Management in mobile wireless networks: The case for client-assistance Suman Banerjee suman@cs.wisc.edu

Management in wired networks Mostly performed through central entities Firewalls Nameservers DHCP servers A logical approach for many basic networking tasks But needs some re-thinking in the wireless domain Many properties in wireless domain are location-specific Can only be observed at the clients and by the clients The observation and experience of clients continuously change with their mobility

Impact of location Recvd: 1, 2, 4 AP-1 Client-A AP-2 Recvd: 1, 3, 4, 5 Sent: 1, 2, 3, 4, 5 Experience is property of location and cannot be always replicated

Client-assisted management AP-1 Mgmt. module Controller AP-2

Client-assisted management AP-1 B C ? Controller AP-2 Controller: Is there interference between clients B and C?

Client-assisted management AP-1 B Tx at time t C Rx at time t and report Controller AP-2 Controller: Is there interference between clients B and C? - Interference test

Client-assisted management AP-1 B C Yes Controller AP-2 Client C: Yes, interference exists

Client-assisted management AP-1 B No C Controller AP-2 At a later time (due to mobility): Client C: No, interference does not exist

Applications of client-assisted management Any RF management in a wireless network Capacity and coverage planning Interference mitigation Hole detection Network-wide transceiver parameter tuning Power control Channel assignment User association, etc. Policy provisioning Wireless security

Example I: Channel assignment AP-2 AP-3 AP-1 What channels to assign to APs?

Example I: Channel Assignment AP-2 AP-3 AP-1 What channels to assign to APs? LCCS may assign same to all APs

Example I: Channel Assignment AP-2 Interference AP-3 AP-1 Correct answer depends on client distribution and association

Example I: Channel Assignment AP-2 AP-3 AP-1 Correct answer should also adapt with client distributions

Example I: Channel Assignment AP-2 AP-3 AP-1 Correct answer should also adapt with client distributions

Example I: Channel assignment [Infocom 2006] 50 APs and 200 clients Client-assisted Throughput Infrastructure-only

Example II: Performance characterization Madison WiFi mesh 200+ APs A few thousand clients Performance on the network is highly variable Kind of information obtainable by instrumenting 1-2 clients over a few days Exploits client mobility Understand cause of variability, isolate performance problems, and automate remedial measures remains part of next steps

Example III: Hole detection

How do we implement a task? A client-assisted management task would need to answer the following questions: What tasklet should which clients perform and when? What information to aggregate back from different clients (possibility of data fusion)? How should an outcome be decided based on this aggregated data? Of course, many more open issues …

Research agenda What functions do we need from clients? Access to firmware? Driver? Application-layer? How can we be minimally intrusive to clients? Can we trust all client data equally? How do we normalize across client feedback? How can we preserve privacy of clients and networks?