Data Communication & Computer Network

  Computer systems and computerized systems help human beings to work efficiently and explore the unthinkable. When these devices are connected together to form a network, the capabilities are enhanced multiple-times. Some basic services computer network can offer are. Directory Services These services are mapping between name and its value, which can be variable value or fixed. This software system helps to store the information, organize it, and provides various means of accessing it. Accounting In an organization, a number of users have their user names and passwords mapped to them. Directory Services provide means of storing this information in cryptic form and make available when requested. Authentication and Authorization User credentials are checked to authenticate a user at the time of login and/or periodically. User accounts can be set into hierarchical structure and their access to resources can be controlled using authorization schemes. Domain Name Services DNS is widely...

  There are several protocols which work for users in Application Layer. Application layer protocols can be broadly divided into two categories: Protocols which are used by users.For email for example, eMail. Protocols which help and support protocols used by users.For example DNS. Few of Application layer protocols are described below: Domain Name System The Domain Name System (DNS) works on Client Server model. It uses UDP protocol for transport layer communication. DNS uses hierarchical domain based naming scheme. The DNS server is configured with Fully Qualified Domain Names (FQDN) and email addresses mapped with their respective Internet Protocol addresses. A DNS server is requested with FQDN and it responds back with the IP address mapped with it. DNS uses UDP port 53. Simple Mail Transfer Protocol The Simple Mail Transfer Protocol (SMTP) is used to transfer electronic mail from one user to another. This task is done by means of email client software (User Agents) the user is...

  Two remote application processes can communicate mainly in two different fashions: Peer-to-peer:  Both remote processes are executing at same level and they exchange data using some shared resource. Client-Server:  One remote process acts as a Client and requests some resource from another application process acting as Server. In client-server model, any process can act as Server or Client. It is not the type of machine, size of the machine, or its computing power which makes it server; it is the ability of serving request that makes a machine a server. A system can act as Server and Client simultaneously. That is, one process is acting as Server and another is acting as a client. This may also happen that both client and server processes reside on the same machine. Communication Two processes in client-server model can interact in various ways: Sockets Remote Procedure Calls (RPC) Sockets In this paradigm, the process acting as Server opens a socket using a well-known ...

  Application layer is the top most layer in OSI and TCP/IP layered model. This layer exists in both layered Models because of its significance, of interacting with user and user applications. This layer is for applications which are involved in communication system. A user may or may not directly interacts with the applications. Application layer is where the actual communication is initiated and reflects. Because this layer is on the top of the layer stack, it does not serve any other layers. Application layer takes the help of Transport and all layers below it to communicate or transfer its data to the remote host. When an application layer protocol wants to communicate with its peer application layer protocol on remote host, it hands over the data or information to the Transport layer. The transport layer does the rest with the help of all the layers below it. There’is an ambiguity in understanding Application Layer and its protocol. Not every user application can be put into A...

  The User Datagram Protocol (UDP) is simplest Transport Layer communication protocol available of the TCP/IP protocol suite. It involves minimum amount of communication mechanism. UDP is said to be an unreliable transport protocol but it uses IP services which provides best effort delivery mechanism. In UDP, the receiver does not generate an acknowledgement of packet received and in turn, the sender does not wait for any acknowledgement of packet sent. This shortcoming makes this protocol unreliable as well as easier on processing. Requirement of UDP A question may arise, why do we need an unreliable protocol to transport the data? We deploy UDP where the acknowledgement packets share significant amount of bandwidth along with the actual data. For example, in case of video streaming, thousands of packets are forwarded towards its users. Acknowledging all the packets is troublesome and may contain huge amount of bandwidth wastage. The best delivery mechanism of underlying IP protoc...

  The transmission Control Protocol (TCP) is one of the most important protocols of Internet Protocols suite. It is most widely used protocol for data transmission in communication network such as internet. Features TCP is reliable protocol. That is, the receiver always sends either positive or negative acknowledgement about the data packet to the sender, so that the sender always has bright clue about whether the data packet is reached the destination or it needs to resend it. TCP ensures that the data reaches intended destination in the same order it was sent. TCP is connection oriented. TCP requires that connection between two remote points be established before sending actual data. TCP provides error-checking and recovery mechanism. TCP provides end-to-end communication. TCP provides flow control and quality of service. TCP operates in Client/Server point-to-point mode. TCP provides full duplex server, i.e. it can perform roles of both receiver and sender. Header The length of ...

  Next Layer in OSI Model is recognized as Transport Layer (Layer-4). All modules and procedures pertaining to transportation of data or data stream are categorized into this layer. As all other layers, this layer communicates with its peer Transport layer of the remote host. Transport layer offers peer-to-peer and end-to-end connection between two processes on remote hosts. Transport layer takes data from upper layer (i.e. Application layer) and then breaks it into smaller size segments, numbers each byte, and hands over to lower layer (Network Layer) for delivery. Functions This Layer is the first one which breaks the information data, supplied by Application layer in to smaller units called segments. It numbers every byte in the segment and maintains their accounting. This layer ensures that data must be received in the same sequence in which it was sent. This layer provides end-to-end delivery of data between hosts which may or may not belong to the same subnet. All server proc...