HP XP20000/XP24000 HP StorageWorks MPX200 Multifunction Router User Guide (569 - Page 134

Modifying the window size and scaling factor The MPX200 window size can be set to a maximum of 32 KB. The scaling factor is used as a multiplier to increase the window size above 32 KB. Modify the window size and scaling factor in the MPX200 Multifunction Router pairs based on the WAN RTT and link speed. To determine the appropriate window size setting and scaling factor, use the pre-populated tables or the following formula. If the recommended TCP window size and scale factor for a given RTT and WAN link speed is not shown in Table 19 through Table 25, use the formula: (RTT (ms) x link rate (Kb/s) x (1 byte/8 bits)) = minimum window size (MWS). Then, convert the MWS to a recommended scale factor by dividing it by the default window size (32,768 bytes). Use Table 18 to determine the scale factor. Table 18 TCP window size scale factors MVS scale result 0 to 2 Scale factor 0 2 to 4 1 4 to 8 2 8 to 16 3 16 to 32 4 32 to 64 5 64 to 128 6 128 to 256 7 256 to 512 8 512 or greater 9 TCP window size and scaling factor recommendations Table 19 through Table 25 provide TCP window size and scaling factor settings for specific WAN environments. These tables are organized by typical link speed. NOTE: The TCP window size recommendations listed in Table 19 through Table 25 are based on low-loss networks (0.0012% average packet-loss ratio over 24 hours). For higher-loss, longer-latency networks, you should reduce the recommended window size and scaling factor by one setting to compensate for the increased number of packet retransmissions. Table 19 T1/DS-1 1.554 Mb/Sec (Bandwidth = 1 Mb) Round trip time (RTT) in ms 250 Window size (bytes) 64K Scaling factor (2n) 1 134 MPX200 FCIP