Architecture for Internet Data Transfer - Lab Report Example

Network and Protocol Processes In accessing X-Stream’s website from the home computers, instructions must be given to the home computer on what to do; these instructions must be understandable to the sender to be able to send them. The computer must convert these instructions that we will refer to as data into a language it understands. The machine language instructions are relayed via a medium from where the data is guided to access the X-Stream website. Various complex and simple processes take place during this data transmission and involves many devices (Shuler). The devices are called end devices or more correctly hosts; which are either the destinations or sources of information transmitted via a network so accessing a network or site remotely involves three elements; a source or sender, a destination and a medium which is the channel through which the data is transmitted. The data transmitted can be in the form of text, graphics, voice or video which are converted into a language the computer understands called binary bits (data is transmitted as a zero or a one: 0I). The bits are then ‘programmed’ or coded into signals or data packets that can be transmitted through a medium over a network. Now sending data as one continuous stream will mean that no other data or devices can use the medium while the data is being transmitted just like a pipeline; if it is delivering gasoline, it cannot at the same time deliver liquid petroleum gas; so the data is broken into smaller packets; a process called segmentation which allows many different data to be transmitted concurrently, this is called multiplexing and segmenting data enhances network reliability so data is not lost easily whenever a break in communication occurs (“3rd Symposium on Networked Systems design and Implementation (NSDI’06), San Jose, California”). This allows data to be transmitted over alternate pathways in the event that some channels are congested using the segments. On reaching the destination, the data bits are then re assembled into a continuous data stream from binary bits into text or video that a human can read. The computer communicates with other computers in the internet using IP addresses which are unique electronic identifiers, using a protocol stack usually found on the operating system. The one used for internet communication is called TCP/IP stack which contains four layers; Application protocols layer that is defined to applications like WWW, or FTP (File Transfer Protocol), a transmission control protocol which is responsible for directing packets of data to specific computers by using a port number. It also has an internet protocol layer that directs data bits to destinations using the IP addresses of the computers and a hardware layer that converts data into data streams or signals such as the network cards or modems. An instruction flows from the sender (computer) from the application to the transfer control protocol then to the internet protocol and finally to the hardware protocol that converts the bits of information into signals transmitted through a medium through the internet. On reaching the destination computer, the signals are converted back to binary bits through the hardware layer then to the internet protocol layer then to transfer protocol layer and then to the application such as a web server software. The internet is made up of many big networks called Network Service providers (NSPs0 connected together in a peer standard. The NSPs exchange data packets with each other and must connect to three network access points (NAPs) and at metropolitan Area Exchanges (MAEs) both of which are called internet exchange points (IXs). Information is then sent around these networked computers to its destinations by routers which contain information tables and switch data packets to the right destination (Serpanos and Wolf 292-302) As soon as one types the web address to be accessed into a web browser (a web browser is a program that is used for internet applications and communications and have a graphical user interface) say http://x-stream.leedsmet.ac.uk/ a set of processes are set into motion. The web address contains different parts; the http:// (http means hypertext transfer protocol) is the scheme that tells the internet browser the protocol to employ in accessing and retrieving the requested web site. The following part www (standing for World Wide Web) is the host and instructs the browser that the website is found in the internet. Note that some networks are found within an organization called an intranet which can only be accessed by computers within that intranet. The part ‘x-stream’ is the domain name of the website and ‘.com’ is the extension which gives an indication of the type of website. A web address (called universal resource locator URL) can have a component that indicates the path a browser needs to follow to fetch the website or material such as /news.html. After entering the correct URL into a web browser, the browser will search for the IP address for the domain name. Computers and servers have a unique addressing system just like a postal or street address that a browser searches for the IP address from the DNS server. DNS stands for Domain Name System which is an industry standard tool that manages website names and domains and contains a database of domain names and a public internet protocol address as well as special networking software (Ostrovsky). The browser first looks in its cache which stores DNS records for a period of time (thirty minutes or less), if it is missing the browser looks for the IP address from the cache of the operating system. If it is missing the browser then looks into the router cache and if no luck it checks the internet service provider (ISP) cache. The ISP DNS server then begins to search for the IP address starting with root name server which is a series of numbers like 198.41.0.6 through to the extension which is a number such as 205.72.121.3 until it gets to the x-stream name server which could be a number like 