1. Communication Protocols II Ninth Meeting

2. TCP/IP family

3. 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).

4. 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 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.

5. 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 Client is starting a mail transaction and gives the user’s email address. RCPT TO akram@auo.com Intended recipients’ e- mail addresses.

6. 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 client is ready to send a message host address. 250 START MAIL INPUT server is ready to receive the message..

7. 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 CRLF (carriage return line feed) = end of message QUIT client closes the connection.

8. Protocol concepts in TCP/IP

9. 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.

10. 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

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

12. Encapsulation