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MPLS WG                                                          J. Ash
Internet Draft                                                   Y. Lee
Document: draft-ash-crlsp-modify-00.txt                            AT&T

                                                       P. Ashwood-Smith
                                                            B. Jamoussi
                                                                  L. Li
                                                               D. Fedyk
                                                             D. Skaleki
                                                        Nortel Networks

                                                              July 1999

                     LSP Modification Using CR-LDP

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
      all provisions of Section 10 of RFC2026 [1].

   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
   The list of current Internet-Drafts can be accessed at
   The list of Internet-Draft Shadow Directories can be accessed at

1. Abstract

   After a CR-LSP is set up, its bandwidth reservation may need to be
   changed by the network operator, due to the new requirements for the
   traffic carried on that CR-LSP [2]. This contribution presents an
   approach to modify the bandwidth and possibly other parameters of an
   established CR-LSP using CR-LDP [3] without service interruption.
   The LSP modification feature can be supported by CR-LDP with a minor
   extension of an _action indicator flag_. This feature has
   application in dynamic network resources management where traffic of
   different priorities and service classes is involved.

2. Conventions used in this document

   L:           LSP (Label Switched Path)
   Lid:         LSPID (LSP Identifier)
   T:           Traffic Parameters

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   R:           LSR (Label Switching Router)
   FTN:         FEC To NHLFE
   FEC:         Forwarding Equivalence Class
   NHLFE:       Next Hop Label Forwarding Entity
   TLV:         Type Length Value

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC-2119 [4].

3. Introduction

   Consider an LSP L1 that has been established with its set of traffic
   parameters T0. A certain amount of bandwidth is reserved along the
   path of L1.  Consider then that some changes are required on L1. For
   example, the bandwidth of L1 needs to be increased to accommodate
   the increased traffic on L1. Or the SLA associated with L1 needs to
   be modified because a different service class is desired. The
   network operator, in these cases, would like to modify the
   characteristics of L1, for example, to change its traffic parameter
   set from T0 to T1, without releasing the LSP L1 to interrupt the
   service. In some other cases, network operators may want to reroute
   a CR-LSP to a different path for either improved performance or
   better network resource utilization. In all these cases, LSP
   modification is required. In section 4 below, a method to modify an
   active LSP using CR-LDP is presented. The concept of LSPID in CR-LDP
   is used to achieve the LSP modification, without releasing the LSP
   and interrupting the service and, without double booking the
   bandwidth. Only a minimum extension on CR-LDP, an action indication
   flag of _modify_ is needed in order to explicitly specify the
   behavior, and allow the existing LSPID to support other networking
   capabilities in the future. Section 5 specifies the action
   indication flag of _modify_ for CR-LDP. In the appendix, an example
   is described to demonstrate an application of the presented method
   in dynamically managing network bandwidth requirements without
   interrupting service.

4. LSP Modification Using CR-LDP

4.1 Basic Procedure

   LSP modification can only be allowed when the LSP is already set up
   and active. That is, modification is not defined nor allowed during
   the LSP establishment or label release/withdraw phases. Only
   modification requested by the ingress LSR of the LSP is considered
   in this draft for CR-LSP. Ingress LSR cannot modify an LSP before a
   previous modification procedure is completed.

   Assume that CR-LSP L1 is set up with LSPID L-id1, which is unique in
   the MPLS network. The ingress LSR R1 of L1 has in its FTN (FEC To
   NHLFE) table FEC1 -> Label A mapping where A is the outgoing label
   for LSP L1. To modify the characteristics of L1, R1 sends a Label

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   Request Message. In the messages, the TLVs will have the new
   requested values, and the LSPID TLV is included which indicates the
   value of L-id1. The Traffic Parameters TLV, the ER-TLV, the Resource
   Class (color) TLV and the Preemption TLV can have values different
   from those in the original Label Request Message, which  has been
   used to set up L1 earlier. Thus, L1 can be changed in its bandwidth
   request (traffic parameter TLV), its traffic service class (traffic
   parameter TLV), the route it traverses (ER TLV) and its setup and
   holding (Preemption TLV) priorities. The ingress LSR R1 now still
   has the entry in FTN as FEC1 -> Label A. R1 is waiting to establish
   another entry for FEC1.

