 0-4095
| | | Change allowed in
| | | both directions
--------------|---------------|---------------|------------------
3) No Tag | Tag |Add/remove Tag | Tag can be
| |field | 0-4095
| | | (note i)
| | |
--------------|---------------|---------------|------------------
4) Tag | No Tag |Remove/add Tag | (note ii)
| |field |
| | |
| | |
--------------|---------------|---------------|------------------
Figure 4: Configuration Options
Allowed combinations:
Raw and other services are not allowed on the same NSP virtual port
(A). All other combinations are allowed, except that conflicting
VLANs on (A) are not allowed. Note that in most point-to-point PW
application the NSP virtual port is the same entity as the physical
port.
Notes:
-i. Mode #3 MAY be limited to adding VLAN NULL only, since
change of VLAN or association to specific VLAN can be done
at the PW CE-bound side.
-ii. Mode #4 exists in layer 2 switches, but is not recommended
when operating with PW since it may not preserve the user's
PRI bits. If there is a need to remove the VLAN tag (for
TLS at the other end of the PW) it is recommended to use
mode #2 with tag2=0 (NULL VLAN) on the PW and use mode #3 at
the other end of the PW.
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IEEE 802.3x Flow Control Considerations
If the receiving node becomes congested, it can send a special frame,
called the PAUSE frame, to the source node at the opposite end of the
connection. The implementation MUST provide a mechanism for
terminating PAUSE frames locally (i.e. at the local PE). It MUST
operate as follows:
PAUSE frames received on a local Ethernet port SHOULD cause the PE
device to buffer, or to discard, further Ethernet frames for that
port until the PAUSE condition is cleared. Optionally, the PE MAY
simply discard PAUSE frames.
If the PE device wishes to pause data received on a local Ethernet
port (perhaps because its own buffers are filling up or because it
has received notification of congestion within the PSN) then it MAY
issue a PAUSE frame on the local Ethernet port, but MUST clear this
condition when willing to receive more data.
Ap B QoS Details
Section 3.7 describes various modes for supporting PW QOS over the
PSN. Examples of the above for a point to point VLAN service are:
- The classification to the PW is based on VLAN field only,
regardless of the user PRI bits. The PW is assigned a specific
COS (marking, scheduling, etc.) at the tunnel level.
- The classification to the PW is based on VLAN field, but the PRI
bits of the user is mapped to different COS marking (and network
behavior) at the PW level. Examples are and E-LSP in an MPLS
network.
- The classification to the PW is based on VLAN field and the PRI
bits, and frames with different PRI bits are mapped to different
PWs. An example is to map a PWES to different L-LSPs in MPLS PSN
in order to support multiple COS over an L-LSP capable network,
or to multiple L2TPv3 sessions [L2TPv3].
The specific value to be assigned at the PSN for various COS is
out of scope for this document.
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Adaptation of 802.1Q COS to PSN COS
It is not required that the PSN will have the same COS definition of
COS as defined in [802.1Q], and the mapping of 802.1Q COS to PSN COS
is application specific and depends on the agreement between the
customer and the PW provider. However, the following principles
adopted from 802.1Q table 8-2 MUST be met when applying set of PSN
COS based on user's PRI bits.
----------------------------------
|#of available classes of service|
-------------||---+---+---+---+---+---+---+---|
User || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
Priority || | | | | | | | |
===============================================
0 Best Effort|| 0 | 0 | 0 | 1 | 1 | 1 | 1 | 2 |
(Default) || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
1 Background || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
|| | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
2 Spare || 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
|| | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
3 Excellent || 0 | 0 | 0 | 1 | 1 | 2 | 2 | 3 |
Effort || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
4 Controlled || 0 | 1 | 1 | 2 | 2 | 3 | 3 | 4 |
Load || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
5 Interactive|| 0 | 1 | 1 | 2 | 3 | 4 | 4 | 5 |
Multimedia || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
6 Interactive|| 0 | 1 | 2 | 3 | 4 | 5 | 5 | 6 |
Voice || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
7 Network || 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
Control || | | | | | | | |
------------ ||---+---+---+---+---+---+---+---|
Figure 5: IEEE 802.1Q COS Service Mapping
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Drop precedence
The 802.1P standard does not support drop precedence, therefore from
the PW PE-bound point of view there is no mapping required. It is
however possible to mark different drop precedence for different PW
frames based on the operator policy and required network behavior.
This functionality is not discussed further here.
PSN QOS support and signaling of QOS is out of scope of this
document.
Martini, et al. [Page 23]
