# Development of Intelligent Core Network for Tactile Internet and Future Smart Systems
## 3 System Structure
OpenFlow switches build their forwarding tables and build the packet processing rules based on the instructions delivered from the SDNC via the OpenFlow protocol. These instructions are deduced from the flow table received from the SDNC. The flow table can be viewed as a set of flow entries. Each of these entries holds a set of instructions to the node [36]. There are only three types of exchanged messages between SDNC and OpenFlow switches that are legalized by the OpenFlow protocol. The first kind is the controller-to-switch messages. This type  
Figure 4: End-to-end system structure. refers to all messages initiated and moved from the controller to any switch, for the issues that are related to Handshaking, configuring the switch, checking status of the switch, and even modifying the switch. A summary of all available controller-to-switch messages supported by OpenFlow 1.4 are collected in Table 2, with the fields and entities of each one [37]. The second type represents all messages transferred from the switch to the SDNC; these messages are referred to as asynchronous messages. Table 3 summarizes all of the asynchronous messages used be OpenFlow 1.4; also, the function and structure of these messages are pointed [37]. The third type is the message exchanged in both directions between SDNC and a switch. These messages are referred to as symmetric messages and have various forms and functions. One of the main symmetric messages is the echo request/response messages that are used by the switch or the SDNC to check latency and measure bandwidth. Another important symmetric message is the error messages that are used to report a connection problem. Error messages are mainly used by the switch to report a request failure. SDNC improve system performance in many terms, such as system latency and user's mobility. One important aspect to reduce the round trip latency is to reduce the number of intermediate nodes that are involved in the communication process and this is introduced by employing SDNC. Moreover, SDNC can foresee the user's mobility as it has access to all features of the user device (including; device type, location, billing information, etc. ), which improves the critical radio access processes, such as handover. In other words, employing SDNC reduces the round trip latency, achieves handover process easily, and also reduces the handover latency. On way to illustrate the benefits of our system is to compare it with the latest traditional Evolved Packet Core cellular network [38]. In the traditional Evolved Packet Core networks, all data traffic flow through the Evolved Packet Core network including the Packet data Gateway (PGW) and the Serving Gateway (SGW). This represents a load on these gateways and leads to an increase in round trip latency. Unlike the traditional systems, our proposed system employs SDN, which removes this barrier and reduces the round trip latency by reducing the number of intermediate nodes that are involved in the communication process. Figure 5 illustrates this comparison between two systems. While, in Figure 4(b), the two eNBs belong to the same Mini-cloud unit, but in Figure 4(c), the two eNBs belong to different Mini-cloud units. Another important aspect is that the SDN structure allows and facilitates adding or changing network functions, which is not offered by the traditional systems. Moreover, network slicing can be done through the SDNC which will be the main feature of the Tactile Internet and 5G systems. Summing up, the advantage of the proposed structure can be summarized in the following points:  
1- the system is more flexible, as routing can be established easily through SDNC,
2- the system is reliable as it relay on the open flow protocol and other standardized technologies,
3- the network function virtualization can be easily implemented powered by the use of SDNC,
4- the requirements for achieving a certain quality of service (QoS) of the system can be supported by SDN.