| PCE Working Group | D. Dhody |
| Internet-Draft | U. Palle |
| Intended status: Standards Track | Huawei Technologies |
| Expires: September 7, 2015 | R. Singh |
| Juniper Networks | |
| March 6, 2015 |
PCEP Extensions for MPLS-TE LSP Automatic Bandwidth Adjustment with stateful PCE
draft-dhody-pce-stateful-pce-auto-bandwidth-04
The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform path computations in response to Path Computation Clients (PCCs) requests. The stateful PCE extensions provide stateful control of Multiprotocol Label Switching (MPLS) Traffic Engineering Label Switched Paths (TE LSP) via PCEP, for a model where the PCC delegates control over one or more locally configured LSPs to the PCE.
This document describes the automatic bandwidth adjustment of such LSPs under the Active Stateful PCE model.
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[RFC5440] describes the Path Computation Element Protocol (PCEP) as the communication between a Path Computation Client (PCC) and a Path Control Element (PCE), or between PCE and PCE, enabling computation of Multiprotocol Label Switching (MPLS) for Traffic Engineering Label Switched Path (TE LSP).
[I-D.ietf-pce-stateful-pce] specifies extensions to PCEP to enable stateful control of MPLS TE LSPs. In this document focus is on Active Stateful PCE where LSPs are configured on the PCC and control over them is delegated to the PCE.
Over time, based on the varying traffic pattern, an LSP established with certain bandwidth may require to adjust the reserved bandwidth over time automatically. Ingress Label Switch Router (LSR) samples the traffic rate at each sample-interval (BwSample) to determine the traffic information as Maximum Average Bandwidth (MaxAvgBw). Further adjustment to the reserved bandwidth should be made at every adjustment-interval automatically.
Enabling Auto-Bandwidth on a LSP results in the LSP automatically adjusting its bandwidth based on the actual traffic flowing through the LSP. A LSP can therefore be setup with some arbitrary (or zero) bandwidth value such that the LSP automatically monitors the traffic flow and adjusts its bandwidth every adjustment-interval period. The bandwidth adjustment uses the make-before-break signaling method so that there is no interruption to traffic flow. This is described in detail in Section 4.1. [I-D.ietf-pce-stateful-pce-app] describes the usecase for auto-bandwidth adjustment for passive and active stateful PCE.
There are two approaches to automatic bandwidth adjustments in case of active stateful PCE -
This document defines extensions needed to support Auto-Bandwidth feature along with mechanism to provide traffic information of the LSPs in a stateful PCE model using PCEP.
This document does not exclude use of any other mechanism employed by stateful PCE to learn real time traffic information etc. But at the same time, using the same protocol (PCEP in this case) for updating and reporting the LSP parameters as well as to support automatic bandwidth adjustment is operationally beneficial.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
The following terminology is used in this document.
Note the additional terms defined in Section 4.1.
An active stateful PCE can update the bandwidth for a delegated LSP via mechanisms described in [I-D.ietf-pce-stateful-pce]. Note that further extension are needed because of following reasons:
Extensions as specified in this document is one of the way for PCE to learn this information. But at the same time a stateful PCE MAY choose to learn this information from other means like management, performance tools.
Auto-Bandwidth feature allows an LSP to automatically and dynamically adjust its reserved bandwidth over time, i.e. without network operator intervention. The bandwidth adjustment uses the make-before-break adaptive signaling method so that there is no interruption to traffic flow.
The new bandwidth reservation is determined by sampling the actual traffic flowing through the LSP. If the traffic flowing through the LSP is lower than the configured or current bandwidth of the LSP, the extra bandwidth is being reserved needlessly and being wasted. Conversely, if the actual traffic flowing through the LSP is higher than the configured or current bandwidth of the LSP, it can potentially cause congestion or packet loss. With Auto-Bandwidth feature, the LSP bandwidth can be set to some arbitrary value (even zero) during initial setup time, and it will be periodically adjusted over time based on the actual bandwidth requirement.
