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Hello so, we will continue our discussion on Computer Networks and Internet Protocol.So, today will be discussing on in this lecture Protocol Stack or a overview of theprotocol stack OSI and TCP/IP; this two protocol stack. Though we’ll be primarilyfollowing the TCP/IP, but just we’ll have a overview of the OSI. So before going intothis protocol stack, that overview of the protocol stacks, what we’ll try to look at, that aquick, we’ll look at a quick, quickly look at the history of this Internet or internetworking;how it evolved over years type of things right.(Refer Slide Time: 01:02)So, if you go to there are two interesting site one is a in a YouTube and also in anothersite where you get lot of history information, but if we try to correlate from differentsources, if you see if you see that the history how this Internet came into picture.(Refer Slide Time: 01:11)So, we start from 1836 when the telegraph, first telegraph message was sent and it hasbeen said that Morse Code, a series of dots and dashes which were used forcommunication and somewhat we find analogy with our today’s binary 0 and 1. Thenbetween somewhere between 58 and 1858 and 66 so, transatlantic there is a part of transatlanticcable.And if you see today also this huge sub submarine cables primarily forms the majorbackbone of the data communication part. And in then came telephone lines whichrevolutionized our way of connecting things and if you see that our earlier networkconnection, these days also there are connections which piggyback on this primarily usethis telephone line as a physical layer. And then gradually somewhere in mid 1950’s or1950 around so, U.S. formed that Advanced Research Project Agency or ARPA. So, thisis one of the major state under Department of Defense which was there and there was a,there was a parallel if means that is not on the network phone, but at the around that timeUSSR launched Sputnik. So, some sort of a, there are there are reports that there is asome counter or some parallel efforts was there.Now in 1962 this ARPANET was formed which primary aimed at finding a networkwhich will allow some sort of a resilient and reliable connectivity during very extremesituations right. So, there is the major thing.(Refer Slide Time: 03:18)And we see that in around 60’s early 60’s the packet switching network developed. So,we will discuss about circuit switching and packet switching in our subsequent lectures.So, it was developed where data is split into small packets which may take differentroutes to the destination. So, the it will follow different routes to the destination, but datais small packets and that the union of all these packets are primarily at the destination orintermediate things, intermediate devices or product also will to continue.In 69 ARPANET commissioned by DoD for research, primarily what does researchnetwork where four major US university came into picture, like University of Californiaat Los Angeles like UCLA that is Stanford Research Institute and then UCSB andUniversity of Utah. So, this is the major four things came into play and it what we see it,it gets a open research motivation other things right. So, long it is under the departmentof defense, it is more of a what we say secured type of things, but here its gets a moreuniversity flavor where the number of research efforts were came into play right. Andthen what we see in 71 that first email program was transmitted, it seems that the firstprogram was the first row of the alphabet in the typical QWERTY keyboard and with 15nodes or with 35, 23 hosts on ARPANET.Then in 73 global networking became some sort of reality connecting in England andNorway. So, it is some sort of across country or across continent.In 74 this packets become more mode of switching that there is evolution of transmissioncontrol protocol and other things came into play right.(Refer Slide Time: 05:38)And 77, what we see that number of email hosts become email is really reality, therewere host where 100 plus host were communicating and there was a steep increase afterthat on overall efforts, 79 news groups were formed, 82 TCP/IP protocol was proposedfor ARPANET. Then there is a major development in 83 when name servers aredeveloped like it is it was becoming difficult to remember the IP in numbers and etcetera,so name servers developed. In 84 DNS came into play; number of host crosses 1000, by87 it crossed 30000.(Refer Slide Time: 06:27)Then we see gradual increase - 89, primary this, our omnipresent dub dub dub or“WWW” concept was coined by Tim Berners-Lee. So, in 90 what we see in first searchengine what was proposed and number of host was 3 lakh plus, around 1,000newsgroups and at the same time ARPANET was cease to exist officially or it where itwent to a distributed development mode and there is no practically that what we sayexistence of ARPANET was not there. In 91 developed user-friendly interface forInternet primarily Gopher, some of you might have heard about it released by wasreleased, and text-based, menu-driven interface axis of Internet resources was possiblethrough Gopher.Then 92 was a more multimedia came into much into play and so called quote on quote“Surfing the net” was term was coined. 93 onwards truly this WWW revolution begins.Number of host cross millions and Mosaic web browser are launched right. So, thenonwards what we have seen as a phenomenal growth with different type of applications,different type of content and so and so forth.