Problems In Basic Mobile Ip Computer Science

Essay add: 28-10-2015, 16:44   /   Views: 149

"This paper describes a separate local and wide area mobility for the performance of existing mobile host protocols can be considerably enhanced. Here Cellular IP concept is proposed which is a lightweight and robust protocol that is optimized to support local mobility but efficiently interworks with Mobile IP to provide wide area mobility support. Cellular IP provides advantage in comparison with the mobile IP where mobile nodes used to migrate frequently its access, which will be the rule rather than the exception as Internet wireless access becomes ever-present. Cellular IP maintains distributed cache for location management and routing purposes. Distributed paging cache maintains the position of 'idle' mobile nodes in a service area. Cellular IP uses this paging cache to quickly and efficiently pinpoint 'idle' mobile hosts that wish to engage in 'active' communications. This approach is beneficial because it can accommodate a large number of users attached to the network without overloading the location management system. Distributed routing cache maintains the position of active mobile hosts in the service area and refreshes the routing state of mobile in response to the handoff of active mobile hosts."

Introduction to the Mobile IP:

Mobile IP is an Internet Engineering Task Force standard protocol which allows the mobile equipment to move from one network to another network without changing the permanent IP address. Each mobile will be identified by its own home address irrespective of the mobile location. Two kinds of entities contain in the Mobile IP implementation. They are Home Agent and Foreign Agent.

Home Agent has information about mobiles permanent address and Foreign Agent has information about mobiles which are visiting its network along with their care-of-address. Basically mobile IP specifies how mobile registers with its home agent and how the home agent routes data to the mobile through tunnel. Mobile IP provides an efficient, scalable mechanism for roaming within the Internet. By using this technology mobile may change their point-of-attachment to the Internet without changing their home IP address. This allows them to maintain its connectivity during roaming.

When a node wants to communicate to the mobile it uses the permanent address of the mobile as the destination address to send the packets which means directly it routes the packets to the home agent and then home agent redirects these packets towards the foreign agent through an IP tunnel by encapsulating the data with a new IP header using the care of address of the mobile node.

When mobile wants to send a data, it sends packets directly to the other communicating node through the foreign agent directly by using its permanent home address as the source address for the IP packets. This is known as triangular routing. If needed, the foreign agent could employ reverse tunneling by tunneling the mobile's packets to the home agent, which in turn forwards them to the communicating node. This is needed in networks whose gateway routers have ingress filtering enabled and hence the source IP address of the mobile host would need to belong to the subnet of the foreign network or else the packets will be discarded by the router.


The process of encapsulating an IP packet within another IP packet for the purpose of routing it to a location other than the one specified in the original destination field. Specifically, when a packet is received by the home agent, it encapsulates the original packet inside a new packet, placing the mobile node's care-of address in the new destination address field before forwarding it to the appropriate router. The path that is followed by this new packet is called the tunnel.

Figure 1 -A mobile node with a foreign agent care-of-address

Home agents and foreign agents are used to broadcast their interest to act as Mobile IP routers through agent advertisements. If a mobile node needs to know immediately the address of a potential agent without waiting for the next advertisement, it can broadcast an agent solicitation message. The mobile node uses these advertisements to determine if it has moved to a new location and where it can attach to a network if it has. If it finds that it is attached with its own home network, no changes takes place. If the mobile node determines that it is on a foreign network, it gets care-of address from the foreign agent. Figure 1 depicts how foreign agent care-of-address obtained. When using a foreign agent care-of address the mobile node registers the IP address of the foreign agent with its home agent (in the figure, this is foreign agent is responsible for relaying packets from the mobile node to correspondent nodes and to the home agent. Alternatively, the mobile node can be directly connected to the foreign network itself and therefore directly communicate with the home agent (in the figure, this machine is given IP address Once a node has obtained a new care-of-address, it registers this address with its home agent.

