## 2 Related Work
Once the MN knows that IP layer mobility has taken place, it forms a new CoA by using the prefix advertised on the new link and again sends a BU to its HA. HMIPv6 adds another level on MIPv6 and separates global mobility from local mobility. HMIPv6 was designed so that the MNs can move within a particular domain without having to update their HA or Correspondent Nodes (CNs) when every time they move. It introduces a new entity called Mobile Anchor Point (MAP) which acts as a local HA of the MNs [4]. When a MN moves into a new MAP domain, it configures two CoA: a Regional CoA (RCoA) on the MAPs link and On-Link CoA (LCoA). It then sends a local BU to the MAP. Following a successful registration with the MAP, a bidirectional tunnel between the MN and the MAP is established. All packets sent by the MN are tunneled to the MAP and vice versa. It should be noted that every time the MN moves within the network, it acquires a new LCoA and sends a local BU to the MAP. However, the RCoA remains unchanged. FMIPv6 is another enhancement of MIPv6 that aims to reduce the handoff delays for mobile connections. It is designed to allow MNs to anticipate their IP layer mobility. In other words, the MNs can discover the new router prefix before being disconnected from the current router. However, as discussed before, the host based mobility protocols involve most of the signaling on the MN's end. This signaling overhead is not appropriate for 6 LoWPAN nodes. These protocols are also network layer solutions that provide mobility-related features at the IP layer. Thus mobility-related signaling packets are carried by IP traffic. However, this solution proves to be expensive if they are directly implemented in 6 LoWPAN that supports MNs. Moreover, these protocols demand a complex host stack which is not feasible for 6 LoWPAN. Additionally, they assume the anchor points of the MN are always available and do not need to go to sleep state. Also, from the security point of view the changes in the temporary local address mean that the MN exposes its topological location to eavesdroppers. The other host based mobility protocols are HAWAII [7] and Cellular IP [5]. In order to forward MN's packets, these protocols involve establishment of host specific routes in the routers. The creation of host-specific routes is initiated and updated by the MNs. Thus these protocols require an active participation from the MNs that can negatively impact MN's lifetime. Also, in HAWAII, when the routers within the domain receive a packet from another MN; then they forward the packets to a router, named as \"the Domain Route Router\". This limits the scope of route optimization even if when the corresponding MNs are near to each other. In the network based localized mobility schemes like PMIPv6 [9], proposed by IETF, the network side performs the mobility-related signaling on behalf of the MN. PMIPv6 introduces several new entities like Localized Mobility Anchors (LMA) and MAG. The mobility entities in the network will track the MN's movements, initiate the mobility signaling and set up the required routing state [9]. However, more specifically, MAG is responsible for tracking the MN's movements to and from the access link and for signaling the MN's LMA [9]. PMIPv6 has several advantages over the host based mobility protocols, thus making it better candidate for 6 LoWPAN mobility management. Firstly, PMIPv6 can be compatible with any global mobility management protocols that are not MIPv6, such as Host Identity Protocol (HIP), IKEv2 Mobility, and Multihoming (MOBIKE) [13]. While it is possible that existing localized mobility management protocols could be used with HIP and MOBIKE, some would require additional efforts to implement, deploy, or even in some cases specify in a non-Mobile IPv6 mobile environment [13]. Also, in PMIPv6, the MN does not need to incorporate any changes in the stack.