RFC 8733: Path Computation Element Communication Protocol (PCEP) Extensions for MPLS-TE Label Switched Path (LSP) Auto-Bandwidth Adjustment with Stateful PCE

2.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

2.2. Abbreviations

PCC:

Path Computation Client¶

PCE:

Path Computation Element¶

PCEP:

Path Computation Element Communication Protocol¶

TE:

Traffic Engineering¶

LSP:

Label Switched Path¶

2.3. Terminology

The reader is assumed to be familiar with the terminology defined in [RFC5440], [RFC8231], and [RFC8281].¶

In this document, the PCC is considered to be the head-end LSR of the LSP. Other types of PCCs are not in scope.¶

The following auto-bandwidth terminology is defined in this document.¶

Maximum Average Bandwidth (MaxAvgBw):

The maximum average bandwidth represents the current 'measured' traffic bandwidth demand of the LSP during a time interval. This is the maximum value of the traffic bandwidth rate samples (Bandwidth-Samples) in a given time interval.¶

Adjusted Bandwidth:

This is the auto-bandwidth 'computed' bandwidth that is used to adjust the bandwidth reservation of the LSP.¶

Sample-Interval:

The periodic time interval at which the measured traffic rate of the LSP is collected as a Bandwidth-Sample.¶

Bandwidth-Sample:

The Bandwidth-Sample of the measured traffic rate of the LSP collected at every Sample-Interval.¶

Maximum-Bandwidth:

The Maximum-Bandwidth that can be reserved for the LSP.¶

Minimum-Bandwidth:

The Minimum-Bandwidth that can be reserved for the LSP.¶

Up-Adjustment-Interval:

The periodic time interval at which the bandwidth adjustment should be made using the MaxAvgBw when MaxAvgBw is greater than the current bandwidth reservation of the LSP.¶

Down-Adjustment-Interval:

The periodic time interval at which the bandwidth adjustment should be made using the MaxAvgBw when MaxAvgBw is less than the current bandwidth reservation of the LSP.¶

Up-Adjustment-Threshold:

This parameter is used to decide when the LSP bandwidth should be adjusted. If the percentage or absolute difference between the current MaxAvgBw and the current bandwidth reservation is greater than or equal to the threshold value, the LSP bandwidth is adjusted (upsized) to the current bandwidth demand (Adjusted Bandwidth) at the Up-Adjustment-Interval expiry.¶

Down-Adjustment-Threshold:

This parameter is used to decide when the LSP bandwidth should be adjusted. If the percentage or absolute difference between the current bandwidth reservation and the current MaxAvgBw is greater than or equal to the threshold value, the LSP bandwidth is adjusted (downsized) to the current bandwidth demand (Adjusted Bandwidth) at the Down-Adjustment-Interval expiry.¶

Overflow-Count:

This parameter is used to decide when the LSP bandwidth should be adjusted when there is a sudden increase in traffic demand. This value indicates how many times, consecutively, that the percentage or absolute difference between the current MaxAvgBw and the current bandwidth reservation of the LSP needs to be greater than or equal to the Overflow-Threshold value in order to meet the overflow condition.¶

Overflow-Threshold:

This parameter is used to decide when the LSP bandwidth should be adjusted when there is a sudden increase in traffic demand. If the percentage or absolute difference between the current MaxAvgBw and the current bandwidth reservation of the LSP is greater than or equal to the threshold value, the overflow condition is said to be met. The LSP bandwidth is adjusted to the current bandwidth demand, bypassing the Up-Adjustment-Interval if the overflow condition is met consecutively for the Overflow-Count. The Overflow-Threshold needs to be greater than or equal to the Up-Adjustment-Threshold.¶

Underflow-Count:

This parameter is used to decide when the LSP bandwidth should be adjusted when there is a sudden decrease in traffic demand. This value indicates how many times, consecutively, that the percentage or absolute difference between the current MaxAvgBw and the current bandwidth reservation of the LSP needs to be greater than or equal to the Underflow-Threshold value in order to meet the underflow condition.¶

Underflow-Threshold:

This parameter is used to decide when the LSP bandwidth should be adjusted when there is a sudden decrease in traffic demand. If the percentage or absolute difference between the current MaxAvgBw and the current bandwidth reservation of the LSP is greater than or equal to the threshold value, the underflow condition is said to be met. The LSP bandwidth is adjusted to the current bandwidth demand, bypassing the Down-Adjustment-Interval if the underflow condition is met consecutively for the Underflow-Count. The Underflow-Threshold needs to be greater than or equal to the Down-Adjustment-Threshold.¶

