Table of ContentsIntroduction 3TCP/IP 4TCP/IP Layering 6Encapsulation and Demultiplexing 8SMTP (Simple Mail Transfer Protocol) 9Mailbox Access & POP3 12Security for SMTP 13Conclusions 15Bibliography 16IntroductionTCP/IP protocol is used by public because of the good elements of the TCP/IP. The elements of TCP/IP are scalability, flexibility, and openness which can be used by different users in any environment. TCP reliability in connection performance is required by the SMTP application so that the email sent wouldnt get lost and it makes SMTP easier in performing the job in view of the fact that SMTP dont have to provide reliability in the application code. Communication that occurs between the server and the client are done by some commands which can be understood easily.
SMTP is simple application protocol based on text, where the recipients send the text messages after they have been confirmed to send it. Most people access their email using POP3, which is an application layer standard protocol for retrieving their email from the isolated server to a local client using TCP/IP connection. The security of the text messages is the main consideration when two people or more are sending text messages to each other. There also would be some prevention against spamming which is protected by password.
1.TCP/IPTCP (Transmission Control Protocol) provide a reliable, connection-oriented, byte stream service. There are exactly two end points communicating with each other on a TCP connection, connection-oriented means the two applications that normally refer to as the client and server must establish a TCP connection with each other before any data can be exchanged.
Reliability can be achieved by actions:Application data is broken into segments with the best suitable size before sending.
The sender in a TCP connection maintains a timer every time it sends segment, and wait for the acknowledgment message (ACK) from the recipient. If the message has arrived before the timer expires, the senders software cancels the timer and continuing with other segment transfer. In the other hand, if the acknowledgement has not received in time, the delayed segment is requested for retransmitting.
TCP maintains an end-to-end checksum on its header and data whose purpose is to detect any modification or error occurred in transit. If a segment arrives with an invalid checksum, TCP discards it, acknowledge of this error, and expect the sender to retransmit.
Normally segments are transmitted as IP datagrams that each been given an individual sequence number, they may sometimes arriving out of order. TCP re-sequences the data after they arrive and pass the data in the correct order to the application.
As TCP segments are sent as IP datagrams, it discards any received data that is duplicated.
TCP provides flow control by limiting its buffer space; this prevents overflowing and data loss due to a fast sending host and a slow receiving destination host....