Abstract

1. User space Coop Manager R-MN DHCP client Stations WPA supplicant Handoff without authentication AP NET_INFO_REQ 1400 1210.0 1200 NET_INFO_RESP DHCP Server RN data packets+ relayed data packets R-MN A-STA 802.11i authentication packets 1000 DHCP_OFFER (client ID) 867.0 IP_REQ (Client ID) 800 Wireless card driver (HostAP driver) L2 . . ms L3 Total Current AP (KEY) Best AP Second best AP 600 Relayed Data Packets DHCP_ACK MAC A MAC B MAC C RN R-MN IP_RESP (New IP) 400 Channel 1 Channel 11 Channel 6 343.0 Subnet ID 1 Subnet ID 2 Subnet ID 3 200 Linux kernel space 15.6 11.4 4.2 0 CR IEEE 802.11 Handoff 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 Stations R-MN ASTA_DISCOV (m) m: multicast u: unicast ASTA_RESP (u) • CR in open network IP_REQ – IP_RESP 867.0 ms L2 handoff 4.2 ms L3 handoff 11.4 ms Total handoff 15.6 ms Packet loss 1.3 packets Cooperation at Layer 2 and Layer 3 Security • 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 802.11 networks, although many of the concepts and problems addressed here apply to any kind of mobile network. MN’s Cache Cooperation Between Stations in Wireless NetworksAndrea G. Forte and Henning SchulzrinneDepartment of Computer ScienceColumbia University, New York • The cache contains L2 and L3 information • 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 • When a handoff occurs, the R-MN can use the information in its cache without having to perform any scanning Implementation and Measurement Results IP Address Acquisition Cooperative Roaming - Overview • Cooperation Manager • ISC DHCP Client • Linux WPA supplicant • HostAP 0.0.4 Wireless Driver • Linux kernel version 2.4.21 • 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 Internet • 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 Cooperative Authentication • STAs can cooperate in a mobile scenario to achieve seamless L2 and L3 handoffs regardless of the authentication mechanism used • In IEEE 802.11 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 • 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 802.11i • 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) • 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 • 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 More information available at http://www.cs.columbia.edu/~andreaf or by email andreaf@cs.columbia.edu