Assigning DID numbers for FXO
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The purpose of DID numbers
Every FXO line has a telephone number associated with it. When you dial that number, the line will be used by the telephone operator to run this call. Only one call can run on a physical line at a time.
Many telephone operator offer additional services for FXO lines. For example, when the line is in use, they allow routing the call to other lines. This makes is possible to have several calls coming in for the same telephone number. For most businesses this is critical for the printing of business cards and communicating which number should be used for calling the company.
DID settings
Because of the old FXO technology, the CS410 can not automatically learn the DID numbers that are connected to the physical lines. Because of this, the customer must manually setup the DID numbers in the web interface.
In most cases, this setup is okay and no further modifications are necessary.
Outbound DID definition
When placing an outbound call to PSTN, the CS410 by default chooses the next free line. Depending on the setup on the network operator side, the presented number will be either the DID number for the chosen trunk or the central number that is used for distributing incoming calls to available FXO lines. In many cases this is okay.
If you explicitly want to specify what DID number an extension should use when placing an outbound call, you must assign a individual dial plan to that extension. In this dial plan, you need to specify in the replacement what line should be used. The concrete setting depends on the FXO gateway that you are using.
For example, on the CS410 a replacement of "sip:\1@localhost;line=1" would send the call to the first PSTN line (the first line has the number 1, the fourth line the number 4).
Inbound DID definition
If you want to assign incoming calls depending on the used line, you need to assign a trunk specifically for that line. In the username and the host name of the trunk you must specify the DID number of the trunk and the domain name (e.g. "localhost"). The outbound proxy must match the IP address of the gateway (e.g. for CS410 "127.0.0.1"). Then the PBX will associate the call with this trunk and you can use the "Send call to extension" setting on the trunk to define the destination of the call.
