The Vertical Handover Mechanism Computer Science Essay

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Mobile device is a simple machine which is commonly used by all of us because of its compatibility and portability. Being as a compact device, it is also used in different applications such as multimedia, web applications. Many recent technologies are found to meet different wireless interface criteria's, such as Wireless Local Area Network (WLAN), Worldwide Interoperability for Microwave Access (WIMAX) and Third Generation Technologies (3G). These technologies will allow the user to move freely and access other networks. To achieve free moving network access, a new technology "Vertical Handover" has been involved. In our discussion, we can have a detailed study on the following vertical handover mechanisms:

Internet Protocol Version Number 6 (IPV6)

Fast Handovers for Mobile Internet Protocol Version Number 6 (FMIPV6)

Y-comm architecture


























Handover is a technique where connection is changed from one communication channel to another channel. For example connection between a WLAN and a 3G network is changed via base stations.

Handover mechanism is divided into two as Horizontal handover and Vertical handover.

Fig 1.1.1 Vertical and Horizontal handover.

Horizontal handover:

It is a controlled mechanism of handover unlike the vertical handover and it is controlled by the signal strength. In horizontal handover the infrastructure is not an issue and transition in connection is based on the signal strength which is received.

Vertical handover:

In vertical handover there is transition in connection between two different channels to support the infrastructure and for efficient mobility between the nodes. It is heterogeneous technique where the parameters and metrics keep changing frequently and this type of handover is controlled using a client which makes it more efficient.

Internetworking Architecture:

There are two main architectures of vertical handover are Loose Coupling and Tight Coupling.

Fig 2.1 Loose and Tight coupling.

Loose Coupling:

In loose coupling the components or elements in the network have very less knowledge among them and are disjoint. Loose coupling reduces the communication or interaction between the components and avoids changes made in one component is not done in the other component. In the above figure there is disjoint mechanism between 3G network and that of a WLAN. In loose coupling the security is not great and the technique is comparatively slow and hence services like VOIP cannot be implemented. The connection is relatively weak but there is control path which is still working or there is interoperability between 3G and WLAN.

Tight Coupling:

In tight coupling, the connection is better than that of loose coupling and security in the tight coupling is efficient. Tight coupling is fast enough for VOIP services. In tight coupling, the two technologies WLAN and 3G are integrated each other. The quality of services is re-used in tight coupling to avoid overhead of provision. This technique is done when maintenance is not an issue.


The three main parameters of vertical handover architecture are Resource Management, Mobility Engineering and Service Management.

Fig 3.1: System Architecture


The resource allocation in a heterogeneous network is done by using resource management. There are two types of allocation namely direct and indirect. In direct allocation parameters such as bandwidth, allocation of channels is done to a particular base station. On the other hand, in indirect allocation the resources are allocated as performance parameter of the network using network capacity to optimize further.

Resource management is another parameter in quality services and used to choose the best packets and headers. This kind of service is applicable both in a mobile station and base station to gather resources.


This parameter is done to provide integration between the networks. Sometimes there is integration between and loose coupling and tight coupling which is used for mobility management. Protocols in OSI layer is implemented using this parameter and other mobility issues.


Services in vertical handover are created using service management namely user profiles, Authentication service, authorization etc. Location of a node is stored using location registers which is a parameter of service management.

Other services may include global positioning which is used for localization and other navigation purposes. It is even used to locate a particular node in a network where mobile nodes can connect to.


Mobility management is another important parameter in vertical handover when there is transition in connection between the base stations. This is done to make sure if the bandwidth, connection and the range of connection is carried in an efficient method. This is done because of the mobility of the nodes, where they keep roaming among base stations and go out of range and hence to keep them connected we need mobility management between the networks.

Mobile Internet Protocol Version 6 (IPv6)

Mobile Internet Protocol is used in mobile nodes for mobility management. This protocol is used for efficient communication among the mobile nodes where their permanent IP address is same. In this version there is also another parameter used for mobility messages. The main components in this version includes home agent, foreign agent. The first one is located in the home network and the second agent is located in the visiting network of mobile node. Home agent is one of the dedicated routers where the identifier and locator are integrated. The home agent communicates with mobile node using care of address and used to find particular destination or region of the mobile node.

When a particular node is communicated to the respective node, the data sent from correspondent node to the home network of the mobile node which is further sent by the home agent to the current location of the mobile node and hence there is a communication link between the nodes. This same procedure is carried out when data or packets are transferred from the mobile node to the correspondent node, i.e. using the home agent and the home address. Mobile IP even tells about the registration mechanism which is authenticated. Moreover path discovery is also done to find out the home and the foreign agents respectively. Tunneling mechanism is carried between these nodes during communication to find exact location.

