Cooperation between stations in wireless networks Andrea G. Forte, Henning Schulzrinne Department of...
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Transcript of Cooperation between stations in wireless networks Andrea G. Forte, Henning Schulzrinne Department of...
Cooperation between stations in wireless networks
Andrea G. Forte, Henning SchulzrinneDepartment of Computer Science, Columbia University
Presented by: Azbayar Demberel
Duke UniversityApril 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 sameL3 handoff: in case the new AP is in different subnet
Motivation Cooperative roaming Results Conclusion
Source: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf
L2 handoff in 802.11
Motivation Cooperative roaming Results Conclusion
L3 handoff in 802.11
Motivation Cooperative roaming Results Conclusion
Handoffs due to mobility
L2 handoff (~100-400 ms) Scanning (>90%) Network authentication Re-association
L3 handoff (~1000ms) 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
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
Store AP Info to CacheSelective Scanning
1
611
Signal Low
1
Cache
KeyBestNext
A
B
C
A
1
6
11
Cache
KeyBestNext
A
B
C
A BB
C
A 6
11
SSID, Channel, SubnetID(e.g. MAC(A), 1, 160.39.5.0)
Motivation Cooperative roaming Results Conclusion
Source: www1.cs.columbia.edu/~ss2020/presentation/L2handoff-poster.ppt
Cooperative Roaming: AP caching
Store AP Info to CacheSelective Scanning
1
611
Signal Low
1
Cache
KeyBestNext
A
B
C
A
1
6
11
Cache
KeyBestNext
A
B
C
A BB
C
A
B CB C A C A
Motivation Cooperative roaming Results Conclusion
Source: www1.cs.columbia.edu/~ss2020/presentation/L2handoff-poster.ppt
L2 cooperation protocol
Mobile node B Mobile node A
2. InfoResp diff(cache A,
cache B)
1. InfoReq (cache A)Random backoff
Mobile node C
1. InfoReq (cache A)
2. InfoResp diff(cache A,
cache C)
Motivation Cooperative roaming Results Conclusion
L3 cooperation protocol
Mobile node B(subnet 1)
Mobile node A(subnet 2)
2. AmnResp (MAC(B), IP(B))
1. AmnDiscover (subnet 1)
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))
Acquire IP, using
MAC(A) from DHCP
server
Motivation Cooperative roaming Results Conclusion
L2 handoff begins
Cache: subnet1(IP(A), IP(router))
Cooperative authentication
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?
Motivation Cooperative roaming 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
Motivation Cooperative roaming Results ConclusionSource: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf
Cooperative roaming vs. 802.11
Motivation Cooperative roaming Results ConclusionSource: http://www.icnp2007.edu.cn/slides/04_aforte-cooperation.pdf
Discussion
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/handoff-lat-acm.pdf
Subnet Discovery (1/2)
Current solutionsRouter 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)
Proposed approach 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 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 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) No buffering necessary
Handoff time: 15ms (open), 21ms (802.11i) Packet loss negligible
ARP Req.NAK
MN DHCPd
DHCP Req.
ARP Req.
Router
ARP Resp.
CN
SIP INVITE
SIP OK
SIP ACK
RTP packets (TEMP_IP)
138 ms
22 ms
4 ms
4 ms
29 ms
Waiting timeIP acquisition
SIP signaling
L2 handoffcomplete
Detecting subnet change
Processing overhead
Experimental Results (1/2)
Handoff Scenarios
Scenario 1 The MN enters in a new subnet for the first time
ever. Scenario 2
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)
Scenario 1 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.
Scenario 2 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.