| | 35 | == Client Component== |
| | 36 | Any mobile device should be able to connect to a network in our testbed and maintain an IP through a vertical or horizontal handover. However, if the handover is to be truly seamless to an application, there needs to be a persistent VNI for the application to use. The VNI abstracts the handover from the application and provides the application with an interface that is persistent for the duration the client is active. In addition to the VNI, the client should also be able to switch between interfaces in a manner that is simple and straightforward to the experimenter utilizing the testbed. |
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| | 39 | Similar to the network-level design, OVSBs are also utilized in the client to achieve a seamless handover. These client-level OVSBs are used in conjunction with a client-level FL OF controller and are installed for each mobility NIC on the client, as shown in Fig. 2. The local FL controller inserts flows in each OVSB via the integrated Static Flow Pusher. These flows route application packets from the client VNI to the NIC of choice. When a decision is made to switch NICs, the client will issue a DHCP request egress the new interface, which will then trigger the aforementioned events in the network-level. As a result, these OVSBs with FL-inserted flows allow the client to seamlessly switch from one network to another. All client-level tasks are encapsulated in shell scripts to provide testbed experimenters with a simple and single command to execute a handover. |
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| | 42 | Each client-level OVSB also contain OVSPPs. To ensure proper routing of packets from the VNI to the NIC of choice, OVSPPs are used to connect the VNI OVSB with the OVSB of each participating NIC installed on the client. (as seen in Fig. 2). The OVSPPs, combined with flows that utilize these OVSPPs, serve to link the VNI to each NIC's OVSB. These flows define the route (and thus the NIC) used by application packets. |
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| | 44 | The use of a VNI introduces a problem when associating with networks and routing packets to the client from the network-level. The MAC address of the VNI must be the same as that of the NIC, otherwise WiFi APs and other access mediums will not accept packets from or know how to route packets back to the client's VNI at the link layer. It is not reasonable to require the modification or "spoofing" of each NIC's MAC address to that of the VNI. The client-level solution to this problem is to perform MAC-rewrite within the client OVSBs. When an application generates packets, they are routed out of the client via flows on each OVSB. These flows contain actions to rewrite the source MAC address of all egress packets from that of the VNI to that of the NIC. The flows also contain actions to rewrite the destination MAC address of all ingress packets from that of the NIC to that of the VNI. This rewrite process allows the client to send and receive packets from its VNI with any associated network on the link layer. Due to a limitation of OF, ARP packets cannot be rewritten with flows; they must be processed instead by a controller. Thus, the client-level FL controller contains a custom module to rewrite all ARP packet MAC addresses within the controller itself. Although out-of-band processing of packets is inefficient as compared to in-band, ARP packets are not frequent, so an occasional rewrite within the controller is a compromise made in our client-level implementation. |
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