(Refer Slide Time: 08:01)(Refer Slide Time: 08:07)And if we look at some of the things, like if we look at that is web explosion; say 84, 94it was around 3.2 this are from different Internet resources. So, means I do not claim thatall are pretty or authentic to the last bit of the number, but it shows that how things growsin a big way. In 95 it was 6.4 million, 97 - 19.5 to in 2001 it is 110 million hosts over 30million websites and so on and so forth and this expansion continues right. It is aexponential or expansive.(Refer Slide Time: 08:49)Also there are some other things like 94 Hotmail came into picture, W3C was founded in1994. 95 - JAVA source code was released and what we see that there are other stars ICQor ICQ type of application in 96 by Israel and then 1998 Google was founded. So, theseare some of the milestone we shows that that not only that growth of the things, theoverall interest of the human community at large to us the to us, the Internet this internetworking.So, we just try to come back where we started from. So, this is a brief after this very briefhistory that how things are there; what we see now it’s a huge volume of applicationsright or huge huge volume of applications on the net. The some of the applications if yousee they are pretty sensitive on error, some of the applications are pretty sensitive ontime, some needs more data to be handled, some needs more accuracy and type of things,and this application form anything and everything feasible for our from day to day life toscientific application and so and so forth right. Rather what you what we see for thistypically for last one decade or so, with the different service, services or internet bitservices being enabled or whole scenario or information system design is movingtowards is a moves towards a what we say service-oriented architecture, this networkbecame a major thing to be considered. With cloud, high performance computing cominginto play, see this overall backbone network plays important role.This any interruption of the network will make the not only make us difficult tocommunicate, but several industry several industrial processes will come into a standstill.So, it becomes a extremely, it is extremely important to have this network in place.So, as I was mentioning in our earlier lecture earlier lecture, that we like to see that thatwhat are the basic protocols, what are the basic processes, methodology, algorithms atthe behind this overall networking right. That is one of our, that is a our major goal of thethings.Now if we just again recap from our earlier talk like we primarily have protocols stackright, we discussed about this, we’ll again little bit re-look on the whole thing. So, thereis a physical layer, data link layer, network layer, transport layer, application layer, rightand it is not necessarily all devices should manifest all the layers right, that also we haveseen right.So, in other sense the application layer at the top is basically the applications what we areworking with. So, the application layer is the output of the so-called application layer ispiggyback or became a payload of the transport layer. The output of the transport layer orwill become a payload for the network layer and subsequently payload for the data linkand then it is the physical layer and the physical layer takes care about the physicalcommunication between two nodes, right, between the two nodes like. So, it can besomewhere wired, wireless and different type of technologies coming into play. So, thatis, that is the basic bottom line of the things.And if you look that different type of services then, the popular services; so to say HTTP,FTP and SMTP are the very popular services at the application layer, not only that if youlook at our these days several web services, these basically piggyback on this sort ofservices. So, it is above application layer right. So, they use application layer like HTTPprotocol is being used to carry some sets of messages or type of things right.Similarly at the transport level we have TCP, UDP, RTP. Some are connection-oriented,connectionless, real time protocols.Then at the network layer we have different protocols like IPv4, IPv6, MPLS; these arethe very prominent protocols. Data link layer, Ethernet is one of the major protocol Wi-Fi, Bluetooth, UMTS and LTE and other protocols which are there and a physical layer isbasically the physical connectivity and it goes on the communication system processesand methodology and technologies. There are some of the protocols as we discussed likeDNS, Domain Name System or SNMP for management protocol or ARP and DHCP forsome of the address resolution protocols. So, these are the protocols which are somewhatcross-layer protocol right. They exist between two layers. So, they basically interfacesbetween the two layers right.So, will discuss these things in details in the subsequent lectures or some subsequenttalks, but this is our all-encompassing things. So, we will be mostly hovering around theTCP; primarily looking out at these major protocols and of course, opening of that whatare the other protocols and other things etcetera.