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Versions: 00                                                            
Network Working Group                                   Adrian Farrel
Internet Draft                                     Old Dog Consulting
Category: Informational
Expires: May 2004
                                                        November 2003

                    Interim Report on MPLS Pre-emption

                draft-farrel-mpls-preemption-interim-00.txt


Status of this Memo

   This document is an Internet-Draft and is in full
   conformance with all provisions of Section 10 of RFC 2026
   [RFC2026].

   Internet-Drafts are working documents of the Internet
   Engineering Task Force (IETF), its areas, and its working
   groups.  Note that other groups may also distribute working
   documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by
   other documents at any time.  It is inappropriate to use
   Internet-Drafts as reference material or to cite them other
   than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be
   accessed at http://www.ietf.org/shadow.html.

Abstract

   This document is an interim report into pre-emption in MPLS systems.

   At the 58th IETF, the MPLS Working Group determined that there are
   several interpretations of how pre-emption should be achieved within
   MPLS systems. This document is the result of the initial enquiries to
   vendors and other implementors into the question of how and why they
   offer pre-emption funtion in their MPLS inplementations.

   This document is intended to be a short-lived document and only
   exists to document the current findings. It will be superceded or
   retired.












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1. Introduction

   The most recent charter of the MPLS working group includes the work
   item to develop a solution for "soft pre-emption" within MPLS
   systems. This work item was contested by some people who regard MPLS
   signaling (and in particular RSVP-TE as documented by [RFC 3209]) to
   already include mechanisms for soft pre-emption.

   A common understanding of the correct behavior during pre-emption
   will be beneficial to vendors trying to get their hardware to inter-
   work, and to network operators trying to offer services in networks
   built from equipment from more than one vendor.

   Without commenting on the correct interpretation of pre-existing
   documents, this document aims to establish the following.

   - Behavioral characteristics of Admission Control in MPLS and GMPLS
     systems.
   - Desired characteristics of pre-emption.
   - A terminology for soft and hard pre-emption.
   - A record of implemented pre-emption behavior.

   If necessary, a subsequent document will describe the conclusions of
   the MPLS working group with regard to the correct interpretation of
   the procedures for pre-emption.

2. Background

2.1 Default PathErr Processing

   [RFC2205] defines RSVP procedures including the procedures for
   handling PathErr messages that are used to report events or errors
   from a downstream node to an upstream node. The predominant use of
   PathErr in [RFC2205] is to report a problem that occurs while an RSVP
   path is being established. There is no specific text that refers to
   the use of a PathErr once a path has been established, but [RFC2205]
   does include the following text.

      PathErr messages are very simple; they are simply sent upstream to
      the sender that created the error, and they do not change path
      state in the nodes though which they pass.

2.2 The Origins of Priority in RSVP

   [RFC2751] introduces the concept of priority to RSVP and suggests how
   it may be signaled using the Policy Data object.

   Priority can be used in this context to modify the traditional first-
   come first-served Capacity-based Admissions Control (CAC) into a
   Priority-based Admisssions Control (PAC).

   [RFC2751] concentrates mainly on PAC and says very little about the
   operation of pre-emption. The following text is relevant.

      When a previously admitted flow is preempted, a copy of the
      preempting flow's PREEMPTION_PRI element is sent back toward the
      PDP that originated the preempted PREEMPTION_PRI object. This PDP,

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      having information on both the preempting and the preempted
      priorities may construct a higher priority PREEMPTION_PRI element
      in an effort to re-instate the preempted flow.

   However, [RFC2750] describes the processing of policy errors as
   follows.

      Policy errors are reported by either ResvErr or PathErr messages
      with a policy failure error code in the ERROR_SPEC object.

2.3 Priority and Pre-emption in MPLS

   [RFC3209] defines RSVP-TE and introduces the concept of setup and
   holding priorities for LSPs. This enables the implementation of
   PAC in MPLS systems, and facilitates pre-emption of a lower priority
   LSP by a higher priority LSP.

   Pre-emption in this case means that some or all of the system
   resources previously reserved for the lower priority LSP are assigned
   to the higher priority LSP.

   [RFC3209] contains the following text.

      When a new Path message is considered for admission, the bandwidth
      requested is compared with the bandwidth available at the priority
      specified in the Setup Priority.

