Door buzzers/enterphones, paging systems to Teams or Skype (What is FXO)

Analog trunks and devices are less and less of a factor in many of the projects that I work on. Areas where I still see analog are branch office trunks, faxes, door buzzers/enterphones, paging systems, and ring-down phones that you might see in a parking lot to contact security or a cab company.

To integrate analog trunks or devices with SfB or Teams, you connect them to a gateway. The gateway can come with two types of ports: FXO, and FXS. FXO is an abbreviation for Foreign eXchange Office, and FXS for Foreign eXchange Subscriber.

So, clear as mud and we’re done here, right? If you’re an old school telecom guy, you know there’s a lot of complexity hidden behind that simple jack in the wall. The good news is for nearly all SfB use cases we can boil things down so they’re very simple.

FXO is a port that you plug a telco trunk line into. FXS is a port that you plug your phone or other device into. Mostly. Confusion pops into the picture when you have paging systems or enterphones, which may oddly use the opposite interface than you’re expecting, or give you the option for both.

You can think of FXO and FXS as North and South on a magnet, or male and female, or whatever pairing you’d like. A FXO device plugs into an FXS device, and all is well, like this:

Your phone, which has an FXO jack on it, plugs into the wall, which is an FXS interface.

Your phone, which has an FXO jack on it, plugs into an Analog Gateway such as the AudioCodes MP-118 gateway FXS port, or an FXO/FXS card in a Sangoma for instance.

The AudioCodes MP-114 gateway FXO jack plugs into the wall, which is an FXS interface.

An AudioCodes MP-114 gateway. From the left are power, Ethernet, RS-232 serial console, two FXS ports and two FXO ports.

Great, so why then would a paging system offer both FXO and FXS interfaces? The answer is that there are two different use cases for the paging system.

One use case is a standalone, where a phone plugs directly into the paging system. You pick up the phone, maybe enter some digits to indicate what zone to page, and you talk away. The paging system is acting as a PBX in this scenario.

The second use case is PBX integrated, where the paging system acts as a phone. You dial the extension for the paging system, it rings and then answers, you maybe enter some digits to indicate what zone to page, and you talk away.

These two use cases also apply to things like enterphones or gate/door buzzers. You can have a phone plugged directly into the enterphone, or you have have the enterphone act as an extension on your PBX.

The standalone option is simple, but restricts you to interacting via a single phone. The PBX integrated option is more complex, but allows you to interact via any phone on the PBX.

Caution: “Interact via any phone on the PBX” in the SfB world means that in a global deployment, you could have a prankster user in New York telling jokes over a paging system in Paris. Configure your dial plans appropriately if your paging system doesn’t offer PIN functionality

If you have a choice between using an FXO port or FXS port on a gateway to integrate with an analog device that offers both, I recommend you pick the FXO port. This has the device act as a PBX, which means that there is no ringing when you call it, and call setup is faster. Disconnects are usually quicker too, which is important if the paging system or enterphone is used a lot.

When you configure the device to plug into an FXO port on the gateway, set the gateway to route calls to that number out via the FXO port you’ve connected it to. If the device will be sending calls to the gateway, set the gateway to

You’ll need to use an FXS port on your device to connect to the gateway’s FXO port. If your device has one port that’s switchable between FXO and FXS, read the manual carefully – I’ve seen some that aren’t clear whether they mean FXO mode is “setting this device to FXO” or “setting this device to talk to FXO”. If it’s really unclear, plug a boring analog phone in. If the line is dead, the device is set to act as an FXS device and the port is configured as an FXO interface.

Unable to move failed-over-to-DR databases back to production Site

I recently came across a scenario, where an Exchange environment that had been configured in a Best Practice state had failed over to the DR site due to an extended network outage at the primary production site, and was unable to re-seed back and fail back over.

The environment was configured very similar as described in the Deploy HA documentation by Microsoft, and had it’s DAG configured across two sites:

Stock example showing DR site relationship

Instead of the “Replication” network that is shown in the above graphic, the primary site had a secondary network (subnet 192.168.100.x) where DPM backup services ran on, the DR site did not include a secondary network.

