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    24Aug, 2014
    Website Development

    Web development is a broad term for the work involved in developing Websites for the Internet (World Wide Web) or the Intranet (private network).
    If you already know what this service is all about and wish to start or continue an ongoing project with me, please check the information page about fees and terms.
    Web development can range from developing a simplest static single page written in plain text, to the most complex web-based Internet applications, electronic business and social network services usually written in one or several Internet compatible programming languages.
    A more comprehensive list of tasks to which web development commonly refers, may include:

    • web design,
    • web content development,
    • client liaison,
    • client-side/server-side scripting,
    • web server and network security configuration, and
    • e-commerce development.

    Among web professionals, “web development” usually refers to the main non-design aspects of building web sites: writing markup and coding. Web development is a collaborative effort between departments rather than the domain of a designated department.
    For small organizations and businesses, web development teams can consist of few people (1 to 10 web developers). Such organizations may only require a single permanent or contracting webmaster, or secondary assignment to related job positions such as a graphic designer and/or information systems technician.
    For larger organizations and businesses, web development teams can consist of dozens and even hundreds of people (web developers), and still, Web development may be a collaborative effort between departments.

    Web development as an industry

    Since the commercialization of the web, web development has been a growing industry. The growth of this industry is being pushed especially by businesses wishing to sell products and services to online customers. Internet sales if growing worldwide.
    For tools and platforms, the public can use many open source systems to aid in web development saving huge amounts of money. A popular example, the LAMP (Linux, Apache, MySQL, PHP) stack is available for download online free of charge. This has kept the cost of learning web development to a minimum. Another contributing factor to the growth of the industry has been the rise of easy-to-use WYSIWYG web-development software, most prominently Adobe Dreamweaver, WebDev, and Microsoft Expression Studio. Using such software, virtually anyone can relatively and quickly learn to develop a very basic web page.
    Knowledge of HyperText Markup Language (HTML) and/or of programming languages is still required to use public domain and shareware software, but the basics can be learned and implemented quickly with the help of help files, technical books, internet tutorials, or face-to-face training. Learning to program computers and servers is not difficult, just time consuming. Learning about the full power of a programing language may easily take one to several years. To call someone a good programmer, he/she may have to have at least 10 years of programming experience using an specific language.
    An ever growing set of tools and technologies have helped developers build more dynamic and interactive websites. Web developers now help to deliver applications as web services which were traditionally only available as applications on a desk-based computer.
    Instead of running executable code on a local computer, users can interact with an online application to create new content interactively, using any text editor or programming platform. This has created a new method in communication and allowed for many opportunities to decentralize information and media distribution. Users can interact with applications from many locations instead of being tied to a specific workstation for their application environment.

    Web based applications allows you to have multiple users, and can be accessed from anywhere in the world

    Examples of dramatic transformation in communication and commerce led by web development include: e-commerce, social networks, dating services, online classifieds, shopping carts.
    Online auction-sites such as eBay have changed the way consumers find and purchase goods and services. Online retailers such as Amazon.com and Buy.com (among many others) have transformed the shopping and bargain-hunting experience for many consumers. Another good example of transformative communication led by web development is the use of blog platforms like Drupal, WordPress, DotNetNuke, BlogsDotNet, etc. Web applications such as WordPress and Movable Type have created easily-implemented blog-environments for individual web sites. The popularity of open-source content management systems such as Joomla!, Drupal, XOOPS, TYPO3 and enterprise content management systems such as Alfresco and eXo Platform have extended web development’s impact at online interaction and communication.
    Web development has also impacted personal networking and marketing. Websites are no longer simply tools for work or for commerce, but serve more broadly for communication and social networking. Websites such as Facebook and Twitter provide users with a platform to communicate and organizations with a more personal and interactive way to engage the public.
    Typical areas
    Web Development can be split into many areas, and a typical and basic web development hierarchy might consist of:
    Client side coding

