This post looks at the fundamental differences between trunked and conventional radio networks.
What are the top level differences between Trunked and Conventional?
In a trunked system:
- The channels are assigned to the user automatically by the system
- The call set up time is several hundred milliseconds
- One channel per site must be used as a control channel.
In an analog conventional system:
- The user manually selects the channels
- The call set up time is almost instantaneous
- No control channels are needed, so all channels are available to the user
Analog FM can be trunked or conventional (MPT1327 is an example of an analog trunked network).
- P25 can be trunked or conventional.
- DMR Tier 2 is Conventional.
- DMR Tier 3 is Trunked.
In a conventional system, the number of users that can be supported is directly proportional to the number of channels available.
Trunked systems take advantage of the fact that not everyone will need a channel at the same time, so the number of users that can be supported grows exponentially with the number of channels. For example:
The diagram tells us:
- Trunked system are more suited for larger groups of users
- Conventional systems are more suited for smaller groups of users.
Tait has a successful history of deploying large trunked or conventional systems. But, the key takeaway here is to be aware of when to use trunked, and when to use conventional. In short often the simplest solution that fits the systems needs will be the right one. Trunked is often more complicated and more costly, if you are unsure which technology is right for you get in touch by dropping a comment below.
Here are some guidelines to help decide whether a trunked or conventional system is the best solution.
- Conventional systems can support about 70 users per channel.
- If the agencies can be split into groups of 70 or fewer users who don’t need to speak to others, use Conventional.
- If the organization has 3 or fewer groups of 70 users or less, then it is sufficient to give each group it’s own Conventional channel.
For systems requiring 4 or more channels per site, the number of users that can be supported on a trunked system will become progressively greater than for a similar number of Conventional channels.
- Trunked radios cost more (typically 2 or 3 times the cost of Conventional radios), but with large systems the costs are partly offset by the need to licence fewer channels.
- Trunked systems always require linking (an IP backbone). Conventional systems can be deployed without linking in the case of smaller rural systems.
Be aware there are times where it makes sense for a system to include both trunked and conventional elements, for example:
- For Fire services, trunked may be a better choice on a shared multi-agency dispatch system, but conventional is more appropriate on the fire-ground for all responsive isolated groups.
- For Rail networks, trunked may be a better choice for the train to dispatch communications, but conventional is more appropriate in shunt yards where a few users need instant call set up.
For further reading, the functional differences between trunked and conventional systems are summarized in the following articles
• Technology Selection conventional or trunked P25:
• Trunked vs. Conventional – Some Clarifications