Minimum-Threshold:

When percentage-based thresholds are in use, they are accompanied by this Minimum-Threshold, which is used to ensure that the magnitude of deviation of the calculated LSP bandwidth to be adjusted from the current bandwidth reservations exceeds a specific non-percentage-based criterion (represented as an absolute bandwidth value) before any adjustments are made. This serves to suppress unnecessary auto-bandwidth adjustments and resignaling of the LSP at low bandwidth values.¶

4.1. Auto-Bandwidth Overview

The auto-bandwidth feature allows automatic and dynamic adjustment of the reserved bandwidth of an LSP over time (i.e., without network operator intervention) to accommodate the varying traffic demand of the LSP. If the traffic flowing through the LSP is lower than the configured or current reserved bandwidth of the LSP, the extra bandwidth is being reserved needlessly and is being wasted. Conversely, if the actual traffic flowing through the LSP is higher than the configured or current reserved bandwidth of the LSP, it can potentially cause congestion or packet loss in the network. The initial LSP bandwidth can be set to an arbitrary value (including zero). In practice, it can be set to an expected value based on design and planning. The head-end LSR monitors the actual traffic flowing through the LSP and uses that information to adjust the bandwidth reservation of the LSP in the network.¶

Bandwidth adjustment must not cause disruption to the traffic flow carried by the LSP. One way to achieve this is to use the make-before-break signaling method [RFC3209].¶

4.2. Auto-Bandwidth Theory of Operation

This section describes the auto-bandwidth feature in a general way. When the auto-bandwidth feature is enabled, the measured traffic rate is periodically sampled at each Sample-Interval by the PCC when the PCC is the head-end node of the LSP. The Sample-Interval can be configured by an operator, with a default value of 5 minutes. A very low Sample-Interval could have some undesirable interactions with transport protocols (see Section 6.6).¶

The traffic rate samples are accumulated over the Adjustment-Interval period (in the Up or Down direction). The period can be configured by an operator, with a default value of 24 hours. The PCC in charge of calculating the bandwidth to be adjusted can decide to adjust the bandwidth of the LSP to the highest traffic rate sample (MaxAvgBw) amongst the set of Bandwidth-Samples collected over the Adjustment-Interval period (in the Up or Down direction) depending on the operator policy.¶

Note that the highest traffic rate sample could be higher or lower than the current LSP bandwidth. The LSP is adjusted (upsized) to the current bandwidth demand (MaxAvgBW) only if the difference between the current bandwidth demand (MaxAvgBw) and the current bandwidth reservation is greater than or equal to the Adjustment-Threshold. The Adjustment-Threshold could be an absolute value or a percentage. The threshold can be configured by an operator, with a default value of 5 percent. Similarly, if the difference between the current bandwidth reservation and the current bandwidth demand (MaxAvgBw) is greater than or equal to the Down-Adjustment-Threshold (percentage or absolute value), the LSP bandwidth is adjusted (downsized) to the current bandwidth demand (MaxAvgBw). Some LSPs are less eventful, while other LSPs may encounter a lot of changes in the traffic pattern. The thresholds and intervals for bandwidth adjustment are configured based on the traffic pattern of the LSP.¶

In order to avoid frequent resignaling, an operator may set a longer Adjustment-Interval value (Up and/or Down). However, a longer Adjustment-Interval can result in the undesirable effect of masking sudden changes in the traffic demands of an LSP. To avoid this, the auto-bandwidth feature may force the Adjustment-Interval to prematurely expire and adjust the LSP bandwidth to accommodate the sudden bursts of increase in traffic demand as an overflow condition or decrease in traffic demand as an underflow condition. An operator needs to configure appropriate values for the Overflow-Threshold and/or Underflow-Threshold parameters, and they do not have default values defined in this document.¶

All thresholds in this document could be represented in both absolute value and percentage and could be used together. This is provided to accommodate cases where the LSP bandwidth reservation may become very large or very small over time. For example, an operator may use the percentage threshold to handle small to large bandwidth values and absolute values to handle very large bandwidth values. The auto-bandwidth adjustment is made when either one of the two thresholds, the absolute or percentage, is crossed.¶

When using the (adjustment/overflow/underflow) percentage thresholds, if the LSP bandwidth changes rapidly at very low values, it may trigger frequent auto-bandwidth adjustments due to the crossing of the percentage thresholds. This can lead to unnecessary resignaling of the LSPs in the network. This is suppressed by setting the Minimum-Threshold parameters along with the percentage thresholds. The auto-bandwidth adjustment is only made if the LSP bandwidth crosses both the percentage threshold and the Minimum-Threshold parameters.¶

