| PCE Working Group | D. Dhody |
| Internet-Draft | U. Palle |
| Intended status: Standards Track | Huawei Technologies India Pvt Ltd |
| Expires: January 05, 2014 | July 04, 2013 |
PCEP Extensions for MPLS-TE LSP Automatic Bandwidth Adjustment with stateful PCE
draft-dhody-pce-stateful-pce-auto-bandwidth-01
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 extensions described in [STATEFUL-PCE] 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 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).
[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 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 3.1.
[STATEFUL-PCE-APP] describes the usecase for auto-bandwidth adjustment for passive and active stateful PCE. Active stateful PCE can use information such as historical trending data, application-specific information about expected demands or policy information, as well as knowledge of the actual desired flow volumes to make smarter bandwidth adjustment to delegated LSPs.
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. At the same time this document does not exclude use of any other mechanism employed by stateful PCE to learn real time traffic information etc.
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 3.1.
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 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 MaxAvgBw and the last MaxAvgBw 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 extensions are needed to support -
Extensions as specified in this document is one of the way for PCE to learn this information. A stateful PCE MAY learn this information from other means (like NMS, OSS etc).
The AUTO-BANDWIDTH-ATTRIBUTE TLV can be included as an optional TLV in the LSP object as described in [STATEFUL-PCE]. Whenever the LSP with Auto-Bandwidth feature enabled is delegated, AUTO-BANDWIDTH-ATTRIBUTE TLV MUST be carried in PCRpt 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=12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
AUTO-BANDWIDTH-ATTRIBUTE TLV format
The type of the TLV is [TBD] and it has a fixed length of 12 octets.
The value contains the following fields:
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 MaxAvgBw determined from the existing TE LSP Traffic flow at every sample-interval. The Report-Threshold percentage is used to determine if there is a need to report the current MaxAvgBw.
When the delegated LSP is enabled with the Auto-Bandwidth adjustment feature, a PCC MAY include the BANDWIDTH object of type 3 [TBD] in the PCRpt message. The definition of the PCRpt message (see [STATEFUL-PCE]) is then extended as follows:
<PCRpt Message> ::= <Common Header>
<state-report-list>
Where:
<state-report-list> ::= <state-report>[<state-report-list>]
<state-report> ::= <LSP>
[<path-list>]
Where:
<path-list>::=<path>[<path-list>]
<path>::=<ERO><attribute-list>
Where:
<attribute-list> ::= [<LSPA>]
[<BANDWIDTH>]
[<RRO>[<BANDWIDTH>]]
[<metric-list>]
<metric-list> ::= <METRIC>[<metric-list>]
The BANDWIDTH object of type 3 [TBD] is encoded along with RRO to report the traffic flow information as the MaxAvgBw.
TBD.
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 SHOULD BE configurable by user.
TBD.
TBD.
TBD.
TBD.
TBD.
TBD.
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 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. |
| [RFC3471] | Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description", RFC 3471, January 2003. |
| [RFC5440] | Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. |
| [IEEE.754.1985] | IEEE, "Standard for Binary Floating-Point Arithmetic ", |
| [STATEFUL-PCE] | Crabbe, E., Medved, J., Minei, I. and R. Varga,, "PCEP Extensions for Stateful PCE (draft-ietf-pce-stateful-pce)", Oct 2012. |
| [STATEFUL-PCE-APP] | Zhang, F., Zhang, X., Lee, Y., Casellas,, R. and O. Gonzalez de Dios,, "Applicability of Stateful Path Computation Element (PCE) (draft-zhang-pce-stateful-pce-app)", |
He Zekun
Tencent Holdings Ltd,
Shenzhen P.R.China
Email: kinghe@tencent.com
Xian Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972913
Email: zhang.xian@huawei.com
Young Lee
Huawei
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Plano, TX 75075
US
Phone: +1 972 509 5599 x2240
Fax: +1 469 229 5397
EMail: leeyoung@huawei.com