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Ethernet 10 Base 2: Thin Ethernet a.       The second Ethernet Implementation defined by IEEE 802 series is called 10 Base 2, Thin Ethernet, Thin net b.       Also called Cheap net because it provides an inexpensive alternative to 10 Base 5 Ethernet, with the same data rate c.       Like 10 Base 5, 10 Base 2 is [...]

Local Area Network A local area network is a data communication system that allows a number of independent devices to communicate directly with each other in a limited geographical area Architectures for LANS Dominated by 4 architectures: a.                   Ethernet, Token Bus, Token Ring å Standards of IEEE and a part of its Project 802 b.                   [...]

Bit-Oriented Protocols a.                   In character-oriented protocols, bits are grouped into predefined patterns forming characters b.                   By comparison, bit-oriented protocols can pack more information into shorter frames A lot of bit-oriented protocols have been developed over the years: a.                   One of these HDLC is the design of the ISO and has become the basis for all [...]

YMODEM YMODEM is similar to X-MODEM with only the following major differences: a.                   1024-Byte data unit b.                   Two CANs to abort Transmission c.                   ITU-T CRC-16 for Error Checking d.                   Multiple files can be sent simultaneously ZMODEM Newer Protocol Combines features of XMODEM and YMODEM BLAST a.                   Blocked Asynchronous Transmission b.                   More powerful than XMODEM c.                   [...]

SLIDING WINDOW ARQ Among several popular mechanisms for error control two protocols are important: Ü Go-back-n ARQ Ü Selective Reject ARQ Three features are added to sliding window flow control to allow for the retransmission of the lost or the damaged frames: a.                   The sending device keeps copies of the transmitted frames until all of [...]

Error Correction And Detection Method ¬ CHECKSUM a.                   Error detection method used by the Higher Layers b.                   Like VRC, LRC, CRC, Checksum is also based on the concept of redundancy One’s Complement Finding one’s complement – Invert every 1 to 0 and 0 to 1 – A and –A are one’s complement of each other [...]

Longitudinal Red Check(LRC) a.                   In LRC, a block of bits is organized in a table (rows and columns) b.                   For example instead of sending 32 bits, we organize them in a table made of 4 rows and 8 columns c.                   We then calculate the Parity bit for each column and create a new row of [...]

Types of Errors ¬ Single Bit & Burst a.       In a single-bit error, a 0 is changed to a 1 or a 1 to a 0 b.       In a burst error multiple bits are changed c.       For Example, a 0.01 second burst of impulse noise on a TX with a data rate of 1200 bps [...]

Digital Data Transmission Do we send one bit at a time or do we group bits into larger groups and if so, How? • Parallel Transmission a.                   Binary data consisting of 1s and 0s may be organized into groups of ‘n’ bits each b.                   By grouping we can send data ‘n’ bits at a time [...]

Signals ¬ Need For Signals a.                   One of the major concerns of Physical layer is moving information in the form of electromagnetic signals across a TX medium b.                  Information can be voice, image, numeric data, characters or any message that is readable and has meaning to the destination user (human or m/c) c.                 Generally, the [...]

Presentation Layer This layer is concerned with Syntax and Semantics of info exchange between two systems • Functions of Presentation Layer Translation The processes (running programs) in two systems are usually exchanging info in the form of character strings, numbers and so on….. The info should be changed to bit streams before being transmitted Because [...]

Critique of OSI Model Reasoning for OSI not getting Widespread Bad Timing(slide) (Apocalypse of Two Elephants) –David Clarke of MIT –If standards are written too early: subject is badly understood and bad standards –If standards are written too late so many companies may have already made investments in doing the same thing with different other [...]

Communication Tasks There are some key tasks that must be performed in a data communication system Elements can be added, deleted, or merged together Transmission System utilization Interfacing Signal Generation Synchronization Exchange Management Error Detection and Correction Flow Control Addressing Routing Recovery Security Network Management ¬ Transmission System Utilization Need to make efficient use of [...]

Binomial Distribution Binomial Distribution Fitting a Binomial Distribution to Real Data • An Introduction to the Hyper geometric Distribution The binomial distribution is a very important discrete probability distribution. We illustrate this distribution with the help of the following example: EXAMPLE Suppose that we toss a fair coin 5 times, and we are interested in [...]

