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    Lesson 04: The Web and HTTP: Learning Outcome

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    Thilan Nawagamuwa
    The document discusses the Hypertext Transfer Protocol (HTTP) and how it facilitates communication between web browsers and servers. It differentiates between non-persistent and persistent HTTP connections and describes the HTTP message format including start lines, headers, and message bodies. Cookies are explained as a way for servers to track users across sessions. Caching and conditional GET requests are also covered as techniques for improving web performance. The key learning is an in-depth understanding of HTTP and how it enables the functioning of the World Wide Web.

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    Lesson 04: The Web and HTTP: Learning Outcome

    Uploaded by

    Thilan Nawagamuwa
    76 views5 pages
    The document discusses the Hypertext Transfer Protocol (HTTP) and how it facilitates communication between web browsers and servers. It differentiates between non-persistent and persistent HTTP connections and describes the HTTP message format including start lines, headers, and message bodies. Cookies are explained as a way for servers to track users across sessions. Caching and conditional GET requests are also covered as techniques for improving web performance. The key learning is an in-depth understanding of HTTP and how it enables the functioning of the World Wide Web.

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    The document discusses the Hypertext Transfer Protocol (HTTP) and how it facilitates communication between web browsers and servers. It differentiates between non-persistent and persistent HTTP connections and describes the HTTP message format including start lines, headers, and message bodies. Cookies are explained as a way for servers to track users across sessions. Caching and conditional GET requests are also covered as techniques for improving web performance. The key learning is an in-depth understanding of HTTP and how it enables the functioning of the World Wide Web.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    76 views5 pages

    Lesson 04: The Web and HTTP: Learning Outcome

    Uploaded by

    Thilan Nawagamuwa
    The document discusses the Hypertext Transfer Protocol (HTTP) and how it facilitates communication between web browsers and servers. It differentiates between non-persistent and persistent HTTP connections and describes the HTTP message format including start lines, headers, and message bodies. Cookies are explained as a way for servers to track users across sessions. Caching and conditional GET requests are also covered as techniques for improving web performance. The key learning is an in-depth understanding of HTTP and how it enables the functioning of the World Wide Web.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 5

    Lesson 04: The Web and HTTP

    4.0 Introduction

    The internet was used primarily by researchers, academics, and university students to log into
    remote hosts, to tranfer files from local hosts to remote hosts and vice versa. The World Wide
    Web was introduced in the 1990s. The web is the intenet application that caught the general
    publics general eye. The the internet is yet another electronic communication technology with
    a major social impact. Email and the Web, two of its most popular applications have changed
    how we live and work. We will cover the Web and its application layer protocol in this section.

    Learning outcome:

    After completing this lesson, you will be able to:

    Differentiate the Nonpersistent and Persistent connections

    Describe the HTTP message format

    Identify the fields in the HTTP message format

    Explain the use of the cookies

    4.1 Overview of HTTP

    HTTP is a protocol that allows Web browsers to talk to servers and exchange information. HTTP
    provides a standard way of communicating between browsers and Web servers so any browser
    can talk to any server, provided that they both conform to the HTTP specification. HTTP expects
    the client to initiate a request and the server to respond.

    Differentiate the Nonpersistent and Persistent connections

    The major difference between nonpersistent and persistent protocol is the number of TCP
    connection(s) that is (are) required for transmitting the objects. Nonpersistent HTTP
    connection requires that each object be delivered by an individually established TCP
    connection.

    1
    Usually there is one RTT delay for the initial TCP connection.

    The parallel TCP connections are used by nonpersistent HTPP to improve the performance,
    i.e., to speed up the response time. Ideally, the shortest time that it can receive all objects is
    two RTT (one for initial TCP, one for request and response) plus the transmission time of the
    largest objects assuming that all the TCP connections can be established simultaneously.

