DISTRIBUTED SYSTEMS

Compare Synchronous and Asynchronous Communication. Synchronous data transfer: sender and receiver use the same clock signal supports high data transfer rate needs clock signal between the sender and the receiver requires master/slave configuration Asynchronous data transfer: sender provides a synchronization signal to the receiver before starting the transfer of each message does not need clock signal between the sender and the receiver o                  slower data transfer rate

List out the uses of RMI registry. Essentially the RMI registry is a place for the server to register services it offers and a place for clients to query for those services. RMI Registry acts a broker between RMI servers and the clients. The server "registers" its services in the registry - hence a RMI Registry can act as a "directory" for many servers/services. The client does not need to know the location of individual servers, and does a lookup on the RMI Registry for the service it needs. The registry, being a naming directory returns the appropriate handle to the client to invoke methods on.

Mention the types of overlay net works. Write atleast the types

Differentiate stream oriented and datagram oriented communication. In modern data networking, it is important to distinguish between datagrams and streams. A stream is what we'd typically think of as a communication channel. Remote logins, file transfers, mail delivery - all use streams. A stream appears to be like a pipeline. It has two endpoints. Data is put in one end and comes out the other. None of the data is duplicated, or discarded, or reorganized in any way. Two streams can be paired together to form a full duplex connection. A datagram, often called a packet, is much more atomic in nature. It is a small piece of data, often required to be less than a maximum length (typically in the 256 to 2000 byte range). Datagrams are completely self contained. They have a source and a destination, but nothing that could be called a connection. Datagrams have no relationship to any others that came before or after them. Although most networking communication uses streams, all Internet transfers are in the form of datagrams. Internet streams are actually emulated using datagrams by the TCP Protocol. To diagnose Internet operation, a packet decoder such as TCPdump is used to view individual packets. This, along with a knowledge of TCP operation, enables the Internet engineer to assemble a mental picture of network operation. Connection Oriented Services There is a sequence of operation to be followed by the users of connection oriented service. These are : Connection is established Information is sent Connection is released In connection oriented service we have to establish a connection before starting the communication. When connection is established we send the message or the information and then we release the connection. Connection oriented service is more reliable than connectionless service. We can send the message in connection oriented service if there is an error at the receivers end. Example of connection oriented is TCP (Transmission Control Protocol) protocol. Connection Less Services It is similar to the postal services, as it carries the full address where the message (letter) is to be carried. Each message is routed independently from source to destination. The order of message sent can be different from the order received. In connectionless the data is transferred in one direction from source to destination without checking that destination is still there or not or if it prepared to accept the message. Authentication is not needed in this. Example of Connectionless service is UDP (User Datagram Protocol) protocol. Difference between Connection oriented service and Connectionless service In connection oriented service authentication is needed while connectionless service does not need any authentication. Connection oriented protocol makes a connection and checks whether message is received or not and sends again if an error occurs connectionless service protocol does not guarantees a delivery. Connection oriented service is more reliable than connectionless service. Connection oriented service interface is stream based and connectionless is message based.

What are the properties of indirect communication? Space uncoupling The sender does not know or need to know the identity of the receiver(s), and vice versa. Time uncoupling The sender and the receiver(s) can have independent lifetimes.

What is tuple space communication? A tuple space is an implementation of the associative memory paradigm for parallel/distributed computing. It provides a repository of tuples that can be accessed concurrently. As an illustrative example, consider that there are a group of processors that produce pieces of data and a group of processors that use the data. Producers post their data as tuples in the space, and the consumers then retrieve data from the space that match a certain pattern. This is also known as the blackboard metaphor. Tuple space may be thought as a form of distributed shared memory.Tuple spaces were the theoretical underpinning of the Linda language developed by David Gelernter and Nicholas Carriero at Yale University.Implementations of tuple spaces have also been developed for Java (JavaSpaces), Lisp, Lua, Prolog, Python, Ruby, Smalltalk, Tcl, and the .NET framework.

Differentiate marshalling and un marshalling. In few words, "marshalling" refers to the process of converting the data or the objects inbto a byte-stream, and "unmarshalling" is the reverse process of converting the byte-stream beack to their original data or object. The conversion is achieved through "serialization".

Mention the characteristics of peer to peer systems. Ensures that each user contributes resources to the system •All the nodes have the same functional capabilities and responsibilities •Their correct operation does not depend on the existence of any centrally-administered systems •They can be designed to offer a limited degree of anonymity to the providers and users of resources •A key issue: placement of data across many hosts – efficiency – load balance – availability

Write about routing overlays. A routing overlay is a distributed algorithm for a middleware layer responsible for routing requests from any client to a host that holds the object to which the request is addressed. Main tasks: – Routing of requests to objects: locating nodes and objects – Insertion and deletion of objects – Node addition and removal • Any node can access any object by routing each request through a series of nodes, using information in the intermediate nodes to locate the destination object. Global User IDs (GUID) also known as opaque identifiers are used as names, but do not contain location information

List out operations involved in DHT. A distributed hash table (DHT) is a class of a decentralized distributed system that provides a lookup service similar to a hash table: (key, value) pairs are stored in a DHT, and any participating node can efficiently retrieve the value associated with a given key. Responsibility for maintaining the mapping from keys to values is distributed among the nodes, in such a way that a change in the set of participants causes a minimal amount of disruption. This allows a DHT to scale to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures. put(GUID,data) remove(GUID) Value=get(GUID)