cisco certification 2020

cisco certification 2020.1.8 Transport Layer Technologies and Protocols 99Connection. The opposite is true for connectionless protocols (e.g., UDP), which do not require any connection to be established before transmitting data. As described in RFC 793, which defines the TCP protocol, TCP "assumes" that the datagrams (IP packets) obtained from the underlying protocol are simple and perhaps unreliable. TCP provides most of the services one would expect a transport layer protocol to provide. This section describes the following services provided by TCP and the following features it has. Multiplexing.As mentioned at the beginning of this section, the TCP protocol is a connection-oriented protocol, which means that before any data can be exchanged over TCP, the two hosts need to go through the process of establishing a TCP connection. This process is commonly referred to as the TCP "three handshake" because three packets need to be exchanged between the two hosts. The main purpose of this process is to synchronize sequence numbers between the hosts in order to exchange data with each other, as shown in Figure1.82. /baThis takes a closer look at those 3 packets that need to be exchanged between the two hosts during the TCP connection establishment phase. The first packet (TCP packet segment in SYN position 1): the TCP client sends a TCP packet segment in SYN position 1 to the server to initiate the process of establishing a TCP connection and to inform the server that this machine wishes to synchronize its sequence number with your machine and establish a TCP connection. The TCP client also includes in this TCP message segment (the sequence number field in the TCP header) an initial sequence number (in this case X) chosen at random by it oThe TCP server will reply to the TCP message segment with both the SYN and ACK bits set to 1, informing the client that it wishes to synchronize the sequence number with your machine. The TCP server will also include in this TCP message segment (the sequence number field in the TCP header) an initial sequence number (Y in this case) chosen at random by it. In the same TCP message segment, the TCP server also sets the value of the TCP header's acknowledgement number field to X+1, indicating that the machine received theFirst, the TCP client application notifies the local TCP layer that the connection can be terminated. Then, the TCP client sends out a TCP message segment with FIN position 1, and the server replies with a TCP message segment with both the SYN bit and the ACK bit set to 1 for acknowledgement. At this point, the server notifies the local application that the peer wishes to terminate the TCP connection. During this time, the TCP client can still receive traffic from the server, but will not send any traffic to the server. Once the server-side application is ready to close the connection, it notifies the native TCP layer that the connection can be closed. The server then also sends out a TCP message segment with FIN set to 1. The TCP client naturally acknowledges this, and after the acknowledgement, the TCP connection is terminated.Figure 1-82 TCP Three Handshakes100 Chapter 1 Network Protocols and Network Device Basics