      If the requested bandwidth is not available a PathErr message is
      returned with an Error Code of 01, Admission Control Failure, and
      an Error Value of 0x0002.  The first 0 in the Error Value
      indicates a globally defined subcode and is not informational.
      The 002 indicates "requested bandwidth unavailable".

      If the requested bandwidth is less than the unused bandwidth then
      processing is complete.  If the requested bandwidth is available,
      but is in use by lower priority sessions, then lower priority
      sessions (beginning with the lowest priority) MAY be preempted to
      free the necessary bandwidth.

      When preemption is supported, each preempted reservation triggers
      a TC_Preempt() upcall to local clients, passing a subcode that
      indicates the reason.  A ResvErr and/or PathErr with the code
      "Policy Control failure" SHOULD be sent toward the downstream
      receivers and upstream senders.

3. Ambiguity

   Confusion and diverse implementations have arrisen owing to the lack
   of definitive instructions for error handling within [RFC3209]. The
   diversity of implementations has been driven both by assumed
   interpretations of [RFC3209] and by the needs of specific Admission
   Control implementations.






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4. Admission Control

   The implementation of Admission Control turns out to be a major
   factor in the decision about how to implement pre-emption within an
   MPLS system.

4.1 Capacity-based Admission Control (CAC)

   CAC operates by allocating system resources to flows (for example,
   LSPs) as a function of the bandwidth requested during signaling and
   the capacity of the links or router that supports the flow. Each
   router is responsible for managing its own resources.

   When a request for more bandwidth than can be supported by the links
   of router is receieved, the CAC request fails and a signaling error
   is returned. The CAC request may fail because the requested resources
   exceed the total available in the system. The request may also fail
   if some resources have already been reserved for other flows meaning
   that the requested resources exceed the currently avilable resources
   on the links or router.

4.2 Policy-based Admission Control (PAC)

   PAC is a modification of CAC that allows the available resources to
   be subdivided by priority. This means that some of the resources can
   be reserved for use only by higher priority flows. High priority
   flows can use high and low priority resources, but low priority flows
   can use only low priority resources.

4.3 Pre-emption

   PAC facilitates pre-emption. A resource request for a high priority
   flow may pre-empt a low priority flow, and commandeer its resources.
   The low priority flow is usually notified through signaling.

4.4 Best-Effort Traffic

   Best-effort traffic does not have any resources specifically reserved
   for it. It is sent on the understanding that if there is no capacity
   at some point in the network it will be discarded. If, however, there
   are resources that are available either because they have not been
   reserved or because the flow for which they were reserved is not
   using them, then the best-effort traffic may get through.

4.5 Statistical Admissions Control

   Some implementations of Admissions Control are statistical. This
   means that CAC requests are managed against a count of available
   resources. When a CAC request is successful the count of available
   resources is decremented.

   PAC may also be managed in a statistical model.

   In a statistical Admissions Control implementation no resources are
   specifically assigned to each flow, and there is no attempt to police
   the flows at transit routers. It is a requirement of successful
   operation that the edge nodes adhere to the implicit contract of

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   their resource requests. Policing is sometimes applied at the network
   edges or through management applications.

   A consequence of this is that if one flow exceeds its contract, other
   flows will suffer.

   It is hard to support best-effort traffic in a statistical CAC
   system.

4.6 Per-flow Admission Control

   Per-flow Admission Control operates as CAC or PAC, and explicitly
   assigns resources for the use by the flow. This means that a flow
   that stays within its contracted limits is guaranteed resources to
   meet its contract regardless of the behavior of the other flows in
   the system.

   A flow that exceeds its contracted limits may see its excess traffic
   discarded. However, if there are unused or unallocated resources in
   the system, the excess traffic may use these.

   Similarly, best-effort traffic can be supported in this Admission
   Control model since it is clear that that traffic should only be
   allowed when there are spare resources.

5. Pre-emption Models

   There are two pre-emption models applicable to MPLS systems.

5.1 Soft Pre-emption

   In soft pre-emption, a higher priority LSP commandeers the resources
   previously assigned to a lower priority LSP. The lower priority LSP
   is not torn down and can continue to forward traffic on a best-effort
   basis.

   Note that resource reservations on other LSRs are not changed, and
   the degradation to best-effort happens only at the point of pre-
   emption.

   A notification is normally sent to upstream and downstream LSRs to
   warn them that the expected levels of service have been disrupted at
   one LSR along the LSP. This allows end-to-end or local repair to be
   performed to re-instate the desired level of service.

