CSE

Data Communications & Computer Networks

UNIT - VIII

WWW and HTTP

  • ARCHITECTURE:
         The WWW today is a distributed client/server service, in which a client using a browser can access a service using a server. However, the service provided is distributed over many locations called sites.

    WEB DOCUMENTS:
         The documents in the WWW can be grouped into three broad categories: static, dynamic, and active. The category is based on the time at which the contents of the document are determined.
    Static document:

    Dynamic document using server-site script:
    Dynamic documents are sometimes referred to as server-site dynamic documents.

    Active document using client-site script:
    Active documents are sometimes referred to as client-site dynamic documents.

    HTTP:
         The Hypertext Transfer Protocol (HTTP) is a protocol used mainly to access data on the World Wide Web. HTTP functions as a combination of FTP and SMTP.
    HTTP transaction:

    Request and response messages:

    Methods:

    NETWORK MANAGEMENT SYSTEM:

         We can say that the functions performed by a network management system can be divided into five broad categories: configuration management, fault management, performance management, security management, and accounting management.
    SIMPLE NETWORK MANAGEMENTPROTOCOL (SNMP):
         The Simple Network Management Protocol (SNMP) is a framework for managing devices in an internet using the TCP/IP protocol suite. It provides a set of fundamental operations for monitoring and maintaining an internet.

         SNMP defines the format of packets exchanged between a manager andan agent. It reads and changes the status (values) of objects (variables) in SNMP packets.
         SMI defines the general rules for naming objects, defining object types (includingrange and length), and showing how to encode objects and values. SMI does not define the number of objects an entity should manage or name the objects to be managed or define the association between the objects and their values.
         MIB creates a collection of named objects, their types, and their relationships to each otherin an entity to be managed.

    We can compare the task of network management to the task of writing a program.
    * Both tasks need rules. In network management this is handled by SMI.
    * Both tasks need variable declarations. Innetwork management this is handled by MIB.
    * Both tasks have actions performed bystatements. In network management this ishandled by SNMP.
    Object identifier:
         All objects managed by SNMP are given an object identifier. The object identifier always starts with 1.3.6.1.2.1.

    Multimedia:
    DIGITIZING AUDIO AND VIDEO:

         Streaming stored audio/video refers to on-demand requests for compressed audio/video files. Streaming live audio/video refers to the broadcasting of radio and TV programs through the Internet. Interactive audio/video refers to the use of the Internet for interactive audio/video applications.
    AUDIO AND VIDEO COMPRESSION:
         To send audio or video over the Internet requires compression. In this section, we discuss audio compression first and then video compression.

    STREAMING STORED AUDIO/VIDEO:
         Now that we have discussed digitizing and compressing audio/video, we turn our attention to specific applications. The first is streaming stored audio and video.
    Using a Web server:

    STREAMING LIVE AUDIO/VIDEO:

         Streaming live audio/video is similar to the broadcasting of audio and video by radio and TV stations. Instead of broadcasting to the air, the stations broadcast through the Internet. There are several similarities between streaming stored audio/video and streaming live audio/video. They are both sensitive to delay; neither can accept retransmission. However, there is a difference. In the first application, the
    communication is unicast and on-demand. In the second, the communication is multicast and live.
    REAL-TIME INTERACTIVE AUDIO/VIDEO:
         In real-time interactive audio/video, people communicate with one another in real time. The Internet phone or voice over IP is an example of this type of application. Video conferencing is another example that allows people to communicate visually and orally.

    RTP:
         Real-time Transport Protocol (RTP) is the protocol designed to handle real-time traffic on the Internet. RTP does not have a delivery mechanism; it must be used with UDP. RTP stands between UDP and the application program. The main contributions of RTP are timestamping, sequencing, and mixing facilities.

    RTCP:
         RTP allows only one type of message, one that carries data from the source to the destination. In many cases, there is a need for other messages in a session. These messages control the flow and quality of data and allow the recipient to send feedback to source or sources. Real-time Transport Control Protocol (RTCP) is a protocol designed for this purpose.
    RTCP message types:

    VOICE OVER IP:

         Let us concentrate on one real-time interactive audio/video application: voice over IP, or Internet telephony. The idea is to use the Internet as a telephone network with some additional capabilities. Two protocols have been designed to handle this type of communication: SIP and H.323.
    SIP simple session:

    H.323 architecture:


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