Characteristics of Communications SystemsThis is a featured page

9.3.1 characteristics of communication systems

Students learn about: Students learn to:
  • communication systems as those that enable users to send and receive data and information
  • the framework in which communication systems function, demonstrated by the following model:
Communications framework
  • the functions performed within the communication systems in passing messages between source and destination, including:
    • message creation
    • organisation of packets at the interface between source and transmitter
    • signal generation by the transmitter
    • transmission
    • synchronising the exchange
    • addressing and routing
    • error detection and correction
    • security and management
  • the roles of protocols in communication
    • handshaking and its importance in a communications link
    • functions performed by protocols at different levels
  • the client server model
    • the role of the client and the server
    • thin clients and fat clients
    • examples of clients such as:
      • web browsers and
      • mail clients
    • examples of servers such as:
      • print servers,
      • mail servers and
      • web servers
  • use applications to create and transmit messages
  • establish a communications link and describe the steps that take place in its establishment

syllabus changes

  • identify, describe specified protocols at different stages of the communication

  • identify client processing and server processing
  • describe the advantages and disadvantages of client server architecture

Term Explanation
Communication System Framework (diagram above)
Protocols Wikipedia - Protocol(Computing)
"In computing, a protocol is a set of rules which is used by computers to communicate with each other across a network. A protocol is a convention or standard that controls or enables the connection, communication, and data transfer between computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, semantics, and synchronization of communication. Protocols may be implemented by hardware, software, or a combination of the two. At the lowest level, a protocol defines the behavior of a hardware connection."
OSI Reference Model
Characteristics of Communications Systems - Information Processes & Technology
What is .com - OSI Reference Model Illustrated

OSI Model
  • OSI Model Video
  • Application Level

    • Application layer
Categorizing protocols and methods in architectural models of
computer networking.
    • Presentation layer
the delivery and formatting of information to the application layer for
further processing or display. It relieves the application layer of
concern regarding syntactical differences in data representation
withinthe end-user systems.
  • Communications Control and Addressing Level

    • Session layer
the mechanism for opening, closing and managing a session
between end-user application processes, i.e. a semi-permanent
dialogue.Communication sessions consist of requests and
responses that occur between applications.
    • Transport layer
A group of methods and protocols within a layered architecture of
network components within which it is responsible for encapsulating
application data blocks into data units (datagrams, segments)
suitable for transfer to the network infrastructure for transmission to
the destination host, or managing the reverse transaction by
abstracting network datagrams and delivering their payload to an
application. Establish a direct, virtual host-to-host communications
transport medium.
    • Network layer
Responsible for end-to-end (source to destination) packet delivery
including routing through intermediate hosts, whereas the Data Link
Layer is responsible for node-to-node (hop-to-hop) frame delivery on
the same link. provides the functional and procedural means of
transferring variable length data sequences from a source to a
destination host via one or more networks while maintaining the
quality of service and error control functions.
  • Transmission level

    • Data Link layer
The protocol layer which transfers data between adjacent network
nodes in a wide area network or between nodes on the same local
area network segment. The Data Link Layer provides the functional
and procedural means to transfer data between network entities and
might provide the means to detect and possibly correct errors that
may occur in the Physical Layer.
    • Physical layer
Consists of the basic hardware transmission technologies of a
network. It is a fundamental layer underlying the logical data
structures of the higher level functions in a network. defines the
means of transmitting raw bits rather than logical data packets over
a physical link connecting network nodes. The bit stream may be
grouped into code words or symbols and converted to a physical
signal that is transmitted over a hardware transmission medium.
The Physical Layer provides an electrical, mechanical, and
procedural interface to the transmission medium. The shapes and
properties of the electrical connectors, the frequencies to broadcast
on, the modulation scheme to use and similar low-level parameters,
are specified here.
Source The beginning of a transmission.
Destination Where the transmission ends up.
Transmitter An electronic device which, usually with the aid of an antenna,
propagates an electromagnetic signal such as radio, television, or
other telecommunications.
Receiver An electronic device that catches the signal sent out by the
Switching and Routing Characteristics of Communications Systems - Information Processes & Technology
Transmission Medium The material on which information signals may be carried; eg, optical fiber, coaxial cable, and twisted-wire pairs.
Message creation
Packets What is a data packet? source:
  • organisation of packets

signal generation In general, the events that generate signals fall into three major categories: errors, external events, and explicit requests.
Generator: An electrical device that generates repeating or non-repeating electronic signals (in either the analog or digital domains). They are generally used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices; though they often have artistic uses as well.
synchronising the exchange Packet based telecommunications networks are being developed to carry Constant Bit Rate (CBR) data streams between source and destination exchanges in the form of multiplexed packets, which are recombined at the destination exchange into a CBR stream. In such a network it is desirable to synchronise the frequency and maintain the phase relation of the recombined CBR stream with those of a source CBR stream arriving at the source exchange.
addressing and routing Perhaps the most complex aspects of IP are IP addressing and routing. Addressing refers to how end hosts become assigned IP addresses and how subnetworks of IP host addresses are divided and grouped together. IP routing is performed by all hosts, but most importantly by internetwork routers, which typically use either interior gateway protocols (IGPs) or external gateway protocols (EGPs) to help make IP datagram forwarding decisions across IP connected networks
error detection and correction In information theory and coding theory with applications in computer science and telecommunication, error detection and correction or error control are techniques that enable reliable delivery of digital data over unreliable communication channels. Many communication channels are subject to channel noise, and thus errors may be introduced during transmission from the source to a receiver. Error detection techniques allow detecting such errors, while error correction enables reconstruction of the original data.
security and management
functions performed by protocols at different levels
client server model A client-server software architecture model distinguishes client systems from systems and communicates over a computer network. A client-server application is a distributed system that constitutes both client and server software. A client software or process may initiate a communication session, while the server waits for a request from a client.
  • role of the client
A client is an application or system that accesses a remote service on another computer system, known as a server, by way of a network.[1]The term was first applied to devices that were not capable of running their own stand-alone programs, but could interact with remote computers via a network. These dumb terminals were clients of the time-sharing mainframe computer.

