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ISDN hub options

We're currently running 200 remote offices (using 1751's) terminating on two Cisco 3640's via frame relay pvcs. We use the network space at both ends of the frame relay links and are using a single OSPF area for routing.

For about 20 of these branches we want to install ISDN backup for situations where the frame relay goes down. We have installed the BRI cards at the remote ends and I'm investigating what equipment we need at the hub end.

Since I don't have a lot of experience with ISDN could somone help me with the following questions :

Which Cisco modules\devices can be used for terminating the 20 incoming ISDN calls ? Would i be right in saying I'd need a PRI module with 20 or so B channels from our Telco.

Considering ISDN and OSPF which dial\backup method and OSPF timings are recommended ? Keeping in mind we want a fast change over since we are running Citrix over the links so the change over needs to be rather fast.

Any suggestions would be appreciated.


Re: ISDN hub options

Yes, a PRI port should do the job. We have 20 sites with a BRI each (2 x 20= 40 b channels) but assuming that not all the remote sites will be down at the same time having just one PRI should be OK. Question is do you any spare NM slot on the two 3640s you presently have?

If yes, then NM-1CT1-CSU or NM-2CT1-CSU can serve the purpose.

If you are looking for a seperate router & maybe have some more interfaces/ functionality to add there...26xx is a good choice.

Thanks, Mak.


Re: ISDN hub options

In the below URL will find good info/sample configs under the section: DDR backup for WAN links.

In order to evaluate which backup scheme fits your requirement the best please refer to:

Thanks, Mak.