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8/7/2019 Computer Networks UNIT-10
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C o n f i d e n t i a l
Course : BCA
Semester : IV
Subject Code : BC 0048
Subject Name : Computer Networks
Unit number : 10
Unit Title : Networking Devices
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C o n f i d e n t i a l
Unit-10 Networking Devices
Networking Devices
Objectives
After going through the presentation, you should be able to:
Describe Repeaters and Hubs
Discuss switches, switching methods
Discuss Bridges, types of bridges
Describe Routers, Gateways, modems proxy server, brouter and
WAPs
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C o n f i d e n t i a l
Unit-10 Networking Devices
Lecture outline
Introduction
Repeaters
Hubs
Switches
Bridges
Routers
Gateways
Other Devices
Summary
Networking Devices
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C o n f i d e n t i a l
Unit-10 Networking Devices
Introduction
To connects LANs, or segments of LANs, we make use of connecting
devices.
Connecting devices are therefore also referred to as networking
devices. They can operate at different layers of the OSI or TCP/IP
reference model.
Internetworking refers to the equipment and technologies involved in
connecting either LANs to LANs, WANs to WANs, or LANs to WANs.
Typical examples of internetworking devices are repeaters, Hubs,
Switches, bridges, routers, and gateways.
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Unit-10 Networking Devices
Repeaters
What is repeater ?
A Repeater is a device that has just two ports. It operates at layer 1 that
is physical layer of the OSI model and TCP/IP model. It simply acts as
transceivers that receives, amplifies, and retransmits information.
A repeater receives a signal and before it becomes too weak or
corrupted, it regenerates the original bit pattern. The repeater then sends
the refreshed signal.
Repeaters are analog devices that connect two cable segments.
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Unit-10 Networking Devices
Inter-connecting two Token Ring networks with a Repeater :
Repeaters may introduce side effects where they add cost to the circuit.
Also they introduce distortion as a result of limited bandwidth, additional
noise and also sometimes they may amplify some other undesirable
noise to the signal.
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Repeaters
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Unit-10 Networking Devices
Uses of Repeaters :
Repeaters are used to either extend a LAN beyond its usual distance
limitation, or to provide electrical isolation, or to accomplish media
conversion.
A Repeater connects segments of a LAN.
A repeater forwards every frame and it has no filtering capability. And
It is a regenerator, and not an amplifier
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Unit-10 Networking Devices
Hubs
What is Hub ?It is a thin wire segment with fixed taps. Each tap is provided with
reliable connector (RJ45) as shown in figure. Hubs are the simplest
network devices, and their simplicity is reflected in their low cost.
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Unit-10 Networking Devices
What is Hub ? ( continued..)
The basic function of a hub is to take data from one of the connected
devices and forward it to all the other ports on the hub. This method of
operation is very inefficient because, in most cases, the data is intended
for only one of the connected devices.
The salient features of Hubs are listed below:
Frames arriving on any of the lines are transmitted on the others.
All lines coming into a Hub must operate at a same speed.
Hubs do not amplify the incoming signal.
Hubs do not understand frames, packets or headers.
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Hubs
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Unit-10 Networking Devices
Classification of Hubs :
Passive hubs: These hubs do not need power because they don't
regenerate the signal.
Active hubs: Regenerate a signal before forwarding it to all the ports on
the device.
Stackable Hubs :It improves the network reliability and manageability.
It also gives a scalable and modular approach.
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Unit-10 Networking Devices
Classification of Hubs : ( continued..)
USB Hub : A USB hub serves as a medium for connecting peripheral
devices to a computer in accordance with a USB standard. A hub typically
includes an upstream port that couples the hub to the host, and several
downstream ports that couple the hub to another hub or peripheral.
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Unit-10 Networking Devices
Switches
What is a switch ?
A switch is like a hub in that it has multiple ports, but internally it has a
table listing which systems are found on each port, and shuttles the
packets where they need to go. Unlike a hub, signals are transmitted
only to the port where they need to go, rather than to all ports.
Some switches and bridges can be used to connect networks that use
different physical protocols, for instance connecting Ethernet with TokenRing. The name for this is a µtranslating¶ bridge or switch.
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Unit-10 Networking Devices
Switches are fast multi-port bridges that provide an economical way to
resolve network congestion.
On the surface, a switch looks much like a hub. Switches can do much
more and offer many more advantages than hubs.
Rather than forwarding data to all the connected ports, a switch forwards
data only to the port on which the destination system is connected.
Switches have two major weaknesses. Under heavy load conditions,
some switches may drop packets, and they lack the ability to filter out or
block unwanted or unauthorized traffic.
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Unit-10 Networking Devices
Switching Methods :
Switches use three methods to deal with data as it arrives:
Cut-through: In a cut-through configuration, the switch begins to
forward the packet as soon as it is received. No error checking is
performed on the packet, so the packet is moved through very quickly.
Store-and-forward: In a store-and-forward configuration, the switch
waits to receive the entire packet before beginning to forward it. It also
performs basic error checking.
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Unit-10 Networking Devices
Switching Methods : ( continued..)
Fragment-free : Building on the speed advantages of cut-through
switching, fragment-free switching works by reading only the part of the
packet that enables it to identify fragments of a transmission.
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Unit-10 Networking Devices
Bridges
Bridges are intelligent devices that operate at layer 2 and are used to
interconnect LANs of the same type.
Packets received on one port may be retransmitted or forwarded on
another port.
A bridge unlike repeaters will not start retransmission until it has
received the complete packet. As a consequence, stations on either side
of a bridge may be transmitting simultaneously without causing
collisions.
