Physical vs. Logical Byte Display

The Event Display window and Event Pane in the Frame Display window show the physical bytes. In other words, they show the actual data as it appeared on the circuit. The Radix, Binary and Character panes in the Frame Display window show the logical data, or the resulting byte values after escape codes or other character altering codes have been applied (a process called frame transformationFrame transformation is the process of adding, removing or altering the physical bytes in a frame as necessary to get the frame into a state where it can be decoded. For example, in Async PPP, frame transformation removes escape characters and alters the next byte appropriately. In frames carrying Van Jacobsen Compression (VJC), frame transformation reconstructs the IP header so that it may be decoded properly. The end result of frame transformation is the logical frame.).

As an example, bytes with a value of less than 0x20 (the 0x indicates a hexadecimal value) cannot be transmitted in Async PPP. To get around this, a 0x7d is transmitted before the byte. The 0x7d says to take the next byte and subtract 0x20 to obtain the true value. In this situation, the Event pane displays 0x7d 0x23, while the Radix pane displays 0x03.