< draft-ietf-pwe3-arch-04.txt   draft-ietf-pwe3-arch-05.txt >
Pseudo-Wire Edge-to-Edge (PWE3) Working Group Stewart Bryant Pseudo-Wire Edge-to-Edge (PWE3) Working Group Stewart Bryant
Internet Draft Cisco Systems Internet Draft Cisco Systems
Document: <draft-ietf-pwe3-arch-04.txt> Document: <draft-ietf-pwe3-arch-05.txt>
Expires: December 2003 Prayson Pate Expires: January 2004 Prayson Pate
Overture Networks, Inc. Overture Networks, Inc.
Editors Editors
June 2003 August 2003
PWE3 Architecture PWE3 Architecture
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of section 10 of RFC2026. all provisions of section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other Task Force (IETF), its areas, and its working groups. Note that other
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The following are co-authors of this document: The following are co-authors of this document:
Thomas K. Johnson Litchfield Communications Thomas K. Johnson Litchfield Communications
Kireeti Kompella Juniper Networks, Inc. Kireeti Kompella Juniper Networks, Inc.
Andrew G. Malis Vivace Networks Andrew G. Malis Vivace Networks
Thomas D. Nadeau Cisco Systems Thomas D. Nadeau Cisco Systems
Tricci So Caspian Networks Tricci So Caspian Networks
W. Mark Townsley Cisco Systems W. Mark Townsley Cisco Systems
Craig White Level 3 Communications, LLC. Craig White Level 3 Communications, LLC.
Lloyd Wood Cisco Systems Lloyd Wood Cisco Systems
XiPeng Xiao Redback Networks XiPeng Xiao Riverstone Networks
Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
Table of Contents Table of Contents
1. Introduction............................................. 5 1. Introduction............................................. 5
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5. PW Encapsulation......................................... 21 5. PW Encapsulation......................................... 21
5.1 Payload Convergence Layer............................ 22 5.1 Payload Convergence Layer............................ 22
5.2 Payload-independent PW Encapsulation Layers.......... 24 5.2 Payload-independent PW Encapsulation Layers.......... 24
5.3 Fragmentation........................................ 27 5.3 Fragmentation........................................ 27
5.4 Instantiation of the Protocol Layers................. 27 5.4 Instantiation of the Protocol Layers................. 27
6. PW Demultiplexer Layer and PSN Requirements.............. 32 6. PW Demultiplexer Layer and PSN Requirements.............. 32
6.1 Multiplexing......................................... 32 6.1 Multiplexing......................................... 32
6.2 Fragmentation........................................ 32 6.2 Fragmentation........................................ 32
6.3 Length and Delivery.................................. 32 6.3 Length and Delivery.................................. 33
6.4 PW-PDU Validation.................................... 33 6.4 PW-PDU Validation.................................... 33
6.5 Congestion Considerations............................ 33 6.5 Congestion Considerations............................ 33
7. Control Plane............................................ 34 7. Control Plane............................................ 34
7.1 Set-up or Teardown of Pseudo-Wires................... 34 7.1 Set-up or Teardown of Pseudo-Wires................... 34
7.2 Status Monitoring.................................... 34 7.2 Status Monitoring.................................... 35
7.3 Notification of Pseudo-wire Status Changes........... 35 7.3 Notification of Pseudo-wire Status Changes........... 35
7.4 Keep-alive........................................... 36 7.4 Keep-alive........................................... 36
7.5 Handling Control Messages of the Native Services..... 36 7.5 Handling Control Messages of the Native Services..... 37
8. Management and Monitoring................................. 37 8. Management and Monitoring................................. 37
8.1 Status and Statistics................................ 37 8.1 Status and Statistics................................ 37
8.2 PW SNMP MIB Architecture............................. 37 8.2 PW SNMP MIB Architecture............................. 38
8.3 Connection Verification and Traceroute................ 41 8.3 Connection Verification and Traceroute................ 41
9. IANA considerations...................................... 41 9. IANA considerations...................................... 41
10. Security Considerations................................. 41 10. Security Considerations................................. 41
1. Introduction 1. Introduction
This document describes an architecture for Pseudo Wire Emulation This document describes an architecture for Pseudo Wire Emulation
Edge-to-Edge (PWE3) in support of [XIAO]. It discusses the emulation Edge-to-Edge (PWE3) in support of [XIAO]. It discusses the emulation
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processing of the data received from a PW processing of the data received from a PW
by a PE before it is output on the AC. by a PE before it is output on the AC.
NSP functionality is defined by standards NSP functionality is defined by standards
bodies other than the IETF, such as ITU-T, bodies other than the IETF, such as ITU-T,
ANSI, ATMF, etc.) ANSI, ATMF, etc.)
Packet Switched Within the context of PWE3, this is a Packet Switched Within the context of PWE3, this is a
Network (PSN) network using IP or MPLS as the mechanism Network (PSN) network using IP or MPLS as the mechanism
for packet forwarding. for packet forwarding.
Protocol Data The unit of data output to, or received
Unit (PDU) from, the network by a protocol layer.
Provider Edge (PE) A device that provides PWE3 to a CE.
PE-bound The traffic direction where information PE-bound The traffic direction where information
from a CE is adapted to a PW, and PW-PDUs from a CE is adapted to a PW, and PW-PDUs
are sent into the PSN. are sent into the PSN.
PE/PW Maintenance Used by the PEs to set up, maintain and PE/PW Maintenance Used by the PEs to set up, maintain and
tear down the PW. It may be coupled with tear down the PW. It may be coupled with
CE Signaling in order to effectively manage CE Signaling in order to effectively manage
the PW. the PW.
Protocol Data The unit of data output to, or received
Unit (PDU) from, the network by a protocol layer.
Provider Edge (PE) A device that provides PWE3 to a CE.
