UCM6208 All circuits Busy when dialing out from specific trunk in SCA


I recently setup a UCM6208 with 8 GRP2614’s in our office when our old ATT Merlin system stopped working.

I’m trying to replicate the old Merlin system.

setup is as follows
UCM6208: Analog Trunk1, Analog Trunk2, Analog Trunk3. all in SCA mode
SCA: Trunk1- 1000-1010(1000 for SCA Trunk, 1001-1008 account1 for Phones and VMPK1 Shared)
SCA: Trunk2- 2000-2010(2000 for SCA Trunk, 2001-2008 account2 for Phones and VMPK2 Shared)
SCA: Trunk3- 3000-3010(3000 for SCA Trunk, 3001-3008 account3 for Phones and VMPK3 Shared)

Now the issue starts when Trying to dial out using Trunk2/3(VMPK2/3), It always wants to use Trunk1.
I can call all 3 trunks using my Cell phone and each Specific Trunk will ring. If I call Trunk1, and then someone tries to use trunk2/3 to dial out we get an all circuits are busy error. If I call trunk2/3 and try and call out Trunk1 there sno issue, If I try and call out Trunk3 it still uses Trunk1 to make the call even though I used VMPK3(which is account 3 tied to turnk3) it still make the call using trunk1.

If I do a test Call to my cell phone from the UCM6028 from Trunk1-3 it uses the correct Trunk.

Now I have also tried setting in outbound routes for each trunk to use a Specific Trunk to see if that would help and it doesn’t. Ive even set a Time for it which is 24/7 to only use that trunk, I have also added in the other 2 Trunks for failovers to try and get this to work but no luck.

I have also tested using SLA that works fine except for in order to dial out using SLA we have to type in the extension the trunk is on which is a pain. so for example Trunk1 is 1000 in SLA, in order to dial out when you pick up the line you 1st wait for dialtone, then dial 1000, then have to wiat for the UCM6208 to confirm usually takes a few seconds then you get dial tone again and then you can Enter the phone number. If you just try and enter a phone number without dialing the lines extension you get an error.

Also zero config for the GRP2614’s are messed up, when you try and setup a VMPK inside the zero config for the phone using SHARED it actually uses LDAP instead so the zero config settings don’t match up with the phone settings, you have to manually log into the phone to make a lot of these changes which defeats the purpose of zero config.

UCM6208 was updated to firmware before i did anything
Phones head to be updated to Beta firmware before UCM would even interact with them, I’ve since updated the phones to Release.


Could you set up an outbound route for each trunk where you have to prepend a specific digit to pick that trunk? Perhaps a leading 7 for trunk one, 8 for trunk 2 . . . . ?

Then have the dial plan drop the first digit before sending the call out of the specified trunk?


we are using VMPK to select which line we want to use, VMPK1 =trunk1, VMPK2=Trunk2, VMPK3=Trunk3. Technically we should just be able to either pick up the phone then hit the VMPK button we want which works, but when the UCM6208 dials out for some reason it will only use Trunk1 regardless of the VMPK Account profile being tied to a specififc Trunk. I will test what you have suggest but im not sure how that would make any difference since the system is already ignoreing the fact that we are already using a Specific trunk to trial and dial out with. We have need to not want to press anything other then dialing the number after we pick the trunk we wnat to make the call from.


Hello Mr. Brian,

The only way for your scenario to succeed is to use SLA Station and make sure your VMPK is in the BLF position. For more complete information, please read the UCM user manual below (page 202):

Hopefully your problem can be solved


SCA in the IP world is shared call appearance where multiple extensions can share a call and react or control it as though one extension. It has nothing to do with trunk selection. The UCM manages the trunk selection depending on how the trunks are configured and the rules are set for both inbound and outbound, but the extensions exert no control over them unless the outbound rules call out a specific trunk based upon source callerID or by a prefix in the dial string. You can monitor the lines, but not control it like you could with a key set in that pressing the button for 'line 1" connects you directly to trunk 1.

While many who migrate from a key system to an IP system wish to mimic the old, such is not always possible in all respects. Your calling in using various trunks was controlled by the provider and had nothing to do with the UCM. They are discrete lines into the system.

The question is why is control over the trunks needed? There are valid reasons one of which is that analog lines may each have a unique callerID associated to them such that when dialing out each will present the callee with the CID of choice. However, many will have the provider mask all the analog lines tp reflect the same CID. If this is the case, then it begs the question of why mimic that which you had when the PBX can manage the lines behind the scenes with no user intervention needed?

You can also use the failover function in the trunks such that you can group them together as one trunk for all 4 FXO ports, or set up the trunks individually and then use failover such that if 1 is not available, it will try 2 and then 3 and 4 if set that way. This would have avoided the busy line you experienced as you told the system to use 1 and it did.


Ive tried SLA, I mentioned this in my 1st post, it doesn’t work how we want.

Ive followed the manual to configure both SLA and SCA. the manual is off in some regards too our outdated and lacking.
BLF with VMPK doesn’t work, it end up giving a grey icon and you when you select one of the VMPK keys with BLF setup it doens’t ao anything. I think theres a firmware issue with VMPK and BLF.

Some of the users who are owners of the business are over 80yrs old and so haveing to have them learn a new system is not possible.

2nd what im wanting to do should be very easy to do.

We have 3 Analog Lines,
1.) Primary(we advertise this as our primary Number)
2.) Rollover(we don’t advertise this Number or have any Caller ID setup becaus eits just mainly used for rollover)
3.) Secondary/Fax(we advrtise this as Secondary number/Fax)

We mainly get Calls on Primary, if Primary line is Busy they rollover to The rolloverLine, and We also get a good call volume on the Secondary/Fax line along with Faxs.

