SIP Trunks - Resilient SIP Trunking from Gamma

SIP Trunking from Gamma is the UK's leading IP telephony/VoIP service, utilising SIP protocol. This provides quality inbound and outbound voice calls. Gamma SIP, compatible with the majority of iPABX/SBCs (including Microsoft Teams/Skype and Cisco), delivers enhanced cloud features including; automatic failover, flexible SIP channels and inbound call control.


  • Choose the number you present
  • Keep your existing telephone numbers
  • Built-in Business Continuity as standard
  • Protect yourself from Fraud with in-built tools
  • It'll work with your existing IP telephony system or SBC
  • Inclusive call minutes to 01,02, 03 and 07 numbers
  • Optional inbound call control on your telephone numbers
  • Carrier-grade core network
  • Ability to increase call capacity quickly and easily
  • Optional PCI compliant payment handling service


  • Full control of outbound call presentation regardless of location
  • Keep numbers important to your business regardless of any relocation
  • Protect from on-site failures with network divert on DDI basis
  • Guard against fraudulent calls
  • Vast choice of compatible IP Telephony systems
  • Value for money and reduce bill shock
  • Improved resilience across the entire estate
  • Simplified architecture using data infrastructure
  • Pay for channels you need, when you need them
  • Achieve PCI compliance cost effectively


£4.25 per unit per month

  • Free trial available

Service documents


G-Cloud 11

Service ID

3 0 1 3 0 9 7 5 8 6 2 8 7 1 5



Sam Winterbottom

0333 014 0555

Service scope

Software add-on or extension
Yes, but can also be used as a standalone service
What software services is the service an extension to
Gamma's Inbound Service
Cloud based or hosted iPBXs
Session Border Controllers
Cloud deployment model
  • Public cloud
  • Private cloud
  • Hybrid cloud
Service constraints
As a VoIP service, calls to 999 via SIP trunks may not be possible, during a service outage where the customer loses total connectivity for example, owing to a power outage or the failure of all data access.
In such circumstances the customer should use their PSTN line or mobile to make the emergency call.
System requirements
  • Conformance tested PABX (Confirm with Gamma)
  • Compatible Session Border Controller (Confirm with Gamma)
  • Appropriately sized data access
  • IP Address Authentication
  • Sufficient SIP Licences on PABX

User support

Email or online ticketing support
Email or online ticketing
Support response times
Gamma's Service Desk is 24x7 and any emails or online tickets are handled as per the below SLA.
General Questions are classified as a severity 4 and have an update SLA of 48 hours.
However, other severity classifications have a response time as per below:
Severity 0 -30 min
Severity 1 -120 min
Severity 2 -4 hours
Severity 3 -12 hours
User can manage status and priority of support tickets
Online ticketing support accessibility
None or don’t know
Phone support
Phone support availability
24 hours, 7 days a week
Web chat support
Onsite support
Yes, at extra cost
Support levels
Gamma provides one level of support for all SIP customers 24x7x365 - included free of charge as part of the service charge. The following service levels apply with target resolution times:

Critical Fault - Loss of service. Multiple services affected - 4 Clock Hours
High - Loss of service - single service - 8 Clock Hours
Medium - Disrupted service - 3 Working Days
Low - Single number destinations or Quality of Service - 7 working days

SIP Trunks with Semafone - Problem(s) affecting single customer which does not impact upon overall service delivery. Software can be used in a limited fashion and business contingency procedures are available - Ticket reference issued within 3 normal business hours. Update with a resolution plan within 9 normal business hours of all mandatory data being received.

Service availability for resilient SIP trunks is 99.99% for core service. Mean Average PESQ Score target of 4.1 for G711 and 3.7 for G729.

