How to Expand Concurrent Call Limit in UCM6208


i have UCM6208 IP PBX,i have setup in extension on two telephones,but in this model of PBX Limit is just 100 Concurrent Call,is there any other solution to solve this, to setup more extensions


Concurrent calls is not extension limit. This 2 are not same (6208 limit is 800 extensions).

Concurrent calls can be extended if UCM not need transcode codecs.

Both are not hardware limit so UCM can handle more simply GS do not take responsibility if you exceed it.


No,i am asking about One extension on two telephones, for example in room i have two telephone one’s extension is 1002 and i want to setup one both telephones,like if i call from other extension must be rang on both telephones.


That is called SIP Forking and yes, the UCM supports it.

See Concurrent Registrations under Extensions.


Yes, that i already done 100 sips, but i want more, but with this model the limit is just 100


Oh, I see. You want to register over 100 phones to a single extension.

My first question is why? What are you trying to accomplish (other than ring 100+ phones)?

Second is why not use a Ring Group instead?

If it is to answer an extension from anywhere, would a BLF key or Call Pickup not work?


We need to be clear - there are concurrent registrations and there are concurrent calls.

Concurrent call is the number of calls that can be accommodated by the PBX at the same time. For the 6208, the spec number is “up to” 100. As Marcin points out, the number is somewhat of an estimated number as it might be able to handle more if the system is not taxed with handling other features and it may be less if doing encryption or other CPU intensive tasks. It is also a limitation based on the phone make & model in use as a phone will not accommodate that many calls.

Concurrent registrations is the number of device that can be registered to the same extension at the same time. This is limited to 10 and there is no way to expand this at our level, only GS could do this, but…

There is good reason to limit the number of devices. Each device is unique in that each will have its own IP. To send a message to an extension is a message to each device that is registered to that extension. So, if 10 devices, is is 1 message to each or 10 in total. As SIP is a Query/Response based protocol, the devices have to respond as well, which means that the PBX not only has to send 10, but must receive 10. This has the potential to cause a lot of traffic and because the messages are sent in a serial sequence, there can be quite a bit of delay induced by adding more devices. If 100 devices were allowed, it may be several seconds between the time the first phone started to ring and the last one started and it may cause someone to try and answer when the call was actually already answered by one of the earlier ringing extensions. There are some other issues as well, but these are for another day.

So, if you want a greater call capacity, you need to upgrade to a 6510 which will accommodate up to 200 calls,. but the concurrent registration limit is still 10 per extension.


Thanks lpneblett
For the Details,but i have one more Question,in a hotel room have two telephones 1516 model one is in the room and other is in the washroom but IP address is different, i have give the same SIP to both in concurrent registration in the Extension,so mt Question is this can i do the same to the other room telephones these are more then two hundreds rooms,hope you understand,because the Customer requirement is he don’t want to give separate extension number to washroom,when someone call from Reception must be ring to both Telephones,because sometimes customer is not in room he maybe in washroom,


Yes you can.
Change concurrent register to 2 on each extension.

Then register both on same number. You will need manually register 2 phone as Zero will not allow to duplicate extension).


Thanks @Marcin


Once you set Concurrent Registrations to 2 phones, Zero Config will allow you to assign that extension to 2 phones.