repeat

rednet.CHANNEL_REPEAT = 65533

-- Find modems
local tModems = {}
for n,sModem in ipairs( peripheral.getNames() ) do
    if peripheral.getType( sModem ) == "modem" then
        table.insert( tModems, sModem )
    end
end
if #tModems == 0 then
    print( "No modems found." )
    return
elseif #tModems == 1 then
    print( "1 modem found." )
else
    print( #tModems .. " modems found." )
end

function open( nChannel )
    for n=1,#tModems do
        local sModem = tModems[n]
        peripheral.call( sModem, "open", nChannel )
    end
end

function close( nChannel )
    for n=1,#tModems do
        local sModem = tModems[n]
        peripheral.call( sModem, "close", nChannel )
    end
end

-- Open channels
open( rednet.CHANNEL_REPEAT )

-- Main loop (terminate to break)
local ok, error = pcall( function()
    local tReceivedMessages = {}
    local tReceivedMessageTimeouts = {}
    local nTransmittedMessages = 0

    while true do
        local sEvent, sModem, nChannel, nReplyChannel, tMessage = os.pullEvent()
        if sEvent == "modem_message" then
            -- Got a modem message, rebroadcast it if it's a rednet thing
            if nChannel == rednet.CHANNEL_REPEAT then
                if type( tMessage ) == "table" and tMessage.nMessageID and tMessage.nRecipient then
                    if not tReceivedMessages[ tMessage.nMessageID ] then
                        -- Ensure we only repeat a message once
                        tReceivedMessages[ tMessage.nMessageID ] = true
                        tReceivedMessageTimeouts[ os.startTimer( 30 ) ] = tMessage.nMessageID

                        -- Send on all other open modems, to the target and to other repeaters
                        for n=1,#tModems do
                            local sOtherModem = tModems[n]
                            peripheral.call( sOtherModem, "transmit", rednet.CHANNEL_REPEAT, nReplyChannel, tMessage )
                            peripheral.call( sOtherModem, "transmit", tMessage.nRecipient, nReplyChannel, tMessage )
                        end

                        -- Log the event
                        nTransmittedMessages = nTransmittedMessages + 1
                    end
                end
            end

        elseif sEvent == "timer" then
            -- Got a timer event, use it to clear the message history
            local nTimer = sModem
            local nMessageID = tReceivedMessageTimeouts[ nTimer ]
            if nMessageID then
                tReceivedMessageTimeouts[ nTimer ] = nil
                tReceivedMessages[ nMessageID ] = nil
            end

        end
    end
end )
if not ok then
    printError( error )
end

-- Close channels
close( rednet.CHANNEL_REPEAT )