 Welcome to the lecture on our networking devices part one. Learning outcomes. By the end of this session, students will be able to explain the operation of internet working devices like repeater and hub. You may pause here the video and try to find out the answer to this question what is the need of internet working. Suppose we have scenarios like this we could have two LANs connected to each other or LAN connected to a VAN or two LANs connected through a VAN. Then we use the networking devices to link them and to use the resources across all the LANs of the VAN. So make the use of the resources very efficiently we go for internet working of the devices. LANs or VAN normally cannot operate in isolation they are to be associated with each other. They are connected to one another or to the internet. We use the devices or networking devices to connect LANs or VANs together. Connecting devices operate in different layers of internet model normally known as OSI model. There are three types of networking or connecting devices. The first is repeater or hub which works at the first layer of your OSI model. Then bridges or sometimes referred as two layer switch. Then the third type is router. The three layer switches sometimes these are known by its three layer structure. In figure one you can see that repeater and routers work at the physical layer of the OSI or internet model. While bridge or two layer switch work at the first two layers means physical and data link layer of OSI model. Router or three layer switch works at all these three level means physical data link and network layer. Repeater operate only at a physical layer. It just simply regenerates the signal over the same network before the signal becomes too weak or corrupted. So by this regeneration it can extend the length to which the signal can be transmitted over the same network. Here the point to note is that it do not amplify the signal it's just regenerate the signal. The repeater just copy the signal bit by bit and regenerate it at the original strength to make it recognizable till at the receiver end. It is a two port device. The data signal within the network can travel a fixed distance before the attenuation alters the integrity of the data. Repeater once receives the signal it just regenerate before it becomes too weak or corrupted. With the reference of OSI model if we see the repeater works at the physical layer and it works as a level one relay which is shown in this figure. This is the OSI model of the transmitter side this is OSI model on the receiver side and repeater work at the physical layer only. The repeater send out the refresh signal or regenerated signal. In the past when the Ethernet LANs were using burst topologies a repeater was used to connect the two segments of LAN to beat or to overcome the length restrictions of the coaxial cable which is shown in this figure number three. Here you can see that this segment one and segment two are connected to each other by this repeater. So the restrictions of length on the cable is overcome by inserting or installing this repeater between these two segments. The repeater do not isolate segments from one another if there is a collision on one segment it is regenerated on the other segment as well. With reference to this diagram suppose we have a collision or corrupted data on this segment it will be as it is forwarded after regeneration by this repeater means it do not isolate the segment one from segment two in case of collisions. When signal initially leaves the transmission station they are clean and easily recognizable. However the signal travels along the cable length it gets weaker and worse. Repeater are often installed along the way to ensure that data packets or data bits reach the destination in recognizable state. The point to note here is that it can't filter the network traffic. Data arriving at one port of the repeater gets sent out on all the other ports connecting other LAN segments of the network regardless of whether it is need to go there or not. The second networking device is Hub. Hub is a hardware device used to connect many computers together while repeaters were used to connect two devices only. Hub is basically a multi-port repeater. A hub connects multiple wires coming from different stations. For example if we consider star topology the centralized connector which connects different stations is just an example of hub. Hub also cannot filter received data just like repeaters. So the data packets are also sent to all the connected devices. In other words the collision domains of all the hosts connected through a single hub remain same. Means suppose we have corrupted data or collided data on a one port then that port data will be broadcasted by the hub to all over the all other ports as well. Hubs are not intelligent to find out best path for the data packets which leads to inefficiencies and wastages. All users connected to a single hub are in a single segment. Every time the received data packet is broadcasted on all other ports which is unnecessary wastage or inefficient use of resources like bandwidth. So hub as those are not intelligent which leads to inefficiencies and wastage of resources. Types of hub. Hubs are either active or passive. Let's see the first type active hubs. Active hub electrically regenerates the signal as it moves out of the connected devices. Active hubs have their own power supply and can clean boost and retransmit the signal along the network. It serves both as a repeater as well as a wiring center. Active hubs are used to extend the maximum distance between the nodes. Another type of the hub is passive hub. Passive hub allows the signal to pass from one computer to another computer without any change. Passive hubs collect the wiring from the nodes and power supply from active hub. They do not have their own power supply. Passive hub transmits signal on the network without cleaning, boosting and it can't be used to extend the distance between the nodes. We know a repeater is a multiport device usually known as a hub. In star topology hub is used to serve as a connecting point at the same point functions as a repeater. In figure number four you can see that all these four computers are connected to a single hub which serves as a connecting point. Let's see the operation of hub. Whenever computer A try to send a data frame to computer B then the frame arrives at the hub then hub regenerates the bit pattern or the frame and it broadcasts. Means it sends out that regenerated frame on all four ports. Once the frame is out on all the frames means it is broadcasted. Every computer connected to this hub receives the frame and only computer B to which the frame is intended is allowed to keep or it just keep the frame and other three computers means computer A C and D will discard the received frame. Means hub just broadcast the received data and it do not have any intelligence or it can't filter the network traffic. We know hub don't have any filtering capability and do not have intelligence to search out from which port the frame should be sent out. It just simply broadcast means it just simply send out the frame on each and every port. Hub do not have intelligence because as they are physical air device they do not have any data link addresses and then as they don't have any data link addresses they don't check for the data link addresses of the received frame so they can't filter the traffic based on the data link addresses. Hub simply regenerates the corrupted bits and send them out on each and every port. Hub can be used to create a multi-tier design or multi-level of hierarchy of stations with backbone hub at its top. The kind of one kind of multi-tier design is shown in this figure where the backbone hub is at the top and other hubs are connected to this backbone hub and the computers are connected to this connecting hub. By creating this multi-tier design we can form a single line with number of many number of or large number of nodes. These stations are connected to the hub with RJ45 connector with maximum segment length of hundred meters. This type of interconnected set of station is easy to maintain and diagnose limitations. Single collision domain ends up in no increase in maximum throughput. Thruput is nothing but a performance measurement parameter of a network. Even if we go for multi-tier design style throughput is also same as a single segment design throughput. Individual LAN restrictions can cause limits on number of modes in same collision domain and on total allowed geographical coverage. Hub cannot connect different Ethernet types. It cannot connect a 10 bus T and 100 bus T LANs together. These are the references. Thank you.