diff --git a/scada-common/comms.lua b/scada-common/comms.lua
index 34de9cb..3007cf9 100644
--- a/scada-common/comms.lua
+++ b/scada-common/comms.lua
@@ -1,16 +1,86 @@
+PROTOCOLS = {
+    MODBUS_TCP = 0, -- our "modbus tcp"-esque protocol
+    RPLC = 1,       -- reactor plc protocol
+    SCADA_MGMT = 2, -- SCADA supervisor intercommunication
+    COORD_DATA = 3  -- data packets for coordinators to/from supervisory controller
+}
 
+-- generic SCADA packet object
+function scada_packet()
+    local self = {
+        modem_msg_in = nil,
+        raw = nil
+        seq_id = nil,
+        protocol = nil,
+        length = nil
+    }
+
+    local receive = function (side, sender, reply_to, message, distance)
+        self.modem_msg_in = {
+            iface = side,
+            s_port = sender,
+            r_port = reply_to,
+            msg = message,
+            dist = distance
+        }
+
+        self.raw = self.modem_msg_in.msg
+
+        if #self.raw < 3 then
+            -- malformed
+            return false
+        else
+            self.seq_id = self.raw[0]
+            self.protocol = self.raw[1]
+            self.length = self.raw[2]
+        end
+    end
+
+    local seq_id = function (packet)
+        return self.seq_id
+    end
+
+    local protocol = function (packet)
+        return self.protocol
+    end
+
+    local length = function (packet)
+        return self.length
+    end
+
+    local raw = function (packet)
+        return self.raw
+    end
+
+    local modem_event = function (packet)
+        return self.modem_msg_in
+    end
+
+    return {
+        receive = receive,
+        seq_id = seq_id,
+        protocol = protocol,
+        length = length,
+        raw = raw,
+        modem_event = modem_event
+    }
+end
+
+-- coordinator communications
 function coord_comms()
     local self = {
         reactor_struct_cache = nil
     }
 end
 
+-- supervisory controller communications
 function superv_comms()
     local self = {
         reactor_struct_cache = nil
     }
 end
 
+-- reactor PLC communications
 function rplc_comms(id, modem, local_port, server_port, reactor)
     local self = {
         _id = id,
@@ -150,4 +220,4 @@ function rplc_comms(id, modem, local_port, server_port, reactor)
         send_keep_alive = send_keep_alive,
         handle_link = handle_link
     }
-end
\ No newline at end of file
+end
diff --git a/scada-common/modbus.lua b/scada-common/modbus.lua
index e6d5eba..6721c44 100644
--- a/scada-common/modbus.lua
+++ b/scada-common/modbus.lua
@@ -1,3 +1,5 @@
+-- #REQUIRES comms.lua
+
 -- modbus function codes
 local MODBUS_FCODE = {
     READ_COILS = 0x01,
@@ -175,9 +177,8 @@ function modbus_init(rtu_dev)
     }
 end
 
--- create new modbus packet
-function new_modbus_packet(txn_id, protocol, length, unit_id, func_code, data)
-    return {
+function modbus_packet()
+    local self = {
         txn_id = txn_id,
         protocol = protocol,
         length = length,
@@ -185,25 +186,34 @@ function new_modbus_packet(txn_id, protocol, length, unit_id, func_code, data)
         func_code = func_code,
         data = data
     }
-end
 
--- parse raw table data as a modbus packet
-function parse_modbus_packet(raw)
-    if #raw ~= 6 then
-        return nil
-    else
-        return new_modbus_packet(raw[1], raw[2], raw[3], raw[4], raw[5], raw[6])
+    local receive = function (raw)
+        local size_ok = #raw ~= 6
+
+        if size_ok then
+            set(raw[1], raw[2], raw[3], raw[4], raw[5], raw[6])
+        end
+
+        return size_ok and self.protocol == comms.PROTOCOLS.MODBUS_TCP
+    end
+
+    local set = function (txn_id, protocol, length, unit_id, func_code, data)
+        self.txn_id = txn_id
+        self.protocol = protocol
+        self.length = length
+        self.unit_id = unit_id
+        self.func_code = func_code
+        self.data = data
+    end
+
+    local get = function ()
+        return {
+            txn_id = self.txn_id,
+            protocol = self.protocol,
+            length = self.length,
+            unit_id = self.unit_id,
+            func_code = self.func_code,
+            data = self.data
+        }
     end
 end
-
--- create raw table data from a modbus packet
-function modbus_to_raw(packet)
-    return {
-        packet.txn_id,
-        packet.protocol,
-        packet.length,
-        packet.unit_id,
-        packet.func_code,
-        packet.data
-    }
-end