Telephony ISDN vs SIP lines

/ Telecoms

ISDN and SIP lines are two of the main telephony options for businesses of all sizes, and each offers its own advantages – so which is right for you?

First of all, it’s worth defining the terms, beginning with the older protocol, ISDN. The Integrated Services Digital Network was the go-to option for business use for many years, and while it is scheduled to be deactivated in 2025, there’s still some good years left in the technology yet.

SIP, meanwhile, stands for Session Initiated Protocol and transmits trunk signals via IP telephony – a technology that has grown in reliability over the years and is now the preferred method for an increasing number of businesses.

ISDN is a scalable option for small and growing businesses, starting with just two voice channels for simultaneous calls, but quite easy to increase to eight or more lines using an ISDN30 circuit – each of these supports up to 30 simultaneous calls, and you can add extra circuits as needed.

Existing copper cables can be used with ISDN circuits, so there are no infrastructure issues, but by transmitting the data digitally you typically get a more professional, business-standard call quality. The lines can also be used to transmit data, with multiple lines offering even better bandwidth for file transfers.

SIP trunking is rapidly becoming the mainstream option of the two, particularly among companies that are preparing well in advance for the 2025 shut-off of BT’s core ISDN infrastructure, by which time all business lines are expected to migrate to IP protocols.

Existing telephone numbers can be ported over to SIP, so there’s no need to change your company literature or ask customers to dial into an unfamiliar-looking IP dialling code.

Whereas ISDN delivers data over voice lines, SIP works the other way around, using high-speed internet connections to transmit your voice data as well as your internet file transfers, emails and so on.

New numbers can be added to your Wide Area Network seamlessly, without the need for additional circuits, as long as you have the bandwidth to support the lines you need on top of your digital data transfers – and combining the voice and data signals is typically more cost efficient.

For many businesses the question in the past has been whether to prioritise clear voice calls via ISDN, or whether SIP trunking that transmits your voice via an IP connection is the better option.

The question really remains unchanged – ISDN has some good years left in it and is still a great option for small businesses and fixed line numbers, while SIP trunking offers good scalability.

Whichever telephony solution you prefer – or if you need advice on which is best for you – Daviker are here to help with all enquiries, with an aim to save you money on your telecoms costs while improving call quality at the same time.