ISDN services are typically limited to the channel blocks in which they are bought (typically 2, 10, 20, or 30), whereas SIP is deployed across a business’s existing WAN. Meaning that provided the bandwidth exists to handle the traffic, channels can be dynamically added or subtracted as they are required. This has the advantage of limiting the amount of unused overhead that has to be purchased in an ISDN model, as well as allowing the business to be able to ramp up the number of SIP channels within minutes, as opposed to the days or weeks required for ISDN.
In a typical ISDN deployment the line and channel block comes with an allocated phone number. The rental charges for which are automatically factored into the cost of the ISDN, whether or not it is needed.
In a SIP based service numbers are separate from the channel blocks, which has the benefit of helping to lower the cost of the service. However, the main benefit is derived from the fact that the phone numbers are not tied to physical locations. This means that calls to SIP numbers can be diverted incredibly easily to other locations. Typically this is done as an automatic failover between multiple office sites, allowing calls for one site to be answered by another site when all the lines are busy.
This same functionality also allows numbers to be redirected in disaster recovery situations. For instance, if a business’s premises were to flood, the phone lines could easily be redirected to a single (or multiple) recovery sites until such time as the service could be restored.
SIP voice is transferred as IP (Internet Protocol), this means that customers with video enabled handsets can make video calls. Although, this kind of functionality is available on an ISDN service – the bandwidth requirements of video over ISDN make this an economically unjustifiable option in today’s marketplace.
Because SIP can be delivered across high bandwidth connections (such as Fibre, EFM and EoC) higher levels of vocal quality can be delivered from end to end. This means that customers can make and receive HD quality voice calls, assuming of course their hand sets are compatible. Additionally, with services not necessarily relying on a single connection, SIP services could utilise a primary service with automatic failover to a second path, which is not available on ISDN.
The bottom line is what it often comes down to for businesses, and for the reasons outlined above SIP almost always wins out over ISDN.
In a SIP deployment the call remains within the business’s MPLS network and is therefore able to avoid the charges for call handoffs by their telecommunications provider. Although external calls will still need to be handed off to the PSTN, because SIP traffic is IP based it is capable of traversing the company’s own MPLS WAN and being handed off without the need to purchase PRI’s.
Even for small businesses this can add up to a lot of savings. Exact figures will obviously vary from business to business, but if you are still using an ISDN based service we would recommend having a chat to Channel today to see what opportunities are available.