4.3. Scaling Considerations

It should be noted that any bandwidth change requires resignaling of an LSP, which can further trigger preemption of lower-priority LSPs in the network. When deployed under scale, this can lead to a signaling churn in the network. The auto-bandwidth application algorithm is thus advised to take this into consideration before adjusting the LSP bandwidth. Operators are advised to set the values of various auto-bandwidth adjustment parameters appropriate for the deployed LSP scale.¶

If a PCE gets overwhelmed, it can notify the PCC to temporarily suspend the reporting of the new LSP bandwidth to be adjusted. Similarly, if a PCC gets overwhelmed due to signaling churn, it can notify the PCE to temporarily suspend new LSP setup requests. See Section 5.7 of this document.¶

5.1. Capability Advertisement

During the PCEP initialization phase, PCEP speakers (PCE or PCC) advertise their support of the auto-bandwidth adjustment feature. A PCEP speaker includes the AUTO-BANDWIDTH-CAPABILITY TLV in the OPEN object to advertise its support for PCEP auto-bandwidth extensions. The presence of the AUTO-BANDWIDTH-CAPABILITY TLV in the OPEN object indicates that the auto-bandwidth feature is supported as described in this document.¶

 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=36         |            Length=4           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Flag                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2. AUTO-BANDWIDTH-ATTRIBUTES TLV

The AUTO-BANDWIDTH-ATTRIBUTES TLV provides the 'configurable knobs' of the feature, and it can be included as an optional TLV in the LSPA object (as described in [RFC5440]).¶

For a PCE-initiated LSP [RFC8281], this TLV is included in the LSPA object with the PCInitiate message. For the PCC-initiated delegated LSPs, this TLV is carried in the Path Computation State Report (PCRpt) message in the LSPA object. This TLV is also carried in the LSPA object with the Path Computation Update Request (PCUpd) message to direct the PCC (LSP head-end) to make updates to auto-bandwidth attributes such as Adjustment-Interval.¶

The TLV is encoded in all PCEP messages for the LSP while the auto-bandwidth adjustment feature is enabled. The absence of the TLV indicates the PCEP speaker wishes to disable the feature. This TLV includes multiple AUTO-BANDWIDTH-ATTRIBUTES sub-TLVs. The AUTO-BANDWIDTH-ATTRIBUTES sub-TLVs are included if there is a change since the last information sent in the PCEP message. The default values for missing sub-TLVs apply for the first PCEP message for the LSP.¶

The format of the AUTO-BANDWIDTH-ATTRIBUTES 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=37             |           Length              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
//                            sub-TLVs                          //
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type:

37¶

Length:

The Length field defines the length of the value portion in bytes as per [RFC5440].¶

Value:

This comprises one or more sub-TLVs.¶

The following sub-TLVs are defined in this document:¶

Future specifications can define additional sub-TLVs.¶

The sub-TLVs are encoded to inform the PCEP peer of the various sampling and adjustment parameters. In the case of a missing sub-TLV, as per the local policy, either the default value (as specified in this document) or some other operator-configured value is used.¶

All sub-TLVs are optional, and any unrecognized sub-TLV MUST be ignored. If a sub-TLV of the same type appears more than once, only the first occurrence is processed, and all others MUST be ignored.¶

The following subsections describe the sub-TLVs that are currently defined as being carried within the AUTO-BANDWIDTH-ATTRIBUTES TLV.¶

 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=1              |           Length=4            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Sample-Interval                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=2              |           Length=4            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Adjustment-Interval                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=3              |           Length=4            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Down-Adjustment-Interval                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=4              |           Length=4            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Adjustment-Threshold                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=5              |           Length=8            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Reserved                       |  Percentage |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Minimum-Threshold                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=6              |           Length=4            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Down-Adjustment-Threshold                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=7              |           Length=8            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Reserved                       |  Percentage |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Minimum-Threshold                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=8              |           Length=4            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Minimum-Bandwidth                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=9              |           Length=4            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Maximum-Bandwidth                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=10             |           Length=8            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Reserved                      |  Count  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Overflow-Threshold                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=11             |           Length=8            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Percentage |             Reserved                  |  Count  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Minimum-Threshold                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=12             |           Length=8            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Reserved                       |  Count  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Underflow-Threshold                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 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=13             |           Length=8            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Percentage |             Reserved                  |  Count  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Minimum-Threshold                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.3. BANDWIDTH Object