Registration with the home agent is performed for the following reasons:

a node has moved to a new foreign network and therefore needs to register

a new care-of-address, a node needs to deregister an old care-of-address with its home agent when it returns to the home network

when a node needs to reregister with the home agent because its previous registration is about to expire.

The above figure-2 illustrates the transmission of registration messages to the foreign agent care-of-address. While mobile node sends the registration request message to the foreign agent below mentioned procedure takes place.

(a). The mobile node requested care-of-address which is determined by the foreign agent's agent advertisement messages. The foreign agent verifies the security authentication information, registration lifetime, supported tunneling method and dispatches the packet to the home agent with its own address. Before that it maintains little information such as link-layer address and source IP address.

(b).The home agent checks the options of requested service and authentication information from the foreign agent. If the request is considered to be valid and serviceable then home agent updates its bindings to record the new care-of-address for the mobile node and sends registration reply to inform about successful or unsuccessful registration.

(c). Upon receiving the reply the foreign agent sends a new authenticated message back to the mobile node. If all these replies indicate a successful registration then mobile will begin to receive its packets tunnelled from the home agent through the foreign agent.

Need for Cellular IP:

One of the principle functions of the mobile IP is to define a way to identify the point on the internet that mobile physically moves from its addressed location. This issue is resolved by providing a "care of" address which enables an IP address can be patched to a different location. However the migration of agents (home to foreign agents and vice versa) will be the rule rather than exception as the internet wireless networks available in all over the place. To address this issue Cellular IP is introduced. For this the network can be separated into local and wide area mobility by which the performance of Mobile IP protocol can be significantly enhanced. Cellular IP is similar to a Local Area Network (LAN) whereas Mobile IP is analogous to a Wide Area Network (WAN). The cellular IP is optimized to support local mobility but efficiently interworks with Mobile IP to provide wide area

mobility support.

Cellular IP maintains distributed cache for location management and routing purposes. Distributed paging cache maintains the location of 'idle' mobile nodes in a service area. Cellular IP uses this paging cache to quickly and efficiently pinpoint 'idle' mobile nodes that wish to engage in 'active' communications. Distributed routing cache maintains the position of active mobile nodes in the service area and frequently refreshes the routing state in response to the handoff of active mobile hosts. These distributed location management and routing algorithms lend themselves to a simple and low cost implementation of Internet host mobility without new packet formats, encapsulations or address space allocation beyond what is present in IP. This approach is beneficial because it can accommodate a large number of users attached to the network without overloading the location management system.

Let us take a case where Cellular IP is not implemented and assume an environment where highly mobile nodes often migrates during active data transfer and expecting the network to take care of handoffs without or very minimal disturbances to the ongoing data transfer. Mobile IP requires that often each node migration there should have been location update message to be sent to far home agents who potentially increase the handoff latency as well as the system load. To overcome this, Cellular IP concept can be implemented by which the frequency of transferring location update message can be reduced. Distributed location management and routing cache should be able to handle the handoffs with minimal latency. In this case mobile node's home agent is only informed when mobile moves into a new access system and it is unaware of nodes mobility within an access network as illustrated in the below figure-3.

Figure-3 Wireless access Networks and Mobile IP

The main advantage of separating local and wide area mobility is that home agents need not be informed about local mobility within a wireless access network. This will become important as cell becomes smaller which increases the node migration and user population also to be considered. By handling the handoff locally the impact of handoff on data transfer can be limited. One more advantage is that when the population in network increases and many people wanted to be in connected mode in internet, unnecessary handoff signalling which could load the system can be minimized through Cellular IP concept and in fact indirectly network capacity also can be increased.

The major concepts which got implemented in Cellular IP concepts. They are

Paging and Routing Mappings


Paging and routing Mapping:

For simplicity and scalability, none of the nodes knows about the exact location of a mobile host in a Cellular IP network. Packets are addressed to a particular mobile are routed to its presently attached base station where each node only knows about its outgoing ports to forward packets. While forwarding the IP, this routing information is local to the host and the node does not have any idea about the wireless access network topology. These information elements are referred as mappings because they map mobile IP addresses to node ports. These mappings are created by mobile that transmitted the packets and then these packets will travel in the access network towards the gateway router on a hop-by-hop basis. By monitoring these packets and mapping sender address to incoming port, nodes of the access network create a hop-by-hop reverse path for the future packets addressed to the given host.