We provide Service Desk and Account Management Teams. Support engineers answer the phones in the Gamma Service Desk and perform first stage fault analysis. If they are unable to resolve the incident will be escalated to Tier 2 and Tier 3 engineers.
Support available to third parties

Onboarding and offboarding

Getting started
Our SIP trunking product does not require specific user training, although we do provide comprehensive user acceptance and handover documentation. We also supply a customer support manual for all contact points and escalations. For an optional bolt on, SIP Trunk Call Manager, we provide comprehensive admin and user training for the web portal and App. This is offered via our tutorial videos, onsite training (additional cost), webinar online training, user documentation and a full help section on the web portal.
We also provide online and webinar training for our web-based billing and reporting tool.
A named Major Account Manager and Customer Development Manager will also be assigned to your account to support you.
Service documentation
Documentation formats
  • HTML
  • PDF
  • Other
Other documentation formats
  • .mpg
  • .doc
End-of-contract data extraction
Our Customer Portal is a secure online space giving customers complete visibility of the assets that we manage for them. We offer a complete view of their estate, including telephone numbers (CLIs), the product related to that number and its geographical location. All invoices are in one place and kept for 12 months for historical billing information on the services you have taken.
This information can be easily downloaded for extraction into excel.
End-of-contract process
At the end of the contract the customer moves onto a rolling 30 day contract on our standard rates. Through our online billing and reporting portal, customer can get their asset list, including numbers that can be ported away and details of the services they currently take with us. This will be provided at no additional cost. It is up to the new provider to port the numbers away.

Using the service

Web browser interface
Supported browsers
  • Internet Explorer 9
  • Internet Explorer 10
  • Internet Explorer 11
  • Microsoft Edge
  • Firefox
  • Chrome
  • Safari 9+
Application to install
Compatible operating systems
  • Android
  • IOS
  • MacOS
  • Windows
  • Windows Phone
Designed for use on mobile devices
Differences between the mobile and desktop service
We have a bolt on App (see pricing sheet) that can be added as an option to SIP Trunk Call Manager. Upon successful download from the relevant app store, the user is able to log in to access a subset of SIP Trunk Call Manager Functionality as available at: The user has access to edit
components of call routing for numbers provisioned on this service and in accordance with their user permissions.
Functionality includes ability to route calls to an alternative destination number/voicemail/divert calls/invoke
pre-configured call plan. Key reporting statistics are also available including Performance graphs and call history.
Service interface
Description of service interface
We have an optional bolt on - SIP Trunk Call Manager. Portal-based, the user is able to log in and has access to edit components of call routing for numbers provisioned on this service and in accordance with their user permissions.
Functionality includes ability to route calls to an alternative destination number/voicemail/divert calls/invoke
pre-configured call plan. Key reporting statistics are also available including Performance graphs and call history.
Accessibility standards
None or don’t know
Description of accessibility
Standard web-browser access with standard accessibility options associated with those web-browsers.
Accessibility testing
Customisation available
Description of customisation
The design of the SIP service can be configured and customised for various designs (Active / Standby, Loadshare, Resilient+, Enhanced). Customer confirms design option during project kick off and then built by Gamma.
The number of concurrent call channels required (subject to minimum number) can be customised subject to sufficient data bandwidth being available.
Whether existing customer DDI numbers are ported from other services. Determined by administrators.
Whether new DDI numbers are required for the service. These can be added by administrators of the service.
If individual call control is required per DDI this can be achieved through a web based customer portal using SIP Trunk Call Manager.
Where the option is taken, customer administrators can manage SIP Trunk Call Manager, a feature-rich, centralised inbound call management service via an easy-to-use web portal and App. The following are customisable:

Call Queuing Day
Time of Day Routing
Hunt Group
Voice Mail
Date Routing
Increased resilience
Auto attendant
Set user access individually
Divert (on busy, on no reply, on failure)
Access to full call statistics
Advanced Statistics


Independence of resources
We undertake a monthly Capacity Planning Forum whereby the utilisation of every network component is reviewed against planning rules and sales forecast to ensure that we have sufficient capacity and overhead to manage our customer's requirements. Additionally there is weekly planning review on capacity management adjustments.
Each SIP customer's resource requirements are taken into account and sufficient network is allocated to them. We also manage our network to spread traffic during very busy periods.


