Nortel BCN with ATM OC3 can't use more than 20 VCI's

[dsullinger]

We have two ATM circuits that are connected to two seperate Nortel (Bay Networks) BCN routers. The routers are running v13.20 code. The circuits are ATM OC3 to the cloud. One cloud is AT&T, the other is Qwest. The ATM is then converted to Frame Relay and Frame is ran to Nortel ARN routers running v13.20 code. We are using PVCs, not SVCs. The SCR is set to a non-zero value for the VCs.

When we try and place more than 20 VCIs on either of the circuits, they will not come up. They show up as down when viewing the VCIs, yet the other 20 come up just fine. We have worked with both AT&T and Qwest with this, and they can't find anything wrong with their settings within the switch framework.

Thoughts?

 

[sschnei]

AH, I remember those days very well.
More than likeley what you have done is exceeded the PCR (peak cell rate) value of your OC3, because you have not changed your PCR value from the default value the router installed. Configure your PCR and SCR (sustained cell rate) values using the following formula. PCR = remote port speed divided by 8 divded by 53. i.e. If your remote port is a 128kb circuit, then the calculation is 128000(bits) divided by 8 = 16000(bytes)divided by 53(atm cell size in bytes)= 301.88 (use 302 as your PCR) SCR = Frame relay CIR divided by 8 divided by 53. On your AT&T side they allow you to burst to your port speed without any degregation so for ease of configuring use SCR as 1/2 of the PCR.

 

[rainman]

This may not be correct but something to consider:

Each interface on an ATM switch has a "Max VCI bits" you need to configure to set what VPI's / VCI's you allow on each interface. Is it possible that you have the "max VCI bits" set too low and the interface is not allowing those VC's?


-Rainman