Transmission Control Protocol (TCP)

Transmission Control Protocol (TCP)
TCP is the heart of the suite, providing a vast array of services, and therefore, is a complicated protocol.
TCP has gone through many revisions in the last few decades.
TCP SERVICES
Process-to-Process Communication
Stream Delivery Service
- TCP, unlike UDP, is a stream-oriented protocol.
- In UDP, a process sends messages with predefined boundaries to UDP for delivery.
- TCP allows the sending process to deliver data as a stream of bytes and allows the receiving process to
obtain data as a stream of bytes. TCP creates an environment in which the two processes seem to be
connected by an imaginary “tube” that carries their bytes across the Internet.
Sending and Receiving Buffers
Because the sending and the receiving processes may not necessarily write or read data at the
same rate, TCP needs buffers for storage. There are two buffers, One way to implement a buffer is to use a
circular array of 1-byte locations as shown in the following Figure. For simplicity, we have shown two buffers
of 20 bytes each.
2
Segments
- The IP layer, as a service provider for TCP, needs to send data in packets, not as a stream of bytes. At the transport layer, TCP groups a number of bytes together into a packet called a segment.
- segments may be received out of order, lost, or corrupted and resent. All of these are handled by the TCP sender with the receiving application process unaware of TCP’s activities.
- Note that segments are not necessarily all the same size.
Full-Duplex Communication
TCP offers full-duplex service, where data can flow in both directions at the same time. Each TCP endpoint then has its own sending and receiving buffer, and segments move in both directions.
Multiplexing and Demultiplexing
Like UDP, TCP performs multiplexing at the sender and demultiplexing at the receiver.
Connection-Oriented Service
- when a process at site A wants to send to and receive data from another process at site B, the following three phases occur:
1. The two TCPs establish a virtual connection between them.
2. Data are exchanged in both directions.
3. The connection is terminated.
- Note that this is a virtual connection, not a physical connection. The TCP segment is encapsulated in an IP datagram and can be sent out of order, or lost, or corrupted, and then resent. Each may be routed over a different path to reach the destination. There is no physical connection. TCP creates a stream-oriented environment in which it accepts the responsibility of delivering the bytes in order to the other site.
Reliable Service
TCP is a reliable transport protocol. It uses an acknowledgment mechanism to check the safe and sound arrival of data.