Communication Fundamentals

Communication Fundamentals

• All communication methods share three elements: a source or sender, a destination or receiver, and a channel or medium.
• Rules or protocols govern all methods of communication, standardising the way that data is sent and received.

Rule Establishment

• Protocols are required for effective communication and include identifying sender and receiver, common language and grammar, speed and timing, and confirmation or acknowledgement requirements.
• Protocols used in network communications also define message encoding, delivery options, formatting and encapsulation, timing, and size.

Message Encoding

• Encoding between hosts must be in an appropriate format for the medium.
• Messages are first converted into bits by the sending host
• Bits are encoded into patterns of sounds, light waves, or electrical impulses, depending on the network media.
• The destination host receives and decodes the signals to interpret a message.

Message Formatting and Encapsulation

• There is an agreed format for letters and addressing letters to ensure proper delivery.
• Putting the letter into the addressed envelope is called encapsulation.
• Computer messages are encapsulated in a specific format, called a frame, before being sent over the network.
• Frames act as envelopes, providing a destination and source address.

Message Size

• Messages may need to be broken down into smaller parts or sentences.
• Long messages have to be broken into smaller pieces to travel across a network.
• Each piece of the message is sent in a separate frame.
• Each frame will have its own addressing information.
• The receiving host reconstructs multiple frames into the original message.

Message Timing

• Access Method: hosts on a network need to know when to begin sending messages and how to respond when collisions occur.
• Flow Control: Source and destination hosts use flow control to negotiate correct timing to avoid overwhelming the destination and ensure information is received.
• Response Timeout: Rules specify how long hosts on the network will wait for responses, and what action to take if a response timeout occurs.

Message Delivery Options

• Unicast Message: one-to-one delivery.
• Multicast Message: one-to-many delivery.
• Broadcast Message: one-to-all delivery.

Network Protocol Overview

• Network protocols define a common set of communication rules.
• Protocols can be implemented in software, hardware, or both.
• Protocols have their own function, format, and set of rules.
• Network Communications protocols enable two or more devices to communicate over one or more networks.
• Network Security protocols secure data to provide authentication, data integrity, and data encryption.
• Routing protocols enable routers to exchange route information, compare path information, and select the best path.
• Service Discovery protocols are used for the automatic detection of devices or services.

Network Protocol Functions

• Devices use agreed-upon protocols to communicate.
• Protocols may have one or more functions.
• Addressing protocols identify senders and receivers.
• Reliability protocols guarantee delivery.
• Flow Control protocols ensure data flows at an efficient rate.
• Sequencing protocols uniquely label each transmitted segment of data.
• Error Detection protocols determine if data becomes corrupted during transmission.
• Application Interface protocols allow process-to-process communications between network applications.

Protocol Interaction

• Networks require the combined use of several protocols.
• Each protocol has its own function and format.
• Hypertext Transfer Protocol (HTTP) governs how a web server and a web client interact; it defines content and format.
• Transmission Control Protocol (TCP) manages individual conversations, guarantees delivery, and manages flow control.
• Internet Protocol (IP) delivers messages globally from sender to receiver.
• Ethernet delivers messages from one NIC (Network Interface Card) to another on the same Ethernet Local Area Network (LAN).

Network Protocol Suites

• Protocols must be able to work with other protocols to be effective.
• Protocol suites are groups of inter-related protocols necessary to perform a communication function.
• Sets of rules that work together help solve a problem.
• Protocols are viewed in terms of layers.
• Higher layers deal with the content of the communication.
• Lower layers are concerned with moving data and provide services to upper layers.

Evolution of Protocol Suites

• There are several protocol suites.
• Internet Protocol Suite or TCP/IP is the most common suite, maintained by the Internet Engineering Task Force (IETF).
• Open Systems Interconnection (OSI) protocols are developed by the International Organization for Standardization (ISO).
• International Telecommunications Union (ITU) developed the AppleTalk Proprietary suite.
• Novell Inc. developed the Novell NetWare proprietary suite.

TCP/IP Protocol Example

• TCP/IP protocols operate at the application, transport, and internet layers.
• The most common network access layer LAN protocols are Ethernet and WLAN (wireless LAN).

TCP/IP Protocol Suite

• TCP/IP is used by the internet and includes many protocols.
• TCP/IP is an open standard protocol suite available to the public.
• It is endorsed by the networking industry and approved by standards organisation, meaning all vendors adhere to it.

TCP/IP Communication Process

• A web server encapsulates data and sends a webpage to a client.
• A client de-encapsulates the webpage for the web browser to display.

Benefits of Using a Layered Model

• Layered models simplify complex network operations by breaking them into manageable layers.
• Two models describe network operations: the Open System Interconnection (OSI) Reference Model and the TCP/IP Reference Model.
• Protocol design is assisted with protocols that operate at a specific layer and have defined information.
• Models foster competition since products from different vendors can work together.
• Technology changes in one layer are prevented from affecting other layers with specific protocol design.
• A common language is provided to describe capabilities across different platforms.

OSI Reference Model

• The Application layer contains protocols for process-to-process communications.
• The Presentation layer codes for data representation.
• The Session layer organises dialogue and manages data exchange.
• The Transport layer segments, transfers, and reassembles data.
• The Network layer facilitates data exchange between identified end devices over the network.
• The Data Link provides methods for exchanging data frames between devices over a common media.
• The Physical layer transmits bits across physical connections through mechanical, electrical, functional, and procedural means.

TCP/IP Protocol Model

• The TCP/IP Protocol Model was created in the early 1970s for internetwork communications.
• It is also called The TCP/IP Model or the Internet Model.
• It is an open Standard protocol.

OSI and TCP/IP Model Comparison

• In the OSI model, the network access layer and the application layer of the TCP/IP model are further divided to describe discrete functions that must occur at these layers.

Segmenting Messages

• Segmenting breaks up messages into smaller units, and multiplexing interleaves multiple streams of segmented data together.
• Segmenting increases speed, allowing large amounts of data to be sent without tying up communication links, and increases efficiency, so only failed segments need retransmission.

Sequencing

• Sequencing messages involves numbering segments for reassembly at the destination.
• TCP is responsible for sequencing individual segments for transmission.

Protocol Data Units

• Each layer of the protocol stack adds information during process of encapsulation.
• The form that the data takes at each layer is the Protocol Data Unit (PDU).
• Application layer PDU = Data.
• Transport layer PDU = Segment.
• Network layer PDU = Packet.
• Data Link Layer PDU = Frame.
• Physical Layer PDU = Bits.

Encapsulation Example

• Encapsulation is a top-down process.
• Each layer performs its process, then passes the data down to the next layer until it is sent as a bit stream.

De-encapsulation Example

• Data is de-encapsulated as it moves up the stack.
• If a layer has completed its process, the header is stripped and passed up to the next layer for processing. The process is then repeated at each layer until a data stream that the application can use.
• Received in bits (bit stream) > Frame > Packet > Segment > Data (data stream).