10 February 2009

Bandwidth throttling and speed tests, how does it work?

Bandwidth Throttling configuration:

Bandwidth throttling is configured on the NS Web admin console at 'Configuration > Altiris Agent > Altiris Agent Configuration' each of the four agent tasks, on the General tab under the Bandwidth/Throttling settings section.

Bandwidth throttling options:
  1. Never throttle.
  2. Enable throttling when connection speed is below <dropdown box>:
    • 500 bytes/sec
    • 1 KB/sec
    • 2 KB/sec
    • 4 KB/sec
    • 10 KB/sec
    • 20 KB/sec
    • 50 KB/sec (default)
    • 100 KB/sec
    • 256 KB/sec
    • 512 KB/sec
    • 1 MB/sec
  3. Throttle regardless of connection speed.
  4. Use the server’s time for throttling settings (none configured by default).

Once bandwidth throttling has been configured, and the throttling configurations have been passed to the Altiris Agent machines, the Altiris Agent uses ICMP (ping) packets to perform the network connection speed tests. This is detailed below in the section Speed Testing Parameters. The returned speed test value is cached for a period of 6 hours.

When there is a scheduled package download task, the Altiris Agent either retrieves the cached connection speed value or it will initiate a new network speed test, and the results will be cached for 6 hours. Once the 6-hour cache expires, the Altiris Agent will request another speed test profile once an advertisement execution or package download begins (see Speed Testing Triggers and Speed Testing Operations below).

Throttling Rules:

When the Altiris Agent is asked to throttle, there are two throttling rules that can be configured:

  1. Relative throttling—This is a user defined percentage of available bandwidth, and it is measure in 0–100 percent.
  2. Absolute throttling—This is a user defined maximum allowed throughput when throttling is enabled; it is measured in bytes per second.
How the throttling process works:
The Altiris Agent:
  1. Sets wait times and buffer sizes that most closely meet the target download speed of the configured relative or absolute throttle rule before starting the package download.
  2. Requests a segment of data from the source.
  3. Receives the data and then waits a specified period of time.
  4. Monitors the download and adjusts to meet the configured throughput.
  5. Requires no additional speed testing.
Speed Testing Triggers:

When the Altiris Agent is instructed to perform a speed test by its configuration policy there are four triggers that can initiate the speed test:

  1. Each Software Delivery task can have a 'Download and run…' option (Advanced tab and 'Download and Execute Options') which determines the location of the file for execution, whether from a server or locally, depending on the available speed.
  2. In the Altiris Agent configuration there is an option Default minimum connection speed to run SWD Packages to test minimum throughput before execution.
  3. In the Altiris Agent configuration there is the same Download and run… option as in the Software Delivery Task, but when applied via the Altiris Agent configuration, it is a global setting which then applies to all tasks.
  4. In the Altiris Agent configuration there is download throttling when the download occurs. This method has two modes of operation: Relative throttling which is a percent of available bandwidth, and Absolute throttling which is simply a value for the throughput allowed.
Speed test operations:

Speed Tests are Directed Against Servers in the Following Manner:

  1. Items 1, 3, and 4 above in Speed Testing Triggers (only with Relative throttling) are tests against the download location.
  2. Item 2 above in Speed Testing Triggers is against the Notification Server, or any Item where the Altiris Agent cannot determine another server to test against will be evaluated against the Notification Server.
  3. Item 4 (with Absolute throttling) does not need a speed test.

Note! Speed testing does not mean packets go on the wire every time one of these decision points is reached. Review the speed test details below under Speed Testing Parameters. Whether it is for a package download or an advertisement execution, the speed testing process is the same.

Speed testing begins with the FQDN name for the server being targeted based on the codebase and the speed is discovered and set; the NetBIOS name is not tested but it set to the same speed. If the FQDN test fails then the NetBIOS name is tested, and the speed is discovered and set.

Bandwidth Throttling when ICMP is turned off:

There are several throttle settings and parameters that need to be understood when ICMP traffic is disabled on the network. Activation of throttling by the Altiris Agent is based on the following options:

  1. Throttle regardless of connection speed, or
  2. Enable throttling when connection speed is below <dropdown box>.

If ICMP traffic is disabled on the network, the option Throttle regardless of connection speed should be selected. If the option Enable throttling when connection speed is below… is selected when ICMP traffic has been disabled, by default throttling is set to 1 KB/sec because the connection speed cannot be verified.

So, threshold settings that are 1 KB/sec or above are always throttled, and the setting of 500 bytes/sec is never throttled.

The configurable values for throttling threshold are:

  • 500 bytes/sec
  • 1 KB/sec
  • 2 KB/sec
  • 4 KB/sec
  • 10 KB/sec
  • 20 KB/sec
  • 50 KB/sec (default)
  • 100 KB/sec
  • 256 KB/sec
  • 512 KB/sec
  • 1 MB/sec

Once the throttling options are selected then the throttling limits come into effect. Again, these limits are:

  1. Relative throttling — This is a user defined percentage of available bandwidth, and it is measure in 0–100 percent.
  2. Absolute throttling — This is a user defined maximum allowed throughput when throttling is enabled; it is measured in bytes per second.

When ICMP traffic is disabled on the network there is no need to initiate speed testing and Absolute throttling is the better choice. The bandwidth limit is already known and the Altiris Agent will throttle to that limit. If Relative throttling is selected, it will still act as an absolute limit as defaults to the option of 1 KB/sec.

Since network throughput is so critical, different Altiris Agent collections should be created based on network throughput. Altiris Agent machines can then be customized based on customized connectivity configurations.

Speed Testing Parameters:

Speed testing is a result of the Altiris Agent pinging the FQDN name for a server being targeted based on the defined codebase, and the speed is discovered and cached; the NetBIOS name is not tested but it set to the same speed. If the FQDN test fails then the NetBIOS name is tested, and the speed is discovered and set.

If the codebase request is to a server that has not been profiled for a connection speed before then a speed test is initiated.

Packets used: Five 1-byte packets and then thirty 400-byte packets. (Note: Older operating systems will only use five 400-byte packets.)

Registry keys:

HKLM\SOFTWARE\Altiris\Communications\MaxServersToCheck (default 6, valid range is 1–100).</I">

            Description: Maximum numbers of servers to check

Values: If over 100 or under 0 then is set to 100; a value of 0 is set to 6

HKLM\SOFTWARE\Altiris\Communications\ IP Expiry (mins) (default 360, valid range is 1–10,080)</I">

Description: Number of minutes before connectivity to a Host is retested

Values: If over 10,080 or under 0 then is set to10080; a value of 0 is set to 1.
HKLM\SOFTWARE\Altiris\Communications\SPEED Expiry(mins) (default 360) 

Additional information

See AKB #39368 for additional information on Speed Testing.

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