Difference between reliable and group communication in ds
Answers
Group Communication
A group is an operating system abstraction for a collective of related processes. A set of cooperative processes may, for example, form a group to provide an extendable, efficient, available and reliable service. The group abstraction allows member processes to perform computation on different hosts while providing support for communication and synchronisation between them.
The term multicast means the use of a single communication primitive to send a message to a specific set of processes rather than using a collection of individual point to point message primitives. This is in contrast with the term broadcast which means the message is addressed to every host or process.
A consensus protocol allows a group of participating processes to reach a common decision, based on their initial inputs, despite failures.
A reliable multicast protocol allows a group of processes to agree on a set of messages received by the group. Each message should be received by all members of the group or by none. The order of these messages may be important for some applications. A reliable multicast protocol is not concerned with message ordering, only message delivery guarantees. Ordered delivery protocols can be implemented on top of a reliable multicast service.
Multicast algorithms can be built on top of lower-level communication primitives such as point-to-point sends and receives or perhaps by availing of specific network mechanisms designed for this purpose.
The management of a group needs an efficient and reliable multicast communication mechanism to allow clients obtain services from the group and ensure consistency among servers in the presence of failures. Consider the following two scenarios:-
A client wishes to obtain a service which can be performed by any member of the group without affecting the state of the service.
A client wishes to obtain a service which must be performed by each member of the group.