1 / 17

File Transfer and Electronic Email in Internet

Lecturer: Maxim Podlesny Sep 29 2008 CSE 473. File Transfer and Electronic Email in Internet. File Transfer Overview. Application protocol: FTP Main parts: client host and server host Parts of interaction: client authentication and file transfer Used transport protocol: TCP. FTP Session.

alpha
Télécharger la présentation

File Transfer and Electronic Email in Internet

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecturer: Maxim Podlesny Sep 29 2008 CSE 473 File Transfer and Electronic Email in Internet

  2. File Transfer Overview • Application protocol: FTP • Main parts: client host and server host • Parts of interaction: client authentication and file transfer • Used transport protocol: TCP

  3. FTP Session • Two TCP connections (out-of-band) • Control connection employing port 21 • Data connection employing port 20 • Data transfer • One data connection per one file transfer • Control information • One control connection per FTP session • User account • Commands to change directory on server side • Commands to put and get a file from server • Keeping state information for each session

  4. Control Interaction • Client commands: • USER <name> • PASS <password> • LIST • RETR <filename> • STOR <filename> • Server reply: • 331: username OK, password required • 125: transfer starting • 425: can’t open data connection • 452: error writing file

  5. Email System Overview • Application protocol: SMTP (Simple Mail Transfer Protocol) • Main parts: • Sender side: agent, mail server • Receiver side: agent, mail server • Used transport protocol: TCP

  6. SMTP • Interaction between mail servers and sender-his mail server • Text of a mail: 7-bit ASCII • TCP connection uses 25 port • Handshaking • One connection for sending a bunch of messages between the servers

  7. Message Structure • From: <…> • To: <…> • Subject: <…> • [MIME headers] • Received: from < > by <> <time> • Inserted to a message by a SMTP receiving server • May consist of several records due to forwarding • <Body of a message>

  8. Comparison with HTTP • HTTP vs. SMTP • transferring files • persistent connections • pull vs. push protocol • any characters vs. 7-bit ASCII • one message per object vs. one message per all objects

  9. MIME • Purpose: sending content different from ASCII text • Placement: additional headers in the message • Structure: • Content-Type header • Indicates the type of non-ASCII data (video file, jpeg file, …) • Content-Transfer-Encoding header • Type of encoding used for non-ASCII data (base64, …)

  10. Mail Access Protocol • Purpose: reading email from receiver’s SMTP server • SMTP – pushing protocol • Getting email is a pulling operation • Protocols: POP3, IM AP, HTTP

  11. POP3 • TCP connection uses port 110 • Phases: • Authentication • Getting access to SMTP server • Transaction • Retrieving messages • Marking messages for deletion • Obtaining mail statistics • Update • Deleting messages • Closing a session • Download-and-keep, download-and-delete

  12. POP3 (cont.) • Authentication • user <name> • pass <password> • Transaction • list, retr, dele • Update • quit • Server response • +OK • -ERR • No support of remote folders for messages

  13. IMAP • Purpose: supporting remote folders • Features: • Maintaining user state information across sessions • Retrieving parts of messages

  14. Web-Based Email • Yahoo, Google, Gmail, … • HTTP: • sending message to client mail server • retrieving message from recipient mail server • SMTP: • interaction between mail servers

  15. DNS • Purpose: translating hostname to IP address • Architecture: distributed system • Additional functions: • Host aliasing • Mail server aliasing • Load distribution • Transport protocol: • UDP • port 53

  16. Structure • Hierarchy: • Root DNS server • Top-level domain (TLD) DNS server • Authoritative DNS server • Local DNS server • Part of DNS • Interaction between end-host and the rest of DNS • Intermediate DNS server • Interaction between TLD and authoritative server • Accelerating performance through caching

  17. DNS Record • DNS resource record: (Name, Value, Type, TTL) • Type: A, NS, CNAME, MX • Name: hostname, domain, alias hostname, alias name of a mail server • Value: IP address, hostname of authoritative DNS server, canonical hostname, canonical name of a mail server • TTL: time of keeping a record in a cache

More Related