Chris Salter wrote:
> Subject: Re: Of e-mail and browsers
I have arbitrarily renamed the stream, as it has drifted off the
topic!
> From: Chris Salter <[log in to unmask]>
> In article <[log in to unmask]
>, dated Thu, 16 Jul 1998 at 23:25:11, Ahmad Risk wrote:
> >HTML is, of course, an interface, unlike HTTP which is a protocol.
>
> Your terminology is a little less precise than usual in this particular
> instance, Ahmad. HTML is a Markup Language and if you choose to describe
> it as an 'interface' then you can also describe Hypertext Transfer
> Protocol in similar terms.
SNIP
There is always a problem with jargon terms, in which a perfectly
good word from one topic is carried over to another, where it
acquires a different meaning.
In the context of computer networks, the words 'interface' and
'protocol' are used as jargon words. When a process running on one
system wishes to communicate with a process running on another system
to which it is connected by a network there are two quite distinct
types of communication required.
Within each of the two systems, it is necessary to move information
from the process onto the software+ hardware that effects the
connection to the physical network, and the transmission across the
network. In order to simplify the implementation, and to provide
re-usable components (ie components that can be used by other
processes), the movement within one system is sub-divided into a
number of 'layers', each dealing with someaspect of the total work.
These layers are arbitrarily described as being 'higher' or 'lower',
with the lowest of all being the one that connects to the physical
network. Between any adjacent pair of layers, there is an
'interface', which defines all meaningful communications, in either
direction, between the adjacent layers. This system of layered
sub-systems is replicated in the two intercommunicating systems.
It is a convenient fiction to think of communication across the
network as taking place between sub-processes running at the same
layer level in each of the two systems. It is a fiction because
the ACTUAL communication is down through the layers in one system,
across the physical link to the other system, and then back up to the
corresponding layer in this second system. Between the equivalently
numbered layers in each pair of communicating systems, there is a
'protocol', which defines all meaningful communications, in either
direction, between the realisations of this layer in the two systems.
I hope that helps.
Mike Wells
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