r and a number of flow identifiers associated with the active connections with the mobile station. Despite the fact that the most significant bits of CID remained unchanged for the active connections between the BS and the MS in the legacy standard, the entire CID was communicated through MAC headers and messages over the airlink, resulting in inefficient use of radio resources. In IEEE 802.16m, the CID has been split into STID and FID, and only the flow identifiers are signaled over the air interface once the connections are established. 5.3 PACKET CONVERGENCE SUB-LAYER The packet CS is a variant of the convergence sub-layer that interfaces the IP network with the IEEE 802.16m MAC CPS. The packet CS performs the following functions by utilizing the services of the MAC layer: Classification of the higher layer PDUs into the appropriate transport connections; Payload header compression; Delivery of the CS PDUs to the MAC SAP for transport to the peer MAC SAP at the receive side; Receipt of the CS SDU from the peer MAC SAP; Rebuilding of any compressed payload header information. The CS on the transmitter side is responsible for delivering the MAC SDUs (or alternatively CS PDUs) to the MAC SAP. The MAC is responsible for delivery of the MAC SDUs to peer MAC SAP in accordance with the QoS, fragmentation, concatenation, and other transport functions associated with the connection's service flow characteristics. The receiving CS is responsible for accepting the MAC PDUs (or alternatively CS SDUs) from the peer MAC SAP and delivering them to the higher layer entity. 5.3 Packet convergence sub-layer 5.3.1 Packet CS Payload Header Suppression The IEEE 802.16-2009 standard convergence sub-layer specifies a native Payload Header Suppression (PHS) scheme which can be optionally used to compress the IP/UDP/RTP payload headers [1]. A comparison of the performance and robustness of the native PHS algorithm and standard ROHC confirms the superiority of the latter. It is expected that all IEEE 802. 16m implementations will utili