t. The values of these parameters stay fixed during the compression process. Those compression parameters are as follows [10]: L: in U-mode and O-mode the ROHC compressor uses a confidence variable L in order to ensure the correct transmission of header information. Timer_1 (IR_TIMEOUT): in U-mode, the compressor uses this timer to return to the IR compression level and periodically resends static information. Timer_2 (FO_TIMEOUT): the compressor also uses another timer in U-mode; this timer is used to go downward to FO compression level if the compressor is working in SO compression level. Sliding Window Width (SWW): the compressor, while compressing header fields like Sequence Number (SN) and Timestamp, uses Window-based Least Significant Bit (W_LSB) encoding that uses a Sliding Window of width equal to SWW. W_LSB encoding is used to compress those header fields whose change pattern is known. When using this encoding, the compressor sends only the least significant bits. The decompressor uses these bits to construct the original value of the encoding fields. k and n: the ROHC decompressor uses a "k out of n" failure rule, where k is the number of packets received with an error in the last n transmitted packets. This rule is used in the state machine of the decompressor to assume the damage of context and move downwards to a state after sending a negative acknowledgment to the compressor, if a bi-directional link is used. The decompressor does not assume context corruption and remains in the current state until k packets arrive with error in the last n packets. 5.2 SERVICE FLOW CLASSIFICATION AND IDENTIFICATION A service flow is a uni-directional flow of packets with a particular set of QoS parameters and is identified by a Service Flow Identifier (SFID). The QoS parameters may include traffic priority, maximum sustained traffic rate, maximum burst rate, minimum tolerable rate, scheduling type, ARQ type, maximum delay, tolerated jitter, service data unit type and size, bandwidth request mechanism to be used, tra