Service usage metrics
Metrics types
Gamma SIP Trunk Call Manager service provides a range of on line call reporting on a per number basis. Full summary reports are provided; how many calls are getting through, where are my customers located, what are my call trends, when are my busy times. Detailed call analysis is available via the advanced statistics package.
Reporting types
  • Real-time dashboards
  • Regular reports
  • Reports on request


Supplier type
Not a reseller

Staff security

Staff security clearance
Conforms to BS7858:2012
Government security clearance
Up to Developed Vetting (DV)

Asset protection

Knowledge of data storage and processing locations
Data storage and processing locations
United Kingdom
User control over data storage and processing locations
Datacentre security standards
Complies with a recognised standard (for example CSA CCM version 3.0)
Penetration testing frequency
At least once a year
Penetration testing approach
‘IT Health Check’ performed by a CHECK service provider
Protecting data at rest
Encryption of all physical media
Data sanitisation process
Data sanitisation type
Deleted data can’t be directly accessed
Equipment disposal approach
A third-party destruction service

Data importing and exporting

Data export approach
Our Web Portal allows users access to their associated number ranges. Typically users will extract their applicable data in Excel or CVS format.
Data export formats
  • CSV
  • Other
Other data export formats
  • Excel
  • PDF
Data import formats
  • CSV
  • Other
Other data import formats

Data-in-transit protection

Data protection between buyer and supplier networks
Private network or public sector network
Data protection within supplier network
  • TLS (version 1.2 or above)
  • Legacy SSL and TLS (under version 1.2)

Availability and resilience

Guaranteed availability
SIP trunk service availability is calculated as:
Total number of minutes in the measurement period – Unplanned Downtime x 100 / Total number of minutes in the measurement period
Note: If a Service is partially available then the Unplanned Downtime shall be calculated in equal proportion i.e. if a service is 50% available then the unplanned downtime will be calculated as 50% x elapsed period of the incident.
Availability Measurement Period: 1 Calendar month
Target availability for SIP Trunk Endpoint Resilient Build:
Core service: 99.99%
Non-Core Services: 99.50%
Not included:
- Outages which are deemed by us to be the result of matters outside of its direct control
- Planned or emergency maintenance works
- User error
(1) Core functions are defined as Gamma Switching infrastructure, transmission equipment and
core network, the service that supports call routing and termination.
(2) Non-Core functions include Gamma Support Systems, access to any relevant portals and feature based services such as Call Plans, Call diverts, Auto Attendant, Call Recording, and Unified Messaging
(3) A Resilient build SIP Trunking means a Gamma approved
configuration such as dual Session Border Controllers offering geographic diversity.
PESQ score target for G711 is 4.1 and G729 is 3.7
Approach to resilience
We hold ISO 22301:2012 Business Continuity Management accreditation. As this information is sensitive, further specific information is available on request.
Outage reporting
A public network status dashboard
Email alerts
Portal alerts
Text messages to opted in mobile numbers
Service desk verbal communication

Identity and authentication

User authentication needed
User authentication
Username or password
Access restrictions in management interfaces and support channels
Relevant only to SIP Trunk call manager services. Customer administrators can set permissions for other users to give them access to certain areas of the portal. They are able to restrict access to certain areas of the management and support interfaces.
Access restriction testing frequency
At least once a year
Management access authentication
Username or password

Audit information for users

Access to user activity audit information
Users contact the support team to get audit information
How long user audit data is stored for
At least 12 months
Access to supplier activity audit information
Users contact the support team to get audit information
How long supplier audit data is stored for
At least 12 months
How long system logs are stored for
At least 12 months

Standards and certifications

ISO/IEC 27001 certification
Who accredited the ISO/IEC 27001
Lloyd's Register Quality Assurance Ltd
ISO/IEC 27001 accreditation date
26 March 2019
What the ISO/IEC 27001 doesn’t cover
ISO 28000:2007 certification
CSA STAR certification
PCI certification
Other security certifications
Any other security certifications
  • NICC ND 1643
  • Cyber Essentials

