ccna preparation time

ccna preparation time.Exam points are at the transport layer, where data segments are used to transport information.4. Multiplexing of connectionsA component may establish multiple connections to another component or multiple components, and multiplexing is required to distinguish between data being transported over different connections. This ensures that the transport layer can send data from a particular application to the correct target device and application, and can give the received data to the correct local application.To do this, the transport layer usually assigns a unique set of numbers to each connection. These numbers are often referred to as port numbers or socket numbers. For each connection, a source port number and a destination port number are assigned. The target port number assigned by the source device is sometimes referred to as a well-known port number or a reserved port number. In the target port number field, the source device uses the appropriate port number to indicate to the target device which application it wants to access. For example, the TCP/IP stack assigns a unique port number to each application.The following are some well-known port numbers used by TCP/IP applications: FTP (20 and 21), Telnet ( 23), SMTP ( 25), DNS( 53), TFTP ( 69), WWW ( 80), and POP ( 110). o In the TCP/IP stack, 0.1023 is a well-known port number. However, some applications use larger port numbers. In fact, TCP/IP uses a 16-bit port number field that can support 65536 different port numbers. The source device assigns a source port number greater than 1023 to a connection. Each connection of the source device has a unique source port number, which allows the source device to distinguish between its own connections. This process is discussed in more detail in Chapter 8.Exam Essentials The transport layer uses the source port number, the destination port number, and the Layer 3 logical address to perform multiplexing of connections.5. Traffic ControlAnother function of the transport layer is to provide optional flow control. Flow control is used to prevent network components from sending too much information to the target device, causing the target device's receive buffer to overflow and thus discard some information. The overflow is harmful because the source device must retransmit all the discarded information. Two basic methods of traffic control are available to the transport layer.. Ready/not ready signaling; . Windowing techniques.