Interprocess Communication: Methods and Protocols

Posted on Jan 15, 2025 in Telecommunication Systems, Sound, and Image Engineering

Interprocess Communication Essentials

Interprocess communication involves sending a message between a socket in one process and a socket in another.

Communication Forms

  • In synchronous communication, sending and receiving processes synchronize with each message.
  • In asynchronous communication, the send operation is non-blocking, and the receive operation can have varied behavior.

Message Destination

Internet protocols send messages to (Internet address, local port) pairs. Processes can use multiple ports to receive messages but cannot share ports.

Reliability

A communication channel is considered reliable if messages are guaranteed to be delivered despite a reasonable number of packet losses.

Message Ordering

Some applications require that messages be delivered in sender order, meaning the order in which they were transmitted.

Sockets

Processes use sockets bound to an Internet address and a local port for communication.

UDP Datagram Communication

UDP involves sending discrete packets of data. Sockets can be blocking or non-blocking.

Blocking Behavior

Sockets typically offer non-blocking sends and blocking receives for datagram communication.

Timeouts

A receive operation that blocks indefinitely is useful for servers awaiting client requests. Timeouts can be implemented for specific scenarios.

Receiving Messages

The receive method retrieves a message without specifying an origin.

Failure Model

A failure model defines reliable communication based on integrity and validity.

Omission Failures

Messages might be dropped due to checksum errors or lack of buffer space.

Ordering Issues

Messages can sometimes arrive out of order.

TCP Stream Communication

API to the TCP Protocol

Originating from BSD 4.x UNIX, the TCP API offers an abstraction of a byte stream for data exchange.

API for Stream Communication

When establishing a connection, one process acts as a server and the other as a client.

Message Sizes

Applications can determine the amount of data written to or read from a stream.

Handling Lost Messages

TCP uses acknowledgments to ensure delivery. If an acknowledgment is not received, the sender retransmits the data.

Flow Control

TCP attempts to match the speeds of processes reading from and writing to a stream, preventing the sender from overwhelming the receiver.

Message Duplication and Ordering

Message identifiers in IP packets enable the recipient to detect and discard duplicates and reorder messages.

Message Destinations

Processes establish a connection before communicating over a stream. Once connected, they can read and write data.

Failure Model

TCP uses checksums to detect and reject corrupted data, ensuring the integrity of communication.

Data Representation and Marshalling

Marshalling and Unmarshalling

This is the process of assembling or disassembling data items into a suitable form for transmission.

XML

Extensible Markup Language (XML) is a textual format for representing structured data, initially intended for self-describing documents.

CORBA’s Common Data Representation

CORBA defines an external representation for structured and primitive data types.

Java’s Object Serialization

Java serialization flattens an object or a tree of objects into a serialized form for storage or transmission.

XML in Detail

XML vs. HTML

HTML defines the appearance of web pages, while XML is used for writing structured documents for the Web.

XML Data Structure

XML data items are tagged with markup strings that describe the data’s logical structure and attributes.

XML in Web Services

XML enables clients to communicate with web services and define their interfaces and properties.

Attributes

A start tag can include attribute name-value pairs, such as id=”123456789″.

Naming Conventions

XML tag and attribute names generally start with a letter, an underscore, or a colon.

Binary Data

All information in XML elements must be expressed as character data.

XML Namespaces

An XML namespace is a set of names for element types and attributes, referenced by a URL.

xmlns Attribute

The xmlns attribute, with a URL value, refers to the file containing namespace definitions.

XML Schema

An XML schema defines the elements, attributes, nesting, and order of elements in a document.

Request-Replay Protocol

This protocol uses doOperation, getRequest, and sendReply primitives for communication.

Message Identifiers

Each message must have a unique identifier for effective management.

Remote Procedure Call (RPC)

RPC allows calling procedures or functions on a remote computer.

RPC vs. Web

RPC is an older technology that provides a mechanism for defining interfaces callable across a network.

XML-RPC

XML-RPC enables programs to make function or procedure calls over a network using HTTP and XML.

XML-RPC Requests

These are a combination of XML content and HTTP headers, specifying parameters and target procedure information.

XML-RPC Responses

An XML-RPC response can contain only one parameter, which may be an array or a struct, allowing complex data to be returned.