To find out which channels are in service, which are out of service, use command,
sh isdn service. Here is a sample output from a Cisco IOS router.
BR1#sh isdn service
PRI Channel Statistics:
%Q.931 is backhauled to CCM MANAGER 0x0003 on DSL 0. Layer 3 output may not appl
y
ISDN Se0/0/1:23, Channel [1-24]
Configured Isdn Interface (dsl) 0
Channel State (0=Idle 1=Proposed 2=Busy 3=Reserved 4=Restart 5=Maint_Pend)
Channel : 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
State : 0 0 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3
Service State (0=Inservice 1=Maint 2=Outofservice 8=MaintPend 9=OOSPend)
Channel : 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
State : 0 0 0 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
BR1#
CCIE Voice notes 
John sums up telepresence from a network perspective, “Telepresence is an interactive real- time application, which means it is delay sensitive, loss sensitive and jitter sensitive. This sounds familiar: it is just like VoIP, with the one difference being that it has huge bandwidth requirements.” It’s that last part that makes things more difficult. No form of QoS can allocate bandwidth that doesn’t exist and it doesn’t have provisions to force the application to downscale the experience based on realtime metrics. …
Good stuff mate. I was wondering if there is a way to test ISDN channels one at a time. For instance I want to test calls are going thru channel number 10, how do I do that? Is there a way to put maintenance block on all the channels and leave only 10 so it picks the calls?
Regards,
Kiran
isdn busy b_channel would busy out a range or a specific channel and you could test calls this way.
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