 Hello everyone, welcome to the lecture on Introduction to TCP-IP. At the end of this lecture, students will be able to enumerate the layers of the TCP-IP and also students will be able to explain each field of TCP-IP header. Now before starting with the TCP-IP protocol suite, let's recall what are the layers associated with the OSI reference model. Now the main similarities between the two models are both of the models share a similar architecture. This can be illustrated by the fact that both of them are constructed with the layers. Both of the models share a common application layer. However, in practice, this layer includes different services depending upon each model. Both models have comparable transport and network layers. This can be illustrated by the fact that whatever functions are performed between the presentation and network layer of the OSI model, similar functions are performed at the transport layer of the TCP-IP model. Now the main differences between the two models are the OSI model consists of seven architectural layers whereas the TCP-IP only has four layers. TCP-IP protocols are considered to be standard around which the internet has developed. The OSI model, however, is a generic protocol independent standard. TCP-IP combines the presentation and session layer issues into its application layer. TCP-IP combines the OSI data link and physical layer into the network access layer. In TCP-IP transport layer provides both connection-oriented and connection-less services and network layer provides connection-less services only whereas in OSI transport layer is only connection-oriented and network layer provides both connection-oriented and connection-less services. The TCP-IP is considered to be a more credible model. This is mainly due to the fact because TCP-IP protocols are the standards around which the internet was developed. Therefore, it mainly gains credibility due to this reason whereas in contrast networks are not usually built around the OSI model as it is merely used as a guidance tool. Now let's see how the packet encapsulation is done at the TCP-IP protocol suite. The packet's history begins when a user one hosts sends a message or issues a command that must access a remote host. The application protocol associated with the command or message formats the packet so that it can be handled by the appropriate transport layer protocol TCP or UDP. TCP divides the data received from the application layer into segments and attaches a header to each segment. Segment header contains sender and receive ports, segment ordering information and a data field known as a checksum. UDP attaches a header to each packet. Each contains the sending and receiving host ports, a field with the length of packets and a checksum. Both TCP and UDP pass their segments and packets down to the internet layer where they are handled by the IP protocol. IP prepares them for delivery by formatting them into units called IP Datagram. IP attaches an IP header to the segment or packets header in addition to the information added by TCP or UDP. Information in the IP header includes the IP addresses of the sending and receiving host, datagram length and datagram sequence order. The data link layer protocols such as PPP format the IP datagram into a frame. They attach a third header and a footer to frame the datagram. The frame header and footer to frame the datagram. The frame header includes a cyclic redundancy check field that checks for errors as the frame travels over the network media. Then the data link layer passes the frame to the physical layer. The physical network layer on the sending host receives the frames and converts the IP addresses into the hardware addresses appropriate to the network media. The physical network layer then sends the frame out over the network media. Now let's see the field associated with the TCP header format. So this is the TCP header format. Now let's see each field one by one. First the source port and destination ports each 16 bits field identify the source and destination ports respectively. These two fields plus the source and destination IP addresses combine to uniquely identify each TCP connection. The sequence number identifies the byte in the stream of data from the sending TCP to the receiving TCP. That the first byte of data in this segment represents. The acknowledgement number field contains the next sequence number that the sender of the acknowledgement expects to receive. The header length gives the length of the header in 32-bit words. This is required because the length of the option field is variable. The 6-bit flags field is used to relay control information between TCP peers. The possible flags include urgent acknowledgement, push, reset, sync and fine finish. The URG flag signifies the this segment contains urgent data. When this flag is set the urgent pointer field indicates where the non-urgent data contained in this segment is being. The acknowledgement flag is set anytime the acknowledgement field is valid. Implying that the receiver should pay attention to it. The push flag signifies that the sender invoked the push operation which indicates to receive wing side of TCP that it should notify the receiving process of this fact. The sync flag and finish flags are used when establishing and terminating a TCP connection respectively. Windowsize field indicates the number of updates from acknowledgement that sender will accept. The checksum covers the TCP segment, the TCP header and the TCP data. This is a mandatory field that must be calculated by the sender and then verified by the receiver. The option field is the maximum segment size option called the MSS. Each end of the connection normally specify this option on the first segment exchanged. It specify the maximum size segment the sender wants to receive. The data portion of TCP segment is optional. These are the references used by me. Thank you.