(Refer Slide Time: 14:53)Now, if I as we are discussing about protocols; so what is the meaning of protocol right,what do you mean by when it is protocol? It maybe for networking or any other aspectsalso we say that the protocol to be maintained etcetera. So, protocol is a controlledsequence of messages that is exchange between the two or more system to accomplish agiven task right. So, when I say that I do FTP communication, I do a SSHcommunication, I do a HTTP or a DNS system resolution, DHCP, so, I do a control set ofmessages right so, that where between two party or multiparty to accomplish given taskright; so, some maybe downloading some documents or some maybe resolving somenetwork configuration IP address and so and so forth.Protocols specifications define this sequence together with the format or layout of themessage that are exchanged right. So, the one is that protocol is a set of messages to beexchanged and there is a protocol specification that the what message, what is thespecification, how many, what is the size, what are the different fields of the messagethose are precisely defined. So, define this sequence define this sequence together with aformat or layout of the message that are exchanged. So, that the other party on receivingthe message can basically decipher based on the specification of the message. Like I sayif I send a particular a DHCP packet, the DHCP receiver can basically open the packetand it knows that these are the way it is sequenced. Similarly for any other protocol. So,that that makes this, what we say inter-operate between variety of things like if I say thatI am following so and so protocol, then I am done with the things that other things. So, Isay I am following IEEE so and so protocol and then the other end basically onlyunderstand the specification no need of any understanding separately knowing that whatis the format etcetera that is that that the that exactly tries to do.So, this so, whole any this sort of distributed, loosely-coupled and autonomous systemsor autonomous systems and services when they communicate, this protocols played aprimary, a very important role.So, in this, basically in this course we try to look at, look whole thing in terms ofdifferent inter-networking protocol which makes it possible to communicate between anytwo devices over the network.
Protocol Stacks- Part 2
Now, one of the very measure effort was made to define the protocols in a bigger, in amore specific way, that is the what we say OSI model of model layers of the networking.Unlike our TCP/IP things were which is a five-layer stack in some cases; there are theyconsidered as a full layer stack will come to that, but nevertheless it is a five-layer stack,OSI is typically seven layer stack right.So, it is it has physical, data link, network, transport, session and presentation additionalthings what we see here and the application. In the TCP/IP also this things are there, butthey are merged with the other layers right.So, physical is primarily as we were discussing, transmission of binary data on a over amedia right; so, this is a thing. So, when I get say digital or binary data which is carriedover the media.Data link is a transfer of units of information, framing and error checking. So, this is thedata link layer consideration, primarily one of the functions which it does.Network layer primarily involved for delivery of packets of information which includesrouting right, rather what will see that network layer it is what we say it is not a reliablelayer. So, it’s a, it delivers packet in a unreliable way means that reliability is notguaranteed.Whereas transport is a provision of end-to-end reliable and unreliable delivery both right.So, though transport layer sits over network layer, it has the protocols supports to for afor giving a provision for end-to-end reliable service or in case of unreliable servicesright.Session establishes and maintains a session, so this is a session layer which establishesand maintenance session.Presentation is data formatting and encryption if any, so that it takes care.Application is network applications are just file transfer, terminal emulation and so andso fort, so all type of application at the application layer. So, these are the primarily thisseven OSI, Open System Interconnection model for networking which takes care ofevery part of the things.So, every network device will have all or some of this layers right. It is not necessary thatall will be enabled like as you are talking that (Refer Time: 20:40) a layer 2 switch is upto, enabled up to layer 2, a layer 3 switch is up to layer 3 and so and so forth, so thatmeans, it is it is it can have one or more layers or all the layers in some cases. So thatmeans, it allows it to the things.As we are discussing, just discussing that packet of the application is piggyback isbecome a payload to the presentation which in terms become a payload to the sessionand so and so forth. Finally, carried over the physical layer to the other end.(Refer Slide Time: 21:12)So, TCP/IP on the other end is one of the very prominent protocol which is being startedlong back and being used or being followed in different, in different type of networkenabled devices. So, it’s a suite of - it’s a suite of protocols that become the dominantstandard for inter-networking right. TCP/IP presents a set of public standards that specifyhow packets of information are exchanged between the computer of one or morenetworks right. It is not only confining the one network, it can be between any twosystem in between any two network.(Refer Slide Time: 21:57)So, if we try to compare these TCP/IP, so somewhere we try to match like this, likephysical, data link, networking etcetera whereas, transport of the TCP/IP takes a little bitof the part of the session and the transport where as the application takes carepresentation and the application and maybe little bit of the session layer. So, this is it is itis not like that something is left out or something new is there, but TCP/IP is somewherein between.
