Cooperation Between Stations in Wireless Networks Andrea G. Forte and Henning Schulzrinne Department of Computer Science Columbia University, New York

1
Cooperation Between Stations in Wireless
NetworksAndrea G. Forte and Henning
SchulzrinneDepartment of Computer
ScienceColumbia University, New York
Security
Cooperation at Layer 2 and Layer 3

• 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 L2L3 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.
MNs Cache

• 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 doesnt 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.columb
ia.edu/andreaf or by email andreaf_at_cs.columbia.ed
u