Transmission media is the medium by which data is transferred.
It can be bounded (cabled) or unbounded (wireless). Data is sent as
signals along transmission media.
Slide 4
Wired Wired Transmission media restricts the signal so that it
is contained within a cable and therefore follows the path of the
cable. It can be shielded to protect from electromagnetic
interference and has recommended distances between nodes.
Slide 5
Twisted Pair Twisted pair is composed of copper wire twisted
together within plastic insulation, and an outer sheath. Twisted
pair can be UTP or STP (shielded or unshielded). The most common is
UTP, specifically CAT-5 or CAT-6.
Slide 6
Twisted Pair Contd UTP is classified into categories where
higher category cable supports higher frequency and hence higher
data speeds. Eg. 16MHz for Cat 3 up to 250 MHz for Cat 6.
Slide 7
Coaxial Cable Coaxial cable was originally for transmitting
analogue TV broadcasts. Coaxial contains a solid copper core, a
nylon insulator, enclosed within an aluminium foil wrap. This is
wrapped inside braided copper and black plastic sheath.
Slide 8
Coaxial Cable Contd Coaxial does not suffer from the
electromagnetic interference that twisted pair can suffer from.
Coaxial cable is expensive and larger than UTP and can transmit on
frequencies tanging from 30MHz to 3GHz.
Slide 9
Optical Fibres Optic fibre is the fastest physical transmission
media. Optic fibre is composed of optical fibres containing light
waves. Light reflects off the inside of the cladding that surrounds
the cable. Both the core and cladding are made of pure glass.
Slide 10
Optical Fibres Contd Light waves are extremely high frequency
electromagnetic waves. Fibre optic operates on frequencies of
around 200,000Ghz 350,000GHz.
Slide 11
Wireless Wireless or unbounded transmission uses the atmosphere
to carry electromagnetic waves between nodes. Wireless has
advantages over wired in that it can traverse rugged ground and
allows nodes to move freely. BUT this makes it susceptible to
interference and unsuitable for high speed critical
connections.
Slide 12
Point to Point Terrestrial Microwave This is used to relay
wireless signals across large distances. A direct and uninterrupted
line of is required between towers. Sequences of transmitters and
receivers, known as transponders, are arranged into chains..
Slide 13
Point to Point Terrestrial Microwave These towers are being
slowly replaced by satellite connections for radio, TV and data
transfer. They were most common in the 1980s.
Slide 14
Satellite Satellites use microwaves to carry DIGITAL signals
from and to both ground based stations and also between satellites
themselves. Satellites contain transponders that amplify and then
re-transmit microwaves on a specific frequency.
Slide 15
Wireless LANS (WLANs) WLANS currently use the 802.11g series,
with frequencies in the vicinity of 2.4GHz. Common applications
include, cordless phones, Bluetooth devices and remote control
toys. WLAN transmits and receives at a maximum of 54Mbps.
Slide 16
Wireless LANs (WLANs)
Slide 17
Bluetooth Bluetooth is a communication system for short range
transmission. It was designed to replace cables connecting portable
devices.
Slide 18
Bluetooth Bluetooth devices automatically recognise each other,
forming an adhoc or piconet network. Low power Bluetooth
connections should be 1m apart whilst high powered can reach up to
100m.
Slide 19
Infrared Infrared waves travel in straight lines hence a direct
line of sight is required between source and destination. Infrared
is only used over short distances. Common applications include
remote control or portable devices.
Slide 20
Mobile Phones Mobile phone networks are split into areas called
cells, hence why mobile phones are called cell phones. Each cell
contains its own central base station that sends and receives data
to and from phones.
Slide 21
Mobile Phones As users roam between cells the base stations
pass the calls onto the next base station.
Slide 22
Slide 23
Here we will look at the devices used to connect nodes to form
a LAN and also to transfer data within a network. Each node
requires a NIC (Network Interface Card) that complies with the
Transmission level protocols on the network.
Slide 24
In most LANs a star topology is used so we need a central node
in the form of a Hub, Switch or Wireless Access Point. Gateways
connect networks that use different protocols whilst Bridges
connect networks using the same protocols. Modems allow LANs to
communicate with WANs and Routers operate at the communication
control and accessing level to direct data along the best path. For
a small LAN the functions of many of the above devices are combined
into a single piece of hardware a Router.
Slide 25
NIC (Network Interface Card) NICs convert data between the
computer into a form suitable for transmission.
Slide 26
Repeater A repeater receives a signal amplifies it and sends
the signal on its way.
Slide 27
Hub A Hub repeats all messages to all nodes on a single LAN
segment. Hubs have been phased out by more intelligent
switches.
Slide 28
Bridge A bridge separates networks into different segments
using the same protocol. Switches have replaced this function more
recently.
Slide 29
Switch A switch is an intelligent hub or a multi- port bridge.
Determines the MAC address of sender & receiver for each
message.
Slide 30
Gateway A Gateway connects between networks. This means a
gateway can connect between protocols.
Slide 31
Wireless Access Point (WAP) A connection point on a wireless
network. The issue here is security. Any user can access the
network. Therefore we use WEP (Wired Equivalent Privacy) & WPA
(Wireless Protected Access).
Slide 32
Modem A modem is short for modulation and demodulation which
are the functions a modem serves. Modems are used to connect a
computer to an ISP. Modems can be ADSL (broadband over existing
copper wire network) or cable (net connection via coaxial
cable).
Slide 33
Router Routers direct traffic over the most efficient path to a
destination. Routing decisions are based on IP addresses. Your
wireless router at home operates as a modem and a gateway to the
wider internet as well as including a variety of security
measures.
Slide 34
Router
Slide 35
Slide 36
A server provides a specific processing services to other nodes
(clients). The following servers are the most common servers founds
within a LAN or network.
Slide 37
ServerDescription File Server A file server manages storage and
retrieval of files and also application software in response to
client requests. This demands large amounts of secondary storage.
These use RAID hard-drives. Print Server A print server controls
access to one or more printers for many clients. This uses a print
queue. Some print servers can take priority requests. Database
Server Database servers run database management system software.
These execute SQL statements and retrieve queries. Mail Server
Governs email networks such as Microsoft Outlook and uses
application and presentation layers of protocol. Web Server Web
servers provide services to web browsers they retrieve web pages
and transmit them back to the requesting client web browser. Proxy
ServerProxy servers are intermediary servers that exists between
clients and main servers. They attempt to fulfil requests instead
of the main server so that wait times are reduced and the main
server gets less traffic.