Configure WAN parameters

When you use NV Network Editor to create an NV profile, you can define the WAN parameters.

Latency and packet loss

Latency defines the amount of time it takes an IP packet to cross the WAN in one direction. Packet loss determines how many packets are dropped.

You can specify latency and packet loss parameters manually, or import them from a recorded .ntx file and customize them in the NV Network Editor.

To specify parameters manually:

  1. In the NV Network Editor, on the WAN page, go to the Latency and Packet Loss tab and select Custom.

  2. In the Latency Curve area, select one of the following options and configure the relevant parameters.

    Option Details
    Fixed

    Latency is fixed at a specified value. Specify the value in the Latency field (between 0 and 8000 milliseconds).
    Uniform distribution

    Latency changes over time (also known as jitter).

    Configure the following parameters.

    • Minimum and Maximum: Specify a range of possible latency values (between 0 and 8000 ms). The latency is changed randomly between the minimum and maximum values.
    • Limit latency change: Enable this option to limit the change in latency between each two consecutive packets to a specified number. Enter the maximum possible change between consecutive packets (in milliseconds). For example, if you enter 45, NV changes the latency by a maximum of 45 milliseconds between two consecutive packets.
    Normal distribution

    Causes latency to fluctuate randomly and non-uniformly around an average value. You can use this option to emulate jitter conditions.

    Configure the following parameters.

    • Average: The average latency (in milliseconds).
    • Standard Deviation: Entering a value in this parameter sets a range for two-thirds of the random values. For example, if the average is 600 milliseconds and the standard deviation is 100 milliseconds, two-thirds of random latency values will be between 500 and 700. This allows you to exert some control over the random change in latency.
    Linear

    Allows you to set a range of latency values, and to indicate the time it takes latency to increase from the minimum to the maximum value in the range.

    Configure the following parameters.

    • Minimum and Maximum: Specify a range of possible latency values (between 0 and 8000 ms).
    • Graph duration: The duration of the full cycle of increasing latency (between 1 and 65,535 seconds). For example, if you define a range of 300 to 400 milliseconds and a cycle duration of 100 seconds, NV will increase latency by one millisecond each second, as the latency increases from 300 to 400 ms. When latency reaches the maximum value, it cycles back to the minimum value.

  3. In the Packet Loss area, select one of the following options and configure the relevant parameters.

    Option Details
    No packet loss WAN behavior is not affected by packet loss. In this case, no packets are lost and the impairment is not applied to network traffic.
    Periodic loss

    One packet is discarded for every specified number of packets that pass through the WAN.

    Enter a number (between 2 and 65535) in the Lose one of every x packets field. For example, if you enter 8, every 8th packet that enters the WAN is discarded.

    Packets are counted separately in both directions. The incoming xth packet and the outgoing xth packet are discarded.
    Random loss

    Allows you to set the probability for losing each packet.

    Loss probability: The probability that any given packet is lost (between 0.01% and 90%). For example, if you enter 2, each packet has a 2 percent chance of being dropped while passing through the emulated WAN cloud.
    Burst loss

    Allows you to introduce a "bursty" packet loss model in the emulated WAN cloud, by setting a number of packets to lose (burst size) every time a loss event occurs.

    Configure the following parameters.

    • Loss probability: The probability that a loss event occurs.
    • Number of lost packets in every burst: The minimum and maximum possible number of packets lost in a loss event (between 1 and 65535). The actual number of lost packets is selected randomly from this range.
    Gilbert-Eliot loss

    Allows you to emulate a good state and a bad state in the network.

    Configure the following parameters for each state.

    • Loss: The average packet loss percentage (from 0.01% to 100%).
    • Change state: The probability that the network leaves the specific state and moves to the other state (from 0.01% to 99.99%). For example, if the tested network has, at any given time, a 10% chance of moving from good to bad and a 50% chance of moving from bad to good, you specify 10 and 50 in the respective Change state fields.

Import and edit recorded network conditions

You can import recorded parameters from an .ntx file directly into a virtual location, as described in Configure a virtual location. Import the recorded parameters into an NV profile using NV Network Editor only if you want to edit the recorded parameters before importing them into a virtual location.

Importing recorded network conditions is supported only for Vuser groups that share the specified bandwidths, not for Vuser groups that allocate the specified bandwidth to each Vuser. For details, see Configure a virtual location.

To import and edit recorded network conditions:

  1. On the WAN page, go to the Latency and Packet Loss tab and select Recorded.

  2. Click Choose file and select the relevant .ntx file.

    A summary of the network conditions is displayed.

  3. Modify the latency and packet loss by selecting a percentage in the Multiply latency values by and Multiply loss value by lists.

