At 05:48 PM 2/7/02, Steven A. Ridder wrote: >What I meant was that SYN in tcp is just a bit that's flipped to 1 to one. >The bit is always there, but when it's turned "on" it means something.
Yes. (So is it bit-oriented? I would say yes, even though the term usually refers to WAN protocols) >I've >never considered it data. IP considers it data. > The get in http or open in ftp is data in the >packet that has to be added to the packet. There is no "get flag" or "open >flag" that needs to be turned on. It's a command, and when sent to an http >server, the server responds. > >Am I right? Yes, it's a command. (Of course a TCP SYN is a command too that a server responds to.) I would add that HTTP and FTP commands and replies are in an HTTP or FTP header. (They aren't part of the actual "user" data, and, in fact, FTP opens a different channel to send the data.) FTP sends commands as strings (using the Telnet protocol). There's no OPEN but there is, for example, a RETR. The client software sends those actual characters in ASCII, followed by a space or CR/LF and maybe an argument, depending on the command. HTTP requests have a request line, with a method, optionally a message header, and the message body. The method is the command, like a GET. It is sent as a string, like the FTP commands. SMTP and POP send string commands too. I asked about routing protocols too. They usually have a header that includes a fixed-length "opcode" or "type" or "command" field that identifies the purpose of the packet. The protocol specifies the valid hex values for this field and what command they represent. They aren't strings, though. And then Howard had yet more examples! I guess programmers can be as creative as they want (despite numerous technical, political, and historical constraints!) Priscilla >""Priscilla Oppenheimer"" wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > That would be like if I asked you how TCP works and you said, isn't TCP > > just data within an IP packet? Now I'm asking you to consider how > > application-layer protocols work. They have operations also. In the case >of > > HTTP, there are many commands. The question is how are the commands > > encoded? It's yet another variety (beyond bit-oriented and byte-oriented) > > that is worth considering. > > > > The data is HTML-encoded text, GIFs, etc, which isn't too interesting >(from > > our perspective). HTTP is rather interesting, however. So is FTP, > > especially since it has a tendency to break in many environments. > > > > And you didn't answer me how TCP operations, such as SYNs are encoded. > > > > Well, we've gotten off topic. I think it should be "on topic," but Cisco > > test developers don't tend to consider these issues. ;-) > > > > Priscilla > > > > > > At 03:51 PM 2/7/02, Steven A. Ridder wrote: > > >""Priscilla Oppenheimer"" wrote in message > > >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > At 03:26 PM 2/7/02, Priscilla Oppenheimer wrote: > > > > > > > > >What is TCP? How is a SYN represented in TCP? > > > > > > > > > >What is HDLC? How is a GET represented in HDLC? > > > > > > > > That was supposed to say HTTP! HTTP, FTP, SMTP, POP and probably >others, > > > > have yet another way of encoding control information. > > > > > >Isn't it all just data within the packets and not flags in a packet, like >in > > >TCP? > > > > > >It's byte-oriented > > > > but a little different. > > > > > > > > And how about routing protocols? For example, how does EIGRP encode an > > > > Update opcode? Is it different from how HTTP, FTP, etc. send control > > info? > > > > And different from TCP? > > > > > > > > > > > > >What is FTP? How is a RETR represented in FTP? > > > > > > > > > >And how about Token Ring with its starting delimiter and ending > > >delimiters? > > > > >And how should one interpret the Ethernet preamble? > > > > > > > > > >Also, aren't all protocols at some level processed a bit at a time? > > > > > > > > > >This is bad as the 7-layer discussions! ;-) > > > > > > > > > >Priscilla > > > > > > > > > > > > ________________________ > > > > > > > > Priscilla Oppenheimer > > > > http://www.priscilla.com > > ________________________ > > > > Priscilla Oppenheimer > > http://www.priscilla.com ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=34801&t=34629 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