Pseudo Wire (PW) A mechanism that carries the essential Pseudo Wire (PW) A mechanism that carries the essential
elements of an emulated service from one PE elements of an emulated service from one PE
to one or more other PEs over a PSN. to one or more other PEs over a PSN.
PW End Service The interface between a PE and a CE. This
(PWES) can be a physical interface like a T1 or
Ethernet, or a virtual interface like a VC
or VLAN.
Pseudo Wire A mechanism that emulates the essential Pseudo Wire A mechanism that emulates the essential
Emulation Edge to attributes of service (such as a T1 leased Emulation Edge to attributes of service (such as a T1 leased
Edge (PWE3) line or frame relay) over a PSN. Edge (PWE3) line or frame relay) over a PSN.
Pseudo Wire PDU A PDU sent on the PW that contains all of Pseudo Wire PDU A PDU sent on the PW that contains all of
(PW-PDU) the data and control information necessary (PW-PDU) the data and control information necessary
to emulate the desired service. to emulate the desired service.
PSN Tunnel A tunnel across a PSN inside which one or PSN Tunnel A tunnel across a PSN inside which one or
more PWs can be carried. more PWs can be carried.
PSN Tunnel Used to set up, maintain and tear down the PSN Tunnel Used to set up, maintain and tear down the
Signaling underlying PSN tunnel. Signaling underlying PSN tunnel.
PW Demultiplexer Data-plane method of identifying a PW PW Demultiplexer Data-plane method of identifying a PW
terminating at a PE. terminating at a PE.
PW End Service The interface between a PE and a CE. This
(PWES) can be a physical interface like a T1 or
Ethernet, or a virtual interface like a VC
or VLAN.
PWE3 Payload Type A identifier used to distinguish between
Identifier an MPLS IP payload and a CW that is not
(PWE3-PID) ECMP safe.
Time Domain Time Division Multiplexing. Frequently used Time Domain Time Division Multiplexing. Frequently used
Multiplexing (TDM) to refer to the synchronous bit-streams at Multiplexing (TDM) to refer to the synchronous bit-streams at
rates defined by G.702. rates defined by G.702.
Tunnel A method of transparently carrying information Tunnel A method of transparently carrying information
over a network. over a network.
2. PWE3 Applicability 2. PWE3 Applicability
The PSN carrying a PW will subject payload packets to loss, delay, The PSN carrying a PW will subject payload packets to loss, delay,
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discussed in more detail in Section 5.3 discussed in more detail in Section 5.3
A packet payload may need sequencing and real-time support. A packet payload may need sequencing and real-time support.
In some situations, the packet payload MAY be selected from the In some situations, the packet payload MAY be selected from the
packets presented on the emulated wire on the basis of some sub- packets presented on the emulated wire on the basis of some sub-
multiplexing technique. For example, one or more frame-relay PDUs multiplexing technique. For example, one or more frame-relay PDUs
may be selected for transport over a particular pseudo-wire based on may be selected for transport over a particular pseudo-wire based on
the frame-relay Data-Link Connection Identifier (DLCI), or, in the the frame-relay Data-Link Connection Identifier (DLCI), or, in the
case of Ethernet payloads, using a suitable MAC bridge filter. This case of Ethernet payloads, using a suitable MAC bridge filter. This
is an FWRD function, and this selection would therefore be made is a forwarder function, and this selection would therefore be made
before the packet was presented to the PW Encapsulation Layer. before the packet was presented to the PW Encapsulation Layer.
3.3.2. Cell Payload 3.3.2. Cell Payload
A cell payload is created by capturing, transporting and replaying A cell payload is created by capturing, transporting and replaying
groups of octets presented on the wire in a fixed-size format. The groups of octets presented on the wire in a fixed-size format. The
delineation of the group of bits that comprise the cell is specific delineation of the group of bits that comprise the cell is specific
to the encapsulation type. Two common examples of cell payloads are to the encapsulation type. Two common examples of cell payloads are
ATM 53-octet cells, and the larger 188-octet MPEG Transport Stream ATM 53-octet cells, and the larger 188-octet MPEG Transport Stream
packets [DVB]. packets [DVB].
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The generic cell payload service will normally need sequence number The generic cell payload service will normally need sequence number
support, and may also need real-time support. The generic cell support, and may also need real-time support. The generic cell
payload service would not normally require fragmentation. payload service would not normally require fragmentation.
The Encapsulation Layer MAY apply some form of compression to some of The Encapsulation Layer MAY apply some form of compression to some of
these sub-types (e.g. idle cells MAY be suppressed). these sub-types (e.g. idle cells MAY be suppressed).
In some instances, the cells to be incorporated in the payload MAY be In some instances, the cells to be incorporated in the payload MAY be
selected by filtering them from the stream of cells presented on the selected by filtering them from the stream of cells presented on the
wire. For example, an ATM PWE3 service may select cells based on wire. For example, an ATM PWE3 service may select cells based on
their VCI or VPI fields. This is an FWRD function, and the selection their VCI or VPI fields. This is a forwader function, and the
would therefore be made before the packet was presented to the PW selection would therefore be made before the packet was presented to
Encapsulation Layer. the PW Encapsulation Layer.
3.3.3. Bit-stream 3.3.3. Bit-stream
A bit-stream payload is created by capturing, transporting and A bit-stream payload is created by capturing, transporting and
replaying the bit pattern on the emulated wire, without taking replaying the bit pattern on the emulated wire, without taking
advantage of any structure that, on inspection, may be visible within advantage of any structure that, on inspection, may be visible within
the relayed traffic (i.e. the internal structure has no effect on the the relayed traffic (i.e. the internal structure has no effect on the
fragmentation into packets). fragmentation into packets).
In some instances it is possible to apply suppression to bit-streams. In some instances it is possible to apply suppression to bit-streams.