Security governance

Named board-level person responsible for service security
Security governance certified
Security governance standards
  • ISO/IEC 27001
  • Other
Other security governance standards
Cyber Essentials
Information security policies and processes
Gamma has deployed an Information Security Management System Manual (ISMS) which meets and is certified to ISO 27001:2013 and Cyber Essentials. It is supported by numerous policies and processes including but not limited to the following:

Information Security Policy
Information Security Incident Policy
Acceptable use policy
Access Control Procedure
Backup Plan
Business Continuity Plan
Confidential Data Policy
Data Protection Policy

The Reporting structure is from employees or customers to the Information Security Manager to the Information security Forum which is attended by several Directors and heads of departments. The Information Security Forum meets monthly to review all security incidents and events and corrective actions are agreed and tracked at this forum.

To raise awareness Gamma use a computer based training platform for Security Awareness which is repeated annually. Line Managers have a responsibility to ensure their staff are aware of and follow these policies.

Operational security

Configuration and change management standard
Conforms to a recognised standard, for example CSA CCM v3.0 or SSAE-16 / ISAE 3402
Configuration and change management approach
Change Control Process covers changes made to operational systems, to mitigate the risks and impacts that any change has and ensures good communication at all stages.
Change Management ensures changes to core infrastructure and services are performed and implemented correctly.
Best practice guidance, aligned to ITIL (OGC), recommends that the starting point for any change should be a review of generic questions or the ‘seven Rs’.
A risk and impact assessment is carried out for each change this involves detailing the assets under change.
The Change Advisory Board (CAB) has a representative from each impacted business area.
Vulnerability management type
Conforms to a recognised standard, for example CSA CCM v3.0 or SSAE-16 / ISAE 3402
Vulnerability management approach
We use failure mode effects analysis process, conducting regular, systematic assessments of vulnerabilities to determine the necessity of safeguards, countermeasures and controls, monitoring for changes to maintain an acceptable level of risk. Includes identifying key information assets and subjecting them to specific risk assessments, assessing exposure to a list of common threats and vulnerabilities, maintaining risk registers, implementing technical, policy, business continuity and management initiatives;
Each patch is assessed and deployed accordingly:
High - Urgently.
Medium - ASAP.
Low - as time permits.
Gamma utilise many Vendor sources and industry RSS feeds, CERT, Ubuntu and Debian. Member of CiSP.
Protective monitoring type
Conforms to a recognised standard, for example CSA CCM v3.0 or SSAE-16 / ISAE 3402
Protective monitoring approach
Gamma utilise GPG 13 guidance. Gamma has built a Security Information & Event Management Solution (SIEM) to identify potential compromises. If a compromise is found it is investigated. A Security Incident is raised to track the investigation, root cause and solutions if required to rectify or improve the situation. We respond to incidents as close to real time as practicable.
Incident management type
Conforms to a recognised standard, for example, CSA CCM v3.0 or ISO/IEC 27035:2011 or SSAE-16 / ISAE 3402
Incident management approach
Gamma has an Incident Management process which has numerous pre-defined sub groups of staff designated for particular products or scenarios. It can be initiated by any member of staff and is managed by the 24/7 Network Operations Centre (NOC). Any incident is reported by the customer to the Service Desk, it is recorded in a customer relationship management tool (CRM) and an Incident report is produced after root cause analysis has taken place. Any Incident reports are made available to end users via pdf.

Secure development

Approach to secure software development best practice
Independent review of processes (for example CESG CPA Build Standard, ISO/IEC 27034, ISO/IEC 27001 or CSA CCM v3.0)

Public sector networks

Connection to public sector networks
Connected networks
  • Joint Academic Network (JANET)
  • Health and Social Care Network (HSCN)


£4.25 per unit per month
Discount for educational organisations
Free trial available
Description of free trial
We can provide free SIP channel rental for a maximum period of 3 months. Customer pays for any calls they make.
We can also provide a general demo account for SIP Trunk Call Manager

Service documents

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