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hello everyone welcome back to the
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computer networks course and we are in
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part two of network protocols and
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communication in part one we have seen
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data communication data flow such as
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simplex half-duplex and full-duplex in
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part one we have also seen about
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protocols and the elements of protocol
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in today's session we will deal more on
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protocols and the importance of protocol
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in computer networks we will also
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understand what is peer-to-peer network
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and client-server network we will now
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have a small recap show on protocol
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whatever the communication pattern is if
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we want effective and good communication
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this cannot happen without protocols it
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is a set of rules that governs data
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communication any data communication
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must be governed by some set of rules
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and we call these rules as protocol
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simply protocol is a rule because these
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protocol determines what is communicated
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in the network how it is communicated in
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the network and when it is communicated
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in the previous lecture we have seen
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there are five elements of a protocol
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let us just recap sure all the five
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elements a protocol deals with message
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encoding message formatting and
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encapsulation message timing message
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size and message delivery options now we
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will see what is message encoding let
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Tom be the user now Tom wants something
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from amazon.com
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he opens the browser and gives the
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request to amazon.com and amazon.com
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responds back with what tom is needed if
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we observe this computer that is Tom's
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computer is connected with a wired
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medium the transmission medium here is
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wired medium this transmission medium is
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also called as a link this computer
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converts the data into signals and sends
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the signal on the transmission medium
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which is the cable here in case if Tom
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wants to access same amazon.com but not
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with a computer now with a smart phone
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now this smart phone is connected to the
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network with the help of a wireless
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medium and Tom's device that is this
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Mart phone converts the data into waves
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because the medium is Wireless in both
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the cases whether it is a wired medium
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or a wireless
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protocols converts the data into signals
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or waves by appropriately identifying
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the device to which it is connected to
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in this case
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Tom's mobile phone that is the
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smartphone converts the data into waves
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and after this data is received by this
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router and it has to forward this to
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router one or router two now this router
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is connected to router one as well as
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router two with the help of a wild
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medium the protocol in this router
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converts these waves into signals this
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is what the very important part of a
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protocol we will now see what is message
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formatting and encapsulation both the
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sender and the receiver must mutually
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agree upon common format so that the
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communication becomes understandable at
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the same time some encapsulation is also
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done with data that it is going to send
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this is going to add few more
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information with the data that is the
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source information and the destination
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information to be precise the IP address
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are added to the data which is going to
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be sent don't worry about this IP
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address now we have a separate lecture
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on IP address for time being now take
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like this every human is identified by
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his name likewise every computer in the
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network or every device in the network
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is identified by its IP address suppose
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if this computer wants to send some data
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with data it is going to encapsulate the
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source IP address and the destination IP
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address this source IP address and
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destination IP address are obviously
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going to be forwarded through any
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intermediary devices when any device
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receives that packet or data it knows
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from where the data is coming and what
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is the destination in order to forward
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the data to the destination it needs
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source information and the destination
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information this is message formatting
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and encapsulation so far we have seen
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message encoding message formatting and
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encapsulation now we will see why
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message timing is to be handled by a
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protocol if the sender is very fast and
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the receiver is a slow receiver and
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obviously receiver cannot handle the
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flow so there are chances for the data
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to get lost
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to avoid this loss due to high speed
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sending
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flow control has to be ensured by the
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protocol that is in what spiel the
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sender have to send that information is
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given to the sender this information
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will be provided to the sender by the
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receiver
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it means if this guy can handle ten data
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packets at a time so that information
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will be sent to the sender so this
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sender will start sending ten packets at
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a time this is very important and this
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is what we call as flow control and
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protocols are going to do this flow
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control at the same time after sending
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the data the sender will wait for a
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certain period of time because the time
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it is waiting in order to receive an
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acknowledgment this acknowledgment is
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really necessary in the network because
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the sender have to ensure that the data
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is received by the destination if the
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acknowledgment is not received on time
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the sender understands that there are
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some loss and it starts retransmitting
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that packet or data again so that there
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is no loss by the receiver so this flow
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control and the acknowledgment timing
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are maintained by protocols in the form
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of message timing the next element of
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the protocol is message size let's see
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an example we have a very big box to be
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transported from one building to other
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to transport the box we are given with a
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very small vehicle this vehicle can
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handle very small box but not that big
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box what will we do in order to do this
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transportation obviously we will break
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the big box into smaller pieces these
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pieces can be handled by the vehicle and
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each small pieces are transported to the
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other building that is the destination
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but there is a problem here there are
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some chances for the pieces to be missed
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during transportation to find it out we
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use numbering scheme that is when we
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break the big box into small pieces we
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will put numbers on every small box so
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that the destination can reassemble it
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in the right way at the same time this
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numbering will also help to identify if
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any packets or pieces are missing
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likewise if there is a big file but the
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link capacity is small so the protocol
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in this computer breaks this big file
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into smaller segments and each segment
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is numbered sequentially now these
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smaller segments can be trans
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voted over the network and this
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numbering will also help us to identify
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the missing packets after receiving all
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the smaller packets this receiver will
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reassemble all the packets with the help
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of the numbering it identifies if there
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are any missing packets this is what
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exactly the message sizing of a protocol
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and finally the message delivery option
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suppose if this guy wants to send
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exactly to one destination say for
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example this web server then one sender
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and one receiver this is an example for
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unicast communication
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this is unicasting because one sender
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and one receiver and the communication
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can also be multi casting it means in
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this network just see this is one
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network and in this network if this
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computer is sending data packets to
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these three computers alone but not to
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this printer and voice over IP phone
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then this will come under multi casting
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because there is a sender and group of
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receivers or not all receivers this is
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multi casting example FM radio if we
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tune on to that frequency then only we
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will receive that signal otherwise we
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will never receive that broadcasting
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means if this guy is sending some data
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packet and everybody in the network will
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receive that data packet this is what
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broadcasting is one sender all receiver
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is called as broadcasting and now we
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will see what is peer-to-peer network in
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a peer-to-peer network every node is
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called as appear and they are in equal
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level it means there is nobody superior
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and there is nobody inferior the problem
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with this is there is nobody in the
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centralized part to administer the
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communication it means whatever rights
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this guy has the same kind of rights
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this guy will also have and there is no
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centralized administration this is
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suitable for smaller applications but
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not for larger applications and the
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problem with this scenario is this
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peer-to-peer network is it is not
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scalable we have already seen what is
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scalability in our previous lecture
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scalability means new devices can be
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added to the network but this is not a
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scalable network why because if this
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computer has only two ports ports means
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how many devices it can be
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with if this computer has two ports then
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only two device can be connected with
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and that is why we call peer-to-peer
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network is not scalable coming to the
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client server network here we will have
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a centralized administration and this
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server is going to do the centralized
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administration and all the data will be
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here and these are all called slaves and
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this is going to be the master
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in other words these are all going to be
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called as planes and this is going to be
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the server that is why we call this
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scheme as client server network it is
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also called as request response model
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say if this guy wants some data from the
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server it first gives the request and
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after accepting the request this server
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gives the response whatever it is
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requested and obviously this is a
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scalable Network even if 100 devices
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wants to participate in the network it
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can be achieved but the problem means we
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are too dependent on the server when
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everyone starts using the server there
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are chances for the server to get
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overloaded and that's it guys
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now we shall recapture what we have seen
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today we have understood what are
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protocols and the role of protocols in
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computer networks we have seen message
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encoding message formatting and
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encapsulation message size message
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timing and messy delivery options in a
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detailed manner with an example and we
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have also understood what is
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peer-to-peer network and what is
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client-server network I hope you enjoyed
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the lecture thank you very much
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you
