2. Recap
In the previous class, you have learnt about
– Ethernet frame format
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3. Objectives
On completion of this period, you would be able
to know about
• Network Hub
• Network Switch
• Store and Forward switch
• Cut through switch
• Adaptive switching mechanism
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4. Network Hub
• Hubs, switches, and routers are all devices used to connect one
or more computers to other computers, networked devices, or to
other networks
• Each has two or more sockets called ports into which one can
plug in the cables to make the connection
• A hub is typically the least expensive, least intelligent, and least
complicated of the three
• Hub takes the signal from one port and sends out to the other
ports after due amplification and pulse shaping
• Hub is a physical layer device
• Hub is a multi-port repeater
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6. Network Switch
• A switch does essentially what a hub does but more efficiently
• Switch also performs amplification, pulse reshaping functions
like hub
• Switch learns about the configuration of the network
• By observing the traffic, it learns which physical address
computer is to which port
• From the observation it prepares a forward table
• When it receives a packet from a port, it reads the MAC address
from the frame header and looks into forward table. Then
forwards the packet only to the port to which the machine with the
destination MAC address is attached
• Therefore Switch works both on physical layer and MAC layer
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10. Store and Forward Switch
• A switch performing store-and-forward will wait to
forward a frame until it has received the entire frame
• Store-and-forward is most often used in environments
supporting reliable physical or data link protocols
• A received frame is often checked for errors before being
forwarded
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11. Store and Forward Switch Contd..
• This type of switch is inherently slower in environments
where upper layer protocols already provide reliable
services
• The tip off that you are dealing with a store and forward
style switch is whether the switch has buffers
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12. Cut Through Switch
• Cut-through switches begin forwarding the frame as
soon as the switch has read the destination address
• A cut through switch will forward the data before it has
completed receiving the frame
• These switches will function at wire speed, forwarding
traffic as fast as it receives it
• Nearly all cut-through switches have no RAM buffers for
storing frames
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13. Adaptive Switch
• Adaptive switch is an advanced switching architecture
• It provides the communications infrastructure with
unprecedented high availability, scalability
• It enables Peripheral Component Interconnect (PCI)-based
telecommunications, data communications and embedded
systems to incorporate 224 PCI bus segments
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14. Summary
In this class, you have learnt about
• Hub is a physical layer device
• Switch is a layer-2 device
• Store and Forward switch stores the entire frame in a buffer
then it reads the header then forwards the frame to the
concerned port
• Cut through switch waits until it receives the frame header,
then it forwards the frame to the concerned port without
actually waiting for the arrival of the complete frame
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15. Quiz
1. Hub is a _________ device
Ans: Physical layer
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16. Quiz
2. Switch works on _________ and
____________layers
Ans : Physical and MAC
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17. Frequently Asked Questions
1. What are the differences between hub and switch?
2. What are the differences between switch and router?
3. What are the differences between store and forward switch and cut
through switch?
4. Explain Store and forward cut through switch mechanism
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