port or can allow the use of enhanced features, it responds with a capability negotiation response message to inform the MS of its decision. The BS may also respond with a CAPABILITY_INDEX which is numerically different than that requested by the MS. The higher the numerical values of the CAPABILITY_INDEX parameter, the more enhanced features or higher protocol revisions are used. The CAPABILITY_INDEX values range from 0 to Nmax, where Nmax denotes the maximum value of the CAPABILITY_INDEX parameter. In the case of failure at any stages of operation, the MS and BS fall back to baseline capability and restart negotiations for a new Capability Class, if necessary [2]. If a privacy key management function is enabled, the BS and MS perform authorization and key exchange procedures. The security procedures provide the users with privacy, authentication, and confidentiality over the air interface. This is done by applying cryptographic transforms to MAC PDUs carried across connections between the MS and BS. Registration is the process by which the MS is granted entry to the network and a managed MS (see Chapter 3 for more information) receives its Secondary Management CID, and thus becomes manageable. To register with a BS, the MS sends a registration request message to the BS. The BS responds with a registration response message that includes the secondary management CID for a managed MS. In IEEE 802.16m, the BS will allocate and transfer a Station Identifier (STID) to the MS through an encrypted registration response message (if management message encryption is supported) and the temporary STID, which was allocated during initial ranging procedure, is discarded. In IEEE 802.16m on successful registration with the BS, downlink and uplink Flow Identifiers (FID) are assigned to the MS without using the dynamic service allocation procedure, in order to activate one pre-provisioned service flow for each downlink and uplink FID which can be used for upper layer signaling (e.g., DHCP). Note that the 16-bit legacy CID has be