Transcript Application of Networks

Central
server
Ring network
Star network
Bus network
2. Network Fundamentals
2.1
Interconnection of networks
BACKBONE2
LAN B
BACKBONE1
LAN A
LAN B
Bridge or
router
LAN C
Local network
LAN E
LAN E
Local network
Local network
Bridge or
router
Local network
Local network
BACKBONE3
2.2
Network topologies
Central
server
Ring network
Bus network
Star Network
Advantages:
Since the data rate is relatively low between central
server and the node, a low-specification
twisted-pair
Star network
cable can be used connect the nodes to the server.
A fault on one of the nodes will not affect the rest
of the network. Typically, mainframe computers use a
central server with terminals connected to it.
Disadvantages:
Network is highly dependent upon the operation of
the central server. If it were to slow significantly then
the network becomes slow. In addition, if it were to
become un-operational then the complete network
would shut down.
2.3
Tree topology
Tree topology
Resources should be grouped logically when
attached to hubs, such as local file servers, printers,
and so on.
Network backbone
Concentrator
(or hub)
Advantages:
Nodes local to a hub can communicate with each
other without the data traffic going onto other
network segments.
A fault on a single computer or a hub does not
bring the whole network down.
Communication between the hub and the
Concentrator
computer has relatively low data transfers, as
(or hub)
opposed to the transfer connected hubs to hubs.
Easy to connect and disconnect to.
Disadvantages:
Network may suffer from slow data transfer if the
network is not planned to reflect tree topology.
Typically network is created with workgroups.
Workgroup
- with printer
- file server
- etc
Most networking technologies now use hubs to
connect to.Typically for Ethernet and Token Ring
networks.
2.4
Star Network
Central
server
Star Network
Advantages:
Since the data rate is relatively low between central
server and the node, a low-specification twisted-pair
cable can be used connect the nodes to the server.
A fault on one of the nodes will not affect the rest
of the network. Typically, mainframe computers use a
central server with terminals connected to it.
Disadvantages:
Network is highly dependent upon the operation of
the central server. If it were to slow significantly then
the network becomes slow. In addition, if it were to
become un-operational then the complete network
would shut down.
2.5
Bus network
All computers have access to
a common bus at the same time
Common bus
Ethernet hub
Bus network
Uses a multi-drop transmission medium.
All nodes on the network share a common bus and
all share communications. This allows only one device
to communicate at a time.
A distributed medium access protocol determines
which station is to transmit. data frames contain
source and destination addresses, where each station
monitors the bus and copies frames addressed to
itself.
Twisted-pair cables give data rates up to 100Mbps,
whereas, coaxial and fibre optic cables give higher bit
rates and longer transmission distances. Gigabit
Ethernet is now available (1Gbps).
A typical bus network is Ethernet 2.0.
Advantages:
Good compromise over the other two topologies
as it allows relatively high data rates.
If a node goes down, it does not affect the rest of
the network.
Disadvantages:
Requires a network protocol to detect when two
nodes are transmitting at the same time.
Does not cope well with heavy traffic rates.
2.6
Token passing ring network
Electronic token
is passed from
node to node
Nodes can only
transmit data when
they capture
the token
Advantages:
All nodes on the network have an equal chance of
transmitting data.
Disadvantages:
If one of the nodes goes down then the whole
network may go down.
Token may get lost, or many tokens are generated.
Difficult to add and delete nodes to/from the ring.
Token Ring
Orderly access to ring.
Single electronic token passes from one computer
to the next around the ring.
Computer can only transmit data when it captures
the token.
Each link between nodes is a point-to-point link and
allows the usage of almost any type of transmission
medium.
Typically, twisted-pair cables allow a bit rate of up to
16Mbps, but coaxial and fibre optic cables are
normally used for extra reliability and higher data
rates.
A typical ring network is IBM Token Ring and
FDDI.
2.7
Token Ring (example data exchange)
Control
Token
(a)
A
(b)
Data
Frame
Ack.
D
B
(c)
C
(d)
Control
Token
Token Ring
Control token rotates round
the ring.
Node wishing to transmit
data captures the token.
Node captures token and
transmits a data frame.
Data frame rotates round
network.
All nodes read the frame and
determine if the data is for
them.
Destination node reads the
data, and sets an
acknowledgement flag.
Data frame continues round
the network, until the source
node receives it.
Source node puts the
control token back on the
ring.
2.8
1
2
3
CSMA/CD
Two nodes transmit
at the same time
Node detect there
has been a collision
Nodes transmit a
jamming signal
CSMA/CD
Ethernet uses carrier sense, multiple access with
collision detection (CSMA/CD).
Nodes monitor the bus (or Ether) to determine if
it is busy. A node wishing to send data waits for an
idle condition then transmits its message.
Collisions can occur when two nodes transmit at
the same time, thus nodes must monitor the cable
when they transmit.
When a collision occurs, both nodes stop
transmitting frames and transmit a jamming signal.
This informs all nodes on the network that a
collision has occurred.
Each of the nodes involved in the collision then
waits a random period of time before attempting a
re-transmission.
As each node has a random delay time then there
can be a prioritisation of the nodes on the network.
All computers have access to
a common bus at the same time
4
Nodes wait a random
period before retransmitting
Common bus
2.9
Routers, Bridges and Repeaters
Router
Network
Data Link
Physical
A router routes with
the network address
(such as the IP address)
Bridge
Data Link
Physical
A bridge routes with
the MAC address
Repeater
Physical
A repeater boosts the
signal
2.10
Repeaters, bridges and routers
Network segment (repeater
extends the network segment)
Router only forwards if the
network address is on another
network. It does not forward
broadcasts.
Repeater
Bridge
Bridge only forwards if the
station (or MAC) address is not
on the connected network
segment that it originated from.
Broadcasts are also passed
over.
Router
Network
segment
bounded by a
router or a
bridge
2.11
Cabling
Work area
station cable
(max: 3m)
Patch
cable/jumper
(max: 6m)
Backbone cabling
(vertical cabling).
Typically fiber optic
cable (to prevent
ground loops and
To run for long
distances)
Telecommunications
outlet/ connector
Horizontal
Cable
(max: 90m)
Wiring closet
2.12
Maximum for twisted-pair
100 m
Hub
200 m
200 m