    • Ajax Asynchronous JavaScript provides new methods of using JavaScript, and other languages to improve the user experience.
    • Flash Adobe Flash Player is a ubiquitous browser plugin ready for RIAs. Flex 2 is also deployed to the Flash Player (version 9+).
    • JavaScript JavaScript is a ubiquitous client side platform for creating and delivering rich web applications that can also run across a wide variety of devices. It is a dialect of the scripting language ECMAScript.
    • jQuery Cross-browser JavaScript library designed to simplify and speed up the client-side scripting of HTML.
    • Microsoft Silverlight Microsoft’s browser plugin that enables animation, vector graphics and high-definition video playback, programmed using XAML and .NET programming languages.
    • HTML5 and CSS3 Latest HTML proposed standard combined with the latest proposed standard for CSS natively supports much of the client-side functionality provided by other frameworks such as Flash and Silverlight

    Looking at these items from an “umbrella approach”, client side coding such as XHTML is executed and stored on a local client (in a web browser) whereas server side code is not available to a client and is executed on a web server which generates the appropriate XHTML which is then sent to the client. The nature of “client side coding” allows one to alter the HTML on a local client and refresh the pages with updated content (locally), web designers must bear in mind the importance and relevance to security with their server side scripts. If a server side script accepts content from a locally modified client side script, the web development of that page is poorly sanitized with relation to security.
    Server side coding

    • ASP (Microsoft proprietary)
    • ColdFusion (Adobe proprietary, formerly Macromedia, formerly Allaire)
    • CGI
    • Erlang, with Linux, Yaws, Mnesia, Erlang (LYME) solution stack
    • Groovy, using the Grails framework
    • Java, e.g. Java Servlets, JSP or WebObjects
    • Lotus Domino
    • Node.js
    • Perl, e.g. Catalyst, Dancer or Mojolicious (all open source)
    • PHP (open source)
    • Python, e.g. Django (web framework) (open source)
    • Ruby, e.g. Ruby on Rails (open source)
    • Scala, e.g. Play Framework, Lift Framework (open source)
    • SSJS Server-Side JavaScript, e.g. Aptana Jaxer, Mozilla Rhino
    • .NET and .NET MVC Frameworks (Microsoft proprietary)
    • Client side + server side
    • Google Web Toolkit provides tools to create and maintain complex JavaScript front-end applications in Java.
    • Dart provides tools to create and maintain complex JavaScript front-end applications as well as supporting server-side code in Dart (programming language).
    • Opa is a high-level language in which both the client and the server parts are implemented. The compiler then decides which parts run on the client (and are translated automatically to JavaScript) and which parts run on the server. The developer can tune those decisions with simple directives. (open source)
    • Pyjamas is a tool and framework for developing Ajax applications and Rich Internet Applications in Python.

    Tersus is a platform for the development of rich web applications by visually defining user interface, client side behavior and server side processing. (open source)
    However, languages like Ruby and Python are often paired with database servers other than MySQL (the M in LAMP). Below are example of other databases currently in wide use on the web. For instance some developers prefer a LAPR setup for development. (LAPR = Linux/Apache/PostgreSQL/Ruby on Rails)
    Database technology

    • Apache Derby *
    • CouchDB *
    • FileMaker
    • Firebird *
    • IBM DB2
    • IBM Notes
    • MariaDB *
    • Mark_Logic
    • Microsoft SQL Server
    • MongoDB *
    • MySQL *
    • Oracle
    • PostgreSQL *
    • Redis *
    • SQLite *
    • Sybase
    • WebDNA

    * open source / public domain

    Practical web development

    Basic
    In practice, many web developers will have basic interdisciplinary skills / roles, including:

    • Information System’s design
    • Web site’s design
    • Graphic’s design
    • Information architecture and copywriting/copyediting with web usability, accessibility and search engine optimization in mind

    The above list is a simple website development hierarchy and can be extended to include all client side and server side aspects. It is still important to remember that web development is generally split up into client side coding, covering aspects such as the layout and design, and server side coding, which covers the website’s functionality and back-end systems.
    Advanced
    Some more advanced web developers will also have these interdisciplinary skills / roles:

    • GUI (Graphic User Interface) design
    • Audio, Video and Animation processing and encoding (for web usage)
    • Flash Capabilities (animation, audio, video, scripting)
    • Web content management system Deployment and/or Content management infrastructure design, development and integration
    • Web applications development, integration and deployment
    • Web server stress testing (how much traffic can a web server running a specific application endure before collapsing)
    • Web site security analysis & testing
    • Web site code optimization (which is an important aspect of search engine optimization)
    • Project management, QA and other aspects common to IT development
    • Advanced customized admin panel (For end-users)
    • Database integration with web applications
    • Security considerations

