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Bandwidth Sizing


NorthStar Controller can be configured to periodically compute a new planned bandwidth for each bandwidth sizing-enabled LSP based on aggregated LSP traffic statistics. NorthStar sends new planned bandwidth information to the NorthStar Path Computation Server (PCS) where the actual computation is done. The PCS determines, based on the new bandwidth requirements and the LSP bandwidth sizing parameters, whether it needs to provision the new planned bandwidth or not.


Only the bandwidth of PCE-initiated and PCC-delegated LSPs can be sized this way. Although nothing will prevent you from applying sizing attributes to PCC-controlled LSPs, no sizing will actually occur.

For bandwidth sizing to occur, you must:

  • Enable NorthStar analytics

    NorthStar supports bandwidth sizing for all PCE-initiated and PCC-delegated LSPs for which it can obtain LSP statistics, either via Juniper Telemetry Interface (JTI), or SNMP collection (scheduled via the Task Scheduler). This means that you must enable/use NorthStar analytics, and confirm that NorthStar is receiving traffic from the LSPs.

  • Configure PCE-initiated and PCC-delegated LSPs so their bandwidth sizing attribute is set to yes (bandwidth sizing enabled). LSPs without this setting are not sized.

  • Create and schedule a bandwidth sizing task in the Task Scheduler, as described in this section.

Bandwidth Sizing on the PCS Versus Auto-Bandwidth on the PCC

Bandwidth sizing can be confused with auto-bandwidth. Table 1 summarizes the differences.

Table 1: Bandwidth Sizing Compared to Auto-Bandwidth


Bandwidth Sizing

Where configured

Router (PCC) via a template

NorthStar (PCS) via web UI or REST API

Supported LSP types






Supported vendor types

Juniper devices


Adjustment period


One centralized schedule applies to all bandwidth sizing-enabled LSPs

Bandwidth computations and bandwidth change decisions

Done by the router (PCC)

Done by NorthStar (PCS)

Aggregation statistics options




X Percentile (80, 90, 95, 99)

Behavior if both are configured

Auto-bandwidth overwrites bandwidth sizing and vice versa.

For this reason, you should not have auto-bandwidth enabled for bandwidth sizing-enabled LSPs.

Note: For PCE-initiated LSPs, this means you must ensure that the name of the LSP does not match any configured label-switched path template that includes the auto-bandwidth parameter.

For PCC-delegated LSPs, this means you must ensure that the auto-bandwidth parameter is not configured on the router.

Requires NorthStar Analytics?


Yes (to acquire LSP traffic statistics)

Bandwidth Sizing-Enabled LSPs

Only bandwidth sizing-enabled LSPs are included in the re-computation of new planned bandwidths. When you add or modify an LSP, you must set the Bandwidth Sizing (yes/no) setting to yes to enable sizing. At the same time, you also set values for the following parameters:

  • Adjustment threshold (%)

    This setting controls the sensitivity of the automatic bandwidth adjustment. The new planned bandwidth is only considered if it differs from the existing bandwidth by the value of this setting or more.

  • Minimum planned bandwidth

  • Maximum planned bandwidth

    The minimum and maximum planned bandwidth values act as boundaries:

    • If the new planned bandwidth is greater than the maximum setting, NorthStar signals the LSP with the maximum bandwidth.

    • If the new planned bandwidth is less than the minimum setting, NorthStar signals the LSP with the minimum bandwidth.

    • If the new planned bandwidth falls in between the maximum and minimum settings, NorthStar signals the LSP with the new planned bandwidth.


These parameters are also described in the context of the Provision LSP window.

Adding a Bandwidth Sizing Task

The bandwidth sizing task periodically sends a new planned bandwidth for bandwidth sizing-enabled LSPs to the NorthStar PCS. The PCS determines whether it needs to provision the new planned bandwidth with a path that satisfies the new bandwidth requirement.

