In. Today's lecture would. Be looking at some of the basic. Concepts, and backgrounds, from computer networks which. Would be useful for us in the subsequent discussions. So. Our topic of discussion today's, review. Of network. Technologies. So. Let us start with some very. Basic concepts, of networking well. You know a computer. Network is essentially, a communication. System for connecting, computers. Now. Why we have computer networks you. Need arised. Out. Of a number of requirements. Of course better. Connectivity. Better. Communication. Were the main reasons, this. Also, allows. You to have better, sharing, of resources. Suppose. You have a printer, connected, with one computer in the network the. Others over the network can also have access to the printer and. To. Top it all network. Allows. Us to bring people together it. Helps us in making the world a really small place these. Are some of the advantages that a network offers. Now. Talking of the types of computer networks that we have. Networks. Can be broadly categorized, into either a local, area network or, a LAN and a. Wide, area network orowan, now. Let us try to see the basic differences. Between the two, well. In a LAN. The. Idea is that the computers, that are connected within, a LAN they. Are within a relatively, small. Geographical. Span, well. When we say relatively, small span, they. May be in the same room a laboratory, same. Building, or within. The same campus. In. Contrast, in a wide area network, the. Hosts, may, be widely dispersed, well, it. Can be across buildings across. Cities. Across continents, anything, across countries, anything. So. Hosts, are computers, in a wide area network, be really. Widely dispersed across. Campuses. Across cities. Countries continents now, if. You want to compare, a LAN or a wine, well. But. Well in terms of economics, a, LAN. Is, cheaper, than a one a LAN is cheaper, one. Is expensive, in, terms of performance and, LAN. Is typically, faster, than. A one. There. Are other logistic, differences, also a LAN. Is under. The control of a single, organisation. That means a LAN has a single, ownership. Suppose. In my organization. I set up a LAN I will, be the owner of that land it is my responsibility to. Manage. Upgrade. If necessary, and to. Configure. It in a way I want to, but. In a 1. Then. A wide area network is not under the control of a single person say, suppose. I want to connect to my friend who is there in some other country, I may, have to go through a number of intermediate service. Providers, and, that. May. Actually mean, I am going through several. You. Can say owners. Whose. Means. This equals awareness, or whose networks, I am going, through in, order to reach my final, destination, so. This. Ownership is another big. Difference, between laner one this, is in terms of the logistics. Just. To compare in terms of some figures with.
Respect To performance. Land. You. Can work at speeds from 10 Mbps up, to 10. Gbps. GB. Means 1, Giga. Means 1000, mega now. Miss. As we stand. Today typically, land speeds today range from 100 Mbps, to one gigabit. Per second those are the typical speeds, we have today but. In contrast in a wide area network, speeds, are as low as 64, kbps to, 8. Mbps. Cost. Was also for. A LAN it. Is mostly a one time cost of course there are maintenance charges but. A very. Rough estimate you. May have to pay about one crore for. A hundred knowed state-of-the-art. Land. But. In contrast, in. A one Simmons. If you go for a 4 Mbps link or an 8 Mbps link the, typical, cost will be same. In 7c, of the order of 30 lakhs per, year this. Cost enough to pay. As a as. An. Annual, maintenance. Order, you. Can say it will be a recurring expense, that. Is. Payable per year so in the long run a one will prove to be much, more expensive. Now. Talking. Of the way data. Flows. From one note to the other in a network. Well. One principle. Of data communication is, called circuit switching. The. Basic concept beyond circuit switching is that a, dedicated. Communication. Path, is established or, required between, two stations. The. Path. That. Is established will. Follow a fixed. Sequence, of, intermediate, nodes and links and. On. Each, link, you define, a logical. Channel and. This. Logical, channel gets dedicated, to the connection, well, what does this logical mean I will just explain why shortly with. Respect to this diagram. Suppose. This node a is, the. Source. And this. Node H is the final, destination. Suppose. We, choose to select, this, path through. Which all packets, will flow, through. The. Intermediate nodes a C. D and G so a C D G H, will. Be the path. Now. This. Is a dedicated, path so all the, messages, that. A wants to send to H will will be following. This path but. In terms of the intermediate, link well. These. Intermediate, links, can, be absolutely, dedicated. Like the first generation telephone. Network. Whenever you dial a piece. Of copper would be dedicated for the connection so, there will be intermediate. Stations. The. Exchanges, for some relay switches will be set on and off and a. Continuous, copper wire or a link would be established between the two parties. But. In reality in a computer network, the. Only links. May not be dedicated, maybe we have in between a very fast, or high-speed, link you. Need only a part of the bandwidth of that link so, maybe that link will be shared but, you will be guaranteed. A. Particular. Bandwidth, on that link so for all practical purposes you, are having a dedicated path, for. The for the kind of bandwidth you want okay that, is circuit switching. So. For circuit switching there are three steps that. Need to be followed for communication. First. Is of course you have to establish a connection this is most important, and this. Connection has to be established. Before. Data transmission. Can begin. Following. Connection, establishment, you need the, actual data transfer. Now. Since a, connection. Has been established and. A dedicated, path is there so. Data, transfer, can proceed, at maximum. Speed without. Any other congestion, so, here the, maximal. Speed of transmission. Which, you want that will be guaranteed by, the intermediate nodes and links and. Finally. When you are done we, have to terminate the connection, this.
