ccna preparation bundle

ccna preparation bundle.Keep in mind the five main functions of the transport layer: connection management, reliable and unreliable transmission of data, flow control, multiplexing, and segmentation.multiplexing, and segmentation.1. reliable connections The transport layer allows for the reliable or unreliable transfer of data between network components. tcp is a transport layer protocol that provides reliable connections. To achieve a reliable connection, sequence numbers and acknowledgements (ACKs) are typically used O For example, when sending a message to a target device, the target device will acknowledge to the source what information it has received; the target device can look at the sequence numbers of the received data segments to determine if there are any missing (discarded during transmission) messages and put the data in the correct order, which in turn will be given to the upper layer application. If there are missing data segments, the target device may request the source to retransmit them. In some protocol stacks, the target device may let the source retransmit all or part of the information (keeping the missing segments). Some reliable connection protocols may also undergo a handshake process when establishing a connection. This handshake process determines whether two network devices canestablish a connection, and negotiates the reference that should be used to provide a reliable connection. In TCP, this is referred to as a triple handshake. TCP and the three handshakes are discussed in more detail in Chapter 8.2. Unreliable connectionsOne of the problems with connection-oriented services such as TCP is that a handshake process is required before transferring data, and also to confirm that all data sent has been received. In some cases (such as when transferring files), this makes sense, as you want to make sure that all the data for the file was successfully transferred. However, in cases where you just want to send the message and get a final answer, the handshaking process adds unnecessary overhead and delay.In TCP/IP, Domain Name Service (DNS) queries are the paradigm that does not lend itself to the use of connection-oriented services. In a DNS query, the device attempts to resolve a fully qualified domain name (FQDN) to an IP address, for which it sends a query to the DNS server and waits for the server to respond. In this process, only two messages are generated: the query from the client and the response from the server. Since very little information is shared between these two devices, it is not reasonable to establish a reliable connection before sending the query. Instead, the device should send the message directly and wait for a response. If there is no response, the application can send the message again or let the user intervene. In the DNS implementation of the operating system, two DNS servers can be configured in the TCP/IP adapter's settings. This way, if the first server does not answer, the application can try to use the second server configured.Since there is no pre-established connection, this service is called a connectionless service. o The TCP/IP stack uses UDP to provide unreliable connections (connectionless service). o UDP is discussed in more detail in Chapter 8.3. segmentationAnother function of the transport layer is to establish, maintain, and remove connections for the session layer, i.e., to handle the actual connectivity mechanism. At the transport layer, the information that is transmitted between network devices is referred to as data segments. In order to divide large amounts of data into smaller chunks supported by the network, segments must be performed. A good analogy for this process is that small rocks are easier to transport through pipes than large rocks.