🚀 go-pugleaf

The original DIX Ethernet had a two-octet "type" field used to identify
the "Client Layer protocol" associated with the frame, and states

	"It (the type) is specified at this level because a uniform
	convention for the placement and assignment of this field
	is considered crucial if multiple higher level protocols are
	to be able to share the same Ethernet network without conflict"

The DIX Ethernet spec has now been superceded by the combination of the
IEEE 802.3 MAC (Medium Access Control) sublayer and the IEEE 802.2 LLC
(Logical Link Control) sublayer. Where is the equivalent of the old "type"
field? 
There are two fields in IEEE 802.2 which at first sight seem to fill the 
bill viz. the DSAP and SSAP (Destination and Source Service Access Point)
Address fields. I have been told by people involved with higher level
ISO protocols that they are using similar fields at the next highest level
(the Network Layer) to distinguish between (ISO) protocols and that the
DSAP and SSAP fields are not intended for this.
What about pre-ISO protocols (TCP/IP, XNS)? How much of the ISO stuff
must they sit on top of before they can co-exist? I get the feeling from 
the ISO camp that they are interested in the end-product (full standard-
isation) rather than any transition process. How are the organisations 
with heavy investment in other higher level protocols managing the 
transition? Are conventions emerging? Am I missing something?

Mail me at 
	tony%brueer@ucl-cs
or
	...mcvax!ukc!reading!brueer!tony

and I will summarise on this newsgroup.

Thanks
Tony Begg.