Has To be done after data transmission, is over, so. Here your you, will be actually deallocating the network resources like links and the bandwidths, that. You had allocated, during. Connection, establishment, okay, these, are the steps. Involved. Drawbacks. Of circuit switching is that the. Channel capacity along. The path gets. Dedicated. Along, the entire. Duration of communication, if. Your communication, goes on for 20 minutes for example then for the entire 20 minutes. The bandwidth will be dedicated, along. The paths you, are establishing, the link. This. May. Be alright, for. Communication. Like. Voice. Because. In a voice. Well continuously. Either you are speaking audio receiving the, line is very, rarely free. But. If you talk about computer. Traffic, it is typically, bursty, in nature. Sometimes. You have lot of traffic but, sometimes there is no traffic so for. This kind of a scenario the. Link will be unutilized. For most parts of the time that, is the drawback and. Secondly. Due to the initial connection setup there. Can be an initial, delay which. For, some, applications, you may not like, or hold or you may not want, these. Are the drawbacks. Of circuit switching. So. To circumvent. These drawbacks we. Actually. Use packet, switching, in modern, day computer, networks. Packet. Switching actually, lays. Its foundation, on, the. Basic technology for long distance data communication, but, today. Packet. Switching is used even in case of, short. Distance communication within, a land within local area network so, such a packet switching has become some kind of a de facto standard in most. Of the networks. So. The. The. Characteristic, feature of packet switching is that the network resources are not, dedicated. A link. Or, the. Bandwidth, on a link can. Be shared. Depending. On the network load. The. Actual performance you, get you, can vary ok. So. The. Basic technology of packet switching has evolved, but, the, underlying. Concept, has remained the same this. Is widely used as I said for long-distance communication, but also for. LAN. Environment, we, use, something.
Like Packet switching in many cases. Now. The essential idea of. Packet-switching, is that when you have a, big. Message, to transmit, the. Message gets, broken, up into, smaller. Chunks or pieces these are called packets and these packets are sent in. Bins one. At a time so. Data, are transmitted, in short packets typically. Few kilobytes. Long. Message is broken up into smaller chunks these, are called packets and, each. Packet, contains a, header, which. Will contain, relevant, information, so that the, packet can reach. The, destination, correctly. So, it will contain information, the. Header in the packet which, will be required for routing. The packet in the proper. Way. So. This diagram shows how a message can be broken up into packets a, message. Gets. Broken, up into three packets and, each. Packet will be having its own. Header. This. Header will allow this packets, to reach. The destination and, to, have the intermediate nodes take the appropriate, decision. To route the packets accordingly. Okay. And. Another. Notable. Feature of packet. Switching is that it is. Based, on so-called. Store-and-forward. Concept. The. Idea is that, say. You, have a node here which wants, to send a data through. Some intermediate, nodes. To. A, final. Destination out here, so. That is that when the first node sends, out a packet. The. Packet has, to be sent, and received. In. Its entirety, by, the next node each. Intermediate, network. Node will, receive, the whole packet. It. Will take a routing, decision, which, route to four because there, can be a number of outgoing links. Which. Outgoing link to follow and finally. It forwards, the packet in the, correct direction. This. Is called store-and-forward because. Each intermediate, node suppose I am an intermediate node well. I will receive the packet in his entirety. And I will store it in a buffer I will. Not try to send, the packet as it has been received I will receive, it fully I will. Check the packet if there are engine transmission errors, there are some checksums, usually. Added to the header then. I will take a decision depending, on the destination address who. Have to followed it next. So. Then I will followed the packet to the next. Node so, store-and-forward. These are the two steps so. Advantages. Of packet. Switching is that since. Links, can be shared so link, utilization, is obviously better this. Is suitable for computer. Generated traffic which I'd mentioned, is bursty. In nature. Since. You are doing packet, buffering, you. Can, perform. Data, rate conversion. Like. I am given example suppose my incoming, link is faster. Than my outgoing link I can, receive packets, at a faster, rate so. I can receive packets and store in a buffer and I, can take my time to send.
