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I need to know the advantages and disadvantages of synchronous and asynchronous communication, automatic and explicit buffering, send by copy and send by reference, and fixed-sized and variable-size messages.

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asked 2020-12-05
I need to know the advantages and disadvantages of synchronous and asynchronous communication, automatic and explicit buffering, send by copy and send by reference, and fixed-sized and variable-size messages.

Answers (1)

2020-12-06
synchronous and asynchronous communication:
Communication between processes takes place by calls to send ( )and receive ( ) primitive. Message passing may be either blocking (synchronous) or non blocking (asynchronous).
Blocking send :- The sending process is blocked until the message is received by the receiving process or by the mailbox
Non blocking send: - The sending process sends the message and resumes operation.
Blocking receive: - The receiver blocks until a message is available.
Non Blocking receive: - The receiver retrieves either a valid message or a null.
(b) Automatic and Explicit Buffering:-
Communication may be director indirect message passing technique. These messages reside in a temporary queue. There are three different ways to implement such a queue.
Zero capacity: - The maximum length of queue is zero. The sender must block until the recipient receives the message.
Bounded capacity: - The queue has a finite length n. Of the queue is not full, when a new message is sent, the message is placed on the queue. And the sender can continue execution without waiting. If the queue is full, the sender must be blocked until space is available in the queue.
Unbounded Capacity: The queue has infinite length. Hence any number of messages can wait in it. The sender never blocks.
Bounded capacity and unbounded capacity is referred as automatic buffering whereas zero-capacity is called explicit buffering.
Send by copy and send by reference :
A message are sent to and received frommailboxes called ports. A system calls are made by message when atask is created, two special mail boxes are created. They are kernel mailbox and Notify mail box. Three system calls are needed for message transfer. They are message send (msg – send) call, which sends a message to mail box. Another is message receive (msg – receive) call, which receive a message and lastly is remote procedure calls also called as RPCs, which are executed via msg-rpe, which sends a message and waits for exactly one return message from the sender.
Public interface channel-work
{
// sends a message to the channel
public abstract void send (object item);
//Receive a message from channel
public abstract object receive ( );
}
Fixed-sized and variable-sized message :-
In fixed-size message passing, fixed-size messages can be sent, the system-level implementation is straight forward .This restriction,however, makes the task of programming more difficult. Conversely,variable sized messages require a more complex system-level implementation, but the programming task becomes simpler.
A message consists of a fixed-length header, followed by avariable-length header, followed by a variable - length dataportion. The header includes the length of message and two mailboxnames. When a message is sent, one mailbox is name is message send mailbox and where it is received is called message receive mailbox.The variable part of a message is a list of typed data items. Each entry in the list has a type, size and value. The type of objects specified in the message is important.
Most communications circuits perform functions described in the physical and data link and data link layer of the OSI Model. There are two general strategies for communicating over a physical link: Asynchronous and Synchronous. Each has it's advantages and disadvantages.
Asynchronous
Sending data encoded into your signal requires that the sender and receiver are both using the same enconding/decoding method, and know where to look in the signal to find data. Asynchronous systems do not send separate information to indicate the encoding or clocking information. The receiver must decide the clocking of the signal on it's own. This means that the receiver must decide where to look in the signal stream to find ones and zero es, and decide for it self where each individual bit stops and starts. This information is not in the data in the signal sent from transmit tingunit.
When the receiver of a signal carrying information has to derive how that signal is organized without consulting the transmittingdevice, it is called asynchronous communication. In short, the two ends do not synchronize the connection before communicating. Asynchronous communication is more efficient when there is low loss and low error rates over the transmission medium because no data is not retransmitted. In addition, there is no time spent at the beginning of setting up the connection. One side simply transmits,and the other does it's best to receive.
synchronous
Synchronous systems negotiate the connection at the data-linklevel before communication begins. Basic synchronous systems will synchronize two clocks before transmission, and reset their numeric counters for errors etc. More advanced systems may negotiate things like error correction and compression.
It is possible to have both sides try to synchronize the connection at the same time. Usually, there is a process to decide which end should be in control. Both sides can go through a lengthynegotiation cycle where they exchange communications parameters and status information. Once a connection is established, thetransmitter sends out a signal, and the receiver sends back dataregarding that transmission, and what it received. This takes longer on low error-rate lines, but is highly efficient in systems where the transmission medium it self (an electric wire, radio signal or laser beam) is not particularly reliable.
Synchronous communication tools removed the geographical barriers. Asynchronous communication tools remove both the geographical and temporal barriers. A side from making the communication that much more accessible, removal of the temporal barrier also has a side effect.
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