   When an LSR Ri along the path of L1 receives the Label Request
   message, its behavior is the same as that of receiving any Label
   request message. The only extension is that Ri examines the LSPID
   carried in the Label Request Message, L-id1 and identifies if it
   already has L-id1. If Ri does not have L-id1, Ri behaves the same as
   receiving a new Label Request message. If Ri already has L-id1, Ri
   takes the newly received Traffic Parameter TLV and computes the new
   bandwidth required and derives the new service class. Compared with
   the already reserved bandwidth for L-id1, Ri now reserves only the
   difference of the bandwidth requirements. This prevents Ri from
   doing bandwidth double booking. If a new service class is requested,
   Ri also prepares to receive the traffic on L1 in, perhaps a
   different type of queue, just the same as handling it for a Label
   Request Message. Ri assigns a new label for the Label Request

   When the Label Mapping message is received, two sets of labels exist
   for the same LSPID. Then the ingress LSR R1 will have two outgoing
   labels, A and B, associated with the same FEC, where B is the new
   outgoing label received for LSP L1. The ingress LSR R1 can now
   activate the new entry in FTN, FEC1 - > Label B. This means that R1
   swaps traffic on L1 to the new label _B_ (_new_ path) for L1. The
   packets can now be sent with the new label B, with the new set of
   traffic parameters if any, on a new path, that is, if a new path is
   requested in the Label Request Message for the modification. All the
   other LSRs along the path will start to receive the incoming packets
   with the new label. For the incoming new label, the LSR has already
   established its mapping to the new outgoing label. Thus, the packets
   will be sent out with the new outgoing label. The LSRs do not have
   to  implement new procedures to track the new and old
   characteristics of the LSP.

   The ingress LSR R1 then starts to release the original label A for
   LSP L1. The Label Release Message is sent by R1 towards the down
   stream LSRs. The Release message carries the LSPID of L-id1 and the
   Label TLV to indicate which label is to be released. The Release
   Message is propagated to the egress LSR to release the original
   labels previously used for L1. Upon receiving the Label Release
   Message, LSR R1 examines the LSPID, L-id1 and finds out that the L-
   id1 has still another set of label (incoming/outgoing) under it.

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   Thus, the old label is released without releasing the resource in
   use. That is, if the bandwidth has been decreased for L1, the delta
   bandwidth is released. Otherwise, no bandwidth is released. This
   modification procedure can not only be applied to modify the traffic
   parameters and/or service class of an active LSP, but also to
   reroute an existing LSP, and/or change its setup/holding priority if
   desired. After the release procedure, the modification of the LSP is

   The method described above follows the normal behavior of Label
   Request / Mapping / Notification / Release /Withdraw procedure of a
   CR-LDP operated LSR with a specific action taken on LSPID. If Label
   Withdraw Message is used to withdraw a label associated with an
   LSPID, the Label TLV should be included to specify which label to
   withdraw. Since the LSPID can also be used for other feature
   support, an action indication flag of _modify_ assigned to the LSPID
   would explicitly explain the action/semantics that should be
   associated with the messaging procedure. The details of this flag
   are addressed in Section 3 below.

4.2 Priority Handling

   When sending a Label Request Message for an active LSP L1 to request
   changes, the setup priority used in the label Request Message can be
   different from the one used in the previous Label Request Message,
   effectively indicating the priority of this _modification_ request.
   Network operators can use this feature to decide what priority is to
   be assigned to a modification request, based on their
   policies/algorithms and other traffic situations in the network. For
   example, the priority for modification can be determined by the
   priority of the customer/LSP. If a customer has exceeded the
   reserved bandwidth of its VPN LSP tunnel by too much, the
   modification request's priority may be given higher.
   The Label Request message for the modification of an active LSP can
   also be sent with a holding priority different from its previous
   one. This effectively changes the holding priority of the LSP. Upon
   receiving a Label Request Message that requests a new holding
   priority, the LSR assigns the new holding priority to the bandwidth.
   That is, the new holding priority is assigned to both the existing
   incoming / outgoing labels and the new labels to be established for
   the LSPID in question. In this way self-bumping is prevented.

4.3 Modification Failure Case Handling

   A modification attempt may fail due to insufficient resource or
   other situations. A Notification message is sent back to the ingress
   LSR R1 to indicate the failure of Label Request Message that
   intended to modify the LSP. Retry may be attempted if desired by the
   network operator.

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   If the LSP on the original path failed when a modification attempt
   is in progress, the attempt should be aborted by using the Label
   Abort Request message as specified in LDP draft [5].

5. Proposed Extensions to CR-LDP for CR-LSP Modification

5.1 _Action indicator Flag_ in LSPID TLV

   As LSPID can be used for other purpose as well, for example, for LSP
   merge or stacking, etc. which are not intended to be covered here,
   an _action indicator flag_ is proposed to be carried in the LSPID
   TLV. This _action indicator flag_ shows explicitly the action that
   should be taken if the LSP already exists on the LSR receiving the
   message. The indicator flag can take 4 bits (right most 4 bits) out
   of the two reserved bytes in the LSPID TLV.  A set of indicator code
   points is proposed as follows:

   0001: modify

   The procedure for code point _modify_ is defined as in the above
   section 2.1. The procedures for others are for future work.

5.2 New Status Code

   Status code                       Type
   Modify request not supported      0x04000008

   This error code can be used to indicate that for some reason, the
   modification attempt on the given LSPID is not allowed by the LSR.
   For example, this can be an attempt that is sent out too soon after
   last modification, before the LSR has completed the procedures in
   the last modification attempt.