5.2 Hard Pre-emption

   In hard pre-emption, a higher priority LSP commandeers the resources
   previously assigned to a lower priority LSP, and the lower priority
   LSP is torn down at the point of pre-emption. That is, the labels are
   released and the entry is removed from the LFIB. Any traffic that
   arrives with the old label is black-holed.

   A notification message is sent to upstream and downstream LSRs to
   inform them of this event and, if the notified LSR is unable or
   unwilling to perform local repair, it may also tear the LSP by
   releasing resources and labels and forwarding the notification.

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5.3 Head-end Teardown

   Note that an ingress LSR that is informed of soft pre-emption may
   respond by explicitly tearing down the pre-empted LSP. Although this
   results in the release of labels and disruption of data traffic, it
   is not counted as hard pre-emption. The distinction between soft and
   hard pre-emption is made only at the LSR where the pre-emption
   occurs, and only at the time of pre-emption.

5.4 Applicability of Pre-emption Models

   It will be observed that since the soft pre-emption model degrades
   the pre-empted LSP to best-effort, it is not well-suited to
   statistical Admission Control. In this mode hard pre-emption is
   more applicable.

   Soft pre-emption can be used in per-flow admission control.

5.5 Methods of Notification

   In the current confusion about the correct method of performing
   pre-emption both soft and hard pre-emption implemtations use a
   PathErr and ResvErr message containing the "Policy Control failure"
   error code to notify upstream and downstream LSRs of the pre-emption
   event.

   There is no way to distinguish from the received message
   whether the pre-emption point performed soft or hard pre-emption.

5.6 Interworking of Pre-emption Models

   The two pre-emption models do not interwork satisfactorily with the
   current usage of the same messages and error codes.

5.6.1 Hard Pre-emption in a Soft Pre-emption Network

   Consider a pre-emption point that applies hard pre-emption in a
   network of LSRs that assume soft pre-emption. The other LSRs will
   assume that the LSP is up and will continue to send traffic which
   will be black-holed.

   The Path refresh from the LSR immediately upstream of the pre-empting
   LSR will be rejected with an error of "Admission Control failure"
   because it will be seen as a new LSP setup request. This error might
   trigger the tear-dwon of the LSP or might simply be propagated to the
   ingress.

   The pre-empting LSR will cease to send Resv refreshes so the LSP will
   eventually timeout from the upstream LSRs.

   Similarly, the downstream LSRs will not receive Path refreshes and
   may receive a ResvErr or ResvTear in response to its Resv refresh.

   In this case there is heavy reliance on the ingress LSP deciding
   that best-effort is not good enough. It must either re-route or
   tear the LSP.


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5.6.2 Soft Pre-emption in a Hard Pre-emption Network

   If the pre-emption point performs soft pre-emption and signals this
   event upstream and downstream to the remainder of the network, and if
   the remainder of the network assumes that hard pre-emption has been
   performed then the worst that happens is that labels are wasted at
   the pre-emption point.

   Upstream of the pre-emption point, the notification of pre-emption
   causes the release of state, rsources and labels. This means that no
   more traffic will be passed to the pre-emption point on the pre-
   empted LSP. Also, no Path refresh will be sent, and the Resv refresh
   received from the pre-emption point may be rejected with a ResvErr or
   ResvTear. In time, the pre-emption point will time-out the LSP and
   release the labels.

   Downstream of the pre-emption point, the Path refresh from the pre-
   emption point may cause the LSP to be re-established. This partial
   LSP will never carry traffic and will be removed when the pre-emption
   point times-out the LSP as described above.

6. Tying Resources to Labels

   An LSP is defined by the existence of entries in the Label Forwarding
   Information Base (LFIB) at each LSR along the LSP. These entries map
   {incoming interface, incoming label} to {outgoing interface, outgoing
   label}.

6.1 Packet-Based Networks

   An LSP may exist with or without reserved resources at each or any
   LSR along its path. An LSP with no resources reserved at any point is
   described as 'best effort'. An LSP with no resources reserved at a
   particular LSR or on a particular link is best effort through that
   LSR or on that link.

   In an MPLS network, a distinction should be drawn between the pre-
   emption of resources (such as buffers) and the pre-emption of labels.
   It is not a requirement that the release of resources forces a
   release of label. The LSP may survive pre-emption with its resources
   removed (best effort) or reduced (degraded).

