ISDN bandwidth - should i get the full 64/128k

[r.dufton]

Hello all,

I use isdn for maintenance and backup links and i have noticed recently that if i 'sh int bri0/0' when the lines are up the available bandwith is much less than either the 64k or 128k i would expect. For example when i use one b channel i would expect 64k and the config reflects this. However, the 'available bandwidth' is only 48k.

Similarily, if i dial both b channels i get only 96k.

I would have expected the full bandwidth on both ocassions. Am i mistaken in expecting this ?

many thanks

Richard

[prafuljaded]

By default the available bandwith is the 75% of the Bandwidth configured on the interface.That is if your interface bandwidth is 64kbps, Your available bandwith will be 75 x 0.75 = 48kbps

To modify the Available bandwith use the interface command : max-reserved-bandwidth yy.

example:max-reserved-bandwidth 90 instead of 75.

And you can view the modified Availbale bandwidth in Show interface bri

[r.dufton]

Hello,

thanks for the reply, I will try this out.

Does this mean that the interface was only running at 48kbps or was it running at 64kbps none the less?

if it was running at 64kbps anyway what is the point of the available bandwidth 48kbps line in 'sh int bri 0/0' ?

thanks

[mmt]

No, your interface was running fine at 64K, but for the sake of QoS configuration, by default only 75% of the interface bandwidth is available. In other words if you setup a policy-map and apply it to the interface, the total bandwidth allocations in the policy-map must not exceed 48K, unless you change this behavior by issuing the command mentioned above.