Lecture 3 Networking Fundamentals Servers and Clients PDF

Lecture 3 Networking Fundamentals Servers and clients  Types of Servers Network Services  1- File servers Provide basic network file sharing and storage management. File sharing is not the same as file transfer. It is not simply the ability to move a file from one syst...

Lecture 3 Networking Fundamentals Servers and clients  Types of Servers Network Services  1- File servers Provide basic network file sharing and storage management. File sharing is not the same as file transfer. It is not simply the ability to move a file from one system to another. A true file-sharing system does not require you to move entire files across the network. It allows files to be accessed at the record level so that it is possible for a client to read a record from a file located on a remote server, update that record, and write it back to the server - without moving the full file from the server to the client.  1- File servers File sharing is transparent to the user and to the application software running on the user's system. Through file sharing, users and programs access files located on remote systems as if they were local files. In a perfect file-sharing environment, the user neither knows nor cares where files are actually stored.  2- Print Servers A print server allows printers to be shared by everyone on the network. Printer sharing is not as important as file sharing, but it is a useful network service. The advantages of printer sharing are: Fewer printers are needed, and less money is spent on printers and supplies. Reduced maintenance: There are fewer machines to maintain, and fewer people spending time fiddling with printers. Access to special printers: Very high-quality color printers and very high-speed printers are expensive and needed only occasionally. Sharing these printers makes the best use of expensive resources.  3- Message Services A messaging server is a program that handles messages that are sent for use by other programs using a messaging application program interface (API). A messaging server can usually queue and prioritize messages as needed and saves each of the client programs from having to perform these services.  4- Mail Servers is an application that receives incoming e-mail from local users (people within the same domain) and remote senders and forwards outgoing e-mail for delivery. A computer dedicated to running such applications is also called a mail server.  5- Application services The capabilities that run software for network clients. enable computer to share processing power. supply server side of client/server applications. Provide processing services and handle requests for file or print services.  6- Network services Network communications are layered Network applications use NOS to get network protocol to access medium. Medium exchange information with other computers. networking process consist of many layers of networking process.  Networking services layers Sending Machine Receiving Machine Application Application Network Software Network Software Network Protocol Network Protocol Network Interface Network Interface Network medium  7- communication server Allow users outside network to access network’s recourses. Permit users on network to access resources outside network. Openness: Communications servers are based on industry standards. Different tools and services may be further integrated on an as- needed basis.  8- Web Servers Web server refers to server software, or hardware dedicated to running said software, that can serve contents to the World Wide Web. A web server processes incoming network requests over HTTP and several other related protocols. The primary function of a web server is to store, process and deliver web pages to clients. The communication between client and server takes place using the Hypertext Transfer Protocol (HTTP).  The Hypertext Transfer Protocol is an application protocol for distributed, collaborative, hypermedia information systems 9- Multimedia Server  Multimedia Server According to the increasing interest to the world of Internet Telephony or VoIP, academic research in this field is raising dramatically. One of the main components in this world is media server which can provide different functionalities. The most important role of a media server can be considered as conferencing Multimedia servers store and manage multimedia objects and deliver data streams in real-time, in response to requests from users. Additionally, they process the stored information before delivery to users. The content may range from long, sequentially accessed videos to composite documents consisting of a mixture of small multiple-media segments (e.g., video, audio, image, text).  Multimedia Server Regardless of the server capacity, with given resources, the objectives of multimedia servers are to maximize the number of clients that can be simultaneously supported (high throughput), to minimize the latency between issuing request and initiation of display (low startup latency), and to support a smooth display without any artifacts (continuous display).  Multimedia Server Architecture Session Initiation Protocol (SIP) Session Description Protocol (SDP) Real-Time Transport Protocol (RTP)  1- Session Initiation Protocol (SIP) is a protocol used for initiating, maintaining, and terminating real-time sessions that include voice, video and messaging applications. SIP is used for controlling multimedia communication sessions in applications of Internet telephony for voice and video calls, in private IP telephone systems, in instant messaging over Internet Protocol (IP) networks as well as mobile phone calling over internet.  Session Initiation Protocol (SIP) SIP resides in the application layer of the network – It establishes, modifies and terminates multimedia sessions (primarily voice and video) between intelligent devices.  Session Initiation Protocol (SIP) In SIP, every network element is identified by a SIP URI (Uniform Resource Identifier) which is like an address. Following are the SIP elements:- User Agent Proxy Server Registrar Server Redirect Server Location Server Presence Server  User Agent It is the endpoint and one of the most important network elements of a SIP network. An endpoint can initiate, modify, or terminate a session. User agents are the most intelligent device or network element of a SIP network. It could be a softphone, a mobile, or a laptop. User agents are logically divided into two parts − User Agent Client (UAC) − The entity that sends a request and receives a response. User Agent Server (UAS) − The entity that receives a request and sends a response. SIP is based on client-server architecture where the caller’s phone acts as a client which initiates a call and the callee’s phone acts as a server which responds the call.  Proxy Server It is the network element that takes a request from a user agent and forwards it to another user. Basically the role of a proxy server is much like a router. It has some intelligence to understand a SIP request and send it ahead with the help of URI. A proxy server sits in between two user agents. There can be a maximum of 70 proxy servers in between a source and a destination.  Registrar Server The registrar server accepts registration requests from user agents. It helps users to authenticate themselves within the network. It stores the URI and the location of users in a database to help other SIP servers within the same domain. Redirect Server The redirect server receives requests and looks up the intended recipient of the request in the location database created by the registrar. The redirect server uses the database for getting location information and responds to the user. Location Server The location server provides information about a caller's possible locations to the redirect and proxy servers. Only a proxy server or a redirect server can contact a location server. Presence Server – Accepts Presence information (Availability information), stores it and distributes it – from and to, endpoints. Eg. Status Messages like Busy, Available.  2- Session Description Protocol It’s impossible to truly understand SIP without understanding its cousin, Session Description Protocol (SDP). While SIP deals with establishing, modifying, and tearing down sessions, SDP is solely concerned with the media within those sessions. SDP consists of three main sections – session, timing, and media descriptions.  Session Description Protocol It is used to describe multimedia sessions in a format understood by the participants over a network. Depending on this description, a party decides whether to join a conference or when or how to join a conference. SDP is designed to be extensible to support new media types and formats.  Session Description Protocol SDP simply provides a format for describing session information to potential session participants. The Structure of SDP Session Level Info Name of the session Time that the session is to be active Media Level Info Media type Port number Media format 3- The Real-Time Transport Protocol (RTP) Real-time programs must guarantee response within specified time constraints, often referred to as "deadlines”.  3- The Real-Time Transport Protocol (RTP) is an Internet protocol standard that specifies a way for programs to manage the real-time transmission of multimedia data over either unicast or multicast network services. RTP is commonly used in Internet telephony applications. Internet telephony is the use of the Internet rather than the traditional telephone company infrastructure. Since access to the Internet is available at local phone connection rates, an international or other long-distance call will be much less expensive than through the traditional call arrangement.  The Real-Time Transport Protocol Unicast is the term used to describe communication where a piece of information is sent from one point to another point. In this case there is just one sender, and one receiver. Multicast is the term used to describe communication where a piece of information is sent from one or more points to a set of other points. In this case there is may be one or more senders, and the information is distributed to a set of receivers Broadcast is the term used to describe communication where a piece of information is sent from one point to all other points. In this case there is just one sender, but the information is sent to all connected receivers.