   Packet LSRs that are incapable or unwilling to offer best effort
   LSPs, MAY choose to offer only hard pre-emption. This might arise
   where admission control is purely an arithmetic accounting function,
   and edge nodes are required to police flows.

   Where soft pre-emption is appplied, it is usual to only release
   resources at the LSRs where pre-emption occurs. That is, the
   resources are left assigned to the LSP at all other LSRs.








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6.2 Non-Packet Networks

   For non-packet switching types (such as lambda switching) there is a
   hard binding between resources and labels. In these cases, it is not
   possible to pre-empt resources without releasing the label.

   Hard pre-emption is usually applied in non-packet networks.

6.3 Separating Signaling State from LSP State

   Some implementations may choose to retain signaling state for an LSP
   even when the labels have been released during hard pre-emption.

   This may be particualrly useful in optical networks where resources
   are manually deprovisioned and reprovisioned.


7. Methods of Signaling Pre-emption

   The poll of vendors and implementors has shown that several methods
   for signaling pre-emption events have been implemented or considered
   for implementation.  These are presented below without comment upon
   their efficacy or properness.

7.1 PathErr and ResvErr with Policy Control Failure Error Code

   As described in [RFC3209] the pre-emption point sends a PathErr
   upstream and a ResvErr downstream. The messages carry the "Policy
   Control failure" error code.

   This mechanism is used in both hard and soft pre-emption
   implementations. In some implementations the ingress automatically
   responds to the PathErr with a PathTear.

7.2 PathErr with State Removal

   Using the mechanism described in [RFC3473] a PathErr is sent upstream
   carrying the "Policy Control failure" error code and with the
   Path_State_Removed flag set. At the same time, a PathTear is sent
   downstream.

   This mechanism is used in hard pre-emption implementations.

7.3 ResvTear and ResvErr

   A ResvTear is sent upstream and a ResvErr carrying the "Policy
   Control failure" error code is sent downstream. The ingress
   automatically responds to the ResvTear with a PathTear.

   This mechanism has been suggested for use in hard pre-emption
   implementations.







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7.4 Notify Message

   The Notify message introduced in [RFC3473] is sent upstream and
   downstream carrying the "Policy Control failure" error code. The
   Admin_Status object is included with the D-bit set to indicate that
   LSP teardown is required.

   This mechanism has been suggested for use in hard pre-emption
   implementations.

7.5 Resv Message with Record Route Object

   A Resv message is sent upstream with a flag in the RRO subobject
   conveying the information about pre-emption for a specific hop.

   This mechanism is introduced in [SOFT-PREEMPT] to provide a way to
   perform soft pre-emption in systems that use the technique described
   in section 7.1 to perform hard pre-emption.

8. Error Codes and State Removal

   The Addmission Control error code in [RFC2205] is defined as carrying
   an Error Value of the form ssur cccc cccc cccc where it is mandated
   that u = 1 to denote

        u = 1: RSVP may use message to update local state and forward
             the message.  This means that the message is informational.

   Note that a ResvErr may carry the InPlace flag in the ERROR_SPEC
   object to indicate that the resources are still in place. This
   is of no particular help during pre-emption.

   GMPLS [RFC3473] introduced the Path_State_Removed flag for inclusion
   in PathErr messages to indicate to an upstrem LSR that the downstream
   LSR has completely removed the Path state for the LSP. The
   implication being that the resources have been freed, the labels
   released, and the LSP torn down.

9. A Side Note on PathErr Processing

   One other factor should be brought into consideration: How is a
   PathErr message handled when it is received for an established LSP
   and the PathErr carries an error code other than "Policy Control
   failure"?

10. Other Requirements

   Two other notes on the requirements of pre-emption can be made.

10.1 Reducing the Impact of Pre-emption

   Where the establishment of one LSP requires pre-emption of resources
   at multiple LSRs, it is desireable that the same LSP be pre-empted
   at each intermediate LSR when possible and subject to the local
   policy.



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   Where the establishment of two or more further LSPs requires
   pre-emption at different points in the network, it is desireable
   that the same LSP be pre-empted in each case where possible
   and subject to the local policy.

   The coordination of LSPs for pre-emption is a matter for individual
   implementations. The protocol messages used to indicate pre-emption
   must make it possible for each LSR to gather sufficient information
   to perform this function.