207.255.122.265; a process termed recursive search (Ostrovsky). Usually the DNS will bring back many IP addresses for a single website. Because there are multitudes of websites, web page owners employ tools like load balancers that forwards an IP address to multiple servers, and having geographic DNS that narrows down an IP address search to a given geographic location. Once the IP address is located, the browser then sends a protocol request (HTTP) to the x-stream web server; a sample request is GET http://x-stream.leedsmet.ac.uk/ HTTP/1.1 Accept: application/x-ms-application, image/jpeg, application/xml+xml Accept-language en_UK User-Agent: Internet Explorer/7.6 Accept-Encoding: zip, deflate Connection: Keep-alive Host: http://x-stream.leedsmet.ac.uk Cookie: datr=126588787-; locale=en_UK; ld=WW; c_user=2112 The GET demand identifies the URL to get while the browser identifies itself via the User-Agent command and says what replies it is going to accept (the Accept and Accept-Encoding commands) while the server is asked to keep the TCP (transfer control protocol) open for further demands using the ‘Connection’ header. Cookies are also included in the sent request for the x-stream domain. The cookies carry data about the user such as a login name and settings (Ostrovsky). The x-stream server then answers with a permanent re-direct which is the response the x-stream server sends back a response to the browsers’ request with the protocol being permanently moved. The response will contain the expiry date, the location of the website http://x-stream.leedsmet.ac.uk/, with the cookie set text that is stored and used for future requests, the type of content of the website, the connection closing information as the date. The ‘permanently moved’ response from the x-stream server tells the web browser where to go the right web address ‘http://x-stream.leedsmet.ac.uk/’ and not ‘http://x-stream.leedsmet.ac.uk/’. Now the x-stream web server does not directly respond with the right web address to the serve’s request instantly as it should; it instead re-directs the browser where to go because of the ranking of search engines. Some web addresses can actually be two sites say http://x-stream.leedsmet.ac.uk/ and http://x-stream.leedsmet.ac.uk/ which a search engine like Google will treat as two different web addresses each with few inward links and categorize/ rank them lower so a permanent redirect instructs the search engine to merge the two web address links into one ranking. The cache could become full with numerous web addresses and so reduce what can be stored in the cache making the web appear slow in accessing repeated sites (Ostrovsky). On receiving the permanent re-direct, the web browser follows it (the re-direct) as it now knows http://x-stream.leedsmet.ac.uk/ is the correct web address and then sends out another ‘GET’ request: GET http://x-stream.leedsmet.ac.uk/ HTTP/1.1 Accept: application/x-ms-application, image/jpeg, application/xml+xml Accept-language en_UK User-Agent: InternetExplorer/7.6 Accept-Encoding: zip, deflate Connection: Keep-alive Cookie: lsd=XW; c_user=2112; x-referrer Host: http://x-stream.leedsmet.ac.uk/ The instructions tell the x-stream web server the address it wants, the language and applications it will accept, identifies itself, asks the web server to keep the connection alive and the host. The server then deals with the request after getting the ‘GET’ request, process the request and sends a request to the requesting browser. Web servers run on software like Apache that accepts HTTP requests then allocates the request to a suitable handler; which is a program like PHP or ASP.Net that reads a browser request and produces the requisite HTML code for the request. The handler also reads the parameters and cookies of the request and may update some server stored information (Ostrovsky). After the step above, the x-stream web server then sends a HTML response to the web browser with information that the content is okay and compressed in zip (actually gzip) format which the browser decompresses and is almost similar to what one views by clicking the ‘View’ button on the web browser and selecting ‘Page source’ from the drop down menu or simple press CTRL+U. The information sent would appear as With additional code (not included)at below the three lines above. With all these information, the browser then starts delivering the HTML rendering the website gradually. On the bottom left pane of the browser one can see word like ‘Transferring data from http://x-stream.leedsmet.ac.uk/ as the indicator bars on the bottom right increase in number. As the web page is loaded, the browser sends ‘GET’ instructions for items set in HTML from the web server and also send instructions that retrieves all the files from their locations on the x-stream servers such as graphics and image files, cascading style sheets (CSS) and java script files. These files are located in URLs whose fetching is the same process as that of getting the web address http://x-stream.leedsmet.ac.uk/ and are searched for in the DNS server, requests sent, redirects sent back and then the browser now goes to the ‘correct’ web addresses. After getting the requisite files, the browser will then send more asynchronous instructions to get additional material such as when in the interactive section of the x-stream website. Or if x-stream has Web 2.0 applications, the browser will continue sending instructions for more pages for example face book links even though the x-stream page has already been loaded. Works Cited Architecture for Internet Data Transfer" 3rd Symposium on Networked Systems Design and Implementation (NSDI ’06), San Jose, California,. Carnegie Mellon University and ‡Intel Research Pittsburgh, 2006. Web. 19 Jan 2012. . Ostrovsky, I. "What really happens when you navigate to a URL." Igor Ostrovsky Blogging. Igor Ostrovsky, 2011. Web 19 Jan. 2012. . Serpanos, D, and T Wolf Architecture of Network Systems Burlington, MA: Morgan Kaufmann, 2011. 292-302. Print Shuler, R "How Does the Internet Work?" Theshulers.com Rus Shuler, 2005 Web 19 Jan. 2012. Read More