Them Over my outgoing link, slowly so. Some data rate conversion, can take place here, and, also. You can have the notion of, packet. Priority, where, the high priority packets will be sent first. They. Will be incurring less delay. Now. Regarding. The mode of the way the packets are transmitted. There. Are two alternate. Approaches. These. Are called virtual circuits, and. Datagram. The. Abstract network model, will be the, same as as shown earlier so, there will be a number of nodes. Abcdefgh. Which, will be connected by links and. The. Main responsibility. Of, the. Packet switching will be to send. The data from some node say a to. A destination, node say H this. Will be the main, responsibility. So. Let us now see what the. Virtual circuit approach. Actually. Is. Virtual. Circuit approach in a sense it is similar, to circuit, switching, in the, sense that all, the, packets will follow, the same path. But. It is different from circuit switching in the sense that. Resources. Along the path are not dedicated, if. The route. Is congested, the. Packets will take longer time if, the root, is not congested the, packets can, move faster, so. The path is fixed, but the. Quality. Of service or the bandwidth. Along the path is not, guaranteed, okay. So. This. Is similar. In concept to circuit switching. Here. Again the. Route has to be established before, the packet transmission starts because. We told you all packets will follow the same path all. Packets, follow the same path and. The. Links, comprising. The path unlike, circuit, switching are not, dedicated. And. An. Analogy, is the modern, day telephone. System. Where. The exchanges, are digital exchanges, none. Of the links are dedicated, they are often shared and whenever. You send a packet. From. Your handset to a destination handset, but, typically, follow the same path but maybe, over a number of shared links. In between. So. In virtual. Circuit approach. If. You try to understand how it actually works well, as I said initially you. Need a connection. Establishment, phase where. The route is established a priori. Now. Once the route is established along the route a packet will, be forwarded, from one node to the other using. That same store and forward scheme. So. Here also although, the same path is followed but. You cannot send the packets, as the bits are received continuously, but we, have to receive a packet, store, and then. Follow to the it's not the, next one will do the same thing it will first receive its tour and then, again followed it to the link that follows in this, so it will go on and. One. Characteristic. Here is that since the route is established a priori. So. In the packet header you need not store. The destination, address explicitly. Rather. You can only store, a virtual, circuit number. Which. Can be carried by each packet, and all. The intermediate, nodes, can, keep, track of the virtual circuit number for. Example, when. The connection gets established. All. The intermediate. Node will have some, entry, made in the routing table that. Well this, is a connection, which is coming from that node. Some. Virtual. Circuit number is assigned say, I, so. If it is coming from virtual, circuit number I then. Will be sending it over this outgoing, link, so. It only looks, at the virtual circuit number of the incoming packet it need not look at any any, address in the, address of the source or destination, only. The virtual circuit number is required. So. So. That said this, requires, each of the intermediate nodes to maintain a table this. Table is created during, the route establishment, phase at. The beginning and the. Table is consulted. When, the packets are forwarded to, the.
Correct Outgoing. Link, now. Here. Since. At the time the packets are actually, coming the. Route is already fixed and already there in the routing table just the routing to intermediate, node what they do they. Are just looking, at the virtual circuit number just. Doing a table lookup and sending, it to the output so. It is not trying to apply any intelligence, so. There is no dynamic, routing decision. That has been taken by the intermediate node it. Is a blind. Table. Lookup right. In, contrast. Datable. Approach is different from virtual circuit in the sense that, there. Is no concept, of a root establishment. Since. There is no root each. Packet, is. Treated, as an independent entity and are. Transmitted, separately. Suppose. There are five. Packets they will be sent independently. One, by one now. Since. They. Are independent. There. Is no history, of the packets maintained, anywhere this, is like. The postal system just, an analogy, like. In a postal system you recall, when. We post. A letter we. Write the, address of the destination and, also we write the. Address of the person who is sending the letter and drop. It in the mailbox. Now. Suppose I write five, letters to the same person and I post them now. As our mail, system works, there. Is no guarantee that the. Mail's. Will. Receive, the destination, in the correct order, there. Is no guarantee as to the time limit exactly. By what date the mail will be delivered and, even. Some mail may, not at all we deliver some mail may get lost so. All these characteristics, are also, true for the Datagram, so. Datagram. Can be used in those application where the application, knows that. These, kind of errors can occur on equal, time delay out, of delivery, of packets some. Packets may get lost, so. If you need error recovery that has to be done by the application, explicitly, but, in general, Datagram. Packet. Switching is fast because. It does not, follow. A fixed route the route might get congested.