    Web development takes into account many security considerations, such as data entry error checking through forms, filtering output, and encryption.
    Malicious practices such as SQL injection can be executed by users with ill intent yet with only primitive knowledge of web development as a whole. Scripts can be used to exploit websites by granting unauthorized access to malicious users that try to collect information such as email addresses, passwords and protected content like credit card numbers and customer’s information.
    Some of this is dependent on the server environment, most commonly Apache or Microsoft IIS, on which the scripting language, such as PHP, Ruby, Python, Perl or ASP is running, and therefore is not necessarily down to the web developer themselves to maintain. However, stringent testing of web applications before public release is encouraged to prevent such exploits from occurring. If some contact form is provided in a website it should include a “captcha” field in it which prevents computer programs from automatically filling forms and also mail spamming.
    Keeping a web server safe from intrusion is often called “Server Port Hardening”. Many technologies come into play to keep information on the internet safe when it is transmitted from one location to another. For instance “Secure Socket Layer Encryption” (SSL) Certificates are issued by certificate authorities to help prevent internet fraud. Many developers often employ different forms of encryption when transmitting and storing sensitive information. A basic understanding of information technology security concerns is often part of a web developer’s knowledge.
    Because new security holes are found in web applications, even after testing and launch, security patch updates are frequent for widely used applications. It is often the job of web developers to keep applications up to date as security patches are released and new security concerns are discovered.
    For your Website development needs, DAPROSE offers you the experience, the skills, and the technology to develop, host, and maintain your Web based applications from the ground up.

    Ready to start some serious business with me?

    Please check the information page about my fees and terms. Or call me at (713) 714-7852 for more information.

    19Apr, 2012
    Working on Estimates

    All services contracted with me will be performed to the best of my knowledge and expertise, all in “good faith”.

    I am trying to put my thoughts together about the constant requests for estimates that I usually receive on the phone, and this is what comes to mind:

    About the project proposal

    Please understand that without a fully written “Project Proposal”, I can not give anyone a true nor a real estimate on anything!
    Any software application, large or small, could have tons of features and requirements, or just very few features which they in turn do depend on many factors that must be considered individually. Each software feature could take several months of programming time to complete while others could be completed in a very few hours or minutes.
    Without a complete list of features demanded “up front”, it is practically impossible to guess the total cost of any application, much less, I would be able to calculate the time it would take to complete any project.
    An “Architect” creates the blueprints/plans for building a new house, and only then an “Engineer” can give you an estimate for building that new house, … (and build it once the price is agreed, if that is the case) , “But, not the other way around”. Asking an Engineer for an estimate about the costs for building a house without having the plans or blueprints to build the house will be impossible for an Engineer to guess the cost just from the imagination. And, … if not impossible, the estimate could be totally inaccurate and unrealistic. If what you are looking for is just my hourly fee, please click here.
    If you do not have the blueprints/plan of the house, (In our case, THE PROJECT PROPOSAL FOR THAT NEW OR EXTENDED INFORMATION SYSTEM YOU NEED), then you must hire an Architect first, (in our case it will be an “Information Systems Analyst”). He/She, a SYSTEMS ANALYST, will be able to create a “COMPLETE PROJECT PROPOSAL” for you and your business.  I am both, a COMPUTER PROGRAMMER, and a SYSTEMS ANALYST. I am fully capable of creating any type of project proposal for your Information System needs
    Once the “Project Proposal” is complete, only then it must be presented to a “Computer Programmer” to obtain a quote or an estimate on the cost to build (and the time it will take) to complete the suggested application; and if agreed to create the application itself.  Got the picture now?
    If you already have the “Project Proposal” then please send it to me ASAP via email to: support@daprose.com so I can give you an estimate on the total cost and time to complete the application;  otherwise, please write me a note stating that you need my “consulting services” first, so we can create the “Project Proposal” together.  In such a case, your full participation will be required and mandatory.

    No middle companies please

    I do prefer to work with the hiring company “directly”, without middle companies please. The reason is that, intermediaries usually want to make 50% or more on each contract, while at the same time I am the one doing all the works, so please!, why should I split so much money with them after all?   Just for a phone call?  No way,  sorry!!  NO MIDDLE COMPANIES PLEASE!!  I do prefer to do my own work search and handle everything by myself.  In most cases, my fees are by far much less than those offered by the big guys.
    .

    Fees and other terms

    For non-time termed contracts  I normally charge $125/hour for consulting or programming services, (paid in advance on a weekly basis), Example: 40 hours x $125 = $5,000), 8 hrs per day minimum.
    I am fully negotiable in situations where a long time contract is anticipated. (Ex: 6/12 month contracts).  If you do not have a complete “PROJECT PROPOSAL”, I can prepare one for you no later than two weeks, but rarely, due to the nature of each work, it may involve several weeks prior to starting any real development/programming project. All fees will be accepted on a minimum of 80 hours, (2 weeks), on a prepaid basis only. No exceptions.

    Refunds, warranties or guaranties

    There are no refunds nor warranties or guaranties of any kind on this type of work.  All services contracted with me will be performed to the best of my knowledge and expertise, all in “good faith”.
    Depending on each project, we may need more time to complete the project. If we both agree to continue, you will be billed for the extra time at the same hourly rate negotiated originally; otherwise, all works completed to the end of the 5th day of work of each contracted week will be delivered to you in full, and all consulting/programming services will be considered as “completed at your full satisfaction”.
    Your involvement and/or availability during the production of the “Project Proposal” is mandatory. Not being able to participate during development time, it does not constitute an understanding to postpone the “end-date” already contracted, which concludes at the end of the 5th day of each contracted week.   Days of work are continuous, never alternated or chosen at free will, otherwise customer will be billed for all the dead times.  (Example of a week contracted: MON-FRI, TUE-MON, WEN-TUE, THR-WEN, or FRI-THR). Unless there was a mandatory holiday, most Project Proposals for small business applications are completed in two weeks.

    Don’t have a project proposal?

    We could also take a second approach to the problem of not having a project proposal. For those individuals who think that “plans and blueprints are not important”, “much less necessary”, because they think all they need is a “barn” and not a “hotel”, then, please provide me with some basic information and I can tell you later what is that I can do with the information you have available.
    For example:
    1)     Provide me with a brief explanation of the project,
    2)     How much money do you want to spend in this project?
    3)     How soon do you need it?
    4)     What platforms will the project be implanted at? (Unix/Linux/Windows/RTOS/Mac)
    5)     What inputs and outputs are involved? (PDAs/Reports/GUIs)
    6)     What are the basic features you want in this project? (Make a list)
    7)     Will this be a 1, 2, or 3 tier information system?

    Prepayment is a requirement

    Contracting any type of software development will require a prepayment before starting any project. Sometimes I may require the full 100% of the total cost “paid upfront”, while other times I may request just a percentage of the total cost paid upfront, in which case, some type of payment arrangements will have to be agreed upon the remaining balance.
     
    See more detailed information about programming at:
    http://daprose.com/?p=1240

    16Jan, 2012
    Client Application Development

    Client Application Development

    Client applications are the closest to a traditional style of application in Windows-based programming. These are the types of applications that display windows or forms on the desktop, enabling a user to perform a task. Client applications include applications such as word processors and spreadsheets, as well as custom business applications such as data-entry tools, reporting tools, and so on. Client applications usually employ windows, menus, buttons, and other GUI elements, and they likely access local resources such as the file system and peripherals such as printers.
    Another kind of client application is the traditional ActiveX control (now replaced by the managed Windows Forms control) deployed over the Internet as a Web page. This application is much like other client applications: it is executed natively, has access to local resources, and includes graphical elements.
    In the past, developers created such applications using C/C++ in conjunction with the Microsoft Foundation Classes (MFC) or with a rapid application development (RAD) environment such as Microsoft® Visual Basic®. The .NET Framework incorporates aspects of these existing products into a single, consistent development environment that drastically simplifies the development of client applications.
    The Windows Forms classes contained in the .NET Framework are designed to be used for GUI development. You can easily create command windows, buttons, menus, toolbars, and other screen elements with the flexibility necessary to accommodate shifting business needs.
    For example, the .NET Framework provides simple properties to adjust visual attributes associated with forms. In some cases the underlying operating system does not support changing these attributes directly, and in these cases the .NET Framework automatically recreates the forms. This is one of many ways in which the .NET Framework integrates the developer interface, making coding simpler and more consistent.
    Unlike ActiveX controls, Windows Forms controls have semi-trusted access to a user’s computer. This means that binary or natively executing code can access some of the resources on the user’s system (such as GUI elements and limited file access) without being able to access or compromise other resources. Because of code access security, many applications that once needed to be installed on a user’s system can now be deployed through the Web. Your applications can implement the features of a local application while being deployed like a Web page.

    15Jan, 2012
    20+ years programming computers

    Your business can safely save tons of money contracting your software development needs with us.  We have over 20 years of experience developing microcomputer software for the entire array of Microsoft Servers and Work Stations.
    We accept programming contracts for clients who want customized software almost anywhere in the world. All applications are developed “in our facility”, according to a predefined set of specifications.

    Software Development Steps

    Preparing a set of “software specifications” require an in-deep analysis of both, the information needs of your clients and end users, and the overall information system structure of your business. Our RAD/JAD Technologies help us to ensure a successful application deployment. There are several determining factors the can contribute to easily understand what a software program is all about, whether or not you need it, and how long will it take to implement it.
    Software programs usually have a direct relationship with “information systems”. They can be a stand alone application, or a part of an integrated system. Whatever is the case, programs are developed according to a predefined set of specifications; and, to ensure success you and I must carefully define and study the following:

    • The project proposal.
    • The hardware and software requirements
    • A preliminary system design
    • A preliminary cost-benefit analysis
    • The source code specifications
    • An indeep analysis of the methodologies to accomplish all requirements
    • The hardware and software selection
    • A prototyping
    • The development and implementation
    • Any necessary training to users and administrators
    • Any possible after-sale maintenance
    • The maintenance of existing systems
    • The integrating systems
    • Any future consultant-client relationship

    Factors to Determine

    We develop useful software systems in compliance with:

    • PLATFORMS
    • DATA
    • REPORTS
    • ALGORITHMS
    • INTEGRATION
    • USER INTERFACE
    • BACKUP AND RECOVERY REQUIREMENTS
    • SPECIAL REQUIREMENTS

    Developmental Software

    Selecting a computer language facilitates program development. The choice of a language is critical, every programming language have different strengths and weaknesses. We develop custom applications for the entire line of Microsoft Windows Servers and Workstations, using the best and latest 2GLs, 3GLs, and 4GLs available in the market. We use all Microsoft Visual Studio Professional platforms.

    Programming Languages Supported

    We support the following programming Languages: Basic, SuperBASIC, PowerBASIC, Visual Basic, Visual Basic .Net, MapBasic, C/C++/C#, Database Management Languages, (DBMS), (xBASE), Clipper, FoxPro/Visual FoxPro, MS-Access/VBA, SyBase, MS-SQL (T-SQL), MySQL, and any SQL compatible language (ex: SQLite, CompactSQL).
    We can also program and design “Internet Applications” using “sockets” and develop/deploy Websites for both the Internet and the Intranet using HTML/HTML5, DHTML/XHTML, ASP/ASP.NET, VBScripts, JScripts, JavaScripts, using ADO, DAO, and ODBC connectivity modules and interfaces. Depending on each individual case, we will delivery the finished product as a source code, as a script file, or as an auto-executable file; tested and documented.

    Key Benefits

    • Fast, compact code.
    • Commented source code.
    • Properly tested and documented.

    Fees

    Our fees are negotiable based on the following different criterias:

    • Platform,
    • Frequency ,
    • Expertise Required,
    • Accessibility; and,
    • Deadline.

    To learn more about estimates, and fees and other terms, please visit:
    http://www.daprose.com/?p=1352

    15Nov, 2011
    WiFi: The Physical Layer

    The three physical layers originally defined in 802.11 included two spread-spectrum radio techniques and a diffuse infrared specification.

    The radio-based standards operate within the 2.4 GHz ISM band. These frequency bands are recognized by international regulatory agencies radio operations. As such, 802.11-based products do not require user licensing or special training.

    Spread-spectrum techniques, in addition to satisfying regulatory requirements, increase reliability, boost throughput, and allow many unrelated products to share the spectrum without explicit cooperation and with minimal interference.

    The original 802.11 wireless standard defines data rates of 1 Mbps and 2 Mbps via radio waves using frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS). It is important to note that FHSS and DSSS are fundamentally different signaling mechanisms and will not interoperate with one another.

    Using the frequency hopping technique, the 2.4 GHz band is divided into 75 1-MHz subchannels. The sender and receiver agree on a hopping pattern, and data is sent over a sequence of the subchannels. Each conversation within the 802.11 network occurs over a different hopping pattern, and the patterns are designed to minimize the chance of two senders using the same subchannel simultaneously.

    FHSS techniques allow for a relatively simple radio design, but are limited to speeds of no higher than 2 Mbps. This limitation is driven primarily by FCC (Federal Communications Commission USA) regulations that restrict subchannel bandwidth to 1 MHz. These regulations force FHSS systems to spread their usage across the entire 2.4 GHz band, meaning they must hop often, which leads to a high amount of hopping overhead.

    In contrast, the direct sequence signaling technique divides the 2.4 GHz band into 14 22-MHz channels. Adjacent channels overlap one another partially, with three of the 14 being completely non-overlapping. Data is sent across one of these 22 MHz channels without hopping to other channels.

    To compensate for noise on a given channel, a technique called “chipping” is used. Each bit of user data is converted into a series of redundant bit patterns called “chips.” The inherent redundancy of each chip combined with spreading the signal across the 22 MHz channel provides for a form of error checking and correction; even if part of the signal is damaged, it can still be recovered in many cases, minimizing the need for retransmissions.

    15Nov, 2011
    WiFi: The Data Link Layer

    The data link layer within 802.11 consists of two sublayers: Logical Link Control (LLC) and Media Access Control (MAC).

    802.11 uses the same 802.2 LLC and 48-bit addressing as other 802 LANs, allowing for very simple bridging from wireless to IEEE wired networks, but the MAC is unique to WLANs.

    The 802.11 MAC is very similar in concept to 802.3, in that it is designed to support multiple users on a shared medium by having the sender sense the medium before accessing it.

    For 802.3 Ethernet LANs, the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol regulates how Ethernet stations establish access to the wire and how they detect and handle collisions that occur when two or more devices try to simultaneously communicate over the LAN. In an 802.11 WLAN, collision detection is not possible due to what is known as the “near/far” problem: to detect a collision, a station must be able to transmit and listen at the same time, but in radio systems the transmission drowns out the ability of the station to “hear” a collision.

    To account for this difference, 802.11 uses a slightly modified protocol known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) or the Distributed Coordination Function (DCF). CSMA/CA attempts to avoid collisions by using explicit packet acknowledgment (ACK), which means an ACK packet is sent by the receiving station to confirm that the data packet arrived intact.

    CSMA/CA works as follows. A station wishing to transmit senses the air, and, if no activity is detected, the station waits an additional, randomly selected period of time and then transmits if the medium is still free. If the packet is received intact, the receiving station issues an ACK frame that, once successfully received by the sender, completes the process. If the ACK frame is not detected by the sending station, either because the original data packet was not received intact or the ACK was not received intact, a collision is assumed to have occurred and the data packet is transmitted again after waiting another random amount of time.

    CSMA/CA thus provides a way of sharing access over the air. This explicit ACK mechanism also handles interference and other radio related problems very effectively. However, it does add some overhead to 802.11 that 802.3 does not have, so that an 802.11 LAN will always have slower performance than an equivalent Ethernet LAN.

    Another MAC-layer problem specific to wireless is the “hidden node” issue, in which two stations on opposite sides of an access point can both “hear” activity from an access point, but not from each other, usually due to distance or an obstruction.

    To solve this problem, 802.11 specifies an optional Request to Send/Clear to Send (RTS/CTS) protocol at the MAC layer. When this feature is in use, a sending station transmits an RTS and waits for the access point to reply with a CTS. Since all stations in the network can hear the access point, the CTS causes them to delay any intended transmissions, allowing the sending station to transmit and receive a packet acknowledgment without any chance of collision.

    Since RTS/CTS adds additional overhead to the network by temporarily reserving the medium, it is typically used only on the largest-sized packets, for which retransmission would be expensive from a bandwidth standpoint.

