Need help on SRST & VG224

Unanswered Question
Apr 9th, 2008

Hello Guys,

I need your help and advice.

We are about to deploy a SRST system on a remote site using 2851 router.

There'll be 3x3560 PoE switches and two VG224 using as a distribution device to

73 ip phones, 35 analog phones , 1 fax machine and 1 conference station.

I found in some document that 2851 can only support 96 number of IP devices as maximum.

Do i need to count 35 analog as 35 ip devices or only 2 devices (VG224)?

Can 2851 router support two VG224 ?

Where do i need to configure the dial plan and destination pattern for IP & analog phones or all the thing must be done on central call manager ?

There is no PSTN connection in our network.

Please help me or kill me :(

Thanks in advance


I have this problem too.
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Michael Mistretta Wed, 04/09/2008 - 16:49

Keep in mind each port in a VG224 is a seperate device. with 73 phones and 35 analogs, this is too much. Which are more critical devices?

I would create a seperate SRST reference for those devices that are not as important.

When devices fail into SRST mode, a virtual dial-peer is configured for them, there is no need to configure seperate dial-peers for each device. The dial-plan should be configured in the 2851. If SRST will be used only for internal calling, given there is not PSTN connectivity, you need only a simple configuration (i.e., ip source-address, max-dn, and max-ephone), with no destination-patterns or session-targets. If the WAN link is down, voip dial-peers are useless.

yelynntun Wed, 04/09/2008 - 22:54

Thank you Michael,

I'm very new to VOIP system.

Can i create a separate SRST reference in one 2851 router ? If that please tell me how to do it .

We 've a connection to Central Office via satellite link ( 1 Mbps downlink & 512 kbps ).

All the thing we want to implement is that we can still communicate within internal office when WAN link's down.

But we need to call to Central Office while we have a connection to there.

Very much appreciate with you help


Michael Mistretta Fri, 04/11/2008 - 11:44

SRST references are created in callmanager. Which version CCM are you running? You can find this in the system menu under srst. Create the approprite reference for those critical devices and a null reference for those that are less important. In the gateway, you need to configure the dial peers directed to the destination of the redundant link. If you want to continue using dial by extension, configure the dial-peers with a destination-patter of wild cards to match the extensions, and prefix them with the extended pattern, alternatively you can use the alias command to match and prefix numbers (recommended). In this way, when a call is placed using the extension, it matches the dialpeer or alias, the prefix is attached, and the call is sent through the PSTN. Hope this makes sense. If you need more specifics, I'll be happy to provide.


yelynntun Tue, 04/15/2008 - 20:11

Please help me Bro

Someone may think i got the help from Mike via mail but i got no reply from mistrettammistretta.May be he's snowing under work.

I attach the draft diagram and sample configuration for this project.

But i found no dialpeers on those configuration.Here's the some part i can't get through those configuration.

sccp ccm group 1

associate ccm 1 priority 1

associate profile 1 register MTPxxxxxxxxxxxx


sccp ccm group 2

associate ccm 1 priority 1

associate profile 2 register CFBxxxxxxxxxxxx


dspfarm profile 1 transcode

codec g711ulaw

codec g711alaw

codec g729ar8

codec g729abr8

codec gsmfr

codec g729r8

maximum sessions 6

associate application SCCP

Somebody please give me a brief explanation and guide line for this project.

I need your help




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