PEARSON’S COEFFICIENT OF SKEWNESS 3 (mean − median ) =standard deviation As you can see, this coefficient involves the calculation of the mean as well as the standard deviation. Actually, the numerator is divided by the standard deviation in order to obtain a pure number. If the analysis of a dataset is being undertaken using [...]

DESIRABLE PROPERTIES OF THE MODE • The mode is easily understood and easily ascertained in case of a discrete frequency distribution. • It is not affected by a few very high or low values. The question arises, “When should we use the mode?” The answer to this question is that the mode is a valuable [...]

Types Of  Data Tabulation Simple bar chart Component bar chart Multiple bar chart Pie chart As indicated in the last lecture, there are two broad categories of data … qualitative data and quantitative data. A variety of methods exist for summarizing and describing these two types of data. The treediagram below presents an outline of [...]

WHAT IS STATISTICS? That science which enables us to draw conclusions about various phenomena on the basis of real data collected on samplebasis A tool for databased research Also known as Quantitative Analysis A lot of application in a wide variety of disciplines Agriculture, Anthropology, Astronomy, Biology, Economic, Engineering, Environment, Geology, Genetics, Medicine, Physics, Psychology, [...]

HISTORICAL-COMPARATIVE RESEARCH (Contd.) Conducting historical-comparative research does not involve a rigid set of steps and, with only a few exceptions; it does not use complex or specialized techniques. Nevertheless, some guideline for doing historical-comparative research may be provided. Conceptualizing the Object of Inquiry An H-C researcher begins by becoming familiar with the setting and conceptualizes [...]

USE OF SECONDARY DATA Existing statistics/documents Prior to the discussion of secondary data, let us look at the advantages and disadvantages of the use of content analysis that was covered in the last lecture. In a way content analysis is also the study of documents through which the writers try to communicate, though some of [...]

RESEARCH DESIGN A research design is a master plan specifying the methods and procedures for collecting and analyzing the data. It is a strategy or blueprint that plans the action for carrying through the research project data. A research design involves a series of rational decision-making choices depending upon the various options available to the [...]

Synchronization Using threads we can use lot of shared variables. These shared variables maybe used by a single thread further more these variables may also be used and changed by several parralle threads. If there are several threads operating at the same time then a particular DC handle can be used in one of the [...]

Calling Conventions Functions used in DLL’s are normally use __stdcall calling convention. __stdcall calling convention is a standard calling convention used by the APIs in Windows. This calling convention cleans the stack after returning the called procedure automatically. No extra code is needed to clean out stack. __stdcall calling convention pushes the arguments in stack [...]

Dialog Box Templates A dialog box template is binary data that describes the dialog box, defining its height, width, style, and the controls it contains. To create a dialog box, the system either loads a dialog box template from the resources in the application’s executable file or uses the template passed to it in global [...]

Scope, Initialization and Lifetime of Variable In the following section, we will discuss the scope and lifetime of variables. Example: Consider the example below: int a; int b; Points to be considered: each { } block creates a new scope variables declared and initialized in a scope are deleted when execution leaves scope note the [...]

Participants Subject · Knows its observers. Any number of Observer objects may observe a subject. · Provides an interface for attaching and detaching Observer objects. Observer · Defines an updating interface for objects that should be notified of changes in a subject. Concrete Subject · Stores state of interest to concrete Observer objects. · Sends [...]

Zero Install As discussed earlier, fat-client architecture posed major challenges in terms of installation and maintenance of the client side of the application, especially when there are large number of client machines. So the idea behind zero install architecture is to develop a system where no installation on the client side is needed. This can [...]

Architectural models Like analysis models, many different kinds of architectural models are developed during the architectural design process. Static structural model shows the major system components while a dynamic process model shows the process structure of the system. Interface models are developed to define sub-system interfaces. Architectural Styles Architectural design may be based upon a [...]

Software Design Introduction Recalling our discussion of software construction process, once the requirements of a software system have been established, we proceed to design that system. During the design phase, the focus shifts from what to how. That is, at this stage we try to answer the question of how to build the system. The [...]

Typical Processes Now we shall discuss processes which are typically modeled using data flow diagrams. These processes transform data in one or the other way but these are found in almost all the automated systems. Following are the examples Processes that take inputs and perform certain computations. For example, Calculate Commission is a process that [...]