SIP Trunks Guide

Updated on October 23, 2023

SIP trunks are a VoIP service that can be provided from an ITSP (Internet Telephony Service Provider) to extend telephony features beyond IPPBX local area. SIP trunks can carry voice calls, video calls, instant messages, multimedia conferences, and other SIP-based, real-time communications services.

Using SIP trunks helps to reduce call rates especially when making long distance calls, since VoIP providers can offer better calling rates compared to local ISP using analog lines.

UCM6xxx series support two types of SIP trunks: “Register SIP trunks”, mainly used to connect with provider’s trunk and “Peer trunks”, that can be used to interconnect multiple IP-PBXs. UCM6xxx series support up to 200 SIP trunks.

This guide describes needed configuration to set up register trunk (with provider) and peer trunk (between two UCM6xxx).

The figure above shows a typical scenario using two UCM6xxx between main and branch offices (connected via peer trunk), and main office UCM6xxx connected to provider via register SIP trunk.

UCM6XXX series include UCM620x series, UCM630x series, UCM630xA series and UCM6510.

Register SIP Trunks

In this guide, we will take company ABC as example. The company has purchased two SIP trunks, the first one will be used for International calls, while the second will be used of national ones.

The ITSP provider gave following trunk information to the company ABC in order to register their trunks.

SIP Trunk Information	Value
SIP Trunk 1
Provider address	sip.provider.com
Username	0655441000
Authenticate ID	0655441000
Password	admin123
Main number	0655441000
Provided DIDs	0655441001 / 0655441002 / 0655441003 / 0655441004 / 0655441005 / 0655441006 / 0655441007 / 0655441008 / 0655441009 / 0655441010
SIP Trunk 2
Provider address	sip.provider.com
Username	0655441100
Authenticate ID	0655441100
Password	admin123
Main number	0655441100
Provided DIDs	0655441101 / 0655441102 / 0655441103 / 0655441104 / 0655441105 / 0655441106 / 0655441107 / 0655441108 / 0655441109 / 0655441110

Setup considerations:

Extensions range on UCM6xxx in main office is 1000 – 1999.
Dialing to international numbers should be prefixed with 99 with no size limits.
National numbers start with 06 with 10-digit length.

Configuration

Below steps to configure SIP Trunk 1 on Main office UCM6xxx. Same steps apply to configure Trunk 2.

Access UCM6xxx web GUI 🡪 Extension / Trunk 🡪 VoIP Trunks.
Click on , in the following screenshot type in Trunk 1 credentials:

Select “Register SIP Trunk” as Type.
Type in a reference name for Provider Name. For example: “Provider_1”.
Enter provider’s FQDN/IP address in Host Name field. In this example: “sip.provider.com”.
Enter Username to register to the provider. In this example: “0655441000”.
Enter Authenticate ID to register to the provider. In this example: “0655441000”.
Enter Password associated with username. In this example: “admin123”.

Click and to store and apply the configuration.

Above steps describe basic configuration needed to register a SIP trunk. Depending on providers, users may need to adjust their settings to successfully register a SIP trunk.

The table below describes main parameters available for Register SIP Trunks:

Basic Settings
Provider Name	Configure a unique label to identify this trunk when listed in outbound rules, inbound rules, etc.
Host Name	Configure the IP address or URL for the VoIP provider’s server of the trunk.
Transport	Configure the SIP transport protocol to be used in this trunk. The default setting is "UDP". UDP TCP TLS
Auto Record	If enabled, calls handled with this extension/trunk will automatically be recorded. Note:
Keep Original CID	Keep the CID from the inbound call when dialing out. This setting will override the “Keep Trunk CID” option. Please make sure that the peer PBX at the other side supports to match user entry using the “username” field from the authentication line.
Keep Trunk CID	If enabled, the trunk CID will not be overridden by the extension’s CID when the extension has CID configured. The default setting is “No”.
NAT	Turn on this option when the PBX is using public IP and communicating with devices behind NAT. If there is a one-way audio issue, usually it is related to NAT configuration or SIP/RTP port configuration on the firewall.
Disable This Trunk	If selected, the trunk will be disabled. Note: If a current SIP trunk is disabled, UCM will send UNREGISTER message (REGISTER message with expires=0) to the SIP provider.
TEL URI	If the trunk has an assigned PSTN telephone number, this field should be set to "User=Phone". Then a "User=Phone" parameter will be attached to the Request-Line and TO header in the SIP request to indicate the E.164 number. If set to "Enable", "Tel:" will be used instead of "SIP:" in the SIP request. The default setting is disabled.
Need Registration	Select whether the trunk needs to register on the external server or not when the "Register SIP Trunk" type is selected. The default setting is No.
Allow outgoing calls if registration failure	If enabled outgoing calls even if the registration to this trunk fails will still be able to go through. Note that if we uncheck the “Need Registration” option, this option will be ignored.
CallerID Name	Configure the new name of the caller when the extension has no CallerID Name configured.
From Domain	Configure the actual domain name where the extension comes from. This can be used to override the “From” Header. For example, "trunk.UCM630X.provider.com" is the From Domain in From Header: sip:1234567@trunk.UCM630X.provider.com.
From User	Configure the actual username of the extension. This can be used to override the “From” Header. There are cases where there is a single ID for registration (single trunk) with multiple DIDs. For example, "1234567" is the From User in From Header: sip:1234567@trunk.UCM630X.provider.com.
Username	Enter the username to register to the trunk from the provider when the "Register SIP Trunk" type is selected.
Password	Enter the password to register to the trunk when "Register SIP Trunk" is selected.
Auth ID	Enter the Authentication ID for the "Register SIP Trunk" type.
Auth Trunk	If enabled, the UCM will send a 401 response to the incoming call to authenticate the trunk.
Auto Record	Enable automatic recording for the calls using this trunk (for SIP trunk only). The default setting is disabled. The recording files can be accessed under Web GUI🡲CDR🡲Recording Files.
RemoteConnect Mode	If enabled, the RemoteConnect related parameters will be set synchronously. Please make the trunk host is allocated by GDMS or it supports TLS.
Direct Callback	Allows external numbers the option to get directed to the extension that last called them. For Example, User 2002 has dialed external number 061234575, but they were not reachable, once they have received missed call notification on their phone, they would mostly call back the number, if the option “Direct Callback” is enabled then they will be directly bridged to user 2002 regardless of the configured inbound destination.
Enable Concurrent Call Alert	If enabled, the "Trunk Concurrent Calls" system event will monitor the number of concurrent calls in this trunk. When the number of concurrent calls in a certain period exceeds the set threshold, an alarm message will be generated. Note: Please turn on the alert for the "Trunk Concurrent Calls" event first.
Two-way Concurrent Calls Threshold	Threshold of all incoming and outgoing concurrent calls through this trunk.
Outgoing Concurrent Calls Threshold	Threshold of all outgoing concurrent calls passing through this trunk.
Incoming Concurrent Calls Threshold	Threshold of all incoming concurrent calls passing through this trunk.
Advanced Settings
Codec Preference	Select audio and video codec for the VoIP trunk. The available codecs are: PCMU, PCMA, GSM, AAL2-G.726-32, G.726, G.722, G.729, G.723, iLBC, ADPCM, H.264, H.263, H.263p and VP8.
Send PPI Header	If enabled, the SIP INVITE message sent to the trunk will contain PPI (P-Preferred-Identity) header. The default setting is “No”. Note: “Send PPI Header” and “Send PAI Header” cannot be enabled at the same time. Only one of the two headers can be contained in the SIP INVITE message.
