lecture: protocols in detail
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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 - PowerPoint PPT PresentationTRANSCRIPT
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 __________________________