Communication Protocols II Ninth Meeting

TCP/IP family

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  simple mail transfer protocol (SMTP) Accessing world-wide web  hypertext transfer protocol (HTTP).

SMTP Exchange of messages between hosts Commands between a mail client and a mail server: READY; HELO; MAIL FROM; OK; RCPT TO; DATA; START MAIL INPUT; QUIT; aou.com Mail Server Server hosts indicates that connection has been established and gives host address. 250 READY aou.com Imad = 250 HELLO auo.com ‘hello from client’, giving clients host address. 250 OK acknowledgement from the server.

SMTP Exchange of messages between hosts Commands between a mail client and a mail server: READY; HELO; MAIL FROM; OK; RCPT TO; DATA; START MAIL INPUT; QUIT; aou.com Mail Server MAIL FROM 250 OK Client is starting a mail transaction and gives the user’s address. RCPT TO Intended recipients’ e- mail addresses.

SMTP Exchange of messages between hosts Commands between a mail client and a mail server: READY; HELO; MAIL FROM; OK; RCPT TO; DATA; START MAIL INPUT; QUIT; aou.com Mail Server 250 OK DATA auo.com client is ready to send a message host address. 250 START MAIL INPUT server is ready to receive the message..

SMTP Exchange of messages between hosts Commands between a mail client and a mail server: READY; HELO; MAIL FROM; OK; RCPT TO; DATA; START MAIL INPUT; QUIT; aou.com Mail Server Send data ends with CRLF 250 OK CRLF (carriage return line feed) = end of message QUIT client closes the connection.

Protocol concepts in TCP/IP

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.

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

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

Encapsulation