So. And some. Other thing is there for. The Datagram, approach. Since. Each Datagram, Arsene independently. So, every, intermediate node has to take routing, decision, dynamically. For. Every, incoming, packet. For. Every, incoming packet you are taking a decision where to followed it, so now, the intermediate. Routing nodes have. Additional. Responsibilities, they, receive a packet, look. At the destination IP address and, take, a decision where to send it this, kind of decisions have to be taken. So. They, again use a routing table but. They. Need the, source, is not that. Much important, at least the destination. Address of the packet. Is. Important. So. The intermediate. Node will take a decision dynamically. Based on the destination. Address, now. The now. Problems, that I'd mentioned that. Due to unequal delays, packets. May be delivered out of order, why. Because. Since. We are not fixing a path two packets may follow two different routes and they. May they. May arrive the destination, in a different order it is always possible and if. There is a problem there is a node, crash, say. Say, a node. B. Comes down momentarily, then. All the packets that were queued. On that node will also, get lost and in. Some systems. If, you do not get acknowledgement, a packet, is retransmitted. So, in such systems even duplicate. Packets may get generated in. The same packet may be delivered, more. Than once. But. Determines. In spite of the problem, has. Some advantages, first. Thing is that it, is faster. Than virtual circuit for smaller number of packets because you. Do not need to have a route establishment, and termination, phase. It. Is more flexible, because. Depending. On, the. Network traffic you can choose the best route in. Virtual circuit once you fix the route all packets, are bound to follow that route but, now if. A link is down or is choked you can choose, an alternate path these. Options are available to you. Back. As we need to host me. Follow. Different paths. So. It can handle. Congestion, or, failed. Linked. Situations. If. You want to compare, the, different approach circuit switching. Virtual. Circuit packet switching on Datagram packet switching. Then. Enough to estimate, delays. The. Total delay that. We encounter. Now. There. Are three types of delays you, can talk. About. The. First type. Is. Propagation. Delay, this. Is the time taken by a data signal to propagate from, one node to the next.
Suppose. I, am trying to send a data signal through, a satellite link, now. The round-trip satellite, link may take as large, as 250, milliseconds, so. Here my propagation, delay will be 250 milliseconds. Propagation. Delay has nothing to do with the speed of the link it, is just a delay, okay. Transmission. Time. Depends. On the speed. Of transmission, say. Here I can have a link which, is working at 64, kilobit per second, I can, have a link which is working at 10 megabits, per second, 1 gigabit per second, these. Figures, tell me how fast I can send out the bits on the link, so. If I have a packet, of a particular, size the, speed of the link will, determine that how many milliseconds, or microseconds, will be required to send out the whole packet okay this. Is the so-called transmission. Time and. Finally. Each of the nodes are doing that store-and-forward. So, there can be some processing, delay in each of the nodes we. Have after storing it, can check whether the packet is correct or not it can high it may have to if. You have to compute a checksum. Then. It may have to consult the routing table were to send it next and if. There are multiple packets. In the queue some. Queuing delay that is encountered, these. Are the additional processing, delay. Now. In case of circuit switching. Here. After, initial, circuit establishment, data. Bits can be sent continuously. Without any delay. Well. When we sick in you ously what. I'm saying is that bit by bit continuous. Well. In circuit, switching there is no concept of a packet once. The circuit is established, if, my total, message. Comprises, of 1 million bits the, 1 million bits will flow continuously. So. The entire, link will, get choked during, that whole period and it will be 100% utilized. Ok. In. Contrast. Virtual. Circuit packet switching. Will. Require, the, so called call request, packets, at the. Beginning, for. Establishing, the, connection so. From one node to the other this, coil request packets will go and finally. It will reach the destination and, from, the destination, there will be an acknowledgment. Or a call except packet which, will follow back through the same route up, to the source so. This forward, and backward. Packers. Will serve.
The Purpose of two things number. One it, will confirm, that the route has been established number. Two it, will allow the intermediate, nodes to to. Update the routing table with the virtual circuit number in a proper way appropriately. So. Call request packet goes and call accept back and returns back and. After. The, packet. Switching is established, this link, is established, packets. Are, sent sequentially. In a pipeline fashion. But. You, remember. That. Here you are not sending the packet continuously, on a bit by bit basis, this. Is on a store. And forward basis. The. Path has been established I sent, the first packet, to the next node. Then. I send the next packet. Well. If you think of the next node the next node will receive the first packet totally, then. It will send it back so. There will be a delay so you can say that each stage, will. Be having a delay equal. To the propagation. Time plus. The transmission, time. So. It is more like a a pipeline, system which is working the packets are moving in a pipeline fashion, it, is not continuous, it is that. My packet it is moving from one hop to the other one note to the other this. Is the basic difference and. In. Case of the. Datagram. Packet switching there. Is no initial call establishment, or, or. At the end called termination delay the, packets are sent out independently. May. Follow different paths, but but, once. A path is followed again. It. Will follow a stolen forward approach. So. For both virtual, circuit and the, Datagram, the. Packets are forwarded using. The stolen, forward approach which will which, will always be there so. When you try to calculate the total delay that is encountered, by a packet you, will have to calculate all the things the, packet transmission, delay the propagation delay and also. Take. Care of the fact that the packet is going to the next node or the next hop. Then. Only. The. Next stop will be sending it back to the next one so, it will have to wait till the whole packet, is received before. It can send it to the next okay. Fine. Now. Let us have. A quick look at, the, so called layered. Network, architecture. Which. Has become, so. Popular in, the. Design of networking systems, well. The. Open, system, interconnection or. OSI, reference model, this. Has become some kind of a model. Against which, this. Two other networking. Protocols, are, compared. Now. Strictly speaking there, is no, implementation, of, this seven. Layer model per, se but. There are other implementations. Which are correlated, to the seven layer model and, they. Are evaluated. Now. This OSI model comprises of seven layers as you shall see shortly, the. Purpose of this layers is that, the.