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The required pre-processing can be divided into two components: The required pre-processing can be divided into two components:
o Forwarder (FWRD) o Forwarder (FWRD)
o Native Service Processing (NSP) o Native Service Processing (NSP)
4.2.1. Forwarders 4.2.1. Forwarders
In some applications there is the need to selectively forward payload In some applications there is the need to selectively forward payload
elements from one of more ACs to one or more PWs. In such cases there elements from one of more ACs to one or more PWs. In such cases there
will also be the need to perform the inverse function on PWE3-PDUs will also be the need to perform the inverse function on PWE3-PDUs
received by a PE from the PSN. This is the function of the FWRD. received by a PE from the PSN. This is the function of the forwarder.
The FWRD selects the PW based on, for example: the incoming AC, the The forwarder selects the PW based on, for example: the incoming AC,
contents of the payload, or some statically and/or dynamically the contents of the payload, or some statically and/or dynamically
configured forwarding information. configured forwarding information.
+----------------------------------------+ +----------------------------------------+
| PE Device | | PE Device |
+----------------------------------------+ +----------------------------------------+
Single | | | Single | | |
PWES | | Single | PW Instance PWES | | Single | PW Instance
<------>o Forwarder + PW Instance X<===========> <------>o Forwarder + PW Instance X<===========>
| | | | | |
+----------------------------------------+ +----------------------------------------+
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| Forwarder + PW Instance X<===========> | Forwarder + PW Instance X<===========>
<------>o | | <------>o | |
| |----------------------| | |----------------------|
<------>o | Single | PW Instance <------>o | Single | PW Instance
| + PW Instance X<===========> | + PW Instance X<===========>
<------>o | | <------>o | |
+----------------------------------------+ +----------------------------------------+
Figure 4b: Multiple PWES to Multiple PW Forwarding Figure 4b: Multiple PWES to Multiple PW Forwarding
Figure 4a shows a simple FWRD that performs some type of filtering Figure 4a shows a simple forwarder that performs some type of
operation. Because the FWRD has a single input and a single output filtering operation. Because the forwarder has a single input and a
interface, filtering is the only type of forwarding operation that single output interface, filtering is the only type of forwarding
applies. Figure 4b shows a more general forwarding situation where operation that applies. Figure 4b shows a more general forwarding
payloads are extracted from one or more PWESs and directed to one or situation where payloads are extracted from one or more PWESs and
more PWs, including, in this instance, a multipoint PW. In this case directed to one or more PWs, including, in this instance, a
both filtering and direction operations MAY be performed on the multipoint PW. In this case both filtering and direction operations
payloads. MAY be performed on the payloads.
4.2.2. Native Service Processing 4.2.2. Native Service Processing
In some applications some form of data or address translation, or In some applications some form of data or address translation, or
other operation requiring knowledge of the semantics of the payload, other operation requiring knowledge of the semantics of the payload,
will be required. This is the function of the Native Service will be required. This is the function of the Native Service
Processor (NSP). Processor (NSP).
The use of the NSP approach simplifies the design of the PW by The use of the NSP approach simplifies the design of the PW by
restricting a PW to homogeneous operation. NSP is included in the restricting a PW to homogeneous operation. NSP is included in the
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| | | | | | | |
|------| |----------------------| |------| |----------------------|
| | | Single | PW Instance | | | Single | PW Instance
<------>o NSP # + PW Instance X<===========> <------>o NSP # + PW Instance X<===========>
| | | | | | | |
+----------------------------------------+ +----------------------------------------+
Figure 5: NSP in a Multiple PWEs to Multiple Figure 5: NSP in a Multiple PWEs to Multiple
PW Forwarding PE PW Forwarding PE
Figure 5 illustrates the relationship between NSP, FWRD and PWs in a Figure 5 illustrates the relationship between NSP, forwarder and PWs
PE. The NSP function MAY apply any transformation operation in a PE. The NSP function MAY apply any transformation operation
(modification, injection, etc.) on the payloads as they pass between (modification, injection, etc.) on the payloads as they pass between
the physical interface to the CE and the virtual interface to the the physical interface to the CE and the virtual interface to the
FWRD. A PE device MAY contain more than one FWRD. forwarder. A PE device MAY contain more than one forwarder.
This model also supports the operation of a system in which the NSP This model also supports the operation of a system in which the NSP
functionality includes terminating the data-link, and applying functionality includes terminating the data-link, and applying
Network Layer processing to the payload is also supported. Network Layer processing to the payload is also supported.
4.3 Maintenance Reference Model 4.3 Maintenance Reference Model
Figure 6 illustrates the maintenance reference model for PWs. Figure 6 illustrates the maintenance reference model for PWs.
|<------- CE (end-to-end) Signaling ------>| |<------- CE (end-to-end) Signaling ------>|
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5.2.1.1 Frame Ordering 5.2.1.1 Frame Ordering
When packets carrying the PW-PDUs traverse a PSN, they may arrive out When packets carrying the PW-PDUs traverse a PSN, they may arrive out
of order at the destination PE. For some services, the frames of order at the destination PE. For some services, the frames
(control frames, data frames, or both control and data frames) MUST (control frames, data frames, or both control and data frames) MUST
be delivered in order. For such services, some mechanism MUST be be delivered in order. For such services, some mechanism MUST be
provided for ensuring in-order delivery. Providing a sequence number provided for ensuring in-order delivery. Providing a sequence number
in the sequence sub-layer header for each packet is one possible in the sequence sub-layer header for each packet is one possible
approach to out-of-sequence detection. Alternatively it can be noted approach to out-of-sequence detection. Alternatively it can be noted
that sequencing is a subset of the problem of delivering timed that sequencing is a subset of the problem of delivering timed
packets, and that a single combined mechanism such as [RFC1889] MAY packets, and that a single combined mechanism such as [RFC3550] MAY
be employed. be employed.
There are two possible misordering strategies: There are two possible misordering strategies:
o Drop misordered PW PDUs. o Drop misordered PW PDUs.
o Try to sort PW PDUs into the correct order. o Try to sort PW PDUs into the correct order.
