Transcript Cooperation between stations in wireless networks

Cooperation between
stations in wireless networks
Andrea G. Forte, Henning Schulzrinne
Department of Computer Science,
Columbia University
Presented by: Azbayar Demberel
Duke University
April 19, 2008
Agenda

Motivation

Cooperative roaming

Results

Conclusion
VoIP and 802.11: terminal
mobility problem
AP
AP
Mobile Node
L2 handoff: in case subnets are the same
L3 handoff: in case the new AP is in different subnet
Source: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf
Motivation
Cooperative roaming
Results
Conclusion
L2 handoff in 802.11
Motivation
Cooperative roaming
Results
Conclusion
L3 handoff in 802.11
Motivation
Cooperative roaming
Results
Conclusion
Handoffs due to mobility
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L2 handoff (~100-400 ms)
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L3 handoff (~1000ms)


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Scanning (>90%)
Network authentication
Re-association
Subnet change discovery
IP address acquisition (>90%)
Application handoff

Informing correspondent node of new IP
address
Motivation
Cooperative roaming
Results
Conclusion
Cooperative roaming:
goals and solution

Fast handoff for real-time multimedia in any network
 Different administrative domains
 Various authentication mechanisms
 No changes to protocol and infrastructure
 Fast handoff at all the layers relevant to mobility
• Link layer
• Network layer
• Application layer

New protocol: Cooperative Roaming
 Complete solution to mobility for real-time traffic in
wireles networks
 Working implementation available
Motivation
Cooperative roaming
Results
Conclusion
Cooperative roaming: overview
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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
Motivation
Cooperative roaming
Results
Conclusion
Cooperative Roaming:
AP caching
Signal Low
1
A
Selective Scanning
Store AP Info to Cache
6
6
1
A
B
11
C
6
1
A
B
11
C
11
Cache
Cache
Key Best Next
A
Key BestNext
B C
A
B
SSID, Channel, SubnetID
(e.g. MAC(A), 1, 160.39.5.0)
Source: www1.cs.columbia.edu/~ss2020/presentation/L2handoff-poster.ppt
Motivation
Cooperative roaming
Results
Conclusion
Cooperative Roaming:
AP caching
Signal Low
1
A
Selective Scanning
Store AP Info to Cache
6
6
1
A
B
11
C
1
A
B
11
C
Cache
Cache
Key Best Next
A
B
C
B C
A
Key BestNext
B C
A
B
C A
Source: www1.cs.columbia.edu/~ss2020/presentation/L2handoff-poster.ppt
Motivation
Cooperative roaming
Results
Conclusion
L2 cooperation protocol
Mobile node B
Random backoff
Motivation
Mobile node A
Mobile node C
1. InfoReq
(cache A)
1. InfoReq
(cache A)
2. InfoResp
diff(cache A,
cache B)
2. InfoResp
diff(cache A,
cache C)
Cooperative roaming
Results
Conclusion
L3 cooperation protocol
Mobile node B
(subnet 1)
Mobile node A
(subnet 2)
1. AmnDiscover
(subnet 1)
Acquire IP,
using
MAC(A)
from DHCP
server
2. AmnResp
(MAC(B), IP(B))
Mobile node C
(subnet 2)
1. AmnDiscover
(subnet 1)
Subnet1: nodeB(
Mac(B), IP(B))
3. IpReq
(MAC(A))
4. IpResp
(MAC(A), IP(A),
IP(router))
Motivation
Cache: subnet1(
IP(A), IP(router))
L2 handoff begins
Cooperative roaming
Results
Conclusion
Cooperative authentication

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Motivation
Cooperative roaming
Cooperation in the
authentication itself not
possible  keys,
certificates (sensitive info)
Use relay node (RN) to
relay packets during
authentication
No bridging delay
Use timeout to
achieve fairness
What about RN mobility?
Results
Conclusion
Experiment environment
2 subnets/AP’s
 4 nodes (1 roamer, 1 helper,
2 sniffers)
 Roamer moved between two AP’s:
perform L2, L3 handoff

…i.e. extremely simple!
Motivation
Cooperative roaming
Results
Conclusion
Experiment results
Motivation
Cooperative roaming
Results
Conclusion
Cooperative roaming
vs. 802.11
Source: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf
Motivation
Cooperative roaming
Results
Conclusion
Cooperative roaming
vs. 802.11
Source: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf
Motivation
Cooperative roaming
Results
Conclusion
Discussion
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Too simple experiment: congestion and
backoff might diminish all the benefits, in
real life
Assumes spatial locality / node “knows”
what the next AP will be.
No info on memory management policies:
how often to ask neighbors
In many places uses magic wand
approaches (e.g. detect subnet change)
CR might benefit from location routing
Application layer mobility, load balancing left
out
Motivation
Cooperative roaming
Results
Conclusion
Summary
Seamless/near-seamless handoff
 Requires cooperation of many other
nodes to achieve the benefits
 Worst case scenario ~ current 802.11
 Room for improvement: mobility
detection, application layer handoff …

Motivation
Cooperative roaming
Results
Conclusion
Thank you
Questions? Comments?
Backup slides
From:
http://www.cs.umd.edu/~waa/pubs/h
andoff-lat-acm.pdf
Subnet Discovery (1/2)

Current solutions

Router advertisements
• Usually with a frequency on the order of
several minutes.

DNA working group (IETF)
• Detecting network attachments in IPv6
networks only.
No solution in IPv4 networks for detecting a
subnet change in a timely manner.
Subnet Discovery (2/2)
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Proposed approach

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Send bogus DHCP_REQUEST (using
loopback address).
DHCP server responds with a DHCP_NAK
From the NAK extract subnet information
such as default router IP address.
The client saves the default router IP
address in cache.
If old AP and new AP have different default
router, the subnet has changed.
Application layer handoff


MN builds a list of {RNs, IP addresses}, one per each possible next
subnet/AP
RFC 3388


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Send same media stream to multiple clients
All clients have to support the same codec
Update multimedia session

Before L2 handoff
• Media stream is sent to all RNs in the list and to MN (at the same time)
using a re-INVITE with SDP as in RFC 3388
• RNs do not play such streams
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After L2 handoff
• Tell CN which RN to use, if any (re-INVITE)
• After successful L2 authentication tell CN to send directly without any
RN (re-INVITE)
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No buffering necessary
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Handoff time: 15ms (open), 21ms (802.11i)
Packet loss negligible
Experimental Results (1/2)
MN
DHCPd
Router
CN
L2 handoff
complete
DHCP Req.
ARP Req.
22 ms
NAK
Detecting
subnet change
138 ms
Waiting time
IP acquisition
ARP Req.
4 ms
ARP Resp.
4 ms
Processing
overhead
29 ms
SIP signaling
SIP INVITE
SIP OK
RTP packets (TEMP_IP)
SIP ACK
Handoff Scenarios
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Scenario 1
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Scenario 2

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The MN enters in a new subnet for the first
time ever.
The MN enters in a new subnet it has been
before and it has an expired lease for that
subnet.
Scenario 3

The MN enters in a new subnet it has been
before and still has a valid lease for that
subnet.
IP Selection (1/3)
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Scenario 1
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Scenario 2
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Select random IP address starting from the
router’s IP address (first in the pool). MN
sends 10 ARP requests in parallel starting
from the random IP selected before.
Same than scenario 1 except that we start to
send ARP requests to 10 IP addresses in
parallel, starting from the IP we last used in
that subnet.
Scenario 3

We do not need TEMP_IP as we have a
valid lease. We just renew the lease.