IPPBX CISCO ip-Phone

[Ammartehsein]

I have 2 office locations. In main office I have dgm pbx server for cisco ip-phones and network range is 192.168.1.0/24. In my branch office I have network 172.16.1.0/16. I have ip-hones there. I have DMVPN tunnels between cisco router for reachibilty between 2 office. 

My question is that what configurations required on branch(2nd office) so that ip-phone can register on pbx server that is located on main office. 

[Flavio Miranda]

@Ammartehsein 

  It would depend on how your network works but you probably have a gateway on the office 2 somewhere if you have a different network. Somewhere on the office 2 in some layer 3 device is holding the network 172.16.1.0 for you and you should add a route on this device telling him how to reach the network 192.168.1.0 on the main office.  Then, you need to do the same thing on the main office and tell the gateway how to reach the network 172.16.1.0.

[Ammartehsein]

Yes, but how IP-phone on branch office knows about pbx server ip. I have cisco router router on both offices as gateway and I added route so that both have reachibilty.

[Flavio Miranda]

 This is how cisco phone knows about Cisco call manager. The process to know BPX server is the same. Just keep in mind that not all cisco phone and not all firmware version is able to join  Non-Cisco phone system.

https://www.ciscopress.com/articles/article.asp?p=1745631&seqNum=4

1. The Cisco IP Phone connects to an Ethernet switchport. If the IP phone and switch support PoE, the IP phone receives power through either Cisco-proprietary PoE or 802.3af PoE.
2. As the Cisco IP Phone powers on, the Cisco switch delivers voice VLAN information to the IP phone using CDP as a delivery mechanism. The Cisco IP Phone now knows what VLAN it should use.
3. The Cisco IP Phone sends a DHCP request asking for an IP address on its voice VLAN.
4. The DHCP server responds with an IP address offer. When the Cisco IP Phone accepts the offer, it receives all the DHCP options that go along with the DHCP request. DHCP options include items such as default gateway, DNS server information, domain name information, and so on. In the case of Cisco IP Phones, a unique DHCP option is included, known as Option 150. This option directs the IP phone to a TFTP server. (You learn more about this in the upcoming section, "Configuring a Router-Based DHCP Server.")
5. After the Cisco IP Phone has the IP address of the TFTP server, it contacts the TFTP server and downloads its configuration file. Included in the configuration file is a list of valid call processing agents (such as Cisco Unified Communications Manager or Cisco Unified Communications Manager Express CME agents).
6. The Cisco IP Phone attempts to contact the first call processing server (the primary server) listed in its configuration file to register. If this fails, the IP phone moves to the next server in the configuration file. This process continues until the IP phone registers successfully or the list of call processing agents is exhausted.

[Ammartehsein]

I understand the concept, But one thing If pbx server is on remote location I just have to specify it's address using option 150, so that ip-phone knows the pbx. Right ?

[Nithin Eluvathingal]

Cisco enterprise version phones use option 150 specified in the DHCP to connect and download configuration files. The option 150 IP address in the DHCP server is the IP address of the server hosting the TFTP service.

Since you are using a third-party PBX, are you using the MPP version of the phones ?

By the way, how did you get the phones in Location to register with the PBX?

[Ammartehsein]

Yes, I am using 6800 Series Cisco ip-phone. I am using dgm pbx. Currently the senario is that in our main office both ip-phones and pbx connected to same switch in same lan network, and phones are automatically registered to pbx server. 

Can you please tell what configuration required on remote site for ip-phone to register on pbx that is located on main office. Both office has reacibilty.

[Roger Kallberg]

How did the phones at the main office know how to register automatically to the PBX? They need to be instructed by something to do that as there is no way they by some act of magic would know how or even that they should do that.

[Ammartehsein]

As I told you both Digium pbx and phones are connected to same network via switch. As switch broadcast message so pbx server receive request, I think that is one reason no configuration required to tell these phone about pbx server as they receive request via switch.