Common use of Implementation Issues Clause in Contracts

Implementation Issues. We will consider a given period T . To simplify, this period will be used both by the group leader or by the member of the group as a period to send their GKA messages. ≥ − A node can be in one of the following two states : member state or group leader state. A node in a member state will enter the process to become a group leader if it has not received IGROUP message for a duration kT . A node which has not received any message from a group leader for a duration kT with k 2 will suppose that there is no group leader and starts the procedure to become a leader. Since a node may not have received a packet of the group leader because this packet has been lost, k must be selected so that the probability that k 1 successive transmissions of a GKA message are lost is small. To become a group leader, the node selects a random integer ir between 1 and a given number l and initializes a timer at irtrtd. trtd is a predefined duration computed to be at least the round trip delay of a message throughout the ad hoc network. With such a figure for trtd we can be sure that if two nodes draw different integers ir and ir' , the node having selected the larger integer will receive the IGROUP message of the other node and then will stop its election process. l must be chosen with respect to the total number of nodes in the network so that the probability that two nodes choose the same integer is small. This back-off procedure is performed to avoid possibly multiple group leader candidates, for instance, when a group is set up or split into two subgroups. When the node in the state member sends its first IGROUP message, it is in the group leader state, see Figure 1. In the group leader state, a node must collect IREPLY messages and form the related IGROUP message. When there is a change in the group (arrival or withdrawal) the group leader must change its contribution. Additionally irrespective of the modification of the composition of the group, the group leader must change its contribution periodically. When a group leader is elected, the latter may choose to wait additional periods before sending a IGROUP containing the contributions of the group members. Doing so, the group leader may avoid unnecessary changes to the session key due to the lack of receipt of all contributions in time. In the group leader state, a node will also look out for IGROUP messages from another group leader. If it receives such a message from another group leader holding a smaller node index, the node changes its state to the member state. In the group member state, a node will have to send IREPLY messages periodically. Like the group leader, a group member must change its contribution periodically with a period P . We will assume that P is a large multiple of T . To simplify the procedure and to avoid unnecessary computations we can assume that the group leader does not instantly include a new contribution of a group member in the IGROUP message, instead it will wait for the change of its own contribution to take into account all new contributions of nodes. This is possible since the contribution of the node member is included in the IGROUP message, see figure 2. Both IGROUP and IREPLY messages must be sent periodically for each interval T . To reduce the probability of collision of these messages, we add a jitter to times when the GKA messages shall be sent by the group members and the group leader. In the table 5, we have given examples of figures for our GKA protocol. We can notice that l and trtd will heavily depend of the number of nodes in the network and of the topology of the network.

Implementation Issues. We will consider a given period T . To simplify, this period will be used both by the group leader or and by the member of the group as a period to send their GKA messages. ≥ − A node can be in one of the following two states : member state or group leader state. A node in a member state will enter the process to become a group leader if it has not received an IGROUP message for a duration kT . A node which has not received any message from a group leader for a duration kT with k 2 will suppose that there is no group leader and starts the procedure to become a leader. Since a node may not have received a packet of the group leader because this packet has been lost, k must be selected so that the probability that k 1 successive transmissions of a GKA message are lost is small. To Then, to become a group leader, the node selects a random integer ir between 1 and a given number l (backoff window size) and initializes a timer at irtrtd. , where trtd is a predefined duration computed to be at least the round trip delay of a message throughout the ad hoc network. With such a figure for trtd we can be sure that if two nodes draw different integers ir and ir' , the node having selected the larger integer will receive the IGROUP message of the other node and then will stop its election process. The backoff window size l must be chosen with respect to the total number of nodes in the network so that the probability that of two nodes choose choosing the same integer is small. This back-off procedure is performed to avoid possibly multiple group leader candidates, for instance, when a group is set up or split into two subgroups. When the node in the member state member sends its first IGROUP message, it is in the group leader state, see Figure 1. In ▇▇▇▇▇.▇▇ the group leader state, a node must collect IREPLY messages and form the related IGROUP message. When there is a change in the group (arrival or withdrawal) the group leader must change its contribution. Additionally Additionally, irrespective of the modification of the composition of the group, the group leader must change its contribution periodically, to maintain the security of the session key. When a group leader is elected, the latter it may choose to wait additional periods before sending a an IGROUP containing the contributions of the group members. Doing In doing so, the group leader may avoid unnecessary changes to the session key due to not having received all the lack of receipt of all contributions in time. In the group leader state, a node will also look out for IGROUP messages from another group leader. If it receives such a message from another group leader holding a smaller node index, the node changes its state to the member state. In the group member state, a node will have to send IREPLY messages periodically. Like the group leader, a group member must change its contribution periodically with a period P see figure 1. We will assume that P is a large multiple of T . To simplify the procedure and to avoid unnecessary computations we can assume that the group leader does not instantly include a new contribution of a group member in the IGROUP message, instead but rather it will wait for the change of its own contribution to take into account all new contributions of the nodes. This is possible since the contribution of the node member is included in the IGROUP message, see figure 2. Both IGROUP and IREPLY messages must be sent periodically for each interval T . To reduce the probability of collision of these messages, we add a jitter to times when the GKA messages shall be sent by the group members and the group leader. In the table 5, we have given examples of figures for our GKA protocol. We can notice that l and trtd will heavily depend of the number of nodes in the network and of the topology of the network.

