Lecture:

Protocols in Detail

PROTOCOLS

file: local file access telnet: login remotely ftp: transfer files http: access web pages

mailto: (send email)

telnet: the client-server model

Client (you)

vs

Server (_____________)

What happens when you say telnet

grove.ufl.edu

Telnet looks up grove’s internet address

You and grove are now considered NVTs

(network virtual terminals)

Terminal Emulation

Needed because you and the server may have different ____________

A safe choice when you’re asked: VT-100 (vt=virtual terminal)

While you’re dialed up

You and grove have virtual

“Keyboards” to send data from one nvt to the other

AND “ Printers” to receive incoming info and display it on the screen

Transmitting TextYour typed text accumulates in a buffer

until it’s signaled to be transmitted (enter or line break)

It goes to the host with telnet commands as to how the other nvt should handle it.

There may be an apparent delay due to packet-switching.

ftp (file transfer protocol)

A permanent procedure that:

uploads (from your local drive to a remote computer)

downloads (from __________to

____________)

ftp Continued

ftp programs use either: 1. words (____ and ____) or 2. click and drag (example: _______)

Two Types of Links Used by ftp

1. command link passes instructions ex: changing directories

2. data link sends files closes automatically when finished

Two transmission formats

1. ASCII sends text files but

alters commands like CR

2. Binary sends files unaltered

HTTP (hypertext transfer protocol)

Transports text (HTML) documents

An Example

http uses

www.cise.ufl.edu/class/cgs3066sp07/syllabus.html

To send the text file “syllabus” to the cache memory of my browser

What’s “cache”?

stores most often-used things (commands or files) so they’re accessible quickly

Two Types of Cache

- Browser Cache (this is what html is using)

- Processor Cache

Browser Cache

- keeps pages, graphics, sounds, and URLs of online places you’ve visited recently

- stored on your hard drive -- for instanceC:\program files\netscape\users\lola\cache

For Privacy, empty cache periodically

sequence using IE:

View (version 4.0) or Tools (version 5.0) Internet Options. General

Temporary Internet Files Delete Files.

History Clear History.

OK

Sequence Using Netscape

Edit (on the tool bar)

Preferences. Advanced expand by clicking + Cache

Clear Memory Cache

Clear Disk Cache. OK

Processor Cache

stores most often used commands so that the processor doesn't have to wait for the (slower) hard drive to get them

More about Processor Cache

- aka high-speed Static RAM (SRAM) operates between CPU and main memory

2 levels L1 built into the processor chip itself –very

small L2 chip(s) external to the processor

Web Pages

An html file is not the same as a web page!

It becomes a web page only when it’s ________________________________

____ (like IE or Netscape).

Public Directories

- For your web page to be accessed by anyone else, it must be on a web server

- and in a public folder within the your root directory

How Public Directories Work

the server gets an http request

it looks for whatever the webmaster decided the public directory should be called

example: public_html

Index Files

-A non-specific request to public_html activates the file named (usually) “index”

- So most main web pages are called index.html

- the index convention applies to subdirectories too

More about Index Files

If there is no index file in your public_html

_______________________________________________

A Final Word on http

- Clicking a link is the same as typing its _______ in the window above

- You don’t have to click on a link to see the url– you can just __________________________