As per [RFC5440], the BANDWIDTH object (Object-Class value 5) is defined with two Object-Type values as follows:¶

Requested Bandwidth:

The BANDWIDTH Object-Type value is 1.¶

Reoptimization Bandwidth:

The bandwidth of an existing TE LSP for which a reoptimization is requested. The BANDWIDTH Object-Type value is 2.¶

The PCC reports the calculated bandwidth to be adjusted (MaxAvgBw) to the stateful PCE using the existing 'Requested Bandwidth' with the BANDWIDTH Object-Type as 1. The reporting of the 'reoptimization bandwidth' with BANDWIDTH Object-Type as 2 is not required as the stateful PCE is aware of the existing LSP bandwidth.¶

5.4. The PCInitiate Message

A PCInitiate message is a PCEP message sent by a PCE to a PCC to trigger LSP instantiation or deletion [RFC8281].¶

For the PCE-initiated LSP with the auto-bandwidth feature enabled, AUTO-BANDWIDTH-ATTRIBUTES TLV MUST be included in the LSPA object with the PCInitiate message.¶

The Routing Backus-Naur Form (RBNF) definition of the PCInitiate message [RFC8281] is unchanged by this document.¶

5.5. The PCUpd Message

A PCUpd message is a PCEP message sent by a PCE to a PCC to update the LSP parameters [RFC8231].¶

For PCE-initiated LSPs with the auto-bandwidth feature enabled, the AUTO-BANDWIDTH-ATTRIBUTES TLV MUST be included in the LSPA object with the PCUpd message. The PCE can send this TLV to direct the PCC to change the auto-bandwidth parameters.¶

The RBNF definition of the PCUpd message [RFC8231] is unchanged by this document.¶

5.6. The PCRpt Message

The PCRpt message [RFC8231] is a PCEP message sent by a PCC to a PCE to report the status of one or more LSPs.¶

For PCE-initiated LSPs [RFC8281], the PCC creates the LSP using the attributes communicated by the PCE and the local values for the unspecified parameters. After the successful instantiation of the LSP, the PCC automatically delegates the LSP to the PCE and generates a PCRpt message to provide the status report for the LSP.¶

For both PCE-initiated and PCC-initiated LSPs, when the LSP is delegated to a PCE for the very first time as well as after the successful delegation, the BANDWIDTH object of type 1 is used to specify the requested bandwidth in the PCRpt message.¶

The RBNF definition of the PCRpt message [RFC8231] is unchanged by this document.¶

5.7. The PCNtf Message

As per [RFC5440], the PCEP Notification message (PCNtf) can be sent by a PCEP speaker to notify its peer of a specific event.¶

A PCEP speaker (PCE or PCC) SHOULD notify its PCEP peer (PCC or PCE) when it is in an overwhelmed state due to the auto-bandwidth feature. An implementation needs to make an attempt to send this notification (when overwhelmed by auto-bandwidth adjustments) unless sending this notification would only serve to increase the load further. Note that when the notification is not received, the PCEP speaker would continue to request bandwidth adjustments even when they cannot be handled in a timely fashion.¶

Upon receipt of an auto-bandwidth overwhelm notification, the peer SHOULD NOT send any PCEP messages related to auto-bandwidth adjustment. If a PCEP message related to auto-bandwidth adjustment is received while in an overwhelmed state, it MUST be ignored.¶

When the auto-bandwidth feature is deployed, a PCE can send this notification to a PCC when it reports frequent auto-bandwidth adjustments. If a PCC is overwhelmed with resignaling, it can also notify the PCE to not adjust the LSP bandwidth while in the overwhelm state.¶

Some dampening notification procedure (as per [RFC5440]) to avoid oscillations of the overwhelm state is RECOMMENDED. On receipt of an auto-bandwidth overwhelm notification from the PCE, a PCC should consider the impact on the entire network. Moving the delegations of auto-bandwidth-enabled LSPs to another PCE could cause further overloading.¶

6.1. Control of Function and Policy

The auto-bandwidth feature SHOULD be controlled on a per-LSP basis (at the PCC (head-end of the LSP) or PCE), and the values for auto-bandwidth parameters, e.g., Sample-Interval, Adjustment-Interval (up/down), Minimum-Bandwidth, Maximum-Bandwidth, and Adjustment-Threshold (up/down), SHOULD be configurable by an operator.¶