Note the following terms:
The traffic rate is repeatedly sampled at each sample-interval (which can be configured by the user and the default value as 5 minutes). The sampled traffic rates are accumulated over the adjustment-interval period (which can be configured by the user and the default value as 24 hours).
The ingress LSR reports the live traffic information to the stateful PCE via the PCRpt message, to avoid multiple reports, the Report-Threshold percentage is used. Only if the percentage difference between the current BwSample and the last BwSample is greater than or equal to the threshold percentage the LSP bandwidth is reported to PCE.
Stateful PCE will adjust the bandwidth of the LSP to the highest sampled traffic rate amongst the set of samples taken over the adjustment-interval. Note that the highest sampled traffic rate could be higher or lower than the current LSP bandwidth. Only if the current MaxAvgBw and the current bandwidth allocation is greater than or equal to the Adjust-Threshold percentage the LSP bandwidth is adjusted to the current bandwidth demand.
Also to avoid multiple LSP re-signaling, sometimes operator set up longer adjustment intervals. However long adjustment-interval can also result in an undesirable effect of masking sudden changes in traffic patterns. To avoid this, the stateful PCE MAY pre-maturely expire the adjustment-interval to accommodate sudden bursts in traffic.
The AUTO-BANDWIDTH-ATTRIBUTE TLV can be included as an optional TLV in the LSP object as described in [I-D.ietf-pce-stateful-pce]. Whenever the LSP with Auto-Bandwidth feature enabled is delegated, AUTO-BANDWIDTH-ATTRIBUTE TLV is carried in PCRpt message. The TLV provides PCE with the 'local configurable knobs' of this feature. In case of PCE Initiated LSP ([I-D.ietf-pce-pce-initiated-lsp]) with this feature enabled, this TLV is included in LSP object with PCInitiate message.
The format of the AUTO-BANDWIDTH-ATTRIBUTE TLV is shown in the following figure:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=[TBD] | Length=16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sample Int | Adj Int | Rpt Threshold | Adj Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AUTO-BANDWIDTH-ATTRIBUTE TLV format
The type of the TLV is [TBD] and it has a fixed length of 16 octets.
The value contains the following fields:
Unassigned flags MUST be set to zero on transmission and MUST be ignored on receipt.
If the above parameters are not specified by the user, based on the local policy at Ingress (PCC) the default value can be encoded.
If no default value is specified at Ingress, value 'zero' can be encoded for the particular field. The stateful PCE can then apply its own default value based on the local policy.
As per [RFC5440], the BANDWIDTH object is defined with two Object-Type values:
The new BANDWIDTH object type 3 [TBD] is used to specify the BwSample determined from the existing TE LSP Traffic flow at every sample-interval when L bit is set in AUTO-BANDWIDTH-ATTRIBUTE TLV. The Report-Threshold percentage is used to determine if there is a need to report the current BwSample.
If Live-Traffic (L-Bit) is not set, PCC only reports the calculated bandwidth to be adjusted (MaxAvgBw) to the PCE. This is done via the existing 'Requested Bandwidth with BANDWIDTH Object-Type as 1'.
When the delegated LSP is enabled with the Auto-Bandwidth adjustment feature with Live-Traffic (L-Bit) set, PCC SHOULD include the BANDWIDTH object of type 3 [TBD] in the PCRpt message. The definition of the PCRpt message (see [I-D.ietf-pce-stateful-pce]) is unchanged.
When LSP is delegated to a PCE for the very first time, BANDWIDTH object of type 1 is used to specify the requested bandwidth in the PCRpt message. To report the live traffic flow information (as the BwSample) the BANDWIDTH object of type 3 [TBD] is encoded in further PCRpt message.
If Live-Traffic (L-Bit) is not set, PCC SHOULD include the BANDWIDTH object of type 1 to specify the he calculated bandwidth to be adjusted to the PCE.
