TCP is a reliable, connection-oriented and byte-stream protocol. Let's look at each of the terms - reliable, connection-oriented, and byte-stream - in detail.Applications that require the transport protocol to provide reliable data delivery use the TCP because it verifies that data is delivered across the network accurately and in the proper sequence.

TCP provides reliability with the help of a mechanism called Positive Acknowledgment with Re-transmission (PAR). Simply stated, a system using PAR sends the data again, unless it hears from the remote system that the data arrived okay and the unit of data exchanged between cooperating TCP modules is called a segment (see Figure below Each segment contains a checksum that the recipient uses to verify that the data is undamaged. If the data segment is received undamaged, the receiver sends a positive acknowledgment back to the sender and if the data segment is damaged, the receiver discards it.The sending TCP module re-transmits any segment for which no positive acknowledgment has been received,after an appropriate time-out period.

Note:

The figure below shows the three way handshake process which is used by TCP.

Host A begins the connection by sending host B a segment with the "Synchronize sequence numbers" (SYN) bit set and this segment tells host B that A wishes to set up a connection, and it tells B what sequence number host A will use as a starting number for its segments. (Sequence numbers are used to keep data in the proper order.) Host B responds to A with a segment that has the "Acknowledgment" (ACK) and SYN bits set and B's segment acknowledges the receipt of A's segment, and informs A which Sequence Number host B will start with. Finally, host A sends a segment that acknowledges receipt of B's segment, and transfers the first actual data.

After this exchange, host A's TCP has positive evidence that the remote TCP is alive and ready to receive data and then as soon as the connection is established, data can be transferred. When the cooperating modules have concluded the data transfers,to close the connection they will exchange a three-way handshake with segments containing the "No more data from sender" bit (called the FIN bit). It is the end-to-end exchange of data that provides the logical connection between the two system.

TCP also helps to views the data it sends as a continuous stream of bytes, not as independent packets. Therefore, TCP takes care to maintain the sequence in which bytes are received and sent.The Acknowledgment Number and Sequence Number fields in the TCP segment header keep track of the bytes.

The TCP standard does not require that each system start numbering bytes with any specific number and each system chooses the number it will use as a starting point.Each end of the connection must know the other end's initial number to keep track of the data stream correctly. The two ends of the connection synchronize byte-numbering systems by exchanging SYN segments during the handshake and the Sequence Number field in the SYN segment contains the Initial Sequence Number (ISN), which is the starting point for the byte-numbering system. For security reasons the ISN should be the random number, though it is often 0.

Each byte of data is numbered sequentially from the ISN, so the first real byte of data sent has a sequence number of ISN+1 and the Sequence Number in the header of a data segment identifies the sequential position in the data stream of the first data byte in the segment. For example, if the first byte in the data stream was sequence number 1 (ISN=0) and 4000 bytes of data have already been transferred, then the first byte of data in the current segment is byte 4001, and the Sequence Number would be 4001 only.

The Acknowledgment Segment (ACK) performs two functions: flow control and positive acknowledgment. The acknowledgment tells the sender how much data has been received, and how much more the receiver can accept and the Acknowledgment Number is the sequence number of the next byte the receiver expects to receive.For every packet,the standard does not require an individual acknowledgment. The acknowledgment number is a positive acknowledgment of all bytes up to that number. For example, if the first byte sent was numbered 1 and 2000 bytes have been successfully received, the Acknowledgment Number would be 2001.

The Window field contains the number of bytes the remote end is able to accept or the window. If the receiver is capable of accepting 6000 more bytes, the window would be 6000 only. The window indicate to the sender that it can continue sending segments as long as the total number of bytes that it sends is smaller than the window of bytes that the receiver can accept and he receiver controls the flow of bytes from the sender by changing the size of the window. A zero window tells the sender to cease transmission until it receives the non-zero window value.

1. The Internet Protocol (IP) is a network-layer (Layer 3) protocol that contains some control information that enables packets to be routed and addressing information.



2. IP is the primary network-layer protocol in the Internet protocol suite and is documented in RFC 791.



3. Along with the Transmission Control Protocol (TCP), IP represents the heart of the Internet protocol.



4. IP has two primary responsibilities: providing connectionless, best-effort delivery of datagrams through an internetwork and providing fragmentation and reassembly of datagrams to support data links with different maximum-transmission unit (MTU) sizes.

An IP packet contains several types of information, as illustrated in the following figure:

The description for IP packet fields is given below:

1. Version: Indicates that the version of IP currently used.



2. IP Header Length (IHL):which indicates the datagram header length in 32-bit words.



3. Type-of-Service:which specifies how an upper-layer protocol would like a current datagram to be handled, and assigns datagrams various levels of importance.



4. Total Length: Specifies the length, in bytes, of the entire IP packet, including the data and header.



5. Identification:which contains an integer that identifies the current datagram. This field is used to help piece together datagram fragments.



6. Flags:which consists of a 3-bit field of which the two low-order (least-significant) bits control fragmentation. The low-order bit specifies whether the packet can be fragmented. The middle bit specifies whether the packet is the last fragment in a series of fragmented packets. The third or high-order bit is not used.



7. Fragment Offset:which indicates the position of the fragment's data relative to the beginning of the data in the original datagram, which allows the destination IP process to properly reconstruct the original datagram.



8. Time-to-Live:which maintains a counter that gradually decrements down to zero, at which point the datagram is discarded. This keeps packets from looping endlessly.



9. Protocol:which indicates which upper-layer protocol receives incoming packets after IP processing is complete.



10. Header Checksum:which helps ensure IP header integrity.



11. Source Address:which specifies the sending node.



12. Destination Address:which specifies the receiving node.



13. Options:which allows IP to support various options, such as security.



14. Data:which contains upper-layer information.