Messaging is an important means of communication between two systems. There are 2 types of messaging. - Synchronous messaging. - Asynchronous messaging

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  • Messaging is an important means of communication between two systems.

    There are 2 types of messaging.- Synchronous messaging.- Asynchronous messaging.

  • Some observations: Client/Server computing is generally based on a model of synchronous communication:Client and server have to be active at the time of communicationClient issues request and blocks until it receives replyServer essentially waits only for incoming requests, and subsequently processes them

  • Client cannot do any other work while waiting for replyFailures have to be dealt with immediately (the client is waiting)Connection overhead;Higher probability of failures.

  • There are two ways to handle failures: 1. Transactional RPC

    Enable more complex interactions with some execution guarantees .

    2. Service replication and load balancing.

    Prevents system from shutting down is service is not available.

  • MOM stands for message oriented messaging.Asynchronous forms of interaction Communication by exchanging messagesMore dynamicUse of queues acting as buffers.

  • client applicationserver applicationinbound queuequeued messages

  • Both synchronous and asynchronous messaging.Guaranteed message delivery.Heterogeneous platforms.Message priority possible.Broadcast messages.Filtering of messages.

  • FeatureMOMRPCMetaphorPost-office likeTelephone likeClient/Server time relationshipAsynchronous. Clients and Servers may operate at different times and speedsSynchronous. Clients and Servers must run concurrently. Servers must keep up with clients.Client/Server SequencingNo fixed sequenceServers must first come up before clients can talk to them.StyleQueuedCall-ReturnPartners need to be availableNoYesTransactional SupportYes (Some Products) Message Queue can participate in the commit synchronizationNo. Requires a Transactional RPC.Message FilteringYesNo

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