newbie VOIP design question

[ajit.shah]

Greetings All,

i want to connect the two PBX trunk line using data circuit. The primary circuit between the locations is DS3 and backup is 2T1.

Is it possible to run G711 (uncompressed) when DS3 is active and when it's down i.e. when 2T1 is active the compressed algoritham automatically changes to G723 ?

Thanks for all you help

[dragos.stroescu]

Yes you can.

By combining the IP routing with multiple voice dila peers for VoIP you can obtain the codec change based on the availability of the DS3 line.

Good luck

Dragos

[ajit.shah]

Dragos,

Thanks a lot. Can you point me out some good tech doc

besides doc cd if it is avaiable ?

I am more concerned about the tracking of primary line.

again thx a lot.

Ajit

[dragos.stroescu · Accepted solution]

Well... not really!

Try to follow the next example:

- on DS3 line you use IP SUBNET A;

- on T1 lines you can use multilink PPP to aggregate the two links into one Multilink interface and use IP SUBNET B.

Let's asume you have the two routers connected via DS3/2xT1 named 1 and 2.

You will use IP addresses like

Router 1

A.1 and B.1 (DS2 respectively Multilink intf)

Router 2

A.2 and B.2 (similarly)

Now you use on router A two dial peers one pointing to A.2 IP address and the second pointing to B.2 (for the same "destination-pattern"!!!).

Dial peers for A.2 uses codec G711 and "preference 10" and dial-peer for B.2 uses G729 (ore else...) with a lower preference (this is the hunting order basically).

If DS3 line is down, the A.2 IP address is unreachable (ensure that from the routing protocol/access lists).

You have to add also on routers the:

voice hunt all (router hunts the dial-peers for all disconnect causes - global config)

and tune the H225 timeout (helping you in faster timeout if the DS3 line is down - as the router STILL tries the first dial-peer) with:

voice service voip

h323

h225 timeout setup X <- no. of secs.

You sould be careful also to the incoming VoIP dial peers to accomodate both codecs by using a codec class (for G711 and G729 codecs).

Apply the symmetrical config on router 2 and all should be basically OK.

Good luck!

[dragos.stroescu]

Sorry about the preference indication... checked in the meantime.

The lower the value the higher the dial-peer preference as per documentation:

preference (dial-peer)

To indicate the preferred order of a dial peer within a hunt group, use the preference command in dial-peer configuration mode. To remove the preference, use the no form of this command.

preference value

value

Integer from 0 to 10, where the lower the number, the higher the preference. The default value is 0 (highest preference).

EXAMPLE:

The hunting algorithm precedence is configurable. For example, if you wish a call processing sequence to go to destination A first, to destination B second, and to destination C third, you would assign preference (0 being the highest priority) to the destinations in the following order:

•Preference 0 to A

•Preference 1 to B

•Preference 2 to C