Download Communication systems

Communication systems

Communication systems enable people and systems to share and exchange data
and information electronically.
 This communication occurs between transmitting and receiving hardware and
software over a network- each device on a network is called a node.
Diagram: Communication system framework from NSW Board of Studies IPT syllabus
(modified).


Protocols- set of rules that components agree on for the communication to be
successful. Protocols are classified according to the level or layer in which they
operate.
Handshaking- establishing and agreeing on which set of protocols will be used
and the specific detail of each protocol must occur before any data can be
transmitted or received.
7. Application
Presentation
6. Presentation
5. Session
4. Transport
Communication and
control
3. Network
2. Data link
1. Physical
Transmission
Diagram: Comparison of the seven layers of the OSI model with the three levels used in
IPT.
Characteristics of communication
system
Overview of protocol levels
 Software used to control and direct the operation of hardware. The
transmitter and the receiver must agree on how the hardware will be used to
transfer messages.
 A large variety of applications transfer data sing a wide variety of operating
systems, protocols, devices and transmission media.
IPT presentation level
7. OSI application layer- the actual data to be transmitted is created by a
software application, this data is organized in a format understood by the
application that will receive the data.
6. OSI presentation layer - the data is reorganized into a form suitable for
subsequent transmission.
IPT communication control and addressing level
5. OSI session layer - this is where communication with the network is
established, commences and is maintained. It determines when a
communication session is started with a remote computer and also when it
ends.
4. OSI transport layer - the transport layer manages the correct transmission
of each packet of data. This layer ensure that packets failing to reach their
destination are retransmitted.
IPT transmission level
2. OSI data link layer - this layer defines how the transmission media is
actually shared. Device drivers that control the physical transmission
hardware operate at this layer.
1. OSI Physical layer – this layer performs the actual physical transfer, hence
it is composed solely of hardware. It converts the bits in each message into the
signals that are transmitted down the transmission media.

Mac Address – Media Access Controller. Address hardwired into each device. A
hardware address that uniquely identifies each node on a network.
Overview of how messages are passed between source and destination
1. Message creation – The message is compiled at the source in preparation
for sending, using some type of software application, and perhaps
collection of message data from one of the system’s users or participants.
2. Organisation of packets at the interface between source and transmitter –
message descends the stack of protocols from the application level down
to where t is ready for physical transmission by the hardware operating at
the transmission level. Each protocol wraps the data packet from the layer
above with its own header and trailer.
3. Signal generation by the transmitter – physical hardware that generate or
encodes the data onto the medium creating a signal. In most cases
transmitters and receivers decode the signal on the medium. This hardware
is controlled by protocols operating at the transmission level.
4. transmission – as the signal travels or propagates through the medium.
Each bit or often pattern of bits moves from transmitter to receiver as a
particular waveform.
5. Synchronizing the exchange – to accurately decode the signal requires the
receiver to sample the incoming signal using precisely the same timing
used by the transmitter during encoding. This ensures each symbol or
waveform is detected by the receiver.
6. Addressing and routing – during transmission data packets may ass
through many different and varied links - particularly when the
communication is over the internet. Furthermore it is likely that packets
forming part of a single file will travel over quite different paths from the
transmitter to the receiver. Each new communication link will have its
own protocol or set of protocols and hence each packet must ascent the
protocol stack unitil it reaches the addressing or routing protocol and then
descent the protocol stack as it is prepared for transmission down the next
path. Ethernet and other transmission level protocols use the receiver’s
MAC address to determine the path leading to the receiver.
7. Error detection and correction – as message descent the stack prior to
transmission many protocols calculate checksums or CRC (cyclic
Redundancy check) values and include the within their headers or footers.
8. Security and management – Many protocols restrict messages based on
usernames and passwords, and other go a step further by encrypting
messages during transmission
Protocols

A formal set of rules and procedures that must be observed for two devices to
transfer data efficiently and successfully.
 POP - (Post office protocol), application layer internet standard protocol used by
the local email clients to retrieve email from a remote server over a TCP/IP
connection.
 TCP/IP – (transmission control protocol/internet protocol)
 SMTP – (simple mail transfer protocol) is an Internet standard for electronic mail
(e-mail) transmission across Internet Protocol (IP) networks.
 MIME – (multipurpose internet mail extension) is an internet standard that
extends the format of email to support; text in characters sets other than ASCII,
non-text attachments, message bodies with multiple parts, header information in
non-ASCII character sets.
 HTTP – (Hypertext transfer protocol) is an application layer protocol for
distributed, collaborative, hypermedia information systems.
 FTP – (file transfer protocol) is a standard network protocol used to copy a file
from one host to another over a TCP/IP – based network, such as the internet.
 SSL (secure socket layer) are cryptographic protocols that provide security for
communications over networks such as the internet.
Ethernet – operates at the IPT transmission level including OSI data link layer 2 and also
at the OSI physical layer 1. Using Ethernet it is possible for two nodes to transmit a frame
at the same time. If these nodes share the same physical transmission line then a data
collision will occur and both frames will be corrupter. Ethernet uses a system called
carrier sense multiple access with collision detection (CSMA/CD) to deal with such
collisions. Modern Ethernet networks prevent collisions altogether through the use of
switches where just two nodes (including switches) exist on each segment.