| < Day Day Up > |
|
In ATM, no framing is imposed and a continuous stream of cells is transmitted. Hence synchronization is required—the receiver has to know where the cell starts. Header error control (HEC) field provides synchronization. A cell delineation algorithm is required to detect the boundaries of the cells. The algorithm is as follows: match the received HEC with the calculated HEC with an assumed cell structure. The cell delineation algorithm is successful if HEC matches x times consecutively, and it is lost if HEC mismatches y times continuously. The values of x and y are design parameters between 5 and 10. Note that greater x implies longer delay in synchronization but robustness against false delineation; greater y implies longer delay in recognizing a misalignment but robustness against false misalignment.
In an ATM network, the cells are transmitted as a stream. Hence, each switch has to identify the beginning of each cell. This is done through the cell delineation algorithm.
| < Day Day Up > |
|