 In my last video, we have seen the basics of Ethernet and the various cabling techniques used by the Ethernet i.e. 10Bes5, 10Bes2, 10BesT and 10BesF. In this video, we will see the cable technologies or cable topologies, encoding techniques and the frame format of IEEE 802.3 standard i.e. Ethernet. Now, the learning outcomes are at the end of this session, student will be able to explain the cable topology and encoding techniques, they will also able to draw, encode a signal of given bit stream, student will be also able to describe each and every field of IEEE 802.3 frame format. Let's start with the cable topologies. Cable topologies means different ways of wiring up a building. So, there are different ways provided by IEEE 802.3. Linear topology, spine topology, tree topology and segmented topology. This diagram shows all four type of topologies. First topology or the figure A shows the linear topology. In this topology, single cable is snagged from room to room and the station A, B and C are tapping over the cable. The another type of topology is spine topology. Here the vertical spine cable is used or this vertical spine cable is run from basement to room whereas the horizontal cable is attached to this vertical cable from floor to floor with the help of repeater or amplifier. The third type of topology is tree topology. Now here the stations are arranged like the branches of tree. The next type of topology is segmented topology which is used to set up the large network. Now here multiple cables are connected with the help of repeater. We know that repeater is the physical layer device and it is responsible for receiving the signal then amplify the signal and transmit that signal to the both direction. Now the next very important topic is encoding technique. So here IEEE 802.3 Ethernet uses two approaches for encoding, Manchester encoding and differential Manchester encoding. Actually when the data is coming from the upper layer to the physical layer then physical layer is responsible for transmitting that data bits into the form of signal. That means this physical layer is responsible for conversion of data bits into the digital signal but it is not necessary that physical layer send that bits in same format or it send that bit as it is. So it convert that bit into different bit by or using the various encoding technique. So there are so many encoding techniques like digital to digital, digital to analog, digital and analog to analog. But here Ethernet uses digital to digital encoding technique. So the Manchester encoding and differential Manchester encoding is used by IEEE 802.3 that is Ethernet. Let's see Manchester encoding. So Manchester encoding can be represented by using two conventions or two ways. The first one is Thomas convention and second one is IEEE 802.3 convention. Where each bit period is divided into two equal intervals. Binary one bit represented as high to low signal like this. So here one is represented high to low where the binary zero represented as low to high that means this is low to high signal. The transition is in the middle of bit. So this is known as transition in the middle of bit. Let me explain this with the help of one example. So the given bit stream is 1, 4 times 0s, 1, 0 and 4 times 1. Now we need to arrange this into a proper manner. So here data bits are arranged like this interval. So here 1, 0, 0, 0, 0, 1, 0, 1, 1, 1. Now to convert this data into digital signal physical layer provides some special specifications. So here digital signal means or how this data is converted into digital signal. So here 1 means high signal. So here it is high and 0 means low. So this is low. But to transmit the data into continuous manner we need to connect it. So we require this interval. So these are two bits 1 and 0. So high to low. Now the next three bits are 0, 0, 0. So here 0, 0, 0 that means low signal. Then again the next bit is 1 that is high signal, again 0 signal, again high signal, 1, 1, 1, 1. This shows the bit or the data bits converted into digital signal. Now let us see Manchester encoding. So as I said 1 represent high to low signal whereas 0 represent low to high signal. So here 1, the first bit is 1 that is high to low signal and the another bit is 0 that is low to high signal. The next bit is again low to high signal, right? This is low to high signal. But to connect these two bits or to send this in a continuous manner we need to attach this. So this is 0. The next again 0, 0, then again 1 that means high to low, 0, low to high and again the remaining 4 bits are high to low, high to low in this manner. So this is Manchester encoding. Manchester encoding having advantage. So always a transition in each bit thus making the synchronization between the sender and receiver is possible. But it has a disadvantage. Because of the greater number of transition it occupies the significantly large bandwidth. Let us see the another encoding technique used by Ethernet that is differential Manchester encoding. So here binary 1 bit indicate absence of transition at the start of interval and binary 0 bit indicate presence of transition at the start of interval. So let us see with the help of same example. So we know how to draw the digital signal and how to draw the Manchester encoding. So the data is 1, 0, 0, 0, 1, 0, 1, 1, 1, 1. So what I said? So here if the 1 bit is present then there is a absence of transition at the start of interval. So this is start of interval. So let us see differential Manchester encoding. So for 1 bit there is high to low signal but there is no transition at the start of interval. Now for 0 there is a presence of transition at the start of interval. So we need to show the transition here. So this is transition but 0 is not low to high. So we need to continue this signal so here high to low. Again the next 3 bits are 0. So therefore again the transition at the start of interval, for next 0 again the transition at the start of interval and for next 0 again the transition at the start of interval. Now the next is 1 bit. So we do not need to show the transition at the start of interval. So here low to high. To make it continue we need to provide here or we need to draw low to high again 0. That means we need to show the transition at the start of interval. So here like this and for remaining 4 ones the data is like this or the signal is drawn like this, understood? So here the data given data is converted in the form of differential Manchester. So physical layer transmit the data in terms of various encoding techniques. Now so the advantages offer better noise immunity. Now when the data is transmitted from source to destination so many interferences are included but this technique differential Manchester encoding provide the better noise immunity. Disadvantages are require more complex equipment, require twice bandwidth as compared to plain binary encoding. Now pause the video think about this question and write down the answer and the question is convert given bit stream into Manchester and differential Manchester encoding bit stream is 1010111. So again arrange this data, convert this bit into digital signal Manchester 1 bit is high, 0 bit is low to high, 1 bit 0 bit and remaining 1 1 bit. Differential Manchester the 1 bit that means there is no transition at the start of interval and if 0 that means we need to show the start of interval sorry start of presence of signal at the start of interval. So in this way differential Manchester encoding. Now the next very important topic is the frame format of IEEE 802.3. So when source transmit the data to the destination data link layer provide the proper frame format that means the structure is required. So here IEEE provide a proper frame format with some fields. So let us see each and every field one by one. So here IEEE 802.3 Ethernet frame format first field is preamble and it reserved 7 bytes with the bit pattern 10101010. It use for synchronization. Second start of delimiter reserved 1 byte with bit pattern 10101011 and it denote the start of frame itself. The next thing is destination address and source address allow 2 byte and 6 byte but the parameter defined for the 10 Mbps baseband standard use only 6 byte address. It provides the ordinary and group address when the MSB bit or the high order bit is 0 then the ordinary address and when the high order bit is 1 then it provides the group address. Again there are two type of addresses multicast and broadcast multicast address that means sending message to a group of station and broadcast means all once in destination field deliver to the all station on the network. Length of data. Length is a 2 byte field indicate the length of entire Ethernet frame. This field can hold the length value between 0 to 65534 but because of some limitation Ethernet provide only 1500 bytes data. Then the data field actual data is inserted in the data field known as payload IP header and the data will be inserted here if the internet protocol is used over the Ethernet. Maximum data length just now I said that 1500 bytes then the padding field data length is less than minimum length that is 46 byte then the padding 0 is added to meet the minimum possible length then the checksum to detect the error present into the frame. So the CRC is the 4 byte field this will contain the 32 bit hash code of data if the checksum computed by the destination is not matches with the checksum computed or after get checksum computed with the send data then the received data is corrupted and then data that data is discarded by the destination. So this is the frame format and each and every field present into the frame provided by IEEE 802.3. These are the references. Thank you.