h are typically vendor specific. The ASN-GW is a logical entity that represents an aggregation of control functions that are either paired with a corresponding function in the ASN (e.g., BS instance), a resident function in the CSN, or a function in another ASN. The ASN-GW may also perform bearer-plane routing or bridging func- tions. A BS is associated with a default ASN-GW; however, the ASN-GW functions may be distributed among multiple ASN-GWs located in one or more ASNs. The ASN functions in an ASN-GW can be divided into two groups, i.e., the Decision Point (DP) and the Enforcement Point (EP) functions. The EP category includes bearer-plane functions and the DP category includes non-bearer-plane functions. If such functional split is implemented in ASN-GW, the EP and DP functional groups would include bearer-plane and non-bearer-plane functions, respectively, and are interfaced using R7 reference point. 2.2.3 Reference Points A Reference Point (RP) is a logical interface between two groups of functions or protocols. All protocols associated with a reference point may not always terminate in the same functional entity, i.e., two protocols associated with an RP originate and terminate in different functional entities [5]. A reference point only becomes a physical interface when the functional entities on either side of it are contained in different physical modules. 2.2 Network reference model Reference Point R1 Reference point R1 consists of the protocols and procedures over the air interface between MS and ASN as specified by the IEEE 802.16-2009 standard [12] and mobile WiMAX system profile [11]. The reference point R1 further includes additional protocols related to the management plane. Reference Point R2 The logical reference point R2, i.e., no direct protocol interface between MS and CSN, consists of protocols and procedures between the MS and CSN associated with authentication, authorization, and IP host configuration management. The authentication protocols in reference point R2 work between the MS and