Network, Or communication, functions, are. Partition. In a well-defined, way into a hierarchical, set of layers, the. Basic objective, is that, we. Are trying to having a systematic, approach to design, of designing. The whole thing at a white one go were trying to divide it up into smaller. Subtasks. And try to address or, design the subtasks. Independently. And. Another. Objective, is that if you want to change one, layer, this. May. Not require you to change the other layers if, you have the design in different layers this. Is one advantage you. Will have. So. The seven. Layers of the OSI model are, these. From the, bottom, physical. Data, Link Network, transport, session. Presentation. And. Application. Now. As well see. In a slide a little later the. Lower. Three layers are, called. Point-to-point, layers, because. These. Layers. Are these you, can say. Protocols. And, software are active in. All. The nodes through which a packet, passes. Suppose, this. Was a source, from. Here the packet is going here from. Here it is coming here from. There it is coming to the final destination so. These are the intermediate, links so. There are three. Point-to-point. Links, through which the. Communication. Passes. On the packet passes so. The lower three layers are active in, all, these four. Nodes, but. The, upper, four layers these are called host-to-host layers, these. Are active, only between, the end nodes, not, between the others this. Is the main difference. Now. Let us start to see what are the basic functions of these. Seven. Layers. The. Function, of the physical layer is to actually, transmit the data in, terms of a raw bit stream. Transmit. Raw bit stream over, a physical, medium, now. When we say physical medium it, can be a copper, where where, the bits are sent as voltages, it. Can be a wireless link through, which bits are sent using, some kind of frequency modulation. It can be an optical fiber where. Bits are sent by switching on and off some light beams so. This. Is how it is done and means it it can also do some kind of encoding, for example instead of sending. The bits in, a straight of example, in the Ethernet protocol they. Use an encoding called, differential, Manchester, so, this, kind of encoding. Is done before you are actually transmitting. The data over, the physical link now. This encoding, gives. Us our advantages, like the, receiver can easily decode the data or. You can have. Possibly. Better utilization, of. The. Link and so on. Data. Link layer the. Next layer. Above physical. This. Tries. To ensure, reliable. Transfer, of frames so at this layer the. The, unit of transmission, of chunks are called frames so. It ensures reliable transfer. Of frames over. A point-to-point. Link. So. The. Data link layer. Takes. Care of two things flow control, and error control. Flow. Control means if the. Senders, and receivers. Their. Speeds, do not match then. The data link layer will, try. To tell the faster person that well you, don't try to send or receive so. Fast go. With my speed otherwise I cannot keep. Pace with you and error. Control is that if some frame. Is in error the. Data link layer protocol can explicitly, send, back a request to the sender that well this, frame this. Either I have not received or I have, received with an error you, please send, the frame again so, in this way the, errors can be recovered. Network. Layer, it. Establishes. Maintains, and terminates, connection, so, it is the network layer which is responsible for routing packets through. Point-to-point, links. Then. Comes the. Transport. Layer there. Is an end-to-end, layer in the sense that all, intermediate. Nodes are, not visible to the transport, layer the transport nerve used the intermediate, natok as a black box only. The source and the destination are, there as if, they are connected via direct, virtual, link. Transport. Layers view is like this and. At. This virtual. Link level this transport, layer also tries to ensure reliable data transfer, with, again error recovery and flow control at, the higher level. Session. Layer it. Manages. Sessions presentation. It. Can provide data, independence. It can provide some sort of data encryption. Conversion. Into a common. Format. And so, on an. Application. Is the actual user application, which which. Is interfaced, here now. In practice, this session presentation application, you, may not very. Clearly distinguish, among these three they. Can be merged into one single block but, this.
