>>>I'd like to understand the difference between socktype ad protocol:

>>>SOCK_STREAM is not the same as TCP and SOCKDGRAM is not the same of
>>>IPPROTO_UDP?

>>>what is the difference between socktype ad protocol?

>> That's a networking question rather than a C question; like the
>> other poster said, the unix newsgroup would be a better place for
>> the details.

>> [OT]
>> The approximate answer is that SOCK_STREAM is a class that includes
>> *any* kind of reliable transport, and SOCKDGRAM is a class that
>> includes *any* kind of transport that handles individual unreliable
>> messages.

>> For example, there are "improved" TCP-like protocols that work better
>> under particular conditions (e.g., some are optimized for high
>> bandwidth and low latency such as LAN links; some are optimized for
>> high error loss and high latency such as talking to spacecraft.)
>> These protocols are not TCP nor UDP, so they are neither IPPROTO_TCP
>> nor IPPROTO_UDP, but they are still SOCK_STREAM or SOCK_UDP.

> <OT>
> The above is not wrong, but originally sockets were intended to be used
> with a variety of protocols, not just IP.  DECnet, XNS, IPX, AppleTalk,
> OSI, VINES, etc. have various sub-protocols similar to TCP and/or UDP
> which would fit into the SOCK_STREAM, SOCK_DGRAM, or other types as well.
> A few were actually even implemented on various systems, but they've
> fallen out of use (obviously).  At the time DARPA contracted BBN to
> implement what came to be known as "BSD sockets", though, nobody had any
> clue IP would eventually obliterate all other networking protocols and so
> they created one complicated syscall that could potentially handle all
> protocols instead of needing a separate syscall for each protocol.
> </OT>