The choice of strategy will depend on: The choice of strategy will depend on:
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clock recovery and timed payload delivery. A particular payload type clock recovery and timed payload delivery. A particular payload type
may require either or both of these services. may require either or both of these services.
5.2.2.1 Clock Recovery 5.2.2.1 Clock Recovery
Clock recovery is the extraction of output transmission bit timing Clock recovery is the extraction of output transmission bit timing
information from the delivered packet stream, and requires a suitable information from the delivered packet stream, and requires a suitable
mechanism. A physical wire carries the timing information natively, mechanism. A physical wire carries the timing information natively,
but it is a relatively complex task to extract timing from a highly but it is a relatively complex task to extract timing from a highly
jittered source such as packet stream. It is therefore desirable jittered source such as packet stream. It is therefore desirable
that an existing real-time protocol such as [RFC1889] be used for that an existing real-time protocol such as [RFC3550] be used for
this purpose, unless it can be shown that this is unsuitable or this purpose, unless it can be shown that this is unsuitable or
unnecessary for a particular payload type. unnecessary for a particular payload type.
5.2.2.2 Timed delivery 5.2.2.2 Timed delivery
Timed delivery is the delivery of non-contiguous PW PDUs to the PW Timed delivery is the delivery of non-contiguous PW PDUs to the PW
output interface with a constant phase relative to the input output interface with a constant phase relative to the input
interface. The timing of the delivery may be relative to a clock interface. The timing of the delivery may be relative to a clock
derived from the packet stream received over the PSN clock recovery, derived from the packet stream received over the PSN clock recovery,
or with reference to an external clock. or with reference to an external clock.
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Figure 10: PWE3 over an IP PSN Figure 10: PWE3 over an IP PSN
Figure 10 shows the protocol layering for PWE3 over an IP PSN. As a Figure 10 shows the protocol layering for PWE3 over an IP PSN. As a
rule, the payload SHOULD be carried as received from the NSP, with rule, the payload SHOULD be carried as received from the NSP, with
the Payload Convergence Layer provided when needed. (It is accepted the Payload Convergence Layer provided when needed. (It is accepted
that there MAY sometimes be good reason not to follow this rule, but that there MAY sometimes be good reason not to follow this rule, but
the exceptional circumstances need to be documented in the the exceptional circumstances need to be documented in the
Encapsulation Layer definition for that payload type). Encapsulation Layer definition for that payload type).
Where appropriate, timing is provided by RTP [RFC1889], which when Where appropriate, timing is provided by RTP [RFC3550], which when
used also provides a sequencing service. PW Demultiplexing may be used also provides a sequencing service. PW Demultiplexing may be
provided by a number of existing IETF tunnel protocols. Some of provided by a number of existing IETF tunnel protocols. Some of
these tunnel protocols provide an optional sequencing service. these tunnel protocols provide an optional sequencing service.
(Sequencing is provided either by RTP, or by the PW Demultiplexer (Sequencing is provided either by RTP, or by the PW Demultiplexer
Layer, but not both). A PSN Convergence Layer is not needed, because Layer, but not both). A PSN Convergence Layer is not needed, because
all the tunnel protocols shown above are designed to operate directly all the tunnel protocols shown above are designed to operate directly
over an IP PSN. over an IP PSN.
As a special case, if the PW Demultiplexer is an MPLS label, the As a special case, if the PW Demultiplexer is an MPLS label, the
protocol architecture of section 5.4.2 can be used instead of the protocol architecture of section 5.4.2 can be used instead of the
protocol architecture of this section. protocol architecture of this section.
5.4.2. PWE3 over an MPLS PSN 5.4.2. PWE3 over an MPLS PSN
The MPLS ethos places importance on wire efficiency. By using a The MPLS ethos places importance on wire efficiency. By using a
control word, some components of the PWE3 protocol layers can be control word, some components of the PWE3 protocol layers can be
compressed to increase this efficiency. compressed to increase this efficiency.
+---------------------+ +---------------------+
| Payload | | Payload |
/=====================\ +--------------------------------+ /=====================\
H Payload Convergence H--+------>| Flags, Frag, Len, Seq #, etc | H Payload Convergence H--+
H---------------------H | +--------------------------------+ H---------------------H | +--------------------------------+
H Timing H--------->| RTP | H Timing H--------->| RTP |
H---------------------H | +--------------------------------+ H---------------------H | +--------------------------------+
H Sequencing H--+ | MPLS Payload Type Ident | H Sequencing H--+------>| Flags, Frag, Len, Seq #, etc |
\=====================/ | +--------------------------------+ \=====================/ | +--------------------------------+
| PW Demultiplexer |--------->| PW Label | | PW Demultiplexer |----+ | PWE3 Payload Type Identifier |
+---------------------+ | +--------------------------------+ +---------------------+ | | +--------------------------------+
| PSN Convergence |--+ +--->| Outer Label or MPLS-in-IP encap| | PSN Convergence |--+ +---->| PW Label |
+---------------------+ | +--------------------------------+ +---------------------+ +--------------------------------+
| PSN |-----+ | PSN |--------->| Outer Label or MPLS-in-IP encap|
+---------------------+ +---------------------+ +--------------------------------+
| Data-link | | Data-link |
+---------------------+ +---------------------+
| Physical | | Physical |
+---------------------+ +---------------------+
Figure 11: PWE3 over an MPLS PSN using a control word Figure 11: PWE3 over an MPLS PSN using a control word
Figure 11 shows the protocol layering for PWE3 over an MPLS PSN. An Figure 11 shows the protocol layering for PWE3 over an MPLS PSN. An
inner MPLS label is used to provide the PW demultiplexing function. inner MPLS label is used to provide the PW demultiplexing function.
