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Dive into the TCP/IP protocol suite, focusing on how messages traverse networks. Learn about the Internet Protocol (IP), which guarantees a best-effort delivery service, and the Transmission Control Protocol (TCP) that ensures reliable, error-free message transportation through end-to-end connectivity. We’ll explore application layer protocols like SMTP for email communication and HTTP for web access, detailing essential commands and their functions. Gain insights into the layered architecture of TCP/IP, encompassing host-to-network interactions, packet management, and protocol encapsulation.
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Communication Protocols II Ninth Meeting
TCP/IP Protocol • IP • Getting messages across the network. • No guarantee, (best-effort delivery service) • TCP • Transport layer protocol • Sits on top of IP • End-to-end connectivity • Guarantees error-free transportation of messages (reliable service) • • Application layer protocols that run on top of TCP are • e-mail • simple mail transfer protocol (SMTP) • Accessing world-wide web • hypertext transfer protocol (HTTP).
SMTP • Exchange of e-mail messages between hosts • Commands between a mail client and a mail server: • READY; • HELO; • MAIL FROM; • OK; • RCPT TO; • DATA; • START MAIL INPUT; • QUIT; Imad@aou.com aou.com Mail Server 250 READY aou.com HELLO auo.com 250 OK Imad = 250 Server hosts indicates that connection has been established and gives host address. ‘hello from client’, giving clients host address. acknowledgement from the server.
SMTP • Exchange of e-mail messages between hosts • Commands between a mail client and a mail server: • READY; • HELO; • MAIL FROM; • OK; • RCPT TO; • DATA; • START MAIL INPUT; • QUIT; Imad@aou.com aou.com Mail Server MAIL FROM imad@auo.com 250 OK Intended recipients’ e-mail addresses. Client is starting a mail transaction and gives the user’s email address. RCPT TO akram@auo.com
SMTP • Exchange of e-mail messages between hosts • Commands between a mail client and a mail server: • READY; • HELO; • MAIL FROM; • OK; • RCPT TO; • DATA; • START MAIL INPUT; • QUIT; Imad@aou.com aou.com Mail Server 250 OK DATA auo.com 250 START MAIL INPUT client is ready to send a message host address. server is ready to receive the message..
SMTP • Exchange of e-mail messages between hosts • Commands between a mail client and a mail server: • READY; • HELO; • MAIL FROM; • OK; • RCPT TO; • DATA; • START MAIL INPUT; • QUIT; Imad@aou.com aou.com Mail Server Send data ends with CRLF 250 OK QUIT client closes the connection. CRLF (carriage return line feed) = end of message
The TCP/IP Layers • Internet layer • Packet routing and avoidance of congestion • The protocol used is the internet protocol (IP). • Transport layer • End-to-end service • The protocols used are transmission control protocol (TCP) and user datagram protocol (UDP). • TCP is a connection-oriented • UDP is a connectionless (video streaming) • Application layer • Large number of high-level protocols. • Telnet, FTP, SMTP, DNS, HTTP • Host-to-network layer • Ethernet in local area networks, • Serial link through a modem and • telephone cable in wide area networks.
Packet are too large = Long delays and re-transmission in case of failures. Packet are too small = Inefficient use of communication channel Packets: Data format Header Footer Header Footer
TCP Header • URG (urgent) • ACK (valid acknowledgement number) • PSH (push or handed) • RST (reset the connection) • SYN (synchronize for handshaking) • FIN (finish sending data)