To schedule a bandwidth sizing task, navigate to Administration > Task Scheduler from the More Options menu.

  1. Click Add in the upper right corner. The Create New Task window is displayed as shown in Figure 1.
    Figure 1: Create New Task Window
    Create New Task Window

    Enter a name for the task, select Bandwidth Sizing from the drop-down menu, and click Next.

  2. Select an aggregation statistics option from the drop-down menu as shown in Figure 2.
    Figure 2: Bandwidth Sizing Task, Step 2
    Bandwidth Sizing Task, Step

    The aggregation statistic works together with the task execution recurrence interval (the period of bandwidth adjustment) that you set up in the scheduling window. NorthStar aggregates the LSP traffic for the interval based on the aggregation statistic you select, and uses that information to calculate the new planned bandwidth. The options in the Aggregation Statistic drop-down menu are described in Table 2.

    Table 2: Bandwidth Sizing Aggregation Statistics Options

    Aggregation Statistic


    80th, 90th, 95th, 99th Percentile

    Aggregation is based on the selected percentile.


    For each interval, the samples within that interval are averaged. If there are N samples for a particular interval, the result is the sum of all the sample values divided by N.


    For each interval, the maximum of the sample values within that interval is used.

  3. Click Next to proceed to the scheduling parameters. The Create New Task - Schedule window is displayed as shown in Figure 3. You must schedule the task to repeat at a specific interval from a minimum of 15 minutes to a maximum of one day. The default interval is one hour. Note

    There is no per-LSP interval. The interval configured here applies to all LSPs for which bandwidth sizing is enabled.

  4. Click Submit to complete the addition of the new collection task and add it to the Task List. Click a completed task in the list to display the results in the lower portion of the window. There are three tabs in the results window: Summary, Status, and History. Note

    You can have only one bandwidth sizing task per NorthStar server. If you attempt to add a second, the system will prompt you to approve overwriting the first one.

Viewing LSP Statistics and Bandwidth

In the network information table (Tunnel tab), you can add optional columns related to bandwidth sizing by hovering over any column heading and clicking the down arrow that appears. Select Columns and click the check boxes to add columns for bandwidth sizing parameters as shown in Figure 4.

Figure 4: Bandwidth Sizing Columns
Bandwidth Sizing Columns

Once added, these columns display in the network information table the values of the parameters you configured for the bandwidth sizing-enabled LSPs.

You can view an LSP’s statistics and bandwidth in graphical form by right-clicking an LSP on the Tunnel tab of the network information table and selecting View LSP Traffic. An example of the display is shown in Figure 5.

Figure 5: Viewing LSP Traffic and Bandwidth
Viewing LSP Traffic and Bandwidth

This example shows the actual LSP traffic (blue line) as well as the signaled (configured) bandwidth (green line). The hide bandwidth/show bandwidth button allows you to toggle back and forth between including and not including the bandwidth in the display.

Logs related to bandwidth sizing are stored in /opt/northstar/logs and include:

  • bandwidth_sizing.log

  • pcs.log

Using Bandwidth Sizing Together with Zero Bandwidth Mode

In Administration > System Settings, there is an option to enable zero bandwidth signaling. By default, this functionality is disabled. When enabled, NorthStar can optimize resource utilization more effectively and more aggressively. This is true, with or without bandwidth sizing, and it affects all PCE-initiated and PCC-delegated LSPs, regardless of whether they are bandwidth sizing-enabled or not.

When zero bandwidth signaling is enabled and NorthStar is receiving traffic statistics for bandwidth sizing-enabled LSPs, NorthStar does the following at the end of the bandwidth adjustment period:

  • Computes the new planned bandwidth.

  • Computes a new path that satisfies the new planned bandwidth.

  • Updates the RSVP link utilization based on the new planned bandwidth and the new path.

  • Provisions the new path with zero bandwidth as opposed to provisioning with the new planned bandwidth.