A control word is used to carry most of the information needed by the A control word is used to carry most of the information needed by the
PWE3 Encapsulation Layer and the PSN Convergence Layer in a compact PWE3 Encapsulation Layer and the PSN Convergence Layer in a compact
format. The flags in the control word provide the necessary payload format. The flags in the control word provide the necessary payload
convergence. A sequence field provides support for both in-order convergence. A sequence field provides support for both in-order
payload delivery and (supported by a fragmentation control method) a payload delivery and (supported by a fragmentation control method) a
PSN fragmentation service within the PSN Convergence Layer. Ethernet PSN fragmentation service within the PSN Convergence Layer. Ethernet
pads all frames to a minimum size of 64 bytes. The MPLS header does pads all frames to a minimum size of 64 bytes. The MPLS header does
not include a length indicator. Therefore to allow PWE3 to be carried not include a length indicator. Therefore to allow PWE3 to be carried
in MPLS to correctly pass over an Ethernet data-link, a length in MPLS to correctly pass over an Ethernet data-link, a length
correction field is needed in the control word. Where the design of correction field is needed in the control word. Where the design of
the control word would alias an IP packet, an MPLS Payload Type the control word would alias an IP packet, a PWE3 Payload Type
Identifier should be interposed between the PW label and the control Identifier (PWE3 PID) should be interposed between the PW label and
word (see 5.4.4). As with an IP PSN, where appropriate, timing is the control word (see 5.4.4). As with an IP PSN, where appropriate,
provided by RTP [RFC1889]. timing is provided by RTP [RFC3550].
In some networks it may be necessary to carry PWE3 over MPLS over IP. In some networks it may be necessary to carry PWE3 over MPLS over IP.
In these circumstances, the PW is encapsulated for carriage over MPLS In these circumstances, the PW is encapsulated for carriage over MPLS
as described in this section, and then a method of carrying MPLS over as described in this section, and then a method of carrying MPLS over
an IP PSN (such as GRE [RFC2784], [RFC2890]) is applied to the an IP PSN (such as GRE [RFC2784], [RFC2890]) is applied to the
resultant PW-PDU. resultant PW-PDU.
5.4.3. PW over MPLS Generic Control Word 5.4.3. PW over MPLS Generic Control Word
To allow accurate packet inspection in an MPLS PSN, and/or to operate To allow accurate packet inspection in an MPLS PSN, and/or to operate
correctly over MPLS PSNs that have deployed equal-cost multiple-path correctly over MPLS PSNs that have deployed equal-cost multiple-path
load-balancing (ECMP), a PW packet MUST NOT alias an IP packet. IP load-balancing (ECMP), a PW packet MUST NOT alias an IP packet. IP
packets are carried in MPLS label stacks without any protocol packets are carried in MPLS label stacks without any protocol
identifier. Historic values of the IP version number [RFC791] identifier. Historic values of the IP version number [RFC791]
[RFC1881] are therefore used to distinguish between IP and non-IP [RFC1883] are therefore used to distinguish between IP and non-IP
MPLS payloads. MPLS payloads.
To disambiguate the PW from an IP flow the PW SHOULD employ either To disambiguate the PW from an IP flow the PW SHOULD employ either
the generic PW control word shown in Figure 12, or an MPLS payload the generic PW control word shown in Figure 12, or a PWE3 PID. Note
type identifier. Note that an MPLS payload with bits 0..3 = 4 is an that an MPLS payload with bits 0..3 = 4 is an IPv4 packet and an MPLS
IPv4 packet and an MPLS payload with bits 0..3 = 6 is an IPv6 packet. payload with bits 0..3 = 6 is an IPv6 packet.
0 1 2 3 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 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| Specified by PW Encapsulation | |0 0 0 0| Specified by PW Encapsulation |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Generic PW Control Word Figure 12: Generic PW Control Word
The PW set-up protocol determines whether a PW uses a control word. The PW set-up protocol determines whether a PW uses a control word.
skipping to change at page 31, line 33 skipping to change at page 31, line 34
If the sequence number is not used, it is set to zero by If the sequence number is not used, it is set to zero by
the sender and ignored by the receiver. Otherwise it the sender and ignored by the receiver. Otherwise it
specifies the sequence number of a packet. A circular list specifies the sequence number of a packet. A circular list
of sequence numbers is used. A sequence number takes a value of sequence numbers is used. A sequence number takes a value
from 1 to 65535 (2**16-1). If the payload is an OAM packet from 1 to 65535 (2**16-1). If the payload is an OAM packet
the sequence number MAY be used to mark the position in the the sequence number MAY be used to mark the position in the
sequence, in which case it has the same value as the last sequence, in which case it has the same value as the last
data PDU sent. The use of the sequence number is optional data PDU sent. The use of the sequence number is optional
for OAM payloads. for OAM payloads.
5.4.4. MPLS Payload Identifier 5.4.4. PWE3 Payload Type Identifier
If technical considerations result in a PW control word that may If technical considerations result in a PW control word that may
alias an IP packet, the control word SHOULD be preceeded by an MPLS alias an IP packet, the control word SHOULD be preceded by an PWE3
payload type identifier. payload type identifier (PWE3 PID).
The MPLS payload type is defined as follows: The PWE3 PID is defined as follows:
0 1 2 3 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 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 1| reserved = 0 | PPP DLL Protocol Number | |0 0 0 1| reserved = 0 | PA | Protocol ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As defined by PPP DLL protocol definition | | As defined by PPP DLL protocol definition |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: MPLS Payload Type Identifier Figure 14: PWE3 PID
PPP DLL Protocol Number [16:31]:
These numbers are assigned by IANA.
Bits 4 to 15 inclusive are reserved for future use and must be zero. The meaning of the fields of the PWE3 PID (Figure 14) is as follows:
PA protocol authority for the user plane or the control plane
protocol ID
0 = PPP DLL
1-15 = Reserved
Protocol ID
Protocol ID following the format defined by the protocol
authority identified in PA.
Bits 4 to 11 inclusive are reserved for future use and must be zero.
