# Towards the Quantum Internet: Satellite Control Plane Architectures and Protocol Design
## 3 System Model
### Protocol  
The proposed protocol is designed for the architecture defined in Figure 2 and it is organized in two main phases:  
1. Management of the connection request between GSs and the setup of the satellite path;
2. Generation of E2E entanglement using the configured satellite path. In order to manage these operations properly, we have also defined a specific packet format, which is depicted in Figure 3. The fields that compose the defined packet are described as follows:  
* Type: This field is composed of 4 bits and it defines the type of packet;
* C: This is a field composed of a single bit. It is useful in order to enable the controller's functionality for a specific satellite if the field Type is set to 3, or if the field Type is set to 8, it is used in order to signal that the inter domain teleport between two border QSRs is completed;
* Duration: This field contains the lifetime of the path. It is important in order to program the opening and closing of the connections between the satellites that compose the path;
* Source: This field contains the address of the source of the message that could be the MCS or a satellite controller;
* Destination: This field contains the address of the destination of the message;
* Previous: Address of the previous satellite;
* Next: Address of the next satellite;
* Teleportation Data: This field contains the classic bits related to teleportation. In the first phase, which is depicted in Figure 4, the MCS processes the connection request from one of the GSs located on the Earth's surface. In this case, the message received by the MCS consists of the Type field set to 0 and the Previous field that contains the IP address of the GS to which it wants to connect. Thus, the controller in the MCS calculates the best paths for all instants of time, creating a list with which it is able to obtain the duration of every best path. At the same time, it sends the connection request to the selected QSRs and a message that has the Type as a field, which in this case is identified with 1 and the Previous field, which contains the address of the station that has generated the request. When the station affirmatively acknowledges the request, the MCS begins to perform the setup of the satellite path by sending messages of Type 2 to each satellite that is part of the selected path, indicating which is the neighboring satellite to connect to. Furthermore, the satellite recovers the value of the field called Duration, in order to set a timer that closes the connection when the path is expired. Once the controller has received notification from the satellites of the selected path that all the connections have been established, the second phase of the protocol begins. As shown in Figure 5, this involves the generation of entanglement on the selected satellite path and has a duration equal to the value specified in the field Duration, which corresponds to the duration of the satellite path. Figure 3: Packet format used by the protocol designed for the proposed architecture. Figure 4: Sequence diagram of the first phase of the protocol. The MCS performs the setup operations on the selected path. Figure 5: Sequence diagram related to the second phase of the protocol. The Controllers placed on the path manage the entanglement generation and swapping operations. The MCS sends to the satellites chosen as controllers a message of Type 3 that indicates the ability to perform certain operations on a domain that is specified in the message itself in the fields Previous and Next. The controller generates two pairs of particles to share with the two adjacent satellites in the path and sends a Type 4 message to the remaining satellites, specifying the satellite with which to perform the entanglement. In addition, the first controller on the path sends a Type 5 message to the second controller in order to negotiate the generation of entanglement between two satellites. In this type of message, the Previous and Next fields indicate the satellites to be interconnected.