From: rfranken@mcs213d.cs.umr.edu (Richard Brett Frankenberger)
Subject: Re: Token Ring vs. Ethernet
Date: Fri, 20 Nov 1992 23:19:11 GMT
Organization: University of Missouri - Rolla

In article <1992Nov20.191046.20897@netcom.com> seifert@netcom.com (Rich Seifert) writes:
>
>Most IBM LAN systems run NetBIOS directly on top of the Data Link. Because
>there is no Network Layer, routers are NOT possible. This is, in fact,
>the reason Source Routing exists in the first place. It is a "mini-Network"
>Layer protocol embedded into the Data Link.
>
>I strongly discourage the use of Source Routing over WANs, since the
>Explorer (route discovery) traffic is incredibly bandwidth-intensive.
>  
I agree with both of these statements; however, they are NOT indications that
EtherNet is superior.  IBM LAN Systems that run NetBIOS do so because the
applications they use require it, and they would run NetBIOS over EtherNet
also.  NetBIOS works on Ethernet or Token-Ring and does require more broadcast
traffic than other protocols, or it can be encapsulated in IPX or IP
to reduce some of that traffic.  his is true on E-Net and TR.
 
In short, yes, NetBIOS has many limitations, but that is a protocol issue, not
a network physical layer issue.
 
Also, one can have a token-ring and not use source routing.  Thus, ANY
limitations of the source-route protocol are limitations of source-routing,
not of Token-Ring.  There are some situations where source-route is the best
option, and one that is not available on ethernet.

>> On ether net, you can get between segments one of two ways.  Transparent
>> bridges or Routers.  On token-ring, you have those two options PLUS  
>> Source-Routing.  Source-Routing is just another option.  You don't have
>> to use it. 
>>
>
>In practice, it is NOT possible to use transparnet bridges in a Token
>Ring environment. First, they are not made by many manufacturers (although
>this is an implementation, not an architecvtural problem). More important,
>IBM Hosts are generally configured with multiple FEPs (3745s) connected
>to redundant backbones for high availability and load sharing. IBM 
>configures (actually, the users configure according to IBM recommendations)
>the two FEPs to have the same MAC address. This is what provides the 
>redundancy and load sharing. When a route discovery is made to the host, the
>station may be connecting to either FEP, without regard. This is the reason
>why IBM makes such widespread use of the Locally administered address
>space, rather than global addressing used by Ethernet.
>
>Transparent bridges require that all devices have unique MAC addresses,
>otherwise the table learning algorithms are unstable. This is one of
>the key invariants of the underlying LAN that Transparent bridges
>demand.
>  
There are transparent birdges for Token-Ring (I believe CrossCom, among
other companies, make them.  Not as widely available as for E-Net, of
course, but they are available).  You can transparently bridge TR except for 
the Duplicate MAC address situation you mentioned above.  
 
What does your IBM Host statement have to do with a problem with Token-Ring.
Basically, you are saying there is a problem with Token-Ring because I am
forced to use source-routeing if I want to redundantly connect FEPs.  I would
submit that there is, by that logic, an even greater problem with Ethernet
because I can't do it at all.  If IBM hosts are not being used, then there is
no problem.  If they are, you can go non-redundant and work with TR and
transparent bridging or go redundant and use source-route.  Its not as if
you can go Ethernet and have transparent bridges AND redundancy.  You can't.
 
>Rich Seifert                    Networks and Communications Consulting
>seifert@netcom.com              (408) 996-0922
>                                (408) 996-2860 FAX

     - Brett

BTW: Some company's routers now cache route-discoveries, so you can have
source-route without a bunch of route-discovery broadcasts.