Indirect Communication Indirect Communication is defined as communication between entities in DS through intermediary with no direct coupling b/w sender & recvr (s).

WHY? Point-to-point communication Participants need to exist at the same time Participants need to know address of each other and identities Not a good way to communicate with several participant

Key Properties Space Uncoupling The sender does not know or need to know the identity of recvr (s) & viceversa Time Uncoupling Sender & recvr can exist independent The sender & recvr donot need to exist at the same time for communication So it’s ok if you get disconnected for a while

Applications scenarios where users connect and disconnect very often –Mobile environments event dissemination where receivers may be unknown and change often –events feeds

One-to Many Communication

It refers to a service where a message is sent to a group and then the message is delivered to all members of the group Sender communicate with a group as a whole without knowing the identity of members

Key Areas of Application Reliable dissemination of information to potentially large numbers of clients Support for collaborative applications, where events must be disseminated to multiple users to preserve a common user view Support for a range of fault-tolerance strategies Data replication System monitoring and management Load Balancing Strategies

Open VS Closed Groups

Group Membership Management

Providing an interface for group membership changes Failure Detection Notification Performing group address expansion

CHARACTERISTICS OF MULTICAST Reliable Multicast Integrity Delivering the message correctly Validity Guaranteeing that message sent will eventually be delivered Agreement If a message is delivered to one process in a group, it is delivered to all process in a group

CHARACTERISTICS OF MULTICAST Ordered Multicast FIFO Causal Ordering Only causally related msgs arrive in the same order everywhere Total Ordering All msgs arrive in the same order everywhere