The Maximum-Bandwidth (and Minimum-Bandwidth) should be set to an acceptable limit to avoid having an impact on the rest of the MPLS-TE domain.¶

The operator should make sure that the Overflow-Threshold is greater than or at least equal to the Up-Adjustment-Threshold. And similarly, it is important to ensure that the Underflow-Threshold is greater than or at least equal to the Down-Adjustment-Threshold.¶

6.2. Information and Data Models

A MIB module for gathering operational information about the PCEP is defined in [RFC7420]. Additionally, the YANG module defined in [PCE-PCEP-YANG] provides both configuration of PCEP as well as operational management. These could be enhanced to provide controls and indicators for support of the auto-bandwidth feature. Support for various configuration knobs as well as counters of messages sent/received containing the TLVs defined in this document could be added.¶

6.3. Liveness Detection and Monitoring

The mechanisms defined in this document do not imply any new liveness detection and monitoring requirements in addition to those already listed in [RFC5440].¶

6.4. Verifying Correct Operations

The mechanisms defined in this document do not imply any new operation verification requirements in addition to those already listed in [RFC5440].¶

In the case in which an invalid value is present, the sub-TLV would get ignored and the previous value will be maintained. In such a case, the implementation SHOULD log the event.¶

6.5. Requirements for Other Protocols

The mechanisms defined in this document do not add any new requirements for other protocols.¶

6.6. Impact on Network Operations

In order to avoid any unacceptable impact on network operations, an implementation SHOULD allow a limit to be placed on the number of LSPs that can be enabled with the auto-bandwidth feature. For each LSP enabled with the auto-bandwidth feature, there is an extra load on the PCC, as it needs to monitor the traffic and report the calculated bandwidth to be adjusted to the PCE. The PCE further recomputes paths based on the requested bandwidth and updates the path to the PCC, which, in turn, triggers the resignaling of the path. All these steps add extra load and churn in the network; thus, the operator needs to take due care while enabling these features on a number of LSPs.¶

An implementation MAY allow a limit to be placed on the rate of auto-bandwidth-related messages sent by a PCEP speaker and received by a peer. An implementation SHOULD also allow notifications to be sent when a PCEP speaker is overwhelmed or when the rate of messages reaches a threshold.¶

Due care is required by the operator if a Sample-Interval value significantly smaller than the default (5 minutes) is used, as small Sample-Interval values, e.g., 1 minute or less, could cause undesirable interactions with transport protocols. These undesirable interactions result from providing insufficient time for transport protocol reactions to a prior bandwidth adjustment to settle down before Bandwidth-Samples are taken for the next bandwidth adjustment.¶

8.1. PCEP TLV Type Indicators

This document defines the following new PCEP TLVs; IANA has made the following allocations from the "PCEP TLV Type Indicators" subregistry of the "Path Computation Element Protocol (PCEP) Numbers" registry as follows:¶

8.2. AUTO-BANDWIDTH-CAPABILITY TLV Flag Field

IANA has created a subregistry to manage the Flag field of the AUTO-BANDWIDTH-CAPABILITY TLV within the "Path Computation Element Protocol (PCEP) Numbers" registry.¶

New bit numbers are to be assigned by Standards Action [RFC8126]. Each bit should be tracked with the following qualities:¶

The initial contents of the subregistry are empty, with all bits marked unassigned.¶

8.3. AUTO-BANDWIDTH-ATTRIBUTES Sub-TLV

This document specifies the AUTO-BANDWIDTH-ATTRIBUTES sub-TLVs. IANA has created an "AUTO-BANDWIDTH-ATTRIBUTES Sub-TLV Types" subregistry within the "Path Computation Element Protocol (PCEP) Numbers" registry to manage the type indicator space for sub-TLVs of the AUTO-BANDWIDTH-ATTRIBUTES TLV. The valid range of values in the registry is 0-65535. IANA has initialized the registry with the following values. All other values in the registry should be marked as "Unassigned".¶

IANA has set the Registration Procedure for this registry to read as follows:¶

This document defines the following types:¶

8.4. Error Object

This document defines a new Error-value for PCErr message of Error-Type 19 (Invalid Operation) [RFC8231]. IANA has allocated a new Error-value within the "PCEP-ERROR Object Error Types and Values" subregistry of the "Path Computation Element Protocol (PCEP) Numbers" registry as follows:¶

8.5. Notification Object

IANA has allocated a new Notification-type and Notification-values within the "Notification Object" subregistry of the "Path Computation Element Protocol (PCEP) Numbers" registry as follows:¶