Implementation Issues. We will consider a given period T . To simplify, this period will be used both by the group leader or by the member of the group as a period to send their GKA messages. ≥ − A node can be in one of the following two states : member state or group leader state. A node in a member state will enter the process to become a group leader if it has not received IGROUP message for a duration kT . A node which has not received any message from a group leader for a duration kT with k 2 will suppose that there is no group leader and starts the procedure to become a leader. Since a node may not have received a packet of the group leader because this packet has been lost, k must be selected so that the probability that k 1 successive transmissions of a GKA message are lost is small. To become a group leader, the node selects a random integer ir between 1 and a given number l and initializes a timer at irtrtd. trtd is a predefined duration computed to be at least the round trip delay of a message throughout the ad hoc network. With such a figure for trtd we can be sure that if two nodes draw different integers ir and ir' irr , the node having selected the larger integer will receive the IGROUP message of the other node and then will stop its election process. l must be chosen with respect to the total number of nodes in the network so that the probability that two nodes choose the same integer is small. This back-off procedure is performed to avoid possibly multiple group leader candidates, for instance, when a group is set up or split into two subgroups. When the node in the state member sends its first IGROUP message, it is in the group leader state, see Figure 1. In the group leader state, a node must collect IREPLY messages and form the related IGROUP message. When there is a change in the group (arrival or withdrawal) the group leader must change its contribution. Additionally irrespective of the modification of the composition of the group, the group leader must change its contribution periodically. When a group leader is elected, the latter may choose to wait additional periods before sending a IGROUP containing the contributions of the group members. Doing so, the group leader may avoid unnecessary changes to the session key due to the lack of receipt of all contributions in time. In the group leader state, a node will also look out for IGROUP messages from another group leader. If it receives such a message from another group leader holding a smaller node index, the node changes its state to the member state. In the group member state, a node will have to send IREPLY messages periodically. Like the group leader, a group member must change its contribution periodically with a period P . We will assume that P is a large multiple of T . To simplify the procedure and to avoid unnecessary computations we can assume that the group leader does not instantly include a new contribution of a group member in the IGROUP message, instead it will wait for the change of its own contribution to take into account all new contributions of nodes. This is possible since the contribution of the node member is included in the IGROUP message, see figure 2. Both IGROUP and IREPLY messages must be sent periodically for each interval T . To reduce the probability of collision of these messages, we add a jitter to times when the GKA messages shall be sent by the group members and the group leader. In the table 5, we have given examples of figures for our GKA protocol. We can notice that l and trtd will heavily depend To test the performance of this new GKA protocol (only the number of nodes unauthenticated version), we incorpo- rated it in the network group management protocol of [4]. The group management of [4] consists of three communication rounds: DISC, JOIN and of GROU P . The DISC stage initiates the topology of group for- mation by calling for interested participants. Each interested participant responds with a JOIN Parameter Value Constraint k 3 large enough to be sure the network.message is not simply lost