To minimize control messaging flow, mappings are not cleared as soon as the handoff completed. Instead they are assigned timers to clear the outdated mappings. To maintain its path of mappings, a mobile host must periodically transmit dummy packets when there was no real data to be sent. The combination of periodically transmitted packets and timed-out mappings ensures about the mobile's roaming information in a service area and a current path of mappings will always exists between the gateway and the mobile's base station. This proposal also helps in easy migration between access networks as nodes does not required any advance information on a mobile to generate mappings and also does not required to be informed while leaving from the current serving node

This timer introduces the following trade-off. Once mobile completes a handoff, its path to the old base station will not be cleared until the mappings are cleared. During this period if packets to be routed to the mobile they are delivered to its current as well as old base station. This result in a waste of resources which can be minimized by selecting a small timeout interval otherwise idle mobile could transmit dummy packets with a period comparable to the mapping timeout which may result in a significant load in the network. To come out of this issue (resource waste due to unused but not-yet cleared mappings) the timeout should be aligned with the packet time scale.

Figure-4 Paging and Routing Caches

To address this issue in Cellular IP two parallel structures of mappings are used. They are Paging Caches (PC) and Routing Caches (RC). These mappings timeout interval is comparable to the access migration frequency. Paging Caches and Routing Caches are independent to each other. RC mappings are only maintained for mobile hosts currently receiving or expecting to receive data and the timeout for this mapping can be in the packet time scale.

The above Figure-4 illustrates the relationship between PCs and RCs. When mobile is in idle state it keeps PCs upto date by transmitting dummy packets at very less interval. Since PCs have a relatively long timeout they follow the roaming mobile closely. If any packets to be sent to the mobile the PC mappings are used to find the mobile and once data started transmitting the host maintains RC mappings either by its outgoing data packets or through the transmission of dummy packets (in case no data available for delivery). Data packets addressed to the mobile are routed by RCs that unlike PCs track the host closely.


Handoff is nothing but migration of cell when data transfer is ongoing and it is been handled automatically. Handoff in Cellular IP is always initiated by mobile. As soon as mobile reaches the new base station the data packets in redirected from old to new base station. The first redirected packets are automatically configures the new path RC mappings. Before expiring of old RC mapping the packets will be routed to both old and new base stations. If the mobile is capable of listening to RF signal from both the base station that is called soft handoff. Since packets are received from both the cell, there is no chance of packets getting lost.While during handoff if mobile received signal only from new base station that is called hard handoff. After hard handoff the lane to the old base station will be deleted upon expiry of timer.

Let's take the example of mobile X migrates from node F to D when data transfer is on-going. Assume that all the nodes contains Routing Caches. After the migration for sometime packets are transmitted to both cell F and D. After the expiration of RC timer the old mapping to E is cleared. The cache in A can't changed during the whole process. During handoff if the mobile goes to unreachable area for a while due to any reason the application layer(TCP) might detect the delay and some packets might get lost. When the mobile reappears to reachable area before the expiration of RC timer the data path would resume again and start continuing the data transfer. If the mobile reappears after the RC timer expiry they are reconfigured by the first packets transmit by the mobile which will not even know about the disruption of data transfers.


Figure-4 Mobile IP/Cellular IP Architecture

This work analyzes the existing problems in Mobile IP and how they are addressed through Cellular IP concept to manage cellular intranet. This can be done by an architecture managed with Mobile IP(macro-mobility) and Cellular IP(micro-mobility) concept. Here architecture is centralized on the gateway and home agent.It is most suited for security needs and client-server traffic models.

Article name: Problems In Basic Mobile Ip Computer Science essay, research paper, dissertation