IEEE 802.3 standard or X.25 token ring framerelay and different sort of protocols.In networking, with TCP/IP the networking is over IP. So, it can be IPv4 or these daysIPv6 transport TCP, UDP, ICMP and this sort of protocol whereas application has a bigbunch of protocols right, it can be variety of protocols. There are issues of which areintermediate protocols where which are between the different cross layer protocolsetcetera, but that is some view so of this TCP/IP stack.(Refer Slide Time: 23:51)Similarly, if you try to look at some other way of looking at it like this is other way of asmentioning that some places it is considered as a four layer stack instead of data link andphysical TCP/IP considered as single layer stack.(Refer Slide Time: 24:08)So, as we are mentioning that use at data at the top is becomes a payload for this nextlayer right and with the application header etc it is it becomes a application data which isa payload for the next layer, which becomes a payload for the which in turn the wholething become a payload for the next layer and so and so forth. Like at the physical layer,physical level, this whole data is transmitted through the underlying physical channelright.So, we will try to see that different protocol structure and what it sizes, including itspayload wherever this it is applicable right in this particular lecture.So, why different type of things what we are looking at because in different booksdifferent Internet resources you will say that different representation. So, I thought that Iwill try to get will put some of the things; so, that we should not get much confused withthe things.(Refer Slide Time: 25:14)Now let us see, consider a typical local area network right. What are will be the typicalcomponent? There are clients, there are servers right. So, client - servers are serving forsome application or something, like there is a FTP server, FTP client; HTTP server orsometimes we say HTTP daemon and HTTP client, like what we use on the browser atmy end is HTTP server, if I accessing “iitkgp ac dot in”, so, it is a HTTP server is therefrom, I am a HTTP client, my browser is HTTP client.And if you look at the network devices, there are several devices repeaters, hubs,transceivers, NICs, bridge, switches, routers; these are the different type of devices wehave to see, which are at different layers like repeaters and hubs primarily at the layer 1whereas, whereas NIC, bridges, layer 2 switches are layer 2 and routers and so forth.(Refer Slide Time: 26:13)So, if I and there are, there is a concept of Local Area Network, Wide Area Network welike to see look at it. So, a WAN is a data communication networking covering a largegeographic span. Unlike LAN, a WAN connection is generally rented from a serviceprovider, so when you go for a WAN connection, it is from the service provider. WANsconnects various sites at different geographic locations so that information can beexchanged.So, what? So, there is a concept of WAN and LAN primarily that way of handling will bedifferent, but nevertheless the devices, etcetera or the way the protocols works remainssame.(Refer Slide Time: 26:50)(Refer Slide Time: 26:58)Now, if we see that so it is a layer 1, layer 2, layer 3 and type of devices. So, let us seethat what so, NIC typically the network interface card which what we are having in ourall systems laptop, PC etcetera are basically having as a layer 2 device. So, it is havingMAC address or sometimes call hardware address which is with that interface card right.So, it is a unique address, so called unique address which is given by the, from the (ReferTime: 27:27) OEM or the manufacturer right. There you may argue there are way tospoof etcetera that we are not going to those business, but we consider that MAC addressis a unique address given by the hardware address given by the things, we’ll come tothose things.(Refer Slide Time: 27:41)So, if I have two computers with NIC cards, the first LAN how to connect? Just connectto end of either cable; only thing that should be a crossover cable; that means, thetransmitter or TX of one should go to the RX and RX of the other should go to that TX.So, it is a crossover cable or what sometimes what we say cross cables right.(Refer Slide Time: 28:06)(Refer Slide Time: 28:13)So, if it is typically can connect 100 meters things at a that maximum things it maybelittle less than that and if I have to go more than that, I require a some repeater or whichamplifies the signal right.And if the business expands and I have cascade of things right; so, one repeater, anotherhub, again hub and go on expanding. So, what it happened that the problem is, that thehubs share bandwidth between all attached devices like typically if it’s a, if it is a say, 10Mbps hub with 8 ports. So, effective bandwidth is 10/8 right. So, it is what we say thatworst case scenario will come like that. So, hubs are layer 1 devices, cannot filter traffic.Most LANs use broadcast topology. So, every device sees everyone and is like if there isa communication is there, so it is everywhere the things are there. So, there are lot ofcollisions and there are lot of things. Though only 1 is sending to 2 only 2 shouldexpand, but all will getting the collision things.