6. PW Demultiplexer Layer and PSN Requirements 6. PW Demultiplexer Layer and PSN Requirements
PWE3 places three service requirements on the protocol layers used to PWE3 places three service requirements on the protocol layers used to
carry it across the PSN: carry it across the PSN:
o Multiplexing o Multiplexing
o Fragmentation o Fragmentation
o Length and Delivery o Length and Delivery
skipping to change at page 34, line 18 skipping to change at page 34, line 27
pulses. pulses.
The comparison to TCP cannot be specified exactly, but is intended as The comparison to TCP cannot be specified exactly, but is intended as
an "order-of-magnitude" comparison in timescale and throughput. The an "order-of-magnitude" comparison in timescale and throughput. The
timescale on which TCP throughput is measured is the round-trip time timescale on which TCP throughput is measured is the round-trip time
of the connection. In essence, this requirement states that it is not of the connection. In essence, this requirement states that it is not
acceptable to deploy an application (using PWE3 or any other acceptable to deploy an application (using PWE3 or any other
transport protocol) on the best-effort Internet which consumes transport protocol) on the best-effort Internet which consumes
bandwidth arbitrarily and does not compete fairly with TCP within an bandwidth arbitrarily and does not compete fairly with TCP within an
order of magnitude. One method of determining an acceptable PW order of magnitude. One method of determining an acceptable PW
bandwidth is described in [TFRC]. bandwidth is described in [RFC3448].
7. Control Plane 7. Control Plane
This section describes PWE3 control plane services. This section describes PWE3 control plane services.
7.1 Set-up or Teardown of Pseudo-Wires 7.1 Set-up or Teardown of Pseudo-Wires
A PW MUST be set up before an emulated service can be established, A PW MUST be set up before an emulated service can be established,
and MUST be torn down when an emulated service is no longer needed. and MUST be torn down when an emulated service is no longer needed.
skipping to change at page 35, line 46 skipping to change at page 36, line 4
7.3.2. Misconnection and Payload Type Mismatch 7.3.2. Misconnection and Payload Type Mismatch
With PWE3, misconnection and payload type mismatch can occur. If a With PWE3, misconnection and payload type mismatch can occur. If a
misconnection occurs it can breach the integrity of the system. If a misconnection occurs it can breach the integrity of the system. If a
payload mismatch occurs it can disrupt the customer network. In both payload mismatch occurs it can disrupt the customer network. In both
instances, there are security and operational concerns. instances, there are security and operational concerns.
The services of the underlying tunneling mechanism, and its The services of the underlying tunneling mechanism, and its
associated control protocol, can be used to mitigate this. As part associated control protocol, can be used to mitigate this. As part
of the PW set-up a PW-TYPE identifier is exchanged. This is then used of the PW set-up a PW-TYPE identifier is exchanged. This is then used
by the FWRD and NSP to verify the compatibility of the PWESs. by the forwarder and the NSP to verify the compatibility of the
PWESs.
7.3.3. Packet Loss, Corruption, and Out-of-order Delivery 7.3.3. Packet Loss, Corruption, and Out-of-order Delivery
A PW can incur packet loss, corruption, and out-of-order delivery on A PW can incur packet loss, corruption, and out-of-order delivery on
the PSN path between the PEs. This can impact the working condition the PSN path between the PEs. This can impact the working condition
of an emulated service. For some payload types, packet loss, of an emulated service. For some payload types, packet loss,
corruption, and out-of-order delivery can be mapped to either a bit corruption, and out-of-order delivery can be mapped to either a bit
error burst, or loss of carrier on the PW. If a native service has error burst, or loss of carrier on the PW. If a native service has
some mechanism to deal with bit error, the corresponding PWE3 service some mechanism to deal with bit error, the corresponding PWE3 service
should provide a similar mechanism. should provide a similar mechanism.
skipping to change at page 39, line 42 skipping to change at page 39, line 42
8.2.2. Service Layer MIBs 8.2.2. Service Layer MIBs
The first layer is referred to as the Service Layer. It contains The first layer is referred to as the Service Layer. It contains
MIBs for PWE3 services such as Ethernet, ATM, circuits and Frame MIBs for PWE3 services such as Ethernet, ATM, circuits and Frame
Relay. This layer contains those corresponding MIBs used to mate or Relay. This layer contains those corresponding MIBs used to mate or
adapt those emulated services to the underlying services. This adapt those emulated services to the underlying services. This
working group should not produce any MIBs for managing the general working group should not produce any MIBs for managing the general
service; rather, it should produce just those MIBs that are used to service; rather, it should produce just those MIBs that are used to
interface or adapt the emulated service onto the PWE3 management interface or adapt the emulated service onto the PWE3 management
framework. For example, the standard SONET MIB [SONETMIB] is framework. For example, the standard SONET MIB [RFC2558] is designed
designed and maintained by another working group. Also, the SONET MIB and maintained by another working group. Also, the SONET MIB is
is designed to manage the native service without PW emulation. Since designed to manage the native service without PW emulation. Since
the PWE3 working group is chartered to produce the corresponding the PWE3 working group is chartered to produce the corresponding
adaptation MIB, in this case, it would produce the PW-CEM-MIB adaptation MIB, in this case, it would produce the PW-CEM-MIB
[PWMPLSMIB] that would be used to adapt SONET services to the [PWMPLSMIB] that would be used to adapt SONET services to the
underlying PSN that carries the PWE3 service. underlying PSN that carries the PWE3 service.
8.2.3. Generic PW MIBs 8.2.3. Generic PW MIBs
The second layer is referred to as the Generic PW Layer. This layer The second layer is referred to as the Generic PW Layer. This layer
is composed of two MIBs: the PWE-TC-MIB [PWTCMIB] and the PWE-MIB is composed of two MIBs: the PWE-TC-MIB [PWTCMIB] and the PWE-MIB
[PWMIB]. These MIBs are responsible for providing general PWE3 [PWMIB]. These MIBs are responsible for providing general PWE3
skipping to change at page 42, line 41 skipping to change at page 42, line 41
We thank: Sasha Vainshtein for his work on Native Service Processing We thank: Sasha Vainshtein for his work on Native Service Processing
and advice on bit-stream over PW services. Thomas K. Johnson for his and advice on bit-stream over PW services. Thomas K. Johnson for his
work on the background and motivation for PWs. work on the background and motivation for PWs.
