One Call, Many Call Centers
In earlier versions of the 911 system the majority of calls were made from the caller's home. These "landline" calls could easily be routed to the appropriate 911 communications center based on the address of the caller. With the increase in 911 calls being made from mobile devices, the structure of the 911 system has had to change in order to find the true location of the caller.
While the technology has improved and there are several ways for today's 911 dispatchers to locate someone calling from a mobile phone, these calls may be initially routed to a regional communications center where the dispatcher is responsible for identifying the exact location of the emergency and determine what type of emergency it is. Then calls can be redirected to a more specific local agency or the most appropriate type of responder (Law, Fire, EMS).
In the few seconds it takes to transfer a call, the caller may interpret the brief silence as being placed on hold. This also explains why some information will have to be repeated. As the caller will now be speaking to a different agency, that dispatcher will want to confirm essential details so that no life-safety information is missed. Obtaining this firsthand, in the caller's own words, is invaluable since it is usually more accurate.
Not every 911 dispatch center is created equal. They come in all sizes and configurations and are as varied as the different communities that they provide service for. Large cities have different needs than small rural communities. Some emergency communications centers employ enough dispatchers that each one works a specific position and is tasked with a singular responsibility. In other centers, the dispatchers are expected to be cross-trained and utilize their multitasking abilities to handle multiple responsibilities at the same time.
In some instances the dispatcher that picks up the ringing 911 line is also responsible for dispatching the officer/firefighter/EMT to the location of the emergency. These dispatchers are alternating their workflow between speaking on the phone and talking over a radio channel (or multiple channels). When speaking on the radio the dispatcher will most likely not be heard on the phone.
While the caller cannot hear the dispatcher it does not mean that the dispatcher can't hear the caller. Even when speaking on a radio channel the caller's end of the phone line remains open so that the dispatcher can continue to monitor the situation. This is why it is important for agencies to recruit, train, and retain 911 dispatchers that possess superior listening skills and the ability to multitask in stressful situations.
Dispatchers Cost Money
Emergency Tele-Communications Centers are just like any other service: customers may be placed on hold because the incoming calls exceed the number of employees available to answer the ringing lines.
Whether they are funded publicly or privately the budgets of these centers must provide for Computer Aided Dispatch (CAD) Systems, telephone infrastructure, radio consoles, etc. Like every other business, a balancing act is applied to hire the appropriate number of dispatchers while keeping enough money in the budget for everything else.