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New Member

isdn bchan-number-order ascending round-robin is applied but not working

isdn bchan-number-order ascending round-robin is applied but not working

ios c3825-spservicesk9-mz.124-21.bin

relevant config


controller E1 0/3/0
 framing NO-CRC4
 pri-group timeslots 1-31


interface Serial0/3/0:15
 no ip address
 encapsulation hdlc
 no logging event link-status
 no snmp trap link-status
 isdn switch-type primary-net5
 isdn overlap-receiving
 isdn incoming-voice voice
 isdn bchan-number-order ascending round-robin
 trunk-group 1
 no cdp enable

my problem is this:-

At the moment calls are leaving on the first available channel of my h323 voice gateway PRI, I can apply this command to the interface fine but it makes no difference the b cannels are always being picked on a first come  first served basis . I have also tried combination "isdn bchan-number-order decending" and "isdn bchan-number-order descending round-robin" but it makes no difference , the first b channel is always selected .

Any ideas , if you think its a bug can u identify the bug id as I cannot find it .

Everyone's tags (1)

Hello I can see that you use


 I can see that you use ascending , that why you hit 1st channel.You have to choose one of these commands ascending or descending

I have a question here , for your incoming calls which channel hits ?.FYI isdn bchan-number-order descending is enable by default , so if you need to change you have to type ascending. Can you just share incoming calls which channel hits?.This is because before you define your outgoing calls , you have to check your service provider channel used, and this to avoid error channel is not available.

Router(config-if)# isdn bchan-number-order {ascending | descending}

Enables B channel selection for outgoing calls on a PRI interface (optional).



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New Member

thanks for the reply  but

thanks for the reply  but without this command it selects the order 1-31 , with the order in any combination it still selects ch1 if free every time  ie ascending/ descending , not applied  or round robin

the i/c calls from the telco come in in the order 31-1


my aim is really to apply bchan-number-order ascending round-robin so in theory if all channels are free it picks up ch1 first , then ch2 etc ..  it is not doing this either ..

so in answer to your reply , it does not matter if i apply ascending or decending  it is always using the order ascending ( first free channel)

hellono , i did not mention


no , i did not mention that. I said as above the default behaviour is descending , but before you are going to change it to ascending you have to check incoming calls to avoid a famous isdn error "channel is not available". So as per your answer you incoming calls from ITSP uses descending , so if you use ascending , no issues for change and everything should be ok .Now , if you are going to isdn ascending from your VG , if you have CUCM , you have to change the configuration of your controller timesolts from up to down . Your outgoing calls will hit starting from Channel 1 -31.



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New Member

This is an h323 gateway ,

This is an h323 gateway , channel selection is done on mgcp gateways . the default is ascending on this gateway , i/c calls are descending .


With no config ( see original input) o/g calls are using ch1 > 31  and i/c calls use b channels 31 > 1