Via Wikipedia
  • role of the server
A server computer is a computer, or series of computers, that link other computers or electronic devices together. They often provide essential services across a network, either to private users inside a large organization or to public users via the internet. For example, when you enter a query in a search engine, the query is sent from your computer over the internet to the servers that store all the relevant web pages. The results are sent back by the server to your computer.

Via Wikipedia
thin clients Wikipedia - Thin Client
"A thin client (sometimes also called a lean or slim client) is a computer or a computer program which depends heavily on some other computer (its server) to fulfill its traditional computational roles.[1] This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself. The exact roles assumed by the server may vary, from providing data persistence (for example, for diskless nodes) to actual information processing on the client's behalf."
fat clients Wikipedia - Fat Client
"A fat client or rich client is a computer (client) in client-server architecture networks which typically provides rich functionality independently of the central server. Originally known as just a 'client' or 'thick client', the name is contrasted to thin client, which describes a computer heavily dependent on a server's applications.
A fat client still requires at least periodic connection to a network or central server, but is often characterised by the ability to perform many functions without that connection. In contrast, a thin client generally does as little processing as possible and relies on accessing the server each time input data needs to be processed or validated."
examples of clients
  • web browsers
Wikipedia - Web Browser

"A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI) and may be a web page, image, video, or other piece of content.[1] Hyperlinks present in resources enable users to easily navigate their browsers to related resources.
Although browsers are primarily intended to access the World Wide Web, they can also be used to access information provided by Web servers in private networks or files in file systems. Some browsers can be also used to save information resources to file systems."
  • mail servers
What is a mail server?
"A mail server (also known as a mail transfer agent or MTA, a mail transport agent, a mail router or an Internet mailer) is an application that receives incoming e-mail from local users (people within the same domain) and remote senders and forwards outgoing e-mail for delivery. A computer dedicated to running such applications is also called a mail server. Microsoft Exchange, qmail"

List of mail servers - Wikipedia, the free encyclopedia
examples of server


  • print server
A computer or device that is connected to one or more printers and to client computers over a network, and can accept print jobs from the computers and send the jobs to the appropriate printers.
  • mail server
A computer process or software agent that transfers electronic mail messages from one computer to another, in single hop application-level transactions. An MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol.
  • web server
A computer program that delivers (serves) content, such as web pages, using the Hypertext Transfer Protocol. The term web server can also refer to the computer or virtual machine running the program.
Parity Bit Check Here is an explanation I gave to Matt Lyell in response to an emailed question through this wiki. (N.B. moved to Other Information Processing)
Handshaking An agreement about which protocol to use to accomplish the exchange of information
Hardware Flow Control Uses a dedicated connection, such as a wire. It is only practical when devices are close enough to be linked with a cable. A common hardware protocol is RTS/CTS (request to send/clear to send)
Software Flow Control Uses a special code sent with the data. It is used for long distance communication. A common software protocol is XON/XOFF (X stands for transmit). IF a break in transmission is needed, then the XOFF command is sent. When transmission is to start again, then the XON command is sent
Communication System Enables people to send and receive data and information
Data Source Produces the data to be sent
Transmitter Encodes the data into a signal suitable for a transmission medium
Transmission Medium A channel, such as a cable, in which the signal is transmitted to the destination. The signal may be changed or distorted during transmission
Receiver Decodes the signal back into the original data or an approximation of the data
Destination Receiver of the information
Bandwidth The capacity of the channel, or transmission medium
OSI Reference Model Divides data communication into seven layers. Each layer expresses the standard, using a protocol. The bottom layers are responsible for transfer of data from one place to another.
Bits Per Second (bps) The maximum number of bits that can be transmitted in one second
Baud Rate The maximum number of data symbols or electrical signals that can be transmitted in one second, i.e. how quickly a signal can be changed from one state (data) to another e.g. 11001100 to 0011011
Checksum A method of checking for errors in data transmission by counting the number of bits in a data packet. A data packet is created by dividing the total data into smaller groups. The count of the bits in a data packet is attached to the data packet. It is used by the receiver to check whether all the bits have arrived successfully. If the count matches, it is assumed that a complete transmission was received
Cyclic Redunacy Check A method of checking data for errors in data transmission using a division process. The data is divided into predetermined lengths and divided by a fixed divisor. The remainder of the calculation is attached and sent with the data. When the data is received, the remainder is recalculated. If the remainders do not match, an error in transmission has occurred.
Parameter A variable that is given a constant value for a particular application
Data Bits The number of bits in each group of data. Each data group is usually sent as a byte, such as a 7-bit ASCII or an 8-bit ASCII
Parity Whether the data contains a parity bit for error detection.
Parity is odd, even or none. detects most errors with about 50% accuracy
an example of an error detected by parity would be for example 1000001 with parity set to 1 making the number of 1s an odd number if this was reversed (eg 11000001) there would be an error?
Stop/Start bits The number of stop and start bits used in asynchronous transmission. This parameter is used to identify each byte. The normal range is between 0 and 2. Some systems only use a stop bit

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