cam@SATURN.ACC.COM (Chris Markle acc_gnsc) (05/31/89)
Folks, (Apologies to those of you who had to read this twice; 1st shot went to "ibmnets" instead of the correct "ibm-nets".) A recent article in MIS Week describes an "agreement" between IBM and Ungermann-Bass (UB), 3Com, and Western Digital (WD) to have the three vendors comply with the NDIS (Network Driver Interface Specification) such that OS/2 EE Version 1.2 will support Ethernet adapters from those vendors. The article goes on to mention how the OS/2 EE version of NDIS allows SNA and NetBIOS to operate over an Ethernet LAN. I was curious as to what "allows SNA to operate over an Ethernet LAN" really means. Any thoughts? One thing that bothers me is that SNA presumes that the data link is "reliable" (ie. SDLC, token ring using LLC type 2 operation, and the 370 channel). The "LLC" used with Ethernet is usually type 1 with no link-level acknowledgments, flow control, or error recovery. For SNA to operate over such a "LLC" would require the equivalent of a transport protocol to be used between SNA and the Ethernet link-level. A type 2 "LLC" with reliable characteristics could be used over Ethernet and then SNA run over that. Is this what people are doing or intend to do? (I use "LLC" to represent "an" LLC versus "the" IEEE 802.2 LLC.) Another question is how address resolution is (or will be) accomplished? Send replies to me or to everywhere; it doesn't matter as I read both and will summarize if I get anything worth summarizing. Chris Markle - ACC
jas@proteon.com ("John A. Shriver") (05/31/89)
When you run SNA over Ethernet (or IBM Token-Ring, a/k/a 802.5), you use 802.2 class 2 LLC. Virtual circuits. They plug in where SLDC fits in the normal SNA stack. Uses SAP's 04, 08, and 0C. Address translation? Haven't you ever seen somebody do an NCP gen? You have to configure all the MAC addresses into all the routing nodes in the SNA network, along with all the possible routes, and their costs. (That's right, if someone replaces an Ethernet or Token-Ring board in a PC, the network manager has to do NCP gens.) There is nothing dynamic in present-day SNA. Maybe in the future LEN version of SNA. But that's OK, all of IBM protocol stacks for the PC use 802.2 class 2. NETBIOS and SNA both do. Why do you think they are stuck doing bridging? An SNA router is rather pricey (a 3725 is two bays, and easily over $100K.) Thus, their NDIS driver will probably include access to 802.2 class 2. Of course, if it's not in board microcode like Token-Ring has, it will run a lot slower on Ethernet. Of course, the only "mainframe" that speaks SNA over Ethernet is still the 9370. (What purpose is there for SNA except to speak to a mainframe?) All of the others only speak SNA over Token-Ring (and SLDC) via 3174 or 3725/3745.