dfh@ecsvax.UUCP (David Hinnant) (05/20/85)
I'm a little confused by the use of the term "ISO Transport Class 4 protocol".
Just what is meant by "Class 4"? Is that really layer 4? Does the ISO
layer 4 protocol have a nice acronym like DoD's TCP?
David Hinnant
SCI Systems, Inc.
...!{akgua,decvax}mcnc!ecsvax!dfh
or ...!{akgua,decvax}mcnc!rti-sel!scirtp!dfhmccallum@opus.UUCP (Doug McCallum) (05/24/85)
> I'm a little confused by the use of the term "ISO Transport Class 4 protocol". > Just what is meant by "Class 4"? Is that really layer 4? Does the ISO > layer 4 protocol have a nice acronym like DoD's TCP? > > David Hinnant > SCI Systems, Inc. > ...!{akgua,decvax}mcnc!ecsvax!dfh > or ...!{akgua,decvax}mcnc!rti-sel!scirtp!dfh ISO Transport Class 4 is a particular version of the ISO transport layer. There are currently 5 classes of transport: Class 0: Simple Class This is a minimum functionality class which provides the minimum functions for connection and data transport. It assumes a fairly reliable network with acceptable error rates. Class 1: Basic Error Recovery Class This class provides a basic transport connection with minimal overhead. It also assumes a reliable network but can recover from disconnects or resets. Class 2: Multiplexing Class This class allows multiplexing multiple transport connections onto a single network connection. It assumes the same type of network as Class 0. Class 3: Error Recover and Multiplexing Class Same as Class 2 but recovers from errors indicated by the network layer. This assumes a network of the same type as Class 1. Class 4: Error Detection and Recovery Class This is the class that deals with detecting errors as well as recovering. It assumes the worst case about the network. Similar to TCP in this respect. There is a lot more detail that I've left out, but this covers the basics. ISO DIS (Draft International Standard) 8073 describes these classes more fully. On the ARPANET, RFC 905 is a version of DIS 8073. Doug McCallum NBI, Inc. {allegra, ucbvax, ut-sally}!nbires!mccallum
dan@haddock.UUCP (05/27/85)
I attended a lecture on this subject a while back. As I recall, the term "ISO Transport Class 4 protocol" does refer to a TCP-like protocol. The different classes of transport layer make different assumptions about the reliability, etc. of the lower layer, and may also provide slightly different services to the next layer up. The American member(s) of ISO pushed for a TCP-like transport layer, with much resistance from the rest of ISO, and the different classes of transport layer were the result. Class 0 is a null layer; it assumes that the layer underneath Transport provides reliable, error-free transmission. The other classes assume different kinds of potential failure of the lower layer. Dan Franklin
larry@anasazi.UUCP (Larry Rodis) (05/28/85)
> I'm a little confused by the use of the term "ISO Transport Class 4 protocol". > Just what is meant by "Class 4"? Is that really layer 4? Does the ISO > layer 4 protocol have a nice acronym like DoD's TCP? > > David Hinnant There are four different classes to the Transport layer(layer 4). Class 4 has the most features of any of the classes and class zero the least. -- Larry Rodis UUCP: {decvax|ihnp4|hao}!noao!terak!anasazi!larry ucbvax!arizona!asuvax!anasazi!larry PHONE: +1 (602)275-0302
larry@anasazi.UUCP (Larry Rodis) (05/28/85)
> > There is a lot more detail that I've left out, but this covers the > basics. ISO DIS (Draft International Standard) 8073 describes these > classes more fully. On the ARPANET, RFC 905 is a version of DIS 8073. The ISO standard is now Recommendation X.224 -- Larry Rodis UUCP: {decvax|ihnp4|hao}!noao!terak!anasazi!larry ucbvax!arizona!asuvax!anasazi!larry PHONE: +1 (602)275-0302
mgh@mtunh.UUCP (Marcus Hand) (05/29/85)
>Just what is meant by ... "ISO Transport Class 4 Protocol"
The classes refer to reliability of transport service provided by the
transport provider which implements the transport layer. Gulp.
They range from class 1 which is "no error detection, no flow control"
to class 5 "flow control, error detection with error correction".
Class 2 is essentially what you would use for a datagram service,
while you would use 4 or 5 for virtual circuit service.
If you're really interested in the ISO OSI-RM you should check out
one of the back issues of the IEEE magazine -- one of them was a special
issue devoted to it. (I think we are talking of the Transactions of IEEE)
Finally, the calsses may be numbered 0-4 and not 1-5 (I forget).
--
Marcus Hand (mtunh!mgh)kjchapman@wateng.UUCP (Kevin J. Chapman) (05/29/85)
The special issue on OSI protocols to which you referred
was the December 1983 issue of the Proceedings of the IEEE
(vol71,no12). There is an article on page 1394 entitled
"The Transport Layer Standardization".
Kevin
P.S. Yes, the classes are numbered 0-4.
--
Kevin Chapman
Computer Communications Networks Group
Waterversity of Uniloo
'Loo, Ont., Canada