This document discusses various concepts related to transmitting and receiving data over networks. It covers topics such as transmission methods (parallel vs serial), transmission direction (simplex, half-duplex, full-duplex), synchronization techniques, protocols, network topologies, access methods like Ethernet and token ring, transmission media, wireless transmission, and network software. The roles of devices like routers, switches, bridges and servers are also outlined.

1. 3.3) Transmitting and3.3) Transmitting and
ReceivingReceiving

2. • Different concepts covered include:
• transmission of data
• protocols
• handshaking
• networks and their topologies
• network access methods
• Transmission of data occurs in two ways:
• parallel transmission
• serial transmission

3. • Parallel transmission is the transmission of
data simultaneously using separate
channels.
• Serial transmission transmits the data one
bit after the other along one channel.
• Parallel is faster, but can only be used over
shorter distances.
• The direction of data flow can be:
• simplex
• half-duplex
• full-duplex

4. • Simplex mode allows transmission in one
direction only.
• Half-duplex allows transmission in either
direction, but only in one direction at a
time.
• Full duplex allows transmission in both
directions simultaneously.

5. • Serial transmission can be either
asynchronous or synchronous.
• Synchronous transmission requires that all
of the data is sent at the same transfer rate.
• The same number of bits is sent each
second.
• Both computers are synchronized through
the use of an internal clock.
• It is faster and more efficient, but quite
expensive as it requires very stable
connections.

6. • Asynchronous transmission is sent at
varying rates and the flow is regulated
through the use of start and stop bits.
• One of the protocols agreed upon during
handshaking is how many start and stop bits
will be used.
• [Diagram 3.10, p.88]
• Protocols are a set of rules that govern the
transfer of data between two computers.

7. • They define:
• how a link is established
• how data is transmitted
• how errors are detected and corrected
• Numerous protocols have been developed
for different technologies.
• [Table 3.1, p.89 – Do the following: IPX,
X.25, ATM, Kermit, TCP/IP, HTTP, FTP,
POP, MIME]

8. • A network is any number of computers and
their peripheral devices connected together
in some way.
• Each device in a network is called a node.
• Terminals are devices that send data to and
receive data from another computer.
• If the terminal has memory and processing
capabilities it is called an intelligent
terminal.
• Personal computers are often called
workstations on a network.

9. • Networks can be either LAN’s, WAN’s or
very rarely, GAN’s
• Local Area Networks (LAN’s) – are linked
computers at one physical location
• Wide Area Network (WAN’s) – connect
computers over several geographical
locations
• Global Area Networks (GAN’s) –
computers and devices connected all over
the world

10. • Network topology is the physical
arrangement of the devices in a network.
• Three common types of topologies are:
• bus
• star
• ring

11. Bus Network

12. Star Network

13. Ring Network

14. • The bus topology is where all devices are
attached to a direct line called a bus.
• Each devices checks that the line is free and
sends its signal.
• If there is a data collision then the sending
terminal waits a random time then attempts
resending.
• If one node fails the system will still work.
• A star topology has a central computer with
each device connected directly to it.

15. • The central computer receives messages
and sends them to the destination device.
• It requires extra cabling because each
device must be connected to the central
computer.
• If one devices fails, the network will still
function unless it is the central computer
that is broken.
• Its speed is determined by the processing
power of the central computer.

16. • A ring topology is an arrangement where all
devices are attached so that the connection
is a continuous loop.
• Data flow is one direction moving from
device to device.
• A ‘token’ is passed along the network and
data packets are attached to the token and
released when they reach the appropriate
node.

17. • There are a number of ways to deal with
multiple users wanting to access the
network.
• The two most common methods are:
• Ethernet
• token ring
• Ethernet is based upon a bus network.
• Ethernet allows data to be sent in both
directions simultaneously.
• This means there will be data collisions and
errors

18. • To overcome this problem, Ethernet uses a
system called Carrier Sense Multiple
Access and Collision Detection
(CSMA/CD)
• In CSMA/CD all nodes have the ability to
sense signals on a network.
• When a node wishes to transmit, it ‘listens’
for a signal on the bus.
• When no signals are detected, it transmits.
• If two nodes transmit at the same time then
a data collision can occur.

19. • When a collision is detected, each device
stops transmitting, waits a randomly
determined time, then transmits again.
• Token ring is a LAN access protocol based
upon ring topologies.
• Special data packets, called tokens, are
continually passed between nodes on the
network.
• Workstations with data to send attach it to a
free token and transmit it.
• A busy token cannot be used by other
nodes.

