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Circuit Telephony Connectors

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The Circuit Telephony Connectors allow you to assign a public or a private directory number to Circuit users, so that they can make and receive phone calls in Circuit, as well as collaborate with non-Circuit users.

There are four types of Telephony Connectors:

  1. Hosted Universal Telephony Connector (hUTC)

  2. Premise Universal Telephony Connector (pUTC)

  3. Advanced Telephony Connector (ATC).

  4. OpenScape Business Telephony Connector.

The main difference between the two Universal Telephony Connectors, hUTC and pUTC, is the deployment model: hUTC is deployed in the Circuit Cloud, whereas pUTC is deployed on premises (as its name says, Premise Universal Telephony Connector).

Up to 150 Telephony Connectors can be deployed within the same Circuit domain.


For details please refer to the End-to-end document (available to authorized partners).

Hosted Universal Telephony Connector (hUTC)

The hUTC is a an application running in the cloud that allows you to connect your SIP-based platform to Circuit using a generic SIP trunk. It requires the following:

  • A static SIP trunk must be established between your voice platform and Circuit.
  • Call routing on your voice platform must be configured.
  • If using TLS, security certificates must be provided.

Any Unify or third-party PBX is supported as long as the SIP Trunk is configured. hUTC requires no additional equipment to be deployed at your enterprise.

The hUTC has a limited size (i.e., less than 100 users per Circuit domain) and therefore it is best suited for small and medium-sized business or for initial customer field trials. The hUTC has higher bandwidth requirements than the pUTC or the ATC, since all connections go to and from the Circuit Cloud.

Premise Universal Telephony Connector (pUTC)

The pUTC allows you to provide secure communication between the OpenScape Session Border Controller (OpenScape SBC) and Circuit, using a secure Web Socket for signaling and UDP/ DTLS for media.

Depending on your network configuration, it might be possible to maintain the media stream locally within your enterprise network. This allows direct conversations between phones connected to your voice platform and Circuit, running inside the enterprise network.

This model requires:

  • A generic static SIP trunk must be established between your voice platform and Circuit.
  • Call routing on your voice platform must be configured.
  • An OpenScape Session Border Controller (OpenScape SBC) from Unify should be deployed on premise (hardware or VM solution) running on the supported server voice platforms

    For more information please refer to OpenScape SBC.

  • If using TLS, security certificates must be provided.

Any Unify or third-party PBX is supported as long as the SIP Trunk is configured.

The pUTC supports larger installations with many hundred audio ports per UTC (hardware and VM performance dependent). In contrast to the hUTC, the pUTC utilizes less bandwidth by leaving the media traffic within the company's network.

Advanced Telephony Connector (ATC)

The Advanced Telephony Connector (ATC) provides a richer set of features in comparison with the Universal Telephony Connectors. This functionality requires an additional interface to the PBX which is only supported on the Unify PBXs, OpenScape Voice and OpenScape 4000. It extends Circuit into an existing telephony environment by turning it into a softphone and enhances teamwork by allowing Circuit members to easily connect with users of the traditional global telephony network.

ATC allows simple and flexible deployment that supports scalability of traffic optimization, where multiple ATC instances can run on the single, virtual or physical machine. It is also easily maintained via the Circuit settings.

The ATC allows to:

  • use One Number Service (ONS), i.e. one phone number and:

    • receive calls at the office phone number, so that no new phone number is required

    • accept an incoming call on all devices, such as web or desktop app, mobile app or desk phone

    • send ONS / office phone number as calling party

  • be mobile and move your calls to your needs:

    • use Circuit clients as softphones

    • pull call from other Circuit clients or desk phone

    • push call to desk phone or alternative phone, e.g. mobile phone

    • fallback option for softphone users that are not logged in (allows to hand over to a predefined alternative number, e.g. mobile phone)

  • control your calls from the Circuit client:

    • you can dial, accept, reject, do blind or warm transfers, hold/resume, alternate or merge to conference and send DTMF (i.e. Dual-tone multi-frequency signaling) for calls on your desk phone; all these are supported for calls performed: a) on the desk phone, under remote control (CTI), and b) when Circuit is used as softphone

    • all phone calls are listed in your phone call conversation (call journal); this includes calls preformed on the desk phone; lost calls are indicated for an easy call back

  • have conference calls:

    • you can add people on the phone to your ongoing meetings (Meeting outcall)

    • local conference dial-ins can be defined which can provide a short dial-in number and avoid call charges beside potential costs for Internet traffic to the Circuit cloud where the conference call's mixing is executed

  • use Circuit Voicemail to record telephony calls received at the office number in Circuit.

OpenScape Business Telephony Connector

The OpenScape Business Telephony Connector is a further development of hUTC that allows you to easily connect your OpenScape Business PBX V2 (with a Service Releases 2 or higher) to Circuit.

The OpenScape Business Telephony Connector requires no additional equipment to be deployed at your enterprise. Embedded into the OpenScape Business, this telephony connector interacts with related infrastructure provided by Unify or Service Provider partners’ clouds. The feature set is thus optimized for that purpose - it provides a simplified setup and maintenance of telephony user data from the OpenScape Business Web Based Administration (WBM).

OpenScape Business connects to Circuit based on dynamic SIP trunk registration with the Circuit clouds hUTCs and its upfront load balancers. To use the hUTC as an OpenScape Business Telephony Connector, make sure that:

  • A Circuit domain-specific API key is entered into your OpenScape Business system. This is needed in order to establish a SIP trunk between OpenScape Business and Circuit, and allow maintenance from the WBM.
  • Call routing is configured on OpenScape Business and OpenScape Business number is linked to the Circuit user.

In most of the cases, the deployment of a Circuit Telephony Connector requires special configuration on the firewall. Our support team will work with your IT department to perform firewall configuration as needed.


For more information you may refer to the following sections:


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