    Setting these values helps you predict future load cases or to prepare some margins of service level over the current status. In these fields, you can enter values between 0 and 200 percent. For example, if you enter 100%, the recorded values are used as they are. If you enter 200%, each recorded value is doubled (multiplied by 200%).

  4. Select a Packet Loss value.

  5. Select a Playback Mode from the following options.

    Mode Details
    Play imported values sequentially While emulating the network, the latency values are used cyclically one after the other in the order in which they were recorded.
    Play imported values randomly While emulating the network, one of the recorded values is picked randomly for each packet. This allows you to experience random values from the real network to predict more network scenarios.

Back to top

Packet effects

Emulate IP routing effects such as disruption of packet order (reordering), packet duplication, and fragmentation.

To configure packet effects:

  1. On the WAN page, go to the Packet Effects tab.

  2. Select the effects you want to emulate, and configure the associated parameters.

    Effect Details
    Out of Order

    To emulate packet reordering, NV can generate an out-of-order event by randomly removing a packet from the data stream, and then returning the removed packet after a random number of subsequent packets have entered.

    Configure the following parameters.

    • Chance: The probability that packet reordering occurs (from 1% to 50%).

    • Packet offset from original: The minimum and maximum number of packets (from 1 to 64) that may enter the data stream before the reordered packet is returned to the stream. A number (the offset) is picked randomly from the range specified by the minimum and maximum values, and the reordered packet is returned to the stream after that number of packets have entered.

      For example, if you indicate a minimum of 5 and a maximum of 10, the removed packet is returned randomly to the data stream after any number of packets between 5 and 10 have entered. To define a specific number as the offset, rather than a random number from within the range, enter the same value for both minimum and maximum.
    Duplicate Packets

    NV emulates duplication by copying a packet that it selects randomly. The number of copies created is picked randomly from a specified range.

    Configure the following parameters.

    • Chance: The probability that duplication occurs (from 1% to 99%).
    • No. of duplicated packets created: The minimum and maximum possible number of copies created for the duplicated packet. To define a specific number of copies, rather than a random number from within the range, enter the same value for both minimum and maximum.
    Fragmentation

    Emulates fragmentation of packets.

    Configure the following parameters.

    • Chance: The probability that fragmentation occurs (from 1% to 99%).
    • Maximum transmission unit: The maximum packet size (from 64 to 1460 bytes) that a gateway along the path route allows. Packets larger than this size are likely to be fragmented or discarded when a fragmentation event occurs.

    Whether or not a packet is eventually fragmented depends on the state of the Do Not Fragment (DF) bit in the packet's IP header and on the policy you select. If the DF flag is set to OFF, the packet is fragmented anyway. If the DF flag is set to ON, the policy you select applies.

    Select one of the following options to define a policy:

    • Ignore 'do not fragment' (df) bit: Fragment the packet.
    • Generate ICMP error message to source: Discard the packet and inform the packet's source, using an ICMP packet.
    • Do not generate ICMP error message to source: Discard the packet without informing the packet's source.

Back to top

Link faults

Link faults consist of effects caused by physical link malfunctions, specifically bit errors and disconnections. NV emulates bit errors by toggling bits at a given frequency. To achieve disconnection in the WAN Cloud, you can configure NV to stop responding for a given period.

To configure link faults:

  1. On the WAN page, go to the Link Faults tab.

  2. Select the effects you want to emulate, and configure the associated parameters.

    Effect Details
    Bit Error

    Emulates bit errors using bit toggling.

    Configure the following parameters.

    • Average error frequency: Bit toggling occurs every time the specified number of bits (on average) has crossed the WAN Cloud.
    • Number of toggled bits: The minimum and maximum possible number of toggled bits. The actual number of toggled bits is picked randomly from this range.
    Disconnect

    Emulates a physical disconnection of the network by dropping all packets that go through the WAN Cloud during a specified period.

    Configure the following parameters.

    • Average disconnection frequency: Disconnection occurs at intervals of the specified number of seconds (on average).
    • Disconnection time span: The minimum and maximum possible duration of the disconnection (in milliseconds). The actual duration of the disconnection is selected randomly from this range.
    Congestion

    Emulates a periodic and momentary rise in WAN Cloud traffic, which results in increased latency and packet loss.

    Note: The Latency and Packet Loss values during the congestion event override the original values (either manually defined or imported).

    Configure the following parameters.

    • Average congestion frequency: Congestion occurs at intervals of the specified number of seconds (on average).
    • Congestion time span: The minimum and maximum possible duration of the congestion (in milliseconds). The actual duration of the congestion is selected randomly from this range.

    • Congestion event properties:

      • Fixed Latency: The latency (in milliseconds) during the congestion period. During congestion, this value overrides the original latency setting.

      • Lose what percent of all packets: The percentage of packets to be lost during the congestion period. During congestion, this value overrides the original packet loss setting.

Back to top

See also: