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dimanche 20 janvier 2013

Cisco HDLC

Cisco HDLC

Cisco HDLC (aussi appelé cHDLC) est un protocole de transmission synchrone sur lien série. Il est au niveau 2 du modèle OSI. C'est une extension du protocole High-Level Data Link Control (HDLC) développé par Cisco. Souvent décrit comme propriétaire car non standardisé, il est, en fait, ouvert et largement distribué. D'autres constructeurs de matériel que Cisco utilisent ce protocole.

Trame HDLC

 

Cette table décrit l'organisation de la trame cHDLC.
Address Control Protocol Code Information Frame Check Sequence (FCS) Flag
8 bits 8 bits 16 bits Variable length, 0 or more bits, in multiples of 8 16 bits 8 bits
  • Le champ address est utilisé pour indiquer le type de paquet : 0x0F Unicast et 0x8F Broadcast.
  • Le champ control est toujours à zéro (0x00).
  • Le champ protocol indique le type de protocole encapsulé dans la trame cHDLC (par exemple 0x0800 pour Internet Protocol).
Source: http://fr.wikipedia.org/wiki/Cisco_HDLC

File Transfer Protocol

File Transfer Protocol

File Transfer Protocol (FTP) is a standard network protocol used to transfer files from one host or to another host over a TCP-based network, such as the Internet.
FTP is built on a client-server architecture and uses separate control and data connections between the client and the server.[1] FTP users may authenticate themselves using a clear-text sign-in protocol, normally in the form of a username and password, but can connect anonymously if the server is configured to allow it. For secure transmission that hides (encrypts) the username and password, and encrypts the content, FTP is often secured with SSL/TLS ("FTPS"). SSH File Transfer Protocol ("SFTP") is sometimes also used instead.
The first FTP client applications were command-line applications developed before operating systems had graphical user interfaces, and are still shipped with most Windows, Unix, and Linux operating systems.[2][3] Dozens of FTP clients and automation utilities have since been developed for desktops, servers, mobile devices, and hardware, and FTP has been incorporated into hundreds of productivity applications, such as Web page editors.
Source: http://en.wikipedia.org/wiki/File_Transfer_Protocol

Internet protocol suite

Internet protocol suite

The Internet protocol suite is the set of communications protocols used for the Internet and similar networks, and generally the most popular protocol stack for wide area networks. It is commonly known as TCP/IP, because of its most important protocols: Transmission Control Protocol (TCP) and Internet Protocol (IP), which were the first networking protocols defined in this standard. It is occasionally known as the DoD model due to the foundational influence of the ARPANET in the 1970s (operated by DARPA, an agency of the United States Department of Defense).
TCP/IP provides end-to-end connectivity specifying how data should be formatted, addressed, transmitted, routed and received at the destination. It has four abstraction layers which are used to sort all Internet protocols according to the scope of networking involved.[1][2] From lowest to highest, the layers are:
  1. The link layer contains communication technologies for a local network.
  2. The internet layer (IP) connects local networks, thus establishing internetworking.
  3. The transport layer handles host-to-host communication.
  4. The application layer contains all protocols for specific data communications services on a process-to-process level. For example, HTTP specifies the web browser communication with a web server.
The TCP/IP model and related protocols are maintained by the Internet Engineering Task Force (IETF).
Source: http://en.wikipedia.org/wiki/Internet_protocol_suite

Internet

Internet

 

The Internet (or internet) is a global system of interconnected computer networks that use the standard Internet protocol suite (TCP/IP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies. The Internet carries an extensive range of information resources and services, such as the inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support email.
Most traditional communications media including telephone, music, film, and television are being reshaped or redefined by the Internet, giving birth to new services such as Voice over Internet Protocol (VoIP) and Internet Protocol Television (IPTV). Newspaper, book and other print publishing are adapting to Web site technology, or are reshaped into blogging and web feeds. The Internet has enabled and accelerated new forms of human interactions through instant messaging, Internet forums, and social networking. Online shopping has boomed both for major retail outlets and small artisans and traders. Business-to-business and financial services on the Internet affect supply chains across entire industries.
The origins of the Internet reach back to research of the 1960s, commissioned by the United States government to build robust, fault-tolerant, and distributed computer networks. The funding of a new U.S. backbone by the National Science Foundation in the 1980s, as well as private funding for other commercial backbones, led to worldwide participation in the development of new networking technologies, and the merger of many networks. The commercialization of what was by the 1990s an international network resulted in its popularization and incorporation into virtually every aspect of modern human life. As of June 2012, more than 2.4 billion people—over a third of the world's human population—have used the services of the Internet.[1]
The Internet has no centralized governance in either technological implementation or policies for access and usage; each constituent network sets its own standards. Only the overreaching definitions of the two principal name spaces in the Internet, the Internet Protocol address space and the Domain Name System, are directed by a maintainer organization, the Internet Corporation for Assigned Names and Numbers (ICANN). The technical underpinning and standardization of the core protocols (IPv4 and IPv6) is an activity of the Internet Engineering Task Force (IETF), a non-profit organization of loosely affiliated international participants that anyone may associate with by contributing technical expertise.
Source: http://en.wikipedia.org/wiki/Internet

Website

Website

 

A website, also written as Web site,[1] web site, or simply site,[2] is a set of related web pages containing content such as text, images, video, audio, etc. A website is hosted on at least one web server, accessible via a network such as the Internet or a private local area network through an Internet address known as a Uniform Resource Locator. All publicly accessible websites collectively constitute the World Wide Web.
A webpage is a document, typically written in plain text interspersed with formatting instructions of Hypertext Markup Language (HTML, XHTML). A webpage may incorporate elements from other websites with suitable markup anchors.
Webpages are accessed and transported with the Hypertext Transfer Protocol (HTTP), which may optionally employ encryption (HTTP Secure, HTTPS) to provide security and privacy for the user of the webpage content. The user's application, often a web browser, renders the page content according to its HTML markup instructions onto a display terminal.
The pages of a website can usually be accessed from a simple Uniform Resource Locator (URL) called the web address. The URLs of the pages organize them into a hierarchy, although hyperlinking between them conveys the reader's perceived site structure and guides the reader's navigation of the site which generally includes a home page with most of the links to the site's web content, and a supplementary about, contact and link page.
Some websites require a subscription to access some or all of their content. Examples of subscription websites include many business sites, parts of news websites, academic journal websites, gaming websites, file-sharing websites, message boards, web-based email, social networking websites, websites providing real-time stock market data, and websites providing various other services (e.g., websites offering storing and/or sharing of images, files and so forth).
Source: http://en.wikipedia.org/wiki/Website

How to Create a Software Startup

How to Create a Software Startup

 There is a glut of overly optimistic literature giving advice and encouragement on entrepreneurship, innovation, and fearlessness in the face of risk. The advice can be quite misleading due to its authors' success bias, because they represent the tiny percentage of people who have succeeded and are given a voice among the infinitely many more people who have failed. Since chances are against most of us who try, the goal of this article is to offer suggestions on how to build a company and give it a chance to stand on its feet, while spending nothing more than the legal fee to register as a company and a domain name. Hopefully it will afford you more time to try to build your company well.

Bootstrapping: What You Can Expect to Achieve

During the bootstrapping stage, as many as possible of the below milestones have to be accomplished in order to ensure the company is able to survive moving forward:
    * A small but solid team has to be gelled and chugging along
    * An early version of the product has to be put on the market
    * Figure out a way to earn a little bit of revenue in the early stages
    * The product has to be gaining some traction
The more of the above a company can accomplish, the better. If none of these are established, there is little chance that the business will become a viable one and the entrepreneur has to take a look at what he or she has accomplished. If, on the other hand, everything falls nicely into place and you are able to accomplish all four of the goals, you may have an incredible new business on your hands that might one day be very successful. If the business is somewhere in the middle, it may be a good candidate for an investment and still have great chances to be successful in the future. Now we'll go through all the necessary steps, pitfalls and considerations to get on the road to accomplishing the above milestones.

The Beginning: The Value of the Original Idea

You probably had a little laugh at the title of this section. Many first-time entrepreneurs and dreamers live in the hopes of a "million-dollar idea." In reality, it is very rare for an idea to be even remotely close to being that valuable. Only years of top-notch execution, continuous innovation, and very hard work will create value. No matter your previous background, there are some common pitfalls. Engineers tend to overdo and business people tend to over-plan; not because they are incompetent, but rather because they are hard workers who are excited about the prospects of their ideas and do what they can before the other parts of the business come along. This is often crippling to the company. One of the first tasks is to build a well-rounded partner team and validate your idea. I won't get into specifics of idea-validation here, as Steve Blank does an amazing job of it in his book "Four Steps to Epiphany" which is a must-read for every entrepreneur, but I will discuss how to build a superstar founding team, starting with the differences in approaches in case your background is technical or in business. What I often hear business people say is, "I am not very technical ..." If this sounds familiar, don't worry, that is understood. Just find a partner who is technical, communicates well, and in whose professionalism you can trust. They will get you up to speed to a level where you need to be. Engineers tend to jump in and do-do-do. But without a clear vision and direction, they often run themselves in circles, over-building unnecessary or overly-complicated features. For their part, engineers might say something similar to "I don't understand business." I myself have been guilty of such a quote. If I could go back in time, I'd advise myself to listen and learn as much and as fast as I can because after a short while, the business environment becomes second nature, fun and fascinating.

Why You Need Partners

Sometimes engineers who have become confident in the business world can pull of a start-up by themselves, but most people need partners. Business people always need engineers for the obvious reason that someone has to actually build the product. Engineers need business people and additional engineers because it is just too difficult for one person to write code, go to business meetings, network, deal with legal issues, do marketing, branding, social media, a slew of other tasks, while keeping a clear mind to maintain focus on their entrepreneurial vision.
Source: http://www.devx.com/webdev/Article/44068

Read-only memory

Read-only memory

Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to need frequent updates).
In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can never be modified. Despite the simplicity, speed and economies of scale of mask ROM, field-programmability often make reprogrammable memories more flexible and inexpensive. As of 2007, actual ROM circuitry is therefore mainly used for applications such as microcode, and similar structures, on various kinds of processors.
Other types of non-volatile memory such as erasable programmable read only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM or Flash ROM) are sometimes referred to, in an abbreviated way, as "read-only memory" (ROM); although these types of memory can be erased and re-programmed multiple times, writing to this memory takes longer and may require different procedures than reading the memory.[1] When used in this less precise way, "ROM" indicates a non-volatile memory which serves functions typically provided by mask ROM, such as storage of program code and nonvolatile data.
Source: http://en.wikipedia.org/wiki/Read-only_memory