[OLUG] WAN/Frame Relay questions

[W. Mark Hagler]

The number of frame relay switches in the middle is of no concern to
you.  The network manages itself, and your PVC's just magically work.

You've got UNI's, NNI's, PVC's, and DLCI's.  The UNI is the User to
Network Interface, and this is the physical circuit that connects the
customer-premise equipment into a port on the frame relay switch.   The
switch is connected to other switches with other circuits, called NNI's,
or Network to Network Interfaces.  The switches will form VC's, or
Virtual Circuits.  A VC that is pre-defined in the switch is called a
PVC.  You can do other stuff like SVC's, or Switched Virtual Circuits,
for other applications.  The VC's are identified by the network with a
DLCI, or Data Link Connection Identifier.  Each endpoint of the PVC is
assigned a DLCI number by the service provider, and you configure your
router with the local and remote DLCI information, and the frame relay
network will figure out the routing internally by the DLCI numbers.

I haven't done network engineering for a while, and this may have
changed, but last I knew you could only put 255 subinterfaces on a
physical port on a Cisco router.  If you're planning on running a
"couple hundred" PVC's I hope you intend to put them on several access
channels.  You can also use virtual templates to overcome the 256
subinterface limit, but things get pretty complicated when you start
doign that.

There's lots of good information on frame relay and related technologies
on the web  at http://www.frforum.com/.

"Williams, John W." wrote:
> 
> I realize this is a little off the Linux topic but thought some of you
> networking guru's might be able to answer a couple questions for me.
> 
> 1st Question:  If a business wanted to set up a couple hundred PVC's over
> public frame relay would there be a single frame relay switch used or a
> number of frame relay switches?  I am under the impression there are a
> number of frame relay switches used which leads me to my second question.
> 
> 2nd Question:  How is the source and destination router identification
> maintained between frame relay switches?  Is there a different type of
> encapsulation used between frame relay switches?
> 
> Any help or links where I might be able to find information on this would be
> appreciated.  Thanks.
> 
> John Williams
> 
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