Re: Is HTTP an Async Protocol
Thanks for the clarification Bruce. I suppose it's a matter of how one
interprets the question, and/or the definition of "HTTP" in the context of
the question. If you say that HTTP is 3 layers, which is true in one sense,
you are including the network and transport layer, which are not
HTTP-specific. TCP/IP and IP are used by many protocols. As the poster was
asking specifically about HTTP, I made an assumption which may or may not
have been correct about what he was asking. However, after your
clarification, I'm sure he has all the information he needs.
--
HTH,
Kevin Spencer
Microsoft MVP
..Net Developer
Who is Mighty Abbott?
A twin turret scalawag.
"Bruce Barker" <brubar_nospamplease_@xxxxxxxxxx> wrote in message
news:O8RR9osJGHA.2212@xxxxxxxxxxxxxxxxxxxxxxx
> you are not quite correct. TCP/IP is an asynchronous protocol (like most
> network protocols). .net api webclient give a sync and async interface to
> the protocol, which may confuse you.
>
> the difference between a synchronous and asynchronous protocol is in
> timing. a synchronous protocol (like an atm switch uses), has standard
> time slices, and packets are guaranteed to be delivered in that timeslice.
>
> HTTP is actually 3 layers
>
> network layer (IP)
> transport layer (TCP/IP)
> session layer (HTTP)
>
> IP is a an asynchronous datagram layer
> TCP/IP is an asynchronous reliable delivery layer, the sender get
> acknowledgement that each packet was received, and the receiver get
> packets delivered in transmit order.
>
> HTTP is a session layer. it is a simple send request, receive a response
> protocol. when the client sends the request, it has no idea of how long
> the response will take.
>
> when a library supplies an api to a network protocol, it can supply a
> blocking or nonblocking api. this is commonly referred to as synchronous /
> asynchronous (but this is not strickly true, most operating systems run
> all code asynchronously, as any real-time programmer will tell you). when
> in blocking mode it looks synchronous, because the next statement will not
> run until the network request completes, while in nonblocking mode you do
> not which code statement will be executing when the request completes.
>
> with a nonblocking api there are two approaches, one where your code polls
> for a completion status (unix i/o approach), and a asynchronous trap
> mode, where a completion routine (delegate in .net terms) is called when
> the request completes.
>
> this is all different then using a seperate thread for calling a blocking
> api.
>
>
> -- bruce (sqlwork.com)
>
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> "Kevin Spencer" <kevin@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
> news:%23NmQTOmJGHA.1028@xxxxxxxxxxxxxxxxxxxxxxx
>>> Simple question (although I guess with a complicated answer). Is HTTP
>>> an async protocol?
>>
>> Short answer, no.
>>
>> Long answer: HTTP is a protocol. "asynch" is not relevant to protocols.
>> "asynch" (ansynchronous) is a term related to programming. It is a
>> reference to how a program performs certain types of operations. In a
>> single-threaded program, the program cannot execute more than one
>> instruction at a time, as a single thread cannot execute more than one
>> instruction at a time. Therefore, any instruction which takes a certain
>> amount of time to execute will "block" the execution of the thread until
>> it is completed. In a multio-threaded program, you have the option of
>> performing operations "asynchronously" (that is, independently of each
>> other, wthout having to wait).
>>
>> A protocol is a standard for communication. Network protocols almost
>> entirely work in the same way that humans communicate. That is, a
>> computer sends a message to another computer, and the other computer
>> responds to that message. Since there are any number of reasons why a
>> response might be delayed, or even not occur, network applications
>> generally use asynchronous threads to communicate with other network
>> resources. This way, the program can create a thread to do the
>> communication, and continue with other work. When the communication
>> thread receives a response, or times out waiting for one, it can notify
>> the application, via an event or callback, which can then react to the
>> response.
>>
>> The HTTP protocol is a networking protocol. It defines a set of standards
>> for applications to communicate on a TCP network. This set of standards
>> is based upon a client-server Request/Response exchange. The client makes
>> an HTTP request of the HTTP server, which then responds with an HTTP
>> response. These requests and responses are at least partially in the form
>> of text, although binary data can accompany the message. The protocol
>> itself, however, is pure text.
>>
>> For a quick and easy "crash course" on HTTP, see:
>>
>> http://www.jmarshall.com/easy/http/
>>
>> --
>> HTH,
>>
>> Kevin Spencer
>> Microsoft MVP
>> .Net Developer
>> Who is Mighty Abbott?
>> A twin turret scalawag.
>>
>> "Bob Badger" <sjdavies47@xxxxxxxxxxx> wrote in message
>> news:1138706228.376283.240430@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>> Hi,
>>>
>>> Simple question (although I guess with a complicated answer). Is HTTP
>>> an async protocol? For instance, if I send a message to a c#
>>> webservice via http what is the protocol actually doing?
>>>
>>> Thanks in advance
>>> Steffan
>>>
>>
>>
>
>
.
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