Solved: Understand Publisher Subscriber Physical Connectivity

svictoryshanmugam · ‎07-28-2011

Good Day Networkers !!!. I know that the CUCM cluster has one publisher and maximum of 8 subscribers with only 4 active call processing servers.

Please find the attached sample CUCM cluster representation. I am not clear on how physically the publisher and subscribers are connected and how they are configured in the CUCM. Please explain. Thanks in Advance.

Joseph Martini · ‎07-29-2011

The servers don't have to be in the same subnet, they can be in different subnets as long as routing works between them. The phone do learn about what TFTP server to connect to using DHCP option 150 or option 66. To load balance between multiple TFTP servers you would need to set the DHCP options for some phones to point to one server and some other phones pointing to other servers. With option 150 you can set 2 TFTP servers a primary and secondary in case the first is unreachable for some reason. The phones learn which call manager to register with from their TFTP configuration file which they download from the server in the DHCP option 150. The config file has the call manager's hostname or IP address so the phones know where to connect to reach the call manager(s). The publisher can interact with endpoint if you choose, it's really up to you. With multiple servers it's more common than not that the publisher is not used for call processing (CCM service stopped) so there is minimal endpoint interaction with the publisher. Lastly for the standby subscribers, those are given to the phones in their configuration file. Within call manager there is a call manager group which contains a list of call manager. The first server in the list is where the phones should register and the others are "standby" as backup should the first server in the list be unavailable.

The best document about this would be the SRND:

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/uc8x.html

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Joseph Martini · ‎07-29-2011

You're welcome. You are exactly correct, the installer asks for the IP address of the publisher if it's not the first node in the cluster. The subscriber will then connect to the publisher which will setup replication after the install to get all the configuration information. The only step before you install the subscriber is to add the new subscriber under System > Server, on the publisher's webpage so that it's "allowed" to connect to the publisher.

View solution in original post

Joseph Martini · ‎07-28-2011

The publisher just needs network connectivty to the other servers in the cluster. There are some route trip time restrictions for communication between the servers as well. All servers have to be able to reach one another too (network connectivity wise). You really don't have to configure the servers differently, when you do your install there is a question if the server is the first in your cluster and if so it becomes your publisher. If it's not the first server it will become a subscriber. Then it's up to the administrator as to if they want to dedicate a TFTP and/or MoH server by activating just those services. Let us know if you have other questions about this.

svictoryshanmugam · ‎07-29-2011

Many Thanks for the answer. So Just network connectvity means they have to be part of the network being in the same subnet right ? Essentially the switch has to be configured of the TFTP Server to provide the details to IP Phones right. So which subscriber's IP Address has to be provided as TFTP Server if all of the subscribers are running TFTP service. I just want to if the subscribers are the active call processing servers, how that is communicated to the IP PHones and Switches. Essentially, the endpoints never interact with Publisher right ? Only the subscribers interact with the Endpoints and they replicate the DB to Publisher. Also how do we configure the standby subscribers ?

If anyone can point to a very good documentation on these details also will be very useful!

Thanks and Cheers !!!

Joseph Martini · ‎07-29-2011

The servers don't have to be in the same subnet, they can be in different subnets as long as routing works between them. The phone do learn about what TFTP server to connect to using DHCP option 150 or option 66. To load balance between multiple TFTP servers you would need to set the DHCP options for some phones to point to one server and some other phones pointing to other servers. With option 150 you can set 2 TFTP servers a primary and secondary in case the first is unreachable for some reason. The phones learn which call manager to register with from their TFTP configuration file which they download from the server in the DHCP option 150. The config file has the call manager's hostname or IP address so the phones know where to connect to reach the call manager(s). The publisher can interact with endpoint if you choose, it's really up to you. With multiple servers it's more common than not that the publisher is not used for call processing (CCM service stopped) so there is minimal endpoint interaction with the publisher. Lastly for the standby subscribers, those are given to the phones in their configuration file. Within call manager there is a call manager group which contains a list of call manager. The first server in the list is where the phones should register and the others are "standby" as backup should the first server in the list be unavailable.

The best document about this would be the SRND:

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/uc8x.html

svictoryshanmugam · ‎07-29-2011

Hi Joe,

Thanks a million for the clear explation and the SRND that is really helpful. I have one question which I would like you to please help me understand. I have done installation of a single publisher in Vmware environment only. During the installation, if this is not the first server in the cluster, will the installater prompt to enter the IP address of the Publisher (ie) the first server in the cluster. And I assume if the IP address of the Publisher is entered then the Subscriber will try to establish communication and replicate to the Publisher based on that right ?

Many Thanks

Joseph Martini · ‎07-29-2011

You're welcome. You are exactly correct, the installer asks for the IP address of the publisher if it's not the first node in the cluster. The subscriber will then connect to the publisher which will setup replication after the install to get all the configuration information. The only step before you install the subscriber is to add the new subscriber under System > Server, on the publisher's webpage so that it's "allowed" to connect to the publisher.

svictoryshanmugam · ‎07-29-2011

Many Thanks Joe for clearing all my queries... Have a Great Day !!!