Summary:
Using Loopback mode for TotalRoam adapters will result in higher data usage. For adapters associated with wireless services, using Loopback mode without proper precautions can cause data usage to exceed the service plan limit.
Symptoms:
Wireless data plan usage limits are exceeded when using Loopback mode in TotalRoam for the network adapter associated with the wireless service.
Cause:
Most modems for wireless networks like CDMA and GPRS enter a dormant state if no traffic is transmitted for a certain amount of time. The amount of time required before a modem enters a dormant state varies among service providers. Once a modem enters a dormant state, it will not receive any data until the modem is taken out of dormant state, typically the next time it transmits data. Using Loopback mode in TotalRoam prevents a modem from entering a dormant state by regularly transmitting a loopback packet to the Gateway. Upon receiving the loopback packet, the Gateway responds with an acknowledgement packet of equal size. This loopback traffic however is counted as data against the wireless service plan by wireless service providers. If TotalRoam is configured to send loopback packets frequently, the associated data traffic can exceed the amount allowed by limited usage plans.
Loopback packets and the loopback acknowledgement are both 69 bytes. The total amount of traffic consumed by loopback packets then can easily be computed based upon the Status Check Interval for the network adapter using the following formula:
Bytes = (69 * 2) * Duration / StatusCheckInterval
Where:
Bytes = total number of bytes transmitted and received
Duration = length of usage period (in seconds)
StatusCheckInterval = value of Status Check Interval (in seconds)
For example, during 8 hours of usage with a 6 second check interval, the amount of traffic generated by loopback packets would be ((69 * 2) * 28800 / 6), or approximately 662 KB.
Resolution:
If a limited plan must be used and loopback packets are needed to keep a modem from entering a dormant state, care should be taken to tune the Status Check Interval for the corresponding network adapter. The Status Check Interval should be set to a level that is (1) below the time that the service provider uses to put modems into a dormant state and (2) results in an amount of loopback packet traffic that when combined with the average client traffic will not exceed the plan amount.
Applies To:
Any subscribed wireless network
Product Version:
All Versions
Platform
All Platforms
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