Subj : Re: network programming in c To : comp.programming From : mwojcik Date : Tue Oct 11 2005 09:46 pm In article <1128953763.182164.254560@g47g2000cwa.googlegroups.com>, "dajava" writes: > makc.the.great@gmail.com wrote: > > > > telnet protocol and others found in "services" file are more like a > > "language" that you speak in over tcp/ip. perhaps, your programmer was > > saying he uses his own "language". Or, to put it another way, Telnet is an application-level (or perhaps presentation-level) protocol, which sits on top of a session-level protocol such as TCP. All communications protocols are "languages" in this sense - they define a vocabulary (message elements) and a grammar (message structures and rules for using them). > "Two key types of application-layer implementations are TCP/IP > applications and OSI applications. TCP/IP applications are protocols, > such as Telnet, File Transfer Protocol (FTP), and Simple Mail Transfer > Protocol (SMTP), that exist in the Internet Protocol suite. OSI > applications are protocols, such as File Transfer Access Management > (FTAM), Virtual Terminal Protocol (VTP), and Common Management > Information Protocol (CMIP), that exist in the OSI suite." That's fairly accurate, except that calling OSI implementations "key" is debatable. While OSI has some currency as a model of data communications, it lost the implementation war to TCP/IP. TCP/IP is nearly the only game in town for general-purpose application networking these days; the various alternatives (OSI, IBM's SNA, assorted protocols developed for PCs, etc) continue to lose ground to it. > I studied "Open Systems Interconnect (OSI) 7-layer model defined by the > International Standards Organization (ISO)." more than 15 years ago. > > It seems that tcp/ip is a different technology I have never studied. TCP/IP doesn't fit the OSI 7-layer model particularly well, but it has a relatively straightforward layered design that's quite easy to understand. There are ample sources for studying it. Uri Raz's TCP/IP Resources List[1] is a good place to start. Basically, IP is a transport-layer protocol; TCP is a session-layer protocol; and Telnet, FTP, HTTP, etc occupy something like a combination of the OSI presentation and application layers. I say "something like" because HTTP, for example, is often used to convey application content directly (eg when serving a web page), but it's also often used to transport a higher-level application protocol (eg SOAP). Other aspects of TCP/IP are harder to fit into the OSI model (the usual example is ICMP, which is "over" IP in the implementation but performs some "lower-level" functions). This has been discussed extensively (perhaps excessively) in places like comp.protocols.tcp-ip. 1. http://www.private.org.il/tcpip_rl.html -- Michael Wojcik michael.wojcik@microfocus.com Therefore, it is possible to enjoy further by using under the Netscape 2.0. However, Netscape will hangup at sometimes. You should give it up. -- roro .