Appendix A: Detecting Slow Network Connections

Algorithm Used by Group Policy to Detect Slow Network Links Group Policy can detect a slow network connection by using an algorithm. The algorithm that Group Policy uses to determine whether a link should be considered slow is as follows: 1. The client computer that is attempting to process Group Policy sends a zero byte file to the authenticating domain controller, or server, which then returns the file to the client. The client measures the time that it takes for the file to complete the roundtrip, and if it is less than ten milliseconds, the client assumes a fast. | Appendix A Detecting Slow Network Connections Algorithm Used by Group Policy to Detect Slow Network Links Group Policy can detect a slow network connection by using an algorithm. The algorithm that Group Policy uses to determine whether a link should be considered slow is as follows 1. The client computer that is attempting to process Group Policy sends a zero byte file to the authenticating domain controller or server which then returns the file to the client. The client measures the time that it takes for the file to complete the roundtrip and if it is less than ten milliseconds the client assumes a fast link is present and sets the fast-link flag. 2. If the roundtrip time in step 1 is more than 10 milliseconds the client saves the roundtrip time. Name this value time_1. 3. Next the client sends a compressed file that is two kilobytes KB in size to the server which then returns the file to the client. The client again measures the time that it takes the file to complete the roundtrip. Name this value time_2. Note The file that is sent to the server in this step is actually a JPEG file. JPEG files are compressed by definition. A compressed file is used because data that is sent through a modem is frequently compressed and compressing the file makes the link appear faster than it really is. 4. The client repeats step 3 two more times. Name these values time_3 and time_4. 5. Next the client subtracts the value for time_1 from time_2 time_3 and time_4. This is done to remove the overhead caused by session setup. Name these values delta_1 delta_2 and delta_3. 6. The average of the values for delta_1 delta_2 and delta_3 is calculated. Name this value avg. 7. Finally the connection speed is calculated as the units are shown for clarity Connection Speed kilobits second 2 2 KB 8 bits byte 1 000 milliseconds second avg milliseconds Because 2 KB of data move through each modem Ethernet card or other device in the link once in each direction a total of 4 KB or two times the