Seven Layers. Have been defined with, with. An eye towards. Distributing. The functionality, across the layer so that if you have an application or. An. Environment, where all these seven functionalities, are required then, you can basically separate. Them out in the different layers just. A. Diagram to show how data. Flows in, the seven layer model. Suppose. This is the source this is the destination and, these. Are two intermediate nodes, a and B. Data. Flows from, s to, a a to. B, and. B. To, D. This. S and D are the final, source. And destinations, and a and B are intermediate, nodes so. So. The other said that. They lower three layers, they. Must, be running on all the nodes including the intermediate nodes so. The lower, three layers are running. On all, the. Nodes. And. The. And upper, four layers. They. Are providing. Some kind of a virtual link as you can see that the transport, layer out. Here, and the, transport, layer out here they, having a direct communication link, these are virtual link but. When the actual data transmission, is, concerned. Say. The the. Application layer which is out here this. Will send the data along this path, the. Data packets. Will. Successively. Flow. Down the seven-layer hierarchy, it, will go down to the physical layer level it. Will actually, reach, the node, ace physical. Layer it, will go up to node is, network. Layer out here so, the network layer it can take a decision where. Because from a there can be again more. Than one outgoing links okay. So. From here again it will choose one, of the outgoing links sent, it to be in, V again it will go up to the network layer again coming down to the physical layer then, it goes to C. To. D and, here. To the destination, and again it again follow the reverse path and moves. All the way up the. Ladder. Up to the application. Layer so. You can see that. In this. Seven. Layer model the. Data. Packets flow down, the hierarchy up down. Up down and again at the final destination up up, to the application layer this, is how the actual message. Transmission. Takes, place across the hierarchy, of the layers and, the, other point note is that the. Intermediate, nodes, through which the. Packets are sent. They. Did, not have any functionality, above, the third layer okay. The lower three layers are essential. Now. We, just. Have a look at the different kinds of internetworking, devices, which. You use in practice. Now. Internetworking, is a general, term internetworking. Means it. Is, a means through, which we can connect several, networks. Together so. When you talk about internet, working devices. We. Are actually trying to talk about devices, using. Which we. Can connect two, or more networks together. So. Let's see, what. Are the main, kinds of internet working devices we have, well. There's. Something called a hub, well. The hub can extend, the span of a single LAN. Well. Hub is a box. In. Which, there. Are several, ports. And in. Each of these ports, you can connect a computer, or you can connect another hub so. In this way you can extend, the span of a LAN a, hub. Is used within, a single LAN, and hub. Can be used to extend the, size or the, capacity of land. At. The next. Higher level you can have something called a bridge. Which. Is also called a layer to switch a. Bridge. Or a switch can. Be used to connect two or more lands together and. This. Works at the data. Link layer or sometimes. Is called the medium access control layer, level, mac. Layers, level. So. Bridge layer 2 switches, they, use not. The IP address, but something, like the ethernet or the MAC address, for.
Taking Decisions, that. How to followed the frames from. One land to the other right. And, at. The next higher level you have the routers, or. The. So called layer 3 switches, this. Can connect any combination, of lands and once they. Work at the network layer level in particular in the internet they. Use their there. Is the IP address they use the IP protocol and the IP address, for. Taking the. Decision. So. A hub, can. Connect several, computers. Inside, a single land a bridge. Can, connect several lands, together a router, can connect lands, with ones it, is most general. Now. A quick look at, some. Of. The typical. Pictures. So. In a typical, campus, wide. Network. Some, is, suppose. You have an organizational, network where there are several departments. So. A typical Network will look like this, there. Will be several. Departmental. Networks and. There. Will be a central, backbone, which. Will be connecting, all the departmental, networks together. Now. If you think of an educational, institution here, also we have the notion of several departments level, buildings, buildings. Are connected together by a network, which. Is called the backbone Network, now. The entire thing is a LAN but. In terms of the way they. Are actually deployed and used, typically. The, speed, of the backbone, network is higher. As compared, to the speed of the departmental, network, because. It is expected that the, that. Backbone network will be carrying more traffic as compared. To the individual. Departmental. Networks. Just. To. Look. At some of the alternate technologies that are available for. The backbone, network. You. Can have Fast. Ethernet you. Can have fiber. Distributed, data interface both. Of which work at 100 Mbps, you. Can have. Atm. ATM. Stands for asynchronous transfer, mode it, works at about 500, Mbps, you. Can have Gigabit, Ethernet which, works at 1000, Mbps or 1 Gbps. For. The department, network you can have switched. Ethernet you. Can