    Persistent HTTP connection without pipelining is that each client (browser) has to wait for
    the previously requested object received before issuing a new request for another object.
    Not counting the initial TCP establishment (one RTT time), each object needs at least one
    RTT plus the transmission time of the object by the server; Persistent HTTP connection with
    pipelining can allow a client to send out multiple (or all) requests, so servers can receive all
    requests at once, and then sending responses (objects) one after another, hence the name
    of pipelining. The shortest time is one initial RTT, another RTT for request and response, plus
    the transmission time of all objects by the web server.

    4.2 HTTP message format

    There are two types of HTTP messages. Request messages and response messages. Both these
    formats are outlined briefly.

    HTTP request format

    GET, most commonly used request to web server for objects


    POST, to fill out a form. In this case, the message format on Slide 229 contains the
    content in the field of Entity Body.
    HEAD, similar to GET command except HTTP responds with no requested objects.
    This is used for debugging. Noticing in both GET and HEAD, the entity body in the
    request message is empty

    The HTTP generic message format is as follows:

    <startline>
    <messageheaders>
    <emptyline>
    [<messagebody>]
    [<messagetrailers>]

    2
    The fields in the HTTP message format

    Get /Index.html HTTP/1.1 Request Line


    Date: Thu, 05 May 2008 21:12:55 GMT General Header
    Connection : close
    Host: www.facebook.com
    From:raj260@yahoo.com Request Header HTTP
    Accept: text/html, text/plain Request
    UserAgent: Mozilla/4.0 (compatible: MSIE 6.0: Windows NT 5.1)
    Entity Header

    Blank Line
    Message Body

    4.3 UserServer Interaction Cookies

    Cookies are short pieces of data used by web servers to help identify web users. It allows
    keeping track of the users that log into their servers and would recognize the user at the next
    log in. A cookie consists of four parts.

    a. Cookies Header line in the HTTP request Message


    b. Cookie Header line in the HTTP response Message
    c. A cookie file kept on the users end system and managed by the users browser
    d. A back end database at the web site.

    Here is how user server interaction happens as a cookie is passed.

    Server send cookie to client in response message (set cookie 19830505) and the client
    presents this cookie in later requests (cookie 19830505)then the server matches the presented
    cookie with server stored information and grants authentication remembering user preferences
    and previous choices.

    3
    4.4 HTTP Content

    4.5 Web Caching

    A cache is a sort of "buffer" or temporary memory: somewhere a machine stores in its memory
    some documents, so that when a request is asking for an already cached document (document
    stored in the cache), we would rather send this document instead of making a complete (and
    long) request to the server. This is very interesting for much requested documents; this can
    reduce the network traffic.

    The trick consists of knowing if the document has been updated. The following diagram shows
    the route followed by a resource when performing a request on it:

    4
    Actually, the client makes its request to a proxy server or any other cache system. Then this
    proxy is going to guess if the requested document (which is also in its cache) has been updated.
    To do so, it is going to use the directives it got when it asked for the document for the first time.
    If it knows nothing about the document, it may perform a HEAD request. According to the reply,
    the proxy is able to know if it should ask for a new version or simply send the version it has in its
    cache. Fortunately this latter case is the most frequent one, and therefore we save time and
    network load.

    4.6 The Conditional GET

    HTTP/1.0 also introduces another nice cache feature: a conditional GET request. This is
    performed with a special directive.

    A conditional GET request will ask the server to send the document if and only if this document
    has changed since the specified date. For the client, it is just a matter of sending the date at
    which it last got the document. If the resource has not changed, the server just sends a very
    short "HTTP/1.0 304 Not Modified" and the client simply uses the version it already has.

    Summary

    You have completed the fourth lesson of Module 2303: Computer Networks. Now you will be
    having an indepth knowledge in HTTP. You will be able to explain about HTTP message format, Non
    persistent and Persistent connections, Cookies, HTTP Content, Web Caching, and the conditional GET.

    The next lesson will be on Introduction to Transport Layer services. Before moving to that
    lesson, check your success of learning with Quiz 4.

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