TCP

In this article we analyze the characteristics of TCP and will try to address, in sufficient depth, the main issues concerning this Protocol.

Reliability

Let's start by saying that TCP is a protocol belonging to the transport layer protocol stack of ISO / OSI. Most Internet applications use, in fact, this protocol which - by its very nature - is characterized by a high degree of reliability.

We will see, in the article, the reason for this statement.

Connection-oriented protocol

TCP is a connection-oriented protocol that since two applications on different terminals, before transmitting data, should establish such a connection handshake (handshake). In this preliminary information and then are transferred to ensure a reliable service conesgna packages.

Full-duplex

The TCP offers a full-duplex where, therefore, the flow of data between sender and recipient is bidirectional; more precisely the data streams, with different directions, can coexist. This means that a generic host can transmit data to another and simultaneously receive data from third host without that undermine the reliability of transmission.

Point-to-point

You can define a generic TCP connection as a point-to-point on that one source and one destination.

That said it is clear that can not be used in multicast mode, or the transfer of data from a sender to multiple recipients in one operation. If we assume that a generic host has to notify the other three hosts something must, of necessity, to establish a separate TCP connection for each destination host.

The operations handled by the TCP are completely invisible to the network-level functions such as forwarding packets reach a router.

Stream-oriented protocol

Furthermore, TCP is a protocol that could be defined as a stream-oriented protocol or the TCP "sees" the data transmitted as a stream of bytes that are ordered that are numbered.

The main features of the TCP

The main features of TCP can be summarized in the list below:

• Reliable data transfer: You are guaranteed a service of reliable data means that all data sent by the sender are delivered to the recipient and without errors. It can happen by mistake between links, that some package gets lost in the network. At this point, the TCP will detect this failure to receive and retransmit the lost packet to proceed (we will see in more detail how this process occurs).
• Reordering of packets correctly: This feature is extremely important for a correct understanding of the message by the destination application. In fact it may happen that packets are delayed conteneti the information within the network because of congestion, and therefore it can happen to arrive at the destination out of order. The task of the TCP is precisely to reassemble it correctly, the message and forward it to the next level.
• Flow Control: The TCP checks that a host in faster data transmission is not to overflow the receive buffer of another host slower. In fact, if the TCP implementation notices that the destination host has difficulty in reading the data in the receive buffer, lowers the frequency of transmission of the sender in order to balance the performance of the two hosts.
• Congestion Control: If the TCP realizes that there is a widespread network congestion requires the sending host to reduce the frequency of packet transmission to avoid congesting the network more.

Definition of MMS (maximum size of segment)

In order to understand the arguments of some article give now the definition of maximum size of the segment that we call MSS.

The MSS value of the parameter is determined by the value of the maximum transmission unit called the MTU or frame size to the largest sustainable link layer. Ultimately, the MSS value is chosen so that a transport-layer segment is transmitted in a single link layer frame.

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