Communication Protocols II Ninth Meeting TCPIP family TCPIP

Communication Protocols II Ninth Meeting

TCP/IP family

TCP/IP Protocol l IP l l l Getting messages across the network. No guarantee, (best-effort delivery service) TCP l l l 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 l e-mail § l simple mail transfer protocol (SMTP) Accessing world-wide web § hypertext transfer protocol (HTTP).

SMTP l l Exchange of e-mail messages between hosts Commands between a mail client and a mail server: l READY; l HELO; Imad@aou. com Mail Server l MAIL FROM; l OK; com. u o DY a A l RCPT TO; E 50 R 2 l DATA; HEL l START MAIL INPUT; LO a uo. co l QUIT; m Imad = 250 Server hosts indicates ‘hello from client’, givingthat clients connection has been established acknowledgement host address. from and gives address. thehost server. 250 OK

SMTP l l Exchange of e-mail messages between hosts Commands between a mail client and a mail server: l READY; l HELO; aou. com Mail Server l MAIL FROM; MImad@aou. com AIL F ROM l OK; imad @au l RCPT TO; o. com l DATA; l START MAIL INPUT; OK 0 5 2 l QUIT; RCP T TO akra Intended recipients’ e. Client is starting a mail transaction m@a uo. co mail and gives theaddresses. user’s email address. m

SMTP l l Exchange of e-mail messages between hosts Commands between a mail client and a mail server: l READY; l HELO; Imad@aou. com Mail Server l MAIL FROM; l OK; OK l RCPT TO; 250 l DATA; DAT l START MAIL INPUT; A au o. com l QUIT; client is ready to is send a message server ready to host address. receive the message. . T 25 AR T S 0 PUT N I MAIL

SMTP l l Exchange of e-mail messages between hosts Commands between a mail client and a mail server: l READY; l HELO; aou. com Mail Server l MAIL FROM; SImad@aou. com end data l OK; ends with l RCPT TO; CRL F l DATA; l START MAIL INPUT; OK 0 5 2 l QUIT; client closes CRLF (carriage returnthe line feed) = connection. end of message QUIT

Protocol concepts in TCP/IP

The TCP/IP Layers l Internet layer l l l Transport layer l l l Packet routing and avoidance of congestion The protocol used is the internet protocol (IP). 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 l Large number of high-level protocols. l l Telnet, FTP, SMTP, DNS, HTTP Host-to-network layer l l l Ethernet in local area networks, Serial link through a modem and telephone cable in wide area networks.

Packets: Data format Header l Packet are too small = Inefficient use of communication channel Header l Footer Packet are too large = Long delays and re-transmission in case of failures.

TCP Header l l l URG (urgent) ACK (valid acknowledgement number) PSH (push or handed) RST (reset the connection) SYN (synchronize for handshaking) FIN (finish sending data)

Encapsulation