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The present world has the benefit of cheap and readily available IP networking. This has made many users the world over benefit from the advantages of networks especially as far as data transmission is concerned. The work of transmission of data via networks needs several procedures performed. For starters, host addresses need to be determined plus a way of mapping names that are human-readable.
It is also imperative to establish a route between the transmitting node and the receiving node. With this done, the next thing would be to break down the data into small packets by the sending node. The receiving node will need a way of reassembling the data packets in the correct order so as to get the correct information. For data integrity to be maintained there needs to be a flow control mechanism by the two nodes to make sure the data is neither lost nor corrupted.
The network reference model, otherwise known as the OSI model is a layered network architecture that was developed by the International Organization for standardization. It defines how any two networked systems to interchange data on the network (Javinn, 2000). The model has seven layers namely, The Application, The Presentation, The Session, The Transport, The Network, The Datalink and The Physical layers. These seven layers can be subdivided into two functional categories with the first three (Application, Presentation and session) falling in the application category and the rest falling in the transport category (Tyson, 2010).
The Network layer is usually referred to as the lowest of the layers in the reference model that is concerned with the end-to-end transmissions of data. This layer provides the means by which data of different sizes can be transmitted from one point; the source, to the other point; the destination, on a network. The network layer has a responsibility of making sure the standards that have been established by the transport layer are maintained (Saltze et al., 1984).
The formation of the Network layer has been informed by the RFC 1958. This is a document that provides guidelines for internet architecture. One of the principles it establishes is the need to come up with a protocol that works well. It is undesirable to have a system designed and approved only to become faulty over time. It was also observed that systems should be simple and easily scalable. Clark (1988) observed that the system developed should be a platform that allows many other infrastructures to work on. These were the foundation blocks for the Network Layer.
The network layer looks at the Internet as a group of interconnected sub-networks. These sub-networks are sometimes referred to as Autonomous Systems which is abbreviated, ASes. The network layer actually isnt a real structure. Instead, there are a number of main backbones that exist. These backbones are built from fast routers and lines with high bandwidth. The backbones are connected to the regional networks which are then attached to different LANS (Kozierok, 2010).
New Technologies
Traditionally, Segments and other devices communicate over the network using static IP addresses. Usually, when data is sent, the address of the destination is determined before the message is routed. But with the advent of new ICTs like PDAs, and Smartphones, there has arisen a need to incorporate these devices into the networks (Perkins, 2010). The challenge is that the traditional network was not designed for mobile devices. The traditional network was built on the TCP/IP protocol suite.
The biggest concern that Host mobility presents is the fact that the traditional suite was not built for mobile devices. While devices are traditionally configured to have static physical addresses, mobile devices often roam from point to point. Several approaches have been used in solving this problem so as to integrate mobile devices into the networks. The general rule of thumb for providing a workable solution is to ensure that the mobility between connection points should not interfere with the existing connections.
Framework Goals
Overly, there are three basic goals used to evaluate frameworks for internet mobility. The very first is the principle of Seamless Transitions. This is important to ensure that the Movement between different networks should not lead to an intermittent loss of the applications. In the event that the connection breaks, then there ought to be a way of re-establishing the connection transparently. The mobile device should not be affected by the different hosts it moves to. The typical protocols used to achieve this are connectionless protocols like DNS.
The second goal is Location Management. This implies that a node should be accessible via a given static identifier even though the device may be mobile. The third goal is that it should be Infrastructure Free. The more closely it is implemented to the peripheries of the network, the more the mobility solution is desirable. A solution that requires support from the network infrastructure will not be as efficient. This goal will ensure that the users have the freedom to move to networks with no limitation of bias to the platform they were designed for.
Mobility at Sub-Network Layer
If we want to detect and join a new network, which is the goal of mobility, then we will need a support Protocol. Primarily, the host needs to be able to establish the link types available in a given area. Taking a device that is enabled with Bluetooth, GPRS an 802.11 for instance, it may only reach a subset of them in a given area. After this assessment is made, the host will subsequently attach to a topology. This was traditionally as easy as plugging in of a wire on a network with a cabling medium. On a wireless network, however, things could be a little bit more complex. An example is the DSDV scheme. It is a routing scheme (Pravin and Perkins, 1994) which can work as a link and allow mobile devices to establish a complete network or networks amongst themselves.
This is however not a globally applicable address that could be used for location management. The DHCP protocol allows for assigning of dynamic IP addresses. This means the protocol can be used to achieve some form of mobility by means of adapting configurations for the new network. Having stated that, it is important to remember the goals of mobility. DHCP can not work to fully guarantee mobility because it is found quite low in the Protocol suite. It would need to co-work with another higher protocol.