have bus based Ethernet, now. Now. If you, try. To look. At a state-of-the-art. Solution, the state-of-the-art, solution, will comprise of a backbone network which, can work at 1 Gbps. You. Can have a department, network which can work at 100 Mbps, switched, Ethernet LAN that is some. Sort of a you. Can say state-of-the-art, network. Now. Just. To look at a department, Network this is a very rough, picture of a departmental, network further. On one side you are connected, to a backbone, by. A very fast link this can be a Gigabit Ethernet link. Now. Inside, the, department, you can have a main Ethernet. Switch. There. Can be several hubs, you. Can. Have your computers, servers. All, connected, to them this. Is just one level I've shown there can be multiple levels, of switches. And hubs. So. This. Is how the network the. Different. Machines, and the servers can. Be connected together inside a network you, have a main switch. In the department, under which, there can be hubs there, can be other switches, and all, the computers, are connected below, that okay, this is how it is done and. For. Connection, to the outside world you can have a scenario, like this. But. Suppose this, is your Institute Network, you. Can have a number of outside connections. Like. You can have a router through. Which you can have multiple links. You. Can have a link with a satellite. Connection you can have a link with a wireless link you. Can have a leased line link you can have a telephone line link through a modem. So. If you have a link through a telephone line typically it is done through a modem but. If you have either leased line radio, link or you can have a satellite. Link or satellite, can be in, the sky you can have a satellite link so. All these links can be through. A router, so. These, are the alternate technologies I am just. Trying. To mention without going, into the detail so. If. You were an organizational, network you will have to solve the problem of connecting, the computers inside, and, also. Will have to solve the problem of how. To connect. These computers to the outside, world will, see how links. To the outside world are, to be made because, ultimately. Your. Task. Will be to have, this machines connected to the Internet and for. Internet you will have to rely. On some. Internet, service provider, which. Will be providing, you a, connection. From. Your LAN. To, the outside world. Okay. So. This. Brings. Me, to the end of, today's. Lecture. But. What I would be, following. In. This. Lecture as well as the lectures to follow is that at the. End of every, lecture I try. To. Give. You some suggestive. Questions or, some quiz questions which, you can try to solve and. Also. I try, to, give. You the solution of the questions that are posed in the previous classes, now. Since in the previous class I did not pose any question, it was an introductory class so.
In This class I'll only. State. The quiz questions, for, today's. Lectures, now. Just one thing I also want to say, that. Whatever has been covered here and whatever. Quiz questions. Had. Been posed at the end of the lecture these are just suggestive. Questions he. Was strongly urged, to. Look. Into, reference material to look into textbooks, to. Work out some more exercises. And problems to. Get, much. Better feeling of the subject, so, that you can be much, more confident, about solving. A problem once it is given to you, now. Let us. Look. At the quiz questions, on today's, lectures. Okay. The. First question says, that. With respect to speed. Of data, transfer, which. Of LAN, or, one. Is faster. This. Is a question second. One what. Is the typical speed, of a modern, Ethernet backbone. LAN. Well. When I say a modern, Ethernet backbone line of course there are alternatives, I am, expecting, that means, you, will be. Telling. The state-of-the-art. Technology what. The. State-of-the-art. Ethernet, technology supports today okay. The. Third question. Why. Is circuit. Switching not suitable, for computer, to computer traffic, I had mentioned that competitive. Computer traffic is bursty in nature I think the answer lies there you can. Try. To figure out the answer, question. Four what. Are the three steps that. Are required for, data. Communication. Using. Circuit. Switching. Question. Five. With. Respect to the sharing, of links. Which. Of. Circuit. Switching or. Packet. Switching is, more. Suitable. Well. Here let, me repeat once that. Although I had. Talked. About this technologies, in, my regular lecture I had talked. About, there. Are some links which. Will be dedicated, some links which are shared but in today's. Technology. None. Of the links. Or the physical, links are, dedicated. What. We see as dedicated are their resources, along the link for. Instance I may, have a link which supports, say. One. Megabit. Per second, in capacity, suppose. I am multiplexing, several, voice. Links, over it each. Voice link requires, 64. Kilobit per second, this, means that. I can carry, 16. Such filings, over this 1 Mbps link, so. I am. NOT, dedicating. The entire link, to any one voice link but I am I, am. Assigning, or dedicating, fixed. 