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Communication Protocols II

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

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Communication Protocols II

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  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 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.

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

  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 250 START MAIL INPUT client is ready to send a message host address. 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 QUIT client closes the connection. CRLF (carriage return line feed) = end of message

  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. 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

  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

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