I'm seeing a lot of guesswork in this thread so let me break it down for you all as someone who deals with this day in and day out.
The counties of Kent, Queen Anne, Talbot, Caroline and Dorchester all have a working agreement that they will handle each others 911 calls in the event of rollovers. The order goes like this as to "who gets whos calls" Dorchester to Caroline, Caroline to Talbot, Talbot to Queen Anne, Queen Anne to Kent and Kent to.....Dorchester. Yes that might cause some confusion on Dorchesters side getting calls from 3 counties away but back to the topic at hand.
A lot of times when we receive calls from Caroline during a rollover situation like a bad wreck on 404 or a house fire we will begin to take the information from the caller to get an idea of the situation. Most of the time we verify the address is in Caroline county and then attempt to transfer the call back to them so they can get the additional information from the caller instead of us gathering the information and attempting to pass it along thru the phone or radio which I'll get to in a second. If we transfer it back and they pick up and process the call no big deal, however if they do not or it takes a large amount of rings to pass thru we will take pertinent information and disconnect with the caller.
The idea behind this system is that no one gets a busy signal, so even if a large event like a wreck is occurring but grandma who lives back in the woods 10 miles away is having chest pains she won't have to wait for someone to answer the call.
Now onto how we pass along information regarding calls. From my experience we primarily use 3 methods of getting information from one county to another, which are, but not limited to the ol' fashioned landline, the MESIN network (which is apparently in the process of being phased out) and the "Intercom". The phone is exactly what you think, we call, give the information and they dispatch. MESIN is of course used by the entire shore so we attempt to keep things short and sweet, usually just to verify cross streets or a call type. And then we have the UMDES IC or "Intercom" which from my knowledge is used primarily Kent and Queen Anne as a console-to-console, plain speech, system that's only used by Eastern Shore FiRST users, as I said Queen Anne and Kent are heavy users and I don't know if Caroline has access to it (I'm the only one from Talbot that I know of who uses it as we still prefer using MESIN).
So there you have it, we don't have any CAD to CAD setup or anything of that matter however we do have an MSAG in Talbot that includes Caroline and Queen Anne counties so I wouldn't put it out of mind that they are planning on transitioning to the same CAD we use at some point which would certainly make it interesting if they were to implement some sort of CAD transfer from county to county.
(Also sorry about the wall of text but I couldn't watch you all squirm trying to figure this out
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