Another technique which mobile IP uses is return route ability where home network is not involved between the mobile and its corresponding node. Some of the parameters are:

1. Home agent: This particular agent is located in home network, where it delegates home address to another particular node and forwards the data to the corresponding node

2. Mobile node (MN): This node is where the permanent address or home address remains the same even if it moves to another network. The mobile node keeps moving between base stations and maintains the same address.

3. Correspondent node (CN): This node tries to communicate with mobile node and has the same functions of a mobile node and it supports reverse route ability.

4. Home network: In this network the home address is present in the mobile node. This is the permanent point of this node.

5. Foreign network: The correspondent node is present in this network and it consists of a foreign address also in it.

6. Visited network: This network is used to find the permanent address of its mobile node.


Mobile IPv6 usually has two addresses such as home and care of address, the first one tells about the identifier and later is used to tell about the location of the mobile node. Mobile IPv6 is used to bind both the addresses transparently and used to provide seamless mobility. Route optimization and maintenance is efficient using mobile IP. Using the second address the visiting or localization address of the mobile node is identified. As a result of this the mobile node is tracked and makes it easy for this node to have data transfer with the moving node using its care of address.


1. A mobile node moves to a random network, the care of address is given to the mobile node by the router accessing the network. This address is configured using the router and the MAC network address and hence to find the location of the node.

2. Binding takes place in the operation of the mobile node access. Binding update is the update which is issued to the home address agent, about the mobile nodes care of address. Then there is binding cache which is between the respective addresses and once this message is sent to the correspondent node, acknowledgment is sent to state that the binding between the two addresses.

3.When a particular request or message is sent to the correspondent node, it passes to the tunnel which the home agent tries to implement the technique encapsulation and after this it forwards it to the communicating or correspondent node.


Fast handover for mobile IPv6 is used because the latency in mobile IPv6 happens because of the latency issue in the connectivity and latency in binding update. This mechanism is used to reduce the overall latency and this is done by providing the access point's subnet whenever a particular node tries to visit a network.

The information of the subnet is found out by the link layer mechanism. The technique works as follows. Care of address is created in each access point by the mobile node and this is done using router advertisement. When the node does not receive the acknowledgment

As a result of this every time a mobile node visits a new network, care of address is created and uses it when a fast acknowledgment is received during the node movements. When it does not use or receive the acknowledgment it adversities a message called unsolicited advertisement neighbor message and if it receives the acknowledgment the message advertised is solicited advertisement message. As a result of this the latency is reduced.

Moreover it will reduce the configuration latency of the care of address and on the other hand reduces the binding update latency by binding the PCoA and the NCoA and a tunnel is created so that the packets are reached to the corresponding node when the mobile node reaches a new subnet and is more efficient.


When MN is about to start the handover mechanism, there is a trigger signal and immediately handover begins. Information contained in the trigger includes NAR. RtSoIPR message is sent to PAR by MN during handover process to identify the access routes which depend upon the information of the trigger. NCoA message is created by MN and binding update which binds PR with PCoA and NCoA. As a result of this packets are forward to the new location.


The FMIPv6 enables the elementary principle of MIPv6 handover. This is achieved by minimizing the overall latency using L2 triggers. Not only has that it helped in the configuration of NCoA, while the MN is not fixed to NAR. However this system still suffers some problems. The basic MIPv6 handover mechanism will come into action only when the MN loses its connectivity with PAR during handover. The latency is linked with different operations which are not addressed in the FMIPv6. This is because DAD results in 33%of the overall handover.

Every time MN starts handoff mechanism packets are forwarded between PAR and NAR and it is based prediction time. There is delay in the packet sent; as a result of this delay time is very tough to calculate. As a result of this packets are lost. The MN has to propose an NCoA irrespective of if it has an IP address assigned by NAR or not. It involves lot of resources depending upon the situation resent and hence NCoA cannot be used by MN.

Y-comm Framework

Heterogeneous networks are facing many key challenges. In order to face those key challenges this Y-comm framework is created. In day to day life Mobile devices are very important in man's life. Now a day the devices which has sufficient amount of interfaces are more common. More number of people is using mobile devices and they need seamless operations while they are moving.

Vertical handover types:-

In Network controlled type, the base station fully controls the handover.

In Client controlled type, the mobile node takes the decision instead of base station, but all the basis resources are provided by the base station only.

Wireless network challenges:

Bandwidth can be upgraded in wired networks but not in the wireless networks. It is because that there is steady spectrum at the user's increases stage.

In modern days, the technology and performance of the peripheral networks in some terms with systems which are used in core network. But we can say that the latency and bandwidth is performing faster in core networks. Using wireless technologies like WLAN and Bluetooth, the peripheral networks are being built. Each and every system has their individual characteristics. We can say that this system characteristic differs from core networks in bandwidth and latency.


