A cyber-physical system depends on stable control and interaction between the many systems and devices connected to the network. Dynamic control middleware, which considers the characteristics of a cyber-physical system, supports the dynamic search and control of devices existing on the global network using Internet protocol version 6 (IPv6). However, systems and devices may connect to a network using a variety of heterogeneous protocols, not just IPv6. To solve the problem of heterogeneous protocols, this paper proposes a routing technique which enables network devices to communicate using different protocols. The proposed network-routing module can register devices with various protocols and improve the stability of the efficient heterogeneous network.
Cyber-physical systems (CPS) [
This paper is organized as follows. In the next section, we discuss related research. The Materials and Methods is comprised of three subsections: Subsection
Dynamic control middleware (DCM) efficiently controls connected devices throughout the IPv6-based global network, across all temporal and physical conditions. To search efficiently, DCM has a two-layer logical architecture consisting of a lower layer and an upper layer. The lower layer consists of control devices (CDs) connected to each local network, and the upper layer consists of control device managers (CDMs) that manage information from lower-layer devices. The upper layer can reduce the number of messages by only sending messages to devices belonging to the same IPv6 multicast group. In addition, because DCM has a two-layer architecture, and not a centralized server structure, devices can discover, search, and control other devices through multicasting, regardless of their global network location. However, DCM supports only IPv6 and in real-world applications, networked systems and devices often use different heterogeneous protocols.
Object-based middleware for smart home network (OSHNet) [
Figure
Extended DCM architecture.
The routing mapper identifies the destination of the message delivered from the upper layer of the EDCM. After referring to the routing table, the routing mapper maps the route to the message destination and adds it to the head of the message.
Table
Example of routing table.
Source | Destination | Interface | Source address | Destination address |
---|---|---|---|---|
CDM | CD-1 | IPv6 | 2001:1F00:388::2 | 2001:1F00:388::3 |
CD-1 | CD-2 | Bluetooth | 01:23:45:67:89:AB | 01:23:45:67:89:AC |
CD-2 | CD-3 | ZigBee | 1001 | 1002 |
Box
01: <Route>3</Route> 02: <Src>CDM</Src> 03: <Dest>CD-3</Dest> 04: <Routing_Table> 05: <Src>CDM</Src> 06: <Dest>CD-1</Dest> 07: <Interface>IPv6<Interface> 08: <Src_Address>2001:1F00:388::2</Src_Address> 09: <Dest_Address>2001:1F00:388::3</Src_Address> 10: </Routing_Table> 11: <Routing_Table> <!-- CD-1 to CD-2 --> 17: </Routing_Table> 18: <Routing_Table> <!-- CD-2 to CD-3 --> 24: </Routing_Table> <!-- End of Routing Table Part -->
Figure
Flowchart of the routing mapper.
Figure
Flowchart of the message forwarder.
If the message transmission fails, a new routing path is established using the CSRQ message to reconfigure the path currently connecting the CDMs. The message forwarder then retransmits the MSG using the modified routing information.
Figure
Flowchart of the message receiver.
Figure
Flowchart of the routing configurator.
When a new CD is connected to a local network in the DCM, all CDs and CDMs use the same network protocol, IPv6, so the new CD sends a direct message to the CDM to register as a lower node of the CDM. However, although the DCM may support heterogeneous networks, the CDM may not support the specific network protocols used by the new CD.
Figure
CDM configuration in ECDM local network.
Tables
CD-1 routing table.
Source | Destination | Interface | Source address | Destination address |
---|---|---|---|---|
CDM | CD_1 | IPv6 | 2001:1F00:388::2 | 2001:1F00:388::3 |
CD-2 routing table.
Source | Destination | Interface | Source address | Destination address |
---|---|---|---|---|
CDM | CD-1 | IPv6 | 2001:1F00:388::2 | 2001:1F00:388::3 |
CD-1 | CD-2 | Bluetooth | 01:23:45:67:89:AB | 01:23:45:67:89:AC |
CD-3 routing table.
Source | Destination | Interface | Source address | Destination address |
---|---|---|---|---|
CDM | CD-1 | IPv6 | 2001:1F00:388::2 | 2001:1F00:388::3 |
CD-1 | CD-2 | Bluetooth | 01:23:45:67:89:AB | 01:23:45:67:89:AC |
CD-2 | CD-3 | ZigBee | 1001 | 1002 |
The following subsections describe the network topology reconfiguration technique applied to solve the problems that occur when a new CD is connected and other connected CDs are abnormally terminated. The proposed network topology reconfiguration technique is based on the CDM configuration shown in Figure
Figure
New controller device connection in heterogeneous networks. (a) A new CD, CD-4, is connected to the EDCM. (b) CD-1 responds to CD-3. (c) A routing path is completed between CD-4 and the CDM.
Figure
CD-4 routing table.
Source | Destination | Interface | Source address | Destination address |
---|---|---|---|---|
CDM | CD-1 | IPv6 | 2001:1F00:388::2 | 2001:1F00:388::3 |
CD-1 | CD-4 | Bluetooth | 01:23:45:67:89:AB | 01:23:45:67:89:AD |
Figure
Dynamic reconfiguration in heterogeneous networks. (a) Intermediate node CD-2 is disconnected. (b) CD-3 searches for a new connection using broadcasting. (c) CD-4 transmits its routing table to CD-3. (d) CD-3 establishes a new routing path through CD-4.
New routing table of CD-3.
Source | Destination | Interface | Source address | Destination address |
---|---|---|---|---|
CDM | CD-1 | IPv6 | 2001:1F00:388::2 | 2001:1F00:388::3 |
CD-1 | CD-4 | Bluetooth | 01:23:45:67:89:AB | 01:23:45:67:89:AD |
CD-4 | CD-3 | ZigBee | 1003 | 1002 |
To test the EDCM proposed in this paper, we constructed the testbed environment illustrated in Figure
Testbed heterogeneous network-routing model.
This test bed assumes that Laptop 1 uses Bluetooth, Laptops 2, 3, and 4 use IPv6, Netbooks 1 and 3 use IPv6 and Bluetooth, Netbook 2 uses IPv6 and IPv4, Tablet 1 uses IPv4, and Tablet 2 uses Bluetooth. We confirmed that control messages are normally transmitted from Laptop 1 and Tablets 1 and 2, which are not IPv6-enabled devices, to Laptop 4, which belongs to a different local area network. Our experiment confirmed that when Netbook 1 or Netbook 3 was disconnected, the routing tables on Laptop 1 and Tablet 2, respectively, were reconfigured. This test demonstrates the stability of the proposed efficient heterogeneous network-routing scheme based on the dynamic control middleware.
Many industries rely on the ability to connect numerous devices to heterogeneous networks to deliver fundamental services, as observed in health care. However, DCM, a middleware for existing cyber-physical systems, only supports IPv6. Therefore, the many devices that do not use IPv6 cannot connect to a DCM-based CSP. In this paper, a network-routing module is designed to support CDM connections through IPv6 and other various network protocols such as IPv4, Bluetooth, and ZigBee. Through the proposed network-routing module, devices with heterogeneous protocols can be registered as components of an EDCM. Furthermore, if an intermediate node in a routing path is removed from the EDCM network, the network recovers dynamically.
Regarding future work, an EDCM network is constructed on a large scale, so it is necessary to study techniques for efficient traffic distribution. Also, authentication techniques to enable only authorized users to control the EDCM controller must be explored. Finally, we also plan to develop an encryption technique suitable for low-performance embedded devices.
The data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (Ministry of Science and ICT) (No. 2017R1C1B5075856).