>Howard, I know we've had this discussion before here on groupstudy. I also
>accept that there remains a lot of confusion of OSI terminology with PC
>terminology. I.e. application on a PC versus OSI application.
>
>That said, I am looking at the Certification Zone OSI paper. (which
>version? I did one.) In it is the
>statement that the application layer provides common services to specific
>application programs, including file transfer, messaging ( not in the sense
>of e-mail messages ), directory lookups, etc. ( I have paraphrased this a
>bit, but I believe this is true to the original sentences )
One of the problems here is that OSI defines the application layer as
running on top of a presentation service. Another problem is that
the OSI application layer definition in OSI has evolved into a much
more object-oriented design. The most recent thinking split layer 7
into certain common services, such as the Application Context Service
Element and Remote Operation Service Element, with the "applications"
such as FTAM and MHS running above them as a set of objects (e.g.,
MHS MTA's, UA's, message stores, etc.). ROSE is the equivalent of
RPC.
Within the OSI protocol development community, there was the Enhanced
Performance Architecture of the Manufacturing Automation Protocol,
which ran a layer 7 messaging protocol, MMS, over null layers 6-3,
using LLC type 3 (that is not a typo) as a reliable connectionless
data link.
>
>If I have a Linux box, and on that Linux box I am running RIP and OSPF, am I
>not running user applications?
No, in the intention of the OSI Management Framework, ISO 7498-4. RIP
and OSPF themselves (well, ISIS in the OSI literature) are layer
management protocols. Their parameterization and control can be,
however, via the MIB (a concept both in CMIP and SNMP).
>Is the operation of those applications using
>services at the OSI application layer? I.e. receiving messages, sending
>messages, doing what might be arguably called "file transfers" etc. ? The
>purpose of the user applications ( as opposed to the OSI application layer )
>is to provide particular functions and distribute particular information,
>is it not?
If you get into detailed OSI documents, you will find that the "user"
protocol stack is assumed to have a user application. Layer
management, on the other hand, is seen as "self-sustaining." See both
the management annex to the reference model and the routing framework
document, as well as the ISIS standard.
>
>
>I agree that it is not the best use of time to spend countless hours
>messages arguing how many angels can dance on the head of a pin.
When I had this problem assigned in a chemistry class, we measured
the head of a pin, then assumed the extreme case of an osmium pin
(highest density element). Assuming that angels dance on the surface
of the pin only, and that angels primarily exist in a particulate
form, compute the surface electron density at the surface of the pin.
Only surface electrons are available as dance floors. If you assume
all angels can instantaneously exchange position during their dance,
the number of angels equals the number of surface electrons. If the
angels must dance to an angel-less electron, ignoring distance, the
number of angels is more like surface density/2.
Faster-than-light travel by use of a face drive is left as an
exercise for the student. It is written that a milliHelen is the unit
of face that causes the launching of one reference Greek ship.
Interpretation of the appropriate documents shows the launch event
occurs instanteously on application of face, without relativistic
constraints.
>
>But I do wonder if the code that results in a BGP table, or an OSPF database
>might by some standards be considered "user applications" which in turn use
>functions that are defined within the OSI application layer ( e.g. file
>transfer - routing updates? - notification messages - hello packets?
>LSA's? )
OSI application services are intended to be transparent to the
service data units presented to them. Layer management protocols are
consider to be specialized transfer functions, generally for
performance reasons.
>
>Yes, routing is a layer three function, but is it incorrect to say that
>there are things going on at other layers that make the layer 3 functions
>possible?
>
>Chuck
That really wasn't the intention of OSI architects.
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