(Refer Slide Time: 29:36)So, the solution is whether we can have a smarter hub or bridge. So, bridge filter trafficbased on the MAC address; that means, as every NIC have a unique MAC address orevery system has a unique MAC address, so, they filter traffic based on the MACaddress. So, how it looks like?(Refer Slide Time: 29:52)(Refer Slide Time: 29:53)(Refer Slide Time: 29:56)(Refer Slide Time: 30:01)(Refer Slide Time: 30:03)So, if I send a instead that bridges, then the traffic are localized right, so localized. So, itthe traffic will not cross these things so that the other parts are bandwidth are not wasted.So, if it is, if there is a multi-port bridge, we primary we say that is a switch or moreprecisely is a layer 2 switch. So, there can be layer 2 switch where it connects etcetera itcan have a connection to the cloud. In this case the cloud is Internet cloud what we meanand that is a I can have we can have this sort of connectivity with the cloud right.(Refer Slide Time: 30:20)(Refer Slide Time: 30:35)So, and then comes the router. If the two networks are different, router filter traffic basedon IP address. The IP address tells the router which LAN segment and segment can pingthe ping belong, in other sense where you can have the things. So, this two networks aredifferent networks. So, one is machine 1 is one network, the machine 2 is in othernetwork this router finds the path from this to this. So, in other sense it is not only filters,the collision it not only divides the collision domain, it also divide the broadcast domainsso, that it is it is only allowed filter the traffic those traffics to the other things.(Refer Slide Time: 31:20)So, what we look at it? So, there are devices at different level. Typically routers are layer3, these are layer 2 switches, there are layer 1 devices and also each device works itslayer, but all the things - where router has the property of data link and also physical.(Refer Slide Time: 31:31)So, any higher layer as all the properties of the lower layer thing so, if you have a routerit as all the other properties. So that means, it can basically do data link layer filteringalso can communicate and all those things right. So, as that layer 3 device but also usesMAC layer and so and so forth right.(Refer Slide Time: 31:51)(Refer Slide Time: 32:01)So, and typically when we’ll come to those things later on it is a what we look at thehierarchical design of network where we have a, that core at the things, then distributionthen the access right. So, the core is very fast, then the distribution is more of policy andthe access is the end mile type of solution.(Refer Slide Time: 32:07)Let us say quickly few points and before we conclude. So, routers by default breaks upbroadcast domain. Broadcast domain set of all devices on a network segment that hear allthe broadcasts send to the segment. Breaking up the network broadcast is importantbecause when the host and the servers sends network broadcast every device on the mustread and process that broadcast right. It may reject or accept based on whether is meantfor that. When a router interface receive the broadcast, it discards the broadcast withoutforwarding to the network, routers also breaks up collision domain right.(Refer Slide Time: 32:59)Switches are not used to create inter-networking so, that is for router. They are employedto add functionality to the Internet LAN. So, switches breaks up collision domain. Itswitches frame from one part to the other part in a switch network so to say that is whythe switch.So, again collision domain in Internet term used to described a network scenario inwhich one particular device sends a packet to the network segment, forcing other devicesin the same segment to pay attention to it. At the same time with different device therewill be collision, loss of data and re-transmission and loss of bandwidth (Refer Time:33:36) It typically found in layer one or hub. So, each and every port on a switch is owncollision domain collision domain and hub represent one collision domain and so forth.So, what we try to say that this different layer of the things has different level offunctionalities right. One is basically that different like at the physical layer is more ofthe physical transmission of the things, whereas data link layer takes care of the filteringat the MAC layer level. And also communicate between so that it is filtered and thecollision domain are divided; routers typically layer 3 device connects to, to devices onthe network; more precisely if we see that it helps in inter-networking.If we go to the transport it connects two processes into machines in the internetwork. So,that is process to process communication is feasible by this transport and the applicationswhat we are interested in what the end user is interested in where the end user basicallyuse this different applications like what we use in inter-networking and type of thingsand also we have seen that every layer processes and piggyback - make its payload andfrom the things.So, let us conclude here. We will continue our discussion on the things as we mentionedthat will go on a top-down approach so will go from application to transport and so andso forth okay. So, we will let us stop here.Thank you.
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