Conference 7.286::fddi

1142.0. "FDDI and Ethernet Extended LAN questions" by TOOIS1::MIRGHANE () Mon Nov 08 1993 09:41

    We are defining a large extended LAN for one of our customer.
    The project includes some 40 VAX machines, 6 DECnis, 2
    DECconcentrators.
    Some machines are directly connected to FDDI via the DECconcentrators.
    Others are only connected to Ethernet.
    Connection between Ethernet segments and FDDI backbone is done through
    DECNIS.
    The following protocols are planned to be utilized:
    	- Direct programmation under LAN driver (datalink) for multicast
    	  messages
    	- TCP-IP
    	- DECNET
    
    We would like some help on the following questions:
    
    1/Is there a way to configure the DECconcentrators so that one can back
    up automatically the other?
    Something like this
    

     ============-+====FDDI network =========-+==========
                  |                           |
           +------+---------+        +--------+--------+
           | DECconcentrator|        | DECconcentrator |
           +-------+-------++        +-+-----+---------+
                   |       |           |     |
                   |       | +---------+     |
                   |       +-+----------+    |
                   |         |          |    |
                   |         |          |    |
                  ++---------+---+   +--+----+---------+
                  |              |   |                 |
                  | VAX          |   | VAX             |
                  |              |   |                 |
                  +--------------+   +-----------------+

    2/I understand from IO users guide that FDDI connected machines and 
    Ethernet connected machines will be able to exchange multicast messages 
    using the Ethernet multicast addresses. The DECNIS bridge being
    responsible for translating frame formats from FDII to Ethernet and
    vice versa. 
    In the users guide I did not see any difference between 
    	a/ sending a message from an Ethernet machine to another Ethernet 
    	   machine
    	b/ sending a message from an Ethernet machine to an FDDI machine.
    
    Is not there any difference or precaution to take before doing this?
    
             
    3/Is it possible to know the origin of the message? (FDDI or Ethernet)
      We plan to use the FC byte in the P5 buffer of the QIO (read/write)
      for that.
      That is an FDDI machine will systematically send the FC byte with a
      value of 82 (for instance). The receiving machine will test this
      byte.
      As You know the FC byte is for priority on FDDI. Is such a use 
      valid? Is there any other method?
    
    4/Is optical bypass implemented on our DECconcentrators?
    
    Thanks very much for quick help.
    Regards.
    Soumetty.
    

    I got some hints for the 2nd question on note 465.3  that I put here.
    However it seems that on FDDI bytes are received in reverse order than
                                                        =============
    bytes over Ethernet. Is this valid? If yes does the driver deal with it
    or is it the responsibility of the application that calls the driver to
    put the bytes in the right order?.
    This is very important for us. Thanks for help.  
    
    
    -----------------------------------------------------------------------------=
Note 465.3                     multicast thru FDDI                        3 of 5
TKTVFS::IDO "Naoki Ido, CSC/TOKYO, EWB, DTN 680-245" 17 lines  13-MAR-1992 05:26
                             -< frame translation >-
    ----------------------------------------------------------------------------
Multicast addresses are transparency among LAN as long as you use the 
translation bridge, but the frame format may be different.
 
When you are using the translation bridge as DECbridge5xx/6xx,

	if system A sends Ethernet V2 frame on ethernet, it will be 
	FDDI SNAP-SAP with Zero OUI frame at system B on the FDDI ring.

	if system A uses IEEE802.2 LLC frame, it will be FDDI 802.2 LLC
	in the ring.

	if system A uses 802.2 SNAP-SAP, it will be FDDI SNAP-SAP with
	original OUI.

-Naoki

	
     

It's not an issue.  That something for the hardware of the
adapter to worry about.