Section: 6.6.4.1 COUNT-C
Content: The ciphering sequence number COUNT-C is 32 bits long. There is one COUNT-C value per up-link radio bearer and one COUNT-C value per down-link radio bearer using RLC AM or RLC UM. For all transparent mode RLC radio bearers of the same CN domain COUNT-C is the same, and COUNT-C is also the same for uplink and downlink. COUNT-C is composed of two parts: a "short" sequence number and a "long" sequence number. The "short" sequence number forms the least significant bits of COUNT-C while the "long" sequence number forms the most significant bits of COUNT-C. The update of COUNT-C depends on the transmission mode as described below (see figure 16c). Figure 16c: The structure of COUNT-C for all transmission modes - For RLC TM on DCH, the "short" sequence number is the 8-bit connection frame number CFN of COUNT-C. It is independently maintained in the ME MAC-d entity and the SRNC MAC-d entity. The "long" sequence number is the 24-bit MAC-d HFN, which is incremented at each CFN cycle. - For RLC UM mode, the "short" sequence number is the 7-bit RLC sequence number (RLC SN) and this is part of the RLC UM PDU header. The "long" sequence number is the 25-bit RLC UM HFN which is incremented at each RLC SN cycle. - For RLC AM mode, the "short" sequence number is the 12-bit RLC sequence number (RLC SN) and this is part of the RLC AM PDU header. The "long" sequence number is the 20-bit RLC AM HFN which is incremented at each RLC SN cycle. The hyperframe number HFN is initialised by means of the parameter START, which is described in section 6.4.8. The ME and the RNC then initialise the 20 most significant bits of the RLC AM HFN, RLC UM HFN and MAC-d HFN to START. The remaining bits of the RLC AM HFN, RLC UM HFN and MAC-d HFN are initialised to zero. When a new radio bearer is created during a RRC connection in ciphered mode, the HFN is initialised by the current START value (see section 6.4.8).