Cell Relay Archive

[Afroz Lateef <afroz.lateef@fnc.fujitsu.com>]

Anouch,

In this case, the CAC should have been run on the output port of the
unit that is connected to the I-port of the switch. Since this is a CPE
and cannot have CAC implemented on it, there is no service affecting
problem.
Because, traffic cannot exceed more than the link capacity. So in TX
side, there is no traffic loss.

Afroz Lateef

anouch gharagozlou wrote:

> 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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