Re: Idea For Group Project.

[Bruce Smith <bruce@xxxxxxxxxxx>]

> >>Not very legal. There is something in the license agreement about prohibiting
> >>people from reverse-engineering the protocol.  
> >I guessed as much. Stupid capitalist software companies :)
> Scott, you're starting to sound like my Russian buddies! :)
> Mat, what license? I didn't agree to no steenkin' licence! AFAIK, I can
> reverse-engineer anything I want! What's illegal about that?
> Nowe, if I had aggreed, it's a different story....

I'm not a laywer, but AFAIK it's probably not illegal to write the 
program, or even give the program away.  But . . .

Is it legal to use the program to save copyrighted audio clips?
(I really don't know, that's why I'm asking.)

> >>Also, technically, it would be VERY
> >>difficult to do with multicast UDP packets...that dosen't mean it wouldn't 
> >>be fun to try :-)  I might just bust out the sniffer after finals are over...
> >Ohh, i didnt realize it was UDP, thats rough. This is starting to look
> >well beyond anything i want to try to tackle.
> Why?

I can tell you why programming UDP is tougher than TCP.
I don't know if it answers your question, but here it is anyway.

With TCP the network protocol guarantees the all packets will be 
received correctly in the same order they were sent (without dups).

With UDP the packets are not guaranteed to arrive in the same
order they were sent, they could arrive in a random order.
In fact, they are not guaranteed to arrive at all!  Or even
duplicate packets may arrive!  No error checking!  It is much 
tougher to write the network program because all error checking, 
data reconstruction, and retransmission requests, must be programmed 
manually.  (all handled transparent to the program by TCP)

Because UDP has less network overhead, it's is a faster protocol.
That's why software that needs to maximize speed uses UDP.  NFS, 
until recently, was strictly UDP (some new versions have TCP options).

And RealAudio uses UDP because of the modem bandwidth limitations.
If you lose a UDP packet or two with audio, it is not that critical.
Newer versions of RealAudio have the option to use TCP, but they warn
you there may be pauses because of the slowness of the TCP protocol.
The reason for the TCP option is because some packet filtering firewalls 
will allow TCP (ack bit set) through, but will not allow any UDP through 
it (because there isn't an ack/established bit in the UDP packet header).

> >>>failing using it as a group project, would anyone want to point me to some
> >>>place where i can get information on how to use sockets in linux? 
> >> Stevens, UNIX Network Programming Volume 1.  .....
> What do you (fellow) bookworms think of "UNIX System V Network Programming"
> by Stephen A. Rago (Addison-Wellesley, 1993) ??

I have "Unix Network Programming" by W. Richard Stevens (Prentice Hall).
It seems like a good book to me, but I really don't have anything to 
compare it with, so I'm not sure I'm qualified to give it a review.

Speaking of books, for people who don't want to write programs, but want
to learn more about TCP/IP networking.  Things like TCP, UDP, ICMP, ack 
bits, ports, sockets, proxies, internet services, and internet protocols.
I HIGHLY recommend (you may not guess it by the name of the book):

Building Internet Firewalls by D. Brent Chapman and Elizabeth D. Zwicky
(OReilly & Associates, Inc.) ISBN 1-56592-124-0.

IMHO this book is far superior to any firewall book I've seen because
it explains how underlying network services work, with pictures!
It shows how services communicate over the network.  Services such as:
SMTP, POP, FTP, FTP-PASV, TFTP, FSP, UUCP, Telnet, rsh/rexec/rlogin, NNTP, 
WWW, Gopher, finger, WAIS, Archie, talk, IRC, MBONE, DNS, syslog, SNMP, RIP, 
ping, traceroute, NTP, NFS, NIS/YP, X11, & lpr/lp.  (just to mention a few ;) 
A lot can be learned from this book, over and above firewalls.

--------------------------------------------
Bruce Smith                bruce@armintl.com
System Administrator / Network Administrator
Armstrong International, Inc.
Three Rivers, Michigan  49093  USA
http://www.armstrong-intl.com/
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