ccna study guide pdf 2020

ccna study guide pdf 2020.TCP's primary responsibility is to provide a reliable, connection-oriented, full-duplex logical service between devices, and TCP establishes a session to send data through three handshakes, as discussed later in the section "TCP's Three Handshakes". TCP supports data recovery, so that the source device will retransmit messages, whether they are lost or damaged. When packets arrive out of order due to data segments going through different paths to the target device, they can be easily rearranged because the segments use sequence numbers to keep track of the order.TCP provides a reliable, connection-oriented logical service through the use of sequence numbers and acknowledgments, provides flow control through the use of windowing techniques, and also provides error detection and correction through the use of checksums, packet reordering, dropping duplicate packets, and retransmitting data segments.As mentioned earlier, TCP uses data units called data segments to transfer information between devices. As described in Chapter 5, IP datagrams contain a protocol field that indicates which protocol is encapsulated in the payload. For TCP, the protocol field has a value of 6, indicating that a TCP data segment is encapsulated.Table 8.1 lists the components of a TCP data segment, which consists of a header and application layer data; without any options, the TCP header is 2 bytes long.The maximum segment length (MSS) refers to the amount of data, in bytes, that a TCP device is willing to receive in a single data segment. The MSS should be set small enough to avoid IP segmentation, which may result in packet loss and excessive retransmissions. For this reason, when establishing a TCP connection, both parties use the MSS option to advertise the MSS; the advertised MSS value depends by default on the data link layer's maximum transmission unit (MTU) and does not negotiate the MSS; instead, each party uses the TCP option field to advertise its supported MSS to the other party. therefore, the MSS values for the two directions of a TCP connection can be very different.Exam Points Be sure to familiarize yourself with the information listed in Table 8.1, especially the following: the TCP data segment contains the sequence number, the acknowledgement number, and the window size.Table 8.1 Components of TCP Data Segments TCP Field Name Length (in bits) DescriptionSource Port 16 Indicates which application the message is sent fromDestination port 16 Indicates which application the message will be received bySequence number 32 Ensures reliability and correct sequence