Although the Exchange databases were mounted and running on the DR server infrastructure, the replication state was in a failed state at the primary site. Running a Get-MailboxDatabaseCopyStatus command showed all databases in a status of DisconnectedAndResynchronizing

DisconnectedAndResynchronizing state

All steps attempted to try to re-establish synchronization of the databases failed with various different error messages, even deleting the existing database files and trying to re-seed the databases failed, with most messages pointing to network connectivity issues.

Update-MailboxDatabaseCopy vqmbd06\pcfexch006 -DeleteExistingFiles

Confirm
Are you sure you want to perform this action?
Seeding database copy "VQMBD06\PCFEXCH006".
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [?] Help (default is "Y"):
The seeding operation failed. Error: An error occurred while performing the seed operation. Error: An error occurred
while communicating with server 'DCExchange'. Error: A socket operation was attempted to an unreachable network
10.50.3.15:64327 [Database: VQMBD06, Server: pcfexch006.xxxxx.com]
    + CategoryInfo          : InvalidOperation: (:) [Update-MailboxDatabaseCopy], SeedInProgressException
    + FullyQualifiedErrorId : [Server=PCFEXCH006,RequestId=e0740b4a-7b94-42f5-b3ad-7ee42632f9c4]
 [FailureCategory=Cmdlet-SeedInProgressException] 2D10AE04,Microsoft.Exchange.Management.SystemConfigurationTasks.UpdateDatabaseCopy
    + PSComputerName        : pcfexch006.xxxxx.com

Looking carefully at the error message, the error says: A socket operation was attempted to an unreachable network 10.50.3.15:64327

Very strange, as when a network test was run, no errors occurred with connecting to that IP and TCP port.

Test-NetConnection -ComputerName DCExchange -Port 64327


ComputerName     : DCExchange
RemoteAddress    : 10.50.3.15
RemotePort       : 64327
InterfaceAlias   : Ethernet
SourceAddress    : 10.50.2.42
TcpTestSucceeded : True

When the test command Test-ReplicationHealth was run, the ClusterNetwork state was in a failed state:

PCFEXCH006      ClusterNetwork             *FAILED*   On server 'PCFEXCH006' there is more than one network interface
                                                      configured for registration in DNS. Only the interface used for
                                                      the MAPI network should be configured for DNS registration.
                                                      Network 'MapiDagNetwork' has more than one network interface for
                                                      server 'pcfexch006'. Correct the physical network configuration
                                                      so that each Mailbox server has exactly one network interface
                                                      for each subnet you intend to use. Then use the
                                                      Set-DatabaseAvailabilityGroup cmdlet with the -DiscoverNetworks
                                                      parameters to reconfigure the database availability group
                                                      networks.
                                                      Subnet '10.50.3.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '10.50.3.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '10.50.3.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '10.50.3.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '10.50.3.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '192.168.100.0/24' on network 'MapiDagNetwork' is not Up.
                                                       Current state is 'Misconfigured'.
                                                      Subnet '192.168.100.0/24' on network 'MapiDagNetwork' is not Up.
                                                       Current state is 'Misconfigured'.
                                                      Subnet '192.168.100.0/24' on network 'MapiDagNetwork' is not Up.
                                                       Current state is 'Misconfigured'.
                                                      Subnet '192.168.100.0/24' on network 'MapiDagNetwork' is not Up.
                                                       Current state is 'Misconfigured'.
                                                      Subnet '192.168.100.0/24' on network 'MapiDagNetwork' is not Up.
                                                       Current state is 'Misconfigured'.
                                                      Subnet '10.50.2.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '10.50.2.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '10.50.2.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '10.50.2.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.
                                                      Subnet '10.50.2.0/24' on network 'MapiDagNetwork' is not Up.
                                                      Current state is 'Misconfigured'.

The Failover Cluster Manager was checked, but no errors were found, and the networks in question were “Up”, and in green status.