6. Intellectual Property Consideration

   Nortel Networks may seek patent or other intellectual property
   protection for some or all of the technologies disclosed in this
   document. If any standards arising from this document are or become
   protected by one or more patents assigned to Nortel Networks, Nortel
   Networks is prepared to make a license available to any qualified
   applicant upon reasonable and non-discriminatory terms and
   conditions. Any such licenses will be subject to negotiations
   outside of the IETF.

7. Security Considerations

   No security issues are addressed in this draft.

8. References

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   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.

   2  Ash, J., et. al., QoS Resource Management in MPLS-Based Networks,
      draft-ash-qos-routing-00.txt, (work in progress).

   3  Jamoussi, B., et. al., Constraint-Based LSP Setup using LDP,
      draft-ietf-mpls-cr-ldp-01.txt, February 1999,(work in progress).

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

   5  Andersson, L., et. al., LDP Specification, draft-ietf-mpls-ldp-
      05.txt (work in progress)

9. Author's Addresses

   Gerald R. Ash                           Young Lee
   AT&T                                    AT&T
   Room MT E3-3C37                         Room MT E3-3A04
   200 Laurel Avenue                       200 Laurel Avenue
   Middletown, NJ 07748                    Middletown, NJ 07748
   USA                                     USA
   Phone: 732-420-4578                     Phone: 732-420-4477
   Fax:   732-440-6687                     Fax:   732-440-6697
   Email: gash@att.com                     Email: younglee@att.com

   Bilel Jamoussi
   Nortel Networks Corp.
   3 Federal Street
   Billerica, MA 01821
   phone: 978-288-4506
   Email: jamoussi@NortelNetworks.com

   Peter Ashwood-Smith                     Li Li
   Nortel Networks Corp.                   Nortel Networks Corp.
   P O Box 3511 Station C                  P O Box 3511 Station C
   Ottawa, ON K1Y 4H7                      Ottawa, ON K1Y 4H7
   Canada                                  Canada
   Phone: +1 613 763-4534                  phone: +1 613 765 3088
   Email: petera@NortelNetworks.com        lili@nortelnetworks.com

   Darek Skalecki                          Don Fedyk
   Nortel Networks Corp.                   Nortel Networks Corp.
   P O Box 3511 Station C                  P O Box 3511 Station C
   Ottawa, ON K1Y 4H7                      Ottawa, ON K1Y 4H7
   Canada                                  Canada
   phone: +1 613 765-2252                  phone: +1 613 763 3268
   Email: skalecki@NortelNetworks.com      fedyk@nortelnetworks.com

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     Application of LSP Bandwidth Modification in Dynamic Resource

   In this section, we gave an example of dynamic network resource
   management using the LSP bandwidth modification capability. The
   details of this example can be found in a previous Internet draft
   presented in the last meeting. Assume that customers are assigned
   with their CR-LSPs. These customers' are assigned with one of the
   priorities as key, normal or best effort. The network operator
   doesn't want to bump any LSPs during an LSP setup, so after these
   CR-LSPs are set up, their holding priority are all assigned as the

   The network operator wants to control the resource on the links of
   LSRs, so all LSRs keep the usage status of its links and based on
   the usage history, each link is assigned a current threshold
   priority Pi. Which means that the link has no bandwidth available
   for Label Request with a setup priority lower than Pi. When a LSP's
   bandwidth needs to be modified, the operator uses policy based
   algorithm to assign a priority for its modification request, say Mp
   for LSP L2. Then the ingress LSR sends Label Request message with
   (Setup Priority = Mp). The rule is then only if there is enough
   bandwidth on the link and, the Setup priority in the Label Request
   Message is higher in priority (Mp numerically smaller) than Pi of
   the link, the Label Request Message will be accepted by the LSR.
   Otherwise, the Label Request message will be rejected with a
   Notification message indicates that there isn't enough resources. It
   should also be note that when OSPF (or IS-IS) floods the link
   available bandwidth information, the available bandwidth associated
   with priority lower than Pi (numerical value bigger) should be
   indicated as _0_. This procedure based on a priority threshold Pi is
   implementation specific and value added. It offers networks
   flexibility to prioritize and control its resources.

   The calculation of Mp is network dependent, based on operator's own
   algorithm. For example, the operator may assign a higher Mp to L2 if
   L2 belongs to a customer with _Key_ priority. The operator may also
   collect the actual usage of each LSP and assign a high Mp to L2 if
   in the past week, L2 has exceeding its reserved bandwidth by 2 times
   on the average, and the customer of L2 agrees to increase its
   bandwidth for a better guaranteed service. Some operator may try to
   increase the bandwidth of L2 on its existing path unsuccessfully as
   there isn't enough bandwidth there. Then the operator is willing to
   change the path of L2 in order to increase its bandwidth, but with a
   lower priority Mp this time as L2 now is routed on its secondary
   path, which should yield priority to the LSPs that are on its
   primary paths here.

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