Hierarchical Mobile IP

 

Introduction:

The Hierarchical Mobile IP (HMIP) protocol handles Mobile IP registration locally using a hierarchy of foreign agents. In HMIP, registration messages are sent by the MNs to update their respective location information. A hierarchical solution is more appropriate to the Internet as it differentiates local mobility from global mobility. The Hierarchical Mobile IP protocol employs a hierarchy of FAs to locally handle Mobile IP registration. Typically, one level of hierarchy is considered where all foreign agents are connected to the gateway foreign agent (GFA). Figure 2 explains the architecture of Hierarchical Mobile IP.

 

Mobile IP:

Mobile IP is a powerful protocol that supports Internet mobility. Micro-mobility approach was introduced because Mobile IP suffers in case of frequent movement, i.e., intra-domain mobility. Micro-mobility protocols aim to handle local movement of Mobile Nodes (MNs) without interaction with the Home Agent (HA) through the Internet. This has the benefit of reducing delay and packet loss during handoff and eliminating registration between MN and possibly distant Home Agents (HA) when MN remain inside their local coverage areas.

Hierarchical Mobile IP:

The Hierarchical Mobile IP (HMIP) protocol handles Mobile IP registration locally using a hierarchy of foreign agents. In HMIP, registration messages are sent by the MNs to update their respective location information. This registration messages will establish tunnels between neighboring foreign agents along the path from the mobile node to a gateway foreign agent (GFA).

As introducing hierarchies is the natural choice for handling micro-mobility issues, several proposals for a ‘hierarchical’ mobile IP exist. HMIPv6 provides micro-mobility support by installing a mobility anchor point (MAP), which is responsible for a certain domain and acts as a local HA within this domain for visiting MNs (see Figure).

 

About HMIP:

The MAP receives all packets on behalf of the MN, encapsulates and forwards them directly to the MN’s current address (link COA, LCOA). As long as an MN stays within the domain of a MAP, the globally visible COA (regional COA, RCOA) does not change. A MAP domain’s boundaries are defined by the access routers (AR) advertising the MAP information to the attached MNs. A MAP assists with local handovers and maps RCOA to LCOA. MNs register their RCOA with the HA using a binding update.

Figure 3: HMIP

When a MN moves locally it must only register its new LCOA with its MAP. The RCOA stays unchanged. To support smooth handovers between MAP domains, an MN can send a binding update to its former MAP. It should be mentioned as a security benefit that mobile nodes can be provided with some kind of limited location privacy because LCOAs on lower levels of the mobility hierarchy can be hidden from the outside world. However, this applies only to micro mobility, that is, as long as the mobile node rests in the same domain.

A MN can also send a binding update to a CN who shares the same link. This reveals its location but optimizes packet flow (direct routing without going through the MAP). MNs can use their RCOA as source address. The extended mode of HMIP supports both mobile nodes and mobile networks.

 

HMIP regional registration:

Operation of Hierarchical Mobile IP shows the difference between normal and regional registration. It can be seen that the first have to traverse the whole of the network fabric to the HA while the others have to reach a local entity, termed in the figure as Gateway Foreign Agent (GFA). For the purposes of managing hierarchical tunnelling the location register is maintained in a distributed form by a set of Mobility Agents (MA), i.e. GFAs, RFAs, in the access network. Each MA reads the original destination address of the incoming packets and searches its visitor list for a corresponding entry.

 

HMIP architecture:

The main driving factors behind the three architectures presented here are efficiency, scalability, and seamless handover support. However, as security will be one of the key success factors of future mobile IP networks, first approaches adding this feature exist.

The extension of the current Hierarchical Mobile IP implementation is needed to investigate complex communication infrastructures for cellular and IP based wireless networks. Therefore, Hierarchical Mobile IP is a most appropriate micro-mobility protocol which can be used and simulated with the network simulator (ns-2). The extensions of the Columbia IP Micro-mobility Suite (CIMS) described in this paper are the source for complex Hierarchical Mobile IP investigations.

 

Figure 4: HMIP architecture

Advantages & Disadvantages:

Advantages

•      Security: MNs can have (limited) location privacy because LCOAs can be hidden.

•      Efficiency: Direct routing between CNs sharing the same link is possible

Disadvantages

•      Transparency: Additional infrastructure component (MAP).

•      Security: Routing tables are changed based on messages sent by mobile nodes. This requires strong authentication and protection against denial-of-service attacks. Additional security functions might be necessary in MAPs

 

Conclusion:

HMIP is considered as an appropriate protocol for micro mobility because it differentiates between local mobility management scheme and global mobility management scheme. To demonstrate the performance, we use a set of simulation developed under CIMS ns-2 extension that supports programming models for HMIP. Simulation was performed for typical Mobile IP and Hierarchical Mobile IP and the scenario was observed and analyzed. Our main focus was to determine packet losses, end-to-end delay, handoff latency and signaling load for both MIP and HMIP.