    Finally, the 802.11 MAC layer provides for two other robustness features: CRC checksum and packet fragmentation. Each packet has a CRC checksum calculated and attached to ensure that the data was not corrupted in transit. This is different from Ethernet, where higher-level protocols such as TCP handle error checking. Packet fragmentation allows large packets to be broken into smaller units when sent over the air, which is useful in very congested environments or when interference is a factor, since larger packets have a better chance of being corrupted. This technique reduces the need for retransmission in many cases and thus improves overall wireless network performance. The MAC layer is responsible for reassembling fragments received, rendering the process transparent to higher level protocols.

    Support for Time-Bounded Data
    Time-bounded data such as voice and video is supported in the 802.11 MAC specification through the Point Coordination Function (PCF). As opposed to the DCF, where control is distributed to all stations, in PCF mode a single access point controls access to the media. If a BSS is set up with PCF enabled, time is spliced between the system being in PCF mode and in DCF (CSMA/CA) mode. During the periods when the system is in PCF mode, the access point will poll each station for data, and after a given time move on to the next station. No station is allowed to transmit unless it is polled, and stations receive data from the access point only when they are polled. Since PCF gives every station a turn to transmit in a predetermined fashion, a maximum latency is guaranteed. A downside to PCF is that it is not particularly scalable, in that a single point needs to have control of media access and must poll all stations, which can be ineffective in large networks.

    15Nov, 2011
    WiFi: High Speed with 802.11a

    802.11a, is much faster than 802.11b, with a 54Mbps maximum data rate operates in the 5GHz frequency range and allows eight simultaneous channels.

    802.11a uses Orthogonal Frequency Division Multiplexing (OFDM), a new encoding scheme that offers benefits over spread spectrum in channel availability and data rate.

    Channel availability is significant because the more independent channels that are available, the more scalable the wireless network becomes. 802.11a uses OFDM to define a total of 8 non-overlapping 20 MHz channels across the 2 lower bands. By comparison, 802.11b uses 3 non-overlapping channels.

    All wireless LANs use unlicensed spectrum; therefore they&qt;&qt;re prone to interference and transmission errors. To reduce errors, both types of 802.11 automatically reduce the Physical layer data rate. IEEE 802.11b has three lower data rates (5.5, 2, and 1Mbit/sec), and 802.11a has seven (48, 36, 24, 18, 12, 9, and 6Mbits/sec). Higher (and more) data rates aren&qt;&qt;t 802.11a&qt;&qt;s only advantage. It also uses a higher frequency band, 5GHz, which is both wider and less crowded than the 2.4GHz band that 802.11b shares with cordless phones, microwave ovens, and Bluetooth devices.

    The wider band means that more radio channels can coexist without interference. Each radio channel corresponds to a separate network, or a switched segment on the same network. One big disadvantage is that it is not directly compatible with 802.11b, and requires new bridging products that can support both types of networks. Other clear disadvantages are that 802.11a is only available in half the bandwidth in Japan (for a maximum of four channels), and it isn&qt;&qt;t approved for use in Europe, where HiperLAN2 is the standard.

    15Nov, 2011
    WiFi: A little about 802.11b

    With 802.11b WLANs, mobile users can get Ethernet levels of performance, throughput, and availability.

    The basic architecture, features, and services of 802.11b are defined by the original 802.11 standard. The 802.11b specification affects only the physical layer, adding higher data rates and more robust connectivity.

    The key contribution of the 802.11b addition to the wireless LAN standard was to standardize the physical layer support of two new speeds,5.5 Mbps and 11 Mbps.

    To accomplish this, DSSS had to be selected as the sole physical layer technique for the standard since, as frequency hopping cannot support the higher speeds without violating current FCC regulations. The implication is that 802.11b systems will interoperate with 1 Mbps and 2 Mbps 802.11 DSSS systems, but will not work with 1 Mbps and 2 Mbps 802.11 FHSS systems.

    The original 802.11 DSSS standard specifies an 11-bit chipping?called a Barker sequence?to encode all data sent over the air. Each 11-chip sequence represents a single data bit (1 or 0), and is converted to a waveform, called a symbol, that can be sent over the air.

