 messages and further impact handover decisions. Target HO Function selects the target or a potential target for the handover. There is an MS-related context in the network or network-related context in the MS that needs to be either transferred and/or updated due to intra-NAP mobility. More specifically, the MS specific context in the context function associated with the serving or anchor handover function needs to be updated. Furthermore, the MS specific context in the context function associated with the serving handover function needs to be transferred to the context function associated with the target hand- over function. This will also require some network specific context in the MS to be updated. The WiMAX network architecture defines the primitives between peer context functions that are used to CHAPTER 2 WiMAX Network Architecture transfer MS specific context between a context function acting as context-server and a context function acting as context-client. The information transfer concerning a specific MS can be trig- gered to populate the context corresponding to the MS at the target base station, to inform the network regarding the idle mode behavior of the MS, and to inform the network of initial network entry of a specific MS. The context function can be further classified into Context-Server, i.e., the context function is the repository of the most updated session context information for the MS, Context-Client, i.e., the context function associated with the functional entity physical air interface link, and Relaying Context Function, i.e., the context function which relays information between the context server and the context client. 2.6.2 CSN-anchored Mobility The CSN-anchored mobility refers to mobility across different ASNs (see Figure 2-6) or alternatively to mobility across different IP subnets, and thereby requires network layer mobility management. The mobile IP protocols are used to manage mobility across IP subnets [29], and to enable CSN-anchored mobility. This section describes mobile 