PPI Mode	Default: Include the trunk’s preferred CID (configured in Basic Settings) in the PPI Header. Original CID: Include the original CID in the PPI Header. DOD Number: Include the trunk’s DOD number in the PPI Header. If no DOD number has been set, the trunk’s preferred CID will be used.
Send PAI Header	If enabled, the SIP INVITE message sent to the trunk will contain PAI (P-Asserted-Identity) header including configured PAI Header. The default setting is “No”. Note: “Send PPI Header” and “Send PAI Header” cannot be enabled at the same time. Only one of the two headers can be contained in the SIP INVITE message.
PAI Header	If “Send PAI Header” is enabled and “PAI Header” is configured as “123456” for instance, the PAI header in the SIP message sent from the UCM will contain “123456”. If “Send PAI Header” is enabled and “PAI Header” is configured as “empty”, the PAI header in the SIP message sent from the UCM will contain the original CID. Note: “Send PAI Header” needs to be enabled to use this feature
Send Anonymous	If checked, the "From" header in the outgoing INVITE message will be set to anonymous.
DOD As From Name	If enabled and "From User" is configured, the INVITE's From header will contain the DOD number. Note:
Passthrough PAI Header	If checked and the option "Send PAI Header" is not checked, the PAI header will be passthrough from one side to the other side.
Send PANI Header	If checked, the INVITE and REGISTER sent to the trunk will contain the P-Access-Network-Info header.
Access Network Info	The access network information is in the P-Access-Network-Info header.
Send Anonymous	If checked, the "From" header in the outgoing INVITE message will be set to anonymous.
Outbound Proxy Support	Select to enable outbound proxy in this trunk. The default setting is "No".
Outbound Proxy	When outbound proxy support is enabled, enter the IP address or URL of the outbound proxy.
Remove OBP from Route	It is used to set if the phone system will remove outbound proxy URI from the route header. If is set to “Yes”, it will remove the route header from SIP requests. The default setting is “No”.
DID Mode	Configure where to get the destination ID of an incoming SIP call, from SIP Request-line or To-header. The default is set to "Request-line".
GIN Registration	If enabled, the UCM will send a GIN REGISTER (generate implicit numbers).
DTMF Mode	Configure the default DTMF mode when sending DTMF on this trunk. Default: The global setting of DTMF mode will be used. The global setting for the DTMF Mode setting is under Web GUI🡲PBX Settings🡲SIP Settings🡲ToS. RFC4733: Send DTMF using RFC4733. Info: Send DTMF using SIP INFO message. Inband: Send DTMF using inband audio. This requires a 64-bit codec, i.e., PCMU and PCMA. Auto: Send DTMF using RFC4733 if offered. Otherwise, an inband will be used.
Enable Heartbeat Detection	If enabled, the UCM630X will regularly send SIP OPTIONS to the device to check if the device is still online. The default setting is "No".
Heartbeat Frequency	When the "Enable Heartbeat Detection" option is set to "Yes", configure the interval (in seconds) of the SIP OPTIONS message sent to the device to check if the device is still online. The default setting is 60 seconds.
The Maximum Number of Call Lines	The maximum number of concurrent calls using the trunk. The default setting is 0, which means no limit.
Packet Loss Retransmission	Configure to enable Packet Loss Retransmission.
Audio FEC	Configure to enable Forward Error Correction (FEC) for audio.
Video FEC	Configure to enable Forward Error Correction (FEC) for video.
ICE support	Toggles ICE support. For peer trunks, ICE support will need to be enabled on the other end.
TURN Relay	Enable TURN Relay This option will allow using TURN servers for media NAT traversal. This option will also be prioritized if ICE Support is already enabled.
FECC	Configure to enable Far-end Camera Control
SRTP	Enable SRTP for the VoIP trunk. The default setting is "No".
SRTP Crypto Suite	The following encryption protocols can be used to encrypt an RTP stream. AES_CM_128_HMAC_SHA1_80 (This is the default used protocol) AES_256_CM_HMAC_SHA1_80 AEAD_AES_128_GCM AEAD_AES_256_GCM
Enable T.38 UDPTL	Enable or disable T.38 UDPTL support.
STIR/SHAKEN	Configure this feature to prevent call spoofing, robocalls and spam calls. Disabled Outgoing Attest: The UCM will only authenticate the caller ID. Incoming Verify: The UCM will only verify if the caller ID is authenticated Both: The UCM will authenticate the oungoing calls as well as verify if the incoming calls are authenticated.
CC Settings
Enable CC	If enabled, the system will automatically alert the user when a called party is available, given that a previous call to that party failed for some reason.
CC Max Agents	Configure the maximum number of CCSS agents which may be allocated for this channel. In other words, this number serves as the maximum number of CC requests this channel is allowed to make. The minimum value is 1.
CC Max Monitors	Configure the maximum number of monitor structures that may be created for this device. In other words, this number tells how many callers may request CC services for a specific device at one time. The minimum value is 1.

