Details of system cutover will depend on your migration plan. Most commonly, the process of retiring the old system and bringing the new one on line is gradual, with the two systems, or at least their parts, coexisting for a while to enable an orderly and controlled transfer of the user fleets.
There are four important considerations for this type of scenario:
When migrating from one trunked system to another on a channel-by-channel basis, the combined capacity of the two systems will be less than that of either one individually. This happens for two reasons; instead of one, two of your channels will serve as control channels, and due to the nature of compounding traffic handling capacity in trunked systems, the average capacity per channel will be reduced.
This temporary capacity reduction may be of no consequence on systems with enough channels. On busy systems the combined reduction may be unacceptable and prompt you to opt for the rare instantaneous cutover mentioned below.
It is important to plan ahead for interoperability between the two coexisting systems. Potential functional capabilities are limited only by budget and common sense. It is possible to design and implement elaborate and expensive solutions providing high level of interoperability, allowing seamless roaming, transparency of advanced signaling, etc. How important, or how much are these worth during the transition time? Is it easier and more economical to opt for the simplest solutions (for example, console patching on demand) while driving towards minimizing the transition time? The answers will vary for different Public Safety organizations based on their particular circumstances.
- Equipment space
In the past, operating two networks simultaneously would probably have caused space issues at some or all of your sites and equipment rooms. However, the smaller equipment footprints of the new technologies mean you can usually support the old and new systems operating simultaneously, without duplicating their space requirement.
- Instantaneous cutover
In some rare cases the cutover may be instantaneous when the old system is taken off the air at the same time when the new system is brought on line. This risky scenario should be designed so that it can be easily and orderly reversed if needed. This type of cutover is typically executed at the time of least radio traffic – such as during early hours of Monday morning.
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