 ఈలాపా� టరా ి అలల౗ి అినినిర్భ����ౌౝం ంథ్ి�.. uations path sign means trial.  섞ers or messages from a sender to a receiver. Absolutely crucial to informally at wash. Did you?  Woman was shocked at different things. the second one is message passing approach, in which the messages can be transferred from sender to receiver. A process is a program in execution. Two computers are communicating with each other. We mean that two processes, one running on each computer are in communication with each other. Each computer of a distributed system may have a resource manager process to monitor the current status of usage of its local resources and the resource manager of all the computers might communicate with each other from time to time to dynamically balance the system load among all the computers. Therefore distributed operating system needs to provide inter-process mechanisms to facilitate such communication activities. This is the diagram of two inter-process communication paradigms. In figure A, the shared data approach can be shown where processes P1 and P2 are sharing the shared common memory. In figure B, the message passing approach can be shown where P1 can process P1 will be sending the message to process P2 and process P2 will be sending acknowledgement to process P1. In this way the communication between two processes can be shown in the message passing approach. Actually in this message passing approach information is copied from sender address space to receiver address space. Distributed system uses message-based inter-process communication IPC for most applications. IPC provides a set of message-based IPC protocol that hides the heterogeneous platforms. Two primitives send and receive is used by the IPC. Two higher level IPC systems are RPC and DSM. Here the meaning of DSM in computers and distributed shared memory is a form of memory architecture where physically separated memories can be addressed as one logically shared address space. A distributed shared memory system implements the shared memory model on a physically distributed memory system. The desired features of message passing approach simplicity, uniform semantics, efficiency, reliability, flexibility and portability. Now we are going to see all the features one by one. Simplicity. Message passing system is simple and easy to use. There is use of clean and simple semantics of IPC protocol and its primitives. Means the message passing system is very simple and easy to use and it is user friendly. And it is independent of heterogeneity. Actually heterogeneity means different computers having different operating systems like windows, linux or masintosh etc. So message passing system having one kind of compatibility so that it will run on all the machines. Independent of underlying network and its aspect means different machines having different hardware configuration and software configuration and having the part of different network. So message passing approach supports all kinds of networks and all kinds of configurations. Uniform semantics. Two types of IPC. One is local communication. Means communication between two processes on same machine and second one remote communication. Means communication of two processes on different machines. Semantics of remote communication should be as close as possible to those of local communication. Same system can be used for local as well as remote communication. Efficiency. Now in efficiency we are reducing the number of message exchange per user avoiding the cost of establishing and terminating connections with the same process for every message. So that it minimizes the cost of maintaining connections and use piggybacking techniques. So we are maintaining once the connection established between the sender and receiver number of messages can be passed from sender to receiver. So there is no necessary of establishing separate connection for every message passing. So this saves the cost of maintaining the connection. So in the context of computer science and digital communication the piggybacking refers to a situation where an unauthorized party gains access to some system in connection with an authorized party. This can happen in several ways including piggybacking on public wireless networks and piggybacking into a password protected systems. Next feature is reliability. So failure as such as node crashes or communication link failure can occur. It intercepts the communication in progress. The messages can be lost. Lost messages handled by the acknowledgement and retransmission technique. Duplicate message handled by the sequence number to messages. So every message here having the sequence number. So that we have to find the lost messages or retransmitted messages. Correctness. Feature related to IPC protocol for group communication. Issues related to correctness or atomicity means apply to all or apply to none. Order delivery means passing the message one after another. Survivability. Messages will be delivered correctly in despite of partial failures. Means in survivability there is partial failure but the messages can be delivered successfully from sender to receiver. Flexibility. IPC permitted should be flexible so that user have choice to specify the type and levels of reliability. So here in flexibility so many things in the user's hand just like type and level of the reliability. Correctness requirement can be chosen. There kind of synchronous or asynchronous communication can be chosen. Now next feature is security. In message passing system provide a secure end to end communication. So authentication of receiver by the sender means sender has to check the proper receiver. Authentication of sender by receiver means receiver has to check the proper sender. Means here we are checking the authenticate sender and receivers in the security point of view. So for protecting the messages we are applying encryption of messages. In this different encryption decryptions, security techniques are used for safe communication. So in this security feature we are providing the data, security to the data and messages. Portability. Two different aspects. Message passing system itself portable means a new IPC facility means inter process communication facility on another system constructed using basic design of an existing IPC. Applications written using primitive of IPC protocol should be portable of a new system means needs to handle heterogeneity and hence uses external data representation format on computers of different architectures. Now we are going to see the structure of message. Here the sender can send the message and receiver can receive the message but there is a specific format or structure of message. So here fixed length header and data of varying size. So header consists of three elements, address, sequence number and structural information. So in this diagram typical message structure can be shown. So this is fixed length header can be shown. After this variable size collection of data type then data in first column data or pointer to the data can be shown. In structural information the number of bytes and type of information can be provided. Then the sequence number can be written for every message. In addresses the receiving process ID and sending process ID can be written. Pause the video and write the answer of the given question. What are the different issues in message passing system? Important issues to be considered. First we have to check who is the sender, who is the receiver. Is there one or multiple receivers? Is received message acknowledged? Should sender wait for acknowledgement? What if node crash or communication link fails during transmission? If receiver does not accept the message then it will be buffered or discarded. Now we are going to see the next concept that is synchronization. Synchronization also occurs between the network nodes to ensure that data streams are received and transmitted correctly and to prevent data collision. It usually uses a clock signal transmitted in sequence with a data stream to maintain proper signal timing. There are two types of semantics used blocking and non-blocking in synchronization. In blocking semantics blocking send is one of the semantics and blocking receives another semantics. So in blocking send the sending process blocked after execution of send until it receives the acknowledgement. In blocking receiving process blocked after execution of receive until it receives a message. Synchronous communication, the non-blocking semantics. In non-blocking semantics send the sending process continues its execution as soon as the message can be copied to sender's buffer. Non-blocking received. The receiver process continues its execution after receiving message into its buffer. These are the references. Thank you.