Cell Relay Archive

[anouch gharagozlou <anouch_c@yahoo.com>]

Hi,

Call/Connection Admition control (CAC)in a cell relay
switch is always acting on the ouput port. But what
happens if the input port is out of capacity and that
is not checked?

Suppose a user connect to the input port (I-port) of a
switch and wants a connection with another user
located just behind the output port (O-port)of the
same switch.

Assume I-port speed is 45Mbps and O-port speed is
155Mbps.
The user asks for a 100Mbps connection. The CAC checks
if the O-port has enough bandwidth left and if it's ok
the connection is established (if no other connection
is using the O-port, 100Mbps being < 155Mbps, the call
succeeds).
But the user will never be able to send at 100Mbps
since the I-port where it is connected has a speed of
45Mbps. The CAC doesn't check that and the
provisioning succeeds while the user isn't aware of
the configuration problem.

This actually happens on a Nortel 7k/15k Passport but
may also happens on other switches. And it is more
problematic when dealing with asymetrical (e.g. ADSL)
connections.

Is this a bug, or the CAC should never checks the
input port for incoming traffic?
In the latter case what is the solution?

Thanks
Anouch

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