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i have aproblem in my ip phones in my company which is
internal call between ip phones is ok
but
outgoing calls cannot be done the mos of time
what happen exactly in unknown time the outgoing calls became down and no client could make an outgoing call untill the administrator go to the voice gateway cisco router 2851 and unplug the isdn cable then plug it again after that the system starts to operate and after a period of time the system goes down again and so on
please i want any help because i am near from losing my job
the sytem tepology is as follow

ip phones connected to 2 cisco switches and one switch is connected to to the cisco gateway and this cisco gateway2851 is connected to the isdn cable which come from telecom company
there is another path for data which is
optical fiper conncted to another cisco router 3500 and this router is connected to a firewall through a switch
and this switch is connected to the first cisco switch

in the configuration of the router 2851 ther is a static route path to fiper cable at 3500 router but there is no direct connection between them
only the path is through the first cisco switch then to fire wall then to 3500 router
and the pvstp is enabled on the first 2 switches

so my imagination is there is aloop cause the pvstp to break down the voice call and the data vlan operate

but i am not sure

what the most possible reasons causes this problem???

please give me your imagination

check scott morris replay on your post; i think it can lead to the problem or give you a good understanding on where to look next.

I send it to you in the private..