We also thank: Ron Bonica, Stephen Casner, Durai Chinnaiah, Jayakumar We also thank: Ron Bonica, Stephen Casner, Durai Chinnaiah, Jayakumar
Jayakumar, Ghassem Koleyni, Danny McPherson, Eric Rosen, John Jayakumar, Ghassem Koleyni, Danny McPherson, Eric Rosen, John
Rutemiller, Scott Wainner and David Zelig for their comments and Rutemiller, Scott Wainner and David Zelig for their comments and
contributions. contributions.
References Normative References
Internet-drafts are works in progress available from
<http://www.ietf.org/internet-drafts/>
[FRAG] Malis and Townsley, "PWE3 Fragmentation and
Reassembly", <draft-ietf-pwe3-fragmentation-02.txt>,
work in progress, June 2003.
[L2TPv3] Layer Two Tunneling Protocol (Version 3)'L2TPv3', J Lau,
et. al. <draft-ietf-l2tpext-l2tp-base-08.txt>, work
in progress, June 2003.
[RFC791] RFC-791: DARPA Internet Program, Protocol Specification,
ISI, September 1981.
[RFC1883] RFC-1883: Internet Protocol, Version 6 (IPv6),
S. Deering, et al, December 1995
[RFC1902] RFC-1902: Structure of Management Information for
Version 2 of the Simple Network Management Protocol
(SNMPv2), Case et al, January 1996.
[RFC2119] RFC-2119, BCP-14: Key words for use in RFCs to Indicate
Requirement Levels, S. Bradner.
[RFC2401] RFC-2401: Security Architecture for the Internet
Protocol. S. Kent, R. Atkinson.
[RFC2474] RFC-2474: Definition of the Differentiated Services
Field (DS Field) in the IPv4 and IPv6 Headers,
K. Nichols, et. al.
[RFC2558] K. Tesink, "Definitions of Managed Objects for the
SONET/SDH Interface Type", RFC2558, March 1999.
[RFC2661] RFC-2661: Layer Two Tunneling Protocol "L2TP".
W. Townsley, et. al.
[RFC2784] RFC-2784: Generic Routing Encapsulation (GRE).
D. Farinacci et al.
[RFC2890] RFC-2890: Key and Sequence Number Extensions to GRE.
G. Dommety.
[RFC3031] RFC3031: Multiprotocol Label Switching Architecture,
E. Rosen, January 2001.
[RFC3032] RFC3032: MPLS Label Stack Encoding, E. Rosen,
January 2001.
[RFC3550] RFC-3550: RTP: A Transport Protocol for Real-Time
Applications. H. Schulzrinne et. al.
Informative References
Internet-drafts are works in progress available from Internet-drafts are works in progress available from
<http://www.ietf.org/internet-drafts/> <http://www.ietf.org/internet-drafts/>
[DVB] EN 300 744 Digital Video Broadcasting (DVB); Framing [DVB] EN 300 744 Digital Video Broadcasting (DVB); Framing
structure, channel coding and modulation for digital structure, channel coding and modulation for digital
terrestrial television (DVB-T), European terrestrial television (DVB-T), European
Telecommunications Standards Institute (ETSI) Telecommunications Standards Institute (ETSI)
[FRAG] Malis and Townsley, "PWE3 Fragmentation and
Reassembly", <draft-ietf-pwe3-fragmentation-00.txt>,
work in progress, October 2002.
[LDPMIB] Cucchiara, J., Sjostrand, H., and Luciani, J., [LDPMIB] Cucchiara, J., Sjostrand, H., and Luciani, J.,
"Definitions of Managed Objects for the Multiprotocol "Definitions of Managed Objects for the Multiprotocol
Label Switching, Label Distribution Protocol (LDP)", Label Switching, Label Distribution Protocol (LDP)",
<draft-ietf-mpls-ldp-mib-09.txt>, work in progress, <draft-ietf-mpls-ldp-mib-11.txt>, work in progress,
October 2002. June 2003.
[LSRMIB] Srinivasan et al, "MPLS Label Switch Router Management [LSRMIB] Srinivasan et al, "MPLS Label Switch Router Management
Information Base Using SMIv2", Information Base Using SMIv2",
<draft-ietf-mpls-lsr-mib-09.txt>, work in progress, <draft-ietf-mpls-lsr-mib-10.txt>, work in progress,
October 2002. June 2003.
[L2TPv3] Layer Two Tunneling Protocol (Version 3)'L2TPv3', J Lau,
et. al. <draft-ietf-l2tpext-l2tp-base-05.txt>, work
in progress, January 2003.
[PPPoL2TP] PPP Tunneling Using Layer Two Tunneling Protocol, [PPPoL2TP] PPP Tunneling Using Layer Two Tunneling Protocol,
J Lau et al. <draft-ietf-l2tpext-l2tp-ppp-02.txt>, J Lau et al. <draft-ietf-l2tpext-l2tp-ppp-02.txt>,
work in progress, June 2002. work in progress, June 2002.
[PWMIB] Zelig et al, "Pseudo Wire (PW) Management Information [PWMIB] Zelig et al, "Pseudo Wire (PW) Management Information
Base Using SMIv2", <draft-ietf-pwe3-pw-mib-00.txt>, Base Using SMIv2", <draft-ietf-pwe3-pw-mib-01.txt>,
work in progress, June 2002. work in progress, June 2003.
