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Types of Communication

Persistent versus transient

Synchronous versus asynchronous

Discrete versus streaming

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Persistent versus Transient

Communication

Persistent: messages are held by the middlewarecomm. service until they can be delivered (e.g. email!" Sender can terminate after e#ecuting send

" $eceiver will get message ne#t time it runs

Transient: messages e#ist only while the sender andreceiver are running" Communication errors or inactive receiver cause the message

to be discarded

" Transport%level communication is transient

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&synchronous v Synchronous

Communication

Asynchronous: (non%bloc'ing! sender resumese#ecution as soon as the message is passed to the

communicationmiddleware software

Synchronous: sender is bloc'ed until"

The )S or middleware notifies acceptance of the message or" The message has been delivered to the receiver or

" The receiver processes it * returns a response

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Discrete versus Streaming Communication

Discrete: communicating parties e#change discretemessages

Streaming: one%way communication+ a ,session-

consists of multiple messages from the sender that are

related either by send order (TCP streams! temporal

pro#imity (multimedia streams! etc.

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Persistence and Synchronicity in Communication

a! Persistent asynchronous communicationb! Persistent synchronous communication

%./

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Persistence and Synchronicity in Communication

c! Transient asynchronous communication

d! $eceipt%based transient synchronous communication

%.

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Persistence and Synchronicity in Communication

e! Delivery%based transient synchronous communication at message delivery

f! $esponse%based transient synchronous communication

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0essage Passing (0P! Systems

1undamentally different approach.

&ll communications primitives are defined in terms

of passing ,messages-.

2nitially 0P systems were ,transient- but these did

not scale wellgeographically.

$ecent emphasis has been on ,persistent- solutions.3

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0essaging Channels

Channels are used to transport messages between multiple distributedapplications and can be implemented using 4ueues

& channel can be used concurrently by multiple applications

0essaging channel patterns:

"Point to point"Publish and subscribe

"datatype

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Point to Point Channel

5nsures that only one consumer consumes anygiven message

The channel can still have multiple consumers to

consume multiple messages concurrently but only asingle receiver consumes any one message.

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Publish and Subscribe Channel

& single input channel that splits into multiple output channels6onefor each subscriber

5ach output channel is configured on one%to%one topology to allowonly one consumer to consume a message.

The event is considered consumed only when all of the consumershave been notified.

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DataType Channel

2n any messaging system there are several separate datatypechannelsfor each type of data.

&ll of the messages on a given channel will contain the same type ofdata.

7ased on data type the service provider sends the data to the channeland the consumer receives data from the appropriate datatypechannel.

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Soc'et Communication

8sing soc'ets clients and servers can set up a connection%oriented communication session.

Servers e#ecute first four primitives (soc'et bind listenaccept! while clients e#ecute soc'et and connect primitives!

Then the processing is clientwrite serverread serverwriteclientread all close connection.

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0essage%)riented Transient Comms.

2nitital efforts relied on the Soc'ets &P2.

9owever DS developers reected Soc'ets:

% ;rong level of abstraction (only ,send- and ,receive-!.

% Too closely coupled to TCP2P networ's " not diverse enough.

/