10.2 When To Apply Pre-emption

   It is normal to apply pre-emption on the reverse leg of LSP setup
   when processing Resv. However, when processing a Path message:

   - The likely need for and possibility of pre-emption may be taken
     into account during path computation and routing.

   - Pre-emption may be applied on the forward leg of LSP setup so
     that, if it is known that pre-emption will be required (if the LSP
     sets up successfully), pre-emption can be performed ahead of time.

   - In bidirectional LSPs (see [RFC3473]), and in particular when the
     resource is bound to the label, it may be necessary to allocate
     resources for the upstream data flow while processing the Path
     message during LSP setup. This may require that pre-emption is
     performed when processing the Path message.

11. Summary of Deployed Solutions

   Appendix A lists some of the deployed solutions according to an
   informal survey of implementors and vendors. This information was
   garnered from a private email survey conducted by the co-chairs of
   the CCAMP working group.

11.1 Soft Pre-emption

   There is only one deployed solution for soft pre-emption.

   - A PathErr with the code "Policy Control failure" is sent
     upstream, and a ResvErr with the code "Policy Control
     failure" is sent downstream.

   There is a further solution for soft pre-emption under development.

   - A Resv message MAY be sent upstream with a flag in RRO subobject
     conveying the information about pre-emption for a specific hop.

11.2 Hard Pre-emption

   There are two deployed solutions for hard pre-emption.

   - A PathErr with the code "Policy Control failure" is sent upstream,
     and a ResvErr with the code "Policy Control failure" is sent
     downstream.



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   - A PathErr with the code "Policy Control failure" and the
     Path_State_Removed flag (see [RFC3473]) set is sent upstream. At
     the same time, a PathTear is sent downstream.

12. Security Considerations

   This is an informational document that introduces no new protocols
   nor protocol extensions. There are no security implications of this
   document.

   The attention of implementors is drawn to the security sections of
   the documents describing the pre-emption signaling features that they
   are implementing.

13. Acknowledgements

   Thanks to Dimitri Papadimitriou, JP Vasseur, Arthi Ayyangar and
   Kireeti Kompella for a detailed discussion and exposee of the
   problems.

14. Intellectual Property Consideration

   The IETF takes no position regarding the validity or scope
   of any intellectual property 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; neither does it represent that it has made any
   effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track
   and standards-related documentation can be found in BCP-11.
   Copies of claims of rights made available for publication
   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
   implementors or users of this specification can be obtained
   from the IETF Secretariat.

   The IETF invites any interested party to bring to its
   attention any copyrights, patents or patent applications, or
   other proprietary rights which may cover technology that may
   be required to practice this standard.  Please address the
   information to the IETF Executive Director.

15. Normative References

   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2205]     Braden, R. (Ed.), Zhang, L., Berson, S., Herzog, S.
                 and S. Jamin, "Resource ReserVation Protocol --
                 Version 1 Functional Specification", RFC 2205,
                 September 1997.

   [RFC2750]     Herzog, S., "RSVP Extensions for Policy Control",
                 RFC 2750, January 2000.


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   [RFC2751]     Herzog, S., "Signaled Preemption Priority Policy
                 Element", RFC 2751, January 2000.

   [RFC3209]     Awduche, D., Berger, L., Gan, D., Li, T.,
                 Srinivasan, V. and G. Swallow, "RSVP-TE: Extensions
                 to RSVP for LSP Tunnels", RFC 3209, December 2001.

   [RFC3471]     Berger, L. (Editor), "Generalized Multi-Protocol Label
                 Switching (GMPLS) Signaling Functional Description",
                 RFC 3471, January 2003.

   [RFC3473]     Berger, L. (Editor), "Generalized MPLS Signaling -
                 RSVP-TE Extensions", RFC 3473 January 2003.

16. Informative References

   [RFC2026]     Bradner, S., "The Internet Standards Process
                 -- Revision 3", RFC 2026, October 1996.

   [RFC3031]     Rosen, E., Viswanathan, A., and Callon, R.,
                 "Multiprotocol Label Switching
                 Architecture", RFC 3031, January 2001.

   [SOFTPREEMPT] Meyer, Maddux, Vasseur, Villamizar and Birjandi,
                 "MPLS Traffic Engineering Soft preemption",
                 draft-ietf-mpls-soft-preemption-01.txt, October 2003,
                 work in progress.

