The new edition builds on the well-established principles developed in the original edition and thoroughly updates that core knowledge. For anyone involved with computer security, including security administrators, system administrators, developers, and IT managers, Computer Security Basics 2nd Edition offers a clear overview of the security concepts you need to know, including access controls, malicious software, security policy, cryptography, biometrics, as well as government regulations and standards.
These frames already contain necessary information of travel from a source to destination. Data link layer is responsible for a node-to-node delivery of data. It has other functionalities like error control, flow control and access control, which is implemented from node-to-node. Error control make sure that correct data is delivered from a node to another node. It detects if there is an error in the frame and retransmits that frame.
Flow control is implemented on the side of the sender to make sure that the flow of data is in control and the receiver is not overwhelmed with the amount of data sent by the sender. Flow control is required when the rate at which the sender is sending data is much more than the rate at which the receiver is processing data.
If flow control is not implemented then the situation may result in congestion, dropping of packets, retransmission, delay, jitter and unavailability of data. Overall performance of the network can be degraded. Another function of this layer is the access control. LLC encapsulates network layer protocols and is responsible for frame synchronization whereas, MAC control the access of medium by different network devices. This is called access control.
When a new device is added into a network or in a situation where multiple devices have to share the transmission channel, MAC has different methods by which it decides who is going to use the medium and how a single resource will be shared by multiple network devices.
This layer provides perfect solution for the delivery of data in the same network with physical addressing. It takes data from the transport layer furtherly divide it into small data packets and send it to the data link layer. This layer provides a solution to the delivery of data packets from one network to another network. That means how the data travel from the source to the destination is decided by this layer. Network layer deals with the routing to tell the most optimum path the data should follow to reach to the last router before the destination successfully.
This layers supports scalability and no matter how many networks far the destination is, the data will be delivered to the destination.
In case of a internetwork communication it is difficult to identify devices that is why network layer uses the logical address that is the IP address for identification. It adds the logical address into the header of each data packet before passing it to the data link layer. Network layer provides perfect solution for sending data across different network using logical addressing.
Transport layer provide a solution for sending messages from process-to-process while maintaining the quality of service functions. Whenever data needs to be send from a process to another process running on a different computer, considering that there can be multiple processes running on a single computer as well, it is first converted into data packets. This layer takes input in form of messages from the application layer directly.
It then breaks the messages into smaller data packets that can be sent over the network. These data packets do not contain any address information, those details are added later in the network layer and data link layer. This layer is responsible for the delivery of entire message from process-to-process. It does not take data as independent data packets unlike other layers, it consider the whole message as data and make sure all the data packet are received in order of sequence.
At the side of receiver all the data packets are combined to form a complete message. In case of a connection oriented transmission a connection is established between a sender and receiver and data is send. A session can be used to allow a user to log into a remote time-sharing system or transfer a file between two machines. The session layer has the option of providing one-or-two-way communication called dialogue control.
Sessions can allow traffic to go in both directions at the same time, or in only one direction at a time. Token management may be used to prevent both sides from attempting the same operation at the same time. To manage these activities, the session layer provides tokens that can be exchanged.
Only the side holding the token is permitted to perform the critical operation. Another session service is synchronization. Consider the problems that occur when transferring a file between two machines and the system crashes not being able to complete the transfer.
This process must be restarted from the beginning. To avoid this problem, the session layer provides a way to insert checkpoints into the data stream, so that after a crash, only the data after the last checkpoint has to be repeated.
It accepts the data from presentation layer and provides services to it and accepts the services of the transport layer. Therefore session layer functionality includes: a Virtual connection between application entities b Synchronization of data flow c Creation of dialog units d Connection parameter negotiations e Partitioning of services into functional groups.
It can be viewed as the translator for the network. This layer may translate data from a format used by the application layer into a common format at the sending station, and then translate the common format to a format known to the application layer at the receiving station.
For example, password encryption. Layer 7: Application Layer This is the level that the user often interacts with. This is where data turns into websites, chat programs and so on.
Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. The OSI model was designed to ensure different types of equipment such as network adapters, hubs, and routers would all be compatible even if built by different manufacturers.
Easy Troubleshooting: Since each layer in an OSI is independent of each other so it makes it easier to detect and solve all errors prevailing in it. Easy Understanding Nature: OSI model is very interactive and even guides us to know what a Model is, how it operates, and common methodologies, how new technologies are developed in existing networks. Security: OSI model have functionality for Encryption and Decryption which has a major contribution for security purpose.
This makes it Reliable. OSI is basically an architecture which only gives us an idea how packets transfer over the network during any communication. OSI enhancements are done time to time for developing new technologies. Scheidell et al. Future implementation in OSI will lead to enhancement in security and many other fields.
Page Research Publish Journals. Download PDF. Data Link Layer It is the layer which is responsible for moving frames from one hop node to the next. The data link layer transforms the physical layer, a raw transmission facility, to a reliable link.
It makes the physical layer appear error-free to the upper layer network layer. In other words, the network layer is responsible for the source-to-destination delivery of a packet, possibly across multiple networks. If two systems are connected to the same link, there is no need for a network layer. But, if the 2 systems are connected to different links with connecting devices between the networks, then there is a need for the network layer to accomplish source-to-destination delivery.
In other words, the transport layer is responsible for process-to-process delivery of the entire message. While the network layer oversees source-to-destination delivery of individual packets, it does not recognize any relationship between those packets.
A process can be said as an application program running on a host. The transport layer ensures that the whole message arrives intact and in order, looking at both eeror and flow control at the source-to- destination level. The services provided by the 1st three layers are not sufficient for some processes. The session layer is the network dialog controller.
0コメント