    These symbols are transmitted at a 1 MSps (1 million symbols per second) symbol rate using technique called Binary Phase Shift Keying BPSK). In the case of 2 Mbps, a more sophisticated implementation called Quadrature Phase Shift Keying (QPSK) is used; it doubles the data rate available in BPSK, via improved efficiency in the use of the radio bandwidth. To increase the data rate in the 802.11b standard, advanced coding techniques are employed.

    Rather than the two 11-bit Barker sequences, 802.11b specifies Complementary Code Keying (CCK), which consists of a set of 64 8-bit code words. As a set, these code words have unique mathematical properties that allow them to be correctly distinguished from one another by a receiver even in the presence of substantial noise and multipath interference (e.g., interference caused by receiving multiple radio reflections within a building).

    The 5.5 Mbps rate uses CCK to encode 4 bits per carrier, while the 11 Mbps rate encodes 8 bits per carrier. Both speeds use QPSK as the modulation technique and signal at 1.375 MSps. This is how the higher data rates are obtained. To support very noisy environments as well as extended range, 802.11b WLANs use dynamic rate shifting, allowing data rates to be automatically adjusted to compensate for the changing nature of the radio channel. Ideally, users connect at the full 11 Mbps rate.

    However when devices move beyond the optimal range for 11 Mbps operation, or if substantial interference is present, 802.11b devices will transmit at lower speeds, falling back to 5.5, 2, and 1 Mbps. Likewise, if the device moves back within the range of a higher-speed transmission, the connection will automatically speed up again. Rate shifting is a physical layer mechanism transparent to the user and the upper layers of the protocol stack.

    One of the more significant disadvantages of 802.11b is that the frequency band is crowded, and subject to interference from other networking technologies, microwave ovens, 2.4GHz cordless phones (a huge market), and Bluetooth. There are drawbacks to 802.11b, including lack of interoperability with voice devices, and no QoS provisions for multimedia content. Interference and other limitations aside, 802.11b is the clear leader in business and institutional wireless networking and is gaining share for home applications as well.

    15Nov, 2011
    WiFi Security

    Security is one of the first concerns of people deploying a Wireless LAN, the 802.11 committee has addressed the issue by providing what is called WEP (Wired Equivalent Privacy).

    The main concerns of users are that an intruder would not be able to:

    • Access the Network resources by using similar Wireless LAN equipment, and

    • Be able to capture the Wireless LAN traffic (eavesdropping)

    Preventing Access to Network Resources
    This is done by the use of an Authentication mechanism where a station needs to prove knowledge of the current key; this is very similar to the Wired LAN privacy, on the sense that an intruder needs to enter the premises (by using a physical key) in order to connect his workstation to the wired LAN.

    Eavesdropping
    Eavesdropping is prevented by the use of the WEP algorithm, which is a Pseude Randon Number Generator (PRNG), initialized by a shared secret key. This PRNG outputs a key sequence of pseude-random bits equal in length to the largest possible packet, which is combined with the outgoing/incoming packet producing the packet transmitted in the air.

    The WEP algorithm is a simple algorithm based on RSA?s RC4 algorithm, which has the following properties:

    • Reasonable strong: Brute-force attack to this algorithm is difficult because of the fact that every frame is sent with an Initialization Vector, which restarts the PRNG for each frame.

    • Self Synchronizing: The algorithm synchronized again for each message, this is needed in order to work on a connectionless environment, where packets may get lost (as any LAN).

    15Nov, 2011
    What is computer networking?

    A network is a collection of connected intelligent computing devices. The connection is not necessarily a fancy one. A connection between two computers by direct cabling is qualified to be a network. By this definition, a workstation which is loaded with a computer, a scanner, and a printer, is not treated as a network.

    A network can consist of two computers connected together on a desk or it can consist of many Local Area Networks (LANs) connected together to form a Wide Area Network (WAN) across a continent. The key is that two or more computers are connected together by a medium and are sharing resources. These resources can be files, printers, hard?drives, or CPU number-crunching power.

    A Local Area Network (LAN) is a smaller network within one location or between several buildings A Metropolitan Network (MAN, politically incorrect, no WOMAN!) is a midsize network spanning the city. A Wide Area Network (WAN) is a giant network spanning across several cities or even several continents.