20. • When the data is received it is replaced with
an acknowledgement and sent back to the
original sending node.
• There are several special purpose hardware
devices used in a successful network.
• They include:
• a network interface card
• servers
• routers and switches
• bridges and gateways
• hubs

21. • A network interface card (NIC) is an
expansion card that links the network to the
computer motherboard.
• The type of NIC depends upon the type of
network.
• A server is a dedicated computer that
provides services to other computers.
• Workstations log on to the server to give
them access to files, applications or
peripheral devices.

22. • Types of servers include:
• file server
• print server
• mail server
• Internet server
• Networks are often linked to other networks
and this requires paths to be established and
signal strength to be boosted.
• Devices used to determine the path between
networks include routers and switches.

23. • Routers maintain a table of available routes
and their conditions.
• It uses this table to determine the best route
for any given data packet.
• Data packets often travel through several
networks and routers before they reach their
destination.
• A switch is similar, but it does not maintain
a table, therefore making it a simpler and
faster mechanism for passing the message
along.

24. • However, they do not always choose the
faster route for the packet to travel along.
• The actual connection between networks is
achieved through bridges and gateways.
• A bridge is a combination of hardware and
software used to link two similar networks.
• Bridges examine each data packet and
forward any that are addressed to a
connected LAN.
• Gateways are combinations of hardware
and software used to link two different
kinds of network.

25. • This usually involves converting different
protocols.
• A repeater may also be used to increase a
diminishing signal.
• Repeaters are less intelligent than bridges or
gateways.
• A hub is a central connecting device within
a network.
• A hub can be considered passive if it just
channels data or it can contain a router to
improve traffic flow.

26. • As well as the devices connected to a
network, we need to consider the
transmission medium.
• Data is transferred along a transmission
medium.
• The capacity of a transmission medium is
called the bandwidth.
• Bandwidth is generally measured in bps
• They can be categorised as wire or wireless.
• Wire transmission involves wires and
cables.

27. • Twisted pair cable consists of two insulated
copper wires twisted around each other to form
a spiral.
• There are two types:
• shielded twisted pair (STP)
• unshielded twisted pair (UTP)
• STP is more often used in ‘noisy’
environments.
• Twisted pair is the slowest medium with
transmission speeds up to 60 Kbps.

28. • Coaxial cable consists of a single copper wire
surrounded by insulation, shielding , then more
insulation.
• It allows transmission with little interference.
• Generally used for under 2kms.
• Bandwidth is around 10Mbps.
• Fibre-optic cables are made from glass fibres
the width of a human hair, that are often
bundled together.

29. • They are:
• free from interference
• very secure
• able to transmit at high speeds
(> 400 Mbps)
• Most LAN’s use twisted pair or coaxial cable
as fibre-optic is too expensive but this is
changing and fibre-optic is becoming much
more common.

30. • There are two types of transmission used:
• baseband
• broadband
• Baseband uses the entire capacity of the cable to
transmit one signal.
• Broadband networks divide the cable so that
several signals can be transmitted simultaneously.
• Most LAN’s are baseband.
• Wireless transmission moves data without a
physical connection.

31. • Wireless includes:
• microwaves
• radio frequencies (RF)
• infra-red (IR)
• satellites
• A microwave is a high frequency radio signal
that requires antennae no further than 50 km
apart.
• It is faster than coaxial or regular telephone
lines and relatively error-free.

32. • Radio frequencies are used for many home and
business wireless networks, usually in the 2.4
GHz range.
• Can have an access point (or hot-spot) or be
done in an ad-hoc manner.
• Satellites can transmit large amounts of data
over large distances.
• Used by major corporations, television
networks and telecommunications.
• IR is used by some devices in LAN’s

33. • Each computer in a network must have
appropriate network software.
• This software is usually organised by a
network administrator.
• Their responsibilities include:
• network security
• software installations and updates
• monitoring daily activity
• enforcing licensing agreements
• developing a storage solution
• performing routine backups

34. • A network operating system (NOS) is an
operating system designed to support
networked computers.
• One part resides on each node with another
part on the server.
• Tasks carried out by a network OS include:
• administration
• file management
• applications
• resource management
• security

35. • An intranet is a private network that uses a
similar interface to the Web.
• It consists of many interlinked LANs.
• It provides access similar to the Internet, but
only to a select group of users (e.g. employees,
students)
• Firewalls monitor the flow of data in both
directions to maintain the security of the
organisation.

36. • An extranet is an intranet that is accessible to
customers, suppliers or others outside the
organisation.
• It provides such information as product
descriptions, answers to frequently asked
questions, warranties and how to contact
customer service.
• Extranets are still limited to accessing select
computer paths and files.