For PCE Initiated LSP ([I-D.ietf-pce-pce-initiated-lsp]) with Auto-Bandwidth feature enabled, AUTO-BANDWIDTH-ATTRIBUTE TLV is included in LSP object with the PCInitiate message. The rest of the processing remains unchanged.
This document defines a new BANDWIDTH type and AUTO-BANDWIDTH-ATTRIBUTE TLV which does not add any new security concerns beyond those discussed in [RFC5440] and [I-D.ietf-pce-stateful-pce] in itself. Some deployments may find the live traffic bandwidth information as extra sensitive and thus should employ suitable PCEP security mechanisms like TCP-AO or [I-D.ietf-pce-pceps].
The Auto-Bandwidth feature MUST BE controlled per tunnel at Ingress (PCC), the values for parameters like sample-interval, adjustment-interval, minimum-bandwidth, maximum-bandwidth, report-threshold, adjust-threshold, Live-Traffic (L-Bit) SHOULD BE configurable by an operator.
[RFC7420] describes the PCEP MIB, there are no new MIB Objects for this document.
Mechanisms defined in this document do not imply any new liveness detection and monitoring requirements in addition to those already listed in [RFC5440].
Mechanisms defined in this document do not imply any new operation verification requirements in addition to those already listed in [RFC5440].
Mechanisms defined in this document do not imply any new requirements on other protocols.
Mechanisms defined in this document do not have any impact on network operations in addition to those already listed in [RFC5440].
This document defines the following new PCEP TLVs; IANA is requested to make the following allocations from this registry.
Value Meaning Reference TBD AUTO-BANDWIDTH-ATTRIBUTE [This I.D.]
This document requests that a registry is created to manage the Flags field in the AUTO-BANDWIDTH-ATTRIBUTE TLV in the LSP object. New values are to be assigned by Standards Action [RFC5226]. Each bit should be tracked with the following qualities:
The following values are defined in this document:
Bit Description Reference 31 Live-Traffic (L-Bit) [This I.D.]
This document defines new object type for the BANDWIDTH object; IANA is requested to make the following allocations from this registry.
Object-Class Value Name Reference
5 BANDWIDTH [This I.D.]
Object-Type
3: MaxAvgBw determined from
the existing TE LSP Traffic
flow.
We would like to thank Venugopal Reddy, Reeja Paul, Sandeep Boina and Avantika for their useful comments and suggestions.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC5440] | Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. |
| [I-D.ietf-pce-stateful-pce] | Crabbe, E., Minei, I., Medved, J. and R. Varga, "PCEP Extensions for Stateful PCE", Internet-Draft draft-ietf-pce-stateful-pce-10, October 2014. |
| [I-D.ietf-pce-pce-initiated-lsp] | Crabbe, E., Minei, I., Sivabalan, S. and R. Varga, "PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model", Internet-Draft draft-ietf-pce-pce-initiated-lsp-03, March 2015. |
| [RFC3471] | Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. |
| [RFC5226] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. |
| [RFC7420] | Koushik, A., Stephan, E., Zhao, Q., King, D. and J. Hardwick, "Path Computation Element Communication Protocol (PCEP) Management Information Base (MIB) Module", RFC 7420, December 2014. |
| [I-D.ietf-pce-stateful-pce-app] | Zhang, X. and I. Minei, "Applicability of a Stateful Path Computation Element (PCE)", Internet-Draft draft-ietf-pce-stateful-pce-app-03, October 2014. |
| [I-D.ietf-pce-pceps] | Lopez, D., Dios, O., Wu, W. and D. Dhody, "Secure Transport for PCEP", Internet-Draft draft-ietf-pce-pceps-03, March 2015. |
| [IEEE.754.1985] | Institute of Electrical and Electronics Engineers, "Standard for Binary Floating-Point Arithmetic", IEEE Standard 754, August 1985. |
He Zekun
Tencent Holdings Ltd,
Shenzhen P.R.China
Email: kinghe@tencent.com
Xian Zhang
Huawei Technologies
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Email: zhang.xian@huawei.com
Young Lee
Huawei Technologies
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