Unlike repeaters, bridges may provide filtering and forwarding services
across the link.
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Unit-10 Networking Devices
Bridge interconnects two Token Ring LANs :
Bridges are networking devices that divide up networks. A bridge
functions by blocking or forwarding data, based on the destination MAC
address written into each frame of data.
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Unit-10 Networking Devices
Types of Bridges :
Three types of bridges are used in networks.
1. Transparent bridge:
A transparent bridge is invisible to the other devices on the network.
Transparent bridges only perform the function of blocking or
forwarding data based on the MAC address.
Transparent bridges are the most popular types of bridges.
2. Translational bridge :
A translational bridge can convert from one networking system to
another. Translational bridges are useful for connecting two different
networks, such as Ethernet and Token Ring networks.
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Unit-10 Networking Devices
Types of Bridges : (continued..)
3. Source-route bridge:
Source-route bridges were designed by IBM for use on Token Ring
networks.
The source-route bridge derives its name from the fact that the entire
route of the frame is embedded within the frame.
This allows the bridge to make specific decisions about how the frame
should be forwarded through the network.
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Unit-10 Networking Devices
Routers
What is Router ?
A router is an intelligent packet sorter, which can look at the ultimate
destination for a packet and analyze the best way to get it there.
A router is often a full - fledged computer system with multiple
network cards and its own operating system.
Routers operate on Layer 3, the network layer that routes data o
different networks.
Router performance is measured using its packet- forwarding rate,
which is the number of packets transferred per second from input to
output port. This rate depends on packet size, and how many protocols
are being supported.
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Unit-10 Networking Devices
Routers
What is Router ? ( continued..)
Unlike bridges and switches, which use the hardware-configured MACaddress to determine the destination of the data, routers use the
software-configured network address to make decisions.
This approach makes routers more functional than bridges or switches,and it also makes them more complex because they have to work harderto determine the information.
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Unit-10 Networking Devices
Routers
Advantages of dedicated hardware routers :
Typically faster than server-based routers
Generally more reliable than server-based routers
Easier to harden against attacks than server-based routing solutions
Disadvantages of dedicated hardware routers :
More expensive than server-based router solutions; extra
functionality may have to be purchased
Often require specialized skills and knowledge to manage them
Limited to a small range of possible uses
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Unit-10 Networking Devices
Routers
Drawbacks of Routers :
They are complex and difficult to install, configure, and manage.
They have a lower packet ± filtering ± and ±forwarding rate ascompared to switches.
They are protocol dependent, and maybe unable to handle someprotocols with out network reconfiguration.
Furthermore, some protocols are not routable.
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Unit-10 Networking Devices
Gateways
Gateways :
A gateway is a network point that acts as an entrance to another
network.
In earlier days a gateway were referred to what we now call a router, and
in fact the gateway and router functions are often combined in the samedevice. Depending on the situation though, a gateway could be a switch
or bridge rather than a router.
Gateways are most commonly used to transfer data between private
networks and the Internet.
A gateway acts as the interface between proximity local area protocols
and wide area protocols. The Internet gateway transfers the packets to
the Internet where Internet routers forward the packets based on the
Internet address.
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Unit-10 Networking Devices
Other Devices
Modem:
Modem is a contraction of the terms modulator and demodulator.
Modems perform a simple function: They translate digital signals from a
computer into analog signals that can travel across conventional phone
lines.
The modem modulates the signal at the sending end and demodulates at
the receiving end.
Proxy Server :
This is a system that sits in between a workstation and the server that
workstation is accessing. The proxy server can also be used to control
Internet access, which is a major issue at some companies.
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Unit-10 Networking Devices
Other Devices
Wireless router :
Wireless routers allow portable electronics to share information and
resources via wireless communications. A router uses a routing protocol
to exchange information with other routers in order to maintain a
consistent view of the network. The routers distinguish data packetsaccording to network protocols and forwards traffic according to network-
level addresses.
Brouter :
Brouter combines the function of a router and a bridge. Local packets can
be routed from one side of the network to the other based on the
destination address, even if they do not conform to any routing protocols.
Packets with the appropriate protocols can be sent on their way to the
outside world.
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Unit-10 Networking Devices
Other Devices
Wireless Access Point (WAPs) :
Wireless network devices gain access to the network via WAPs.
WAPs are typically deployed as part of a larger network infrastructure,
but in some environments, such as small businesses or home offices,
they can operate completely independently of a normal network.
When a WAP connects to a wired network, it is often referred to as a
wired access point because it joins the wireless portion of the network
with the wired portion.
WAPs are fairly innocuous, hub-like devices; the only giveaway to their
function is the antennae that protrude from the box.
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Unit-10 Networking Devices
Summary
To connects LANs, or segments of LANs, we make use of connecting
devices.
Connecting devices are therefore also referred to as networking
devices.
They can operate at different layers of the OSI or TCP/IP reference
model.
Hubs and switches provide a mechanism to connect devices to a
network that is created with twisted-pair cabling.
Switches offer a speed advantage over hubs because they can use
full-duplex communications. Bridges allow network traffic to be confined to certain network
segments, thereby reducing the amount of network traffic.
Routers are devices that connect networks and thereby create
internetworks.
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Unit-10 Networking Devices
A gateway is a device that translates from one data format to
another; it can be a hardware device or a software application.
A modem translates a signal from digital to analog so that it can be
transmitted across a conventional phone line.
WAPs are a relative newcomer to the networking equipment field.
Wireless network clients use WAPs to connect to the network.
Summary
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