Looking further at the output of the Test-ReplicationHealth shows that the current state is “Misconfigured”, so let’s see how that replication traffic is configured. The following shows the output of Get-DatabaseAvailabilityGroupNetwork

RunspaceId         : 57e140b2-15ad-4822-9f94-3e1b0d34f491
Name               : MapiDagNetwork
Description        :
Subnets            : {{10.50.3.0/24,Up}, {10.50.2.0/24,Up}}
Interfaces         : {{DCExchange,Up,10.50.3.15}, {pcfexch005,Up,10.50.2.36}, {pcfexch006,Up,10.50.2.42}}
MapiAccessEnabled  : True
ReplicationEnabled : True
IgnoreNetwork      : False
Identity           : VarDAG2016\MapiDagNetwork
IsValid            : True
ObjectState        : New

RunspaceId         : 57e140b2-15ad-4822-9f94-3e1b0d34f491
Name               : ReplicationDagNetwork01
Description        :
Subnets            : {{192.168.100.0/24,Up}}
Interfaces         : {{pcfexch005,Up,192.168.100.218}, {pcfexch006,Up,192.168.100.217}}
MapiAccessEnabled  : False
ReplicationEnabled : True
IgnoreNetwork      : False
Identity           : VarDAG2016\ReplicationDagNetwork01
IsValid            : True
ObjectState        : New

An attempt was done to reset the network state by disabling the automatic configuration and re-enabling it with the following commands:

Set-DatabaseAvailabilityGroup VarDAG2016 -ManualDagNetworkConfiguration $true
Set-DatabaseAvailabilityGroup VarDAG2016 -ManualDagNetworkConfiguration $false

No change, and the seed attempt failed again.

An attempt to remove the Backup network (Here named “ReplicationDagNetwork01“) from the replication traffic was done with the following commands:

Set-DatabaseAvailabilityGroup VarDAG2016 -ManualDagNetworkConfiguration $true

Set-DatabaseAvailabilityGroupNetwork -Identity VarDAG2016\ReplicationDagNetwork01 -ReplicationEnabled:$false

No change was seen, and the seed attempt failed.

Looking further at the what options the command had, the “IgnoreNetwork” option was used:

Set-DatabaseAvailabilityGroup VarDAG2016 -ManualDagNetworkConfiguration $true

Set-DatabaseAvailabilityGroupNetwork -Identity VarDAG2016\ReplicationDagNetwork01 -ReplicationEnabled:$false -IgnoreNetwork:$true

Still no change, so I set back the autoconfiguration with the command:

Set-DatabaseAvailabilityGroup VarDAG2016 -ManualDagNetworkConfiguration $false

Running Get-DatabaseAvailabilityGroupNetwork | fl showed no visible change, but the Site-to-Site tunnel showed a massive uptick in usage, so I ran the Get-MailboxDatabaseCopyStatus command, and it showed all databases that were in a status of DisconnectedAndResynchronizing synchronizing! I retried the reseed process, and it worked!

I’m not sure why the Set-DatabaseAvailabilityGroupNetwork command showed no visible changes, but it’s obvious the changes did occur, that the replication was disabled over the BackupNet (192.168.100.x) and forced over the correct network.

Audiocodes Mediant VE SBC only shows InternalIF OSN

After configuring Audiocodes’ VM based SBC in a single NIC state, a need come up where a WAN interface needed to be brought online. When attempting to set an IP to the interface group the following error was displayed:

nwDevTable_CrossValidateRow: Validation failed, the ethernet group (index 1) already contains the OSN interface. No other device can be configured on this group. MATRIX DeviceTable: Unable to Activate Line(1) since it is invalid

As we can see, the Ethernet Device Status shows InternalIF OSN is the only other available device.

IP Interface Status doesn’t show much help either:

An idea attempted was exporting the configuration ini file, adding the configuration entries for the second NIC, applying the changed configuration file and restarting appears to bring it up, but it still had a red state of down/unknown. (the WAN_DEV Ethernet Device was created in the config file)

The following steps were taken to get the Audiocodes VM to work:

  • Delete the logical Virtual Machine network interface
  • Restart the VM
  • Add a new NIC to the VM
  • Restart the VM

Once those steps were taken, the interface came up, and the IP was active!