You're right, LLC Type 3 doesn't appear to be in the IEEE Logical Link
Control 802.2 specification.
The IEEE 802.2 document says there are two types of operation:
"With Type 1 operation, PDUs shall be exchanged between LLCs without the
need for the establishment of a data link connection. PDUS shall not be
acknowledged, nor shall there by any flow control or error recovery."
"With Type 2 operation, a data link connection shall be established between
two LLCs prior to any exchanges of information-bearing PDUs. The normal
cycle of communication shall consist of the transfer of PDUs containing
information from the source LLC to the destination LLC, acknowledged by
PDUs in the opposite direction. With Type 2 operation, the control of
traffic between the source LLC and the destination LLC shall be effected by
means of a numbering scheme, which shall be cyclic within a modulus of
128..... etc. etc. etc."
In other words, Type 1 is connectionless and Type 2 is connection-oriented,
as we all know. Type 1 doesn't use acknowledgements. Type 2 does use
acknowledgements.
In addition, IEEE 802.2 defines two classes of LLC. A Class I LLC shall
support Type 1 operation only, whereas a Class II LLC shall support both
Type 1 and Type 2 operations.
Thanks for the info on LLC Type 3. Even though it's not in the IEEE
document, it's still informative to learn about an additional method of
communications, that is, connectionless with acknowledgements.
Study question: are there any other examples of protocols that use
acknowledgements but don't require a connection establishment? I can think
of one that we use quite regularly...
Priscilla
At 12:09 PM 12/16/00, Howard C. Berkowitz wrote:
> >Hi All,
> >
> >LLC Type 1 = Unacknowledged Connectionless = TCP/IP, IPX, OSI, NetBIOS
> >over IP/IPX etc....
> >LLC Type 2 = Connection Oriented = SNA, NetBIOS over NetBEUI
> >
> >LLC Type 3 = Acknowledged Connectionless = ???
> >
> >I can't find a specific example of a service using the Type 3 LLC.......
> >
> >Anyone help with an example where Type 3's are used?
>
>
>LLC Type 3 documentation is hard to find, because it was developed in
>a standards-oriented context beyond the IEEE. In fact, I don't think
>it ever actually became part of 802.2.
>
>LLC 3 was developed by the Manufacturing Automation Protocol industry
>group, of which the lead company was General Motors. It was designed
>for real-time process control of factory robots, using the
>Manufacturing Message Protocol at layer 7, null OSI layers 6 through
>3, LLC3 at the upper part of layer 2, and IEEE 802.4 token bus at MAC
>on down.
>
>The typical configuration would be:
>
>
> Cell controller ---|
> loaded with MMS
> command files via FTAM
> file transfer
>
> OSI FTAM -------->MMS-------->MMS-controlled robot
> OSI ASN.1 BER -
> OSI Session -
> OSI TP4 -
> OSI CLNP - -
> LLC 1 LLC3 LLC3
>
> Factory network----802.4 ----802.4---
> (local to cell)
>
>
>The stack with null layer 3-6 was called the MAP Enhanced Performance
>Architecture stack, and had sufficiently tight timing requirements
>that no form of relaying -- routing, bridging, etc., would be used
>inside the manufacturing cell. The factory network that connected
>the cell controllers, however, had full stacks (note that they ran
>LLC1 and relied on TP4 for reliable transfer). The factory network
>could contain routers and bridges.
>
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Priscilla Oppenheimer
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