[PWTCMIB] Nadeau et al, "Definitions for Textual Conventions and [PWTCMIB] Nadeau et al, "Definitions for Textual Conventions and
OBJECT-IDENTITIES for Pseudo-Wires Management" OBJECT-IDENTITIES for Pseudo-Wires Management"
<draft-ietf-pwe3-pw-tc-mib-00.txt>, work in progress, <draft-ietf-pwe3-pw-tc-mib-01.txt>, work in progress,
June 2002. June 2003.
[PWMPLSMIB] Danenberg et al, "SONET/SDH Circuit Emulation Service [PWMPLSMIB] Danenberg et al, "SONET/SDH Circuit Emulation Service
Over MPLS (CEM) Management Information Base Using Over MPLS (CEM) Management Information Base Using
SMIv2", <draft-ietf-pwe3-cep-mib-01.txt>, work in SMIv2", <draft-ietf-pwe3-cep-mib-01.txt>, work in
progress, October 2002. progress, October 2002.
[RFC791] RFC-791: DARPA Internet Program, Protocol Specification,
ISI, September 1981.
[RFC1191] RFC-1191: Path MTU discovery. J.C. Mogul, S.E. Deering. [RFC1191] RFC-1191: Path MTU discovery. J.C. Mogul, S.E. Deering.
[RFC1883] RFC-1883: Internet Protocol, Version 6 (IPv6),
S. Deering, et al, December 1995
[RFC1889] RFC-1889: RTP: A Transport Protocol for Real-Time
Applications. H. Schulzrinne et. al.
[RFC1902] RFC-1902: Structure of Management Information for
Version 2 of the Simple Network Management Protocol
(SNMPv2), Case et al, January 1996.
[RFC1958] RFC-1958: Architectural Principles of the Internet, [RFC1958] RFC-1958: Architectural Principles of the Internet,
B. Carpenter et al. B. Carpenter et al.
[RFC1981] RFC-1981: Path MTU Discovery for IP version 6. J. McCann, [RFC1981] RFC-1981: Path MTU Discovery for IP version 6. J. McCann,
S. Deering, J. Mogul. S. Deering, J. Mogul.
[RFC2022] RFC-2022: Support for Multicast over UNI 3.0/3.1 based [RFC2022] RFC-2022: Support for Multicast over UNI 3.0/3.1 based
ATM Networks, G. Armitage. ATM Networks, G. Armitage.
[RFC2119] RFC-2119, BCP-14: Key words for use in RFCs to Indicate
Requirement Levels, S. Bradner.
[RFC2338] RFC-2338: Virtual Router Redundancy Protocol, [RFC2338] RFC-2338: Virtual Router Redundancy Protocol,
S. Knight, M. Shand et. al. S. Knight, M. Shand et. al.
[RFC2401] RFC-2401: Security Architecture for the Internet
Protocol. S. Kent, R. Atkinson.
[RFC2474] RFC-2474: Definition of the Differentiated Services
Field (DS Field) in the IPv4 and IPv6 Headers,
K. Nichols, et. al.
[RFC2661] RFC-2661: Layer Two Tunneling Protocol "L2TP".
W. Townsley, et. al.
[RFC2784] RFC-2784: Generic Routing Encapsulation (GRE).
D. Farinacci et al.
[RFC2890] RFC-2890: Key and Sequence Number Extensions to GRE.
G. Dommety.
[RFC3022] RFC-3022: Traditional IP Network Address Translator [RFC3022] RFC-3022: Traditional IP Network Address Translator
(Traditional NAT). P Srisuresh et al. (Traditional NAT). P Srisuresh et al.
[RFC3031] RFC3031: Multiprotocol Label Switching Architecture, [RFC3448] RFC3448: TCP Friendly Rate Control (TFRC): Protocol
E. Rosen, January 2001. Specification, M. Handley et al. January 2003.
[RFC3032] RFC3032: MPLS Label Stack Encoding, E. Rosen,
January 2001.
[SONETMIB] K. Tesink, "Definitions of Managed Objects for the
SONET/SDH Interface Type", RFC2558, March 1999.
[TEMIB] Srinivasan et al, "Traffic Engineering Management [TEMIB] Srinivasan et al, "Traffic Engineering Management
Information Base Using SMIv2", Information Base Using SMIv2",
<draft-ietf-mpls-te-mib-09.txt>, work in progress, <draft-ietf-mpls-te-mib-10.txt>, work in progress,
November 2002. June 2003.
[TFRC] M. Handley et al, "TCP Friendly Rate Control (TFRC):
Protocol Specification" <draft-ietf-tsvwg-tfrc-05.txt>,
work in progress, October 2002.
[VPLS] M. Lasserre, "Virtual Private LAN Services over MPLS",
<draft-lasserre-vkompella-ppvpn-vpls-03.txt>, work in
progress, January 2003.
[XIAO] Xiao et al, "Requirements for Pseudo-Wire Emulation [XIAO] Xiao et al, "Requirements for Pseudo-Wire Emulation
Edge-to-Edge (PWE3)", Edge-to-Edge (PWE3)",
(draft-ietf-pwe3-requirements-04.txt), X Xiao et al. (draft-ietf-pwe3-requirements-06.txt), X Xiao et al.
work in progress, December 2002. work in progress, June 2002.
Editors' Addresses Editors' Addresses
Stewart Bryant Stewart Bryant
Cisco Systems, Cisco Systems,
4, The Square, 250, Longwater,
Stockley Park, Green Park,
Uxbridge UB11 1BL, Reading, RG2 6GB,
United Kingdom. Email: stbryant@cisco.com United Kingdom. Email: stbryant@cisco.com
Prayson Pate Prayson Pate
Overture Networks, Inc. Overture Networks, Inc.
507 Airport Boulevard 507 Airport Boulevard
Morrisville, NC, USA 27560 Email: prayson.pate@overturenetworks.com Morrisville, NC, USA 27560 Email: prayson.pate@overturenetworks.com
Full copyright statement Full copyright statement
Copyright (C) The Internet Society (2002). Copyright (C) The Internet Society (2002).
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