Transcript Computer communication

Computer communication
Networks
Topologies
Bus Network
Terminator
‘Workstation’
‘Client’
‘Terminal’
‘Node’
Computer
Terminator
Backbone
Server
(optional)
Topologies
Bus Network
Terminator
‘Workstation’
‘Client’
‘Terminal’
‘Node’
Computer
Network interface card (NIC)
T connector – plugs into NIC
Terminator
Backbone
Server
(optional)
Topologies
Bus Network
• All components are connected via a backbone.
• At each end of the backbone is a terminator which stops
signals ‘bouncing back’ down the network.
• Each network interface card is passive: they all listen to the
backbone for signals addressed for them.
• Signals are sent in both directions of the backbone at the
same time.
• Only one computer can transmit successfully at any one time,
however this is not regulated so collisions and data corruption
do occur.
• A protocol called CSMA-CD (carrier sense multiple access
collision detection) is used to handle this problem.
Topologies
Bus Network
• Bus networks work well under small loads: small
number of computers, small demand for
resources. Under heavy loads it can be very slow
or completely grind to a halt.
• If a machine goes down it doesn’t affect the
network.
• A break in the backbone will result in the whole
network going down.
• Bus topologies were popular in the early 1990’s.
Today, better technologies (switched Ethernet)
have superseded simple bus topologies.
Topologies
Bus Network
• Collisions on a Bus network
– Problems arises when two computers transmit
onto the bus a the same time. The voltage
pulses form each computer will eventually
collide, resulting in higher voltage swings. A
protocol is used to decrease the chance of
this. This is CSMA/CD – Carrier Sense
Multiple Access with Collision Detection.
Topologies
Bus Network
• Collisions on a Bus network
Topologies
Ring Network
• Each computer is
responsible for passing the
message on.
• Can use token passing
• Special packet is passed
around altered by a
computer if it needs to
send data
Topologies
Star Network
• Common network
• Connected by switches and
hubs.
• Better performance than
bus networks
Topologies
Classifications of Networks
• Can you come up with definitions of the
following
– LAN
– WAN
– MAN
– PAN
– VPN
Topologies
Classifications of Networks
• Can you come up with definitions of the
following
– LAN – Local Area Network
– WAN – Wide Area Network
– MAN – Metropolitan Area Network
– PAN – Personal Area Network.
– VPN – Virtual Private Network.
Topologies
Task
Answer questions on page 129.