Subject: Scalability of DLSW

From: "Shannon Nix" <[email-masked]>
Date: Thu, 15 Jul 93 10:02:17 EST

How practical is the concept of requiring a persistent connection between 
all Data-Link-Switches?

Lets consider a large network with a central application mainframe.  Lets 
assume that there are DLSW routers at a hundred different locations which 
are adjacent to stations which wish to reach applications on that 
mainframe. If all DLSW implementations were configured in a full mesh 
configuration (we'll assume for now this is practical for the user to 
administer),  then the router adjacent to the mainframe must 
support 200 persistent TCP connections.  Perhaps I'll show my ignorance of 
TCP implementations by asking this - but does this seem practical?

Another alternative would be to segment the network into a number of DLSW 
sub-clouds sharing one or more common LAN segments.  This however requires 
that much of the traffic now be switched through three or more DLSW 
implementations.  In effect, you have now layed a static, virtual circuit 
topology on top of a dynamic packet switching topology.  Results are:

1)  Non-optimal Routes
2)  Increased switching latency
3)  Increased chance of circuit failure

It would seem more scalable if:

1)  Explorations were propagated using a broadcast or spanning tree 
    facility.
2)  ICANREACH returns the IP (or other) address of the dest boundary DLSW.
3)  A single, on-demand connection is brought up between the two     
    boundary DLSWs ( when one or more sessions are active between the two)

Just wondering,
Shannon
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