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In light of the impending ISDN switch-off, many businesses are currently evaluating the advantages and disadvantages of ISDN in comparison to its more contemporary counterpart, SIP(or SIP Trunks), to determine whether making the switch is a viable decision before the impending deadline. (For more information about the BT ISDN Switch Off)

Understanding ISDN and SIP:

ISDN (Integrated Service Digital Network) has been the primary solution for businesses' communication needs for many years. It is a set of digital communication standards designed for the transmission of voice and data. ISDN relies on physical copper and fibre lines interconnected through telephone exchanges across the globe.

On the other hand, Session Initiation Protocol (SIP) refers to the set of rules that enable the initiation and termination of communication sessions, such as voice calls between two individuals utilising an IP connection. SIP trunking is the service that allows the practical implementation of this protocol. In essence, SIP and SIP trunks constitute an on-premise solution for a telephone system that employs virtual phone lines rather than physical wires, transmitted over a broadband connection.

What are the Benefits and Negatives of ISDN?

Pros and Cons of ISDN

  • Proven Reliability: ISDN has a long track record of reliable service, with high-quality voice calls typically delivered over dedicated fibre or copper circuits.

  • Fexibility: ISDN allows for multiple numbers, often known as Direct Dial-In (DDI) numbers.

Drawbacks of ISDN

  • Limited Scalability: ISDN may hinder business growth plans, as it does not easily expand to accommodate new users or changing requirements.

  • Installation and Downtime Costs: Expanding or relocating your office can be expensive due to installation costs and potential downtime. Moving numbers may be challenging, leading to the need for call forwarding and additional costs.

  • Limited Failover Options: ISDN lacks robust options for maintaining inbound and outbound calls when the circuit experiences an outage.

  • Limited options to keep inbound/outbound calls in service if ISDN circuit becomes unavailable.

  • High Rental Costs: Ongoing equipment rental and call charges can be expensive.

  • Slow Fault Resolution: Some ISDN faults can take up to 72 hours to repair.

  • Decreased Expertise: With current technology trends, fewer engineers are trained on ISDN phone lines, making support less accessible.

  • Limited DDI Redundancy: In the event of an outage, all DDI numbers can only be diverted to a single number.

Discover the low-down on the BT ISDN Switch-off

Exploring the Advantages and Disadvantages of SIP (Trunking)

Benefits of SIP

  • Cost Savings: SIP typically offers lower call costs, including free internal calls between sites and free calls to UK local, national, and mobile numbers. Businesses can expect to save up to 50% on line rental and 25% or more on call expenses.

  • Number Flexibility: SIP allows you to select your own phone number without geographical constraints.

  • Streamlined PBX Management: SIP trunking reduces the number of Private Branch Exchanges (PBXs) you need to maintain while retaining existing phone numbers, even if you relocate.

  • Scalability and Control: SIP trunks provide the flexibility to add or remove lines and adjust call routing as your business grows or evolves.

  • Remote Work and Disaster Recovery: SIP is adaptable for routing calls to remote workers and is ideal for disaster recovery scenarios.

Drawbacks of SIP

  • Broadband Reliability: SIP can pose challenges if delivered over an unreliable broadband link.

How to make the move from ISDN to SIP

Download our free ebook from our Info Hub.

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Transitioning from ISDN to SIP

For businesses looking to make the transition from ISDN to SIP, we recommend checking out our free ebook available for download on our Info Hub. This resource provides valuable insights and guidance on the migration process.

So, Which Option Should Your Business Choose? ISDN or SIP?

Given the phasing out of ISDN, with the inability to purchase additional ISDN lines after September 2023 and a mandatory migration and switch-off period between April and December 2025 (refer to the BT ISDN Switch-off blog for details), SIP emerges as the logical choice. SIP trunking offers numerous advantages, including cost-effectiveness, flexibility, control over phone numbers, and quicker installation, making it the best alternative to ISDN for businesses looking to adapt to the changing communication landscape.

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