Connection Analysis

Although the speed achieved may match expectation for the connection, a low data flow QoS score means that the data flow between the server and the workstation was not consistent. There can be several reasons for this such as data congestion along the route or data loss which invokes recovery. The lower the QoS percentage, the more erratic the data flow. Many applications can be severely affected by poor data flow quality regardless of data throughput speed, for example media applications such as video or voice may become jerky. Voice (VoIP) telephony will become garbled. If you suspect that the connection was in use by another application try running the test again to validate if the problem is persistent.

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The test recorded a TCP maximum delay that exceeded the natural TCP forced idle delay as a result of the connection's trip time. This indicates that there may be problems with consistent data flow between the server and the client. A poor data flow QoS reading is also likely if the max TCP delay is much higher in comparisons to the trip time. Common reasons for this type of problem are packet loss and duplicates. The test graph view will show the TCP delay over the time of the test. Height and width of the 'orange' delay line shows the delay consistency.

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Retransmit Timeouts cause major problems for applications and should always be zero for a quality connection. A timeout is a packet level alarm that occurs when the sending TCP (download data) has not had confirmation that the sent packet(s) have been received.

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Packets Retransmitted reports the number of packets that have been resent from the sending end. It does necessarily mean that the retransmit was caused by a timeout (which is the worst type of retransmit, see Retransmit Timeout) it can also be a fast retransmit. Both signify a quality problem on the connection, retransmits occur if packets are lost or late and consume bandwidth slowing application performance. Imagine a phone call where the line quality was so bad that you keep asking the other party to repeat what they just said. This will cause the call to take much longer to complete as a result of all the retransmitted information.

Bytes Retransmitted reports the quantity of bytes that have been resent by the sender. It does necessarily mean that the retransmit was a timeout it can also be a fast retransmit. Retransmits occur if packets are lost or late which can include acknowledgement packets. Imagine a phone call where the line quality was so bad that you keep asking the other party to repeat what they just said. This will cause the call to take much longer to complete as a result of all the retransmitted information.

Packets not in order cause a problems because TCP data must be processed in order. It could be that the missing packet contains the decimal point for your pay packet! Or it is a frame in movie that you are watching. As soon as data is out of order all packets that follow the missing data can no longer be processed until the missing data is recovered.

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Packets outside TCP Window occur when a connection has very erratic latency, meaning packets take wildly different lengths of time to travel to the destination or the acknowledgements take varying times to return then TCP can retransmit data that arrives outside the buffer space for the current TCP window.

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Duplicate Packets report all packets that have arrived more than once. Duplicate packets cause a performance problem. First they reduce throughput speed by stealing bandwidth from valid packets needed by the application (duplicates have to be thrown away). Second they create a hole in the data which increases latency for the valid data.

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Bytes lost report packets that are missing resulting in all the following packets being out-of-order. This obviously causes a problem because TCP data must be processed in order. For example it could be that the missing packet contains the decimal point for your pay packet! Or it is a frame in a movie that you are watching. As soon as data is out of order all packets that follow the missing data can no longer be processed until the missing data is recovered.

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