If someone is talking on Primary then, we default to using the Secondary/Fax line to make calls out, If both Primary and Secondary lines are being used then we use the Rollover line to call out.

Being able to select what line we want shouldn’t be an issue with any phone system considering you can setup Specific accounts for those in the phones themselves. So its not like you cant do it, however we need some of the Features of old Key systems because everyone in the office need the ability to barge in on calls or to put someone on hold and anyone or phone in the office can then pickup that line.

Ive tried several different online resources to setup,

ive watched Youtube videos of poeple doing this and it works for them the issue being they don’t show if every fetaure works and or if it does work they don’t state what firmware versions they are on and some are using differnt modle phones and UCM.


Hello Mr. Brian,

I understand now, Sir. Maybe you can try the failover function mentioned by Mr. Larry (Mr.@lpneblett) above. You can set failover trunk on your outbond route. You don’t have to use vmpk to select a trunk if you use this method
I hope this method works for you, Sir


Per my 1st post I mentioned I already Tried failover and it doens’t work. I don’t think they read my entire post either.

No Matter what i try when using SCA mode when trying to dial out it will only use Trunk1 regardless of use selected trunk2 or trunk3 via VMPK per the install instructions for SCA.

And with SLA you have to dial the extension number of the trunk account just to get an outside line which defeats the purpose of emulating an old KEY system.


I did read your post and I was not addressing SCA/SLA specifically and asked why SCA/SLA was really needed and how the trunks can work as I use failover frequently. I do not use SCA or SLA, but I may play with it later on today just to see.


I tried Prepend but the same issue occures, For some reason it will only use Trunk1, regardless. I found another video By a voip supplier and grandstream doing a webinar, i watched but kinda confused on it but they do mention a second method to configure SLA.

again though we don’t see it actually being used just showing how to setup.


I guess the question is which do you want SLA or SCA?

As stated in my earlier, SCA has nothing to do with the trunks. If you want to monitor the line and be able to select, then use the SLA on the trunk settings.

Using the GS UCM trunk manual as a guide for SLA, I used a GRP2614 and configured accordingly and have no issue in using the function where I can use the BLF to both monitor the status of a trunk (in use, idle and not connected) and I can also use the BLF to select a line and make a call out of same. As soon as I plug a POTS line into a port for the SLA trunk, the BLF key lights up green. I have one BLF set for each of my two trunks and they are treated in the UCM as different rather than as a group.

I have labeled FXO 1 as Trunk_1 and FXO as Trunk_2 and these are populated in the phone as such:

I have SCA disabled as I assume you really want SLA.


Hello Mr. Brian,

Actually, I already knew from the start what scenario you want to use for the telephone system you are using in your first post. You want to control the access of your analog telephone line through the VMPK key, don’t you, sir? Please correct me if I’m wrong. Therefore, my first reply was to use the SLA function because this function can accommodate exactly your plan. Then in your first post, you have tried using this SLA function but failed. You don’t like to use this function because you have to wait for the dial tone then press the number 1000 then wait for the confirmation then press the destination number after it turns out to be an error. Therefore, in my first reply, I suggest you change the VMPK key function to BLF. This is intended so that you do not have to wait for the dial tone again, then press the number 1000 and so on. With the BLF on the VMPK key, you no longer need to wait for the dial tone then press the number 1000 and so on, you simply press the vmpk key then you can directly press the destination number, that’s what I meant. You want the SCA method so that the scenario you want can run, of course, you can’t, Sir, because SCA cannot control the access of your analog telephone line. Whatever effort that you or other people who want to make the SCA work for your plan, the results will be in vain, sir. Actually, there are 3 ways that analog telephone lines can be used interchangeably :

  1. SLA, this working method is manual.
  2. Failover Trunk, this method works automatically without having to be controlled via VMPK key.
  3. Collect all analog telephone lines into one analog trunk, this method works automatically without having to be controlled via VMPK key too

But of these three methods, I chose number one because I saw you wanted to be able to control analog telephone lines manually.
My mistake was in posting my second answer. I do not see if you have used this failover trunk method and failed, and my mistake in the second post was that I should suggest that you double-check the SLA settings, there might be an error there or there are other things that affect the SLA failure that you have made, for example, as stated by Mr. Larry above, namely deactivating the SCA feature and removing the failover trunk or specific trunk. I apologize for my mistake.
In order for the SLA to function properly, please note the instructions below:

  1. You must disable the SCA feature on the extension numbers that you have previously made on your ucm6208. Make sure each extension number that you have created is configured as shown below:
  2. Clear the failover trunk and specific trunk for each analog that you have made before.
  3. Then follow the methods that have been shown by the video that you have sent before, including the methods that have been mentioned by Mr. Larry.

That’s all I want to say, all depends again on you. I am sure the success of the method that has been done by Mr. Larry above, will also succeed for you if you want to try it one more time.

Good luck, Sir


I’m thinking what you want is not SCA as this doesn’t apply to trunks, but extensions.
I haven’t used VMPK, but I’m curious whether the outbound routes of the 3 trunks have unique leading characters like 1,2 or 3 like “1X.”, “2X.”, “3X.” because your problem looks like a dial pattern problem prolly what is sent to the UCM only matches with trunk 1.
Pain with SLA? you could do a speed dial key so you don’t have to dial and wait.
GRP series… yeah, I’m with you on that, but have you tried GDMS?
I think if you told us what you want to achieve would be more helpful, instead of telling us what you have done and is not working.