Achieving IP mobility allows a Mobile Node (MN) to move between different subnets without changing its permanent IP address or dropping active connections. In standard IP routing, addresses represent fixed physical locations, so when a device moves to a new network, its IP becomes technically invalid.
To solve this, Mobile IP (MIP) introduces a framework using specific agents and addresses to ensure seamless communication.
1. Key Components of IP Mobility IP mobility is achieved through the interaction of three main entities:
• Home Agent (HA): A router in the MN’s original "home" network that keeps track of the MN’s current location and tunnels packets to it.
• Foreign Agent (FA): A router in the "visited" network that assists the MN by providing a temporary point of contact.
• Care-of Address (COA): A temporary IP address that reflects the MN's current physical location in the foreign network.
2. The Mobility Process Achieving mobility involves four critical steps:
A. Agent Discovery
The MN must first determine if it is at home or in a foreign network.
• Agent Advertisement: Agents periodically broadcast "beacons" to announce their presence.
• Agent Solicitation: If the MN doesn't hear a beacon, it can actively send a request to find an available agent.
B. Registration Once the MN moves and acquires a COA, it must inform its Home Agent.
• The MN sends a Registration Request to the HA (often via the FA).
• The HA updates its Mobility Binding table, mapping the MN's permanent IP to its current temporary COA.
C. Tunneling and Encapsulation To deliver data to the MN at its new location, the HA uses a "virtual pipe" called a tunnel.
• Encapsulation: When a packet arrives at the home network, the HA wraps it in a new IP header.
• The new header uses the HA's address as the source and the COA as the destination.
• Decapsulation: The tunnel endpoint (either the FA or the MN itself) strips the outer header and delivers the original packet.
D. Routing Efficiency
• Triangular Routing: Standard Mobile IP follows a path from the Correspondent Node (CN) → HA → MN.
• Direct Delivery: In the reverse direction, the MN typically sends packets directly to the CN using standard IP routing to maintain efficiency.
3. Mobility in Modern Networks (IPv6) In IPv6, mobility is simplified because many of these features are built-in:
• No Foreign Agent Needed: Every node can generate its own COA using auto-configuration.
• Route Optimization: IPv6 allows the MN to inform the CN of its new location directly, eliminating the need for data to pass through the Home Agent and reducing latency.
IPv6, also referred to as IPng (IP next generation), was developed to extensively modify the IP protocol to accommodate the massive growth and modern demands of the internet. It overcomes the primary drawback of IPv4, which is address exhaustion.
Key Advantages of IPv6
• Larger Address Space: Provides a vastly increased number of available IP addresses compared to IPv4.
• Better Header Format: Uses a streamlined header designed for more efficient processing by routers.
• New Options and Extensions: Allows for new features and future protocol extensions without breaking existing infrastructure.
• Support for Resource Allocation: Includes mechanisms to better handle quality of service (QoS) for different types of traffic.
• Support for More Security: Security features are integrated more deeply into the protocol architecture.
IPv6 Features for Mobility IPv6 simplifies mobility management compared to standard Mobile IPv4 by incorporating several advanced features directly into the protocol:
• Secured Registration: No special external mechanisms are required for securing IP registration processes.
• Address Auto-configuration: Every IPv6 node can generate its own address automatically, reducing dependence on DHCP.
• Neighbor Discovery: Integrated mechanisms for nodes to discover other nodes on the same link.
• Direct Binding Updates: Every IPv6 node can send binding updates to another node, which helps in optimizing communication paths.
• Soft Handover and Decapsulation: Mobile Nodes (MN) can decapsulate packets themselves, and soft handovers are possible to ensure continuous connectivity.
MIPv6 (Mobile IPv6) MIPv6 is a subset of the IPv6 protocol suite designed specifically to support mobility. It is an update of the Mobile IP standard that allows mobile devices to be authenticated and maintain connectivity while moving between different networks using their IPv6 addresses.
Limitations Despite its advancements, IPv6 does not inherently solve all firewall or privacy problems related to network communication.
The Need for Micro Mobility Standard Mobile IP (MIP) is primarily designed for macro mobility, which involves relatively slow-moving hosts shifting between distant networks. It lacks sufficient support for fast handoff control and paging.
The fundamental needs for Micro Mobility mechanisms are: • Reduced Signaling Overhead: To keep frequent updates caused by local changes (switching points of attachment within the same domain) away from the Home Network (HN).
• Improved Performance: To inform the Home Agent (HA) only about major movements, thereby reducing latency and network load during local transitions.
• Support for Highly Mobile Hosts: Providing robust connectivity for devices that move quickly across small cell areas.
Cellular IP (CIP) Cellular IP is a specialized micro-mobility protocol that complements Mobile IP by providing local mobility support for highly mobile hosts.
1. Core Concept CIP is designed to be a simple and flexible protocol that separates idle hosts from active hosts. This allows the network to efficiently manage a large number of users without overloading resources.
2. Architecture The architecture of a Cellular IP network consists of three major components:
• Gateway (GW): Acts as the bridge between the Cellular IP access network and the global Internet (Standard Mobile IP). It serves as the point where macro mobility ends and micro mobility begins.
• Base Station (BS): These are the points of attachment for mobile devices. They are responsible for routing data packets and managing local radio resources.
• Mobile Host (MH): The user device that moves within the Cellular IP domain.
3. Functional Mechanisms
Cellular IP manages mobility through three primary functions:
• Routing: CIP uses specialized routing tables that are updated dynamically as the Mobile Host sends packets. Unlike traditional IP, it maintains paths at the host level rather than the network level.
• Paging: To save battery and reduce signaling, idle hosts do not update their location constantly. The network uses a paging mechanism to "search" for an MH only when an incoming packet needs to be delivered.
• Handover: CIP supports local handoff/mobility between Base Stations within the same wireless access network. This ensures that as a user moves from one BTS to another, the connection remains stable without needing to involve the Home Agent in the distant home network.
HAWAII is a micro-mobility scheme designed to handle local movements within a specific domain efficiently.
HMIPv6 is an enhancement of Mobile IPv6 (MIPv6) that introduces a hierarchy to the mobility management process.