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The Telephony Application Server (SVI-TAS) enables the rapid delivery of converged services across IMS, NGN and Legacy SS7 networks. The SVI-TAS enables operators to leverage existing infrastructure, extend return-on-investment and rapidly deploy new services.

API Operation

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The Telephony Application Server (SVI-TAS) operates over clearly defined API’s that present an abstracted version of the underlying DIAMETER, SIP, CAMEL, MAP etc signalling. It can be driven by either Squire Technologies python based client (SVI-TAC) or by operators 3rd party applications, and provides an extremly flexible, service driven platform with huge benefits:

tas api network diagram

USSD Gateway

Unstructured Supplementary Services Data (USSD) is a session based protocol used in 2G/3G networks to send text between a mobile phone and an application program in the network. Unlike SMS there is no store and forward as USSD transactions only exist for the length of a session. USSD applications are generally menu driven as able to push text in menu format to subscriber handsets.


  • Pre-Paid Roaming – USSD used in the network to check in real-time
    subscriber has enough credit for call
  • Pre-paid subscribers – use USSD to manage and top-up their accounts
  • Mobile Money – subscribers able to make payments and purchases
    via their phones menu driven USSD interface

Example Case Study

Working with a 4G mobile operator rolling out roaming services they needed to insure that pre-paid subscribers credit checks operate correctly in 3G networks.

Some 3G networks perform credit checks via USSD. The SVI-TAS integrated with a DIAMETER SVI-IWF product is deployed in the clients 4G network to deliver the required USSD to DIAMETER messaging inter-operability. In a subsequent phase of the project the client decided to provide their subscribers with a full USSD driven menu application. This was interfaced and configured using the SVI-TAS to provide the HTTP interface to their OCS platform. This flexibility and ease of deployment allows our clients to rapidly evolve and extend functionality according to their requirements.

ussd gateway diagram


The SVI-TAS supports the 3GPP IMS component the IM-Service Switch Function (IM-SSF) 3GPP 23.278 providing a seamless bridge between an IMS network (SIP) and a CAMEL based SS7 Intelligent Network.

When an operator initially deploys an IMS network they are unlikely to be able to enable all the revenue services available to their existing legacy subscribers. To insure continuity of service the IMS network can leverage the existing Intelligent Network through the IM-SSF component.

im-ssf diagram

Reverse IM-SSF

In “reverse” the IM-SSF allows legacy subscribers to access the new services available in an IMS network. It is the glue that allows legacy subscribers to access new services run from SIP application servers – i.e Mobile PBX, OTT etc.

rim-ssf diagram

Example Services

Subscriber Authentication
Mobile Number Portability
Billing and Charging
Fraud Detection
Lookups and Dips 800
Call Barring
Call Forwarding
Equipment Identity Register (EIR)
Location Based Services

Interface Support







Commercial Off The Shelf

Supplied on standard Dell servers optionally with dedicated E1/T1/STM-1 support.

Virtual Deployment

Virtual Machine deployed on industry-standard servers in a data centre environment using a hypervisor, i.e. VMware.

Cloud Deployment

Delivered as a Virtual Network Function (VNF) in AWS, OpenStack, Nokia and Google cloud infrastructure.

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Further Information

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Squeezing more from IMS, NGN 
and Legacy Networks Whitepaper

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Find out more about our
SVI-DSC Diameter Signalling Controller

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Download our SVI-TAS Presentation