Praise for Fundamentals of WiMAX

356 Chapter 10 • WiMAX Network Architectureeither only during HO periods or always. Another method to achieve data integrity, applicableonly for downstream traffic, is multicasting at the anchor DPF to the serving DPF and one ormore target DPFs. Synchronization of data packets during HO may be achieved by usingsequence numbers attached to the MSDU in the ASN data path. Alternatively, the anchor DPFcan buffer the data during HO; when a final target BS is identified, the serving BS may be askedto return to the anchor DPF all unsent packets and to the target BS all unacknowledged packets.10.8.2 CSN-Anchored Mobility for IPv4CSN-anchored mobility refers to mobility across different ASNs, in particular across multipleforeign agents. For Release 1, the WiMAX specifications limit CSN anchored mobility tobetween FAs belonging to the same NAP. CSN-anchored mobility involves mobility across differentIP subnets and therefore requires IP-layer mobility management. As discussed in Chapter 7,mobile IP (MIP) is the IETF protocol for managing mobility across IP subnets. Mobile IP is usedin WiMAX networks to enable CSN-anchored mobility.The WiMAX network defines two types of MIP implementations for supporting CSNanchored mobility. The first one is based on having a MIP client (MN) at the MS, and the otheris based on having a proxy MIP in the network that implements the MN in the ASN on behalf ofthe MS. With proxy MIP, IP mobility is transparent to the MS, which then needs only a simpleIP stack. Coexistence of proxy MIP and client MIP in a network is also supported. When bothare supported in the network, the MS should support either mobile IP with client MIP or regularIP with proxy MIP.10.8.2.1 Client MIP-Based R3 Mobility ManagementHere, the MS has a MIP-enabled client that is compliant with the IETF mobile IP standard (RFC3334). The client in this case gets a CoA from an FA within the ASN. As the client moves acrossFA boundaries, the client becomes aware of the movement via agent advertisements, does a MIPregistration with the new FA, and gets a new CoA from it.Figure 10.11 shows the network elements and protocol stacks involved when using a clientMIP implementation. The MS gets its HoA from the HA in the CSN of the home NSP or the visitedNSP. In case the HA is assigned in the visited CSN, MIP authentication occurs between thevisited HA and the home AAA, with the security exchanges being transparent to the visitedAAA server. On the other hand, when the HA is assigned by the home CSN, both the HAaddress and, optionally, the DHCP server address or the MS home address are appended to theAAA reply of the home AAA server.In addition to RFC 3344, client MIP is also expected to support several MIP extensions inWiMAX networks. These include reverse tunneling, based on RFC 3024; FA challenge/response, based on RFC 3012; NAI extensions based on RFC 2794; and mobile IP vendor-specificextensions, based on RFC 3115.