64. Kbps. Or, 64. Kbps of dedicated, bandwidth, to, each voice link this, is what I mean. By, dedicating. A logical, link. Means. Across a path. Look. Now. Question number 6. Among. Virtual circuit and Datagram. Which. Approach, requires, less, information in, the packet header. Well. For answering this quiz this question, you need. To understand, that, how, the, packets. Are forwarded in. Virtual. Circuit and Datagram. What. Are the roles of the, intermediate, nodes, and what. Kind of, information. The intermediate, nodes are using, to. Take the routing decision so. I think the answer will come from there. Seven. Which. Are virtual circuit and Datagram makes, better. Utilization of the links simple. Eight, which. A virtual circuit and Datagram will, guarantee. Order. Delivery of packets in the, absence, of any errors. Nine. Under. What circumstances. Will. The Datagram. Method, of. Packet. Delivery prove. Useful. See. Here I had. Mentioned. The lecture that Datagram. Method will. Be faster in general but. You can try. To figure out what kind of applications. May. Gain. By using, using. Datagrams. Because. One thing is true I had mentioned. Datagrams. Do. Not guarantee. Delivery. The, destination, there can be some packets. Which are not received, some, out of order. Delivery. So. Some applications. Which. Would. Not mind if this kind of things, happen. They. Will be or or, some environment, where the chances, of errors occurring a less most. Of the packets will be following, in. The same path so. Here. You can try. To. Find. Out some environment, or some situations, where this. Kind of. Things. Exist and and. Datagram. Packet switching would. Be advantageous. Number. Ten, five. Packets need to be sent from host a to another host P. Five. Means a small, number, which. Of, virtual. Circuit or Datagram reef faster. Number. 11 a small numerical problem. For. A 5, kilobytes, size packet. Sent. Over a 10. Mbps. Transmission, link what. Is the transmission, time of the packet this was can very easily calculate what is, the time taken for one, full packet to, get transmitted, over this link. Number. To elf again a small numerical question a. 600. Byte packet. Is. Sent over. A 20, kbps, point-to-point, link, whose, propagation. Delay is also specified, the. Propagation delay recall, is, the time taken for 1 bit to go from one end of the channel to the other it, has nothing to do with the speed of the channel okay these two are different. After. How much delay will, the packet reach the destination.
Just. Here I am giving a hint, here. The. Total delay will be equal to the. Propagation delay plus, the packet transmission delay okay. This, you must calculate. In this way. Which. Layers in the OSI model are, the host-to-host. Layers. What. Is the responsibility, of the network layer in the OSI model. What. Is the responsibility, of the datalink layer in the OSI model. What. Is the basic difference between a, bridge. And a, router. So. I believe we, have discussed all these things you should not find in difficulty, in answering these questions. Now. In. Our next. Module. Will. Be starting, our discussion on tcp/ip. Which. Will be laying. You. Can say the. Foundation for. Our future, discussions. On. Network. Routing architectures. Internet. Protocols, and other technologies. So. With this we come to the end of today's lecture thank. You. This. Lecture is entitled. Tcp/ip. Part. 1, so. In this module 2 we. Would be, covering. The topics in three lectures here. Would be mainly talking about the TCP. IP. Protocols. In fact TCP. IP is not a single, protocol it is a suit. Or a family of protocols we. Would be looking at some. Of the important, members of this. Family but first. Let us try to understand, what DCP. IP is and how. It. Has evolved, over, a period of time. Okay. So. Talking. About the Internet. TCP. IP is. A. Protocol. Which. Well. You can say it started, as early as in the 1970s. And it. Got very quickly accepted, by, a white, community, of users in. Fact, when. The internet. Came into the being TCP. IP was the prime vehicle, which. Was used to. Connect. The computers, in the internet and to allow them to communicate. Over. The network. Using. Tcp/ip the computers, were able, to communicate, among. Each other and also. Another, very important, thing they. Were able to, share. Some resources, across. The network. Some. Of the resources, like. Disk. Space or some, of the some. Of the expensive, equipments, were. Expensive. In those days and over. The network it was possible, to share those, resources. Now. Let us have a very quick look at. The. Important, members of the, tcp/ip, family. This. Diagram. Summarizes. The. Different important, family members in tcp/ip, of course. At the lower level we. Have the data link and the hardware layers this. Refers to the network interface card as I told you. Typically. We, use Ethernet. At this. Level at. The. Next higher level this is the network layer level in. Tcp/ip. The. Protocol, that. Works at the network layer level is, called Internet, Protocol or in, short IP. So. IP is, the main protocol, which is working at the network. Layer level but. In addition, there. Are several auxiliary protocols. Like Internet. Control, message protocol. Group. Message protocol, address resolution. Protocol. And, reverse. Address resolution protocol. Which. Also. Works. At the network layer level but. They. Have, specific. Functions, like. ICMP. Is. Used, to. Generate and send some error messages like. For example address, resolution protocol. Is used, to translate, from. An IP address into, an Ethernet address, for example so, IGMP and rarp also has some specific. Purposes. But. In a typical. Application you. Will be using Internet Protocol, these protocols, are typically, hidden from the applications, these. Are invoked, and used. In. A transparent, way as a user, you, will not be able to see that they are being used or, as a programmer, also you, will not be using them directly.
2019-03-19