The two key networks are Peripheral network and Core network.

As said earlier, clearly we can say that hurdles are completely different from the other network.


Vertical handover is performed in order to support many number of interfaces. Vertical handover is something about that the connection is establishing from one to another network other than the same network. All the OSI model layers are deeply affected by vertical handovers. Both the frameworks are high speed wired networks in this model. 2 OSI models are

required inorder to obtain this. For this only reason, Y comm architecture is framed. C:\Users\pashams\Desktop\osi-model.jpg

Peripheral Framework:

This quality of service supports vertical handover technique in wireless network.

Layer 1 - The Hardware Platform Layer:

This layer specifies the components and technologies that includes modulation techniques and electromagnetic waves management. It acts as an interface between hardware and upper layers.

Layer 2 - The Network Abstraction Layer:

This layer creates an interface for the entire network which uses this architecture. This interface maintains and controls the working of the network. This layer provides information about networks.

Layer 3 - The Vertical Handover Layer:

The mechanisms for vertical handover are specified in this layer. For better performance of the vertical handover layer, the network abstraction layer must provide latest information about the interfaces and the state of the wireless networks.

Layer 4 - The Policy Management Layer:

The occurrences of handover decision are made by this layer. This layer has two types of categories. They are:



Reactive Policy: This policy is called by the network when changes are made. These are connected to mobile node.

Proactive Policy: These policies will know the networks condition at a particular location before the node reaches the location.

Layer 5 - The End Transport System:

TCP is the main protocol which works for this layer. The work of this layer is to monitor the moving data sent to and from the mobile node. Since almost all peripheral networks are wireless, it is necessary to check the operation of the network and transport layers are efficient. The purpose of introducing this layer is based on the TCP, which is very slow in adapting the network conditions after performing vertical handover.

Layer 6 - The Quality of Service:

This layer is used to provide quality of service needed by the application. When the mobile moves around, the dynamical changes are been provided by this layer. The QoS have two different types. They are:

Download QoS

Upward QoS

The download QoS is used to specify the applications required by the QoS.

The upward QoS applications adapt themselves according to the changes in the network conditions.

Layer 7 -Application Environments:

The work of this layer is to provide the mechanisms and the routines needed to build an application. The toolkit approach is used in building a complete application layer.

Core Framework:

This framework is used to handle all core networking problems. They support the peripheral network and network resource management.

The core framework consists of seven layers. The first two layers are as same as in peripheral framework. The main difference between these two framework is that peripheral framework requires software to support a mobile node in network whereas core framework runs on the technology in the base station.

Reconfigurable network layer:

This layer provides a control plane for (re)configuring networking resources in the core network, which includes network switching elements such as mobile switching centres, gateway GPRS. This layer is also used by the vertical handover layer to acquire resources which is required for vertical handover in peripheral framework.

The network management layer:

It is the most important layer, which uses programmable network layer to build class networks with various hardware and software components together. An individual operator is assigned for each network to control the network. In order to do this operation, this layer must provide authentication, access control, accounting and charging systems and also support the policy mechanisms that would tell the operators which components can be used on their networks.

The network transport system:

It describes about the network and transport mechanisms in the core network. It uses TCP/IP in the core network.

Network QoS layer:

This layer provides the quality in core network. It is also takes the responsibility to build and maintain QoS at different points in the system.

The service platform:

This layer allows different agents for the installation and operation of various of services in a secure and restricted way


In this framework, both peripheral framework and core framework are joined to represent a environment to support heterogeneous devices.

These two frameworks have a common base which includes hardware platform layer and network abstraction layers. These Layers are divided in terms of functionality but the corresponding layers interact with each other.

Security issues in Y-comm Architecture:

There is no separate layer for security in Y-Comm Architecture,because security is required for all levels in the architecture.

There are three levels of security which are needed in peripheral and core subsystems.

Network architecture security (NAS):

It deals with the management of different wireless technology and controlled from policy and management layers.

Network transport security (NTS):

This deals with end to end transport through y-comm and is controlled from layer 5.

Service and Application security (SAS):

It deals with running applications and services. The security layer is present in Qossecurity (QoSS) and is considered as a part of QoS. If any changes in security must be viewed as changes in QoS.

CONCLUSION: We had discussed about the mobility schemes and how vertical handover is used in heterogeneous networks to overcome the connectivity problem and provide seamless transition mobility. In mobile IP we solved the problem of having two addresses which results in IP conflict and maintaining one permanent address. Communication between the mobile nodes is relatively efficient even if there is any change in the topology of the network. In mobile IP there are certain disadvantages such as latency due to handover and binding update. To overcome this we used FMIPv6 to control the latency thus making communication between the nodes more efficient. On the other hand, in Y-comm technology we have both peripheral and core network with more security control and efficient handover takes place.