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CAC complex scenarios - please help!!!

I have read the CAC section of the SRND and I think I'm still confused on certain sections of the document. Would greatly appreciated anyone help on this :-)

Just assume RSVP is not a feasible option for now...

Re: Diagram 1

i) In this scenario, how many CCM clusters would you have & why? Would you put a cluster to each hub and remote site (i.e. to all sites)?

Ii) If each site has it's own cluster, how many GK would you use and why?

Re: Diagram 2

Iii) Assume it is a "Centralized model" where the HO hosts the only CCM cluster, do you see any problems in terms of CAC?

Iv) What would you configure for the location for the Non-GK controlled trunk between hub office (site D) & HO (site G)?

V) Do you ever configure any locations for the HO site? Or just leave the HO phones and HO Intercluster trunk as "none"?

Vi) Say if site A makes 7 calls to site B, and if site C also makes 8 calls to site B simultenously, can site B still call HO? I think the answer is no. Location CAC is not really designed to support multi-tier environment? anything we can do to fix this problem if the scenario has to be in Centralized model?

(N.B:- I have changed the location to be 'number of calls' rather than 'bandwidth' for simplicity)

Re: Diagram 3

Vi) In the centralized model,.If we have to reserve a certain bandwidth along all links end-to-end by RSVP, how is that differenet from using CAC? Don't we still need to over-pump the links? Say if a certain path along the RSVP path reserves 60 calls, wouldn't we need to RSVP for 60 calls through the whole path just like CAC?

Re: Diagram 4

Vii) For Tail End Hop off, assume all the voip dial peer has been setup on all the VGs, and the Route Pattern at Centralized CCM has been setup to point to the local VG (at site G) as Route List. But If the bandwidth between the hub (site D) & HO (site G) are all used up, but I want the user at site H to still be able to call the PSTN, can I use AAR in this scenario?



Re: CAC complex scenarios - please help!!!

Case 1:

I would do independent clusters in this case. Two Callmanagers at each hub (having its own cluster). Remote sites can run SRST. For trunking between the two clusters, all you need is one Gatekeeper.

If RTT between the two Hubs is < 40 ms, you can put callmanagers at both hubs in the same cluster. In this case you dont need GK's. You can use Locations based CAC.

Case 2:

There is a single point of failure between HO and hub. You can use SRST or CME on all the remote sites hanging off the hub and also at the hub. If you use locations based CAC in this scenario, you may end up having problems because its not a true Hub and spoke topology.

Case 3:

I am a rookie when it comes to RSVP. So I would pass that on to somebody else.

Case 4:

Location bandwidth between hub and HO is independent of location bw between HO and site H. So AAR will not kick in.

Community Member

Re: CAC complex scenarios - please help!!!

Hi thisisshanky,

Re: Case 1 (Diagram 5)

i) At Hub (site D), shall the 'locations' for the 3 x Non-GK intercluster trunk be left as 'none'?

ii) For the 'locations' for GK Inter-cluster trunks, shall they be set to 'none' as the traffic passing thru the GK are already being managed by GK already?

iii) If Hub (site D) wants to make 30 calls to site E, F, G & H at any time, would the total interzone bandwidth for ZoneA be 70 calls?

iv) Now, assume Zone B (site E, F, G & H) only needs to make 20 calls in total back to Zone A at any time, but since Zone A needs to make 70 calls as per iii, what should we do at GK?

bandwidth interzone ZoneA '70 calls'

bandwidth interzone ZoneB '20 calls' (would this restrict ZoneA to only be able to make 20 calls to Zone B?)

Re Case 2:

Can you please explain more on what problems will be faced since you mentioned it is not a true hub & spoke?

Re Case 3:

Can anyone else please shed some light on RSVP?

Re Case 4:

I'm a bit confused between the difference between the following 3 ways of setting up PSTN fallback if WAN bandwidth is insufficient in GK scenario

Say I want to call extn 3xxx on the remote office. The intercluster prefixs are *801, and the PSTN digits for the site is 9231-3xxx.

Method 1:

Configure a route list that contains two route groups. The first route group contains the intercluster trunk that routes outgoing calls over the IP WAN. Second route group contains the Voice Gateway.

Method 2:

Just on the Voice Gateway:

dial-peer voice 1 voip

destination-pattern 8013xxx

session target ras

preference 0

dial-peer voice 2 pots

destination-pattern 092313xxx

port 1/0:23

preference 1

Method 3:


Another extra Q regarding bandwidth for GK.

According to Cisco SRND, GK uses double the bandwidth as the codec call rate, so...

G.711 - GK uses 128kbps

G.729 - GK uses 16kbps

However, this is excluding all Layer 2, IP & RTP overhead... so when i am planning for number of calls, what values should i use as 'bandwidth per call'?



Community Member

Re: CAC complex scenarios - please help!!!

Any ideas?

Would greatly appreciated anyone help on this =)

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