Locations for bandwidth control and AAR – Automated Alternate and SRST

Locations for bandwidth control and AAR – Automated Alternate

Routing and SRST

Example in a CENTRALIZED CALL MODEL(locations only work in

this model as the CUCM provides call control for all sites)

with CUCM in Dallas and remote office in Little Rock with all

VOIP phones getting signalling from Dallas CUCM and calls

using the WAN bandwidth need to control the bandwidth that is

allowed calls, we will say WAN is 768Kpbs connection

Create 2 locations:

Dallas – Audio Bandwidth 768Kpbs
Little Rock – Audio Bandwidth 768Kbps

Then assign phones to location Dallas or Little Rock

Calls between phones in same location do not subtract from

total only calls between different locations

G.711 subtracts 80Kbps(64Kpbs plus overhead)
G.723 subtracts 24Kpbs
G.729 subtracts 24Kpbs
On average CUCM adds 16Kpbs for overhead to codec for CAC

(Call Admimission Control)

Another example with 3 locations:

Dallas has 45Mb
Little Rock has 768Kbps
Atlanata has 1.5Mbps

Setup for locations as follows:
Dallas Audio Bandwidth Unlimited (compared to other sites

with less bandwidth)
Little Rock stays at 768Kbps
Atlanta 1500Kbps

need to use Independent WAN bandwidth control using H.323

Gatekeeper or SIP Proxy, meaning that it is not under control

of any CUCM cluster, gatekeeper can be linux box or other

application running on another OS

AAR – Automated Alternate Routing

1. Configure External Phone Number Mask – this is the mask

that will be added to the extension number for the PSTN to

see, also is display on phone

2. Configure Service parameters and AAR Groups – Like

‘registry’ for call manager change Automated Alternate

Routing Enable* to True also add to

Out-of-Bandwidth Text* message to say “Please Try Again

Later” (only allowed 23 characters in 4.x) to avoid calls of

panic NO BANDWIDTH, also AAR Network Congestion Rerouting

AAR Groups – Prefix Digits to add between locations for

example 9 for PSTN calls local or 91 for PSTN long distance

3. Configure DN to use AAR Group – Under device line

configuration add AAR Group

4. Configure AAR CSS – AAR Calling Search Space Under device

configuration, need to give access to Long Distance PSTN CSS

SRST on Remote Routers:

1. Call-Manager-Fallback
2. IP Source-address
3. Max-Ephones (what you have a license for)
4. Max-DN

SRST on Call Manager (CUCM):

1. under Device Pool Configuration SRST Reference field (if

not using Default Gateway) configure SRST Reference under

System SRST

For FULL SRST dialing would need to setup Dial Peers on the

SRST Router for complete dialing



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