Cooperation Between Stations in Wireless Networks Andrea G. Forte and Henning Schulzrinne Department of Computer Science Columbia University, New York A malicious MN might try to re-use the relaying mechanism over and over without ever authenticating In order to prevent this: - Each RELAY_REQ allows an RN to relay packets for a limited amount of time (time required to authenticate) - RELAY_REQ frames are multicast. All STAs can help in detecting a bad behavior and only nodes of the multicast group can send such frames - RNs can detect if the R-MN is performing the normal authentication or not (Authentication failures can also be detected) Abstract In a wireless network, mobile nodes (MNs) repeatedly perform tasks such as layer 2 (L2) handoff, layer 3 (L3) handoff and authentication. These tasks are critical for real-time applications such as VoIP. We propose a novel approach, namely Cooperative Roaming (CR), in which MNs can collaborate with each other and share useful information about the network in which they move. We show how we can achieve seamless L2 and L3 handoffs regardless of the authentication mechanism used and without any changes to either the infrastructure or the protocol. In particular, we provide a working implementation of CR and show how, with CR, MNs can achieve a total L2+L3 handoff time of less than 16 ms in an open network and of about 21 ms in a Robust Security Network (RSN). We consider behaviors typical of IEEE networks, although many of the concepts and problems addressed here apply to any kind of mobile network. Implementation and Measurement Results More information available at or by Stations can cooperate and share information about the network (topology, services) Stations can cooperate and help each other in common tasks such as IP address acquisition Stations can help each other during the authentication process without sharing sensitive information, maintaining privacy and security Stations can also cooperate for application-layer mobility and load balancing Security  Cooperation among stations allows seamless L2 and L3 handoffs for real-time traffic  15.6 ms in open networks  21.4 ms in networks using IEEE i  Completely independent from the authentication mechanism used  It doesn’t require any changes in either infrastructure or protocol  It does require many STAs supporting the protocol and a sufficient degree of mobility  Sharing information  Power efficient  Many other applications: application layer mobility, access control, load balancing, service discovery (3G networks, bluetooth, mesh networks) Cooperation Manager ISC DHCP Client Linux WPA supplicant HostAP Wireless Driver Linux kernel version Cooperation at Layer 2 and Layer 3 MN’s Cache  The cache contains L2 and L3 information IP Address Acquisition Each MN saves L2 and L3 information in its cache. This information and the information in the DHCP client lease file is then shared with other MNs using a request/response model and exchanging NET_INFO multicast frames. A node receiving such information (R-MN) will use it to populate its cache By comparing Subnet ID of old and new AP, R-MN can detect a change in subnet R-MN has to discover which MNs can help it in acquiring a new IP address for the new subnet (A-STAs) R-MN will acquire one IP address for each possible subnet that it might move to Why Cooperation? Same tasks Layer 2 handoff Layer 3 handoff Authentication Multimedia session update Same information Topology (failover) DNS Geo-Location Services Same goals Low latency QoS Load balancing Admission control Service discovery Internet Cooperative Roaming - Overview Channel 6Channel 11Channel 1 Subnet ID 3Subnet ID 2Subnet ID 1 MAC CMAC BMAC A Second best APBest APCurrent AP (KEY) Handoff without authentication CRIEEE Handoff ms L2 L3 Total R-MNStations NET_INFO_REQ NET_INFO_RESP R-MN Stations ASTA_DISCOV (m) ASTA_RESP (u) m: multicast u: unicast R-MNA-STA IP_REQ (Client ID).... DHCP Server DHCP_OFFER (client ID) DHCP_ACK IP_RESP (New IP) Coop Manager Wireless card driver (HostAP driver) DHCP client User space Linux kernel space WPA supplicant 11.4 msL3 handoff 4.2 msL2 handoff 15.6 msTotal handoff 1.3 packetsPacket loss msIP_REQ – IP_RESP  CR in open network Relayed Data Packets i authentication packets RN data packets + relayed data packets R-MNRN AP Cooperative Authentication One selected STA (RN) can relay packets to and from the R-MN for the amount of time required by the R-MN to complete the authentication process STAs can cooperate in a mobile scenario to achieve seamless L2 and L3 handoffs regardless of the authentication mechanism used In IEEE networks the medium is “shared” Each STA can hear the traffic of other STAs on the same channel Packets sent by the non- authenticated STA will be dropped by the AP but will be heard by the other STAs on the same channel The selected A-STA can cooperate with the R-MN and acquire a new IP address for the new subnet on its behalf while the R-MN is still in the OLD subnet When a handoff occurs, the R-MN can use the information in its cache without having to perform any scanning