Chapter 4
 Understand
network connectivity.
Peer-to-Peer network & Client-Server network
 Understand
network topology
Star, Bus & Ring topology
 Understand
 Network
congestion control techniques
equipment
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 The
arrangement of nodes (hosts, machines, computers,
printers, etc.) is called topology.
 The
way the networks are arranged, constructed is called
topology.
Node 1
Node 2
•This is called a n = 2 network
•If both the nodes are computers, then
it is called a point-to-point network
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 Network
consist of two or more nodes, connected by one or
more channels.
 When
many computers and peripherals are connected to a
common communication channel, it is called a multi-point
network or multi-node network.
Node 1
Node 2
Node 3
Node 4
Printer
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 Any
devices such as a hard disk or printer that are accessed
and used by all the nodes on the network are called shared
resources.
 Two
kinds of relationship exist between the connected nodes
Peer-to-Peer network.
 Cooperative processing.
 Distributed processing.
Client – Server network.
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 In
a Peer-to-Peer network, all the computers in the network are of
same standing (level) and neither is a master or a slave (ServerClient).
 A way
to enhance the use of resources is cooperative processing,
the sharing of processing tasks between two or more processors,
either within or between computers.

Distributed processing is the dispersion of the data processing
among computers in multiple sites.
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 In
Client - Server relationship, the nodes are not equal. One
node is the Server (master) and the rest of the nodes are
Clients (slave).
 All
the clients request service from the server, such as file
space, common printer, and shared processing.
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Client
Client
Client
Hub
Server
Client
Client
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 In
the client – server architecture, if the clients have no
storage nor the processing capabilities, then the clients are
called dumb terminal.
Example old mainframes systems.
 In
current client – server architecture, most of the clients
have processing capabilities.
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 The
client – server architecture is the basis for the current
day Local Area Networks and Wide Area Network.
 In
client – server architecture, the client can be of two types
Thin Client – they have very limited processing and storage
capabilities.
 Example – Smart phones.
Fat Client – they have large storage and processing capabilities.
 Example – Desktop and Laptops.
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Client Desktop
Client Laptop
Hub
Server
Client IPad
Client –
Smart
phone
Client Laptop
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 Advantages
Resource sharing.
Share processing.
Easy maintenance.
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 Network
Operation systems
Example Microsoft Windows 2003/2008 Server OS.
 A networking
device
Hub, Switch, Router.
 Network
 Media
CATegory
Definiti
on
Means
Usage
3
10Base
T
10 Mbps on baseline
Ethernet
5
100Base
T
100 Mbps on baseline
Fast Ethernet
6
1000Bas
eT
1000 Mbps on
baseline
Giga Ethernet
Interface Card (NIC)
(Wire)
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 Geographical
arrangement of a network’s components is also
called a topology.
 Topology
can be of two types
Physical Topology – how the wiring is laid out.
Electrical Topology – how the nodes use the path.
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 The
 All
most common type of the network topology.
the cables from the end nodes (clients and server) are
connected to a central point – Hub or a Switch.
Client PC
Active
Node
Client PC
Client Scanner
Client
Client Laptop
Client Printer
Hub
Client
Server
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Client
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 In
the star topology, the end nodes acquire the attention of
the central node before communication can take place, this
process is called polling.
 One
disadvantage of star topology is congestion.
If the central active node is busy, then the network becomes
congested.
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 In
a bus topology, all the nodes are connected to a single,
central wire called as bus.
 One
major drawback of a bus topology is the single point of
failure.
If the central wire fails, then the entire network breaks down.
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Client
Client
Client
Server
Client
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 In
the ring topology, each node is connected to the one
above node and the one below node.
 All
the messages pass around the ring and each transmitted
node will see part of the message.
 In
order to transmit, a node must possess a token.
 At
any time, only one node can have a token.
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Client
Client
Client
Server
Client
Client
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 Collision
occurs when two or more nodes transmit at the
same time.
 Collision
can make all the communication in the network to
stop.
 There
are two methods of collision control
Collision Avoidance.
Collision Detection.
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 In
a star topology, all the end nodes are connected to a
central node. So, before communicating, the end nodes must
get the attention of the central node – polling.
Central node will poll/ query all the end nodes to check if some end
node is ready to transmit or the central node is ready to receive any
message from the end nodes.
The end nodes will poll/ query the central node to signal that they are
ready to transmit, and will wait till the central node is ready.
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 Only
one node in the ring topology will have the token, only
that node will have the permission to send the messages.
 Once
the node is finished with sending the message, it will
release the token for the other nodes to use.
 In
the ring topology, messages are passed from one node to
the next until the messages reaches the destination.
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 Collision
detection – react to the collisions, instead of
avoiding it.
 The
bus topology uses carrier sense multiple access/
collision detection (CSMA/ CD).
 Carrier
sense is the primary way of gaining the access to the
central wire/ bus.
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 The
node willing to transmit will sense the carrier (central
wire). If there are no signals on the carrier, the node will
broadcast the message.
 All
the nodes in the network will get the message, but only
the correct recipient will be able to access the message.
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 To
build a network, certain networking devices are used
Repeater.
Hub.
Switch.
Router.
Gateway.
Bridge.
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 A repeater
is a simple hardware device that receives a weak
signal and regenerates it.
 Since
the repeater creates a new signal, the distortion or
attenuation is removed and the signal is made stronger.
 Repeaters
are used at Layer 1( Physical) of the OSI Model.
 Repeaters
are generally used to extend the coverage of a
network by extending the length of the segment.
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 A hub
is a hardware device that physically connects multiple
cables, providing a common connection point.
 Hubs
are passive devices. They will forward a message to all
the nodes connected via the ports.
 Hubs
will divide the bandwidth among all the nodes.
 Hubs
are used at Layer 1( Physical) of the OSI Model.
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 A switch
is a special type of hub.
 A switch
is an active device.
 Switch
operates at the second layer (DLL) of OSI model.
 A switch
will forward the packets only the correct destination.
 A switch
will not divide the bandwidth, thus the transmission
speed is higher.
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 A bridge
is software or a hardware device that connects two
LAN’s or two segments of the same LAN.
 Bridge
 Two
is a layer 2 (DLL) device.
LAN’s or the two segments of the same LAN must use
the same data link protocol.
Example (Ethernet, Token, Ring)
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 Transparent
Bridge: Connects two LAN’s that use the same data
link protocol.
Ethernet network– Ethernet network.
Token ring network – Token ring network.
 Translating
Bridge: Connects two LAN’s that use different data link
protocol.
Ethernet network– Token ring network.
Token ring network – Ethernet network.
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 Routers
are hardware devices used to forward the data
packets between different networks.
 Routers
intelligent devices, they have routing protocols and
store the path information in the routing tables.
 Routers
operate at the third layer (Network) of OSI model.
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 Routers
can be static or dynamic.
Static – the routing table cannot be changes.
Dynamic – the routing table can change depending on the situation to
find the next best route.
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 A gateway
is a node on a network that serves as an entrance
to another network.
 Gateway
is a device that uses software to connect networks
with different architecture by performing protocol conversion
at the application level.
 Gateway
operates at all the 7 layers of the OSI Model.
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Network Device
OSI Layer
Repeater
Layer 1 – Physical Layer
Hub
Layer 1 – Physical Layer
Switch
Layer 2 – Data Link Layer
Bridge
Layer 2 – Data Link Layer
Router
Layer 3 – Network Layer
Gateway
All 7 Layers
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Going up from
switches – Routers –
Gateways, the
capabilities,
complexities and the
cost increases.
Gateways
Routers
Switches
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