After saving the new VoIP trunk, it will be displayed under Web UI 🡪 Extension / Trunk 🡪 VoIP Trunks as shown below. Press to edit trunk settings if needed.

Once the trunk has been created, users can check its registration status under System Status 🡪 Dashboard page.

Note

If status shows “Rejected”, it means that UCM6xxx didn’t get registered with the provider. Verify that provider’s server is reachable from UCM6xxx and double confirm trunk credentials.

DID/DOD Configuration

Direct Inward Dialing (DID)

DID (Direct Inward Dialing) is a service provided by the ITSP to subscribers using IP-PBX, adding possibility to route incoming calls to a specific DID to a specific extension. Using DIDs, it will allow extensions to be reachable from outside directly without going through main office number.

In this example, following DIDs have been provided with first trunk “Provider_1”: 0655441000 / 0655441001 / 0655441002 / 0655441003 / 0655441004 / 0655441005 / 0655441006 / 0655441007 / 0655441008 / 0655441009 / 0655441010.

Company wants to redirect incoming calls to specific extensions using provided DIDs.

UCM6xxx in main office is using extensions range: 1000 – 1999.

Note

Make sure DID Mode is set correctly under trunk advanced settings. Provider may include DID number in “Request-line” or “To-header”.

Following configuration can be done to achieve this:

Access UCM6xxx Web UI 🡪 Extension/Trunk 🡪 Inbound Routes. Select “Trunk 1” and press “Add” button.
In DID Pattern field, enter “_0655441XXX”.
Configure ByDID as Default Destination and check “Extension” in “DID Destination” options.
Configure Strip field. In this example: Strip=6 to remove first 6 digits from incoming number and keep last 4 digits. If call is coming to 0655441007, UCM6xxx will strip 065544 and keep 1007.
Click and to apply configuration.

Direct Outward Dialing (DOD)

The UCM6xxx provides Direct Outward Dialing (DOD) which is a service of a local phone that allows extensions within a company ABC’s UCM to connect to outside lines directly.

We will use Company’s ABC trunk 0655441000 with 11 DIDs associated to it. At the moment when a user makes an outbound call their caller ID shows up as the main office number which is 0655441000. This create a problem as the CEO would like that his calls to comes from his direct line. This can be accomplished by configuring DOD for the CEO’s extension. Other group member also can benefit from DOD to have their own line showed when making calls.

Steps on how to configure DOD on the UCM6xxx:

To setup DOD go to UCM6xxx Web UI 🡪 Extension/Trunk 🡪 VoIP Trunks page.
Click to access the DOD options for the selected SIP Trunk.
Click “+ Add DOD” to begin your DOD setup.
For “DOD Number“, enter one of the numbers (DIDs) from your SIP trunk provider. In this example, we will enter in the number for the CEO’s direct line (0655441000).
Enter a name for the DOD in the “DOD Name“.
If extension number need to be appended to the DID number click on “Add Extension”.
Select an extension from the “Available Extensions” list. Users have the option of selecting more than one extension. In this case, we would select the CEO’s extension. After making the selection, click on the button to move the extension(s) to the “Selected Extensions” list.
Click and to apply configuration.

Users can press “Edit DOD” to check/add/delete extensions that are associated to a particular DOD.

Create Outbound/Inbound Routes

In this section we will give an example of creating Outbound and Inbound Rules for trunk 1 “Provider_1” to allow receiving incoming calls and to be redirected to IVR and to allow outgoing calls to be made.

Create Inbound Routes

Access UCM6xxx Web UI 🡪 Extension/Trunk 🡪 Inbound Routes. Select “Trunk 1” and press “+ Add”.
In DID Pattern field, enter “_X.”. This allows all incoming calls to be received.
Set IVR as Default Destination. (Assuming IVR is pre-configured).
Click and to apply configuration.

Note

On UCM630x series, you can also configure the name of the Inbound Route Name, it is optional.

As for time condition based inbound route, please refer to section TIME CONDITION.
Special ringing tone option is called Ringback tone on the UCM63xx series.

Create Outbound Routes

Go to Web UI 🡪 Extension/Trunk 🡪 Outbound Routes.
Click on “+ Add” button to create a new outbound route.
Enter the Calling Rule Name, Pattern and choose “Provider_1” in Use Trunk.

In below figure, we set “Pattern” to “_06XXXXXXXX” to allow only dialed numbers with leading 06 and 10-digit length to be accepted. Extensions with privilege “Internal” or higher can use this route/trunk.

Users can add comments to a dial plan by typing “/*” and “*/” before and after each comment respectively, in our example we can set the pattern to: “_06XXXXXXXX /*route1*/ ”

Another outbound route should be set using “Provider_2” with following parameters:

Pattern: “_99X.” (to allow only dialed numbers with leading 99 to be authorized).
Privilege: International for instance.
Strip: “2” (to remove prefix 99 before calling out).

To dial international numbers such as 0016175669300, users need to have privilege “International” in used extension and dial 990016175669300.

For time condition based Outbound Routes, please refer to TIME CONDITION.

Info

When DOD Number and Name configured, they are sent in the From and Contact headers in the SIP messaging.

Peer Trunk

In this chapter, we will consider that company ABC has a branch office equipped with UCM6xxx, and they want to be able to communicate between the two offices.

Assuming following:

Both UCM6xxxs have public IP addresses.
Or both UCM6xxx are on the same LAN/VPN using private or public IP addresses.
Or both UCM6xxx can be connected through a router using public or private IP addresses (with necessary port forwarding or DMZ).
UCM6xxx in main office is using extensions range 1XXX, while UCM6xxx in branch office is using extensions range 2XXX.