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Re: Frame Relay encap vis-a-vis point-to-point at UUNET

  • From: Vijay Gill
  • Date: Tue Sep 22 12:46:42 1998

On Mon, 21 Sep 1998, Charles Sprickman wrote:

> On Mon, 21 Sep 1998, Nathan Stratton wrote:
> 
> > Even with the new CT3 cards on the Cisco, there are still many benefits to
> > using the Cascades to aggerate T1 customers.
> 
> Please, share...
> 
> I like the CT3 card, but I'm not familiar (except as a customer) with the
> Cascade solution and its benefits beyond economics...

There are several issues regarding mechanisms for the best, most efficent
ways of accepting traffic into the network, henceforth referred to as
Connection Admission Control. There is a whole bunch of theory behind CAC,
but to simplify in this case....

Data traffic is bursty.  Most customers do not use all of their allocated
bandwidth all of the time.  Statistical multiplexing allocates bandwidth
according to demand.  Data traffic bandwidth requirements vary over time
for most connections, and utilizing this fact allows gain in efficiency.
Such a scheme assigns less than the peak bandwidth rate to connections
(i.e.  if everyone started to send the full bandwidth at all times, the
connections would start experiencing packet drops and/or delay till buffer
capacity is exceeded and the sources do not go into congestion
control/avoidance phase). However, all channels sending all data at peak
capacity at all times is fairly rare and traffic monitoring will point out
the trouble spots before they start dropping packets.

Coming back to the Cascades, they allow Statistical multiplexing of
connections, giving a cheaper overall cost and allows more connections per
unit of hub resources consumed.  This results in cost efficiencies. 

Also, they reduce wiring complexity.  For example, you take the 3 HSSI
cards and use them to connect to 3 cisco HSSI ports.  Once these
connections are tested, the only change needed to add, say, a mixture of
ChT3 cards, E1 cards, HSSI cards etc, is to stick them into the Cascade. 
This allows you to aggregate several different types of user connections
without changing anything on the routers on the back end. 

New technology will result in faster uplinks, allowing higher density
connections, eg, the current single port ChDS3 cards may be replaced by
4xChDS3 cards in newer switches.

The end result is to maximise the number of (hopefully) paying customers
per unit of hub resource consumed.

-vijay

--
Vijay Gill                         |The (paying) customer is always right.
wrath@cs.umbc.edu, vijay@umbc.edu  |                  - Piercarlo Grandi
http://www.gl.umbc.edu/~vijay      | Eagles may soar, but weasels don't get
These are my opinions only.        | sucked into jet engines.






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