- It is responsible for moving frames from one hop to next hop.
---- ( Features / Responsibilities ) ----
Divides the stream of bits received from the network layer into manageable data units called Frame.
Physical addressing Adds header to frame to define the sender and/or receiver.
Imposes a flow control mechanism to avoid overwhelming the receiver (rate at which data are absorbed by receiver is less than the rate of data produced in the sender).
Adds reliability to the physical layer: by adding mechanism to detect and retransmit damage or lost frames.
Uses a mechanism to organize duplicate frames.
Achieve through a trailer added to the end of frame.
Two or more devices are connected to the same link, data link layer protocol are necessary to determine which device has control over the link at time.
- Grady Booch approach is known as object oriented design.
- The main aim is to establish a base for the implementation of object oriented systems.
- This methodology consists of identification of interfaces at various levels.
- The main concern of this method is the iterative process and creativity of the designer in order to develop OOD.
- It follows incremental and iterative life cycle.
- It combines analysis, designan implementation and provides a sound object oriented software engineering process for analysts, designers and developers.
- The Booch methodology can be broadly divided into two processes: macro process and micro process. It is a high-level process followed by development team throughout the life cycle.
1. Macro proces
- In the first phase, the requirements are established using context diagrams and prototypes. The outcomes of this phase are core requirements of the system.The analysis process involves requirement capturing and understanding.
- It involves what of the system. This phase consists of construction of use cases, identification and prioritization of risks.
The design phase focuses on the construction of architecture of the system and involves the following
- Identifying horizontal layers
- Mapping classes to subsystems
- Release planning
- Attaching risks identified in the analysis phase to releases.
- The evolutionary phase involves implementation of the system and each release adds to the functionality of the system.
- The maintenance phase consists of post-deployments activities.
2. Micro proces
It is a lower level process.
Following recursive steps are followed in OOD micro process:
- The first step involves finding class and objects at different levels of abstraction. The next identifies the semantics by finding the meaning of the classes and objects in terms of attributes and operations. It also involves determining the use of an object by another object.
- Identification of relationship involves the process of determining the interaction amongst the classes and objects.
- The relationships identified include inheritance, uses and instance of.
- The last involves specification of interface amongst classes and objects and their implementation. It identifies data type of attributes and signature of operations.
- Here no formal notations for constructing visual diagrams are given.
- Smart card is an equipment that comprise of an embedded integrated circuit chip also known as ICC. This ICC can either be a self-asserting micocontroller or matching intelligence with inbuilt memory or just a memory chip lone. A smart card gets connected to the reader only when its directly physically contacted or with the aid of a remote contactless radio-frequency interlace
- There are basically two types of smart cards.
1. Contact Smart Card
A contact smart card ought to be introduced within a smart card reader with a direct physical union to a conductive contact tray noticed on the surface of the smart card, in general the surface is gold plated. Over this substantial contact points processing of commands, data, and card status takes place.
2. Contactless Smart Card
A Contactless smart card as the name suggests it only needs close immediacy with the card reader. The card reader as well as the card has antennae, and both devices communicate with the help of RF (radio frequency) above this contactless link. Some contactless cards also generates power for the inbuilt chip from this electromagnetic field produced. The range of the signals are generally one-half to maximum 3 inches for non-battery powered smart cards, this is perfect for applications like- payment that necessitates an extremely fast card interlace and entry in a building.
Smart Card Applications
Some of the most common smart card applications are
- Credit cards
- Satellite TV
- Computer security systems
- Electronic cash
- Wireless communication
- Government identification
- Loyalty systems (like regular consumer points)
- Jacobson methodology is known as object Oriented SE. It contains the following five models:
- The requirement model: The aim of this model is to gather software requirements.
- The analysis model: The goal of this model is to produce ideal, robust and modifiable structure of an object.
- The design model: it refines the objects keeping the implementation environment in mind.
- The implementation model: It implements the objects.
- The test model: The goal of the test model is to validate and verify the functionality of the system.
- The requirement model focuses on capturing functionality of the system through use cases and actors and determining the interfaces amongst the use cases.
- In the analysis model, an ideal model is developed while not considering the implementation environment. It involves the identification of interface objects, database related objects and objects representing control between interface and database related objects.
- The objects are grouped into subsystems. In the design model the objects identified in the analysis model are refined to the actual implementation environment. These objects are known as blocks.
- These blocks are converted into modules in the implementation model and finally the modules are integrated and tested in the test model.
- Normally, only one user uses a specific client at a time. A client connects to a server to send and receive information. Think of a client as a program that gets information from somewhere else. A server is usually a large computer capable of providing data to many clients at the same time. The word server can mean the physical computer or piece of hardware, or it can refer to the actual server software or daemon running on that machine. A daemon is a program that offers a service to other programs, usually over a network. It accepts requests from clients, processes the requests, and returns the results to the requesting client. Although the client and server can be on the same machine, they are usually on separate machines connected by some kind of network.
- The World Wide Web (WWW) uses this client/server model to allow millions of users to access Web sites all over the world. A Web server is a specific type of server that knows how to communicate with clients using the HyperText Transfer Protocol (HTTP). A protocol is just a standard set of rules that allow a client and server to communicate. For a client and server to communicate, they must speak the same protocol. HTTP allows clients to request documents and servers to respond with those documents.
- Web servers wait for clients to connect and when a connection is established, they receive a request from the client and then respondâ€”usually returning a document or image. The Web server process is usually referred to as the HTTPD, or HTTP daemon.
- The main goal of any Web server is to provide documents to clients. The first Web servers were very simple and did little more than this. Todayâ€™s Web servers are full of features that allow them to do more than just respond to simple requests for static documents, and many provide easy-to-use graphical user interfaces for administration and customization. Todayâ€™s servers support options that allow the creation of dynamic documentsâ€”documents that are generated on the fly, not stored on disk.
- There are two big server and also available many version of it.