17. Authors' Addresses

   Adrian Farrel
   Old Dog Consulting
   Phone:  +44 (0) 1978 860944
   EMail:  adrian@olddog.co.uk

18. Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights
   Reserved.

   This document and translations of it may be copied and
   furnished to others, and derivative works that comment on
   or otherwise explain it or assist in its implementation may
   be prepared, copied, published and distributed, in whole or
   in part, without restriction of any kind, provided that the
   above copyright notice and this paragraph are included on
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   Standards process must be followed, or as required to
   translate it into languages other than English.

   The limited permissions granted above are perpetual and
   will not be revoked by the Internet Society or its

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   successors or assigns. This document and the information
   contained herein is provided on an "AS IS" basis and THE
   INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE
   DISCLAIMS 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.



Apendix A Implementation Reports

A.1 Company 1

   Hardware vendor.

A.1.1 Soft Pre-emption

   A Resv message is sent upstream with a flag in the RRO subobject
   conveying the information about pre-emption for a specific hop.

   Not currently deployed. Implementation under development.

A.1.2 Hard Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream.

   Significantly large deployment.

A.1.3 Processing of Other PathErrs for Established LSPs

   Unknown.

A.2 Company 2

   Hardware vendor.

A.2.1 Soft Pre-emption

  Not currently supported.

A.2.2 Hard Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream.

   Significantly deployment.

A.2.3 Processing of Other PathErrs for Established LSPs

  Unknown.



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A.3 Company 3

   Hardware vendor.

A.3.1 Soft Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream. The ingress always responds with PathTear.

   Some deployment.

A.3.2 Hard Pre-emption

   Not supported.

A.3.3 Processing of Other PathErrs for Established LSPs

   PathErr is informational only. It does not disrupt the state of
   existing LSPs.

A.4 Company 4

   Software vendor.

A.4.1 Soft Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream.

   Considerable deployment.

A.4.2 Hard Pre-emption

   Not supported.

A.4.3 Processing of Other PathErrs for Established LSPs

   PathErr is informational only. It does not disrupt the state of
   existing LSPs.

A.5 Company 5

   Hardware vendor.

A.5.1 Soft Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream.

   Some deployment.





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A.5.2 Hard Pre-emption

   A PathErr with the code "Policy Control failure" and the
   Path_State_Removed flag (see [RFC3473]) set is sent upstream. At the
   same time, a PathTear is sent downstream.

   Some deployment.

A.5.3 Processing of Other PathErrs for Established LSPs

   PathErr is informational only. it does not disrupt the state of
   existing LSPs.

A.6 Company 6

   Hardware vendor.

A.6.1 Soft Pre-emption

   Not supported.

A.6.2 Hard Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream. The ingress always responds with PathTear.

   Under development.

A.6.3 Processing of Other PathErrs for Established LSPs

   State is retained, but ingress always responds with PathTear.

A.7 Company 7

   Software vendor.

A.7.1 Soft Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream.

   Significant deployment.

A.7.2 Hard Pre-emption

   A PathErr with the code "Policy Control failure" and the
   Path_State_Removed flag (see [RFC3473]) set is sent upstream. At the
   same time, a PathTear is sent downstream.

A.7.3 Processing of Other PathErrs for Established LSPs

   Depends on Path_State_Removed flag.




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A.8 Company 8

   Hardware vendor.

A.8.1 Soft Pre-emption

   Not supported.

A.8.2 Hard Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream.

   Some deployment.

A.8.3 Processing of Other PathErrs for Established LSPs

   The LSP is torn down.

A.9 Company 9

   Hardware vendor.

A.9.1 Soft Pre-emption

   Not supported.

A.9.2 Hard Pre-emption

   A PathErr with the code "Policy Control failure" is sent upstream,
   and a ResvErr with the code "Policy Control failure" is sent
   downstream.

   Some deployment.

A.9.3 Processing of Other PathErrs for Established LSPs

   Unknown.

A.10 Company 10

   Hardware vendor.

A.10.1 Soft Pre-emption

   Not supported.

A.10.2 Hard Pre-emption

   Not supported.

A.10.3 Processing of Other PathErrs for Established LSPs

   The LSP is torn down.

   Some deployment.

Farrel                                                            Page 1