Mobility at the Network Layer
In the network layer addresses are usually assigned administratively. They belong to specific segments on the Internet. The TCP/ IP suite has globally-usable addresses. It is at this layer that routing of packets takes place. There are usually two methods that could be employed to provide mobility at the network layer. The first method is by use of specific routes. In this method, hosts have a given route and this route changes as the hosts move. While this approach is simple, it loses the quality of scalability due to an uncountable number of nodes on the internet today. This negates this option as a solution for mobility on the internet.
The second option is the using of sub-networks. It meets the demands of the present day internet and conforms to the mobile IP standards (Perkins, 2010). The main advantage of having mobility support at this layer is that the network layer lies almost at the center of the OSI reference model. This vantage point means that mobility support can benefit all the higher layers of the OSI reference model. The implication of this is that there is a considerable reduction in the effort that will be used but even more importantly is the fact that there will be a limited number of bugs. It also ensures that all the security holes have been sealed (Plummer, 1982).
When dealing with Mobile IP addresses, there is usually a need for home agents. These home agents are usually in the same network that a mobile devices address belongs to. A mobile device will usually send a notification to a home agent whenever it changes connectivity. On retrieval of this message, the home agent will forward any available packets for the mobile device to it. These packets are forwarded via IP tunnels to the physical location of the node. Regardless of where the mobile device is situated, it will always send data packets using its home network IP address. This has been designed to ensure that the device will never lose a connection to other network segments.
Apart from this, there is the important advantage of security. If it were not possible to authenticate the packets source, it would be a serious security hole for connection hijacking and remote-redirection. The Mobile IP makes use of cryptography in the authentication of updates done locally to enforce security and preserve the ACID qualities of a transaction. It is a very tedious and hard exercise to efficiently implement cryptographic algorithms. This gives the IP addressing of Mobile devices an edge since it greatly cuts down on the possibilities of many different authentication methods being applied in the other protocols at the higher levels.
Drawbacks
Having seen the advantages of the Network layer implementation, it is important to consider the shortcomings it has. The very first disadvantage is the issue of triangle routes. These are the routes that are formed in between mobile nodes and remote hosts. When packets are sent to the remote host, they go direct to it whereas those sent to the mobile device have to route through the home agent. Sometimes, this could be a great distance away which could cause unnecessary delays. This could also lead to problems with the higher layers (Balakrishnan et al., 2007).
The other disadvantage is the reliance to the Home Agents. This has the implication that there can be a connectivity failure should there be a problem with the home network. In addition, servicing of the mobile nodes greatly puts on overloads on the networks. The home agents are also overburdened by sniffing packets as well as making sure the tunnels are available for communication (Matt et al., 2010).
A mobile device will always use a static IP. This is still true even when the device is no longer at home. The firewalls may block this device assuming it to be spoofing on the network. The irony that this causes is that while the aim was to maintain mobile connectivity, one may actually end up loosing it. There is however a remedy to this. It involves the using of another tunnel when sending back packets to the Home agent. However, this may again result into the triangle route problem.
Another issue of concern is the fact that the transport set in the reference OSI model, where the network and transport layers are found, may not have the technical ability needed to alert the application set layers that mobility has taken place either by relocation of the mobile device or by switching from one Network to another. Consequently, the Protocol may instantiate a reset if it detects an intermittent timeout. This implies that the transmission may have to be forcibly suspended.
IP handover is a procedure rather than an event. It involves various steps. Firstly, the Mobile device has got to detect its movement. It then finds a way of establishing a connection consequently updating the home agent with its present location. In the event that the mobile device is not connected in during this process, the data packets on the network that are meant for the device could be lost. The only solution to this would need the modification of the routers used for the internet on the network.
Even in the light of all this disadvantages, there is still good ground to find mobile IPs to be desirable. With the guidelines set out by Clark (1988) being adhered to, it is possible to have an efficient and reliable interconnection of networks involving the mobile devices.
References
Balakrishnan, H. et al. (2007). TCP Performance over Asymmetric Satellite Links with Real-Time Constraints. Computer Communications. 30(7), 1451-1465.
Clark, D. (1988). The Design Philosophy of the DARPA Internet Protocols.ACM Computer Communications Review. 18(4), 106-114.
Javinn, T. (2000). OSI 7 Layers Reference Model For Network Communication. Network Management and Security. Web.
Kozierok, C. (2010). Network Layer functions. The TCP/IP Guide. Web.
Matt, B., et al. (2010) Trust Management and Network Layer Security Protocols. Columbia University. Web.
Perkins, C. (2010). IP Mobility Support for IPv4. Network Working Group. Web.
Plummer, D. (1982). Ethernet address resolution protocol: or converting network protocol addresses to 48.bit ethernet address for transmission on ethernet hardware. STD 37: RFC 826.
Pravin, B. & Perkins, C. (1994). Highly dynamic destination-sequenced distance- vector (DSDV) for computer networks. ACM SIGCOMM Computer Communication Review, 24(4), 234-244.
Saltze, J. et al. (1984). End-To-End Arguments in System Design. New York: Routkledge.
Tyson J. (2009). How the OSI works. Web.
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