Application Protocols

• Telnet
• FTP
• WWW
• SMTP
• NNTP
• IRC
• Multimedia

Telnet

• one of the first ARPAnet applications
• terminal on client:
  • must implement terminal functions, e.g. cursor positioning
  • generally blocked reading from keyboard AND socket
  • single thread: select or poll system calls
  • multiple threads
• shell on server:
  • must be able to redirect shell input and output
  • on Unix, creates a pseudo TTY

Telnet Options

• negotiated at start of connection
• toggle options: WILL, WONT, DO, DONT:
  • if I send WILL, DO is ack
  • if I send DO, WILL is ack
  • if I send WONT, I will not
  • if I send DONT, you cannot
• options:
  • terminal type
  • who echos
  • flow control
  • environment variables

FTP

• File Transfer Protocol
• the other early ARPAnet application:
  1. establish control connection
  2. loop: over control connection, negotiate which file to transfer
  3. open data connection
  4. transfer file
  5. return to "loop"
• uses connection closing to mark end of file
• file transfer modes:
  • ASCII (converts Unix "\n" to "\n\r")
  • binary (no conversion)
• ftp://host/file

WWW

• HTTP 1.0: close of connection shows end of data
• HTTP 1.1: persistent connections
• SSL: secure socket layer:
  • use public keys to negotiate a secret key
  • use secret key to encrypt data
  • need certification to trust public key (or: how do you know who you are talking to?)
• Java
• electronic commerce
• information "push"

SMTP

• Simple Mail Transfer Protocol
• keywords based:
  • From indicates beginning of message
  • "." (on a line by itself) indicates end of message
• many hosts willing to relay (forward) mail
• for security, most hosts only willing to forward within AS

NNTP

• Network News Transfer Protocol
• netnews, usenet
• broadcast somewhat similar to that in project 3:
  • "routers" (forwarding systems) keep track of articles they have already seen, refuse to forward them again
  • articles identified by posting system IP, posting system sequence number
• article expiration, cancellation
• unix clients: rn, trn, xrn
• some web browsers had (have?) ability to read usenet

IRC

• Internet Relay Chat
• similar to telnet
• chat room identified by: system IP, system-specific identifier (string)

Multimedia

• Internet telephony:
  • cheaper
  • lower quality?
• videoconferencing
• desktop: how do you do multimedia without a real-time system?
  • fast system
  • low quality
  • hardware assist
• MIME encodings: how do you know your reader will:
  • be able to decompress?
  • be able to read your format?